[ARC5] Power Supplies for Your ARC-5

[Paul H. Anderson]

Hi folks,

I may not fully understand the power supply situation, but my experience
suggests that the Lambda 9A supply I have is more than enough for these
small dynos and motors.  They have output voltage sensing feedback on
them, so the current is clamped at 9 amps (in my case), by dropping
voltage as needed, but the voltage does not drop to zero except in total
failure.

The dyno starts with strong authority - no slow windup.  I have another
lab power supply that puts out 9 amps, and when running dynos on it, the
starting current appeared to be 4-5 amps.  I know that the resolution of
my observation isn't accounting for the true peak value (the one measured
in milliseconds), but a good clamping circuit should have no problem with
that.

Let me get the model numbers tonight.  I have several, and I'm confident
that any of them have the guts to do a DM-33 dyno.  One that may not is a
lab supply that only put out 1amp (tried it on my R-391 motor, and it
didn't have enough guts to do it).  The DM-33 is really a small, small
electrical motor, and a few amps "should" be enough.  No need for more
than 10 amps, at any rate.

The supplies listed below are a lot more expensive than is needed to run
one dyno and the receiver.  The issue of switcher noise may still be a
problem, however.

I'm wondering if power supply design and manufacturer varies enough so
that one PS at 9amps might work fine, whereas another "crowbars" to zero
volts?  The lambda designs that I'm familiar with just don't do this.

I tried to get some idea of RF noise on the power supplies by looking at
it with my scope while the supply is under load, but what I'm able to tell
with my experience and tek-465 scope doesn't allow me to see any
apparently significant levels of 60 or 120C or RF noise.  I welcome
pointers to information about how properly test this.

I think I have a smaller 3AMP 28V lambda - I believe it will have no
problem running my ARC-5 with DM-33 dyno - I'll see if I can try it
tonight and report back on that, too.

But, one has to remember that these radios were operated in a bomber, and
I strongly doubt that they had squeaky clean power supplies back then.  
The dyno itself is probably a big contributer of noise, at least more so
than the power supplies I use.

Paul

On Tue, 15 Jan 2002, David Stinson wrote:

> The current ratings written on the dynamotors
> are the running currents.  The starting surge current
> will be much higher.  I don't remember off hand what 
> the starting current for a DM-33 or DY-8 is, but I think
> it's around 25 amps.
> Most of these supplies have protection against surges.
> If you use a lower-current supply, 
> most will "crowbar" and go to zero until reset.
> A 10-12 amp supply will run your receivers OK,
> but it won't start a DY-8 or DM-33.
> 
> You can overcome this by using some large capacitors
> in a bank to provide the surge current, while the power supply
> provides the running current.  24 volts in batteries will 
> also work.  Old IBM printers and antique
> main frame computer equipment contain lots of these big
> caps, where they served the same function.
> 
> If you use a switcher, you'll likely need to build an 
> RF bypassed enclosure.  They're designed for lasers and
> RFI isn't usually an issue for those applications.
> 
> Some 24-28 volt supplies at higher currents 
> on the Bay right now:
> 
> 1322466303
> 1690276274
> 1062389767
> 1688821631 (good deal on this one but will need shielding).
> 
> 73 Dave Stinson AB5S