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Posted by richard on June 9, 2009, 12:08 pm
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>
>>
>>
>> > Anyone happen to know if the poles on a single phase alternator field
> coil
>> > (rotor) are opposite such as they are on a 3-phase alternator? I
> applied
>> > *some* voltage to it but don't know how much is OK and don't want to
> burn
>> > it
>> > out but it seems, so far, that the poles are the same on both sides
> (i.e.
>> > N
>> > and N and not N on one side and S on the other). Also, would the
>> > field
>> > coil
>> > be getting 120 volts on a 120/240 volt generator? I have this idea
>> > but
>> > before I waste my time I need to find out why it won't work ;-)
>> >
>>
>> There should be one N and one S if it only has two poles. If more than
>> that, it should alternate N, S, N, S and so on. The voltage applied to
> the
>> field winding is seldom anywhere near the same as the output voltage and
>> it's always DC. (although once in a while the rectifier is mounted
>> right
> on
>> the rotor so you can apply AC to the rotor's slip rings).
>>
>> Typical car alternator uses DC on the field winding, applied via two
>> slip
>> rings. Although it is only one coil, the metal pieces on each side have
>> inter-woven fingers so that alternating 'fingers' are opposite polarity
> (N,
>> S, N, S as I mentioned above). One alternator has as many as 28
>> 'fingers'
>> so that's 14 N poles and 14 S poles, interwoven.
>>
>> Surprisingly, a rotor for a three-phase machine and a single-phase
>> machine
>> have the same number of poles and winding. The only difference between
>> three-phase and single-phase is in the stator (armature) winding, not
>> the
>> rotor (field) winding.
>>
>> daestrom
>>
>>
>
> What I have in mind is to use a field coil from a single-phase alternator
> to
> produce three-phase (or more) power by winding three coils (or six
> perhaps)
> for a new stator. This particular field coil has a tapered mount so it
> would be direct-drive. It has slip rings so I could apply the excitation
> current directly and control it for the desired output. That all depends
> upon whether or not the coils are still OK. The generator I saved it
> from
> had a melted stator but the field coils appear to be OK but I'm not sure
> if
3-phase motors already existed. Why bother? You can't increase more
voltage and current because there is no room left to add. Bigger wire
would mean lower voltage, high current output, you need both. You should
forget about modifying existing motors, the reason is they are all glued
with industrial Epoxy.
> it's one coil wound on two poles or two seperate coils. Like I said I
> tried
> applying some DC voltage and didn't get any definate answers but I did
> get
> quite a zap when I disconnected the DC source so something is still
> working.
> All I would need to do is to make a brush holder, mount the non-engine
> end
> in a bearing, and one way or another position the stator coils around it.
> And rectify it, of course. Since there is some residual magnetism in the
> field coil I think it will self-excite just like my Delco car alternator
> does. But I don't know how much DC voltage it will need to excite and
> end
> up producing, say, 80 volts at 3600 rpm, but I think that will be
> controlled by the number of turns on the stator coils. To answer Jim
> Wilkins the coil was originally for a single-phase, 120/240 3600 rpm
> generator but I would be running it at 3600 maximum and slowing down the
> engine to control my output voltage (and adjusting the field current as
> needed too). Before I get started I just want to be pretty sure of what
> I
> have to work with. It sounds like, from what everyone said, that the
> pole
> should be correct for my purposes. :-D
>
>
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