Multimeter

Read up everything here:

Mrcheerful

Close. But not foolproof.

Like anything else in life, it's a doddle if you know what you're doing.

Just a basic £5-£7 multimeter will do you.

Basic tests:

- put the multimeter on the right range (20V range is fine) and probe plug-ins for measuring volts

- get the car started and fast idling, put the probes on battery + and -, check the voltage across the battery, should be at least 13.8V otherwise the alternator isn't charging the battery.

- put on the main beam and the rear windscreen demist, should still be 13.8V or above the alternator isn't capable of supplying the load and still keeping the battery charged

- switch off the engine and all electrics, make sure there's no courtesy light on or anything

- switch meter range and probes plug-ins to measure current (amps). 100mA range or something should be fine. Be careful because the meter now forms a short circuit between the probe tips

- undo one of the battery terminals (make sure you've got your radio code and etc. etc.). Connect the meter probes between the battery terminal and the connector you took off. Meter shouldn't read more than a few tens of mA. If it reads significantly more, something on the car is draining the battery.

- if it passes both the above tests then the battery is both being charged effectively and not being drained unduly and therefore is 99% certain to be knackered.

If you want to test the battery's ability to crank the car, measure the volts across the battery + and - while someone cranks the engine, shouldn't drop lower than about 6-8V.

or even "...should still be 13.8V or above *otherwise* the alternator isn't capable..."

Meaning that if you have a starting problem and the car passes the above tests, then your problem is almost certainly a dud battery.

If it gets down to 6V then it probably won't start.

True, any battery dropping that low is pretty moribund...unless the problem is that the starter's having to work too hard because something's too stiff.

Thanks Mrcheerful going to give it a read now.

cheers this has been a quick reference guide just about to read the FAQ from mrcheerfuls post

Is this the sort of multimeter I would need ?

Measures temperature to :) I could stick it in my wifes ears and know right before she goes mad disappear :)

Very concise post Vim; might I just add that checking the battery voltage after the car has stood all night and before attempting to start it will give a good indication of its health. Anything above 12.6V is OKish, below

12.4V either that battery is not holding its charge or a circuit is draining it.

Chris

Is it possible that should you have a lot of electrical load e.g headlights, CD player, sat nav, that the drain would be sufficient such that the battery will not charge, or even discharge while driving?

Not likely unless there are modifications

I would just add that be careful you don't fry the meter doing this test. Depending on the car but in my experience when a connection is first made the electronics (central locking, ECU, alarm etc) try to grab a lot of current when a connection is first made before settling down to a few mA's. What I do is first bridge the battery terminal & post with a wire to allow the surge of current, then connect the DMM and remove the wire.

No modifications, unless you count the sat nav, which is just plugged into the cig lighter.

No that wouldn't do it.

Looks ok but might be more than you need.

;-)

Useful for balancing central heating rads and checking oven temperatures.

I've not come across a modern car like this - although some older ones couldn't maintain all their accessories at once.

Only likely thing to upset a modern car is a very high power sound system.

Okay doke.

*Goes off to find a time when I can do without my car so Ford can take a look*

Does look feature packed for what I need but argos is near and I have a few extra quid so might come in handy for some other complex projects down the line.