How to test a battery cable?

[misha]

By the time I lug a battery, a headlight, and clips to rig a junkyard tester, I would have clicked on Ancor wire, lugs, and made my own.

I'm with abscate on this.

[scot850]

I hear you guys load and clear. However, I like original. I have the equipment to test stuff so why not? I'm retired and need amusement!

I have headlights and fan motors and a voltage source so why not??

Appreciate your views!

Neil.

[misha]

You forgot the main thing...engine temperature under the hood.

[scot850]

Isn't that what a heat gun is for?

Neil.

[misha]

[MrAl]

I have seen/read stuff on this, but how do you test a battery cable to know if it is good? As anyone who knows and has removed one of these cables, it is a major pain as Volvo routes the +ve cable though a couple of metal ties that have to be removed, but then also through the main wiring harness at the bottom of the radiator. To remove it requires taking 2 x M6 bolts out of the top of the front engine mount and then using a pair of channel locks to try to fight the 2 tanks on the top of the cover to remove it. Then you have to cut open a plastic corrugated shroud over the wiring and then finally, cutting through a bunch of electrical tape before disconnecting the wire at the starter.

Finally you can remove the cable.

It would be good to know if the cable was good before doing all this for nothing. I cleaned the cable I pulled yesterday and then tested the continuity which read 0 ohms. Is that of any use as a measurement?

Is the only way to measure this and get a true reading of the cable being good is to fit it and then see if it heats up and do a voltage drop test? If so, what does a good cable read?

Thanks,

Neil.

Hi Neil,

I had changed out the heavy battery cables on older cars but back then it was a hell of a lot easier.

I had also worked on very high power converters that use very heavy gauge wire for the buss supply like 8 and 6 and 4 AWG.
The test done was to run the converter at full load and feel the ends of the wire to see if they got hot. If they got hot that meant that the crimp was not done right. It was rare to find one bad though because the crimp tool was very expensive and worked very well.

As to testing out of the vehicle, the best you can do with a multimeter alone is to test for continuity. If the wire is open you will know that with the test, but that's the only test that will show any real results with a meter alone. To test it right, you have to supply a current like 100 amps for at least a few minutes, but even a few seconds will tell you if it is very bad.

The procedure would be to supply the wire with a current of say 100 amps and measure the temperature rise of the wire on the outside of the wire, near the middle of the length, and also the very ends. The worst-case test would be to see if the insulation can hold up as the wire heats up, but I suppose for a car it may be good enough just to know the voltage drop across the wire. You can look up the resistance of the wire and then calculate the voltage drop for a good wire using that information. You would need a good meter though, one that measures down perhaps to 100 microvolts, maybe lower. You would compare the reading to what you found using the resistance of the wire and the current going through the wire at the time.

For the supply of current, you would use one or more batteries, and for a load one way is to use a 12vdc to 120vac converter with a heavy load like a room electric heater. 1200 watts at 120v is 10 amps, and so at 12v that is 100 amps if the converter was 100 percent efficient. Since the converter would probably be 80 percent or lower, that would mean around another 25 amps, so with a 1200 watt heater you could expect over 100 amps through the wire.

Obviously this test is not that easy to set up that's why most people just change it out. For me, I was lucky enough to get mine off back then and solder the hell out of the crimp connector. That worked well, but I had to use a propane torch to heat up the wire to solder it right, and that is not particularly easy to do either.

The most common failure is the crimps as the wire would only have a problem if it was flexed repeatedly during use. The strands could get thinner in some parts of the wire because of that. It's difficult to say how likely this is to happen on a car though.

Another way is to inspect the entire length of wire and look for anything obviously wrong.

If this is one of the heavy wires then it may only have a serious problem when starting the car. That would be another way to test it, but only if the wire is still on the car. You would set the meter up to measure the voltage across the entire wire by clamping onto the connectors at each end, then crank the car over several times in succession, watching for a larger voltage drop than found through looking up the resistance of the wire.

If you can move the wire back and forth you may be able to tell if the crimp is bad or any strands broken near the connectors.

There are more advanced ways to test metals these days but the test equipment is way too expensive. You'd have to know someone who worked at a place that did this, and see if the tests work for stranded wires too.

