Electrical/alternator problem

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Electrical/alternator problem

February 12, 2012, 01:02:17 pm

I need some expert help.

After driving about 2 hours this AM, my voltage readings dropped to 12.2V. That is, the dash gauge (confirmed by the VMSpc) and the audix display both went to about 12.2.

Boost switch was not on; inverter was on running 2 laptops; headlights were not on, but had been on for first hour; Aquahot was on diesel with only the bay thermostat on (so two radiators on active); dash heat/defrost on. I believe the batteries to have been fully charged at outset.

I turned on the generator. That brought the audix (house batteries) reading up to the usual 14V or so. When I switched on the boost that brought the dash and VMS up to 14.1V also.

I drove 30 min or so before turning off the boost to see what would happen. Dash and VMS read 14.1V, as they should, until I stopped about an hour later.

Is the 12.2V reading I got the alternator output? If the engine/alternator was off, the dash would read the engine batteries and the audix would be reading the house batteries. But, how could the alternator output be 12.2? Is there a most-likely culprit here?

Thanks,
Mike
2003 U-295

Re: Electrical/alternator problem

Reply #1 – February 12, 2012, 01:33:27 pm

It does appear that the alternator or the voltage regulator that are driven by the engine are not delivering a charge voltage to the starting battery. One easy way to test this is to turn off BOOST and anything that is driven by the starting battery (headlights, dash radio, etc) and measure the voltage at the starting battery terminals; then start the engine and measure again. Be sure you are on the terminal and not on the clamps.

If the engine-driven charging system is working you should see a slow increase in battery voltage over time... a tenth of a volt (or so) every minute or two.

If there is no slow increase then check the house batteries without the boost on. Since the engine-driven alternator will charge both sets of batteries these, too, should either show a full charge (if fully charged) or a slow increase in voltage at the terminals while the engine is on.

If the house batteries increase slowly but the starting battery does not (and remains low) then you probably have either a bad battery or a disconnect in the charging system wiring between the alternator and the battery bank. Check the connections at the battery. Is the battery voltage as measured on the wires the same as measured on the battery terminals? If not, then you have a connection problem.

If you are not seeing a slow voltage increase on either battery bank with the engine running (and the batteries not fully charged) then follow the system back and measure at the alternator output (being careful to avoid getting tangled up in belts and pulleys). This point should read pretty close to the same voltage at the battery terminals. If it reads higher then there is a disconnect between the battery and the alternator. If it reads the same (e.g.: no increase in measured voltage over a few minutes' time) then it seems likely there is a problem with the alternator. These can be checked easily on a test stand at most places that service vehicle electrical systems.

I think I've run through all the permutations here... but if I haven't I'm sure someone will notice and let us know.

Good luck,
Craig

Re: Electrical/alternator problem

Reply #2 – February 12, 2012, 01:52:18 pm

Actually, the easiest place to check voltage is at the DIODE BASED ISOLATOR. Check for 14+ VDC at the IN wire from the alternator with the engine running. And around .6 VDC less at the OUT to the house and chassis batteries.

Brett

Re: Electrical/alternator problem

Reply #3 – February 12, 2012, 02:39:24 pm

Thanks for the quick response.

I had checked the voltage at the isolator before I shut down and both legs showed 14+. Unfortunately, I didn't stop and check it when I had the problem; remember that my gauges went back to the proper 14.1 after I had driven a while.

Since then I found a loose connection at the house battery terminal on the isolator. I don't see how this would create the problem though, since the alternator is reading (regulated by) the voltage from the engine batteries and that connection at the isolator is solid. Both battery banks seem fully charged and the isolator seems to be working properly.

Thanks a lot for your help.
Mike
2003 U-295

Re: Electrical/alternator problem

Reply #4 – February 18, 2012, 01:31:52 pm

Quote from: wolfe10 – February 12, 2012, 01:52:18 pm

Actually, the easiest place to check voltage is at the DIODE BASED ISOLATOR. Check for 14+ VDC at the IN wire from the alternator with the engine running. And around .6 VDC less at the OUT to the house and chassis batteries.

