low voltage regulation
rasqual
upwards. I need to light several grain of wheat lamps in parallel with
consistent brightness regardless of voltage on the tracks.
The lamps together draw about about 80 mA at 1.7 V, which is their
ideal brightness.
Zener, regulator, somethin' -- my problem is what to do from 1 to
1.7.
I'm tempted to just have a battery in there and use a charging circuit
when the V is over what the circuit needs to charge the battery(s),
and just run the lights of it(them).
Is there an obvious circuit I've missed considering? I don't think a
voltage multiplier would do the trick for current requirement.
Phil Allison
"rasqual"
** One solution is to use high frequency AC on the tracks in addition to
whatever voltage runs the locos.
A voltage of about 1.7 volts rms at say 20 kHz should have virtually no
effect on model electric DC motors and be inaudible too.
One simply capacitor couples the voltage to the tracks an uses a series cap
inside the loco for each lamp - 4.7uF, 50 volt bi-polar types would do
fine for both jobs. Long as the tracks are kept clean and wheels make good
contact, lamp brightness is reasonably steady. Remote control of lamp
brightness is made simple too by just varying the AC voltage level.
However, an on-board battery supply cannot be beaten for steady light -
that will even keeps going if the loco crashes.
..... Phil
MooseFET
> I have a model train scenario, where track voltage varies from a volt
> upwards.
upwards to what?
A fairly simple switching regulator could be used. Getting one to
start at 1V is a bit tricky but once it is going, it will continue to
run.
The polarity of this DC reverses to back the trains up, doesn't it?
This makes it way harder to do but still possible.
Another way to go would be to use pulse width modulation to control
the train speed. This would make extracting a constant voltage much
easier.
o...@uakron.edu
classical way is to run 30 khz AC on the tracks, injected on top of
the DC for the motors. the loco motors will not respond to the AC,
and life is good. Of course the lamps are AC coupled with a cap to
block the DC. The industry term is "constant current lighting" if you
your looking for a module.
Steve
o...@uakron.edu
And there is one on ebay right now for 99 cents starting.
Perhaps the modern way of a half farad cap , a diode and some leds
might be better? 30 minutes of light is not bad....
Steve
amdx
"Phil Allison" <phila...@tpg.com.au> wrote in message
news:77hlbvF...@mid.individual.net...
Mike
JosephKK
Since you appear to be talking of equipment that is powered by being
"on track" the battery thing may be the best bet. Moreover if you
switch to current drive you may be able to replace the GOW bulbs with
LEDs.
Electronworks.co.uk
them of at least 1.7V. White and Blue LEDs considerably more.
Look on TI or Maxim's website for buck boost converters and see what you can
find. The MAX1771 shows a SEPIC converter (which is the same as a buck boost
configuration), but only works to 2V. Find a lower voltage chip and there is
your answer
Failing that, use a boost converter and switch it out when the input voltage
is above the desired output voltage
--
Bill Naylor
www.electronworks.co.uk
"JosephKK" <quiett...@yahoo.com> wrote in message
news:vu6j15ppsdodhi1hv...@4ax.com...
rasqual
> ** One solution is to use high frequency AC on the tracks in addition to
> whatever voltage runs the locos.
>
> A voltage of about 1.7 volts rms at say 20 kHz should have virtually no
> effect on model electric DC motors and be inaudible too.
>
> One simply capacitor couples the voltage to the tracks an uses a series cap
> inside the loco for each lamp - 4.7uF, 50 volt bi-polar types would do
> fine for both jobs. Long as the tracks are kept clean and wheels make good
> contact, lamp brightness is reasonably steady. Remote control of lamp
> brightness is made simple too by just varying the AC voltage level.
Thanks to everyone for their response; after considering each option
this one seems the most practical approach.
It turns out that the light gives the proper illumination when
overdriven somewhat, at 2.5 VDC.
Is anyone aware of a low component-count solution for injecting the AC
-- perhaps a single chip + trimmer pot solution (powered off some
fixed DC)? This could be doable with well under 100 mA.
rasqual
> Is anyone aware of a low component-count solution for injecting the AC
> -- perhaps a single chip + trimmer pot solution (powered off some
> fixed DC)? This could be doable with well under 100 mA.
This seems to be a good method, but I'm still wondering what I should
use as an AC power source at 20 khz. Argh.
Jan Panteltje
<scott.m...@gmail.com> wrote in
<e370c51f-227e-43ca...@n21g2000vba.googlegroups.com>:
>On Jun 2, 12:19�am, rasqual <scott.marqua...@gmail.com> wrote:
>
>> Is anyone aware of a low component-count solution for injecting the AC
>> -- perhaps a single chip + trimmer pot solution (powered off some
>> fixed DC)? This could be doable with well under 100 mA.