Sorry I don't have anything else here, but this might be one of the hardest tests to do with limited equipment. That's probably why everyone does a change out instead of testing for faults. Careful inspection is probably the best bet for now.

In the wire table, #4 wire has 0.249 Ohms/1000 feet, so 3 feet would have:
3*0.249/1000=0.000750 Ohms approximately. You can see why this is hard to measure.
If you pump 10 amps through it, which is the limit of many under $70 power supplies, you will measure about 7.5 millivolts, which requires a decent meter or at least a cheaper one that can measure down with a resolution of 100 microvolts. They make some really good bench meters that can easily do this but they are above $200 most of the time, and not sure how much you would want to pay for one.
Alternately, you can calibrate a cheaper meter for the approximate voltage range to be measured and then use the cheaper one. If you were willing to send me your meter I could check it with a high end voltmeter in the range you would need to measure, then send you the calibration data and return the meter to you. This would allow a rough check as long as you could supply 10 amps through the wire.

I do have to ask though, what made you think the wire was bad or at least needed testing, or is it you just wanted to be able to test a wire you were going to purchase from a junk yard?

[volvolugnut]

I have seen/read stuff on this, but how do you test a battery cable to know if it is good? As anyone who knows and has removed one of these cables, it is a major pain as Volvo routes the +ve cable though a couple of metal ties that have to be removed, but then also through the main wiring harness at the bottom of the radiator. To remove it requires taking 2 x M6 bolts out of the top of the front engine mount and then using a pair of channel locks to try to fight the 2 tanks on the top of the cover to remove it. Then you have to cut open a plastic corrugated shroud over the wiring and then finally, cutting through a bunch of electrical tape before disconnecting the wire at the starter.

Finally you can remove the cable.

It would be good to know if the cable was good before doing all this for nothing. I cleaned the cable I pulled yesterday and then tested the continuity which read 0 ohms. Is that of any use as a measurement?

Is the only way to measure this and get a true reading of the cable being good is to fit it and then see if it heats up and do a voltage drop test? If so, what does a good cable read?

Thanks,

Neil.

Hi Neil,

I had changed out the heavy battery cables on older cars but back then it was a hell of a lot easier.

I had also worked on very high power converters that use very heavy gauge wire for the buss supply like 8 and 6 and 4 AWG.
The test done was to run the converter at full load and feel the ends of the wire to see if they got hot. If they got hot that meant that the crimp was not done right. It was rare to find one bad though because the crimp tool was very expensive and worked very well.

As to testing out of the vehicle, the best you can do with a multimeter alone is to test for continuity. If the wire is open you will know that with the test, but that's the only test that will show any real results with a meter alone. To test it right, you have to supply a current like 100 amps for at least a few minutes, but even a few seconds will tell you if it is very bad.

The procedure would be to supply the wire with a current of say 100 amps and measure the temperature rise of the wire on the outside of the wire, near the middle of the length, and also the very ends. The worst-case test would be to see if the insulation can hold up as the wire heats up, but I suppose for a car it may be good enough just to know the voltage drop across the wire. You can look up the resistance of the wire and then calculate the voltage drop for a good wire using that information. You would need a good meter though, one that measures down perhaps to 100 microvolts, maybe lower. You would compare the reading to what you found using the resistance of the wire and the current going through the wire at the time.

For the supply of current, you would use one or more batteries, and for a load one way is to use a 12vdc to 120vac converter with a heavy load like a room electric heater. 1200 watts at 120v is 10 amps, and so at 12v that is 100 amps if the converter was 100 percent efficient. Since the converter would probably be 80 percent or lower, that would mean around another 25 amps, so with a 1200 watt heater you could expect over 100 amps through the wire.

Obviously this test is not that easy to set up that's why most people just change it out. For me, I was lucky enough to get mine off back then and solder the hell out of the crimp connector. That worked well, but I had to use a propane torch to heat up the wire to solder it right, and that is not particularly easy to do either.

The most common failure is the crimps as the wire would only have a problem if it was flexed repeatedly during use. The strands could get thinner in some parts of the wire because of that. It's difficult to say how likely this is to happen on a car though.

Another way is to inspect the entire length of wire and look for anything obviously wrong.

