One for the auto electricians, please

[kevinrbeech]

Hi Guys,
This is one for the electrical experts, not my Discovery either, but the bike.
For what it's worth the bike is a CB 500, that's a Honda for those not familiar.

Ok about 3 weeks ago the battery was getting progressively more flat, time to get a new one I thought. Bought new battery and all was fine..... for two weeks.

Put volt meter across terminals, 12, 13 and 14 volts plus, in fact after a few minutes it reached 18 volts. Took battery in and put on charge, charge light came on. After about 5 mins charge light went off, fully charged.

Put battery on bike next day and all was fine. Rode 20 miles to work with lights on, battery flat. After lots of messing about as above I decided to commit to a new rectifier/regulator, a silly little black box, for £131 (that's almost as bad as LR parts)

Fitted the part this morning, rode to work no problem. Started bike at work, all ok, rode 10 miles with the lights on and battery was flat again. Put battery on charge two minutes later fully charged light comes on.

Put volt meter across terminals again and volts remain at 12 - 14 constant, depending on revs.

So has the faulty regulator/rectifier "cooked" the battery by trying to pump 18 volts into it for two weeks.

Sorry this is a bike question but the theory is the same and I value the opinion of some of the techies on here far more than on the bike forums.
Cheers,
Kevin

[street_moto]

Hi Kevin,
basically, I'm pretty sure you've answered your own question, it's like a cascade effect when the regulator/rectifier goes, battery can fry, then the alternator, fuses and bulbs blowing etc. Console yourself that a battery is relatively cheap compared to the Reg/rec! Strangely enough I've just had to replace the Reg/rec on my NC30, Achilles heel of the NC30. That was £43 delivered from Germany off ebay, Honda item.
Out of curiosity, what charger are you using? A car charger will toast a bike battery after a while!
I use an Optimate 3SP, all singing, all dancing apparrently! However when I had my supermoto and the battery gave up (poor OE one) I bought the Optimate. and after a while of being on charge the Optimate said it was good to go, yet the battery wouldn't even light a bulb, let alone turn over a 660cc lump! Ended up buying a Red Top deep cycle battery for that, excellent quality if a tad on the expensive side!
Sorry for rambling on!
Basically, I'd buy a new battery!
Regards Dave

[street_moto]

Oh, forgot to mention, a worth while tip. Put some thermal compound/paste, something like arctic silver on the back of the rectifier to help with heat dispersion. Again, cheap enough on ebay.
Regards Dave.

[kevinrbeech]

Hi Dave,
Thanks for the reply. Yeah, battery is cheap, also the new rectifier has fins, unlike the old one. I'm encouraged by the fact that this one does not allow the 18volts through.
One other thing though, for the last 9 months or so the headlamps have not been at full strength all of the time, I first suspected a bad earth but now it seems that this is probably linked to the charging problem. I just don't want it to be the alternator, they're about £400.
That said, when on tick-over the lights are dim, they brighten as the revs increase around 1500-2000, this would suggest the circuit is charging, but as soon as you turn the engine off, the battery will not turn it over again, put it on the 6amp charger for the night and it will start the bike no problem to go to work, then 8 hours later to come home. Turn the lights on and there is nothing left even though it is giving 13-14 volts.
Kevin

[street_moto]

Hello again Kev, does sound as though the battery has given up the ghost.
The replacement Reg/rec I bought also has fins as opposed to the old one.
You can test your alternator if you have a Haynes manual for it and a multimeter. Not difficult.
Basically there are three wires going to the alternator all yellow on my NC30, you test each one to earth, should be no circuit and then between each of the yellows, should be a reading of between 0.1 to 1.0 Ohms on mine anyway.
Regards Dave.

[Lacy]

Might be worth checking to see if there is a current drain on the bike. Disconnect the positive lead from the battery and connect an ammeter beween the battery post and the lead.....start on the highest current setting and switch down through the ranges until you see a reading (if any). On a bike with no alarm I would expect to see little or no current drain at all.

Other than that, make sure your main connections are clean and tight especially the main earth lead from the battery.