Rectifier Over Voltage Problem

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Hubbskiboy
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Bike owned: GK76A 1994 and 1990
Location: Stourbridge, West Midlands
Rectifier Over Voltage Problem

Post by Hubbskiboy » Thu Sep 12, 2019 4:07 pm

Your help with this one would be much appreciated lads.
I suspect that the original OEM rectifier has never worked on my bike since I bought it.
Tell tale signs were the melted connector block to the battery, so I bunged on the voltmeter and it wasn't kicking out anything (voltage dropped when revved to 5k).
So I chucked that one in the bin straight away.
Luckily I had another spare OEM rectifier that I borrowed from another bike hoping that would be problem solved.
Unfortunately it killed my battery pretty quickly so again I checked the voltage it was kicking out on my voltmeter.
The actual regulator and connectors were getting red hot again.
The voltage output levelled out at about 15.2v when it was idling at about 2k with a bit of choke.
I immediately shut the bike off so I didn't kill another battery.
Surely this is way too high a voltage for the charging system?
Question is what are my options?
I'm considering buying a decent aftermarket Mosfet Rectifier from this guy - wwwroadstercycle.com
His stuff gets good reviews and it is effectively an upgrade. FH020AA (Which is the one he recommends for our bikes) costs about £125 + shipping.
A cheaper option would be some sort of switching regulator to install between the 'current' rectifier and the battery.
This would control the voltage and stop it going over 14v.
Anyone else had these problems?
Ta,
Hubbskiboy.
Last edited by Hubbskiboy on Thu Sep 12, 2019 4:48 pm, edited 1 time in total.

Hubbskiboy
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Bike owned: GK76A 1994 and 1990
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Re: Rectifier Over Voltage Problem

Post by Hubbskiboy » Thu Sep 12, 2019 4:10 pm

I forgot to mention -
before I installed the 2nd rectifier I put brand new connector blocks on both the 2 way and 3 way connections from the rectifier.
So resistance from those parts shouldn't be a problem.

moforockband
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Bike owned: GK73a SP CRM250 mk3
Re: Rectifier Over Voltage Problem

Post by moforockband » Fri Sep 13, 2019 11:21 am

Anything over 15 volts will fry your battery, well done in turning it off! Are your batteries new I take it, and YTX9BS?
You can use any reg/rec as long it is of roughly the same size or larger. I have a bike engined car which I put a R1 2006 unit on with a CPU fan, and that's the most demanding scenario there is.
I think as long as your battery and reg/rec are good, you have a fault elsewhere. ie the earth connection to your reg /rec is high resistance..
You can disconnect the generator plug and measure the AC between each yellow wire (phase), and I think it should be around 50 VAC.
Clean off any corrosion on the earth strap that connects to the RH side of the back of the crankcase. (10mm bolt)
Lastly make sure the reg rec's you are using only have 3 yellow, 1 red and 1 black wire. Some have a voltage sense wire which you do not want.

Hubbskiboy
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Re: Rectifier Over Voltage Problem

Post by Hubbskiboy » Fri Sep 13, 2019 11:53 am

Hi Mofo.
The battery is a brand new Shido YTX9-BS, so I don't want that fryed as they are easily damaged.
The rectifier is a very old OEM model off a 1990 bike, although it may not be the original (who knows!).
So I can disconnect the generator plug with the engine running? 50v AC current between each wire correct?
Don't see how the rectifier is earthed as there are only 5 cables that run into it.
I'm going to bypass the loom and connect the power leads straight to the battery with new 33amp cable and an inline 25amp fuse to prevent overheating.
I'm also going to buy a secondhand FH020AA rectifier off ebay and see if that works any more efficient.
Can't remember seeing an earth strap on the back of the crankcase, so I'll have a look for it later.

moforockband
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Re: Rectifier Over Voltage Problem

Post by moforockband » Fri Sep 13, 2019 12:13 pm

If your SHido is lithium, dont connect it, use some cheap lead acid until you have the problem solved.
If you simply disconnect the reg/rec the bike will run but not charge, no need to faff around with cables.
With bike running you are measuring AC VOLTAGE between the yellows. Most service manuals ask for a certain revs but 2000 will be fine. This just checks that your stator is OK. I reckon yours probably is, but need to check everything before throwing money all over the place :)
The reg/rec is earthed through the black wire on the connector block.

Hubbskiboy
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Re: Rectifier Over Voltage Problem

Post by Hubbskiboy » Fri Sep 13, 2019 12:24 pm

So if I bypass the loom and connect the rectifier straight to the battery, which has the most direct and unrestricted earth point, that should solve any bad earth problems?
50 volts AV seems to be a hell of a lot.
Just browsing through the electrical section in my original GK76A manual and it doesn't seem to mention any output levels from the stator.
However, there is an electrical chart in the back with some japanese symbols that I cannot make out, which I will replace as question marks.
???? 13-16 ??????? 5000rpm.
Which I would take an educated guess means that at 5000 revs the standard OEM rectifier should be putting out between 13-16 volts.
I'll take a photo if you need one.
If it's normal to put out that kind of voltage from the OEM rectifier then I will definitely need to upgrade to a new FH020AA.

moforockband
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Re: Rectifier Over Voltage Problem

Post by moforockband » Fri Sep 13, 2019 4:42 pm

Yes but that's phase to phase ac voltage which is always high. I remember reading a Honda tech doc that it was 44v when at 4000rpm on my old cbr1000rr. That kept burning stators out. Fixed it in the end.
You don't often see ac voltage readings, but the usual measure through the stator coils (yellow wires) which should be about 1 ohm, and infinite to ground.
Your ground connection to your reg/rec must be 0 ohms.
The Red wire goes straight to the battery + and main fuse feed.
You don't want to see >14.5 volts or your battery will get very toasty. A friend of mines battery boiled at 20 volts.

Hubbskiboy
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Re: Rectifier Over Voltage Problem

Post by Hubbskiboy » Thu Sep 19, 2019 7:23 pm

Mofo. Just been perusing the UK manual for the GSF400, which is pretty much the same engine.
Figures quoted for rectifer output in volts should be between 13.5 and 15.5v, so my rectifier was withing these tolerances.
Also it says that anything below 70v AC from the stator means that it is faulty and should be replaced.
I've bought a 2nd hand 2016 Mosfet rectifier off eBay and will try to fit it on my bike as an upgrade.
It's actually a lot bigger than than the standard and the bolt holes are wider.
OEM bracket is 63mm wide and new one needs to be about 68mm.
Any suggestions on where and how I can mount it?
The rear footrest brackets are also getting in the way!!!!
Why isn't anything straight forward?!!!!


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