Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss
discharging caps
109 views
Skip to first unread message
John Larkin
Apr 17, 2012, 5:30:44 PM4/17/12
to
I'm designing a box that has +48 and -48 power supplies, each bypassed
with 44,000 uF. I figure it will take forever to discharge when the
power is switched off, and I don't want to waste a heap of power on a
bleeder.
So I figured I could put an LED on the board to alert our test people
that the board is still hot, and have a DISCHARGE pushbutton. So what
I'm thinking is
http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
better than buying a switch rated for 1 amp at 100 volts DC.
I wonder if I could dump the energy into a mosfet, namely get rid of
the power resistors and add a smaller source resistor, to make the
power fet into a current sink. It's tempting, but then it might blow
up. There's about 100 joules to dump.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Robert Macy
Apr 17, 2012, 5:50:57 PM4/17/12
to
On Apr 17, 2:30 pm, John Larkin <jlar...@highlandtechnology.com>
wrote:
Is the MOSFET die about that size?
What's the rule of thumb for abuse on a resistor? Isn't it more than
20X rating? for a single event.
that's what? 450 ohm for 10 seconds?
Hmmm..how about an incandescent 60w bulb?
wrote:
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
> --
>
> John Larkin Highland Technology, Inc
>
> jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
> --
>
> John Larkin Highland Technology, Inc
>
>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom laser controllers
> Photonics and fiberoptic TTL data links
> VME thermocouple, LVDT, synchro acquisition and simulation
As a comparison, look at the size of your 5J and 10J MOV parts.
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom laser controllers
> Photonics and fiberoptic TTL data links
> VME thermocouple, LVDT, synchro acquisition and simulation
Is the MOSFET die about that size?
What's the rule of thumb for abuse on a resistor? Isn't it more than
20X rating? for a single event.
that's what? 450 ohm for 10 seconds?
Hmmm..how about an incandescent 60w bulb?
John Larkin
Apr 17, 2012, 6:08:26 PM4/17/12
to
can certainly get a mosfet rated for 100, or even 300 watts, but lots
of mosfets die if you try to run up to their rtaed dissipation at
higher voltages. You can see that in the SOAR curves. And the heat
does have to go somewhere, and heat sinks are expensive.
>
>Is the MOSFET die about that size?
>
>What's the rule of thumb for abuse on a resistor? Isn't it more than
>20X rating? for a single event.
>that's what? 450 ohm for 10 seconds?
50 watts*1 second, and pretty hot at 50 watts*3 seconds, which would
be 150 joules each, 300 for the pair. So the resistors look safe. It's
not like this will be used more than maybe 20 times ever.
>
>Hmmm..how about an incandescent 60w bulb?
mechanically. Where do I get a pcb-mount 60 watt lightbulb?
Spehro Pefhany
Apr 17, 2012, 6:12:20 PM4/17/12
to
On Tue, 17 Apr 2012 14:30:44 -0700, John Larkin
<jla...@highlandtechnology.com> wrote:
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
Why not use a little PCB-mount power relay (powered from the
<jla...@highlandtechnology.com> wrote:
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
unfiltered supply)?
That way you don't need the LED or the pushbutton- it's always
discharged to a safe condition shortly after the power is turned off.
Or use a MOSFET and a bright blinkie-LED if you want solid state,
automation and confirmation, but the control gets a bit more complex.
Discharging from + to - might warrant some analysis to make sure there
are not any conditions under which Bad Things might happen of the
polarities of one of the supplies relative to ground flips.
John Larkin
Apr 17, 2012, 6:28:38 PM4/17/12
to
On Tue, 17 Apr 2012 18:12:20 -0400, Spehro Pefhany
<spef...@interlogDOTyou.knowwhat> wrote:
>On Tue, 17 Apr 2012 14:30:44 -0700, John Larkin
><jla...@highlandtechnology.com> wrote:
>
>>
>>
>>I'm designing a box that has +48 and -48 power supplies, each bypassed
>>with 44,000 uF. I figure it will take forever to discharge when the
>>power is switched off, and I don't want to waste a heap of power on a
>>bleeder.
>>
>>So I figured I could put an LED on the board to alert our test people
>>that the board is still hot, and have a DISCHARGE pushbutton. So what
>>I'm thinking is
>>
>>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>
>>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>>better than buying a switch rated for 1 amp at 100 volts DC.
>>
>>I wonder if I could dump the energy into a mosfet, namely get rid of
>>the power resistors and add a smaller source resistor, to make the
>>power fet into a current sink. It's tempting, but then it might blow
>>up. There's about 100 joules to dump.
>
>Why not use a little PCB-mount power relay (powered from the
>unfiltered supply)?
The supplies are commercial switchers, so I don't have an unfiltered
<spef...@interlogDOTyou.knowwhat> wrote:
>On Tue, 17 Apr 2012 14:30:44 -0700, John Larkin
><jla...@highlandtechnology.com> wrote:
>
>>
>>
>>I'm designing a box that has +48 and -48 power supplies, each bypassed
>>with 44,000 uF. I figure it will take forever to discharge when the
>>power is switched off, and I don't want to waste a heap of power on a
>>bleeder.
