'94 850: battery drain, elec, issues MVSOLVED battery cable Topic is solved

[jgc470]

I am interested in the use of IR thermometer to detect this electrical problem; have others used this tool to track down DIY Volvo problems? I recently had a short in my 850, and testing point to point can be time consuming. Thoughts?

[regent]

Depending on the KIND of electrical problem, ringing point to point may be the only method allowable (example: short circuit - you do not want to troubleshoot this one with power on )
IMHO, IRT is a great supporting tool if you need to pinpoint poor contact in a power circuit where heat builds up due to losses in active resistance - but far, far away from being a universal troubleshooting approach.
Another example where it won't work is a 'small current circuit' (such as the coolant temperature sensor wiring) where a difference in temperature would be very minute (or just theoretical) and therefore inconclusive...

[timmybdaddyof3]

+1 to regent
Heat testing in general is a great way to find high current resistance, but it is in no way 100% conclusive...although in this case it was a great quick diagnose, the electrical problem being diagnosed was large enough to literally kill the car...another issue to consider, especially in the automotive side and with a problem like this was....the positive and negative terminal at the battery will in theory be at about the same temperature, the positive wire and the ground strap on the motor will be at very different temperatures, and you have no absolute point of reference as to how much heat seen on the starter wire is due to resistance vs radiant engine heat....you do know absolutely that if you have 12.6v across the positive and negative battery terminals you should have the same across the starter lug, alternator lug and the negative battery post.

All that aside, if you are suspecting a connection (as was in this case) 95% of the time you can find a problem using a good IR thermometer....in theory both the wire and the connector should be the same temp (and in the case of big plastic connectors they will actually be cooler)...but again, ambient temperatures (because of where the wires physically are located and whats around them) must be considered.

[sethhahn]

True, ambient heat from the idling engine adds complexity to the analysis. Any point along the positive cable could vary +/- 30 degF due to engine heat alone, but in this case the high current and resistance was significant enough to make it obvious that high temps were not incidentally due to the location in the engine compartment.
In short, the voltage drop was the biggest factor in identifying the problem, but only the IR readings made it possible to identify the exact trouble spot in the circuit.
Doing these tests before AND after also gave me the confidence to know that my issue was resolved.

[timmybdaddyof3]

analysis - great choice of word...i will use a multi-meter (both resistance and voltage) to diagnose, and temps to analyze and confirm.
In my first post the reason i did not suggest using temps is due to the fact that i have met one to many people who do not know how to analyze the results of a diagnostic procedure.
The more i am here the more i like the people on this board

[regent]

That's right, you are in the right forum.

In fact, analytical skills aren't always required...

In simple terms, TroubleShooting takes at least two:
1. One (1) person - this would be the Trouble Maker.
2. At least one (1) more, preferably a marksman - to do the Shooting part.
Easy.

[dosbricks]

I will play person #1, since I have been down this road with the S70 a couple of times. Keep an eye out for this problem to recur in a couple of years. Is there a person #2 who can explain why?

Also watch for corrosion creeping up the red wire bundle coming off the +terminal that goes to the fuse box.

[regent]

I forgot to mention - the qualification requirements for Person # 1 include a good deal of ducking skills or else game is over in a very short order

As for the recurring problems, that is trend analysis on top of troubleshooting, and one would usually find either poor design (selection of material or process) or poor workmanship (to include any combination thereof) to be the root cause of most repeat issues.

I think that we are here because:

1. We want to help the stealerships drop out of business sooner,
2. We love fixing our volvos regardless of what we encounter,
3. Most important: we enjoy helping each other with the fixes as best as we can

[jgc470]

Thanks to all for thoughts and suggestions on IR use. I bought an IR device, and add it to my electrical tool kit.