Well... as luck would have it, our weekend camping trip was canceled for two reasons... the first was that the campground was not open as the web page suggested and second our house AND engine batteries were clearly not charging while we were driving the 68 miles to the (closed) campground. We had also discovered that the service station where we tried to re-fill our propane tank (1/4 full) had no way to connect to our tank and the propane distributor (Ferrelgas) was closed on Friday. Running the generator charges the batteries (even the engine batteries with BOOST on) but we were low on propane. So we turned around and drove the 68 miles back home and got there just before dark. It's a free camping spot with electriicity!!! We plugged in, made dinner, watched a movie and went to bed.

Ahh... the joys of motor homing.

So my question is... where is the diode isolator on a '93 U225? Is it the assembly mounted on the bulkhead forward of the battery bank with the circuit breakers?

Craig

Re: Electrical/alternator problem

Reply #5 – February 18, 2012, 06:14:35 pm

The isolater on my former 93, U225 was behind the drivers side rear wheel mud flap. It was an aluminum veined box with several large battery cables and was bolted to a piece of sheet metal along side of the boost solenoid. Open the back bay door on the drivers side a look up and to the left.

Re: Electrical/alternator problem

Reply #6 – February 18, 2012, 06:21:41 pm

Be aware that a failed diode based isolator can be wired around to get you home. Just connect all cables/wires to one terminal.

Be sure to mark where they came from and return them to their original location when after you turn off the engine.

Brett

Re: Electrical/alternator problem

Reply #7 – February 20, 2012, 07:48:44 pm

Quote from: Kent Speers – February 18, 2012, 06:14:35 pm

The isolater on my former 93, U225 was behind the drivers side rear wheel mud flap. It was an aluminum veined box with several large battery cables and was bolted to a piece of sheet metal along side of the boost solenoid. Open the back bay door on the drivers side a look up and to the left.

Kent... that is exactly where I found mine; thanks for the tip. I can't see any obvious problems but I did discover that there is zero voltage at the alternator where the large red cable terminates. There are four terminals on the diode isolator; does anyone know where they go (nothing is marked). There is also a small solenoid. I am wondering what purpose the solenoid serves in the system. Normally zero voltage at the alternator would make me pretty suspicious that the alternator itself is faulty but with all these diodes and solenoids in the circuits (and no schematic) I am not as certain. On my pickup with the same engine (but different alternator) I have 13vdc at the alternator... but no diodes/solenoids.

Anyone know where to buy a replacement alternator if it comes to that?

Craig

Re: Electrical/alternator problem

Reply #8 – February 20, 2012, 08:30:29 pm

When you checked for voltage was the engine running? With the engine running there should be around 14 volts at the large red positive terminal on the altenator and if it has a small red wire going to the regulator on the altenator it should have battery voltage on it and that is what excites and measures voltage for the regulator. the isolator terminals has one that goes to the house batteries. the center terminal should be from the altenator which you should be able to determine by the voltage and one of the terminals goes to the chassis batteries. the fourth terminal I think has a jumper to one of the other terminals on the isolator

Re: Electrical/alternator problem

Reply #9 – February 20, 2012, 08:35:13 pm

Quote from: red tractor – February 20, 2012, 08:30:29 pm

When you checked for voltage was the engine running? With the engine running there should be around 14 volts at the large red positive terminal on the altenator and if it has a small red wire going to the regulator on the altenator it should have battery voltage on it and that is what excites and measures voltage for the regulator. the isolator terminals has one that goes to the house batteries. the center terminal should be from the altenator which you should be able to determine by the voltage and one of the terminals goes to the chassis batteries. the fourth terminal I think has a jumper to one of the other terminals on the isolator

Yup... the engine was running... zero volts to the large red connector on the alternator. I did not measure the voltage to the small red wire. I'll recheck this tomorrow with the information on the isolator. Thanks for the info. But it does look like alternator to me right now... interesting in that it looks like a relatively new alternator too.