>>
>>So I figured I could put an LED on the board to alert our test people
>>that the board is still hot, and have a DISCHARGE pushbutton. So what
>>I'm thinking is
>>
>>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>
>>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>>better than buying a switch rated for 1 amp at 100 volts DC.
>>
>>I wonder if I could dump the energy into a mosfet, namely get rid of
>>the power resistors and add a smaller source resistor, to make the
>>power fet into a current sink. It's tempting, but then it might blow
>>up. There's about 100 joules to dump.
>
>Why not use a little PCB-mount power relay (powered from the
>unfiltered supply)?
version. And if anything went wrong, something would catch fire. My
test people are smart enough to turn off power before they push the
DISCHARGE button. And I'd need a relay rated for 1 amp, 100 VDC, 48
volt coil.
>
>That way you don't need the LED or the pushbutton- it's always
>discharged to a safe condition shortly after the power is turned off.
>
>Or use a MOSFET and a bright blinkie-LED if you want solid state,
>automation and confirmation, but the control gets a bit more complex.
>
>Discharging from + to - might warrant some analysis to make sure there
>are not any conditions under which Bad Things might happen of the
>polarities of one of the supplies relative to ground flips.
>
I'll check.
John
Phil Hobbs
Apr 17, 2012, 6:51:43 PM4/17/12
to
John Larkin wrote:
>
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
> --
I assume you have antireversal diodes on the rails, right?
>
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
> --
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
John Larkin
Apr 17, 2012, 7:08:57 PM4/17/12
to
On Tue, 17 Apr 2012 18:51:43 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:
>John Larkin wrote:
>>
>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>> with 44,000 uF. I figure it will take forever to discharge when the
>> power is switched off, and I don't want to waste a heap of power on a
>> bleeder.
>>
>> So I figured I could put an LED on the board to alert our test people
>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>> I'm thinking is
>>
>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>
>> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>> better than buying a switch rated for 1 amp at 100 volts DC.
>>
>> I wonder if I could dump the energy into a mosfet, namely get rid of
>> the power resistors and add a smaller source resistor, to make the
>> power fet into a current sink. It's tempting, but then it might blow
>> up. There's about 100 joules to dump.
>>
>> --
>
>I assume you have antireversal diodes on the rails, right?
>
>Cheers
>
>Phil Hobbs
I figure the switching power supplies will take care of that. But I
<pcdhSpamM...@electrooptical.net> wrote:
>John Larkin wrote:
>>
>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>> with 44,000 uF. I figure it will take forever to discharge when the
>> power is switched off, and I don't want to waste a heap of power on a
>> bleeder.
>>
>> So I figured I could put an LED on the board to alert our test people
>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>> I'm thinking is
>>
>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>
>> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>> better than buying a switch rated for 1 amp at 100 volts DC.
>>
>> I wonder if I could dump the energy into a mosfet, namely get rid of
>> the power resistors and add a smaller source resistor, to make the
>> power fet into a current sink. It's tempting, but then it might blow
>> up. There's about 100 joules to dump.
>>
>> --
>
>I assume you have antireversal diodes on the rails, right?
>
>Cheers
>
>Phil Hobbs
suppose I should verify that.
mike
Apr 17, 2012, 7:28:51 PM4/17/12
to
On 4/17/2012 3:28 PM, John Larkin wrote:
> On Tue, 17 Apr 2012 18:12:20 -0400, Spehro Pefhany
> <spef...@interlogDOTyou.knowwhat> wrote:
>
>> On Tue, 17 Apr 2012 14:30:44 -0700, John Larkin
>> <jla...@highlandtechnology.com> wrote:
>>
>>>
>>>
>>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>>> with 44,000 uF. I figure it will take forever to discharge when the
>>> power is switched off, and I don't want to waste a heap of power on a
>>> bleeder.
>>>
>>> So I figured I could put an LED on the board to alert our test people
>>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>>> I'm thinking is
>>>
>>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>>
>>> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>>> better than buying a switch rated for 1 amp at 100 volts DC.
>>>
>>> I wonder if I could dump the energy into a mosfet, namely get rid of
>>> the power resistors and add a smaller source resistor, to make the
>>> power fet into a current sink. It's tempting, but then it might blow
>>> up. There's about 100 joules to dump.
>>
>> Why not use a little PCB-mount power relay (powered from the
>> unfiltered supply)?
>
> The supplies are commercial switchers, so I don't have an unfiltered
> version. And if anything went wrong, something would catch fire.
Thems is incendiary words...pun intended.
> On Tue, 17 Apr 2012 18:12:20 -0400, Spehro Pefhany
> <spef...@interlogDOTyou.knowwhat> wrote:
>
>> On Tue, 17 Apr 2012 14:30:44 -0700, John Larkin
>> <jla...@highlandtechnology.com> wrote:
>>
>>>
>>>
>>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>>> with 44,000 uF. I figure it will take forever to discharge when the
>>> power is switched off, and I don't want to waste a heap of power on a
>>> bleeder.
