Voltage drop to alternator '98 V70

[bmdubya1198]

I've been trying to diagnose some electrical issues, and after replacing my alternator, I still have a voltage drop. It's better than before, but it's still not great.
According to Volvo, the voltage drop should be no more than 0.2 V from the battery positive to the alternator.
These are my numbers...

0.07 V at idle with all accessories OFF
0.34 V heat and fan on high, rear defrost on, headlights on, 2k RPM

As for the negative side, it's fine. 0.03 V with the same things on at 2k RPM.

What can cause this 0.34 V drop? Could it be the voltage regulator? I tested continuity on the positive cable, and from battery positive to starter B+, it's about 0.02 ohms. Same reading from bat+ to alternator B+ and starter B+ to alternator B+. So I don't think the cables are an issue. From what I can see, they are in good condition as well.
I tested the alternator with the procedure in the Chilton's manual, and it's good (within 0.5-2.5 V difference between battery voltage, alternator voltage, and alt. voltage w/ load at 1,500 RPM). Like I said, AutoZone tested the alternator as well and it came back good.

[misha]

I allready adviced you to replace b+cable.It goes from battery to starter and from starter to b+ on altermator.Usually the 1st part goes bad...from battery to starter.
That's why a voltage drop test is needed and it is telling you that you have 0.34v of voltage drop on positive side.
It MUST be replaced with 2awg(25mm2) cable or higher.Thinner ones are not even an option.
You can make it yourself or buy Volvo cable....it's your call.

[Herb Goltz]

Replace the positive cable-- you've got a pretty significant voltage drop-- I'll bet that cable gets pretty hot after the car runs for a while-- on my 2000 V70 the pos cable got too hot to hold onto even with a smaller voltage drop. The cable ends may look good on the outside, but they can be corroded inside, causing the high resistance and generating heat.

I would also be inclined to replace the voltage regulator/brush assembly since you've already noted uneven brush wear.

[tryingbe]

#1: I would get the 1/0 gauge welding cables.
#2: 15ft would do all the cables, alternator to starter, starter to battery, engine block ground, chassis ground.
#3: I ground both at the battery, see below pic.
#4: See below
#5: I sanded the block down to get a good surface and just ground.

I upgraded my alternator to starter, starter to battery, battery to ground, and battery to chassis cables with thick 1/0 gauge welding cable. It's at least 70% thicker than stock.

Here are what you want to buy.

http://www.ebay.com/itm/181074818504?ss ... 1497.l2649

http://www.ebay.com/itm/261298170208?ss ... 1497.l2649

http://www.harborfreight.com/hydraulic- ... 66150.html

And two battery terminal that you can get at your auto part store.

With everything on, the voltage drop between the pos of the alternator and the pos end of the battery is now .07 V vs .7 V before.

[abscate]

Lets see,,,adding up your loads I get an estimate of about 204 Watts electrical load at idle - 204 Watts/12 Volts = 17 Amps

Voltage drop on battery cable will thus be 17 Amps * 0.02 Ohms = 0. 34 Volts

What did you measure again??

[bmdubya1198]

I'll go ahead and replace the positive cable then. Probably the voltage regulator as well. Thanks guys!

[bmdubya1198]

Lets see,,,adding up your loads I get an estimate of about 204 Watts electrical load at idle - 204 Watts/12 Volts = 17 Amps

Voltage drop on battery cable will thus be 17 Amps * 0.02 Ohms = 0. 34 Volts

What did you measure again??

I measured the voltage drop between the positive battery terminal and the alternator B+ terminal.

[abscate]

I faked the numbers to appear like I knew what I was talking about.

20 milliOhms resistance is quite a bit in a big cable

[wizechatmgr]

* reads this thread...* Takes note... Guess what I may be doing tomorrow? =p

[bmdubya1198]

I faked the numbers to appear like I knew what I was talking about.

20 milliOhms resistance is quite a bit in a big cable

I should have expected that from you
I'm no electrician, but I thought those equations looked weird.

Now that you mention that though, that does seem low. I was just comparing against the numbers from touching the leads together, and I got the same. But that isn't the most accurate number to compare anything to, and that IS a big cable to not be a perfect 0.

* reads this thread...* Takes note... Guess what I may be doing tomorrow? =p

I haven't changed anything yet, but I would recommend taking a look and testing things! Good preventive maintenance.