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Old 06-19-2018, 03:52 PM   #26
ZVOLV
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Everything I've seen says a good alternator should be putting out around 14.5v. Also it says 14v on the sticker.



Nope.
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Old 06-19-2018, 04:18 PM   #27
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if everything is working correctly then over-tightening the belt won't make any difference

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I thought it must be the pulley slipping since jacking up the belt tension made an improvement, but the paint marks haven't moved.
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Old 06-19-2018, 04:59 PM   #28
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There are a few places where you could get a large voltage drop in the charging system. It may be time to do some of the voltage drop checks that z always suggests. To charge the battery the B+ wire on the alternator goes to the starter. Then uses the positive battery cable to connect to the battery to charge it. Anywhere along that path could affect what ends up at the battery. Also the ground on the alternator goes to the block. Where it connects to the block is a spot to check. Then the block ground aka negative battery cable provides the negative side of the circuit to charge the battery and run everything. So the block ground from the negative battery cable is another spot where you can have a sneaky voltage drop.
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Old 06-19-2018, 07:12 PM   #29
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The voltage drop test is legit! I mostly use it for slow crank diag on modern v8 trucks that intermittent slow or no crank.

By using jumper wires and running a redundant ground/power like suggested is also a great way to rule out the cables. It's worth busting out the meter and doing a few voltage drop tests, especially in the ground side. I wouldn't want to see much more than. 100 or 200 mv drop on the cables. Read up on how to do it. I'm not gonna tap it all out.

All that being said, if your battery is up in the 13's, it's charging. I wouldn't chase your tail too much on this one. You may find poor crimps using a volltage drop test and find much more current by replacing tired old corroded cables. Especially that alt ground cable that fails all the time. Especially on a greasy 240 down low covered in oil.
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Old 06-19-2018, 09:38 PM   #30
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Nope.
My other car makes 14.5v at idle with a 55a Bosch alt and an even bigger battery than in the wagon.

I cleaned all the main connections (Starter motor and battery ground) and replaced the alternator ground. One of the first things I did was a voltage drop test.

But yeah, I'm not really sweating about it anymore. Makes enough juice to run everything and charge the battery.
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Old 06-20-2018, 04:16 PM   #31
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What did your voltage drop say?
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Old 06-20-2018, 11:44 PM   #32
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Originally Posted by philski o'flood View Post
over-tightening the belt won't make any difference
Except for premature alternator bearing failure. I use some sort of belt dressing on a cleaned belt. An old candle has so many uses, including this and as a dry lube of house door strikers!

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Originally Posted by dl242gt View Post
the block ground from the alternator
Beefing up that wire gained my 760T .5v under light and heavier load.

Also, the dash gauge reads low compared to a DVOM under the hood.
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Old 06-21-2018, 03:02 PM   #33
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What did your voltage drop say?
Just did one. .2v drop on positive, .5v negative with everything turned on at idle. The alt ground cable is a lot skinnier than the positive, I bet beefing it up would help a little.
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Old 06-21-2018, 03:54 PM   #34
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500 millivolt drop is a lot. When I check battery cables, I do a clear flood crank and if they read more than 250 millivolts the cables get replaced. They usually look great too.

I would replace that ground wire and repeat.
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Old 03-09-2019, 11:29 PM   #35
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Well I think the Desno just died. Good belt tension, very little resistance to pos/neg terminals, battery light works normally. Light turns on with ignition and goes out with startup even though the Denso produces no power at all.

What options are out there for a Denso sized or smaller alternator?
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Old 03-10-2019, 11:22 AM   #36
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Never seen a Volvo alternator put out 14.5V. 13.5-13.8 with no load. And my Denso 100 amp alternator works very well- pulled from a junkyard years ago- a nice upgrade.
You should have a ground from engine to body that is the same gauge as the battery cable.
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Old 03-10-2019, 11:40 AM   #37
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Bosch 100 amp alternator from 1992 940 Turbo on my 1988 760 charges at 14.2 volts. No issues with cold winter starts. Using group 40R battery meant for a Ford. Group 40R is an International spec battery with 11 inch long case without end mounting lugs or carry handle.
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Old 03-10-2019, 12:17 PM   #38
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14.2 in Indiana. 14.5 in Connecticut. Never 14.5 in Georgia. Makes sense, since charging voltage is adjusted by temperature.
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Old 03-10-2019, 01:01 PM   #39
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Never seen a Volvo alternator put out 14.5V.
My diesel did. I'm probably gonna use the 55a alt from that.
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Old 03-10-2019, 01:32 PM   #40
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Denso 100a unit in my 240 did have a broken regulator. It happens. Car ran fine with it just low-ish voltage and idle was unstable.
Idle is 14.2v now and sometimes drops from low alternator rpm (under drive pulley). Ground and positive cables new, I think I used 16mm² or 25mm², that's awg 6 or 4. Good enough for the 100 amps the alt puts out, though slightly thicker would not have hurt. Voltage drop positive or negative connection to battery is minimal.
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Old 03-10-2019, 01:40 PM   #41
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The dash voltmeter is a useless diagnostic tool, with the Volvo's craptastic electrical system.

You have to check the voltage at the battery.
Rubber mounted alternators are notorious for breaking the ground wire as are wrenches who forget to install the ground wire.
The dash grounds suck and it is common to see dash voltage gauge drop with the AC on or high defrost.

I have found interconnects on the main harness melted due to the use of spade connectors.
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Old 03-10-2019, 02:06 PM   #42
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Nevermind. Found a crappy connection in the exciter circuit at the firewall connector. 14.20v at idle now.
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Old 03-12-2019, 10:37 PM   #43
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Nevermind. Found a crappy connection in the exciter circuit at the firewall connector. 14.20v at idle now.
Great! Thanks for sharing the solution.
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Old 03-13-2019, 12:26 PM   #44
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Nevermind. Found a crappy connection in the exciter circuit at the firewall connector. 14.20v at idle now.
You could pull that exciter wire off of the alternator, once it started charging, and the charging voltage would remain the same as it would be with it connected well. I think maybe you checked the 14.2 with the motor still cool. Check again after that alternator gets warmed above the exhaust manifold for a while, you might find it closer to 13.8V. Unlike some Delco systems of yore, the small wire in a Volvo is a stimulus for initial field current, rather than a sense wire in a voltage regulator. Try it.
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Old 03-19-2019, 05:16 PM   #45
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Quote:
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Nevermind. Found a crappy connection in the exciter circuit at the firewall connector. 14.20v at idle now.

well all righty.
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