testing a car batteries terminals with a DMM with continuity setting- beeping!

Hi Doey,

Do you have a big problem? Well yes, I think you do.
I am not trying to be offensive but with great sincerity I would say that the big problem is your lack of understanding and experience of electrical matters and the use of DMM's and testing techniques.

Although it may appear simple and there are people who will tell you that is is simple, testing and properly understanding the results can be fairly complex. It is easy to arrive at false conclusions.

For a start, it is inappropriate to be trying to do "continuity" tests whilst the battery, or any other voltage source is connected to the circuit. Secondly, a DMM continuity test may not correctly indicate that some current may flow when there is a 12v source applied.

If you wish to determine if current is "leaking" from your battery to the cars circuits then the appropriate method is to set the DMM to "Amps or milliamps", disconnect the wiring from the battery terminal post and connect the DMM between the battery terminal and the wiring. Any current "leakage" will then be indicated on the DMM. Finding just which circuit or device that is consuming that current is another matter but generally can be determined by progressively disconnecting sections until the current indication ceases. Note that some few milliamps current drain is normal due to such things as ECU, radio, security etc.

Doey,

Very risky using the meter's continuity tester when there is a battery connected - too easy to let all the smoke out of it! This also extends to gear that may have a charged capacitor, as the capacitor may store suficient charge to do damage.

First, provided there is no battery or other source of charge in the circuit, it shouldn't matter which way round you connect a continuity tester. If there is a diode involved, measuring continuity can be misleading. (A diode conducts in only one direction, so will give diferent answers depending on which way round you connect to it. They also have a significant voltage drop, so, depending on the meter, may appear open circuit when in fact they will conduct at voltages higher than the meter is using - can be very confusing.)

I suspect that your meter has died, but if it's still working, I'd proceed as follows: You have quite a bit of stuff connected to the battery and my approach would be to fully charge the battery, then disconnect individual bits to decide where your discharge path is.

You could insert your multimeter in series with one aux battery terminal and measure the current flowing from the battery, BUT, there will probably be smoothing capacitors in both your chargers, and the inrush current when you make the connection will very likely blow the fuse in the meter. My preference would be to insert a low value resistor (less than an ohm) between a battery terminal and all connections, then measure the voltage across that resistor. Using ohms law (volts/resistance= amps) will allow you to safely measure current flow. (Ideally, a 1/1000 or 1/100 ohm resistor so you get a direct readout in amps when measuring millivolts.) Now connect and disconnect every suspect item until you find the offender. My bet is on the 240V charger that probably has an internal blead resistor to discharge it's output capacitor.

Why does the contnuity checker's beep change? Dunno, but probably covered in paragraph1!

"My second battery wasnt holding charge so i started to look over the system, got the multimeter out and checked for voltage, checked the isolator for continuity and switching etc. I came accross that there seemed to be continuity between the + and - points but only when the + leads were touching the - points on the car (earth etc) but the beep sounded different, not as pronounced. no matter where i checked. I thought- ah ha..... i have a short. I completely isolated the aux battery, regulator and charger and tested it again at the isolator- still continuity????" Not sure just what you were measuring and just where, but by now your meter has probably died - I think you checked for contuity directly across a battery which would be instant death to some at least of its functions.

"I disconnected the isolator and checked directly at the main battery (still connected to the vehicles wiring etc) and there was still continuity??? i started the engine and it stopped. turned the engine off and it started again????" As above.

"Is it normal to have some continuity between + and - ? or at least some low resistance or similar? enough to triggered the multimeter to indicate a circuit?" As above.

John

hi
thanks for your replies.

after reading back through my OP i realise it sounded confusing. my apologies. You guys did well to decipher it.

I understand all that you have said.

cheers

In truth, for some time I have found my cranking battery falling-off in charge when not being used. So I am now about to do just what I advised above..... connect a milliammeter and see if there is a draining load. If not then I have a self-discharging battery..... oh woe!