Charging system issues

[Mr.Kodama]

Hi guys,

I just bought a used 2004 GS500F U.S model at the end of June this summer and after about a month of problem-free riding I started experiencing a slew of issues that had me on and off (but mostly off) the bike for the past month and a half. I've learned a ton through all the research and repairs I've had to do but I'm about at my tether's end with this one. Here are the facts:

- after sitting for a couple weeks, old battery too weak to start bike, read ~11.6V at rest, as low as 3-4V but usually ~6-8V when under load trying to start the bike. Battery was obviously gone but this is when I started to suspect trouble with the charging system
- replaced with new AGM battery, reads ~12.9-13V before starting the bike. ~12.6-12.8V @ idle, slowly decreasing in voltage; ~14V @ 3000-4000 rpm, drops a bit to 13.8-13.9V @4500+ rpm
- thought it might be a stator issue, went through all the electrics tests in the Hynes manual and on this forum. Stator tested a little weak on its AC voltage output at 68-69V @ 5000 rpm for all 3 readings
- rec/reg tested fine
- consulted good local motorcycle mechanic and he confirmed my suspicions after quickly testing with a multimeter, advised me to replace stator and rec/reg and to check all wiring connections
- replaced both stator and rec/reg with Rick's Electric's aftermarket stator and rec/reg for my bike
- new rec/reg reads fine, and new stator passed all tests and reads over 75V @ 5000 rpm for all 3 readings, so I know the parts are not the issue, but still getting same low readings on the battery
- read on another thread that dirty/corroded terminals could be the issue, and although after a cursory look-over the wiring seemed alright, I started checking the terminals for corrosion and faulty wiring and have been cleaning some of the old ones in the stator/rec-reg/battery circuit (vinegar, baking soda, brush, dry, contact cleaner, let evaporate, reconnect) but I've still no luck

I can only assume the problem is in the wiring at this point but I'm still a newbie and might be missing something. Does anyone have any advise as to what the issue might be and what I could do to fix it? Should I continue to check through all the block connectors/terminals/wiring on the bike?

The battery is still being charged enough to maintain a full charge so I've started commuting on the bike again as there isn't much left of the riding season here in southern Ontario, but the issue is still there and lingers in the back of my mind (along with all the other issues the bike has), making me feel uneasy. I'd really appreciate any help anyone could offer. Thanks in advance!

[user11235813]

I am not an electrical expert but I've gone through similar 'problems'. It sound like you were already getting enough voltage to charge the battery. Maybe the issue is just too many short trips that simply requires you to put the battery on a good quality charger every few months.

68-69VAC is not a little weak. Because that's already going to convert to a lot more than the 14VDC that you need, from what I understand the important metrics is that the three phases should be about the same reading.

[mr72]

you can eliminate a pigtail connector between the reg/rect and stator, which likely has lots of corrosion in the connector body and will eventually cause the wires to melt.

Cleaning these wires won't work, you have to replace them. They get corroded under the insulation and form high-resistance wires which not only drop voltage but also create lots of heat. You can either replace the pigtail (from the reg/rect connector to the stator bullet connectors) or just eliminate it altogether. Since you already replaced both stator and reg/rect I'd just order a new pigtail assy and replace it. Then the low-voltage side of the reg/rect, replace all wiring from the reg/rect to the battery, starter relay, and to ground. I think I used #8 wire when I did mine. Makes a huge difference.

BTW if you just got another shunt-type reg/rect then it still likely won't charge at idle or at under maybe 3K-4K rpm, that's normal. If you want it to charge under 2k rpm you need a MOSFET reg/rect, which is retrofit from another bike. But the shunt reg/rect will work fine as long as all of the wiring is mint and you don't do a whole lot of very short trips. In any case I recommend a battery tender if you are either taking short trips or leaving the bike parked more than a week at a time.

[Mr.Kodama]

Thanks for the responses guys, and sorry for taking so long to respond myself. So it sounds like I didn't need to replace either the stator or rec/reg after all. Oh well, live and learn I guess.

As for the whole pigtail assy, both stator and rec/reg came with new wiring and connectors, so the only one that isn't new is the side that plugs into the rec/reg from the bike (since the stator had a new connector and the rec/reg had two). I looked at that connector a little closer and some of the insulation on that connector's wiring looks like it has melted a little bit, so I suppose it already has a decent amount of corrosion going up it. I'll likely rewire what you recommended when the riding season is nearing its end or during the winter, but for now I'm going to ride as much as possible since the battery is still being charged back to full every time I ride (I don't make many very short trips). mr72, when you say #8 wire, is that SWG or AWG? Also, did you find that a little large to work with since much of the wiring in that area of the bike (apart from the battery) seems to use something close to 18 gauge wire? Any tips you can offer for rewiring those sections?

I did purchase a good smart charger with my new battery and have been keeping an eye on the voltage since this whole fiasco occurred, so if the voltage does drop I'll be sure to put it on the charger. Thanks again for all the help guys, I really appreciate it.

[mr72]

That's #8 AWG.

For current-carrying wiring, use #8.

The regulator-rectifier takes input from the stator on one connector, that's lowish current and up to like 85VAC. I would not use anything less than 14AWG for that side. The factory wiring is too small and will overheat. I might have even used 12AWG on mine.

The output of the regulator-rectifier is 14VDC or so, and many amps of current. I would highly recommend going no smaller than #10 on any of these wires. There's basically power and ground, but IIRC there are two +14V wires and one ground. Don't quote me, look at your own bike. The +14V wire that goes to the battery to charge it needs to be #10 or more. The wire that goes from the battery to the starter solenoid needs to be #8 or larger. I would just rebuild this entire wire path if I were you. You have a new reg/rect, don't want to melt down the new connector by connecting it to the old one where it will severely overheat.

BTW the reg/rect has to do something with all of the energy that it's dumping from the high-voltage input, and it turns it into heat. It radiates this not only into the heat sink on the reg/rect but also through the wires. So the wire and connectors from the reg/rect get heated directly. It's just the nature of diodes. This accelerates the overheating of these wires. The real problem is on the other side though, since there's a connector in between and it gets corroded over time adding a high resistance joint which adds a lot more heat, And this additional heat gets conducted down the wire and melts the insulation into the wire, allows air into the wire jacket and corrodes the wire making it even worse. It's a vicious spiral that will end with a fire if you don't catch it.

[Mr.Kodama]

Great, thanks for all the info mr72. I'll start mapping it out and get to work as soon as I can.

I've browsed around and haven't really been able to find any distributors in Ontario/Canada of those double-barreled terminals that are so often used on the bike. I mean, I could always just use the more standard ones found at auto parts stores, but I want to keep the bike looking as close to stock as I can (or at least keep the connectors more or less the same). In the end it isn't that big a deal, but does anyone know a shop or site where I can acquire some?

[Sandgroper57]

Try Eastern Beaver, they will most likely have what you are after.

[Mr.Kodama]

Thanks Sandgroper57. Looks like he ships from Japan but the parts look to be of good quality.