Battery Charging Problems
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From: Colorado
Battery Charging Problems
My battery (idiot) light goes on and I look at the voltage meter on my 1991 F250 7.3Liter Diesel and I notice that the meter is reading below normal. As murph's law would have it my batteries (there's two to turn over the diesel) died. Without much thinking I picked up a lifetime warranty 70 amp alternator from Napa. I installed it last weekend and charge both batteries. The battery idiot light was still on and the batteries drained again. So last night I picked up two Optima batteries and new battery cables too. I installed them this morning and the battery light is still on. I drove back to Napa to have them test the alternator. They said they couldn't since it was still in the truck. I'm fine with that and will do it once I can grab a ride up to Napa from a friend. In the mean time I was wondering if you guys have any advice.
Thanks,
Bart
Thanks,
Bart
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Joined: Apr 2004
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From: Lafayette, IN
A 70 amp alternator sounds kinda small for 2 batteries. Many of the newer dual-battery setups run a 130ish amp alternator. Plus, charging dead batteries with your alternator is a bit of a strain--it's better to pull the batteries and put them on a trickle charger for half a day to a day each. I'd also check all the wiring between your batteries and starter, to make sure you have good wiring and good connections. A weak connection could be arcing which is a huge power loss.
Jason
Jason
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From: Langhorne, PA
Go to NAPA beg them to return the old alt. You need a 3rd gen alternator. It is worth it, even if you are stuck with the new 70A alt and have to sell it for what you can get on Ebay.
You need an alternator that works, if your old alternator has an external fan under the pulley, and two plugs, I know for sure that is a lousy product.
Go to Sears( or whoever) and let them test the charging system, if the alt is bad, exchange it at NAPA for a third gen, if they don't know what you're talking about, then go to a professional starter/alternator rebuilder.
The only problem is that you will have to rewire the alternator connections. The original set-up won't work, one plug has to be cut off. there is a tech article about 3rd gen alts at fordfuelinjection .com
The 3rd gen alt that fits your bracket is good for 100A, it has better parts in it and a smaller pulley, to produce the juice you need. As long as you don't have any major electrical accesories this alt is fine.
You need an alternator that works, if your old alternator has an external fan under the pulley, and two plugs, I know for sure that is a lousy product.
Go to Sears( or whoever) and let them test the charging system, if the alt is bad, exchange it at NAPA for a third gen, if they don't know what you're talking about, then go to a professional starter/alternator rebuilder.
The only problem is that you will have to rewire the alternator connections. The original set-up won't work, one plug has to be cut off. there is a tech article about 3rd gen alts at fordfuelinjection .com
The 3rd gen alt that fits your bracket is good for 100A, it has better parts in it and a smaller pulley, to produce the juice you need. As long as you don't have any major electrical accesories this alt is fine.
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From: Colorado
Thanks for the replies guys. I checked the alternator, there is only one plug on it. It's a rebuild from Bosch, so it should be up to the task... who knows though. This truck has 301K on her and she did it all with the original alternator, which was a 70 amp alternator. I'm guessing 70 amps is enough if it lasted this long, and with the optima red tops (http://www.optimabatteries.com/publi...e/starter.html) batteries being brand new I feel fairly certain I've good batteries.
ALL of the cables are new as well. There's two negative cables, one from each battery that grounds to the engine block as well as the body. And the positive cable is one large cable that runs from driver side battery to the passenger side battery and then to the starter. So I should be good from this perspective as well.
Hopefully it is just the alternator and a bech test from Napa will show that. If the bench test comes back and says the alternator is OK I'm basically lost in the dark... can't imagine what else it could be.
bart
ALL of the cables are new as well. There's two negative cables, one from each battery that grounds to the engine block as well as the body. And the positive cable is one large cable that runs from driver side battery to the passenger side battery and then to the starter. So I should be good from this perspective as well.
Hopefully it is just the alternator and a bech test from Napa will show that. If the bench test comes back and says the alternator is OK I'm basically lost in the dark... can't imagine what else it could be.
bart
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From: Langhorne, PA
If the original alternator made it 300K, that is amazing! 
It seems that the 90 and 91 electrical systems are different than trucks built before and after those two years, according to Haynes. (A bit of trivia)
I am assuming that NAPA gave you the exact same alt, and you compared them side by side before leaving the store.
A couple questions. What transmission is in the truck?
Is the voltage regulator attached to your alternator(internal reg) or mounted elsewhere, perhaps on the firewall or fender?
There are two alts available according to the Haynes manual, a standard alt with external reg. and a 165A Alt with internal reg.