If this is one of the heavy wires then it may only have a serious problem when starting the car. That would be another way to test it, but only if the wire is still on the car. You would set the meter up to measure the voltage across the entire wire by clamping onto the connectors at each end, then crank the car over several times in succession, watching for a larger voltage drop than found through looking up the resistance of the wire.

If you can move the wire back and forth you may be able to tell if the crimp is bad or any strands broken near the connectors.

There are more advanced ways to test metals these days but the test equipment is way too expensive. You'd have to know someone who worked at a place that did this, and see if the tests work for stranded wires too.

Sorry I don't have anything else here, but this might be one of the hardest tests to do with limited equipment. That's probably why everyone does a change out instead of testing for faults. Careful inspection is probably the best bet for now.

In the wire table, #4 wire has 0.249 Ohms/1000 feet, so 3 feet would have:
3*0.249/1000=0.000750 Ohms approximately. You can see why this is hard to measure.
If you pump 10 amps through it, which is the limit of many under $70 power supplies, you will measure about 7.5 millivolts, which requires a decent meter or at least a cheaper one that can measure down with a resolution of 100 microvolts. They make some really good bench meters that can easily do this but they are above $200 most of the time, and not sure how much you would want to pay for one.
Alternately, you can calibrate a cheaper meter for the approximate voltage range to be measured and then use the cheaper one. If you were willing to send me your meter I could check it with a high end voltmeter in the range you would need to measure, then send you the calibration data and return the meter to you. This would allow a rough check as long as you could supply 10 amps through the wire.

I do have to ask though, what made you think the wire was bad or at least needed testing, or is it you just wanted to be able to test a wire you were going to purchase from a junk yard?

MrAI,
Thanks for a practical review of my thought experiment of how to test a battery cable. Your ideas are well founded and a low cost test does not appear possible.
volvolugnut

[scot850]

Al, many thanks for all the helpful info. The best I can do is a 30V DC power supply, not sure what the current rating is! I can make up a simple load like a headlight and/or interior fan motor that can run at load for a long time. Starter motors is another but they are not designed to run continuously.

I have a thermal remote thermometer which I can use for temperature measurement.

The downside to testing an old battery cable is like any electrical wire with bare ends exposed in an unfriendly environment. That is water ingress. Now at the top end at the battery, the cable is enclosed in a rubberized collar so should be fairly well protected. It is the starter end that is the potential issue as it is not enclosed by heat-shrink and is more exposed. However, the cable is usually fairly vertical. I looked at the cable I removed and it had clear oxidation where it was exposed by the crimp. I liberally sprayed it with De-ox and it bubbled nicely and then rubbed the outer surface with a brass brush. It cleaned up pretty well, but in reality you would need to remove the crimped end to clean it fully, but I believe it is good enough. From what you, Abscate and others have said the only test static you can do with a meter is pretty much for a cable that is badly damaged for continuity and it give 0 ohms. So at least it is not severed!

This is just for a back up so I guess if I really want to and have no other projects to do, I could make up another test rig as suggested, and see what happens for the sake of science! Realistically that is a long way down a long list!!

The car I own is currently (no pun intended!!) starting with no issues, so at the mileage we are doing and the fact it is not used in winter it will be a long time probably until another cable is needed. Then there are other peoples cars that I occasionally work on. But again, those are cars where budgets are very tight for the owners so a used cable in worst case is the way forward.

I may still look at the possibility of disassembling the cable and removing the ends for re-use and see if I can re-fit them with new cable and possibly solder the wire ends in place for protection as much as better connectivity, and then heat shrink both ends.

Thanks again for your valuable input.

Neil.

[MrAl]

I have seen/read stuff on this, but how do you test a battery cable to know if it is good? As anyone who knows and has removed one of these cables, it is a major pain as Volvo routes the +ve cable though a couple of metal ties that have to be removed, but then also through the main wiring harness at the bottom of the radiator. To remove it requires taking 2 x M6 bolts out of the top of the front engine mount and then using a pair of channel locks to try to fight the 2 tanks on the top of the cover to remove it. Then you have to cut open a plastic corrugated shroud over the wiring and then finally, cutting through a bunch of electrical tape before disconnecting the wire at the starter.

Finally you can remove the cable.

It would be good to know if the cable was good before doing all this for nothing. I cleaned the cable I pulled yesterday and then tested the continuity which read 0 ohms. Is that of any use as a measurement?

