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How do you check the alternator is ok ??

2K views 8 replies 6 participants last post by  Mojoinco 
#1 ·
Hi,

My battery (1year old) is going flat all the time.

How do I check if the alternator is working ok ??

Also my engine management light comes on quite a bit when I'm riding. Usually when I'm accelerating. It goes back off again after a few seconds.

It's a Tiger 900 ('99).

Look forward to your replies, many thanks in advance.

Graeme.
 
#2 ·
Very easy way is park bike in front of garage doors at night and let the bike idle then rev it, if lights go brighter it should be charging. Or if you can borrow a multi meter it should read about 13.8 volts across the battery with the engine reving a bit 2K+.

However if the battery is knackered it can draw so much current the alternator cant cope and will show low voltage. However it should still increase from the idle votage.

My bet is battery.

But if you get a new battery always always trickle charge it before fitting. Once you put the acid in, a battery it will have enough charge to start the bike. However it will draw so much charge that it can damage the plates inside the battery and it will fail in about 18 months. This is why dealers replace so many batteries under warranty. Becasue they cant be arsed to charge them first.
 
#3 ·
In addition to what Nobby's said...

Any sign the battery's been fired at all, any seeapge of acid or corrosion on it ?

I've had two flat battery problems ever :-

1 - flat battery, bike just stopped. All seemed well but RAC guy came along, performed a quarter turn on the screw holding the connector to the terminal and problem solved. He said ot wasn't uncommon even when the connection looks tight for it not to be good enough to keep charging.

2 - fried regulator/rectifier. Uusual story, battery goes flat so you buy another this works for a while then starts to fail. how quickly that happens varies, though cold weather tends to administer the coup de grace. My VFR rectifier went but was only failing when it got hot so short runs seemed to charge the battery, it was taking it out for longer runs trying to get a decent charge that was cooking it.

If you can charge the battery with an Optimiser or equivalent so that it show fully charged, l;eave it overnight and if its lost charge it's goosed. If it holds charge though and then goes flat in the bike, it's your charging circuit.

But the glowing lights when rev'd will tell you if that's working ok.
 
#5 ·
Hi Graeme,

As an addition to that, if your battery wasn't a problem before, it's likely to be now.

What a lot of people don't appreciate is that the internal structure of a standard automotive battery is designed to deliver maximum starting power, but the downside of this is that the battery does not tolerate being used cyclically (or flattened). When you flatten a starter battery completely, a certain amount of irreparable internal damage is done; how much depends on the degree to which it is sulphated, and the length of time it is left in that state.

After several complete discharge cycles, you should consider the battery as junk - unless you're prepared to be stranded somewhere on a cold night :(

[ This message was edited by: tcowjww on 2006-11-03 03:24 ]
 
#6 ·
Yep, he's right.

An optimiser type charger can recover a battery to some extent and the better ones will tell you if it's completely goosed but if you've got one that won't take a full charge, however well it holds it, it'll let you down sooner or later.

Best pay that £30 up front.
 
#8 ·
I don't know where you can get a decent battery for that. Mine cost me £65 - although I was in a bit of a rush.
If you want a good battery cheap dont go to a Bike shop but look for a Trade Motor Facters that usually sell car stuff and ask them. I got a battery for my Blackbird for under £40 that way.

I agree with FifeTiger that loose battery conecters is very common.
 
#9 ·
Don't overlook cleaning the terminals. My dear departed gramps always said that most batterys weren't bad, just dirty. And more often than right he embarrassed me to remember it. The terminals (usually the negative is worst) oxidize (yes, rust). They will have a dark color or even black looking crust on them. Use a small wire brush, until they are shiney. Then coat it all with a layer of vaseline (petroleum jelly), grease, or paint (auto parts stores sell a spray can of lacquer, usually a red color in the USA).
 
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