I guess you have an external reg, since you say the alt in your truck has one plug. Now, I wonder if it is a bad reg, I didn't notice in the posts if you had changed that.
These are the color wires I see in the Haynes manual if it helps:
Alternator;
1 Battery - Black/orange
2 Field - Orange/Light Blue
3 Stator - White/Black
Regulator:
1 Charge Meter( instrument cluster) - light green/red
2 Field - orange/light blue
3 stator - white/black
4 "A" terminal - yellow/white ..this wire has a radio noise suppresion capicitor on it
It seems that the 90 and 91 electrical systems are different than trucks built before and after those two years, according to Haynes. (A bit of trivia)
I am assuming that NAPA gave you the exact same alt, and you compared them side by side before leaving the store.
A couple questions. What transmission is in the truck?
Is the voltage regulator attached to your alternator(internal reg) or mounted elsewhere, perhaps on the firewall or fender?
There are two alts available according to the Haynes manual, a standard alt with external reg. and a 165A Alt with internal reg.
I guess you have an external reg, since you say the alt in your truck has one plug. Now, I wonder if it is a bad reg, I didn't notice in the posts if you had changed that.
These are the color wires I see in the Haynes manual if it helps:
Alternator;
1 Battery - Black/orange
2 Field - Orange/Light Blue
3 Stator - White/Black
Regulator:
1 Charge Meter( instrument cluster) - light green/red
2 Field - orange/light blue
3 stator - white/black
4 "A" terminal - yellow/white ..this wire has a radio noise suppresion capicitor on it
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From: Colorado
Thanks 924x2150.
Napa did give me the same alternator, it was clocked 90 degrees off, but that's not big deal I guess. My tranny is the E4OD (it's been rebuilt twice and isn't in the best of shape now unfortunately). The voltage regulator is on the fender, I replaced that on Sunday and it didn't help. It's looking like I should take it for a diagnostic check at Napa. I'll let you know what happens.
bart
Napa did give me the same alternator, it was clocked 90 degrees off, but that's not big deal I guess. My tranny is the E4OD (it's been rebuilt twice and isn't in the best of shape now unfortunately). The voltage regulator is on the fender, I replaced that on Sunday and it didn't help. It's looking like I should take it for a diagnostic check at Napa. I'll let you know what happens.
bart
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Aren't diesels 24v systems? ie - one battery has neg to ground and the positive to the neg of the other battery...
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From: Colorado
Well get a load of this. My $100 positive battery cable jumped out of the retainer loop and rubbed up against the vacum pump belt. The cable was shredded so I replaced it again but this time put an electrical tie around the cable and retainer loop. But still, the system is not charging. I really feel like I have replaced everything. Cables/Batteries/Alternator/Voltage Regulator. I still haven't taken the alternator back out to have Napa bench test it. I'll have to do that next week. I'll let you guys know what happen.
Thanks
Bart
Thanks
Bart
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From: Colorado
I'm back at it! Took the alternator off and had Napa bench test it. It turns out that it was a bad alternator. So they replaced it and we bench tested it before leaving the store. I installed the working alternator and the system still isn't charging 
So, just to review:
1 - 2 New Batteries
2 - 2 new negative battery cables
3 - 1 new positive battery cable
4 - 1 new voltage regulator
5 - 1 new alternator
I put a voltage meter between a ground and the positive lead on the alternator and it's getting 12.4V, which sounds right to me. I was wondering if there's anyone that knows what they voltage should be to the alternator. Also, am I missing something?
Thanks,
Bart
So, just to review:
1 - 2 New Batteries
2 - 2 new negative battery cables
3 - 1 new positive battery cable
4 - 1 new voltage regulator
5 - 1 new alternator
I put a voltage meter between a ground and the positive lead on the alternator and it's getting 12.4V, which sounds right to me. I was wondering if there's anyone that knows what they voltage should be to the alternator. Also, am I missing something?
Thanks,
Bart
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From: Langhorne, PA
All I can say is you want 13.6 volts at the battery terminals when the engine is idling fast. If there is anything over 13 vdc at the batteries I would disregard the gauge and try and run the truck.
I forget why I asked you what tranny you have
I lost my "tranny of thought" 
Have you been able to use the starter to crank the engine, I would like to eliminate the starter as a culprit.
REmove the battery wires and unplug the regulator, make sure that the yellow/white wire to the reg, is not shorted to ground, there is a capacitor on that wire and it should read open to ground.
PS the Haynes has the 1991 E4OD Diesel truck as having a 165A alternator.
