Cafe Racer Forum banner

1982 Suzuki gs750t wont charge while running.

2030 Views 24 Replies 7 Participants Last post by  crazypj
My 82 gs750 won't charge while running. I've been told it's the reg/rec, the battery, or the stator itself. I have a brand new li-Ion battery just installed, so it's not that. Reg/rec is also brand new, but it's possible. Best guess is the stator. Any thoughts?
1 - 7 of 25 Posts

This is what I could find for my bike. I don't know much about regulators.
To clarify: it wasn't charging while I had a Cycle Gear Megaboost in it. That one shorted out, so I upgraded to Li-ion, but have not run it yet. I'm still working on the bike, so I haven't ridden it again. I just went to @DesmoDog s post on the regulator, but it's an old thread. Do you know where I can get a modern regulator?
What does your shop manual say for checking the charging system? It's relatively easy to check the output to see if there is any, but a manual will cover it in specific terms. Do you have questions with what it's saying? If you don't have a shop manual for your specific bike, buy one before you spend any more money on charging systems.

When I googled info on regulators I came up with this link:

Does your battery have a built in BMS? If it doesn't, I wouldn't use it no matter what regulator you have. Fun fact - you can kill your lithium battery by putting too many volts into it, and you can kill it by discharging it too far. Yep, discharge it too far and it's game over, no recharging. Toss it and buy a new one. A built in BMS will typically protect against that and shut things down before the battery is damaged.

Did you get a lithium specific charger with your battery, or is the charger you're using safe to use with lithium batteries? A built in BMS also allows you to use some chargers that aren't lithium specific. Even with BMS though, a charger with an anti-sulfation cycle can harm the battery.

I'm a big fan of lithium iron batteries. I COMPLETELY understand why some people are not and would agree the best bet with vintage bikes is to check/optimize everything and then install an AGM battery. (I DETEST lead acid batteries, I don't care how cheap they are). That said I won't be running a lithium in either of my single cylinder projects. There comes a point they aren't worth the cost/hassle/risk of using.

Here is the aftermath of what can happen when you put a BMS protected battery into a 30 year old Ducati with no other safeguards and then roll the dice thinking it will all work. Spoiler alert - the bike said "Built in BMS? Bitch, please. Hold my grappa and watch THIS!"

And finally - if you must jump on the lithium bandwagon make sure you are buying a lithium IRON battery, and not a lithium ION battery. It's confusing, but there is a difference. Lithium iron batteries do not tend to burst into flames like lithium ion batteries have been known to do. I'm not sure but I think most motorcycle starting batteries are lithium iron. It gets confusing though, I once bought a less expensive brand and it was labeled iron on the box but ion in the documentation!
New setup. Lithium battery, Rick's electric lithium rated r/r, all the stator wires are now connected properly (they weren't before), and the stator makes 70 VAC stable @5000 rpm. The manual says the 80s model should make 80vac. Still not charging. Is 10vac difference indicative of a bad stator? The LED lights maintain a constant draw, which kills the battery. The other problem is that when the battery dies, the bike dies. At speed, while riding. That shouldn't be happening. What is mis connected to cause the battery to affect the motor?
I don't know much about the electrical, but I didn't have to change much to make the lights work. I just added a diode kit for the front turn signals. Also, I thought the coils ran off the signal generator, and the battery just powered lights and accessories.
I've been told by numerous people, that if you disconnect the battery, the bike will still run.
1 - 7 of 25 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.