[ARC5] Dynamotor Capacitor

[J. Forster]

The dynamotor is actually more complez than I thought originally. It has
been pointed out to me that the armature and field are not independant, as
assumed in most analyses. Rather, they are oupled by their mutual
inductance.

I would like to know if the input side of the dynamotors (mainly for the
receivers) are Shunt or Compound wound (ie, do they have shunt or shunt &
series fields).


Let me just throw this out. Perhaps the capacitor is chosen to resonate
the dyno coils?

It is clear that any coil of wire has a self-resonant frequency. In some
vibrator PSs, I believe the snubbing cap is chosen to resonate the
transformer to minimize arcing.

The same trick seems, at least, possible w/ a dyno. I don't know as yet.

-John

===============




> 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
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