[ARC5] Dynamotor Rewiring

[Michael Hanz]

On 9/13/2016 5:31 PM, Robert Eleazer wrote:
> I have a rather unusual dynamotor with the following ratings: Input 21 
> VDC, 3.3 Amps.  Output 260 VDC 0.135 Amps,  I have it apart and plan 
> to rewire it, taking the two field coils, which are in series, and 
> rewire them in parallel.  I calculate that with 12 VDC input it should 
> then produce about 170 VDC output, which should work well for powering 
> a BC-652-A.

I'm assuming you calculated that output voltage with an equation 
Vo=(12/10.5)*(21/12)*260?  I wish dynamotors were that linear, but I've 
never found one that behaves nicely when you depart significantly from 
its design parameters.  Keeping the field strength roughly the same by 
paralleling the coils is a good start. However, a reduction in armature 
motor drive voltage, while it _will_ slow down the motor speed, will 
also usually introduce a bit more instability in the output voltage 
side.  You shouldn't expect the good voltage regulation of a dynamotor 
operated near its design center.  Now, it may not matter to a BC-652-A, 
so little is lost by trying it.  On something like a WWII panadapter, 
you would probably see the scope trace jumping up and down to drive you 
nuts.

> For rewiring the field coils, I assume should I hook them up so that 
> the currently used leads (+ and -) are in the same location and have 
> the new leads I will create go to the opposite ends?

Yup.

  -  Mike  KC4TOS
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