CB350K drains battery

[florence]

Does anyone know why the battery runs flat when the bike is left for a week?  I should point out that I haven't left anything switched on.  All electrical things seem to work normally but if I leave the bike even for a few days, I have to disconnect the battery.

Recently, I forgot about this problem, left the bike for a fortnight and now the battery won't hold charge at all.

[hairygit]

Battery is just old or knackered? If the battery is running down when not using the bike, disconnect the positive (+) lead and put an ammeter across from the lead to the terminal and see if there is any electrical drain on the bike with the ignition off.

[SteveD CB500K0]

Caused by internal leakage and is the sign of a battery that is not long for this world.

Sorry.



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[florence]

the battery is brand new but I seem to have killed it.

Good idea about meter from terminal.  I will try.

[AshimotoK0]

Leaky selenium rectifier  or faulty voltage regulator mounted under battery box. Eliminate regulator by temporarily  totally disconnecting ..it's basically an electronic 'crowbar' dumping excess current to ground .... like a more sophisticated Zener diode as fitted to old Triumph twins.......of course it could also be a duff battery. If it proves to be a faulty rectifier then replace with the later silicon type as fitted to later models or an aftermarket one.

This one looks a bit grotty but is the silicon later type (genuine Honda). DK are bound to have one too.

http://www.ebay.co.uk/itm/Honda-CB-350-K-1973-Used-Regulator-Rectifier-Unit-/370759516187?hash=item5652fd401b:g:Bf4AAMXQVgBRHPe4

Or you could graft in this or similar

http://www.ebay.co.uk/itm/BRIDGE-RECTIFIERS-RS-262-315-25AMPS-200VOLTS-/322597610746?hash=item4b1c50e4fa:g:zHUAAOSw03lY6j8F

[mike the bike]

I'd go along with the dodgy rectifier theory, check by disconnecting it.   Just out of interest,  how many phases has the alternator got. 
If it's 3, then you need 2 rectifiers.

[AshimotoK0]

I'd go along with the dodgy rectifier theory, check by disconnecting it.   Just out of interest,  how many phases has the alternator got. 
If it's 3, then you need 2 rectifiers.

Like most 60's '70's Honda Twins it's only single phase system with a night/day tapping on the alternator windings.

If you find it's the 3-wire voltage regulator that you suspect is at fault,  I can electrically test it for you to check it's operation if you wish. I also have a spare if needed. They are made by Hitachi. They are a much more precise 'current dump' than bikes that rely on the battery alone to provide regulation or a relatively imprecise single high power Zener diode (mounted on finned heatsink thingy between fork stanchions on '60's/70's Triumphs  . The Hitachi regulator is quite a neat design really, especially for the late 1960's when it was introduced) but epoxy encapsulated so not really fixable if found to be duff.

[florence]

I'll have a look at the rectifier today.  The bike has been off the road for twenty two years but I seem to remember it used to do this before but when it was in regular use it didn't matter as it would never stand long enough to be a problem. 

Presumably, leaving a battery discharged for two weeks is very damaging?  It was brand new but it won't hold charge any more.

[hairygit]

Try getting a replacement battery under warranty (if they argue tell them you consider it to not be of merchantable quality, therefore you will consult trading standards) as it should not die so quickly.

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[AshimotoK0]

Try getting a replacement battery under warranty (if they argue tell them you consider it to not be of merchantable quality, therefore you will consult trading standards) as it should not die so quickly.

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+1 ... you will find that some cheapo batteries will suffer from sulphation and won't take charge after deep discharge and flat for a couple of weeks. A Yuasa one in my daughter's Micra was flat for well over that period but charged up fine  ... they will never know it's been in deep discharge anyway as the the cases are no longer usually  transparent plastic. On the old ones (clear plastic walls)  you could see the white suphate deposits on the lead. If you do get a refund worth getting a Yuasa one if you can afford it.

[Moorey]

Before replacing/refunding they are within their rights to send it back to the manufacturer to see if it comes within the terms of warranty. A lot depends on who you bought it off. Batteries are terrible to try and claim back on. There are too many get outs for them. How its been discharged, how deep its been discharged, how its been charged. All will be in the terms and conditions of the warranty.
As said a lot depends on who you bought off.
Good luck.

[florence]

the battery is from Oregon Products, you know, the chainsaw and garden machinery people.  It's actually for a ride on lawn mower but same spec as for CB500.  I will take it in to the shop and see what they say.