paralleling relay coils

[bhav...@gmail.com]

I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.

-bhavj

[Uwe Hercksen]

bhav...@gmail.com schrieb:

> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>

Hello,

the current through one coil is 40 mA, the five coils take 200 mA. A
1N400x is good for 1 A. If these five relays are not far away from each
other, only diode will do in my opinion. The current flowing through the
diode should not be much larger than the current flowing through all
coils together.

Bye

[Phil Hobbs]

Make sure you use the low-voltage one, 1N4001. Higher-voltage diodes of
that series have long turn-on delays, so they aren't much good for
suppressing inductive kicks.

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 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net

[bhav...@gmail.com]

The relays stacked together and trace length is approx 70 mm from 1st relay coil to the 5th relay coil. So, do you think it would be a better option to place the diode across the coil of the middle (3rd) relay?

[bhav...@gmail.com]

Thanks. Would it be better to use 1A schottky than normal diodes like 1N400x?

[Phil Hobbs]

On 8/16/2013 10:26 AM, bhav...@gmail.com wrote:
> On Friday, August 16, 2013 7:03:04 PM UTC+5:30, Phil Hobbs wrote:
>> On 8/16/2013 8:05 AM, Uwe Hercksen wrote:
>>
>>>
>>
>>>
>>
>>> bhav...@gmail.com schrieb:
>>
>>>
>>
>>>> I am connecting five 12V relay coils in parallel to switch five
>>
>>>> different loads. Is it necessary to have fly-back diode for each relay
>>
>>>> coil or just one 1N400x diode in parallel is sufficient? Each coil is
>>
>>>> 300 ohms.
>>
>>>>
>>
>>> Hello,
>>> the current through one coil is 40 mA, the five coils take 200 mA. A
>>> 1N400x is good for 1 A. If these five relays are not far away from each
>>> other, only diode will do in my opinion. The current flowing through the
>>> diode should not be much larger than the current flowing through all
>>> coils together.
>>

>> Make sure you use the low-voltage one, 1N4001. Higher-voltage diodes of
>> that series have long turn-on delays, so they aren't much good for
>> suppressing inductive kicks.

> Thanks. Would it be better to use 1A schottky than normal diodes like 1N400x?
>

The 1N4001 should be fine, but do use at least a 60V transistor to drive
the relays.

[bhav...@gmail.com]

BCX56 is the transistor. Relay coils are connected between emitter and ground. 12V is applied at the collector.

[Phil Hobbs]

Oh, that's easy then. When the emitter goes low, current will continue
to flow without interruption until it decays. No spikes to worry about
at all, no diode needed, as long as you don't open-circuit the base.

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

[Phil Hobbs]

One more thing: Do watch out for oscillation. Putting 100 ohms or so in
series with the base will usually cure it. (A transistor with its
collector and base at the same voltage is still in normal bias, and can
still oscillate.)

[John Larkin]

It doesn't matter where the flyback diode is located.


--

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
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

[Nico Coesel]

bhav...@gmail.com wrote:

>I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>

I always use a transistor or MOSFET with internal diode. No need for
an external diode.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

[bud--]

On 8/16/2013 5:23 AM, bhav...@gmail.com wrote:
> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>
> -bhavj

may be of interest
http://web.archive.org/web/20110104003731/http://relays.tycoelectronics.com/appnotes/app_pdfs/13c3264.pdf

[John Larkin]

The OP should post his schematic. I've seen interesting things, like
putting TTL levels into a base and expecting 12 volt swing at the
emitter.


--

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 drivers and controllers

Photonics and fiberoptic TTL data links

VME thermocouple, LVDT, synchro acquisition and simulation

[Phil Hobbs]

I was sort of assuming that it was CD4000 CMOS, but you're right, you
never can tell.

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

[bhav...@gmail.com]

On Friday, August 16, 2013 4:53:17 PM UTC+5:30, bhav...@gmail.com wrote:
> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>
>
>
> -bhavj

Here is the schematic I quickly drafted. All the 5 coils and fly back diode are in parallel and will be connected to 12V_RLY_COIL.

https://picasaweb.google.com/106331244879972692887/August162013?authuser=0&authkey=Gv1sRgCI_Wuvvh_NXi3AE&feat=directlink#5912784366042056882

[Jeff Liebermann]

On Fri, 16 Aug 2013 15:52:54 GMT, ni...@puntnl.niks (Nico Coesel)
wrote:

>bhav...@gmail.com wrote:
>>I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>>

>I always use a transistor or MOSFET with internal diode. No need for
>an external diode.

The idea is for the diode to protect the switching device (xsistor,
FET, whatever) from the switching spike. The diode is usually placed
near the coil connections so that the current produced by the spike
does not couple to nearby circuits, as it would if the diode were
placed on or in the switching device. If the switching device and the
relays are all located very close together, it probably doesn't
matter. However, if the relays are scattered all over the PCB, it
might be better to suppress the spikes at the source, near the coils.

