Alternator and Battery test with multimeter

battery do not need to be disconected

do not use the amps in this way, use 20volts DC not 20amps

Err, no. Wiring the meter in series with the battery is used to check the current being drawn - and you need to be careful in doing this or you'll blow up the meter.

To measure voltage you don't disconnect anything on the car. Make sure the meter leads are in the correct sockets and set the meter to the 20 *volt* range. Then simply meter red to battery positive and black to negative. What you're then looking for is a difference of about 2 volts between the engine off and running voltages. With a maximum of about 14.4v with it running.

I will say it's a bit of a worry you don't seem to know the difference between AC and DC, though. ;-)

Thanks for that. I have no idea about hitngs electric I've spent most of the afternoon reading about multi meters! I'm absolutely diabolical when it comes to electrickery thingies.

.....better go an learn what the differnce of ac/dc is. From memory it stands for alternating current and direct current f*ck knows what it does :-s ... still best to say I don;t know and get help and learn about it :) before frying anything

To add to that i thought ac dc were a rock band :-P

So if I set it correct to 20 v dc I won't damage my meter right ? (not to sure what you mean't there)

on 18/02/2007, tishtash supposed :

No, better/safer to disconnect the negative terminal first and always reconnect this last. To check the current flow, you only need to disconnect one terminal, which obviously from the forgoing would be the negative. Putting the meter on the amps range in series with this on the DC range, you need to be careful to make sure you do not exceed the meters rating (10amps did you say?) - so don't turn the ignition on or headlights etc. or the meter will be damaged.

No, it needs to be on the DC volts range and in parallel with the battery - or red connected to the +ve, black to the -ve of the battery.

13.4v at 2-3,000 rpm would probably indicate a problem. Expect 13.8 to 14.4v on a light loading of the system.

Harry Bloomfield expressed precisely :

I have just reread your above para and to test the voltage of battery and or alternator you do not need to disconnect anything - just set it to 20v DC and put the probe tips onto the battery, +ve and -ve.

The red goes to the thinner lead which should be disconnected from the battery + and the black to the battery + although if it's a digital meter it won't matter much which way around the meter is connected as you'll just get a '-' sign on the meter (set it to DC). Indeed the '-' sign will come and go as you go from charge to discharge. If it's an analogue meter the needle will swing hard left on discharge and right on charge.

IMPORTANT NOTE!:- DO NOT PUT THE METER IN SERIES WITH THE THICK BATTERY LEAD to the + terminal, just the thinner lead. (The meter won't pass the current and will burn out in a dazzling display of smoke and flames!!!)

It's just as easy to put the meter across the battery with the engine off, (Set it for 20+ VDC usually 25V) note the reading (probably 11-12V) then start her up and so long as the Volts go up a bit (anything up to

15V) the charging system is probably fine. Alternators usually work or don't so I wouldn't get bogged down with precise charging currents if your electronic skills are limited. I'd do it this way.

If the ignition warning light goes out when the engine runs, the system is probably charging.

Hope that helps.

You're usually safe enough on voltage measurements. The problem comes with current measurement if you either overload the meter or get the connections wrong - at best it can blow a fuse, at worst, the meter.

Sorry to be thick here I really don't understand what you mean.... What does putting the meter in series with the thick batter lead mean ?

Thanks all for the help and info, I think I have a grasp of what to do. That last bit is basically all I need to do. So to recap just set meter to 20/25 volts dc engine off red probe on postive battery terminal and black on negative (does it matter which probe goes on first?) and take reading ? )while here I was just wondering does it matter if I touch the battery terminal or the clamp>)

alternater test with engine on and lights on, demiter etc do the same thing and not reading ?

Is that it basically in morons terms ? :) I can be a bit thick as you can see with such things!

thanks

Just set the meter to 25V DC and put it across the battery then start it up. If the voltage goes up you are ok.

If the red ignition light goes out anyway there is nothing wrong with the alternator and it's probably simply a knackered battery.

tishtash expressed precisely :

Which ever way is the easier for you.

Any metal part which has metal to metal contact with the battery terminal will be fine.

Why not start with an ordinary torch battery for some basic practise with the instrument first?

In theory, it doesn't matter at all, but I have seen a poor battery clamp contact drop several volts between the clamp and the terminal post, so make sure the clamp is clean and tight.

"tishtash" wrote in message news: snipped-for-privacy@bt.com...

If this comment has been already said then please forgive me as my newsserver has been limping along since maintenance on the 16th / 17th.

Tishtash do not consider disconnecting the battery at all to run any tests, you stand to do more damage to the diode / rectifier pack than you intend to save by testing it yourself given the level of uncertainty you seem to have. Putting a standard multimeter onto an Amps range for example then popping the test leads onto battery terminals will just induce a massive short-circuit. Putting the meter onto the dc voltage range of 20v and ensuring you have the test leads plugged into the common and voltage sockets on the multimeter (and not the amps sockets) will ensure the meter is protected through its own internal resistance etc. Method advised:- a) Check voltage across +ve and -ve terminals of battery with the multimeter set to 20v dc. With the meter connected and still reading dc volts you can crank the car on the starter and note the voltage, it will drop to approx 10v if the battery is ok but will be lower (8v) if on its way out and not able to supply the required current. Although this value will vary somewhat dependent upon car / engine size and type, battery capacity, temperature etc. b) Once car starts -do not rev but let car tick-over- and note voltage. It should rise slowly towards 12.5v, then if you bring the engine speed up to a steady 2000rpm the voltage displayed should increase to about 14v quite quickly. c) With the engine ticking over again turn on main beams, heated rear window, fan and voltage will drop again. Rev engine to 2000 rpm and if the alternator is outputting anything worthwhile the voltage measured at the battery will rise to approx 14v. If it does not, turn off the loads one at a time and note the result. At the very least an average car should maintain more than 13v at 2000rpm with the usual winter night time driving accessories turned on. e.g. lights, fan.

Hi Gio,

Thank you for the concise post, I guess you could see me struggling with it :) I'm thankful for the information and nudge in the right direction. Only I could over complicate something relatively simple.

I've printed that out to use as a reference and some of the other posts in this thread.

Thanks again all for taking the time. Once I get my results down on paper I shall post them, just if anyones interested as it been a bit of a learning day for me with the help you all you kind folks helping me.

Definitely will give the meter a try on out fuses (contuinuity), lights, batteries and get familiar with the handling and function of it.

Thanks for the idea harry.

I've just had an idea (!!!)

Just plug your multimeter into the cigar lighter. No need to open the bonnet at all! You get to work the accelerator as well which you might have trouble doing under the bonnet.

You are right especially with cars like ours with a fly-by wire- setup and no throttle cable, providing you do not short the connections of course ;-). An easy / quick way to get some idea of the charging circuit condition is to point the car headlights at a wall at night, put on all the electrical items then observe the brightness of the lights. Rev the engine and the lights should brighten to their full brilliance if all is reasonable. A similar test with the lights on when starting the car will again show a dimmed headlight beam but one that enables you to gauge battery condition / capacity with practice :-)

Hope you manage the job ok. To post the results is a good idea, then we all learn in one way or the other. Take care.