Is my alternator dying?

**mongoswede** · 03-24-2011, 08:49 AM

Originally posted by tmckeon88

My series IIA 88 has always run fine but recently I'm noticing some electrical issues. It charges and starts OK, but I can't run many electrical items at once- if I run the radio, it keeps cutting out when the lights are on or when I put the turn signal on. If I run the heater fan, the lights dim and the wipers slow down. Is this a sign that the alternator is not putting out enough amps? I have a negative earth system and an aftermarket Motorola alternator - sorry, I don't know the output of it. It's been in the truck since I've owned it (1994) and probably much longer than that. If I get a new alternator, what do people recommend for some additional output? I find it odd that the battery has been charging fine all along and my charge light does not come on usually. It started fine all through the cold weather this winter. Any thoughts?

Thanks,
Tom

Your description makes me think of a couple of things but in general you are low on available amperage. Alternators don't usually gradually decay....they are more of the give up the ghost and fail variety but anything is possible. It could be a bad internal or external voltage regulator depending on how it is setup. If it was a conversion it may have its own internal regulator that may or may not be replaceable.

How old is your battery? Its possible that your battery is getting weak and the alternator maybe be ok. The Alternator's job is to keep the battery charged and offer that extra electrical oomph when needed. The truck primarily runs off of the battery. When batteries start to go they often don't charge so well and while they may start the truck smoothly they may drag the alternator down.

You could also inspect your battery cables and grounding straps. As these get older they can build up internal resistance and reduce charging output and efficiency. The best cables I have found are the ones I made from 2 gage welding cable. The welding cable is very efficient at conducting electricity. Replace all your ground and battery cables with this beefing setup and be amazed at how much better everything works.

**LaneRover** · 03-24-2011, 09:06 AM

Also check to see if the fan belt that spins the alternator is tight enough.

**bmohan55** · 03-24-2011, 05:04 PM

Mine was dying a slow death like you discribed. I could watch my dash light fade in and out at a stop light, and they reall took a dive when I used turn signals or the blower. I replaced mine with a standard unit from our hosts and those problems went away.

**tmckeon88** · 03-24-2011, 05:20 PM

I think it may well be that my fan belt is not super tight- the alternator is pushed all the way to the end of the adjustment arm but the belt still has nearly an inch of wiggle room on it. It also squeals something terrible when I have the heater running - is the alternator working harder when there's more electrical load?

I don't think I even know what the voltage regulator looks like - I would guess this is an internal VR unit, since there's nothing on the outside. If I get a chance I'll get numbers off it.

Does the alternator offered through our hosts have enough amperage output? Seems like I hear people talking often about Delco aftermarket ones. I don't want to fry my aged wiring but I also think I need more power. I will definitely check and clean my battery connections.

**LaneRover** · 03-24-2011, 05:57 PM

Yes the alternator works harder under a greater load. I would go and get a belt that is slightly shorter - slightly. OR a new belt of the exact same kind come to think of it.

**gudjeon** · 03-24-2011, 07:08 PM

Sometimes, and more times than not, in my experience, is that battery terminals could use a cleaning. I have also seen blown diode(s) ruin alternator efficiency. I know they would usually blow after a week or two of jump-starting someone. Regardless, start with simple stuff first and work your way down the list.

**Donnie** · 03-25-2011, 09:52 AM

Originally posted by tmckeon88

My series IIA 88 has always run fine but recently I'm noticing some electrical issues. It charges and starts OK, but I can't run many electrical items at once- if I run the radio, it keeps cutting out when the lights are on or when I put the turn signal on. If I run the heater fan, the lights dim and the wipers slow down. Is this a sign that the alternator is not putting out enough amps? I have a negative earth system and an aftermarket Motorola alternator - sorry, I don't know the output of it. It's been in the truck since I've owned it (1994) and probably much longer than that. If I get a new alternator, what do people recommend for some additional output? I find it odd that the battery has been charging fine all along and my charge light does not come on usually. It started fine all through the cold weather this winter. Any thoughts?

Thanks,
Tom

If you can turn the alt pulley with your hand you need a new belt. if you have a diode shorted, it will drain your batt. if you have an open diode & good hearing, you can hear a faint whine coming from the alt. either will cause a low output. the description that you have given indicates to me that I would pay first attention to the belt....HTH.....donnie

**Jim-ME** · 03-25-2011, 12:54 PM

I have a voltage gauge that does not show the actual number of volts but has a normal range. When I turn on everything it drops to the lower end of the "scale". When I'm idling the red charge light barely glows but I can see it and it drives me nuts. I've done the amp draw calculations and I'm always less than the 45A the alternator is supposed to put out. I'm thinking that my pulley should be smaller to turn the alt faster but it was the original pulley on the alt that came with my engine. I'm not sure that more alt output is the answer and I'm about the look into a smaller pulley. In short I feel your pain.
Jim

**I Leak Oil** · 03-27-2011, 07:51 PM

What RPM are you idling at Jim? You have a tach on the diesel if I remember right. Where are you taking your signal from?

**Jim-ME** · 03-28-2011, 04:41 AM

It idles at about 675 rpms. There is a sensor on the fuel pipe to the #1 injector which picks up on the fuel pulse in the line.
Jim

**I Leak Oil** · 03-28-2011, 05:52 AM

Was curious to where you were pulling the signal from because you could be reading high. Probably not with one of those systems though. Is 675 rpm in spec for your 2.5? Sounds a little low but is probably fine.

**Jim-ME** · 03-28-2011, 11:46 AM

Thats what Matt Browne set it at so I've left it alone.
Jim

**mongoswede** · 03-28-2011, 06:02 PM

Originally posted by Jim-ME

I have a voltage gauge that does not show the actual number of volts but has a normal range. When I turn on everything it drops to the lower end of the "scale". When I'm idling the red charge light barely glows but I can see it and it drives me nuts. I've done the amp draw calculations and I'm always less than the 45A the alternator is supposed to put out. I'm thinking that my pulley should be smaller to turn the alt faster but it was the original pulley on the alt that came with my engine. I'm not sure that more alt output is the answer and I'm about the look into a smaller pulley. In short I feel your pain.
Jim

In most systems the charge light only comes on when the system is not charging. Perhaps this is different in old Rovers. Typically the charge light connects to the back of the alternator and uses the alternator for ground. The terminal that the charge light connects to has 0 voltage when the engine is not running or before the alternator has excited (induced a field and started to charge). Once the truck starts and the alternator activates then there will be a voltage on that connection point. Because there is now a voltage the lamp light will go out because it no longer has a ground.

Also.....alternators do not typically output their maximum amperage all the time. They react to the current demand as need. So if you have a healthy battery and are not running any electrical items you will run at a lower amperage. If you turn everything on and are loading down the ignition system then you will draw more current and the alternator will respond.

Things to keep in mind:

Running a smaller pulley on an alternator will spin the alternator faster and help generator more charging. However it will also require a good tight belt as it reduces the mechanical advantage of the belt on the pulley.

Alternators do have a maximum rpm that they can run at. In a rover engine it is unlikely you will ever get close to that rpm. but in a higher reving engine it is wise to take note of your alternator pulley diameter to prevent overreving and alternator failure.

Is my alternator dying?

Is my alternator dying?

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