Battery not charging XJ750 82

[XRKID]

Gidda after many of times recharging my battery I've decided enough is enough and wanna fix this problem. My xj is producing 14.7v @ 2000rpm like it says in the manual and i checked this across the battery and off the loom but the battery still keeps going dead. I don't know on to whether to buy no new reg/rec unit or could it be something else, cheers.

[tri boy]

Get hold of a small Hydrometer first.
Check the specific gravity of the battery about 2-3hrs after charging.(low acid level due to excessive topping up/"gassing").
Possibly the Batt cells have become sulphated/ damaged, and not holding a charge.( any grunge visible at the base of the cells?).Should appear whitish.
Current "draw" may also be a fault to consider.(elec system leaking current with the key off).
Also check wiring for obvious damage/wear.
Good luck.

[Paul in NZ]

Ditto the hydrometer... although its hard to find one small enough for a bike battery these days

What you could do is charge the battery - put it in the bike and check everything is OK. Disconnect the battery and leave it overnight - reconnect and check if its Ok or not. If it's OK the battery is prob OK and the system is draining the battery.

[surfer]

Sounds like your charging system is doing fine if it is kicking out 14.7v. Sounds as if your battery is not holding a charge.

Take the battery out and do a visual inspection, sometimes it is possible to see if one of the cells is damaged.

Are the fluid levels topped up? How long have you had the battery? Did you by chance top it up with anything else other than distilled water?

If you can't get your hands on a hydrometer take the battery to a bike shop and get them to check it for you. Most shops are pretty obliging. They should be able to tell you whether it is holding a charge or not.

Good luck

[XRKID]

yer battery is fine, holds charge no problem left it sitting in the bike for a week and could start it the next day and still had heaps of gusto left in it. i checked the resistance on the coil windings and the are double of what they are ment to be, could this be effecting the amperage that is charging the battery, as there is enough voltage to charge the battery maybe there is just not enough current( due to the high resistance in the windings) to push the voltage into the battery to charge it. cheers. P.S Is a new battery and shows no sign of sulfation.

[Trouss]

Pop an ammeter in line to see what your getting current flow wise. . . Refer to battery specs for minimum charging current?

It is generally surprisingly low, well lower than you would expect.
And you would expect a resonalbly high resistance on a low voltage alternator.

[Wired1]

I'm confused, when is it going dead? If it is holding a charge for a week are you saying it goes dead while you are riding it? To charge the battery you have to have more voltage across it than in it, this makes the current flow into the battery, so the 14.7 volts sound right as long as this is measured across the battery when the bike is running and the battery is connected up. So if it is losing charge then when sitting idle it is either a fault in the wiring or a faulty battery. As the battery is new I would check out the wiring. If it is going flat when you are riding it then it must be faulty wiring. In this case you are draining more charge than the battery and alternator can produce combined, so that's a fairly sizeable fault.

[XRKID]

I'm confused, when is it going dead? If it is holding a charge for a week are you saying it goes dead while you are riding it? To charge the battery you have to have more voltage across it than in it, this makes the current flow into the battery, so the 14.7 volts sound right as long as this is measured across the battery when the bike is running and the battery is connected up. So if it is losing charge then when sitting idle it is either a fault in the wiring or a faulty battery. As the battery is new I would check out the wiring. If it is going flat when you are riding it then it must be faulty wiring. In this case you are draining more charge than the battery and alternator can produce combined, so that's a fairly sizeable fault.

I think it maybe the battery, cause i was stumped when it has 14.7 volts running through it and when i rode round for several hours with lights on and all, upon returning i tried starting it up again and you could hear how weak the battery was due to the startor noise. But then again when i charge it with my 12v battery charger is holds charge fine. and i have kept it in the bike for a week(fully charged) and its held its charge fine. So i dunno. It's Got me.

[tri boy]

I think it maybe the battery, cause i was stumped when it has 14.7 volts running through it and when i rode round for several hours with lights on and all, upon returning i tried starting it up again and you could hear how weak the battery was due to the startor noise.

This has me suspecting a charging fault, because the alternator windings are what are supplying power for the lighting system more or less directly when they are on. The battery is primarily a starting power supply system, and a circuit storage system. If the windings are struggling to keep up supply for what ever reason, the battery will be run low of stored energy.
Check that the wiring to and from the regulator is good, and that you have voltage to it with the key on.
This sounds like a bit of a curly fault, and some input from a knowledgeable local may save you alot of frustration.

[Wired1]

OK, that explains it. The battery will charge up and hold a charge so the battery is OK may be too small for the job. When you are riding around with the lights on you are using more energy from the battery than is being replaced by the alternator. You could also check that your rectifier is 100% as a lot of bikes use a three phase alternator and three phase recitifier. If the rectifier is partly gone it will still appear to be charging as measured by the 14.7 volts but you will only be getting a third of the current or energy from the alternator. If your bike is approaching 20 years old this is most likely the case. So (1) check that your battery amphour rating is the same as your bike specs and (2) test the rectifier - for which you need the workshop manual and a multimeter - or take it to an autoelectrician and they will do it.

[XRKID]

was talking to a few local bikeys and came up with the same type of answer. So have came to two conclusions. 1) replace rec/reg unit 2) check for massive power drain(unlikely). Did a check on the rec/reg unit and came up with all diods are blowen. (or mulitmeter is blowen(very unlikey as new)and wasn't wired up wrong )
Cheers for the help.

[FROSTY:Me]

EXACTLY what battery are you running?
Should be a CB12 La2
I agree with the above advice
Something not mentioned is --Have you checked that the starter motor brushes arent nearly worn out?