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Discussion Starter · #41 · (Edited)
I'd add a couple of tweaks perhaps: With fixed strength permanent magnets, core permeability and core design then it's the number of turns and RPM that determines the voltage (rate of change of flux * number of turns essentially).
Switching to LED's does reduce the stator (and Reg/Rec) load if you have a series regulator, but not with shunt regulation (which is what you meant I think).
It might depend on what scenario you're thinking of, but I wouldn't say the primary limiting factors of perm mag generator output are the regulator or the available RPM (tho obviously they could be a limit on the final available output). I believe generator output tends to level off at higher RPMs due to core losses and increasing reactance at higher frequencies. It's not a particular area of specialism of mine, so as always I stand to be corrected, but based on basic electrical/electronic knowledge. The dc resistance remains essentially the same but the inductive reactance increases proportionally to the rpm.
edit: (response to @pidjones)
 

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Discussion Starter · #42 ·
Why are you using thicker wire? is that how the output is increased with these?
To add a bit to clarify previous reply: Although it's not my own aim here particularly, it IS one way of increasing output a little. We're talking about increasing output at idle (or low speeds at least) I'm assuming. Generally there is plenty of power at higher revs but it may sag a bit at low speeds depending on lighting load etc. Basically you want to get the output sufficient at low rpm, and then the regulator has to take care of the excess at higher rpm.

The voltage that you get at idle at the battery is from the voltage generated in the stator but that voltage drops across the internal resistance of the stator windings (and a bit more across the regulator) before it hits the bike. Increasing the thickness of the stator winding wire reduces the internal resistance in the stator (assuming the same number of turns of wire) and can therefore increase the output.

BUT the reason I added a touch of vagueness to my previous reply is that it isn't necessarily quite so straightforward! Firstly there are lots of different generator/stator wiring and regulation design variations as @pidjones reminded me... The best solution may be to wire the stator differently, use unused poles or whatever if you have them.

You could also add more windings to get a higher voltage but there are trade-offs. That will increase winding resistance again, increase heat generated in the stator and so on...

If you increase the output at idle by increasing the wire thickness then at higher RPM the regulator, if it's a shunt type, will have to dump more current which it might not like.. (I'm not worrying about this because I've gone for series regulation.)

Another consideration is that thicker wire can be more awkward to wind with and needs more space in the stator.

Hope that makes some sense.
 
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Discussion Starter · #44 ·
Before I get onto the next stages of the rebuild, does anyone know of a good high temperature impregnating insulating varnish?

This is for sealing and strengthening the windings not for repairing the core insulation.

Needs to be available in small, not industrial, quantities here in the UK. (And not high priced..).
I didn't have a lot of luck so far with googling around.

Can be 2-part epoxy, or one part solvent based curing.

I do a have a small tin of usable varnish, which I picked up on the fly with the rest of the materials for this job. It isn't bad ('F' grade, ~150ºC long term IIRC) but I would rather have a higher temperature grade (eg. H-grade 180ºC-200ºC) if something can be easily had.
 

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Thanks for the info Fred.

Interesting to hear about the outcome of your own epoxy repair efforts. Do you know where your 955 stator failed again after a year? I mean was it in the same spot you repaired, or somewhere else? (I'm assuming you mean it failed short to ground again.)
I think I wound the enamel because of the way I wound (yeah same word) the coils. Secondly I replaced the thyristor shunt RR w/ a FET shunt RR. So the load on the stator was even higher.

That said I burnt one pole of the GT stator shortly after having switched to sh775. It may have been damaged before the switch though.
So far so good. But I bought a spare stator and next time long haul i'll get a stator + seal + tools. Needed tools are small.
 

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He refers to the coating on the core as powder coat not epoxy
Powder coating is actually epoxy.
He doesn't want to repair the core insulation because it takes a lot of time to cut pieces of glass fiber just the right size (possibly several layers of 50 gr/m²) and epoxy it. Stabilize the whole w/ electic tape then once cured remove the tape. No professional has the time to do so. The alternative would be to remove the core and coat it again. But then you need an oven (18°C) w/ a static electricity generator. They usually use a contractor/provider to do the powder coating.

BTW capton is probably the only tape that will handle the heat. But is may memory serves capton tape is very rigid.
 

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Before I get onto the next stages of the rebuild, does anyone know of a good high temperature impregnating insulating varnish?
Epoxy resin (again).
This is for sealing and strengthening the windings not for repairing the core insulation.

Needs to be available in small, not industrial, quantities here in the UK. (And not high priced..).
I didn't have a lot of luck so far with googling around.

Can be 2-part epoxy, or one part solvent based curing.
You don't want to add solvent in epoxy. You would alter the mechanical properties.

The only way to rend the epoxy thinner is to warm is up. In addition you will reduce the curing time.

example: https://www.mack-kayak.com/resines-epoxy/850-resine-epoxy-hydrocarbures.html
115°C après post-cuisson: after post heating (in oven warm up after the curing. say 60°C/1 hour).