Craig

Re: Electrical/alternator problem

Reply #10 – February 20, 2012, 09:02:02 pm

I believe the 4 terminal isolator is made for a dual alternator system. I think FT used them because they are larger and can handle more amps. On my coach the two center terminals were jumpered together with the alternator connected to one of them. The two outside terminals were connected to house and chassis batteries respectively.

Re: Electrical/alternator problem

Reply #11 – February 21, 2012, 12:20:12 am

Craig, Any good alternator/starter shop can bench test your alternator in just a few minutes. Please be aware that FT uses 4 wire alternators and some shops are not familiar with them. FT can provide you with a wiring diagram probably. These good shops can also rig a common GM "J" Frame alternator to work as a four wire in an emergency, I have one as a spare that cost me two hundred bucks.
IMHO Alternator problems are mainly caused by charging into batteries that are depleted or very low in voltage. My practice is to use boost switch for a few hours to see that chassis batteries are charged before starting, that way the alternator is not stressed in trying to charge battery after depletion from starting effort. This may not be a scientific explanation but in practice it has worked for me.

Gary B

Re: Electrical/alternator problem

Reply #12 – February 21, 2012, 12:26:41 am

Gary... thanks for that tidbit... I had not known they were 4-wire alternators. I'm sure I can find a shop around here somewhere that can test the alternator. Not especially looking forward to removing it. If someone catches me in the act I'll have to marry the engine.

If all my joints bent properly it wouldn't be too bad.

Any idea what that solenoid below the diodes is for? I was kinda hoping that was the problem.

Craig

Re: Electrical/alternator problem

Reply #13 – February 21, 2012, 12:33:32 am

Craig, Not sure about yours but in general you will find TWO solenoids near Isolator, One is starter solenoid and the other is the boost solenoid. Test is easy, if it won't start suspect start solenoid, if you turn boost on you should hear a click on one solenoid. IN A PINCH if solenoid is bad you can jump terminals with your jumper cable ( one of them ). OR you can connect both heavy cables together to get home. Also newer solenoids will have two small posts, if so all you have to do is run a ground wire from one post to a reliable;e ground.
When removing an alternator tape off or otherwise insulate each wire and cable as you take them off and mark them. Nasty burn can result if you ground the positive cable and if you reverse them on install you can fry a new alternator.
ON EDIT, Four wire alternators are also termed EXTERNALLY EXCITED.
Gary B

Re: Electrical/alternator problem

Reply #14 – February 21, 2012, 12:40:12 am

One of the two small terminals must have voltage when ignition is on and no voltage when ignition is off. If voltage is missing, alternator output voltage will be zero. The 'other' small terminal is connected to start battery and will always have about 12.6-volts.

Re: Electrical/alternator problem

Reply #15 – February 21, 2012, 09:36:46 am

Craig, sending this drawing may help some in identifying the wires.

Re: Electrical/alternator problem

Reply #16 – February 21, 2012, 11:38:46 am

Quote from: Bobby Carter – February 21, 2012, 09:36:46 am

Craig, sending this drawing may help some in identifying the wires.

Thank you, Bobby!!! That diagram is a great help! It appears that there may be no exciter voltage. I'll recheck it today.

Craig

Re: Electrical/alternator problem

Reply #17 – February 27, 2012, 12:08:11 pm

I had to wait for the weekend so the DW could help me; she turned the ignition key on and off (and started the engine once) while I checked voltages.

There is 12.2vdc at the alternator's "ign" post when the ignition key is turned on. But when the engine is started there is still no voltage at the output of the alternator.

Unless there is some other issue I don't know about, I'm thinking that the alternator is defective and needs to be replaced or rebuilt. Anyone have an "alternative" theory? Is there a voltage regulator somewhere that could account for this?

