[ARC5] Dynamotor Capacitor

[J. Forster]

>> That only applies if the dyno is supplied by a source w/ considerable
>> inductance, like a generator or a long length of wire.
>>
>> If the dyno is w/in a foot or two of a car batter or other low impedance
>> supply, you don't see big spikes.
>
> I'm sorry I don't buy what you're saying.
> If you think about the two brushes, one will always break contact before
> the other, and at that instant there will be a large back emf developed
> between that contact and the other brush that is still yet to break
> contact.

Yes, BUT that large EMF is on the armature of the machine....  on the
OTHER side of the brusghes from the capacitor.

> The polarity of the emf at the o/c contact is the opposite of the battery
> polarity at that brush (that's why it's called a back emf), and this emf
> will therefore ADD to the battery voltage through the other (still
> contacting) brush. The battery will therefore play no part in suppressing
> the back emf, which it would do if the polarities were the same.
>
> There will therefore be an attempt to spark from the open circuited
> contact
> to the brush that just left it. This is most undesirable, on account of RF
> hash and brush wear.
>
> Far from suppressing the spikes, the battery actually makes them
> fractionally worse by adding 28V to the several hundred volts of back emf.

No.

I'll write this up later. I've got stuff to do now.

-John

===============
>
> 73 de Neil ZL1ANM
>
>
> On Tue, Mar 25, 2014 at 3:15 PM, J. Forster <jfor at quikus.com> wrote:
>
>> That only applies if the dyno is supplied by a source w/ considerable
>> inductance, like a generator or a long length of wire.
>>
>> If the dyno is w/in a foot or two of a car batter or other low impedance
>> supply, you don't see big spikes.
>>
>> -John
>>
>> ==================
>>
>>
>>
>> > The back EMF spike at every break of the brushes can have extremely
>> high
>> > voltage spikes. 73 - Mike
>> >
>> > Mike B. Feher, N4FS
>> > 89 Arnold Blvd.
>> > Howell, NJ, 07731
>> > 732-886-5960
>> >
>> >
>> > -----Original Message-----
>> > From: arc5-bounces at mailman.qth.net
>> [mailto:arc5-bounces at mailman.qth.net]
>> > On
>> > Behalf Of Mark K3MSB
>> > Sent: Monday, March 24, 2014 9:35 PM
>> > To: ARC5
>> > Subject: [ARC5] Dynamotor Capacitor
>> >
>> > I just finished a complete rebuild of the dynamotor for my BC-456.
>> >
>> > I'm curious why the  0.006 uF shunt capacitor across the 28V side is a
>> 2KV
>> > cap.  That seems awfully high.
>> >
>> > 73 Mark K3MSB
>> >
>> > Sent from my Android phone
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