The Haynes is probably wrong
PS Make sure your trailer harness isn't shorting to chassis behind the truck.
Good Luck, and stop buying so many parts
I forget why I asked you what tranny you have
I lost my "tranny of thought" Have you been able to use the starter to crank the engine, I would like to eliminate the starter as a culprit.
REmove the battery wires and unplug the regulator, make sure that the yellow/white wire to the reg, is not shorted to ground, there is a capacitor on that wire and it should read open to ground.
PS the Haynes has the 1991 E4OD Diesel truck as having a 165A alternator.
The Haynes is probably wrong
PS Make sure your trailer harness isn't shorting to chassis behind the truck.
Good Luck, and stop buying so many parts
Last edited by 924x2150; Jun 6, 2005 at 09:34 PM.
Fleet Mechanic
Joined: Nov 2003
Posts: 1,372
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From: West Cornwall, CT
It might be time to figure out if the alternator is providing any output. The easy way to do this is to take a voltage reading between battery positive and ground with the engine off. Expect about 12.4 volts if the batteries are charged. If so, the batteries are OK.
Start the engine and take voltage readings at the same spot. You shoud see 13.5 volts or better at idle. Voltage should increase a bit as you run the engine up to a fast idle. If the voltage does not increase, the alternator is not charging. It sounds like this is the case.
If the alternator is not providing any output, the problem could be with the alternator, voltage regulator or wiring from the regulator to the alternator. You replaced just about everything and if all of the new stuff works there probabaly is a bad connection between the regulator and alternator.
Lou Braun
Start the engine and take voltage readings at the same spot. You shoud see 13.5 volts or better at idle. Voltage should increase a bit as you run the engine up to a fast idle. If the voltage does not increase, the alternator is not charging. It sounds like this is the case.
If the alternator is not providing any output, the problem could be with the alternator, voltage regulator or wiring from the regulator to the alternator. You replaced just about everything and if all of the new stuff works there probabaly is a bad connection between the regulator and alternator.
Lou Braun
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From: Colorado
It starts right up so I think we can rule out the starter. Here's the various VDC readings with the negative voltage meter cable grounded to the frame and positive cable touching the positive terminal on the passenger side:
engine not started: 12.30VDC
engine at idle: 12.26VDC
engine at 1500 RPM: 12.24VDC
engine at 2000 RPM: 12.21VDC
So from where I'm standing it looks like I'm charging at all and as the RPM's go up I'm using more and more volts.
This is my first time dealing with the electrical side of trucks at this level of detail, so any advice will be appreciated.
Thanks,
bart
engine not started: 12.30VDC
engine at idle: 12.26VDC
engine at 1500 RPM: 12.24VDC
engine at 2000 RPM: 12.21VDC
So from where I'm standing it looks like I'm charging at all and as the RPM's go up I'm using more and more volts.
This is my first time dealing with the electrical side of trucks at this level of detail, so any advice will be appreciated.Thanks,
bart
Fleet Mechanic
Joined: Nov 2003
Posts: 1,372
Likes: 14
From: West Cornwall, CT
The voltage readings you took show that the alternator is not charging the batteries.
If your '91 alternator setup is like my '95, you should have one large terminal at the back of the alternator with a heavy gage wire leading from it to the batteries. This wire also has a built-in fused link which will blow if there is a short anywhere. Your diesel probably has two links, one for each battery. I'd check for continuity between the alternator output terminal and each battery positive post.
There should also be a smaller plug-in terminal on the side of the alternator. The terminal actually connects to the voltage regulator that is mounted on the alternator itself (at least on my '95). This terminal connector leads to the ignition switch and to the idiot light that shows if you are charging. I think this connector also provides field excitation to the alternator to make it charge. Check to make sure that this connector is fully installed.
With luck, this problem is being caused by a poor connection.
Lou Braun
If your '91 alternator setup is like my '95, you should have one large terminal at the back of the alternator with a heavy gage wire leading from it to the batteries. This wire also has a built-in fused link which will blow if there is a short anywhere. Your diesel probably has two links, one for each battery. I'd check for continuity between the alternator output terminal and each battery positive post.
There should also be a smaller plug-in terminal on the side of the alternator. The terminal actually connects to the voltage regulator that is mounted on the alternator itself (at least on my '95). This terminal connector leads to the ignition switch and to the idiot light that shows if you are charging. I think this connector also provides field excitation to the alternator to make it charge. Check to make sure that this connector is fully installed.
With luck, this problem is being caused by a poor connection.
Lou Braun