>>>
>>> So I figured I could put an LED on the board to alert our test people
>>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>>> I'm thinking is
>>>
>>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>>
>>> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>>> better than buying a switch rated for 1 amp at 100 volts DC.
>>>
>>> I wonder if I could dump the energy into a mosfet, namely get rid of
>>> the power resistors and add a smaller source resistor, to make the
>>> power fet into a current sink. It's tempting, but then it might blow
>>> up. There's about 100 joules to dump.
>>
>> Why not use a little PCB-mount power relay (powered from the
>> unfiltered supply)?
>
> The supplies are commercial switchers, so I don't have an unfiltered
> version. And if anything went wrong, something would catch fire.
My
> test people are smart enough to turn off power before they push the
> DISCHARGE button.
Think that's a false assumption. Who among us has never done a stupid
> test people are smart enough to turn off power before they push the
> DISCHARGE button.
thing?
I'm paranoid when it comes to product liability.
If you adhere to standard safety practices, there are lots of places
to place blame.
Once you add a button that says, "press this to be safe", YOU become
the primary target. The injured party testifies that he pressed the
discharge button before the explosion. Maybe your discharge circuit
failed...maybe it didn't. Doesn't matter. You're screwed!
I think the legal ramifications of this decision far outweigh the
technical issues.
George Herold
Apr 17, 2012, 7:54:24 PM4/17/12
to
On Apr 17, 5:30 pm, John Larkin <jlar...@highlandtechnology.com>
wrote:
I've got a little few watt heater. (120 C operating temp) I put both
the transistor and resistor on the thing I'm heating. Each disipates
about 1/2 the power at normal operating conditions. That seems
safest.
George H.
wrote:
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
> --
>
> John Larkin Highland Technology, Inc
>
> jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
> --
>
> John Larkin Highland Technology, Inc
>
>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom laser controllers
> Photonics and fiberoptic TTL data links
> VME thermocouple, LVDT, synchro acquisition and simulation
I'd keep the resistor. I have no equations to back this up.
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom laser controllers
> Photonics and fiberoptic TTL data links
> VME thermocouple, LVDT, synchro acquisition and simulation
I've got a little few watt heater. (120 C operating temp) I put both
the transistor and resistor on the thing I'm heating. Each disipates
about 1/2 the power at normal operating conditions. That seems
safest.
George H.
Tim Williams
Apr 17, 2012, 8:32:05 PM4/17/12
to
Put in more screws. If it takes a hundred seconds to discharge, 50 screws
should be about right.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"John Larkin" <jla...@highlandtechnology.com> wrote in message
news:svmro7hdg45ta45u3...@4ax.com...
should be about right.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"John Larkin" <jla...@highlandtechnology.com> wrote in message
news:svmro7hdg45ta45u3...@4ax.com...
Dave Platt
Apr 17, 2012, 8:27:40 PM4/17/12
to
In article <jmkubn$u06$1...@dont-email.me>, mike <spa...@gmail.com> wrote:
>On 4/17/2012 3:28 PM, John Larkin wrote:
> My
>> test people are smart enough to turn off power before they push the
>> DISCHARGE button.
>Think that's a false assumption. Who among us has never done a stupid
>thing?
I agree, that's a poor assumption to make. Even if it's 99.99%
>On 4/17/2012 3:28 PM, John Larkin wrote:
> My
>> test people are smart enough to turn off power before they push the
>> DISCHARGE button.
>Think that's a false assumption. Who among us has never done a stupid
>thing?
correct, if you do this operation 10 times a day, you'll blow up
something about once per three years if you have only a single machine.
I'm a software guy... and I don't trust software for safety
interlocks. If you've got a processor driving the gate of something
that can only sustain a 10% duty cycle without burning up, then it's a
*very* good idea to have a hardware safety to disconnect the drive
if the duty cycle exceeds this for more than a very short period of
time. All it takes is one software or processor glitch when the drive
is "on", the code jumps off into the weeds and never turns off the
drive, and you've got a fire on your hands.
I don't trust "wetware" any more than I trust software, for this sort
of safety. Human brains simply aren't reliable enough... and that's
just as true of smart people as unsmart people.
That's why electrical-worker safety regs require lockout and tagging
protocols (with one lock per worker!) on circuit breakers. It avoids
those embarrassing "Oh, I just did a thinko... and now I have to go
apologize to the grieving widow" moments.
In this situation, I'd stick a relay in the switched mains circuit,
and wire it up to disable the DISCHARGE button... make the discharge
circuit a no-op if the mains are still live.
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
dagmarg...@yahoo.com
Apr 17, 2012, 11:20:16 PM4/17/12
to
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
That's a gross SOA violation--a FET-buster.
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
http://www.vishay.com/docs/91266/91266.pdf
@ 50Vds it's good for 2A x 10mS = 1J.
With the resistors it looks great.
