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Permanent magnet generators

2K views 16 replies 8 participants last post by  75R20 
#1 ·
I am busy rebuilding (redesigning is probably a better description) a Fischer Panda genset and it has a simple generator with permanent magnets to charge the genset's own starter battery. On the original setup, there is an electronic controller unit that does a miriad of stuff one of which is regulating the output of this little generator. That electronic controller is MIA.

The space in the enclosure is too small for anything but this little generator and I reckon that its design is so simple it's probably as reliable as the sunrise. So please don't recommend that I replace it with an alternator - if I could I probably wouldn't but that's academic because I can't. :p

My question is: Alternators are regulated by the current input into the fields which increases (or not) the strength of the electro-magnetic field which thus produces a commensurate current output. But this little thingy can't be done that way (I don't think). Does anyone know how to regulate the output on a permanent magnet generator?

Anyone have any ideas? :confused:
 
#6 ·
Hi!

Two ideias that might be interesting to consider, assuming you haven't thought about them yet:

1-A simple load dump like this one here (allready extensively discussed)
Hey Pedro,

Thanks for the lead. I have a few questions.
  • So if I need more than 55w of input then all I need to do is add Q2/L1 pairs in.
  • How do they fit in?
  • Will each pair give me another 55w? I believe that 55w at 12V = 4.6A. So I would want to do quite a lot better than that.
  • Does that mean I will end up with a bank of lights coming on when the battery gets to a full charge?
  • Does the multiple of the Q2/L1 pairs mean that the residual current draw will go up?
Altogether, other than that I don't want to light up the local village with a string of lamps burning, it looks like a simple enough solution.

I may just put one together and try it. Thanks
 
#5 ·
Thanks for that and you're right, the FP circuitry is complex indeed. That's why I have ripped it all out and have reverted to basics that I understand. Whilst the original stuff is complex, the generator I'm talking about is as simple as it gets. A set of windings inside a spinning magnet pack with two wires coming out. That's it.

I don't want to cloud the issue with the complex nature of what used to be - the FP stuff is ALL gone.

Have you any ideas on how to do this? Pedcab seems to have something of a solution.
 
#9 ·
Your formula is pretty impressive (means squat to me) so you could be right but there is a problem with that.
  • The little generator charges the battery that starts the engine of the genset. This means that the battery is always near to a full charge because the engine starts with the first flick of the key.
  • The little gen is also a very secondary consideration when it comes to revs because the main genset is tasked with charging a depleted house bank so it may need to run for a couple of hours at a rev setting that suits the output of the main genset.
  • In the meantime the little gen is busy cooking its battery.
  • So regulating the little guy is even more important than regulating the main output.
But thanks for the thought. Oh and yes, they really are permanent magnets.:)
 
#10 ·
Have you verified that the output is DC and not AC ?

Sounds like it could be an AC output, and if it is...it just needs a rectifier and or a rectifier/regulator to charge the "start" battery
Yep, once again, I don't know the answer. But it appears to only have one winding and I believe that to generate AC there needs to be more than one. There is no rectification. there are only two wires coming from the windings. I reckon it's DC. This is a really simple little thingy.

But thanks also, I will have that fact determined
 
#11 ·
Sure sounds like your basic dirt bike/outboard charging system to me. Coil of wire, wrapped around an "iron" core (laminated is even better)
spin a magnet around it in close proximity, (induction) Tada...........you've got AC.
Check the output. I believe you will find it to be AC.
Depending on the goverend speed of the generator, you may not need a regulator. Simple, crude, realible........ KISS principles..
Good luck
Kary
S/V Mariah
#49080
 
#13 ·
Thanks for the advice . . . .

I managed to get a regulator. Looks like a rudimentary piece of kit - just a square ally heatsink with three terminals sticking out the bottom. One each goes to the two wires coming from the generator and a third that goes to a switched battery positive.

Costs a little bomb though - NZ$275.Imay be out of touch but it seems a little expensive.

I'm also lead to believe that these little generators only put out 4 or 5 amps. I guess that's enough.
 
#15 · (Edited)
Do you actually need the little generator ?

I mean you have a big generator, why not just put a charger on it and charge the start battery with that and leave the little generator out of the loop altogether. You said it was for charging your house bank, you could just charge the generator battery like it was your boat's starting battery.

I know someone who lost the generator/alternator on his garden tractor so he just carries the battery to the garage when it needs a charge and charges it up, which it rarely needs. It is just a battery for a small starter motor afterall.
 
#17 ·
Glad you got the part you needed, but it sounds like you got taken. What you describe is a simple bridge rectifier, and they run ~ $2.00 USD. The connections are simple, 2 for the outputs, and 1 DC positive, with the case going/bolted to ground.
Best of luck
Kary
S/V Mariah
#49080
 
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