[ARC5] Dynamotor Capacitor

[Bruce Long]

ken
I agree with you on all points.

it would not surprise me is a arc5 receiver dyno could generate turn off spikes in excess of 1kv.  And i think other motor, relay loads on the aircraft 28vdc buss could generate even bigger spikes.

Don't assume my comments are based on unclearness on your part,  I had a really busy day at work yesterday and was reading the emails on this string in a hurried, not careful basis.

To the mortification of the orignalists on this list I humbly suggest that the dynomotor 28vdc connection could benefit from the application of a suitably rated uni-polar TVS- transient voltage suppressor leaving the capacitor to clean up what remains from the truncated spike.

I mitigate  the enormity of my crime of suggesting an non-original modification of the venerable equipment by meekly pointing out this bit of devil spawned alteration can be removed and the equipment restored to original state as god and ARC intended with minimal effort.    







On Tuesday, March 25, 2014 8:14 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
 
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