[ARC5] Dynamotor Capacitor

[Kenneth G. Gordon]

On 25 Mar 2014 at 16:12, Bruce Long wrote:

> It seems to me the original ARC designers did not select the dyno bypass 
> capacitor voltage rating on the basis of the largest amplitude voltage spike
> that could be generated by the receiver dyno but rather from the largest spike
> that could be created, typically a load dump spike- that could be generated by
> any large 28vdc load on the aircraft 28vdc buss.

Yes. That is my thinking on it too. Although I am not very good at 
communicating my ideas (all you have to do is ask my wife about that) that is 
what I have been trying to say.

 
> I can't say I have a detailed knowledge of WW2 28vdc power systems but I think
> the load dump spike from a prop pitch motor or the aircraft engine starter
> motors coudl be really impressive.

Starter motor spikes are quite impressive. I speak from experience from 
grabbing the hot lead of a Model "A" starter motor (6 VDC) as a friend 
started the engine then got off the switch. I let go of that lead really quick. I 
was also quite surprised.

> As a partial reality check I think I remember the design standard for 12vdc
> automotive electronics is to resist 600 volt load dump spikes. I think there is
> an old National applications sheet or data sheet for one of their 12vdc
> automotive service IC audio amplifiers that has a discussion of the largest
> voltage spikes that can be expected in a 12vdc automobile buss.
> 
> If my memory is correct, then a 2kv rating for the arc-5 receiver 28v bus bypass
> is not out of line.

I wouldn't think it was either. All I was trying to say was that the dynamotor 
alone could not possibly have enough inductance to cause a 2KV spike.

> We are talking about the 28vdc bypass?

Yes.

Ken W7EKB