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Old 06-16-2018, 03:52 PM   #1
Cwazywazy
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Default Charging woes

1988 245 turbo with electric fan. Dave Barton wiring harness, about a year old. Basically, I've got a brand new battery and a Denso 100a from Philski. With the old 80a Bosch it'd go up to ~13.5v after starting and then immediately drop to ~12v and go down from there if I used headlights or anything. Same voltage at the back of the alt and the battery terminals. Replacing the brushes/regulator made zero difference. No resistance to ground on the alternator body. Belt tension is fine.

Now with the Denso it's almost exactly the same, except I was getting a steady 13.5+ when it was idling with nothing on, but driving with AC it got down to about 11v. I'm pretty stumped at this point, and a bit mad that I replaced what was probably a good alternator..
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Old 06-16-2018, 04:32 PM   #2
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Is the ground wire at the alternator good?
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Old 06-16-2018, 04:36 PM   #3
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Is the ground wire at the alternator good?
Looks to be good enough, no resistance to ground.
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Old 06-16-2018, 04:48 PM   #4
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To check the alternator ground wire. Put the clip end of a test light to the positive B+ on the alternator and touch the probe of the test light to the alternator case. A resistance check is good but be sure some current will pass through the circuit as well. A light bulb test light not a led one.

13.5v is too low without accessories on. Is this a rebuilt or a good used Denso? I've experienced bad regulators giving low output on the Denso alternators. Plus with the newer batteries a slightly higher voltage set point is good. For example a 14.4 set point or there is even a 14.6v one available on ebay.
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Old 06-16-2018, 05:05 PM   #5
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Good used with new brushes.
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Old 06-16-2018, 06:16 PM   #6
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Definitely not the alt ground.
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Old 06-16-2018, 07:15 PM   #7
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Maybe check for a circuit that is drawing a bit too much current like a window switch stuck or something like that? Stereo amp on? Could be a bad regulator?
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Old 06-16-2018, 07:20 PM   #8
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Maybe check for a circuit that is drawing a bit too much current like a window switch stuck or something like that? Stereo amp on? Could be a bad regulator?
I kinda doubt that I'd have two bad alternators behaving the same way, especially since I replaced the regulator on the first one with no change.
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Old 06-16-2018, 08:46 PM   #9
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.3 ohms between the battery and alternator positive terminals, exciter wire is at battery voltage with key on, battery light works as normal, and 0 ohms between alternator body and negative terminal. I replaced the ground wire cause the old one was looking kinda crappy, but nothing changed.
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Old 06-16-2018, 10:30 PM   #10
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Old 06-16-2018, 10:51 PM   #11
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Revving the engine has zero effect on voltage, if that means anything.
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Old 06-17-2018, 09:43 AM   #12
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IF belts do not slip....
IF you have supplied an additional path to ground for the alternator.... Say from alternator case to the battery via jumper cable AND you have supplied an additional path to B+ at the battery via another nice big lead.... Perhaps the other wire in that set of jumper cables.... And you still get lower then expected voltage with accessories on...

What does that leave for a fault OP?
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Old 06-17-2018, 02:37 PM   #13
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Okay, so I took my extra long crowbar and tightened the crap out of the belts, got a definite improvement. 12.6v with everything on, rises to 13 if I rev it. 13.5v everything off. (Battery was under 12v before starting.) Marked my crank pulley with paint and it doesn't appear to be slipping. A jumper wire from the battery to the alt made no difference.

I think I replaced the belts when I did my engine rebuild, but I'm not sure..
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Old 06-17-2018, 04:05 PM   #14
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Pull the alternator and have it tested at Advance Auto. You are making this too hard. If the wiring is good, the alternator is bad.
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Old 06-17-2018, 06:08 PM   #15
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Pull the alternator and have it tested at Advance Auto. You are making this too hard. If the wiring is good, the alternator is bad.
Yup, you're right. Alt is bad.
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Old 06-18-2018, 01:11 PM   #16
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Check state of health of the battery first.
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Old 06-18-2018, 03:09 PM   #17
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Brand new group 65 battery. Fully charged it and threw on new Dayco belts since the old ones were looking a bit glazed. Still can't get 14v out of it with no load.
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Old 06-18-2018, 05:36 PM   #18
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How is the battery in the multi meter? Have you tried a different meter with a known good battery just to be sure it's not an inaccurate reading?
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Old 06-18-2018, 09:43 PM   #19
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How is the battery in the multi meter? Have you tried a different meter with a known good battery just to be sure it's not an inaccurate reading?
I'm using the volt gauge and a nice multimeter, they both give the same readings.

I've got a solid 13v with the AC and lights on, more like 13.6v with no load, which is good enough for now. I may try replacing the regulator.

Last edited by Cwazywazy; 06-18-2018 at 09:49 PM..
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Old 06-18-2018, 09:51 PM   #20
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Those Densos always go bad for some reason. I stick with the Bosch 100 amp alternators now and haven't looked back.
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Old 06-19-2018, 08:14 AM   #21
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Quote:
Originally Posted by Cwazywazy View Post
I'm using the volt gauge and a nice multimeter, they both give the same readings.

I've got a solid 13v with the AC and lights on, more like 13.6v with no load, which is good enough for now. I may try replacing the regulator.
get one of them fancy adjustable voltage regulators, more expensive up front but modern good quality batteries can charge to a higher voltage than the stock regulator can provide

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Those Densos always go bad for some reason. I stick with the Bosch 100 amp alternators now and haven't looked back.
I want a 100a alternator but I don't want to mess with the stock 80a at this point. It hasn't let me down for a decade, besides a brush replacement
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Old 06-19-2018, 01:12 PM   #22
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Maybe they good bad for you...

but not for the 200 other T-brickers that have got Denso alts from me over the last 14 years I've been hanging around here

The alt he got from me was tested and worked perfect in my 240.

There was something wrong with crazy's charging system before he got the Denso

and now there is still something wrong



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Those Densos always go bad for some reason. I stick with the Bosch 100 amp alternators now and haven't looked back.
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Old 06-19-2018, 01:31 PM   #23
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Originally Posted by philski o'flood View Post
Maybe they good bad for you...

but not for the 200 other T-brickers that have got Denso alts from me over the last 14 years I've been hanging around here

The alt he got from me was tested and worked perfect in my 240.

There was something wrong with crazy's charging system before he got the Denso

and now there is still something wrong
I'm sure you're right, I just can't figure out what's wrong. At least now it's pumping out enough juice to power everything, but I'd still like to see 14v.

I've tested all the wiring and the battery light circuit. All seems to be good. 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, 03:42 PM   #24
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Why do you think 14v is where it should be?
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Old 06-19-2018, 03:51 PM   #25
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Quote:
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Why do you think 14v is where it should be?
Everything I've seen says a good alternator should be putting out around 14.5v. Also it says 14v on the sticker.
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