Alternator not charging; known good alternator and battery. Any Ideas?

DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
Okay, sorry for the long delay.

The problem was two-fold: bad diodes and bad regulator.

The alternator was draining [shorting] to ground at an equivalent of a ~1.5amp draw. As my 1amp trickle charger couldn't keep up over night it was sucking the battery down.

Additionally, the regulator was not regulating.. so under charging at low rpm [discharging] and overcharging at high rpm [16.5v at 4000rpm].

Luckily my 14cux is still alive!

Thanks to everyone for the angles!

I picked up a used alternator (with good diodes and bearing) with a bad regulator and popped in a new regulator and all is well. It runs up to 14.5v at ~2300rpm and stays above 12.6 at idle.

One other todo:

My shortened belt is a little loose, so I need to get a slightly shorter one.. I think its causing slippage when the alternator is heavily loaded [see: https://discoweb.org/index.php?thre...draulic-power-steering-conversion-done.101124 ]
 

WaltNYC

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Mar 3, 2010
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NYC
Nearly all the manuals you might ever want/need can be found in the google drive folder linked in my signature. have at it
 

RVR OVR

Well-known member
Dec 9, 2004
368
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IL
I chased around smilar issues for over a year. Drove me nuts. I had an alternator rebuilt as well as bought used ones. It would get better then get worse. I was avoiding buying a new alternator because an OEM one was a lot of money and everyone is always all "the ones made in china suck and fail!!!"

I ended up thinking I was getting a deal from Atlantic British and getting an "OEM one" from them for under $200. Turned out it said made in china right on it. I hooked it up and all the problems went away and I am always showing high charge rates. I used to dip down below 12V on my meter when idled at a light with the heater on high, radio, and headlights on. Those problems are no more - zero issues, none.

I think your 12.6 is stil low, but up to you. I would just bite the bullet and get a new alternator from AB to be 100% sure it wasn't a coumpound issue.

Tom
 
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DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
I chased around smilar issues for over a year. Drove me nuts. I had an alternator rebuilt as well as bought used ones. It would get better then get worse. I was avoiding buying a new alternator because an OEM one was a lot of money and everyone is always all "the ones made in china suck and fail!!!"

I ended up thinking I was getting a deal from Atlantic British and getting an "OEM one" from them for under $200. Turned out it said made in china right on it. I hooked it up and all the problems went away and I am always showing high charge rates. I used to dip down below 12V on my meter when idled at a light with the heater on high, radio, and headlights on. Those problems are no more - zero issues, none.

I think your 12.6 is stil low, but up to you. I would just bite the bullet and get a new alternator from AB to be 100% sure it wasn't a coumpound issue.

Tom
While you're route is the right one.. I am a' glutton for punishment.

I agree that 12.6v is too low .. heck, that's essentially the base voltage of the new healthy battery.

I will swap the belt for a tighter one tomorrow and report back. :)

Then it's diodes and the slip rings.
 

DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
Update: New, shorter multi V-belt (7PK1664, GoodYearBelts.com: 1070655) installed. It is a little too tight.. not enough to kill bearings, but enough that the tensioner does not have enough travel to allow it to slip on; I pulled the top alternator bolt and dropped the alt just enough to install it. The tension really wasn't bad so I'll go with it for now.

Unfortunately this did not address the low voltage charging problem. It is certainly charging..but it's just not charging much. With no/light load (highway ~2500rpm @70ish mph) it charged at 14.5 for about 20 minutes and then it dropped down to 12.6 like a switch was thrown.

Also, when I got back from a ~2hr drive I put the thermal-IR gun on the alternator and it was showing 300ºF at the outer stator windings (the ones you can see from the top-center). That seems pretty hot imo... Hell, that's hotter than the exhaust manifold was showing at that stage of cool down. :p

RVR OVR is right, I think I am splashing good money after bad on this one.

Does anyone know of interesting and easy oversized alternators and or smaller (7-rib) pulleys? I wouldn't mind finding a pulley that's 1/4 inch smaller in diameter.
 

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DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
If you have a bad body ground and a good chassis ground the thing could be charging but the difference in ground will affect the voltage the cluster is seeing. I would check your grounds by measuring voltage from battery pos to a body bolt or ground. Then compare that to the reading you get from battery pos to the alternator case. Another thing I do is run the engine and turn on all the loads. Like blower brake lights heated screen heated seats. Lights on high beam. The whole shooting match. Then make those measurements.
Did all that. Grounds are good.

