MOSFET or Series? Info here - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 4 (permalink) Old 06-11-2017, 09:33 PM Thread Starter
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MOSFET or Series? Info here

I found this thread on another forum when looking up the differences between the MOSFET-style FH020AA R/R vs the Series-style SH775BA, both of which are the same form factor but the SH775 (Series) appears to be a better performer for bikes that like to overheat their stators (kinda like ours)...

Triumph Rat Forum - Series vs MOSFET RR

The basic conclusion of the thread was that a Series RR can potentially draw as little as half the current a MOSFET draws from the stator, due to the more efficient design and the regulating method used. Essentially it seems the Series-type regulates what it draws from the stator based on load, while the MOSFET regulates what it outputs to the battery, meaning that a MOSFET draws all it can from the stator at all times and then wastes it, while the Series draws only what it needs from the stator.

Now this is not to trash the MOSFETs at all (as of this posting I have one on my bike and it's a fantastic upgrade over stock) but to inform everybody that the Series-style SH775 may be a superior RR for our bikes due to the fragile nature of the stator.

So, what's the difference?

Well, they are the exact same form factor as the FH020AA, so if you've already installed one you can swap right out. If not, every bit of information already available on the forum regarding an RR upgrade still applies except you would buy a different model RR. The series type will (in theory, at least, not confirmed by testing on VN750's) draw less current from your stator, reducing the load on it, and allowing it to run at cooler temperatures, which is much easier on it and better for longevity.

Where do I find one?

They can be found just like the MOSFET's, through Roadstercycle, on eBay, or through some other channels if you're looking for brand new. That's $150 or so, I believe. Your other option is to search for a used Polaris 800 Regulator and confirm in the online listing that the item is marked on the top as SH775BA/SH775AA. These can be had for ~$45 or so.

I figure this thread might be of particular interest to those who are considering upgrading to or have a MOSFET on their bike and might like to be less paranoid about stator failure in the future, especially seeing how hard a quality stator for our bikes is to find these days.

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post #2 of 4 (permalink) Old 06-13-2017, 10:55 AM
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Seems like a good idea in theory, but I don't have time right now to dig into all the technicalities. However, it seems contrary to info that's been available. Such as, the stator output being mostly constant, except during low rpm, and there being no way to limit that. The magnetic field on the windings is present even if all the stator wires are disconnected, correct? A simple piece of copper in a moving magnetic field produces heat in the copper.

Just offhand, one r/r may handle disposal of excess current better than another, but I'm not yet convinced an r/r can limit stator output. At least not without some additional circuitry in the stator itself. Again, I'm just going off what I've seen about the stator output, and haven't had time to look into the link you posted.

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post #3 of 4 (permalink) Old 06-13-2017, 11:34 AM
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a series RR can limit the amount of current (not voltage) the windings provide. good way to think of it is that the stator is like the electric outlet in your wall. Always live (voltage), but no current flows until a load is placed on it (plugging in something).

while excessively high voltage can damage a stator (insulation failure), its the current that generates the majority of the heat.

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post #4 of 4 (permalink) Old 07-01-2017, 06:44 AM
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Just picked up a Series R/R (Polaris 4012941) off Ebay and will be installing it soon. As ubertalldude says, several different bike forums use Series R/R in place of their shunt oem units and swear by the SH775 (Series) claiming it's superior to the oem standard shunt and better than the FH020AA mosfet R/R.

Be SURE to AVOID new aftermarket SH775 R/R units on Ebay that sell for roughly $55. They are NOT series units as claimed! Real SH-775 R/R sell for approximately $180-200. I picked up a used one off a 2014 Polaris 570 ATV for $37 shipped. Search Ebay for part number 4012941.

Will post results after I have it installed.

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