P80 V70 00 NA battery cable question?

[scot850]

I know there is a current (no pun intended) thread on re-building the negative battery cables but I did not want to take that on a tangent.

Does anyone know if there is a resistance value or any other way to test the +ve and -ve cables for fit for purpose? At the age the cars are now, and probably still many with their original cables in place, they are possibly past their best in terms of performance.

My buddy who bought my 00 V70 NA is having a charging issue or low output from his alternator. He has a voltmeter installed in the car and it is only reading around 12.9V in regular running. If I recall a good alternator/charging system should be at somewhere around 13.4V +

He has fitted a new battery and is now planning a new voltage regulator. Before he rushes out to do this we would like to test the cables if possible to make sure he is replacing the correct parts.

Any guidance/advice is appreciated.

By coincidence, I was at the junkyard and thought I would figure out how the 99-00 cars route the +ve battery cables. What a stupid way to do it if you ever have to replace it. I think I would just cut the ends off and route the +ve cable with zip ties to the starter and beyond!

I pulled the +ve cable anyway as it looked in really good shape. Top end is fully cable wrapped and the other end at the starter only had a light layer of corrosion that removed quickly with a few wipes with a brash bristle brush. Again I want to see if this can be tested in some way to keep as a spare should I need it.

Thanks,

Neil.

[MrAl]

You could measure the voltage drop in the wires with a decent digital meter and use Kirchhoff's Voltage Law which states the the algebraic sum of voltage drops around a closed path equals zero.
What this really means in terms of the wire itself is that if the alternator is putting out say 14v and the positive lead drops 2 volts that's too much when charging. It would be good to turn on some stuff like headlights and heater so there is more current flow to test the wire with because with wires that thick you need a decent current to get a good idea what is going on.
If you have another car to compare it with even better.
Also, have to check the ground connection. That's where the alternator bolts to the metal part of the car such as the engine itself or whatever it bolts too. If those bolts are not tight it could cause a voltage drop there too.
Measuring the output of the alternator may help also. If the output is 14v and the battery only sees 12v then that's too much of a loss.
Of course if there are crimped connectors they could be a problem too in old wiring.
I dont think copper itself goes bad though unless it gets oxidized then connections could become faulty and wire diameter could decrease if it is really bad corrosion.

Some of these parts are best tested in their actual application because a test jig would just have to replicate what happens in the real application anyway. This is also true of inductors that are used for high current in converter circuits because to test one outside of the application you'd just have to build up something that is very similar to the actual application anyway and that can get expensive. Might as well test it "in circuit" as that's really the best test anyway.

[abscate]

Use Mr Al’s method above. With lights on, the cables are running something like 20-30 amps

A 0.1 ohmresistance would drop the voltage from alternator peg to battery peg of 2-3 volts , easily measured.

It’s hard to measure small resistances.

I would love to know the engine housekeeping amperagewith no accessories on, that might come out of Shagg troubleshooting

[scot850]

So, as abscate knows, my electricery skills are poor at best, so let me ask some questions for my brain to understand better.

I have one of those units that are supposed to measure the battery condition as well as the alternator output. My concern with that is that for every battery I have owned, it has always said that the battery is bad, even when brand new on all our cars, so how likely is that to tell me the correct output of the alternator?

So how do I measure the actual alternator output? Presumably the +ve meter cable does to the output (red) cable from the alternator, but where does the black (-ve) tester lead go?

If I put the -ve lead onto the =ve battery connection that is only reading what output gets to the battery but does not tell me if the loss is in the cable or just the bad alternator output?

Appreciate the help guys!

Neil.

[abscate]

Black lead always goes to the negative battery terminal for those tests. Best to clip it on so that it stays static.

Wrap your red lead in some electrical tape do thst just the tip is showing so you don’t have to worry about shorting thst lead to ground

Now do two tests with black test lead attached yo negative on battery

Test 1…key off and out.

Touch red lead to battery red. Should be a nice healthy 12.5 volts or more
Now touch the red to the hot starter terminal, and the alternator post

You’ll get the same voltage reading , plus or minus 0.05 volts.

All you are doing here is measuring the battery voltage.