--
Cheers,
James Arthur
John Larkin
Apr 18, 2012, 1:25:14 AM4/18/12
to
On Tue, 17 Apr 2012 20:20:16 -0700 (PDT), dagmarg...@yahoo.com
wrote:
Oh, I wouldn't use that fet. It would have to be some monster.
>
>With the resistors it looks great.
Yeah, I should play it safe and stay low-tech on this one.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Multichannel arbitrary waveform generators
wrote:
>
>With the resistors it looks great.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Phil Allison
Apr 18, 2012, 2:20:57 AM4/18/12
to
"John Larkin"
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
It requires a button to be pressed and held down by an operator - Murphy's
Law will apply.
If one electro is not charged, faulty or has a broken connection, all hell
may break loose.
At the very least, hefty reverse diodes across each electro are essential.
... Phil
Jan Panteltje
Apr 18, 2012, 5:15:08 AM4/18/12
to
On a sunny day (Tue, 17 Apr 2012 14:30:44 -0700) it happened John Larkin
<jla...@highlandtechnology.com> wrote in
<svmro7hdg45ta45u3...@4ax.com>:
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
tium experiment
That is exactly what I do in the tritium experiment with the power MOSFET
that has as only purpose heating the hot plate.
Small source resistor, CMOS opamp and feedback, Tim added a capacitor.
For a fixed input voltage the current is constant.
If you want power limiting during dischange add a 2$ PIC and also monitor
voltage across the MOSFET, and drive the MOSFET from filtered PWM [1].
Maybe you need a 3V button cell to keep that computah running to the last
volt (Vgs you need).
Oh what fun...
:-)
[1] you need power limiting as you cannot just current limit,
at high voltages you need less discharge current.
[2] you need to automate the triggring, either by a micro switch if
box is opened, ligh tdetector, mains presence detector, IR proximity,
or whatever.
[3] Giving training courses and exams, with a certificate when passed
to your customers technicians at 1000$ an afternoon helps make money too.
[4] Hey I tho <censored becauce of politcal incorrectness>
<jla...@highlandtechnology.com> wrote in
<svmro7hdg45ta45u3...@4ax.com>:
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
That is exactly what I do in the tritium experiment with the power MOSFET
that has as only purpose heating the hot plate.
Small source resistor, CMOS opamp and feedback, Tim added a capacitor.
For a fixed input voltage the current is constant.
If you want power limiting during dischange add a 2$ PIC and also monitor
voltage across the MOSFET, and drive the MOSFET from filtered PWM [1].
Maybe you need a 3V button cell to keep that computah running to the last
volt (Vgs you need).
Oh what fun...
:-)
[1] you need power limiting as you cannot just current limit,
at high voltages you need less discharge current.
[2] you need to automate the triggring, either by a micro switch if
box is opened, ligh tdetector, mains presence detector, IR proximity,
or whatever.
[3] Giving training courses and exams, with a certificate when passed
to your customers technicians at 1000$ an afternoon helps make money too.
[4] Hey I tho <censored becauce of politcal incorrectness>
Jasen Betts
Apr 18, 2012, 8:37:18 AM4/18/12
to
On 2012-04-17, John Larkin <jla...@highlandtechnology.com> wrote:
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
can you use burn the energy in the ESR of the caps, perhps using an SCR.
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
--
⚂⚃ 100% natural
--- Posted via news://freenews.netfront.net/ - Complaints to ne...@netfront.net ---
Michael A. Terrell
Apr 18, 2012, 9:08:28 AM4/18/12
to
John Larkin wrote:
>
> Robert Macy wrote:
> >
> >Hmmm..how about an incandescent 60w bulb?
>
> That would be neat electrically, and fun to watch, but messy
> mechanically. Where do I get a pcb-mount 60 watt lightbulb?
Where have you been for the last 100 years? There have been surface
> Robert Macy wrote:
> >
> >Hmmm..how about an incandescent 60w bulb?
>
> That would be neat electrically, and fun to watch, but messy
> mechanically. Where do I get a pcb-mount 60 watt lightbulb?
mount incandescent lamps since the first workable light bulb.
http://www.buyacehardware.com/cooper-wiring-surface-mount-lamp-socket-3211216.html
<https://www.google.com/search?q=surface+mount+lamp+socket&num=100&hl=en&newwindow=1&safe=off&client=firefox-a&hs=v1&rls=org.mozilla:en-US:official&prmd=imvns&source=univ&tbm=shop&tbo=u&sa=X&ei=pLuOT8iUOIGQ9QSthZWPDg&ved=0CIYBEK0E&biw=1280&bih=815>
--
You can't have a sense of humor, if you have no sense.
John Larkin
Apr 18, 2012, 11:28:55 AM4/18/12
to
On Wed, 18 Apr 2012 16:20:57 +1000, "Phil Allison" <phi...@tpg.com.au>
wrote:
>
>"John Larkin"
>
>
>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>> with 44,000 uF. I figure it will take forever to discharge when the
>> power is switched off, and I don't want to waste a heap of power on a
>> bleeder.
>>
>> So I figured I could put an LED on the board to alert our test people
>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>> I'm thinking is
>>
>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>
>** That looks like a very dodgy scheme.