In my checkered past, I helped design an HF automatic antenna tuner.
There were about 20 relays that would cycle a collection of inductors
and capacitors through a binary search pattern until a suitably low
VSWR match was found. Tuning speed was important, so some of the
relays sometimes sounded like buzzers. The now ancient microprocessor
used (Intel 8748) was rather sensitive to noise. However, it wasn't
RF that was causing temporarily insanity in the uP. It was switching
transients traceable to back EMF from the relay coils. Nobody had
mentioned to the PCB layout person that the flyback diodes needed to
be close to the relay coils. The next PCB revision moved them much
closer, which produced far less noise. The rest of the noise was
caused by trying to open or close all 20 relays at once (ground
bounce), which required adding some filter caps and some slight delays
in the firmware. I don't think this will be a problem with only 5
relays in parallel unless there's sensitive circuitry nearby.



--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Harry Dellamano]

<bhav...@gmail.com> wrote in message
news:83ca1537-cbda-407c...@googlegroups.com...

Sorry, you have just been demoted to SCI Electronics Basic!
Harry

[Martin Riddle]

"John Larkin" <jla...@highlandtechnology.com> wrote in message
news:27ps09d2v1isfcscn...@4ax.com...

I was thinking the same thing with a NPN and the collector tied to the
12v rail,
you'd need to take the Base above the 12v rail to turn it on.

Cheers

[bloggs.fred...@gmail.com]

On Friday, August 16, 2013 2:28:55 PM UTC-4, bhav...@gmail.com wrote:

>
> https://picasaweb.google.com/106331244879972692887/August162013?authuser=0&authkey=Gv1sRgCI_Wuvvh_NXi3AE&feat=directlink#5912784366042056882

Is that supposed to be funny?

[Spehro Pefhany]

Harry is right.. there are multiple issues.

1) Can we assume you're trying to drive the relays with a
3.3V CMOS output, and 3.3V in should turn the relays "on"?

1a) If so, is the common for the 3.3V supply same as the ground
shown?

2) Any particular reason you want a high-side driver
(so one side of the relays is grounded)?

3) Is this an automotive 12V system with the associated
transient issues?

4) What's with the 100uF cap across the relays, and the
0.1uF cap, for that matter?

--sp

[John Larkin]

Sorry, that won't work. Assuming the other end of the relay coils
return to ground, you'd only get about 2 volts across the coils.

[Tim Wescott]

Pulling the base up to 12V would leave around 11.3V on the emitter, which
would be enough to turn the relays on.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

[Phil Hobbs]

Nah, your average 12V relay will pull in around 9V. 11.3ish is fat city.

[Phil Hobbs]

Oh, dear. That'll give you about a volt and a half on the relay coils.

Get rid of D1 and both caps, connect R67 to the base of Q2, move Q3 to
where C152 is now, and invert the logic level (low=ON).

[amdx]

Why is it that nobody helps the guy, rather than just letting him
know you're all smarter than him.

The more common method to drive a relay is;
+12v to one side of relay, other side of relay goes to the collector of
an NPN transistor, emitter of transistor goes to ground. Put a 1k
resistor in series with base of transistor and apply your 3.3v the 1K
resistor.
Install diode across relay.
Is there a reason you don't want to do it that way?

Mikek

*1K value can be adjusted.

[John Larkin]

On Fri, 16 Aug 2013 18:24:54 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>On 8/16/2013 2:28 PM, bhav...@gmail.com wrote:
>> On Friday, August 16, 2013 4:53:17 PM UTC+5:30, bhav...@gmail.com wrote:
>>> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>>>
>>>
>>>
>>> -bhavj
>>
>> Here is the schematic I quickly drafted. All the 5 coils and fly back diode are in parallel and will be connected to 12V_RLY_COIL.
>>
>> https://picasaweb.google.com/106331244879972692887/August162013?authuser=0&authkey=Gv1sRgCI_Wuvvh_NXi3AE&feat=directlink#5912784366042056882
>>
>Oh, dear. That'll give you about a volt and a half on the relay coils.
>
>Get rid of D1 and both caps, connect R67 to the base of Q2, move Q3 to
>where C152 is now, and invert the logic level (low=ON).
>
>Cheers
>
>Phil Hobbs

Looks like he wants to switch the coils and regulate the coil voltage
down to 12. 18V is a bit much, 2.2x the normal coil dissipation.

[bloggs.fred...@gmail.com]

Could be automotive relays with one terminal at frame ground, then he needs a high side switch.

[bloggs.fred...@gmail.com]

On Friday, August 16, 2013 6:19:14 PM UTC-4, Phil Hobbs wrote:
> > you'd need to take the Base above the 12v rail to turn it on.
>
>
>
> Nah, your average 12V relay will pull in around 9V. 11.3ish is fat city.
>
>

Not at max operating temperature...and depending on relay design, you could be looking at 40oC core temp rise in steady state.

[Phil Hobbs]

I've obviously led a sheltered life, since I've never seen a 12V relay
datasheet where pull-in wasn't guaranteed at well below 11.3V. Do you
have an example?