With good diodes and new regulator it is still exhibiting this wonky behavior.

I agree that it acts like a loose ground but everything checks out. Many years ago I had an engine<->chassis/body ground problem [woven copper cable from engine to firewall was overheated and thus heavily oxidized].

Do any of you guys have normal operating temps for the alternator?

I am looking at installing the late d2 alternator for the extra amps [https://www.maniacelectricmotors.com/new150ampalf1.html] and then sorting the tach signal separately.
 

JUKE179r

Well-known member
Sep 14, 2016
767
95
Suffolkshire, UK
No recorded temps for the alternator.
In my 2001 Disco 2 4.0L I installed that specific Bosch 150A alternator for a P38 RR 4.6L Thor V8. No issues for the last 2 years with same fuse, the stock positive battery cables and beefier 0AWG negative ground cables.
 
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DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
I am also looking at this 200amp unit.. but they include an "overdrive pulley" out of the box.. which means they don't know shite about pre-GEMs rovers and their alternator tach signal...


Have any of you dealt with PowerBastards before? Their alternators are all new parts (housing as well)... so it looks interesting (though VERY EXPENSIVE).
 
Hi, there is MF1 that cuts alternator charge to the battery.
The best way to destroy an alternator is by cutting connections when running. Alternator has coils that have an inductive load. When you cut connection, current they generate cannot find an outlet except through "puncturing" one of its rectifier diodes on alternator board. In fact, it is typical way for it to break. For example when brushes wear out and charge is interrupted suddenly, or when ground connection is cut. I would advise never doing tests like the one Discoclay are describing.

Regards
 
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DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
Hi, there is MF1 that cuts alternator charge to the battery.
The best way to destroy an alternator is by cutting connections when running. Alternator has coils that have an inductive load. When you cut connection, current they generate cannot find an outlet except through "puncturing" one of its rectifier diodes on alternator board. In fact, it is typical way for it to break. For example when brushes wear out and charge is interrupted suddenly, or when ground connection is cut. I would advise never doing tests like the one Discoclay are describing.

Regards
Sorry, what did I describe?
 

DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
Well, my used alternator with new regulator is discharging 24/7. So...as per [someone up there^] I capitulated and bought a cheapo new alternator.. it will be here tomorrow. Once this is sorted I will be adding a second alternator, per prior comments, where the power steering pump used to be. I think I can get an identical stocker to fit, and I may try to fit a later 150a model or a delco 1-wire. I will create a new/separate thread for that, when the time comes.

It will look roughly like this (it's leaning forward because it's just pressed against the head with a plastic wrapper):
 

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DiscoClay

Well-known member
Mar 18, 2021
548
119
Chapel Hill, North Carolina, USA
Following up on this post:
I went through THREE alternators (all Magneti Marelli units). It turns out there is alway one diode that just melts.

I made plans to use a non-Magneti-Marelli unit (Thanks to Amazon Vine alternatives crop up occasionally for very low cost) and I acquired a few candidates. Then I bought a GEMS 4.0 from a '97 NAS disco from fellow discoweb member @Korrythelori... which came with a working MM alternator (GEMS MM though)..
It turns out that he ALSO went through three alternators to land on a good one!

The problem with the GEMS MM is that the tach reading is off (high); the pulley looks identical so I didn't measure it and so I current surmise this is due to it being wired differently; if I recall (and I may well be in error.. EE lessons were many, many years ago):
* the difference between a wye config and three independent phases sharing a ground buss is that (with the wye config) the neutral point can carry differential current which effectively balances the phases (their output), whereas independent phases do not balance. The three-independent phases configuration of the MM in the pre-GEMS, 14CUX NAS discos (aka: 1995 only along with a few 94's that snuck in) makes providing a good tach signal challenging when using other alternators.

Anyways, the new-used MM alternator is working fine and I have installed the second, slightly larger alternator (130a) where the power steering pump used to be. The system provides a rock solid 13.8v-14.1 even at bogged idle speeds (~500rpm) with every electrical appliance running (except the winch.. which I will test at some point).

Pics prior to final clean up (everything worked at this point but I was tidying up the fiddlybits): https://discoweb.org/index.php?thre...-steering-conversion-done.101124/post-1140390

It turns out I **still** have something causing a slow drain on the battery though ;-P The next project is to hunt it down and kill it. Then back to the headlights (mentioned in the included thread).
 

kris812

Well-known member
Jun 11, 2014
428
160
Tucson AZ

YT short showing how to find parasitic drains