>
>It requires a button to be pressed and held down by an operator - Murphy's
>Law will apply.
There will be a bright orange LED on to remind the test tech that the
board is hot. They turn off power and push the button until the LED
goes off. I've done this before on other, bigger amps, and it worked
fine, no problems, but I used a chassis-mount power rocker switch and
a big aluminum-case bolt-down resistor.
Passive bleeders burn a lot of power and are slow and expensive.
>
>If one electro is not charged, faulty or has a broken connection, all hell
>may break loose.
>
>At the very least, hefty reverse diodes across each electro are essential.
>
>
>
>... Phil
>
Across each cap? They are soldered to a PC board. If the connection to
the board is bad - unlikely - the connection to a diode will be bad,
too.
I checked my switching power supplies. Each, when off, seems to have
about a schottky drop in the reverse direction, so there's no worry
about reversing a supply through the discharge resistors.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
wrote:
>
>"John Larkin"
>
>
>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>> with 44,000 uF. I figure it will take forever to discharge when the
>> power is switched off, and I don't want to waste a heap of power on a
>> bleeder.
>>
>> So I figured I could put an LED on the board to alert our test people
>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>> I'm thinking is
>>
>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>
>** That looks like a very dodgy scheme.
>
>It requires a button to be pressed and held down by an operator - Murphy's
>Law will apply.
board is hot. They turn off power and push the button until the LED
goes off. I've done this before on other, bigger amps, and it worked
fine, no problems, but I used a chassis-mount power rocker switch and
a big aluminum-case bolt-down resistor.
Passive bleeders burn a lot of power and are slow and expensive.
>
>If one electro is not charged, faulty or has a broken connection, all hell
>may break loose.
>
>At the very least, hefty reverse diodes across each electro are essential.
>
>
>
>... Phil
>
the board is bad - unlikely - the connection to a diode will be bad,
too.
I checked my switching power supplies. Each, when off, seems to have
about a schottky drop in the reverse direction, so there's no worry
about reversing a supply through the discharge resistors.
--
John Larkin Highland Technology Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
lang...@fonz.dk
Apr 18, 2012, 12:28:29 PM4/18/12
to
On 18 Apr., 07:25, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Tue, 17 Apr 2012 20:20:16 -0700 (PDT), dagmargoodb...@yahoo.com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Tue, 17 Apr 2012 20:20:16 -0700 (PDT), dagmargoodb...@yahoo.com
> wrote:
>
>
>
>
>
>
>
>
>
> >On Apr 17, 5:30 pm, John Larkin <jlar...@highlandtechnology.com>
> >wrote:
> >> I'm designing a box that has +48 and -48 power supplies, each bypassed
> >> with 44,000 uF. I figure it will take forever to discharge when the
> >> power is switched off, and I don't want to waste a heap of power on a
> >> bleeder.
>
> >> So I figured I could put an LED on the board to alert our test people
> >> that the board is still hot, and have a DISCHARGE pushbutton. So what
> >> I'm thinking is
>
> >>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> >> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> >> better than buying a switch rated for 1 amp at 100 volts DC.
>
> >> I wonder if I could dump the energy into a mosfet, namely get rid of
> >> the power resistors and add a smaller source resistor, to make the
> >> power fet into a current sink. It's tempting, but then it might blow
> >> up. There's about 100 joules to dump.
>
> >That's a gross SOA violation--a FET-buster.
> >http://www.vishay.com/docs/91266/91266.pdf
>
> >@ 50Vds it's good for 2A x 10mS = 1J.
>
> Oh, I wouldn't use that fet. It would have to be some monster.
>
>
>
> >With the resistors it looks great.
>
> Yeah, I should play it safe and stay low-tech on this one.
>
> --
>
> John Larkin Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
>
>
>
>
>
>
>
>
>
> >On Apr 17, 5:30 pm, John Larkin <jlar...@highlandtechnology.com>
> >wrote:
> >> I'm designing a box that has +48 and -48 power supplies, each bypassed
> >> with 44,000 uF. I figure it will take forever to discharge when the
> >> power is switched off, and I don't want to waste a heap of power on a
> >> bleeder.
>
> >> So I figured I could put an LED on the board to alert our test people
> >> that the board is still hot, and have a DISCHARGE pushbutton. So what
> >> I'm thinking is
>
> >>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> >> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> >> better than buying a switch rated for 1 amp at 100 volts DC.
>
> >> I wonder if I could dump the energy into a mosfet, namely get rid of
> >> the power resistors and add a smaller source resistor, to make the
> >> power fet into a current sink. It's tempting, but then it might blow
> >> up. There's about 100 joules to dump.
>
> >That's a gross SOA violation--a FET-buster.
> >http://www.vishay.com/docs/91266/91266.pdf
>
> >@ 50Vds it's good for 2A x 10mS = 1J.
>
> Oh, I wouldn't use that fet. It would have to be some monster.
>
>
>
> >With the resistors it looks great.
>
> Yeah, I should play it safe and stay low-tech on this one.