[Phil Hobbs]

On 8/16/2013 8:33 PM, John Larkin wrote:
> On Fri, 16 Aug 2013 18:24:54 -0400, Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote:
>
>> On 8/16/2013 2:28 PM, bhav...@gmail.com wrote:
>>> On Friday, August 16, 2013 4:53:17 PM UTC+5:30, bhav...@gmail.com wrote:
>>>> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>>>>
>>>>
>>>>
>>>> -bhavj
>>>
>>> Here is the schematic I quickly drafted. All the 5 coils and fly back diode are in parallel and will be connected to 12V_RLY_COIL.
>>>
>>> https://picasaweb.google.com/106331244879972692887/August162013?authuser=0&authkey=Gv1sRgCI_Wuvvh_NXi3AE&feat=directlink#5912784366042056882
>>>
>> Oh, dear. That'll give you about a volt and a half on the relay coils.
>>
>> Get rid of D1 and both caps, connect R67 to the base of Q2, move Q3 to
>> where C152 is now, and invert the logic level (low=ON).
>>
>> Cheers
>>
>> Phil Hobbs
>
> Looks like he wants to switch the coils and regulate the coil voltage
> down to 12. 18V is a bit much, 2.2x the normal coil dissipation.

You're probably right--the actual intention is sort of hard to gauge
from the schematic. In that case, the OP could keep the zener.

[Spehro Pefhany]

On Fri, 16 Aug 2013 17:33:42 -0700, the renowned John Larkin
<jla...@highlandtechnology.com> wrote:

>On Fri, 16 Aug 2013 18:24:54 -0400, Phil Hobbs
><pcdhSpamM...@electrooptical.net> wrote:
>
>>On 8/16/2013 2:28 PM, bhav...@gmail.com wrote:
>>> On Friday, August 16, 2013 4:53:17 PM UTC+5:30, bhav...@gmail.com wrote:
>>>> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>>>>
>>>>
>>>>
>>>> -bhavj
>>>
>>> Here is the schematic I quickly drafted. All the 5 coils and fly back diode are in parallel and will be connected to 12V_RLY_COIL.
>>>
>>> https://picasaweb.google.com/106331244879972692887/August162013?authuser=0&authkey=Gv1sRgCI_Wuvvh_NXi3AE&feat=directlink#5912784366042056882
>>>
>>Oh, dear. That'll give you about a volt and a half on the relay coils.
>>
>>Get rid of D1 and both caps, connect R67 to the base of Q2, move Q3 to
>>where C152 is now, and invert the logic level (low=ON).
>>
>>Cheers
>>
>>Phil Hobbs
>
>Looks like he wants to switch the coils and regulate the coil voltage
>down to 12. 18V is a bit much, 2.2x the normal coil dissipation.

He could use this as a $2 one-chip solution: TL751M12QKVURQ1
(active low input).

It's possible to modify the given circuit a bit and make it work okay
too.. eliminate the caps, connect R68 to the input voltage (and make
it 10K), reduce R67 to 330 ohms, add Q1 same type as Q3, E to ground,
C to base of Q3, base to input through 2K. It will have a higher
dropout voltage than the regulator solution so examine carefully the
high ambient temperature (at the relay)/low input voltage condition.
(this is also active low input).


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

[John Larkin]

I scribbled a few circuits, until I ran out of paper.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Relay_Drivers.pdf

Oh, 1117s need an output cap.

--

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

Photonics and fiberoptic TTL data links

[bhav...@gmail.com]

Thanks for taking time to draw them. Yes, as you said I am trying to regulate as well as switch the power to the coils. In the fig-1, why is that pnp needed instead of resisting to limit current?

[Spehro Pefhany]

I really like (4). Short and to the point.

[Spehro Pefhany]

On Fri, 16 Aug 2013 21:34:45 -0400, the renowned Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>On 8/16/2013 8:49 PM, bloggs.fred...@gmail.com wrote:
>> On Friday, August 16, 2013 6:19:14 PM UTC-4, Phil Hobbs wrote:
>>>> you'd need to take the Base above the 12v rail to turn it on.
>>>
>>>
>>>
>>> Nah, your average 12V relay will pull in around 9V. 11.3ish is fat
>>> city.
>>>
>>>
>>
>> Not at max operating temperature...and depending on relay design, you
>> could be looking at 40oC core temp rise in steady state.
>>
>
>I've obviously led a sheltered life, since I've never seen a 12V relay
>datasheet where pull-in wasn't guaranteed at well below 11.3V. Do you
>have an example?
>
>Cheers
>
>Phil Hobbs

Hi, Phil:-

Consider a relay such as this one:-

http://media.digikey.com/pdf/Data%20Sheets/Tyco%20Electronics%20P%20B%20PDFs/ORWH.pdf

Pull in voltage is rated at 8.4V for the 12V nominal relay. That's
specified "without pre-energization at ambient temperature 23°C" (fine
print).

If you require the type F insulation (155°C) they offer, then the coil
resistance could then be more than 50% higher than at 23°C, so the
guaranteed minimum pull-in voltage would actually be more than 12VDC!

