Checking for battery draw with DVM

Hattrick · Dec 19, 2014

I have a 1989 Case/IH 235 tractor that seems to draw the battery down if I leave the battery connected. I only have a digital multimeter. If I measure the voltage between the ground cable and the negative post of the battery with the key off it shows about 1 volt. I checked for amps and the draw was minimal in the mV range. I think I have read here before that it is hard to check the draw correctly dith a DVM. Can anyone shed some light on this?

Thanks

gab · Dec 19, 2014

Change your meter to milli amps and read between neg. post and cable, less than about 35 ma reading I would think would be good.

Bob M · Dec 19, 2014

Easy to do the a DMM:

1 - Set your DMM to the 10 amp DC range and plug the red lead into the "10 AMP" socket on the meter.

2 - Disconnect the grounded (negative) battery cable from the battery post.

3 - With everything turned off (ign, lights, etc) stick the positive (red) DMM probe on the ground cable clamp and negative (black) probe on the battery neg post. The meter will read the standby the draw. (If it reads 0.00, switch to a lower current range (eg 300 ma) and reposition the red jack on the DMM if required and repeat the test).

IMPORTANT! Don't turn on any electrical load while doing this test!!

If the meter shows more than 20 ma or so of drain, remove fuses one at a time until the offending circuit is located.

If the drain persists after all the fuses have been checked, drain is likely a faulty alternator. Verify by removing the output (heavy wire) and control (plug) wiring from the alternator. If the drain disappears the alternator needs attention.

Phil Tibbetts · Dec 20, 2014

Possible alternator drain?

farmboy48 · Dec 20, 2014

my 1466 IH will drain the battery in a few hours, replaced alternator, no difference, put old alternator on w-6 with no problem. Is there a diode in the system for preventing this as we use when we convert from gen to alt. I have been just pulling the control plug on the alt when I leave tractor sit. Just haven't had the time to troubleshoot properly.

Owen Aaland · Dec 21, 2014

(quoted from post at 18:16:51 12/20/14) my 1466 IH will drain the battery in a few hours, replaced alternator, no difference, put old alternator on w-6 with no problem. Is there a diode in the system for preventing this as we use when we convert from gen to alt. I have been just pulling the control plug on the alt when I leave tractor sit. Just haven't had the time to troubleshoot properly.

Assuming you are dealing with a 10SI alternator. if pulling the plug on the alternator cures the symptoms and changing the alternator with a known good did not, check the voltage on the #1 terminal. There should be about six volts with the key on and no voltage with the key off. There is no diode on the diesel tractors but there is a resistor. Power for the #1 terminal comes from the key switch through the resistor and then to the alternator.

If you tractor is an early model with a 10DN alternator there should be no voltage on either small terminal with the key off. With the key on there should be about six volts on the F terminal and no voltage on the R terminal. With the engine running the voltage will vary on the F terminal depending on alternator demand. The voltage on the R terminal when running should be about 6 -7 volts AC.

farmboy48 · Dec 21, 2014

Thanks Owen, It is a 10si alternator, I will have to check this out when I get thru the snow and to the shed. May have to wait until spring. I notice I do get a spark when reconnecting plug before trying to start it. So mayhaps I am getting voltage to it thru the switch even when in off position, or possibly picking up voltage somewhere else in the harness.

tnx again, Dick ND

Checking for battery draw with DVM

Hattrick

Member

gab

Well-known Member

Bob M

Well-known Member

Phil Tibbetts

Well-known Member

farmboy48

Member

Owen Aaland

Well-known Member

farmboy48

Member

Similar threads