Checking for drain on 12 volt battery; can I use a 10 ohm 10 watt resistor instead of a 1 ohm 10 watt resistor?

If the drain is anywhere near an Amp, a 10 Ohm resistor is too high - with a one Amp drain, there will be a 10V drop across the 10 Ohm resistor, but only 1V across the 1 Ohm. The largest drain you can comfortably measure with a 10 Ohm would be about 100mA - which would be a 1V drop... but that's not much of a drain on the battery.

If you're looking for a parasitic drain that is making the battery go dead within a few days, it's going to be on the order of an Amp or more, so the 1 Ohm is a better choice.

Why not just use the Amp meter setting? Most meters will allow you to measure up to 10A... so don't turn anything on - just connect one meter lead to the negative battery terminal, other lead to the negative cable, set meter to 10A DC and look for the drain with all off. This should allow you to measure any drain between 10A and 10mA or so.

Depending on the age of the vehicle you will always have some drain on the battery. You have the ecu, alarm system on some. radio memory and whatever toys that may be in the vehicle. If you are looking for a battery drain, try disconnecting the battery overnight and see if it still starts. Most batteries over 3 yrs tend to drop voltage in less than 10 hrs yet test fine when fully charged. That would be the fist step. Most sources of current draw are the alternator or starter. Depends on the vehicle. During the 90`s Lincoln`s used to catch fire in the steering column hours after they were shut off. You can also pull fuses on suspected circuits with your voltmeter in place until you see a change. Also remember that by disconnecting the battery you will have reset your computer in your vehicle and it may take several minutes for it to relearn

10 Watt Resistor

this is how to check THE CORRECT WAY disconnect the NEGATIVE hook up a 12 volt test light between the cable and terminal touch the cable to the NEG post for about 5 seconds to ex sight any relays that the car might have then separate the cable from the terminal KEEPING THE TEST LIGHT CONNECTED **IMPORTANT PART** if the light is on you have a draw . at that point you can use any meter to measure volts / millivolts or amps /milliamps HOOKED UP THE SAME AS THE TEST LIGHT JUST DO NOT DISCONNECT THE TEST LIGHT ONCE IT COMES ON or you will be reading other than the draw

I don't understand exactly what your trying to do.Battery drain can be checked by disconnecting your positive battery cable and connecting a multi meter between the battery and the cable.Set the meter on DC millivolts and it will read any current drain.

Edit opps Thunder is right i meant milliamps not volts

1

Andy is correct except for one mistake ... set the DVOM to milliAmps. Anything above 50mA is too much.

use a taillight bulb and solder soem wires to it thenn check each circuit