Somewhat less than nominal voltage is normally okay if the input
voltage is regulated and/or the environment is fairly benign, but
that's not always true. Probably sluggish turn-on doesn't help relay
life either. I don't like unnecessarily to give away voltage in a
relay driver (eg. by using darlingtons).

[Phil Hobbs]

Fair enough, if you're running that hot. Of course in your business, it
would probably pull in at a volt or so. ;)

[John Larkin]

On Fri, 16 Aug 2013 22:30:20 -0400, Spehro Pefhany

I like 7, assuming the firmware cooperates.

[John Larkin]

The resistor value could be a problem. If it's too big, there will be a lot of
voltage drop in the resistor, because of the base current. If it's too small, it
will get hot when its low side is grounded by the little mosfet. There may be no
value that works.

Your relays need 200 mA. If the NPN transistor has a guaranteed beta of 100, you
could need 2 mA of base current. Assume that when you have 12 volt power, you
want at least 11 volts on the relays; the transistor drops 0.7, so that leaves
0.3 for the resistor. The resistors has to be 150 ohms. Now let the supply go up
to 18 and turn on the mosfet. The current through the resistor becomes 120 mA
and it dissipates over 2 watts.

If you think the relays will operate with less voltage, use a bigger resistor,
and it might work. But it's a messy compromise.

[Phil Hobbs]

The other approach would be to use #7 with a small resistor, and use the
processor to measure the supply and PWM the relays appropriately. A
Schottky catch diode would help.

[Spehro Pefhany]

On Fri, 16 Aug 2013 19:43:05 -0700, the renowned John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:

>
>
>I like 7, assuming the firmware cooperates.

Possible pattern-sensitive relay operation frightens and confuses me.

[John Larkin]

On Fri, 16 Aug 2013 23:37:37 -0400, Spehro Pefhany
<spef...@interlogDOTyou.knowwhat> wrote:

>On Fri, 16 Aug 2013 19:43:05 -0700, the renowned John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>I like 7, assuming the firmware cooperates.
>
>Possible pattern-sensitive relay operation frightens and confuses me.
>
>

Man up!

If the controller guarantees enough off time for the cap to charge, a couple
hundred ms maybe, it works. Saves power, too.

[John Larkin]

On Fri, 16 Aug 2013 23:06:35 -0400, Phil Hobbs

Or no resistor, no measurement. The uP could drive the relays ON at 100% duty
cycle initially, but then drop down to something like 70% after a reasonable
pull-in delay.

[Jeff Liebermann]

On Fri, 16 Aug 2013 19:08:34 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:

>I scribbled a few circuits, until I ran out of paper.
>https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Relay_Drivers.pdf
>Oh, 1117s need an output cap.

Nice. I like #7. Cheap and easy.

I was thinking of a ULN2003 hex darlington array, with built in
flyback diodes, would work:
<http://www.ti.com/lit/ds/symlink/uln2003a.pdf>
One hex section per relay.
One spare section.
No extra parts, no regulator, no added diodes.
Slightly easier wiring if the relays are scattered all over the PCB.
Approx 200-300 milliwatt device dissipation when relays are energized.

At 3.0V from the GPIO pin, input current is about 500ua which 3.3V
CMOS should handle. If it's a Rasberry Pi, the default GPIO output
pull up or down current is 8ma, which is more than enough.

I don't see any advantage to this scheme, except that it makes
troubleshooting a bit easier since the relays can be energized
individually.


--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Jeff Liebermann]

On Fri, 16 Aug 2013 21:34:45 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>I've obviously led a sheltered life, since I've never seen a 12V relay
>datasheet where pull-in wasn't guaranteed at well below 11.3V. Do you
>have an example?

I don't have an example. When working with automotive type relays, I
assume that they will work within 10% of nominal voltage (13.6 VDC)
without difficulty, 15% to the limits of the maximum ratings, and 20%
if you're lucky and can control the temperature. Obviously, this
varies with the situation, but has been a good general rule for first
approximations.

In the marine radio biz, marketeering decided that the radios needed
to operate on the battery running the trolling motor on small
motorboat used for fishing. Normally, it's a half dead automobile
battery quickly charged before going fishing. Some crude measurements
showed that such a derangement was likely to bring the battery voltage
down to as low as 10.0 VDC[1]. Since the radios were for emergencies,
it was assumed that if it was that low, the boat was having a genuine
emergency. Ignoring the improbability of the scenario, marketing was
deemed always right by management, and must be obeyed. Note that this
exercise was to be performed on the entire line of products (about 10
different model radios at the time).

So, I took a radio that was designed for 11.5 to 15.5VDC (+/- 15%) and
tried to squeeze another 10% out of the lower end of the voltage
range. This was initially quite a trick because the internal
regulators were all set to 9.1 VDC. After the regulators were
convinced not to oscillate (and later replaced with LDO regulators),
the audio amplifier stopped motorboating, making the Class C stages
stay in Class C operation, and some bias points moved, I found that
the T/R relay was having a problem. Because of the low turn on
voltage to this relay, it was taking longer than normal to energize.
During this delay, the transmitter would be putting out full power
into an open circuit. That would cause the VSWR protection circuit to
kick in, which would eventually cause the relay to play buzzer. The
resultant arcing across the contacts usually fried the relay or
produced a high resistance connection.