Test2

Start car, lights on

Now the system is at alternator voltage. Something like 13.5 volts at idle
Current is now flowing to power the lights and. Engine, about 12-15 amperes (amps)

Pushing that current through the wire from the alternator robs some of the voltage , and the exact loss follows ohms law

Voltage drop = resistance x current

You will typically see a slight , like 0.1V drop , between the alternator to starter, and starter to battery connections when loaded

[scot850]

Ok, I follow all that. My buddy was saying he is only seeing 12.9V in the car when running on his aftermarket installed voltmeter. Now how accurate that part is I don't know. I have 3 different multi-meters and I can get different reading on those.

So at what point would you look at swapping the battery cables out?

Thanks again!

Neil.

[MrAl]

So, as abscate knows, my electricery skills are poor at best, so let me ask some questions for my brain to understand better.

I have one of those units that are supposed to measure the battery condition as well as the alternator output. My concern with that is that for every battery I have owned, it has always said that the battery is bad, even when brand new on all our cars, so how likely is that to tell me the correct output of the alternator?

So how do I measure the actual alternator output? Presumably the +ve meter cable does to the output (red) cable from the alternator, but where does the black (-ve) tester lead go?

If I put the -ve lead onto the =ve battery connection that is only reading what output gets to the battery but does not tell me if the loss is in the cable or just the bad alternator output?

Appreciate the help guys!

Neil.

Hi Neil,

I have never had much faith in battery testers that are supposed to test the battery itself except for the voltage reading.
I had a battery in my old Hyundai i just got a few months previously and it started to die as it would not turn the engine over very well. I took it back to the auto parts store they put a 'tester' on it and it said it was good, of course. I still asked for a replacement so i got a new one.

The best way i know of to test the alternator output is to use a DC clamp on ammeter. This is the type that has two jaws that open up when you press the side button. You then put the open jaws around the wire, then let go, and the jaws close. With the car running you will see the current reading from the alternator to the battery. I believe the current should be around 10 amps or something like that, as a minimum, or possibly more. Using the arrow on the clamp meter you can tell if the current is charging the battery or discharging the battery. With the arrow pointing toward the battery, a positive reading means it is charging, a negative reading it is discharging.
It is probably best to compare readings with that of another car. Once you get a few readings you will get a feel for what it should be.
Mine measures 10 amps or so when charging, nothing extra turned on, in the daytime. That is maybe 1 or 2 minutes after starting the car.
It may be a little hard to get the clamp jaws around the wire, but it did work ok on mine. The best wire is the positive lead that goes right to the battery. It may have a smaller wire too and then just clamp it around both. The smaller wire may come from the alternator but you can check that out. I have a pic but it's not very good i'll try to get a better pic of this.

The DC clamp on current meters are a bit more expensive than the pure AC clamp on meters. I payed about $60 USD for mine while some of the AC ones are only around $20 but you need a DC meter to measure a battery current.
Some of them also have a surge reading 'catcher' that can catch a large peak current such as when you first turn something on or when you start the car and the starter draws a huge current for a few seconds. It will catch and hold that reading. You may not need that, but definitely need the DC type meter for batteries of course because they are DC devices and the alternator charges with a DC current.

The meter i use is made by Mastech. It's not the best manufacturer out there but their stuff works pretty well and is a bit cheaper than some main brand stuff such as that made by Fluke. If you want a really good meter get a Fluke but be prepared to pay top dollar. Could be $150 USD but i have not priced them in a long time because why bother

I'll see if i can get a better pic within a day or two.

[scot850]

Thanks Al. Appreciate the education and the help.

I will look into the equipment you mention. The Fluke meters were horribly expensive last time I looked. I know their name from woring in industry. They were expensive even 25 years ago pricing!

Neil.

[MrAl]

Thanks Al. Appreciate the education and the help.

I will look into the equipment you mention. The Fluke meters were horribly expensive last time I looked. I know their name from woring in industry. They were expensive even 25 years ago pricing!

Neil.

Hi,

Yeah in all the years ive worked in electronics i never bought a single Fluke. ive always managed to find something good but less cost. i also compared readings with more expensive stuff and they always come out very very close.
Often you dont even need absolute accuracy either just repeatability. If you read 12.8v on Monday you want to be able to measure 12.8v on Friday if it really is the same voltage on both days.