How to find if the battery or charger is faulty?

Well the double insulated bit won't help at all and whatever short circuit protection there is, let's just say it probably isn't NASA quality. :-)

Yeah but the something doesn't have to be charging.

If you have a multimeter, measure voltage across the battery while charging, should be at least 13.8V. Or if you know how to use it to measure current, check for charging current into the battery (make sure you use suitable high amp range, 10A or whatever).

If not, get a 12V rated sidelight bulb or similar and connect it across the battery terminals so it illuminates (use jump leads or whatever if necessary but be careful not to short). If the charger is working you should see a small but appreciable increase in brightness when you connect the charger, and drop in brightness when you disconnect it.

I checked with a multimeter and there is 11.7V across the terminals while charging. When I take away the leads the voltage is still 11.7V across the battery on it's own. I'm not sure if I measured the current correctly as you seem to imply that there is more to it than chacking the voltage but I saw a '10A' seeting on the multimeter dial so I flicked to it and placed the leads across the terminals again(with the charger attached) and I get 0.00. Is this the right way to measure the current? If it is then does it sound like that the charger broke when I shorted it's leads?

Unlikely to work but worth a shot: unplug the charger, give it a minute, plug it back in, try again, see how the volts looks this time.

Well you just have to connect it in series with the current you're charging, is all (so it sits between the charger lead and the terminal that the lead was previously connected to, so the current flows through the meter), and with the meter set to the appropriate current measurement range (10A in this case), and with the multimeter leads plugged into the correct holes in the meter (10A and Common I would imagine).

No. Not at all. See above about putting meter in series with the current so it flows through it. If you had the multimeter plugs in the right holes for current measurement, this would have resulted in shorting the battery through the meter and very quickly blowing the 10A current range fuse. If it only ever measured 0.00A then this probably didn't happen, unless the fuse blew instantaneously or was already blown. More than likely you didn't have the leads in the right holes.

Quite likely.

It's "its" by the way :-)

The charger isn't, then.

snipped-for-privacy@.remove.ghosh.co.uk (Rob Beattie) wrote in news:4565dd38.34705640 @news.cable.ntlworld.com:

Sounds like you blew the charger. Check to see if it has a fuse anywhere you can replace, the one I just bought from Halfords does.

Almost certainly by a fuse.

RTFM or go looking for that fuse.

DG

Well I managed to get hold of an old battery(around 10 years old) that my brother had lying around and when I connected it to the charger it was showing 75% instantly. I'm going to see if it charges tommorrow but I am a bit puzzled as the voltage across it is only 8.5V both connected and unconnected to the charger. Also I had a go at measuring the current again and still get 0 or rather a reading that is flickering from 0.01A to 0.03A but no larger. I should be getting more when on fast charge surely? This current(or lack of) was displayed by both batteries and I used the series method you suggested with the meter put between one of the terminals and charger leads. You were also right about me not plugging the multimeter leads into the right holes but I suppose that was a blessing in disguise as it stopped the meter from blowing when I tried to measure directly across the terminals. In light of these new developments what do you reckon is going on now?

Your chargers blown it's fuse.

If you set the multimeter to *any* current range and then connected *across* the battery, you now have a non-working multimeter in addition to a non-working charger. If it's a decent meter, you may just have blown an internal 10A fuse. (Possible as it's showing 0.00.) If it's not, you've fried it!

To measure current, the meter needs to be connected in series with the load.

As others have said, if there is no change in the *voltage* across the battery terminals with the charger on or off, there is no charging taking place.

With the greatest of respect, I don't see a great future for you as an auto electrician :-)

Chris

Well that indicates that your charger isn't charging (which we've established) and also that that 10 year old battery is long since shagged if it's showing 8.7V when off-load. It'll have lost all its charge and destroyed itself internally many years since.

Yes, several amps at least.

This current(or

Try connecting a bulb across the (newer) battery so it illuminates. Then put the multimeter in series with the bulb and check that a) the bulb lights still and b) the multimeter reads about one-twelfth of whatever the rated wattage of the bulb is. This confirms you are using your meter to measure current correctly and the meter is working and no blown fuses.

Your charger is still dead. As others have said, look for a fuse in it (never thought of that, dur).

(Meaning that attempting to charge it isn't a representative test of anything useful.)

The only way to check if the charger is functioning is to connect the multimeter in series (in line) with the battery. If the connections to the charger are shorted together the protective fuse has blown if not and the connection has been made for a while then 1 of the four diodes on the bridge circuit has blown but this is usually associated with a noticable bang. Always set the multimeter onto its range before connecting . You can check the 10A circuit using a bulb and battery as earlier described.

I'm not sure to whom you are replying as you have left nothing of the post in to give us a clue, but basically what you have posted is twaddle.

Chris

Not so. It can't be charging if it's not producing volts higher than the battery off charge.

On cheapo chargers, the fuse is normally a car "blade" type, you can usually see the arse-end of it sticking out of the bottom. It's quite difficult to spot...

Just giving an update. It's all sorted now. I found the fuse sticking out of the underside of the unit but that was only because there was a spare in the charger's box and I recognised the bottom of it. I used the meter to confirm that the fuse was indeed blown so switched the spare in. It is now charging so thanks to all that helped.

me neither!! But I have changed the fuse and now the charger is working at least.