Flat battery? Bike won't start.

My wee bike is sickly...

After a few hours of riding the other week, I decided (foolishly) to give the yellow demon a wash. I might have used a little too much water/overzealous hosing and when I tried to start her there was a little splutter and then... nothing. Wouldn't start, and after a while when I tried to start her there was just a little click.

So, rather shamefully, I called out the RAC. They couldn't find the initial fault (ar$e/elbow and all that), but managed to jump start it, I went for a little spin, and then thought all was ok. Got to uni the next day, and back, and the day after... nothing.

I put a new battery in and she was fine for about a week and a half, then today I went to work (30 mins ride), on the way back she started fine, I pull up at the petrol station, put petrol in, then... NOTHING!!! Arrrrgh!

It clicked a little, but wouldn't start. In the end I got a little dude to jump start me, rode 20 minutes, got home. AND NOW SHE STARTS!

wtf is wrong with my bike?? Izzit the regulator rectifier? Have I broken yet another battery? Alternator? Is it the colour?

HALP!

xx

[jambo]

OK here we go.

First off: A battery simply holds the charge it's been given, provided nothing is draining from it. This sounds bloody obvious, but many people are told to fit new batteries because the old ones are flat. Just because it's empty doesn't mean it's duff. Take the battery out and put it on charge until it's nice and full. Now we have a known amount of charge in the battery making the tests useful, and easier.

A run of something like 10 miles is needed on average to put back in what you take out by starting the average bike, so if you bump start one, or jump start it go on a good long run. You are starting from nothing so make sure there's plenty in there before you need another start. Or put it on the Battery charger when you get home.

At this point it's well worth checking that:
1) The charging circuit is up to scratch
2) There is no drain on the battery when the bike's off.

You will need a multi meter for this. Plug the battery in, and test the DC Voltage across both terminals, you should get around 12.5V or there abouts. Start the bike and test again, you should now get about 14.5V. Get someone to Rev the engine, you should see the voltage stay steady and not increase with revs. If all of that looks OK then the charging circuit should be OK.


Switch the bike off. Now undo the -ve terminal, and switch the multimeter to measure current, in amps. Connect the terminals between the earth cable and the -ve battery terminal so that any current flowing from the battery to the black lead has to go through the multimeter. You should get a reading of almost 0, a few milliamps at most. If you get a significantly high number, current is draining from the battery, probably through chaffed wiring or similar.


Jambo