It was easy enough to replace the 12 VDC relay coil with an 8 VDC
equivalent, except that the coil would fuse open during burn-in at
15.5 VDC. So, I added a current source in series with the 8 VDC
relay, and wasted some power. That worked.

I don't recall exactly what voltage the T/R relay was running on, but
my guess is that it was fairly close to 11.0 VDC with 13.6 VDC
applied. Between the battery and the relay were numerous connectors,
power cables, two fuses, on-off switch, internal wiring, transistor
PTT switch, etc. At 50-100 mv drop per connection, these voltage
drops add up. Also, at whatever current the transmitter was pulling
(about 6A in low power), the voltage drop only gets worse.

When I first saw the 12v to 18v power spec on the faulty schematic, I
tried to guess what was powering this contrivance. My best guess is a
wall wart transformer, diode bridge, and minimal filter capacitor. No
regulation. That's not the best power source available and is likely
to cause problems unless the characteristics of the wall wart are
known. I would think that regulating the wall wart voltage might be
better than regulating just the relay voltage.


[1] Despite my bad attitude towards making the radio run at 10.0 VDC,
it later became an important selling point and was maintained as a key
design spec because none of the competing products even came close.

[upsid...@downunder.com]

On Fri, 16 Aug 2013 15:54:59 -0500, Tim Wescott
<t...@seemywebsite.really> wrote:

>>> The OP should post his schematic. I've seen interesting things, like
>>> putting TTL levels into a base and expecting 12 volt swing at the
>>> emitter.
>>>
>>>
>> I was thinking the same thing with a NPN and the collector tied to the
>> 12v rail,
>> you'd need to take the Base above the 12v rail to turn it on.
>
>Pulling the base up to 12V would leave around 11.3V on the emitter, which
>would be enough to turn the relays on.

One should also consider the expected ON/OFF ratio. If it is 50%/50%
or unknown, it does not matter, but if it is 1%/99% or 99%/1% the
driver circuit should consume current only at the shorter period and
select topology (PNP/NPN CE/CC) accordingly.

This topology also determines, if it can be driven by ordinary 3.3/5 V
TTL or if some special 15/30 V tolerant open collector drivers are
needed.

[Robert Baer]

bhav...@gmail.com wrote:
> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>
> -bhavj

Best for each relay to have a series resistor, and a diode in series
with resistor across the coil.
The diode-resistor combo is to snub flyback; the resistor decreases
snub current and thus allows faster relay release; prolly 30-200 ohms.
That coil-resistor/diode network should have that series resistor
mentioned, and should drop 5-10% of total (5V) voltage applied; these
tend to balance coil drives and isolate spikes - which decreases what i
call phase adding (more like EMI adding like crazy).

[upsid...@downunder.com]

On Fri, 16 Aug 2013 17:46:06 -0700 (PDT),

In that case, use a PNP transistor at 12 V, the base goes through a
resistor to a 15 V tolerant open collector TTL output or to a NPN
transistor driven by a 3.3 V controller pin through a resistor.

[Robert Baer]

John Larkin wrote:
> On Fri, 16 Aug 2013 07:24:32 -0700 (PDT), bhav...@gmail.com wrote:

>
>> On Friday, August 16, 2013 5:35:54 PM UTC+5:30, Uwe Hercksen wrote:
>>> bhav...@gmail.com schrieb:
>>>
>>>
>>>

>>>> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>>>
>>>>
>>>

>>> Hello,
>>>
>>>
>>>
>>> the current through one coil is 40 mA, the five coils take 200 mA. A
>>>
>>> 1N400x is good for 1 A. If these five relays are not far away from each
>>>
>>> other, only diode will do in my opinion. The current flowing through the
>>>
>>> diode should not be much larger than the current flowing through all
>>>
>>> coils together.
>>>
>>>
>>>

>>> Bye
>>
>> The relays stacked together and trace length is approx 70 mm from 1st relay coil to the 5th relay coil. So, do you think it would be a better option to place the diode across the coil of the middle (3rd) relay?
>
> It doesn't matter where the flyback diode is located.
>
>
Yep! Got one that came back to its pigeon coop; clipped its wings!

[upsid...@downunder.com]

On Fri, 16 Aug 2013 17:33:42 -0700, John Larkin
<jla...@highlandtechnology.com> wrote:

>https://picasaweb.google.com/106331244879972692887/August162013?authuser=0&authkey=Gv1sRgCI_Wuvvh_NXi3AE&feat=directlink#5912784366042056882
>>>
>>Oh, dear. That'll give you about a volt and a half on the relay coils.
>>
>>Get rid of D1 and both caps, connect R67 to the base of Q2, move Q3 to
>>where C152 is now, and invert the logic level (low=ON).
>>
>>Cheers
>>
>>Phil Hobbs
>
>Looks like he wants to switch the coils and regulate the coil voltage
>down to 12. 18V is a bit much, 2.2x the normal coil dissipation.

One should remember that the relay turn on current is greater than the
hold on current.