>
>This seems to be a good method, but I'm still wondering what I should
>use as an AC power source at 20 khz. Argh.
Use a small balanced transformer, secondary in series with the DC.
2 transistors to dive it push pull, capacitor to tune it,
feedback from output to have it generate a sine wave?
Jasen Betts
> On Jun 2, 12:19 am, rasqual <scott.marqua...@gmail.com> wrote:
>
>> Is anyone aware of a low component-count solution for injecting the AC
>> -- perhaps a single chip + trimmer pot solution (powered off some
>> fixed DC)? This could be doable with well under 100 mA.
>
> This seems to be a good method, but I'm still wondering what I should
> use as an AC power source at 20 khz. Argh.
a 555 driving a half-bridge? frequency precision is not important harmonics
probably aren't either.
rasqual
>
> > ** One solution is to use high frequency AC on the tracks in addition to
> > whatever voltage runs the locos.
>
> > A voltage of about 1.7 volts rms at say 20 kHz should have virtually no
> > effect on model electric DC motors and be inaudible too.
>
> > One simply capacitor couples the voltage to the tracks an uses a series cap
> > inside the loco for each lamp - 4.7uF, 50 volt bi-polar types would do
> > fine for both jobs. Long as the tracks are kept clean and wheels make good
> > contact, lamp brightness is reasonably steady. Remote control of lamp
> > brightness is made simple too by just varying the AC voltage level.
>
> Thanks to everyone for their response; after considering each option
> this one seems the most practical approach.
>
> overdriven somewhat, at 2.5 VDC.
>
> Is anyone aware of a low component-count solution for injecting the AC
> -- perhaps a single chip + trimmer pot solution (powered off some
> fixed DC)? This could be doable with well under 100 mA.
OK, I have a progress report with a conundrum.
Coupling the AC (10-20 kHz) to the tracks with a cap (I note the
suggestion of a transformer elsewhere in this thread) works fine, and
the DC power supply we're using to motor the train does not defeat the
AC -- so long as a train is not on the tracks. However, the moment a
train is put on the tracks the light goes out -- our AC is apparently
defeated.
When we put the AC directly across one of the motors used in the
trains, a bulb connected in parallel will light just fine, though.
I'm inferring that something about a DC motor *in operation* presents
a very different reactive load, which is defeating our AC completely
(the motor may as well be a short).
I'm definitely baffled by this. Any ideas or suggestions?
Thanks -
rasqual
> I'm definitely baffled by this. Any ideas or suggestions?
>
> Thanks -
Gah. Forgot to say that the above symptom is, indeed, on account of
trying this while lacking something -- an inductor to separate the DC
power supply from the rail (to isolate the AC to the track).
What kind of inductor would be necessary to isolate capacitance in the
power supply from the AC we're injecting? Not being an engineer,
what's freaking me out here is the complexity of the reactive
supercircuit this coupling of AC through a cap and coupling of DC
through an inductor are creating, where a motor -- inductive itself --
is consuming the DC (while presenting an open to the AC) and a
resistive incandescent is consuming the AC (in series with a cap to
present an open to the DC).
I learned about basic reactive circuits back in the day, but this is
like some multivariate calculus. I'm definitely out of my comfort
zone.
:-(
ehsjr
Your inductor must be rated for at least the maximum steady DC
current that the DC supply can furnish, because of the possibility
of a short across the tracks. The inductor will present inductive
reactance of 2*pi*f*L to the AC. Larger L (inductance) gives
greater isolation.
The higher the current and the higher the needed inductance,
the higher the cost. If the frequency, worst case, is 10kHz,
and you use 2 miliHenry inductance, the DC supply could load
your AC supply about 13 mA. If you have a 100 mA AC supply and
your lamp draws 80 mA, that should work. 20kHz would be better,
reducing the load to about 7 mA. And higher inductance would
reduce the loading, by increasing isolation.
Ed
rasqual
> rasqual wrote:
>
> > What kind of inductor would be necessary to isolate capacitance in the
> > power supply from the AC we're injecting? Not being an engineer,
> > what's freaking me out here is the complexity of the reactive
> > supercircuit this coupling of AC through a cap and coupling of DC
> > through an inductor are creating, where a motor -- inductive itself --
> > is consuming the DC (while presenting an open to the AC) and a
> > resistive incandescent is consuming the AC (in series with a cap to
> > present an open to the DC).