>
> --
>
lang...@fonz.dk
Apr 18, 2012, 12:36:22 PM4/18/12
to
On 18 Apr., 05:20, dagmargoodb...@yahoo.com wrote:
> On Apr 17, 5:30 pm, John Larkin <jlar...@highlandtechnology.com>
> wrote:
>
>
>
>
>
>
>
>
>
> > I'm designing a box that has +48 and -48 power supplies, each bypassed
> > with 44,000 uF. I figure it will take forever to discharge when the
> > power is switched off, and I don't want to waste a heap of power on a
> > bleeder.
>
> > So I figured I could put an LED on the board to alert our test people
> > that the board is still hot, and have a DISCHARGE pushbutton. So what
> > I'm thinking is
>
> >http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> > Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> > better than buying a switch rated for 1 amp at 100 volts DC.
>
> > I wonder if I could dump the energy into a mosfet, namely get rid of
> > the power resistors and add a smaller source resistor, to make the
> > power fet into a current sink. It's tempting, but then it might blow
> > up. There's about 100 joules to dump.
>
> That's a gross SOA violation--a FET-buster.http://www.vishay.com/docs/91266/91266.pdf
> On Apr 17, 5:30 pm, John Larkin <jlar...@highlandtechnology.com>
> wrote:
>
>
>
>
>
>
>
>
>
> > I'm designing a box that has +48 and -48 power supplies, each bypassed
> > with 44,000 uF. I figure it will take forever to discharge when the
> > power is switched off, and I don't want to waste a heap of power on a
> > bleeder.
>
> > So I figured I could put an LED on the board to alert our test people
> > that the board is still hot, and have a DISCHARGE pushbutton. So what
> > I'm thinking is
>
> >http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> > Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> > better than buying a switch rated for 1 amp at 100 volts DC.
>
> > I wonder if I could dump the energy into a mosfet, namely get rid of
> > the power resistors and add a smaller source resistor, to make the
> > power fet into a current sink. It's tempting, but then it might blow
> > up. There's about 100 joules to dump.
>
>
> @ 50Vds it's good for 2A x 10mS = 1J.
it on the limit but: it will barely do 500mA @ 100V, and the voltage
> @ 50Vds it's good for 2A x 10mS = 1J.
will quickly drop
abs. max Pd 60W, so that will also be just under the limit, and again
the voltage will
drop start to drop.
looks like anything over ~100ms is same as DC so the 2.5C/W tjc should
count
so with a block of alu big enough to eat the 150J without getting more
than a few deg
hotter even that little fet might just survive
>
> With the resistors it looks great.
>
> --
> Cheers,
> James Arthur
bloggs.fred...@gmail.com
Apr 18, 2012, 3:04:15 PM4/18/12
to
Spehro Pefhany
Apr 18, 2012, 4:43:58 PM4/18/12
to
protect just about anything.
JW
Apr 19, 2012, 5:44:00 AM4/19/12
to
On Wed, 18 Apr 2012 08:28:55 -0700 John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote in Message id:
<m0nto7199apsur575...@4ax.com>:
>On Wed, 18 Apr 2012 16:20:57 +1000, "Phil Allison" <phi...@tpg.com.au>
>wrote:
>
>>
>>"John Larkin"
>>
>>
>>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>>> with 44,000 uF. I figure it will take forever to discharge when the
>>> power is switched off, and I don't want to waste a heap of power on a
>>> bleeder.
>>>
>>> So I figured I could put an LED on the board to alert our test people
>>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>>> I'm thinking is
>>>
>>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>
>>
>>** That looks like a very dodgy scheme.
>>
>>It requires a button to be pressed and held down by an operator - Murphy's
>>Law will apply.
>
>There will be a bright orange LED on to remind the test tech that the
>board is hot. They turn off power and push the button until the LED
>goes off. I've done this before on other, bigger amps, and it worked
>fine, no problems, but I used a chassis-mount power rocker switch and
>a big aluminum-case bolt-down resistor.
>
>Passive bleeders burn a lot of power and are slow and expensive.
How about a passive bleeder that's switched into the circuit when the
power switch is turned off?
Seems obvious, but maybe I'm missing something?
<jjla...@highNOTlandTHIStechnologyPART.com> wrote in Message id:
<m0nto7199apsur575...@4ax.com>:
>On Wed, 18 Apr 2012 16:20:57 +1000, "Phil Allison" <phi...@tpg.com.au>
>wrote:
>
>>
>>"John Larkin"
>>
>>
>>> I'm designing a box that has +48 and -48 power supplies, each bypassed
>>> with 44,000 uF. I figure it will take forever to discharge when the
>>> power is switched off, and I don't want to waste a heap of power on a
>>> bleeder.
>>>
>>> So I figured I could put an LED on the board to alert our test people
>>> that the board is still hot, and have a DISCHARGE pushbutton. So what
>>> I'm thinking is
>>>
>>> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>>
>>
>>** That looks like a very dodgy scheme.
>>
>>It requires a button to be pressed and held down by an operator - Murphy's
>>Law will apply.