Radio amateurs sometimes use "24 V" relays with 12 V car battery by
charging capacitors to 12 V at off state and when switched on, the
capacitor is in series with the 12 V feed, thus producing 24 V, but of
course, after a while, the voltage drops to 12 V, which is sufficient
hold for most 24 V relays.

In this case, I would not bother to regulate the 12-18 V input at
switch on (let the transistor be hard on), but after a while drop the
relay voltage to something like 6-9 V, which should give a sufficient
hold current. This will reduce the relay dissipation significantly.
Some of the dissipation moves to Q2 at steady state, but as the total
current drops, the total dissipation also drops.

[upsid...@downunder.com]

On Fri, 16 Aug 2013 21:21:54 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:

>>The other approach would be to use #7 with a small resistor, and use the
>>processor to measure the supply and PWM the relays appropriately. A
>>Schottky catch diode would help.
>
>Or no resistor, no measurement. The uP could drive the relays ON at 100% duty
>cycle initially, but then drop down to something like 70% after a reasonable
>pull-in delay.
>

PWMing 200 mA though big inductances seems to me as asking for
troubles, at least in EMC compliance testing, if not earlier.

If the processor only has digital outputs, then PWMin might be OK, but
I would still keep Q2 as a linear regulator, dissipating a lot of
power and low pass filtering the base drive to remove most of the PWM
waveform.

[bloggs.fred...@gmail.com]

As a rule you can assume the relay pull-in voltage is just equal to the nominal coil rating at the maximum of the spec'd operating temperature range. This will be due to increases in magnetic circuit reluctance as well as winding resistance.

[amdx]

>
> Thanks for taking time to draw them. Yes, as you said I am trying to regulate as well as switch the power to the coils. In the fig-1, why is that pnp needed instead of resisting to limit current?
>

BTW, is it automotive?

[bloggs.fred...@gmail.com]

On Friday, August 16, 2013 10:08:34 PM UTC-4, John Larkin wrote:

>
> https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Relay_Drivers.pdf
>
>
>

LM1117 doesn't have the Vin,max handling for the job. Bad choice.

[bhav...@gmail.com]

On Saturday, August 17, 2013 5:38:18 PM UTC+5:30, amdx wrote:
> >
>
> > Thanks for taking time to draw them. Yes, as you said I am trying to regulate as well as switch the power to the coils. In the fig-1, why is that pnp needed instead of resisting to limit current?
>
> >
>
>
>
> BTW, is it automotive?

No. Its an industrial device.

[bhav...@gmail.com]

How does fig-4 work? The DEPL NFET part in particular.

[John Larkin]

On Sat, 17 Aug 2013 11:52:13 +0300, upsid...@downunder.com wrote:

>On Fri, 16 Aug 2013 21:21:54 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>>The other approach would be to use #7 with a small resistor, and use the
>>>processor to measure the supply and PWM the relays appropriately. A
>>>Schottky catch diode would help.
>>
>>Or no resistor, no measurement. The uP could drive the relays ON at 100% duty
>>cycle initially, but then drop down to something like 70% after a reasonable
>>pull-in delay.
>>
>
>PWMing 200 mA though big inductances seems to me as asking for
>troubles, at least in EMC compliance testing, if not earlier.
>

As far as inductance goes, the bigger the better.

The PWM frequency can be kept low, a few KHz maybe. Any EMI will be at the 200th
harmonic or something insane like that, so the spectral energy will be minute.
You wouldn't expect any EMI trouble from a 300 mA buck switcher running at 5
KHz.

>If the processor only has digital outputs, then PWMin might be OK, but
>I would still keep Q2 as a linear regulator, dissipating a lot of
>power and low pass filtering the base drive to remove most of the PWM
>waveform.
>

Schematic?

[John Larkin]

A depletion fet is normally ON and acts like a constant-current device. It acts
like a resistor to pull up the base, but the current doesn't ever go high as it
would if you used a resistor.

An LND150 would regulate to maybe 1.5 mA, so you'd need a transistor with a beta
of 200 min. There are other depl parts with higher Idss.

Not all of my circuits are always guaranteed to be non-silly, especially when I
do seven in a couple of minutes for free. The next step, for any circuit, is to
apply math.

[John Larkin]

On Sat, 17 Aug 2013 05:40:24 -0700 (PDT), bloggs.fred...@gmail.com
wrote:

>On Friday, August 16, 2013 10:08:34 PM UTC-4, John Larkin wrote:
>
>>
>> https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Relay_Drivers.pdf
>>
>>
>>
>
>LM1117 doesn't have the Vin,max handling for the job. Bad choice.

Why do you keep saying stupid stuff, when data sheets are free online?

[John Larkin]

My circuit 7 does that. The controller would have to ensure that the caps have
time to charge.

One should check the relay data sheet to make sure any such scheme is safe.

[John Larkin]

Translation, anyone?

[Phil Hobbs]

Depends on how fast. It's a buck topology, so there's not that much
high frequency content, and all it would need is to be above audio. I
was wanting to keep the RC to protect the +18 supply from all the
switching schmutz.

