[ARC5] Power Supplies for Your ARC-5

[J. Forster]

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.

> 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.

It will take a MIGHTY capacitor bank to start a dynamotor. Simply put:

Q (charge) = I (current) x T (time)

Q = C (capacitance) x V (Voltage)

therefore I*T = Q = C*V

in this case, the V is the allowable voltage drop during startup. Putting in
reasonable numbers:

I =25 amps, T=1 sec, V=(28-23volts)=5

25 * 1 = C * 5;  solving C = 5.............. FARADS, ie 5,000,000 microfarads.

That's a pretty big capacitor.

Think about floating batteres.. That's what I use for my No 19 MK III set, and
it works just fine. Marine batteries in a fiberglass case are ideal.

Good luck,
-John