>
>There will be a bright orange LED on to remind the test tech that the
>board is hot. They turn off power and push the button until the LED
>goes off. I've done this before on other, bigger amps, and it worked
>fine, no problems, but I used a chassis-mount power rocker switch and
>a big aluminum-case bolt-down resistor.
>
>Passive bleeders burn a lot of power and are slow and expensive.
power switch is turned off?
Seems obvious, but maybe I'm missing something?
John Larkin
Apr 19, 2012, 10:29:13 AM4/19/12
to
there's no AC power coming in. The switch is actually part of the AC
inlet/filter assembly, so I can't add a pole to it or anything like
that. So I'd have to sense 120-240 VAC and drive a discharge device.
This box will be CE/UL tested, so any primary circuits have to be
reviewed and hipot tested and all that. Hassle.
If anything went wrong with the logic, the resistors would smoke.
Unless I used huge power resistors.
A constant-power bleeder might be interesting, something with bipolar
transistors or depletion mosfets, but it would still need a heat sink.
100 joules into a 2-watt sink would still take 50 seconds to
discharge.
Michael A. Terrell
Apr 19, 2012, 10:52:51 AM4/19/12
to
JW wrote:
>
> How about a passive bleeder that's switched into the circuit when the
> power switch is turned off?
>
> Seems obvious, but maybe I'm missing something?
current bleeders? They worked well enough on high voltage, high current
power supplies in broadcast transmitters. I've also seen them on PC
board paneling routers, to keep idiots from losing their fingers.
Spehro Pefhany
Apr 19, 2012, 11:28:38 AM4/19/12
to
On Thu, 19 Apr 2012 07:29:13 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
>I'd have to tell when the power switch is off, or actually when
>there's no AC power coming in. The switch is actually part of the AC
>inlet/filter assembly, so I can't add a pole to it or anything like
>that. So I'd have to sense 120-240 VAC and drive a discharge device.
>This box will be CE/UL tested, so any primary circuits have to be
>reviewed and hipot tested and all that. Hassle.
>
>If anything went wrong with the logic, the resistors would smoke.
>Unless I used huge power resistors.
>
>A constant-power bleeder might be interesting, something with bipolar
>transistors or depletion mosfets, but it would still need a heat sink.
Just a SMPS operating into a resistor would perform that function.
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
>I'd have to tell when the power switch is off, or actually when
>there's no AC power coming in. The switch is actually part of the AC
>inlet/filter assembly, so I can't add a pole to it or anything like
>that. So I'd have to sense 120-240 VAC and drive a discharge device.
>This box will be CE/UL tested, so any primary circuits have to be
>reviewed and hipot tested and all that. Hassle.
>
>If anything went wrong with the logic, the resistors would smoke.
>Unless I used huge power resistors.
>
>A constant-power bleeder might be interesting, something with bipolar
>transistors or depletion mosfets, but it would still need a heat sink.
>100 joules into a 2-watt sink would still take 50 seconds to
>discharge.
switch in a load to kill it when it goes well out of tolerance
(obviously it has to withstand a short transient at turn-on, and the
supply must not current limit and fail to start- or it could be
inhibited at power-on with a bit more complexity).
Eg. if supply >= 85V then draw 20mA = 2W (12 seconds to get to 85V)
if supply < 85V then switch a 12 ohm resistor on (time constant 0.26
s), such as those Welwyn planar parts. Even the smallest can handle
100J. If you're worried about smoking the resistor, it could be
protected (at some cost in complexity).
bloggs.fred...@gmail.com
Apr 19, 2012, 1:03:42 PM4/19/12
to
On Tuesday, April 17, 2012 5:30:44 PM UTC-4, John Larkin wrote:
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
>
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
>
>
> --
>
> John Larkin Highland Technology, Inc
>
>
> John Larkin Highland Technology, Inc
>
> jlarkin at highlandtechnology dot com
> http://www.highlandtechnology.com
>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom laser controllers
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Photonics and fiberoptic TTL data links
> VME thermocouple, LVDT, synchro acquisition and simulation
Isn't that IRFR120 a bit risque here, with an absolute max of 100V VDS?
bloggs.fred...@gmail.com
Apr 19, 2012, 11:27:47 PM4/19/12
to
John Larkin
Apr 19, 2012, 11:59:31 PM4/19/12
to
--
John Larkin Highland Technology Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
Winston
Apr 21, 2012, 1:56:08 AM4/21/12
to
John Larkin wrote:
>
>
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
Can you replace the switch with NC relay contacts driven
>
>
> I'm designing a box that has +48 and -48 power supplies, each bypassed
> with 44,000 uF. I figure it will take forever to discharge when the
> power is switched off, and I don't want to waste a heap of power on a
> bleeder.
>
> So I figured I could put an LED on the board to alert our test people
> that the board is still hot, and have a DISCHARGE pushbutton. So what
> I'm thinking is
>
> http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
> Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
> better than buying a switch rated for 1 amp at 100 volts DC.
