SOHC.co.uk Forums > CB750

Is the battery to blame?

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Menno:
There is a very easy way to check whats wrong.
And it is safe as well....

Start your bike.
Let it idle.

Disconnect your battery from the bike while idling.

If the bike dies immediately when you pull the cable it is likely to be your altenator or regulator.
If the bike keeps running it is defenately not your altenator or regulator and you could say it comes down to your battery.

check:
https://youtu.be/xF6WUvqC1Xc

Tomb:
Do you have heated grips?

14V would be better than 13.5v when revving to 2500, so charging is a little down, and IF running extras like heated grips could just overwhelm the charging,

If your bike starts Ok when you get it out for the ride its sounds like your battery is adequate, then runs Ok until ticking over at the lights, I'd be looking at charging first. And rec/regs are a known week point on the CBRs, I've changed a few on CBRs. They can be had for as little as £6 on ebay from China, if you buy them buy two and mount them on a BIG heatsink and side by side so when the first one fails you can simply swap the connector to the next. Or buy 1 quality replacement.

MarkCR750:
Thanks for the replies, apologies the results I previously posted were misleading, I got some better results today, working in the light taking my time etc, so 14.7v at 3.2k revs 12.5v at 1.2k lights off, --------------11.75v at 1.2k, 11.8v at 3.2k lights on. So it looks as though the alternator is good but when the lights are on they taking a lot of voltage!, could this be a battery fault ? (Electrics as you can tell are not my thing).
I.e it appears to charge fine until the lights are switched on.

Bryanj:
not normally, alternator or regulator fault

kevski:
If you have checked all of your connections and earths, with this bike at 3.2krevs with everything on you should be getting a full 14v back to the battery, 14.7 with nothing on is getting on for 15v and that shouldn't be happening, this will kill the battery, what would help is a battery that is known to be good then all connections checked with a meter for resistance, if this all checks out, check the voltage coming from alternator before it gets to the reg/rec, if that checks out ok move on to the reg/rec, from what you have already posted i would be looking at the charging system.

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