Battery/Charging issues...still...

Retired MVS Contributor · Post by **Retired MVS Contributor** » 27 Nov 2010, 07:07

You still have a problem, but don't waste your time researching that 214 mv drop...It is well within spec...The instructions you followed said that drop should be no more than .2 volts...That equals 200 mv, and the 14 microvolts more is insignificant...It is so small that it could be meter error...

You said that your ohm meter readings were >1 ohm...That means MORE than 1 ohm...Was that I typo on your part, meaning it was really <1 omh (less than 1 ohm) or did it realy read >1 ohm?...This is important because if it was more, it means you have located a problem...

Jerry

Post by **Pauloil** » 27 Nov 2010, 07:19

I agree the volt drop is close and would use that criteria alone.
haven't read anywhere about how useful measuring resistance is. I do recall using ohm meter in the past to check and find bad spark plug wires. I used to figure wires were ok if the ohms were 6-9.

zhenya · Post by **zhenya** » 27 Nov 2010, 07:26

Yes, resistance was LESS than 1 ohm. Sorry!

Last cable to test is that B+ cable - anyone know where that terminates?

Post by **precopster** » 27 Nov 2010, 07:53

Pauloil wrote:I agree the volt drop is close and would use that criteria alone.
haven't read anywhere about how useful measuring resistance is. I do recall using ohm meter in the past to check and find bad spark plug wires. I used to figure wires were ok if the ohms were 6-9.

Remembering the formula of Ohm's Law from electronics trade school V(voltage) = I(current) x R(resistance) therefore ideally maximum voltage occurs when resistance is at its lowest ie zero ohms. Anything higher than zero ohms is expressed as a negative value for example 100 ohms is expressed as .01 ohms ( if memory serves me correctly)

If cables had 6-9 ohms with that much current being drawn by the forever flattening battery going through them they would use energy and heat up in no time. And if you have 6-9 ohms over three feet I can guarantee you will have 12-18 ohms over six feet. That's a lot of voltage drop!! Zero or under 1 ohm ohm cables are always best.

Post by **Pauloil** » 27 Nov 2010, 08:53

precopster wrote:
Pauloil wrote:I agree the volt drop is close and would use that criteria alone.
haven't read anywhere about how useful measuring resistance is. I do recall using ohm meter in the past to check and find bad spark plug wires. I used to figure wires were ok if the ohms were 6-9.
Remembering the formula of Ohm's Law from electronics trade school V(voltage) = I(current) x R(resistance) therefore ideally maximum voltage occurs when resistance is at its lowest ie zero ohms. Anything higher than zero ohms is expressed as a negative value for example 100 ohms is expressed as .01 ohms ( if memory serves me correctly)

If cables had 6-9 ohms with that much current being drawn by the forever flattening battery going through them they would use energy and heat up in no time. And if you have 6-9 ohms over three feet I can guarantee you will have 12-18 ohms over six feet. That's a lot of voltage drop!! Zero or under 1 ohm ohm cables are always best.

ok. basically that was yrs ago before i knew how to use a meter. I don't know what scale or range I had it on at that time, but used the resistance values obtained to find a bad wire once. what I have read in volvo information about testing low alternator output is the first thing to do is voltage drop testing on the cables.

Post by **JRL** » 27 Nov 2010, 10:31

zhenya wrote:Yes, resistance was LESS than 1 ohm. Sorry!

Last cable to test is that B+ cable - anyone know where that terminates?

FUSE BOX, can't miss it.
If the end connector is burned that could be a problem
B+ cables go notoriously bad on 99s and newer for some reason, not so much on 98 and earlier cars.

Retired MVS Contributor · Post by **Retired MVS Contributor** » 27 Nov 2010, 15:42

precopster wrote:
Pauloil wrote:I agree the volt drop is close and would use that criteria alone.
haven't read anywhere about how useful measuring resistance is. I do recall using ohm meter in the past to check and find bad spark plug wires. I used to figure wires were ok if the ohms were 6-9.
Remembering the formula of Ohm's Law from electronics trade school V(voltage) = I(current) x R(resistance) therefore ideally maximum voltage occurs when resistance is at its lowest ie zero ohms. Anything higher than zero ohms is expressed as a negative value for example 100 ohms is expressed as .01 ohms ( if memory serves me correctly)

If cables had 6-9 ohms with that much current being drawn by the forever flattening battery going through them they would use energy and heat up in no time. And if you have 6-9 ohms over three feet I can guarantee you will have 12-18 ohms over six feet. That's a lot of voltage drop!! Zero or under 1 ohm ohm cables are always best.

100 ohms is 100 ohms and .01 ohms is 10 one hundreds of an ohm...That is still greater than zero ohms...No cable or wire can ever be zero ohms, it will always be greater than zero...Resistance cannot go negative...

Most spark plug wires today are resistance wires and the resistance will vary depending on it's length...Many spark plug wires are not wires at all...They have a carbon trace core, and pulling on the wire can stretch it and break the trace...

Jerry

Retired MVS Contributor · Post by **Retired MVS Contributor** » 27 Nov 2010, 15:59

As pointed out, one of those B+ wires goes into the fusebox and will be obvious...It is very important that his wire is in solid condition...Another of those B+ wires goes to the B+ terminal on the alternator...This one is VERY important because if it is not solid the alternator cannot fully charge the battery, even if the alternator is good...You can check it's condition by measuring it's voltage drop...Do this by connecting the multimeter negative lead to the postive battery terminal and the multimeter positive lead to the B+ terminal on the alternator...Voltage drop with the engine running should be fractions of a volt...

Jerry

Post by **precopster** » 27 Nov 2010, 17:01

[100 ohms is 100 ohms and .01 ohms is 10 one hundreds of an ohm...That is still greater than zero ohms...No cable or wire can ever be zero ohms, it will always be greater than zero...Resistance cannot go negative...

Most spark plug wires today are resistance wires and the resistance will vary depending on it's length...Many spark plug wires are not wires at all...They have a carbon trace core, and pulling on the wire can stretch it and break the trace...

Jerry[/quote]

Good point Jerry, My memory served me badly in this case so .001 is the corrct way of expressing it in a formula. For example 1Kohm or 1,000ohms would be expressed in the formula V = I x R as 0.0001
Many meters are not sensistve enough to show that a cable is in fact 0.00015 ohms for example. Gold plated cables get as close to dammit to the ideal zero ohms, that's why they're used in audio applications. They just show 0.00 on the scale if they are digital. If they are analogue meters it's a guessing game. But we are getting way off the beaten track, now.

zhenya · Post by **zhenya** » 27 Nov 2010, 20:20

JRL wrote:
zhenya wrote:Yes, resistance was LESS than 1 ohm. Sorry!

Last cable to test is that B+ cable - anyone know where that terminates?
FUSE BOX, can't miss it.
If the end connector is burned that could be a problem
B+ cables go notoriously bad on 99s and newer for some reason, not so much on 98 and earlier cars.

First place I looked - pic on page 1 of this thread. I don't see anything but some wiring looms. Am I just missing it?

Battery/Charging issues...still...

Re: Battery/Charging issues...still...