> Your inductor must be rated for at least the maximum steady DC
> current that the DC supply can furnish, because of the possibility
> of a short across the tracks. The inductor will present inductive
> reactance of 2*pi*f*L to the AC. Larger L (inductance) gives
> greater isolation.
> The higher the current and the higher the needed inductance,
> the higher the cost. If the frequency, worst case, is 10kHz,
> and you use 2 miliHenry inductance, the DC supply could load
> your AC supply about 13 mA. If you have a 100 mA AC supply and
> your lamp draws 80 mA, that should work. 20kHz would be better,
> reducing the load to about 7 mA. And higher inductance would
> reduce the loading, by increasing isolation.
OK, the plot thickens. Inductors upwards of 2 mH work as you say;
however, there's a new problem.
Whenever the motor is powering up to speed (that is, DC is increased
to the tracks through the isolation inductor, and the motor's current
is increasing), the AC signal we're injecting is attenuated
dramatically. Once the motor reaches an RPM proportional to the raised
DC level again, the AC signal is not attenuated. If we stall the motor
(stop its rotation), we lose the AC again.
We're using a cap to isolate a rectifier on the train engine, which
feeds the incandescent light of interest.
We had one "success" that we wouldn't believe until we checked it, and
it was a good thing. The inductor we're using for isolating the track
power supply from the AC injection point is a common mode toroid.
Without thinking much about the common core, in frustration we wired
the motor (in the engine) through the other side of the toroid in an
attempt to prevent the motor from shunting our AC -- or whatever the
heck it's doing. Darned if it didn't work -- any change in DC or motor
speed, power, load, etc. resulted in our lamp keeping consistent
illumination.
Then we realized the common core was involved, and that's a bit of an
issue unless we want the train to have a pair of wires running to the
inductor back at the power source, under the layout. ;-)
Argh.
So then we tried to figure out how we could replicate, reactively,
whatever the heck was causing the faux success. So tantalizingly
close. Basically, what worked was having the DC opposing on both
coils, with the AC all on one side:
Pin 1: Power supply +
Pin 2: Injection point of AC to track rail 1
Here's where the track commutes the power to the engine
Pin 3: Pick off the AC with a cap and send to rectifier
Pin 4: Motor high side, and then ground on track rail 0
...and of course we can't do that, because it's a common core that
would need to be in two places. And I can't replicate that on the
engine side alone, as far as I can tell.
I reckon I'm presumptuous imagining that anyone in their right mind
would take pains to advise me without a schematic for this mess. ;-)
If a summary would help, it's this -- a DC motor (brushes) under load
seems to suck AC through it like a vacuum cleaner. Even an inductor in
series (a second one, not the one with a common core to the power
supply) does not prevent the motor from just sucking the living
daylights out of the AC.
This is where I come up short on theory, and I'd be glad of any
insights. One additional problem is that the solution should ideally
allow for changes to motor power without the light suffering any
changes in brightness. I can imagine doing that with a big cap, but
darned if our common core gaffe didn't keep the light perfectly
consistent. Geez.
rasqual
> This is where I come up short on theory, and I'd be glad of any
> insights. One additional problem is that the solution should ideally
> allow for changes tomotorpower without the light suffering any
> changes in brightness. I can imagine doing that with a big cap, but
> darned if our common core gaffe didn't keep the light perfectly
> consistent. Geez.
Argh. Thought we had it for a bit there. I put another common mode
inductor on the ground side of things, and wired the second side of it
to the high side of the motor. It worked perfectly. But alas, I then
noticed that I'd clipped the AC signal to the ground-side inductor on
the opposite side of the DC -- which isn't real because the rail
supplies both.
:-/
ehsjr
If you put a 2 mH inductor in series with the motor,
it will exhibit about 250 ohms impedance at 20 kHz.
From what I understand of your description, I think you
will need to do something along those lines. Install
the inductor on the engine, in series with the motor,
to test. You can figure out the mechanical work needed
to install it inside, once you have tested and know
whether it works or not.
Please post your results - inquiring minds want to know! :-)
Ed
rasqual
> Please post your results - inquiring minds want to know! :-)
I'm going to have to post a schematic. Sorry I haven't to date.
The problem just now is that when the motor is under load, the A/C
signal is dramatically attenuated -- even with an inductor isolating
aboard the engine. THAT is something I don't understand.
I'll scribble something and get back!
- S
rasqual
> Please post your results - inquiring minds want to know! :-)
OK, here's the upshot after reading the current coming out of the
LM386: Whenever we apply DC to the tracks and the motor starts
turning, the current draw on the power amplifier at frequency
dramatically increases.
