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How to check starter voltage draw
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valleybusman
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Jan 27, 2009, 9:28 PM
Post #1 of 4
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How to check starter voltage draw
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Okay I checked my 83 6.2 diesel Blazer for charging and batteries . I have a full 14.5 volts at 2000 rpms . My batteries hold a charge and are in good shape (14 months old . Okay I replaced the starter around Christmas time because that starter burned up . So Loren how do I check to see if the starter is drawing to much voltage . By the thanks for your help !!!!! Today it acted like it would die out before starting ? It was really cold today and I have access to a snap on scope if that helps . Thanks !!!!
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Loren Champlain Sr
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/ Moderator
Jan 28, 2009, 4:14 PM
Post #2 of 4
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Re: How to check starter voltage draw
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Starter draw is measured in how many amps it takes to crank the engine. (not sure if I said that correctly). Anyway, you'll need to see what kind of amperage it (the starter) is drawing during crank. Too much, and it'll drain the batteries, and eventually ruin them.....and, visa-versa. Not real common, but poor cables can cause enough of a voltage drop to kick you in the pants, too. Diesels require A LOT of amperage, especially, when cold. Make certain that the batteries you put in are rated high enough to handle the requirement. Most shops have equipment that can run these tests for you and generally a nominal charge for doing so.
Loren
SW Washington
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zmame
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/ Moderator
Jan 28, 2009, 4:40 PM
Post #3 of 4
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Re: How to check starter voltage draw
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You can take a meter put it on VDC and put positive probe on clamp and negitive proble on post and get somone to crank it that will tell you how much voltage is being droped from the clamp to post shouldn't read anymore than 0.5v
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DanD
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/ Moderator
Jan 31, 2009, 7:59 AM
Post #4 of 4
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Re: How to check starter voltage draw
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Considering that this is a diesel, I would say 400 to 500 initial draw, when first energized and 200 to 250 during cranking would be acceptable. As Loren said; most any creditable shop can do this test for you, at a reasonable cost. High rate ammeter, knife switch or inductive pick-ups are not cheap to buy.
Batteries, battery cables and cable connections will all have an affect on current draw. There are other things (engine mechanical, engine management) as well but we’re only talking electrical.
Many techs’ get caught condemning a starter motor for excessive draw when it was a connection or cable issue. Any time I see high draw on a circuit, I will perform voltage drop tests on the system.
On a starting circuit I would connect one voltmeter lead to the battery positive terminal and the other to the starter’s main positive terminal. The same for the negatie side of the circuit; voltmeter connected between the battery terminal and starter case.
You should see zero voltage with the system not energized. Once you energize the circuit and the starter motor is cranking; you shouldn’t see any more then .25 volt to at the very most .5 of a volt.
The voltage showing on the meter is the voltage that is lost through the cable and or the cable connections.
The battery may have 12 to 15 volts but the starter is only seeing whatever is left after the cable. As voltage goes down, current flow goes up (to a point of to low a voltage and no crank).
When done properly you can pin point the exact spot in the circuit where it has gone bad. Just keep moving the voltmeter lead that was at the starter backward through the circuit towards the battery until you see an acceptable voltage loss.
Dan.
Canadian "EH"
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