These are Leece-Neville alternators (externallye excited) and I've found a 4833LGH alternator for $319 on eBay. It's rated at 185amps. This alternator has mounting ears 180-degrees apart (12 o'clock and 6 o'clock). It's hard to see the arrangement on my Cummins but it looks like it's the same. Any ideas?

I'd hate to parcel out $319 (plus shipping) only to discover that it's something simple. On the other hand, I'd have a spare alternator, at least.

Craig

Re: Electrical/alternator problem

Reply #18 – February 27, 2012, 12:40:56 pm

Craig,

My advice would be to call Leece-Neville and ask for the name of the nearest authorized alternator shop certified by them.

We have a different alternator, but that is exactly what I did. They recommended a shop near us-- all they do is overhaul alternators-- have 6 employees doing just that.

Generally less than 1/2 the price of a new one and no shipping. New bearings, brushes and fix whatever is wrong with the electrical part (such as diodes). Could it be something more major-- sure, but not real likely. Certainly worth them checking it out for you.

Brett

Re: Electrical/alternator problem

Reply #19 – February 27, 2012, 04:40:37 pm

Brett... that sounded like a great idea and so I launched into a search for Leece-Neville's home site. There are tons of Leece-Neville distributors and resellers but I couldn't find any reference to their home site or factory authorized repair facilities. So I just called a local shop and they agreed that it was the alternator and probably a blown diode.

So I'll have to remove the alternator. This should be fun. I think I'll hire a local mechanic off craigslist to help since crawling around over and under the engine bay is no longer my cup of tea. Worth hiring a young guy to do that. One ad says he just had his first kid and needs the extra bucks.

I do need to get the alternator off so I can decide whether to get it rebuilt and re-installed or just buy a new one and use the rebuilt one as a spare.

Thanks for the help... and if anyone knows the mounting details of the alternator on the Cummins 5.9L 1993 U225 engine that would be handy.

Craig

Re: Electrical/alternator problem

Reply #20 – February 27, 2012, 07:37:08 pm

I had an intermittent problem with my alternator and finally found the self resetting circuit breaker for the exciter voltage was going bad. It would go off and on and finally failed completely. $3.00 later and a few minutes to replace the circuit breaker and the problem is solved.

Re: Electrical/alternator problem

Reply #21 – February 27, 2012, 08:32:52 pm

Craig, I believe the alternator on my 89 GV was probably the same or very similar to the one on yours. It exhibited the same exact issue you're having. 0V at the + terminal. I had a rear engine radiator so removing the alternator wasn't nearly as enjoyable as the side radiator rigs. Anyway, I decided before pulling the entire alternator I'd replace the voltage regulator since that's just a couple screws. Bingo, worked like a charm and was much cheaper. Think it ended up being $20 - $30 or something like that.

Good luck!
Benjie

Re: Electrical/alternator problem

Reply #22 – February 27, 2012, 09:47:16 pm

Benjie... yes... the rear radiator makes removing the alternator a PITA. Does anyone happen to know where the voltage regulator might be in a '93 U225? I'm willing to give that a try.

Thanks,
Craig

Re: Electrical/alternator problem

Reply #23 – February 27, 2012, 11:23:52 pm

Craig, it's on the alternator - Removal and installation of the 102200 Voltage Regulator.

FYI... I believe Leece Neville has a new PN for it, but if you take it off and take it to any alternator shop they should be able to match it with a new one. At least that's all I had to do with mine!

Re: Electrical/alternator problem

Reply #24 – February 27, 2012, 11:35:53 pm

In my opinion, it is always better to rebuild my existing alternator to eliminate problems trying to match up which replacement to use. But it is important to find an 'old fashioned' alternator/starter rebuild shop. Every part can be easily replaced and the total will be less than a new unit. We have had ours rebuilt several times. Last year's rebuild, I asked for a voltage regulator that has an external screw driver adjustable voltage regulator, which has helped keep charging voltages in line during 100 degree days.

I also ran a new circuit breaker protected voltage sense wire directly to start battery bank from our inverter panel.

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