The high temp epoxy painting used for coating the brake calipers is also a possible solution. In general epoxy paint stands the heat.
 

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I'd add a couple of tweaks perhaps: With fixed strength permanent magnets, core permeability and core design then it's the number of turns and RPM that determines the voltage (rate of change of flux * number of turns essentially).
Switching to LED's does reduce the stator (and Reg/Rec) load if you have a series regulator, but not with shunt regulation (which is what you meant I think).
It might depend on what scenario you're thinking of, but I wouldn't say the primary limiting factors of perm mag generator output are the regulator or the available RPM (tho obviously they could be a limit on the final available output). I believe generator output tends to level off at higher RPMs due to core losses and increasing reactance at higher frequencies. It's not a particular area of specialism of mine, so as always I stand to be corrected, but based on basic electrical/electronic knowledge. The dc resistance remains essentially the same but the inductive reactance increases proportionally to the rpm.
edit: (response to @pidjones)
DeCosse did a set of measurement a while back that shows that one of the limitation factor is the core saturation that limit the short circuit amperage.
 

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Discussion Starter · #50 ·
Powder coating is actually epoxy.
I just learnt something new!

BTW capton is probably the only tape that will handle the heat. But is may memory serves capton tape is very rigid.
Yes. This is why I've used 'Kapton' as an additional insulation layer. It's not stretchy - but it's thin so you can crinkle it around a bit without adding much bulk and it will be held down by the windings. (I did initially consider PTFE tape, but shelved the idea, possibly too soon).
 

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Discussion Starter · #51 ·
DeCosse did a set of measurement a while back that shows that one of the limitation factor is the core saturation that limit the short circuit amperage.
I haven't seen that one from decosse. I'm not totally sure that makes sense to me. I may be missing something here but if the permanent magnets are strong enough to saturate the core they will do it at low speeds - at high RPM my instinct is that (apart from the increasing inductive reactance due to increasing rate of change) the magnet flying past won't be able to magnetise the core fast enough to gain anything more.
 

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I haven't seen that one from decosse. I'm not totally sure that makes sense to me. I may be missing something here but if the permanent magnets are strong enough to saturate the core they will do it at low speeds - at high RPM my instinct is that (apart from the increasing inductive reactance due to increasing rate of change) the magnet flying past won't be able to magnetise the core fast enough to gain anything more.
it's the (Ampere x turn) that saturate the core. In other worlds it's the current flowing through the wires x the number of winding turn.
 

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Discussion Starter · #53 ·
You don't want to add solvent in epoxy. You would alter the mechanical properties.

The only way to rend the epoxy thinner is to warm is up. In addition you will reduce the curing time.
I didn't mean I wanted to thin the epoxy. I meant there are solvent-evaporation type varnishes, and 2-part curing typs - either would be fine if they have suitable electrical, thermal, chemical resistant properties.

example: https://www.mack-kayak.com/resines-epoxy/850-resine-epoxy-hydrocarbures.html
115°C après post-cuisson: after post heating (in oven warm up after the curing. say 60°C/1 hour).

The high temp epoxy painting used for coating the brake calipers is also a possible solution. In general epoxy paint stands the heat.
I"ll take a look at the link - thanks. From a quick glance it looks interesting, though not quite in my 'cheap' category perhaps.
 

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post #10
 

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Discussion Starter · #55 ·
it's the (Ampere x turn) that saturate the core. In other worlds it's the current flowing through the wires x the number of winding turn.
That would make more sense in a transformer than a generator. In a transformer the ampere-turns in the primary winding can be sufficient to magnetically saturate the core, but in a permanent magnet generator the core is magnetised by the permanent magnet passing by. This induces a current in the coil and that current creates a magnetic field opposing that of the magnet. The faster you try to change the magnetic filed the bigger it pushes back (inductive reactance).
 

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Discussion Starter · #56 ·
That said I burnt one pole of the GT stator shortly after having switched to sh775. It may have been damaged before the switch though.
Same here. SH775 => Stator burnout. But I know my stator was acting suspiciously for quite a while, with intermittent low charging voltage when hot - before I installed the series RR.
Then it burned out not so long after installing the SH775.

My diagnosis is: Less current heating, but now higher voltages drilling away through the leakage paths in the damaged insulation. (And hence my obsession in this thread with insulation :) )
 

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Discussion Starter · #57 ·

post #10
Ahh - the venerable charging system diagnostics sticky !

OK... I have read that thread in the past, including post #10, but I didn't pay much attention to the caption on the graph! The shape of the output curve looked reasonable to me - but I didn't read the comment "Fortunately the rotor saturates at 27A".

I presume that annotation on the graph was made by posplayr on the Suzuki forum where DEcosse got the graph from. I think that's just loose or different use of terminology, or a misinterpretation by posplayr of what's happening. I haven't tried to track it all back to the source - I think it's just a note on a graph meaning 'fortunately the generator runs out of steam at this point'! (I just noticed it also refers to the rotor saturating.)
 

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Discussion Starter · #58 ·
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