I have a 2007 Buyang 50cc quad that runs very well but the battery charging system does not work. The power wire connecting the voltage regulator to the battery gets very hot and the battery discharges quickly even when the quad is not running. Any ideas other than just replace the voltage regulator? Thanks!

 

Unplug the voltage regulator. If the battery draining, and hot wire phenomena quits then your regulator is bad.

But normally this would just blow the main fuse. You don't have fuse blowing problems? Or did you put a bigger fuse in? Check the fuse value in any case. It should *not* be more than 7 amps. If it is bigger than that then you may have damaged the stator.

Respond back, get a meter ready and we can test to see if your stator is working...

 

I unplugged the voltage regulator - battery doesn't drain nearly as fast and the wire does not heat up any more. Progress!

I assume the main fuse is fine because the unit still runs. Unfortunately I can't find where the fuse is located. The power wire runs straight from the battery to the starter relay than to the starter. No fuse between the voltage regulator and the battery either.

If you have some suggestions on testing the stator I would like to try it - thanks for all your help.

 

So your regulator is bad. That is progress as you stated already.

Your battery should absolutely have a fuse feeding everything other than the big fat wires feeding the starter motor through the solenoid. Usually the fuse is located within 6 inches of the battery positive terminal on a small gauge red wire feeding the harness. On some quads the fuse is located inside the solenoid itself, and an extra terminal on the solenoid going to a small gauge wire is the "fused" output. But on other quads the fuse has been hacked out (a stupendously bad idea). You need to find that fuse (or lack thereof) and check it's value - and remedy that situation if you don't have one. Seven amps maximum for a 50cc quad. If you don't have a fuse I can help you install one.

Look at the wires from your stator (coming out of the engine side cover). How many wires, and what are the colors? Note (really important): I only want the wiring harness side colors on any connector set if they differ from the wire colors on the short pigtail wires coming out of the engine. Again this is really important.

 

I will have to add a fuse. It appears that the previous owner had done some jerry rigging and maybe the fuse removal was part of it.

4 wires coming out of the stator and connecting to the Harness.

Yellow
White
Blue w/ White Stripe
Black w/ Red Stripe

Green wire comes out of the stator and bypasses the harness. This would be the 5th wire out of the stator.

 

First put in a fuse. You can buy in-line fuses at any autoparts store. They are essentially a fuse holder of some sort (with fuse installed) with wires coming off each end. Find the *small* red wire off the battery (not the big one feeding the starter via the starter solenoid), cut that wire and splice in the fuse across those cut wires. Wire nuts (hardware store in the household electrical department) work well if you don't have a soldering iron. Sometimes the small red wire comes off the solenoid which is nearby the battery - and connected to the battery with a big heavy red wire.

To check you stator, leve the voltage regulator unplugged. Start up the quad and let it idle. Set your meter to measure AC volts on the 50 volt scale. Then measure the following on the regulator connector in the wiring harness:

1) The voltage on the yellow wire to ground.
2) The voltage on the white wire to ground.
3) The voltage between the yellow and the white wires.

What do you measure for each of those three tests? For ground you can use the negative battery terminal, the engine chassis, or the green wire coming out of the stator. In fact, it might be a good idea to use all three grounds for each of the three tests. You should get *identical* readings for each of the three tests - no matter which ground you use. If you don't then document that so we can find out why .

 

I failed to mention in the prvious post *why* we are measuring the stator output...

Two things:

1) We want to see if the stator has been damaged by being driven by the battery through a bad shorted regulator. By measuring the voltages we can see if the stator is still producing proper voltages (which it won't if the stator is wrecked by excess heat).

2) By looking at the voltages we can also determine what the topology of you stator windings are. Do you have the dual output single ended drive, or the differential isolated drive. Some call this the half wave or full wave rectified version. We need to replace the bad rectifier with the proper type to match you stator.

 

Well...not looking so good if all three tests were supposed to produce the same voltage...

Yellow wire to ground: 18V
White wire to ground: 22V
White to Yellow: 5V

In the tests to ground, the readings were identical to each ground source (negative terminal, Chassis, Green Wire).

Resistance between White and Yellow is very high - jumps around between 900 and 1500 ohms.

 

Well actually the stator voltages look OK. Your resistance readings don't.

But I suspect measurement error on the resistance readings. All three wires should measure close to zero ohms - but not exactly zero. We should be seeing something less than an ohm. I would redo the resistance tests just to be sure. Remember that you must use the "lowest" ohms scale you have - like 20 ohms full scale or even 2 ohms if you have it. 900 to 1500 ohms is just plain wrong, but I wouldn't think you'd get the right voltage readings if that were really the case.

If you can get the resistance reading to read right then it looks like you have the half wave style 4 pin regulator.