[John Fields]

On Sat, 17 Aug 2013 08:55:52 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:

>On Sat, 17 Aug 2013 01:13:56 -0800, Robert Baer <rober...@localnet.com> wrote:
>
>>John Larkin wrote:

.
.
.

>>> It doesn't matter where the flyback diode is located.
>>>
>>>
>> Yep! Got one that came back to its pigeon coop; clipped its wings!


>Translation, anyone?

---
Pigeons... Flyback... Coop... Wings

--
JF

[John Larkin]

On Sat, 17 Aug 2013 11:18:29 -0500, John Fields <jfi...@austininstruments.com>

wrote:

>On Sat, 17 Aug 2013 08:55:52 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>On Sat, 17 Aug 2013 01:13:56 -0800, Robert Baer <rober...@localnet.com> wrote:
>>
>>>John Larkin wrote:
>.
>.
>.
>>>> It doesn't matter where the flyback diode is located.
>>>>
>>>>
>>> Yep! Got one that came back to its pigeon coop; clipped its wings!
>
>
>>Translation, anyone?
>
>
>---
>Pigeons... Flyback... Coop... Wings

[John Larkin]

Given one driver, five parallel coils, one diode, and an optional resistor, I
can't see how you'd get any difference in EMI. What is "phase adding"?

A clamped relay coil, actuated now and then, won't make significant EMI.

[Martin Riddle]

"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in
message news:o93v09tpamaopokev...@4ax.com...

> On Sat, 17 Aug 2013 05:40:24 -0700 (PDT),
> bloggs.fred...@gmail.com
> wrote:
>
>>On Friday, August 16, 2013 10:08:34 PM UTC-4, John Larkin wrote:
>>
>>>
>>> https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Relay_Drivers.pdf
>>>
>>>
>>>
>>
>>LM1117 doesn't have the Vin,max handling for the job. Bad choice.
>
> Why do you keep saying stupid stuff, when data sheets are free online?
>

Operating Vin is only 15V, Device Max is 20v.
Vdrop is 1.4v at 800ma

I wouldn't use it at 18v.

Cheers

[John Larkin]

On Sat, 17 Aug 2013 16:28:24 -0400, "Martin Riddle" <marti...@verizon.net>
wrote:

Abs max is 20, and 18 is less than 20. But the part I posted is obviously the
ADJ version. With 18 in and 12 out, the regulator only sees 6 volts.

It will lose just about a volt at 300 mA. One should check the relay data sheet
to make sure that's OK.

[bloggs.fred...@gmail.com]

Circuit #2 produces neg voltage across coil on turn-off, bad choice. Circuit #5 also potential transient over-voltage at turn-on due to diode capacitance. Circuit #3 is really strange, hard to say but likely PNP is saturated so coil -Vdiode at turn off is applied to output of 1117. Y

[John Larkin]

On Sat, 17 Aug 2013 18:27:37 -0700 (PDT), bloggs.fred...@gmail.com

I drew what it does. When the mosfet is on, there's +1.25 volts across the relay
coil.

>Circuit #5 also potential transient over-voltage at turn-on due to diode capacitance.

That's insane.

> Circuit #3 is really strange, hard to say but likely PNP is saturated so coil -Vdiode at turn off is applied to output of 1117. Y

Ditto insane. It's a simple voltage regulator followed by a switch. When the
switch disconnects the coil from the regulator, they are disconnected.


Threads like this are fun. It's amazing how many people, even people who work in
electronics, don't understand simple circuits.

[josephkk]

On Sat, 17 Aug 2013 05:06:50 -0700, bloggs.fredbloggs.fred wrote:


> As a rule you can assume the relay pull-in voltage is just equal to the
> nominal coil rating at the maximum of the spec'd operating temperature
> range. This will be due to increases in magnetic circuit reluctance as
> well as winding resistance.

Pretty close. And very good design advice. In reality it will be about
10% lower, and no better than that over full rated temperature range.

?-)

[bloggs.fred...@gmail.com]

On Saturday, August 17, 2013 11:15:19 PM UTC-4, John Larkin wrote:

>
> > Circuit #3 is really strange, hard to say but likely PNP is saturated so coil -Vdiode at turn off is applied to output of 1117. Y
>
>
>
> Ditto insane. It's a simple voltage regulator followed by a switch. When the
>
> switch disconnects the coil from the regulator, they are disconnected.
>

That's not how that works and you know it.

[Spehro Pefhany]

On 18 Aug 2013 05:35:58 GMT, the renowned josephkk

Yeah, my impression is that they set the original design specs based
on unregulated power from the mains plus temperature. Those
hairy-eared relay designers didn't really add vast unnecessary margin.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

[John Larkin]

On Sun, 18 Aug 2013 05:56:22 -0700 (PDT), bloggs.fred...@gmail.com
wrote:

If you disagree, post an serious explanation or a Spice file.