This is with an inductor in series with the motor on the engine,
supposedly isolating the engine from the AC (the AC goes through a cap
to the rectifier).
Even with a large inductor (100 mH or more), this is true.
When I read the motor side of its isolation inductor with a 'scope
(thanks, Craigslist!), there's plenty of AC there. What the heck?
Also, when the motor's running the circuit is tuned differently; a
higher frequency to the track illuminates the light brighter. With the
motor off, a lower frequency is better.
The motor itself is introducing no AC component to the circuit.
This is baffling.
ehsjr
> On Aug 14, 9:39 pm, ehsjr <eh...@NOSPAMverizon.net> wrote:
>
>
>>Please post your results - inquiring minds want to know! :-)
>
>
> OK, here's the upshot after reading the current coming out of the
> LM386:
Dammit! Stop right there. WHAT 386 ?? That's the first time
you've mentioned a 386. Where's the schematic????????????????
> Whenever we apply DC to the tracks and the motor starts
> turning, the current draw on the power amplifier at frequency
> dramatically increases.
>
> This is with an inductor in series with the motor on the engine,
> supposedly isolating the engine from the AC (the AC goes through a cap
> to the rectifier).
>
> Even with a large inductor (100 mH or more), this is true.
>
> When I read the motor side of its isolation inductor with a 'scope
> (thanks, Craigslist!), there's plenty of AC there. What the heck?
>
> Also, when the motor's running the circuit is tuned differently; a
> higher frequency to the track illuminates the light brighter. With the
> motor off, a lower frequency is better.
>
> The motor itself is introducing no AC component to the circuit.
>
> This is baffling.
Yes, and it will continue to be baffling until you use some
rigor in your posting. You mention power amplifier, current
draw increases dramatically, plenty of AC, frequency, a cap,
brighter
There is not a specific given for any of that. For example,
there's no description and no diagram of how you measured
"plenty of AC" or what "plenty" means.
You said you were going to post a schematic. Do it.
Ed
rasqual
> You said you were going to post a schematic. Do it.
When exasperation reaches the level my wife can show, I know I'm in
trouble. ;-)
This is what I'm using currently:
http://web.mit.edu/6.s28/www/schematics/lm386.htm
I cobbled this together quickly, FWIW:
http://snurl.com/roab6
The two rails couple the layout box on the left to the engine on the
right. The AC is injected where shown, from the LM386 circuit. The DC
is applied to the left of the inductor.
At the engine, the AC is isolated from the motor via the inductor, and
coupled to the rectifier through the cap. The lamp is then illuminated
by the derived DC.
The problem is that a load across the motor -- which draws more
current through the rails, of course -- also results in more current
drawn from the signal generating circuit (the LM386). That's based on
direct AC current measurement where the signal's injected on the left
side. I don't understand that.
I'd imagine it has to do with the overall circuit tuning. When the
motor is sped up by increasing the DC voltage applied the rail, the
lamp extinguishes until the motor comes up to speed, reducing DC
current draw. The lamp gradually brightens again as the motor current
draw ramps down.
However, the lamp does not brighten fully to where it was when the
motor was not runnning (no DC applied to rails). I noticed that
adjusting the frequency of the AC upwards -- from 20 kHz to 25 or more
-- resulted in a brighter bulb again. My untutored inference is that
the DC voltage and/or the additional current draw is changing the
tuning of the circuit.
Thanks for bearing with me on this. It's been WAY too long since I've
been in this stuff, and I was never knowledgeable about motors and how
they interact with circuits.
Pardon the wrong symbols, BTW. I just d'loaded TinyCAD quickly to do
this, and the libraries seemed incomplete. Is there a better open-
source app for this?
ehsjr
What is the the power source for the 386? What is the
signal generator feeding its input? Why are you using
a bridge rectifier between C1 and the lamp? Get rid of it.
You can draw in ascii. Examples:
---[R1]--- ---[C1]---
---|<--- (for diode) ---[Rly]--- (for relay)
---[2mH]--- (for a 2 miliHenry inductor)
/c
---| NPN (for NPN transistor)
\e
And so forth.
Ed
spamme0
Some things.
1) this is done all the time. Call up the hobby shop and ask them what
they do.
2) Aren't there model railroad newsgroups or websites where you can
talk directly to people who have done this?
3) Put AC on the track. Use the + half to drive the train and
the negative half to drive the light.
rasqual
> What is the the power source for the 386? What is the
> signal generator feeding its input? Why are you using
> a bridge rectifier between C1 and the lamp? Get rid of it.
