Ohming (test the resistance of) the batt cable?
10-18-2018, 04:47 PM
#1
Race Director
Thread Starter
Ohming (test the resistance of) the batt cable?
In pursuit of my starter issue (heat soak slow crank) it's been suggested and I agree I ohm the cable since it's now in the trunk so 10-15 ft? voltage drop & all that.
So who knows (plz no guess) what the nominal range would be. THX.
So who knows (plz no guess) what the nominal range would be. THX.
10-18-2018, 05:07 PM
#2
Burning Brakes
Hello,
A typical Ohm Meter will not test the cable, it needs to be tested under a heavy load. Cables usually fail at the lug connection point and sometimes fail in the middle though rarely.
The point that the lug is crimped to the cable is critical and must be done correctly or high resistance under load will be the result.
Who made the long cable for you and what gage is the wire?
Douglas in Green Bay
A typical Ohm Meter will not test the cable, it needs to be tested under a heavy load. Cables usually fail at the lug connection point and sometimes fail in the middle though rarely.
The point that the lug is crimped to the cable is critical and must be done correctly or high resistance under load will be the result.
Who made the long cable for you and what gage is the wire?
Douglas in Green Bay
10-18-2018, 05:55 PM
#3
Race Director
Thread Starter
Hello,
A typical Ohm Meter will not test the cable, it needs to be tested under a heavy load. Cables usually fail at the lug connection point and sometimes fail in the middle though rarely.
The point that the lug is crimped to the cable is critical and must be done correctly or high resistance under load will be the result.
Who made the long cable for you and what gage is the wire?
Douglas in Green Bay
A typical Ohm Meter will not test the cable, it needs to be tested under a heavy load. Cables usually fail at the lug connection point and sometimes fail in the middle though rarely.
The point that the lug is crimped to the cable is critical and must be done correctly or high resistance under load will be the result.
Who made the long cable for you and what gage is the wire?
Douglas in Green Bay
10-18-2018, 06:17 PM
#4
Not sure what typical volt meter you’re referring to, every one I’ve used will ohm a wire run and at the least show you a return or a complete circuit if one exists. I’m not sure how that’s going to help with a starter heat soak issue though.
10-18-2018, 08:47 PM
#6
Melting Slicks
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Location: Ex DPRK, now just N of Medford, OR
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Ohm meter wont pass enough current for an accurate test. It will show continuity, but that isn't relevant at the amperage required by the starter.
Check for voltage drop under load... First I'd check battery voltage while cranking at the battery, then connect voltmeter + to starter hot lead and voltmeter - to chassis ground, and check at the starter for full battery voltage while cranking (will be different from full voltage at rest...). If it's much lower (I think .5volt is max spec, but don't take that as gospel), Move the - lead to the engine block and retest... that will eliminate the negative cable from the equation. If it's still low, make sure it's not just dirty...
Check for voltage drop under load... First I'd check battery voltage while cranking at the battery, then connect voltmeter + to starter hot lead and voltmeter - to chassis ground, and check at the starter for full battery voltage while cranking (will be different from full voltage at rest...). If it's much lower (I think .5volt is max spec, but don't take that as gospel), Move the - lead to the engine block and retest... that will eliminate the negative cable from the equation. If it's still low, make sure it's not just dirty...
10-19-2018, 08:21 AM
#7
Advanced
Your accurate test is to measure voltage drop across cable while starting. You place one end of your lead close to starter and other lead at battery. You should not have anymore voltage than 0.1 volts. When the cable is bad, you will have close to 1.0 volts.My son just bought a 2009 zo6 and he started having what I thought was heat soak issues.I replaced the battery, the starter and crank sensor. While doing the starter, I found that the power cable nut at the starter was loose. I replaced it anyways, since car had 40,000 miles. The battery post nut was also installed incorrectly. The nut that is wedge shaped was holding cable to the post and the flat nut was tightening the post to the battery. I swapped the nuts and now the post tightens properly to battery. Just some things to consider.
10-19-2018, 08:29 AM
#8
thing knower
um couldn't you disconnect the battery terminal and test with a jumper cable run around the outside to the jump lug on the fuse box?
just thinking outside the box
just thinking outside the box
Last edited by drewz06; 10-19-2018 at 08:29 AM.
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froggy47 (10-19-2018)
10-19-2018, 08:40 AM
#9
Melting Slicks
There is one other test that you can conduct; actually two. Takes two people...
1) With the cable installed and someone in the driver's seat, and with an ohm meter between the positive/negative (do for both) post of the battery and the clamp of the cable, try to start the car. The reading should not vary when the starter engages and the reading should be near zero (most meters will not register zero unless you calibrate them to do so) - 1 or 2 is good.
2) Same test as above, except the second probe is connected to the cable just forward of the clamp, via a straight pin through the cable's insulation.
This will test the cables ability to pass current via the positive/negative connections. A huge variation in the ohm reading is sure to be the source of the problem.
You can also run this test under the hood if you use your imagination...
1) With the cable installed and someone in the driver's seat, and with an ohm meter between the positive/negative (do for both) post of the battery and the clamp of the cable, try to start the car. The reading should not vary when the starter engages and the reading should be near zero (most meters will not register zero unless you calibrate them to do so) - 1 or 2 is good.
2) Same test as above, except the second probe is connected to the cable just forward of the clamp, via a straight pin through the cable's insulation.
This will test the cables ability to pass current via the positive/negative connections. A huge variation in the ohm reading is sure to be the source of the problem.
You can also run this test under the hood if you use your imagination...
Last edited by pcguy2u; 10-19-2018 at 08:47 AM. Reason: Flaky mouse and fingers
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froggy47 (10-19-2018)
10-19-2018, 12:49 PM
#10
Race Director
Thread Starter
Your accurate test is to measure voltage drop across cable while starting. You place one end of your lead close to starter and other lead at battery. You should not have anymore voltage than 0.1 volts. When the cable is bad, you will have close to 1.0 volts.My son just bought a 2009 zo6 and he started having what I thought was heat soak issues.I replaced the battery, the starter and crank sensor. While doing the starter, I found that the power cable nut at the starter was loose. I replaced it anyways, since car had 40,000 miles. The battery post nut was also installed incorrectly. The nut that is wedge shaped was holding cable to the post and the flat nut was tightening the post to the battery. I swapped the nuts and now the post tightens properly to battery. Just some things to consider.
10-19-2018, 12:50 PM
#11
Race Director
Thread Starter
Your accurate test is to measure voltage drop across cable while starting. You place one end of your lead close to starter and other lead at battery. You should not have anymore voltage than 0.1 volts. When the cable is bad, you will have close to 1.0 volts.My son just bought a 2009 zo6 and he started having what I thought was heat soak issues.I replaced the battery, the starter and crank sensor. While doing the starter, I found that the power cable nut at the starter was loose. I replaced it anyways, since car had 40,000 miles. The battery post nut was also installed incorrectly. The nut that is wedge shaped was holding cable to the post and the flat nut was tightening the post to the battery. I swapped the nuts and now the post tightens properly to battery. Just some things to consider.
10-20-2018, 04:30 PM
#14
You should have no more than .5 of a volt when doing a voltage drop test. Don't waste your time with a ohm test.
Your still chasing your hot soak problem?
Your still chasing your hot soak problem?
Last edited by sccaGT1racer; 10-20-2018 at 04:49 PM.
