I bought a used 150cc atv. I think it's a tao tao. Not sure but it's from the same manufacturer. My battery kept falling dead. I changed it, it held a charge, I checked the voltage output while running and it's @ 13v and the atv runs well. Just that after using it, if I turn it off for a sec and tryin to start it again, the battery is dead. I replaced the regulator and it worked fine but shortly after, it went out again. What could be the problem? The battery is good so that's not it. Where can I get a wiring diagram so I can trace it out and see if anything was crossed. I can tell he tried to do repair work on it himself. Everything else on the atv looks good but he may have wired something wrong.

 

Here is a wiring diagram of my 150cc ATV:





It is not a TaoTao, but the wiring is probably similar to yours.

You said you measured 13 volts while the engine was running. This measurement is not accurate enough to determine if the battery charging system is working. We need 1 more significant digit in the measurement. 13 volts could mean 12.6 volts (rounded off), and that would mean your charging system is definately *not* working. or it could mean 13.4 volts (rounded off) in which case your charging system *is* working, albeit on the low side.

This is what you need to do: Start up the quad, make sure the headlights are off, run the engine at a fast clip (3000 rpm), and simultaneously measure the battery voltage with your meter. It should read 13.5 volts to 14.5 volts. If it falls withing this range your charging system is working. Too high a voltage means you quad is overcharging. Too low a voltage means it isn't charging.

When you say your battery is dead, how are you determining this? What is the voltage right across your battery terminals when the starter is turning (or trying to turn)? If you jump the quad battery to your car does that make the starter turn at normal speed?

While working on this problem it is important to use your charger to keep the battery charged. Batteries left in a discharged state are ruined very quickly.

 

I'm sorry. I have 3 atvs and 2 of them I'm working on. The latest one wasn't staying charged and they guy I bought it from said he had the same problem. Well THAT one was the bad battery. It's taken care of. The one I'm having the big problem with has a good battery. It ran fine when I got it. Charged and everything. Wasn't long before that changed. The battery kept dieing. It was getting low to 12v going to the battery. I changed the regulator and measured 13.6 -14 something. Now it's back to the low voltage again. I can jump the battery using the car, it start right up and run like nothing's wrong but when I shut it down, I'd better have a booster near by or I'll be pushing it back home.

 

I'm assuming we are talking about a 150cc GY6 engine. If not then we'll have to back up and take a different path than this one:

I sounds like your new regulator got the charging system working for while then it quit. It may be intermittent or your second regulator just may have been defective and suffered an early demise.

Get your quad started and do the 3000 rpm battery voltage test with the headlights off. If it reads low then kill the engine and disconnect the regulator connector. Measure the battery charge stator winding resistance with your meter by measuring the resistance between the yellow and white wires in the wiring harness connector (sometimes it is two yellow wires). It should read 1 to 2 ohms.

Turn on your handlebar kill switch so the quad won't start. Switch your meter over to read AC volts. Measure the AC voltage on the same two wires in the wiring harness (regulator is still disconnected) while cranking the engine at normal cranking speed (jump the battery if it isn't charged). You should read about 9.5 volts AC while cranking.

If you have the right resistance for the battery charge winding and your AC voltage measurements at cranking speeds is OK then you have another bad regulator. It can happen.

If you have low AC voltage from the battery charge winding then we need to look further at the stator.