>
> You can draw in ascii. Examples:
> ---[R1]--- ---[C1]---
> ---|<--- (for diode) ---[Rly]--- (for relay)
> ---[2mH]--- (for a 2 miliHenry inductor)
>
> /c
> ---| NPN (for NPN transistor)
> \e
>
> And so forth.
On the test bench I just have a variable power supply on the LM386;
the circuit's working well with 9VDC. Likewise, I have a signal
generator that's letting me vary the frequency.
The bridge is not needed with the cap isolating rail DC from the lamp,
true enough. It's there because we're forward-looking to some on-board
electronics. We can't use the rail DC because that can vary from
several volts down to nothing.
I'm heading over to the shop, and we'll lean down to the cap and see
how things work. I'm just baffled by the way the circuit draws a
quarter amp from the amp circuit when the motor is under load. I think
that quarter amp is killing the signal, then, so on the one hand I
think "I need to deliver more current on the amp's output!" but on the
other I just wish I knew why a motor under load is causing the circuit
to load the AC so much.
spamme0: There's no in-between commercial system that does this.
Trains either run simply on DC with no rail-delivered action such as
light control, OR they're digitally controlled engines with a constant
power applied to the tracks. My fabricator is an expert in the O scale
trains, and no one's doing this. (3) not possible. among other
things, trains need to go in reverse. :-)
Off to the shop to play again. Meanwhile, the technical question is
this: why does a loading mother change the tuning of the reactive
components in this schematic, such that the AC source is insanely
loaded and the AC effectively gets shunted to nothing?
- S
ehsjr
> On Sep 10, 12:02 am, ehsjr <eh...@NOSPAMverizon.net> wrote:
>
>
>
>>What is the the power source for the 386? What is the
>>signal generator feeding its input? Why are you using
>>a bridge rectifier between C1 and the lamp? Get rid of it.
>>
>>You can draw in ascii. Examples:
>> ---[R1]--- ---[C1]---
>> ---|<--- (for diode) ---[Rly]--- (for relay)
>> ---[2mH]--- (for a 2 miliHenry inductor)
>>
>> /c
>> ---| NPN (for NPN transistor)
>> \e
>>
>>And so forth.
>
>
> On the test bench I just have a variable power supply on the LM386;
> the circuit's working well with 9VDC.
What tests have you done to verify that the circuit is
working well? Working well means it is delivering
a healthy signal at the output *while under load*.
> Likewise, I have a signal
> generator that's letting me vary the frequency.
Is the ground from the sig gen connected to the 386 ground
and to the track ground?
>
> The bridge is not needed with the cap isolating rail DC from the lamp,
> true enough. It's there because we're forward-looking to some on-board
> electronics. We can't use the rail DC because that can vary from
> several volts down to nothing.
>
> I'm heading over to the shop, and we'll lean down to the cap and see
> how things work. I'm just baffled by the way the circuit draws a
> quarter amp from the amp circuit when the motor is under load. I think
> that quarter amp is killing the signal, then, so on the one hand I
> think "I need to deliver more current on the amp's output!" but on the
> other I just wish I knew why a motor under load is causing the circuit
> to load the AC so much.
>
> spamme0: There's no in-between commercial system that does this.
> Trains either run simply on DC with no rail-delivered action such as
> light control, OR they're digitally controlled engines with a constant
> power applied to the tracks. My fabricator is an expert in the O scale
> trains, and no one's doing this. (3) not possible. among other
> things, trains need to go in reverse. :-)
>
> Off to the shop to play again. Meanwhile, the technical question is
> this: why does a loading mother change the tuning of the reactive
> components in this schematic, such that the AC source is insanely
> loaded and the AC effectively gets shunted to nothing?
>
> - S
The bridge is dropping ~ .7 volts on each side of the AC.
That's one reason to get rid of it.
Next: what is the frequency measured at the rails with the
motor load and without the motor load? If the frequency
drops, the inductive reactance drops, and the current draw
goes up. What is the p-p measurement at the output of
the 386 and at the rails when the motor is loading the rails?
Drawing a quarter amp from your 386 is way too much - it
may have killed the chip. Double check your inductors
to verify they are 2 milihenry, not 2 microhenry.
Either you don't have 20 kHz through the inductor or
it is not 2 mH. You can't draw 250 mA from your circuit,
unless the frequency is a lot lower than 20 kHz, or the
inductor is lower than 2 mH.
Ed
JosephKK
wrote:
And AAcircuit make that so much easier. Just remember you must post
in a fixed space font for either to work.
rasqual
> And AAcircuit make that so much easier. Just remember you must post
> in a fixed space font for either to work.
Geez, that's a sweet app.
Thanks for the tip.