[John S]

On 8/18/2013 10:09 AM, John Larkin wrote:
> On Sun, 18 Aug 2013 05:56:22 -0700 (PDT), bloggs.fred...@gmail.com
> wrote:
>
>> On Saturday, August 17, 2013 11:15:19 PM UTC-4, John Larkin wrote:
>>
>>>
>>>> Circuit #3 is really strange, hard to say but likely PNP is saturated so coil -Vdiode at turn off is applied to output of 1117. Y
>>>
>>>
>>>
>>> Ditto insane. It's a simple voltage regulator followed by a switch. When the
>>>
>>> switch disconnects the coil from the regulator, they are disconnected.
>>>
>>
>> That's not how that works and you know it.
>
> If you disagree, post an serious explanation or a Spice file.

I'd like to see it, too!

John S

[John Fields]

On Sat, 17 Aug 2013 09:25:38 -0700, John Larkin

<jjla...@highNOTlandTHIStechnologyPART.com> wrote:

>On Sat, 17 Aug 2013 11:18:29 -0500, John Fields <jfi...@austininstruments.com>
>wrote:
>
>>On Sat, 17 Aug 2013 08:55:52 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>On Sat, 17 Aug 2013 01:13:56 -0800, Robert Baer <rober...@localnet.com> wrote:
>>>
>>>>John Larkin wrote:
>>.
>>.
>>.
>>>>> It doesn't matter where the flyback diode is located.
>>>>>
>>>>>
>>>> Yep! Got one that came back to its pigeon coop; clipped its wings!
>>
>>
>>>Translation, anyone?
>>
>>
>>---
>>Pigeons... Flyback... Coop... Wings
>
>Translation, anyone?

---
Oh, my, little Johnny didn't get it?

No big surprise...

--
JF

[John Fields]

On Fri, 16 Aug 2013 11:28:55 -0700 (PDT), bhav...@gmail.com wrote:

>On Friday, August 16, 2013 4:53:17 PM UTC+5:30, bhav...@gmail.com wrote:
>> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>>
>>
>>
>> -bhavj
>

>Here is the schematic I quickly drafted. All the 5 coils and fly back diode are in parallel and will be connected to 12V_RLY_COIL.
>
>https://picasaweb.google.com/106331244879972692887/August162013?authuser=0&authkey=Gv1sRgCI_Wuvvh_NXi3AE&feat=directlink#5912784366042056882

---
If you can use solid-state relays to accomplish your goal, the
requirement for the flyback diode will go away, as will the
requirement for the relatively high current needed to drive the relay
coils.

What can you tell us about your loads and how they need to be driven?



--
JF

[bloggs.fred...@gmail.com]

I know, and it's real easy to blow a coil open with over-voltage, +15% usually does it, sometimes less.

[Jon Lark]

On Friday, August 16, 2013 7:23:17 AM UTC-4, bhav...@gmail.com wrote:
> I am connecting five 12V relay coils in parallel to switch five different loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.
>
>
>
> -bhavj

Just a general comment on the topic of relay coil transient suppression: While connecting a diode across the coil is a common practice, the technique has its drawbacks. Robert Baer alluded to this in his earlier post. The diode increases the release time of the relay. Even if you are not concerned with switching time per se, a slow release can cause excessive contact arcing and even welding. My favorite technique is to connect a diode in series with a Zener and place the combination across the coil. This allows the voltage across the coil to rise, thus minimizing the increase in release time, while keeping the voltage across the driver transistor within safe limits. This topic is discussed at length in the “Engineers; Relay Handbook” published by the National Association of Relay Manufacturers. In my copy (Fifth Edition) it’s covered in paragraph 15.3.9 under the topic “Suppressing Relay-Coil Transients.”

[Spehro Pefhany]

In that case, here's another idea:-


\
+12~18V _ _ o o
| )|
1N4003 - )|
^_)|
|
|
|
100K ||-+
___ ||<- SiA408DJ
o--|___|--------+---||-+
| |
0/3.3V \| |
2N4401 |----+
>| |
| .-.
| | |
| | | 2.5R
| '-'
| |
+----- +
|
===
GND

It's even possible this is short-circuit resistant if you treat the
MOSFET well thermally.

[bhav...@gmail.com]

Looks to be easy way. I think it should be NPN.

[Spehro Pefhany]

On Mon, 19 Aug 2013 07:22:22 -0700 (PDT), bhav...@gmail.com wrote:

>
>Looks to be easy way. I think it should be NPN.

Right, thanks. The P/N is correct, symbol is wrong.

--sp

[Jasen Betts]

On 2013-08-18, bloggs.fred...@gmail.com <bloggs.fred...@gmail.com> wrote:
> On Saturday, August 17, 2013 7:41:48 PM UTC-4, John Larkin wrote:
>> On Sat, 17 Aug 2013 16:28:24 -0400, "Martin Riddle" <marti...@verizon.net>
>

> Circuit #2 produces neg voltage across coil on turn-off, bad choice.
> Circuit #5 also potential transient over-voltage at turn-on due to diode capacitance.
> Circuit #3 is really strange, hard to say but likely PNP is saturated so coil
> -Vdiode at turn off is applied to output of 1117.

huh?
oh, you means the powersupply turn-on/off, not the relay?




--
⚂⚃ 100% natural

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