Is the only way to measure this and get a true reading of the cable being good is to fit it and then see if it heats up and do a voltage drop test? If so, what does a good cable read?

Thanks,

Neil.

Hi Neil,

I had changed out the heavy battery cables on older cars but back then it was a hell of a lot easier.

I had also worked on very high power converters that use very heavy gauge wire for the buss supply like 8 and 6 and 4 AWG.
The test done was to run the converter at full load and feel the ends of the wire to see if they got hot. If they got hot that meant that the crimp was not done right. It was rare to find one bad though because the crimp tool was very expensive and worked very well.

As to testing out of the vehicle, the best you can do with a multimeter alone is to test for continuity. If the wire is open you will know that with the test, but that's the only test that will show any real results with a meter alone. To test it right, you have to supply a current like 100 amps for at least a few minutes, but even a few seconds will tell you if it is very bad.

The procedure would be to supply the wire with a current of say 100 amps and measure the temperature rise of the wire on the outside of the wire, near the middle of the length, and also the very ends. The worst-case test would be to see if the insulation can hold up as the wire heats up, but I suppose for a car it may be good enough just to know the voltage drop across the wire. You can look up the resistance of the wire and then calculate the voltage drop for a good wire using that information. You would need a good meter though, one that measures down perhaps to 100 microvolts, maybe lower. You would compare the reading to what you found using the resistance of the wire and the current going through the wire at the time.

For the supply of current, you would use one or more batteries, and for a load one way is to use a 12vdc to 120vac converter with a heavy load like a room electric heater. 1200 watts at 120v is 10 amps, and so at 12v that is 100 amps if the converter was 100 percent efficient. Since the converter would probably be 80 percent or lower, that would mean around another 25 amps, so with a 1200 watt heater you could expect over 100 amps through the wire.

Obviously this test is not that easy to set up that's why most people just change it out. For me, I was lucky enough to get mine off back then and solder the hell out of the crimp connector. That worked well, but I had to use a propane torch to heat up the wire to solder it right, and that is not particularly easy to do either.

The most common failure is the crimps as the wire would only have a problem if it was flexed repeatedly during use. The strands could get thinner in some parts of the wire because of that. It's difficult to say how likely this is to happen on a car though.

Another way is to inspect the entire length of wire and look for anything obviously wrong.

If this is one of the heavy wires then it may only have a serious problem when starting the car. That would be another way to test it, but only if the wire is still on the car. You would set the meter up to measure the voltage across the entire wire by clamping onto the connectors at each end, then crank the car over several times in succession, watching for a larger voltage drop than found through looking up the resistance of the wire.

If you can move the wire back and forth you may be able to tell if the crimp is bad or any strands broken near the connectors.

There are more advanced ways to test metals these days but the test equipment is way too expensive. You'd have to know someone who worked at a place that did this, and see if the tests work for stranded wires too.

Sorry I don't have anything else here, but this might be one of the hardest tests to do with limited equipment. That's probably why everyone does a change out instead of testing for faults. Careful inspection is probably the best bet for now.

In the wire table, #4 wire has 0.249 Ohms/1000 feet, so 3 feet would have:
3*0.249/1000=0.000750 Ohms approximately. You can see why this is hard to measure.
If you pump 10 amps through it, which is the limit of many under $70 power supplies, you will measure about 7.5 millivolts, which requires a decent meter or at least a cheaper one that can measure down with a resolution of 100 microvolts. They make some really good bench meters that can easily do this but they are above $200 most of the time, and not sure how much you would want to pay for one.
Alternately, you can calibrate a cheaper meter for the approximate voltage range to be measured and then use the cheaper one. If you were willing to send me your meter I could check it with a high end voltmeter in the range you would need to measure, then send you the calibration data and return the meter to you. This would allow a rough check as long as you could supply 10 amps through the wire.

I do have to ask though, what made you think the wire was bad or at least needed testing, or is it you just wanted to be able to test a wire you were going to purchase from a junk yard?

MrAI,
Thanks for a practical review of my thought experiment of how to test a battery cable. Your ideas are well founded and a low cost test does not appear possible.
volvolugnut

Hi there,

Yeah, unfortunately most people want low cost and that's the real limiting factor I guess.
I had two 10 amp power supplies but I had to give them away because nobody wanted to buy them due to the shipping costs. That means I would have to rig up a car battery too now to power the test.

