SOHC.co.uk Forums > CB750
Charging troubles
Bryanj:
Not wanting to be awkward but many years back i had a 500 with a standard car H4 and halogen bulb and that charged OK, admittedly i was younger and a raving nutter so the engine was rarely below 5,000 rpm anywhere BUT the 500 has a smaller output and it coped albeit just, and i never had to externally charge the battery
If all the connections are in good order and the parts OK it SHOULD charge over 4-5,000 rpm.
It really needs methodical checking with a voltmeter and if the OP can get one to use i will happily go through tests NOT in the manual to check it all out.
the-chauffeur:
So I haven't been able to do any running tests yet, although I have established a couple of things:
Battery immediately after charge - ignition off: ~13.2v
Same battery 6 hours later - ignition off: ~12.8v
Same - ignition on (all other circuits off): ~12.1v
Not sure whether that tells us anything, but after re-reading the chapter in Hondaman's book on the charging system, I went back and checked the ground wire loop that connects to the frame under the seat lock bracket. Turns out that there was minimal contact between the metal on the loop and the frame - I hadn't removed any of the powdercoat, so the only real contact point was where the loop touches the the fastener that holds the bracket to the frame.
I've corrected that now . . . and I think the idiot lights glowed brighter when I turned on the ignition. I'm guessing that lack of connectivity won't have helped the effectiveness of the electrical system . . .
More news as I get to run more tests.
SteveD CB500K0:
Those voltages look fine. All that proves though is that it is charged!
You need 14-14.5V at 3000(ish) revs to prove the charging system.
Sent from my iPhone using Tapatalk
the-chauffeur:
Quick update . . . not much to add 'cos I've spent the day pulling the back end off my ST1100.
Take it from me that it's a whole lot of work just to replace an o-ring that seals the alternator (one of the most complex jobs short of pulling the engine). Still, it's given me an excuse to get the swingarm re-powdercoated - it's the bike's 20th birthday this year, and fortunately I waxoyl'd the swingarm as soon as I got it (about 8 years back). At nearly 70,000 miles, there's some minor surface rust that'll clean off with beadblasting, before it's re-powdered and finally re-waxoyl. And then another 5 hours or so putting the whole lot back together, with new bearings and all.
Anyways, the main earth on the 750's fine - the engine has been out a couple of times, which has taken the powdercoat off the main earth join. Battery's held charge at around 12.6v overnight, so it looks like the battery's good despite its depletion when riding with the light on . . . which brings me on to . . .
. . . the advice I'm getting that I'm probably not riding right to keep the battery charged. From what I've read, most folks who mix modern and older bike find the biggest headache is adjusting riding style to cope with braking changes, but for me it's the opposite; I'm uncomfortable keeping engine revs high. Maybe it's something to do with my style of riding or choice of bikes (particularly the ST) but I don't much find the need/opportunity to exceed 4k revs, and generally find that around town requires much less. I know there's nothing wrong with it, but adapting my riding to keep the revs up on the 750 really doesn't feel right (outside of motorway-type riding).
Bryanj:
If you don't want to keep the revs up you will have to go back to the standard Stanley headlamp with puny bulb mate and that needs 3,500 rpm to give the battery a charge as well!
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