>
> I wonder if I could dump the energy into a mosfet, namely get rid of
> the power resistors and add a smaller source resistor, to make the
> power fet into a current sink. It's tempting, but then it might blow
> up. There's about 100 joules to dump.
by the switched side of the line?
That way, the dump starts automagically.
--Winston
Jasen Betts
Apr 21, 2012, 4:47:46 AM4/21/12
to
> If anything went wrong with the logic, the resistors would smoke.
> Unless I used huge power resistors.
> A constant-power bleeder might be interesting, something with bipolar
> transistors or depletion mosfets, but it would still need a heat sink.
> 100 joules into a 2-watt sink would still take 50 seconds to
> discharge.
Something like this? (not these transistors though, ones rated for
the voltage)
Version 4
SHEET 1 880 680
WIRE -784 32 -800 32
WIRE -672 32 -784 32
WIRE -576 32 -672 32
WIRE -528 32 -576 32
WIRE -432 32 -528 32
WIRE -224 32 -432 32
WIRE -576 48 -576 32
WIRE -528 48 -528 32
WIRE -432 48 -432 32
WIRE -224 64 -224 32
WIRE -784 96 -784 32
WIRE -288 112 -384 112
WIRE -864 128 -864 32
WIRE -672 128 -672 32
WIRE -576 128 -576 112
WIRE -528 128 -528 112
WIRE -528 128 -576 128
WIRE -480 128 -480 112
WIRE -480 128 -528 128
WIRE -384 128 -384 112
WIRE -480 144 -480 128
WIRE -784 192 -784 160
WIRE -224 192 -224 160
WIRE -384 208 -384 192
WIRE -864 240 -864 208
WIRE -832 240 -864 240
WIRE -832 272 -832 240
WIRE -864 304 -864 240
WIRE -784 304 -784 256
WIRE -784 304 -864 304
WIRE -672 304 -672 208
WIRE -672 304 -784 304
WIRE -480 304 -480 288
WIRE -480 304 -672 304
WIRE -384 304 -384 272
WIRE -384 304 -480 304
WIRE -224 304 -224 272
WIRE -224 304 -384 304
FLAG -832 272 0
SYMBOL voltage -864 112 R0
WINDOW 3 -59 232 VLeft 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PWL(0.001 100 1 100 1.0001 0)
SYMBOL cap -800 96 R0
SYMATTR InstName C1
SYMATTR Value 44000µf
SYMBOL cap -800 192 R0
SYMATTR InstName C2
SYMATTR Value 44000µf
SYMBOL diode -864 48 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D1
SYMBOL res -688 112 R0
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL cap -464 144 M0
SYMATTR InstName C3
SYMATTR Value 1000µ
SYMBOL npn -288 64 R0
SYMATTR InstName Q1
SYMATTR Value 2N3055
SYMBOL pnp -384 48 R90
WINDOW 3 -48 13 VRight 2
SYMATTR InstName Q2
SYMATTR Value 2N2907
SYMBOL diode -560 48 M0
SYMATTR InstName D2
SYMATTR Value MURS120
SYMBOL res -496 304 M180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 100
SYMBOL res -240 176 R0
SYMATTR InstName R3
SYMATTR Value .1
SYMBOL diode -400 208 R0
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL diode -400 128 R0
SYMATTR InstName D4
SYMATTR Value 1N4148
SYMBOL cap -544 48 R0
SYMATTR InstName C4
SYMATTR Value 100µ
TEXT -938 350 Left 2 !.tran 10
Nico Coesel
Apr 21, 2012, 6:09:57 AM4/21/12
to
John Larkin <jla...@highlandtechnology.com> wrote:
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
I'd add a bleeder as well. I don't like high voltages sitting
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
somewhere for a long time after a device is switched off. Is there no
way to cut back on the capacitance?
--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------
josephkk
Apr 28, 2012, 5:54:58 PM4/28/12
to
On Tue, 17 Apr 2012 14:30:44 -0700, John Larkin
need a $1.00 mosfet though. (rated 2000 A pulse).
?-)
<jla...@highlandtechnology.com> wrote:
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
Given your instrumentation capability i would try it and see. You may
>
>
>I'm designing a box that has +48 and -48 power supplies, each bypassed
>with 44,000 uF. I figure it will take forever to discharge when the
>power is switched off, and I don't want to waste a heap of power on a
>bleeder.
>
>So I figured I could put an LED on the board to alert our test people
>that the board is still hot, and have a DISCHARGE pushbutton. So what
>I'm thinking is
>
>http://dl.dropbox.com/u/53724080/Circuits/Cap_Discharge.JPG
>
>Turns out that using a 30 cent mosfet and a 15 cent pushbutton is
>better than buying a switch rated for 1 amp at 100 volts DC.
>
>I wonder if I could dump the energy into a mosfet, namely get rid of
>the power resistors and add a smaller source resistor, to make the
>power fet into a current sink. It's tempting, but then it might blow
>up. There's about 100 joules to dump.
need a $1.00 mosfet though. (rated 2000 A pulse).
?-)
0 new messages