[MrAl]

Al, many thanks for all the helpful info. The best I can do is a 30V DC power supply, not sure what the current rating is! I can make up a simple load like a headlight and/or interior fan motor that can run at load for a long time. Starter motors is another but they are not designed to run continuously.

I have a thermal remote thermometer which I can use for temperature measurement.

The downside to testing an old battery cable is like any electrical wire with bare ends exposed in an unfriendly environment. That is water ingress. Now at the top end at the battery, the cable is enclosed in a rubberized collar so should be fairly well protected. It is the starter end that is the potential issue as it is not enclosed by heat-shrink and is more exposed. However, the cable is usually fairly vertical. I looked at the cable I removed and it had clear oxidation where it was exposed by the crimp. I liberally sprayed it with De-ox and it bubbled nicely and then rubbed the outer surface with a brass brush. It cleaned up pretty well, but in reality you would need to remove the crimped end to clean it fully, but I believe it is good enough. From what you, Abscate and others have said the only test static you can do with a meter is pretty much for a cable that is badly damaged for continuity and it give 0 ohms. So at least it is not severed!

This is just for a back up so I guess if I really want to and have no other projects to do, I could make up another test rig as suggested, and see what happens for the sake of science! Realistically that is a long way down a long list!!

The car I own is currently (no pun intended!!) starting with no issues, so at the mileage we are doing and the fact it is not used in winter it will be a long time probably until another cable is needed. Then there are other peoples cars that I occasionally work on. But again, those are cars where budgets are very tight for the owners so a used cable in worst case is the way forward.

I may still look at the possibility of disassembling the cable and removing the ends for re-use and see if I can re-fit them with new cable and possibly solder the wire ends in place for protection as much as better connectivity, and then heat shrink both ends.

Thanks again for your valuable input.

Neil.

Hi Neil,

You're very welcome. I always help when I can although it's usually on electronic sites where many students do not know how to do their homework (ha ha). On those sites we run into discussions on the simplest things all the way to highly theoretical and try to come up with new answers to old question as well as the new ones. You could also visit one of those sites too and see what everyone has to say.

As to the cleaning of the cable, when I did mine way back when I had to 'unstrand' it a little and clean each and every strand before I soldered it. The copper really has to be clean for that or it may not stick in some places which means higher resistance. When you do that though, you get a super well-connected connector.

Back in the days in the power supply industry, the word around was that a crimp is better than solder, but that may have been for mechanical reasons. The wire just outside of the crimp connector is always subject to small movements which repeat over years. The crimp may offer a little more wiggle room so the wire does not break. Come to think of it, everything was crimped from #22 to #4 wire unless it was on a circuit board and soldered to a trace. One of the inspectors from Israeli Aircraft also said that crimps were better and probably would have rejected units that were made with soldered connectors instead of crimps.

The best I can do it buy a somewhat cheaper meter and calibrate it and send it off to you.
There might be another way too though. I think it was Analog Devices that makes a super accurate voltage reference chip. It outputs a fixed voltage, and you can order different fixed voltages. The ones I remember were 2.048 volts and 4.096 volts. What you would do is use one of those chips (not hard to do) and use a precision resistive divider to divide the voltage down to the range you are most interested in. For example, if you use two 1k resistors you get 1.048 volts from the 2.048 volt model. If you use a 1k on the bottom and 127k on the top, you get a divide by 128 network and that would give you 0.016 volts at the center tap. You could check the meter with that, and for a meter that has a resolution down to 100uv it would read 0.0160 volts but if it was reading a little high it might read 0.0161 volts. Once you know what the meter reads you can use that to estimate the voltage you actually measure later.

In case you never did a resistive divider before, it is just two resistors in series (that is one lead form one resistor is soldered to one lead of the other resistor) and then the two open leads are connected to the power source, and the center where the two resistors meet is the output that would be that 0.0160 volts. it's really easy to do this, but you have to order some precision resistors like 0.1 percent tolerance, or if 1 percent accuracy is ok for you then just 1 percent resistors. You may have to make that 127k resistor up from two or more other resistors though if that is not a standard value.