Warm alternator when engine is cold

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Warm alternator when engine is cold

July 27, 2020, 10:13:28 pm

As you may remember, I changed my alternator from hehr power line 15 to car quest hd 28si on my 1991 grand villa

I thought it was working fine. But Today when I was cleaning the coaches. I Just realized that the alternator is warm all the time. This reminds me when I was driving few days ago from shop to storage place, the voltage meter jump between 12 to 14 constantly.

What could be wrong? Do I have a bad alternator again?
Thanks

Re: Warm alternator when engine is off

Reply #1 – July 27, 2020, 10:42:26 pm

I just solved a problem with the battery discharging quite a bit overnight and going flat after a few days. There was a load somewhere but I could not figure out where. Everyday the alternator belt would squeal when I first started it. I was having problems with the AC/heater blower so decided to change the solid state resistor where it mounts on the blower under the hood. After I removed the air filter for the AC, I pulled the connectors and reached down to pull the unit off, it burned my hand. It had gone bad and was constantly using juice, not enough to run the fan, but enough to drain the battery. It comes on a direct line from the battery, no ignition switch, no fuse.

So, after reading this $%%$, you could have a rogue regulator on the alternator. Check to see if it's using any juice when everything is turned off.

Pierce

Re: Warm alternator when engine is cold

Reply #2 – July 27, 2020, 10:45:26 pm

Pierce,

Very ODD. The dash HVAC fan is normally wired to an ignition-hot circuit.

For it to be on with the ignition off is puzzling???

Re: Warm alternator when engine is cold

Reply #3 – July 27, 2020, 11:29:41 pm

So you're saying the alternator could be bad?

the alternator was bought from advanced auto parts about a month ago.

I will bring to the shop and let them check out. Hope it is still under warranty.

Re: Warm alternator when engine is cold

Reply #4 – July 27, 2020, 11:53:14 pm

Hard to figure out at this distance but here is the quote: I thought it was working fine. But Today when I was cleaning the coaches. I Just realized that the alternator is warm all the time.

All I'm saying is that if the engine is cold and the alternator is warm, there has to be a reason. Seems simple to check in the morning to see if it indeed is warmer than the surrounding components. If it is, the only think causing it to be warm would be electricity flowing to ground somewhere in the alternator. Should not be difficult to check with it in place.

Pierce

Re: Warm alternator when engine is cold

Reply #5 – July 28, 2020, 07:22:59 am

jiaxinxi,

We need to do some investigating and need more info before we can say the alternator is bad. You say that the voltage is swinging from 12 to 14 volts. This leads me to think the alternator is working.
Do you still have a battery isolator?
If so you need to check it to see if one of the diodes have failed?
If you have an isolator did they sell you a DUVAC alternator?
(This is not a brand this is how the alternator sees it needs to go to work, it will have a place for 4 wires to hook up)
If not a DUVAC alternator how did you hook it up to work?
Sounds like you are back feeding into the alternator and it is just figuring out where it is coming from.
The swinging voltage could be caused by a bad connection on you sense wire.
In other words you may be dealing with 2 problems that will need to be sorted out.

Mike

Re: Warm alternator when engine is cold

Reply #6 – July 28, 2020, 08:41:43 am

Suggest getting a DC clamp meter for your toolbox.

Amazon.com: Extech MA445 True RMS 400A AC/DC Clamp Meter with NCV: Home...

This one has a low current - 40 amp range, good for measuring parasitic current draw.

I would measure current on all wires before pulling alternator.

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.

Re: Warm alternator when engine is cold

Reply #7 – July 28, 2020, 09:24:50 am

To start with, disconnect the wires one at a time and then watch and listen when you touch the wire back to the terminal. You may find that one of the wires sparkes a little. That will tell you where to go from there. How manys wires does it have?

Pat,

Re: Warm alternator when engine is cold

Reply #8 – July 28, 2020, 09:38:46 am

Quote from: Pamela & Mike – July 28, 2020, 07:22:59 am

jiaxinxi,

We need to do some investigating and need more info before we can say the alternator is bad. You say that the voltage is swinging from 12 to 14 volts. This leads me to think the alternator is working.
Do you still have a battery isolator?
If so you need to check it to see if one of the diodes have failed?
If you have an isolator did they sell you a DUVAC alternator?
(This is not a brand this is how the alternator sees it needs to go to work, it will have a place for 4 wires to hook up)
If not a DUVAC alternator how did you hook it up to work?
Sounds like you are back feeding into the alternator and it is just figuring out where it is coming from.
The swinging voltage could be caused by a bad connection on you sense wire.
In other words you may be dealing with 2 problems that will need to be sorted out.

Mike

The alternator is not DUVAC. There are three wires Positive/Negative/Sense Wire. The positive connects to the middle post of the isolator, Negative connects to the ground. Sense wire connects to the isolator post which connects to the engine battery. I really don't see any other way of connecting to alternator.

Quote from: pthurman48 – July 28, 2020, 09:24:50 am

To start with, disconnect the wires one at a time and then watch and listen when you touch the wire back to the terminal. You may find that one of the wires sparkes a little. That will tell you where to go from there. How manys wires does it have?

Pat,

Three wires, Positive/Negative/Sense Wire
What do I need to do next when I identify the wire sparks?

Re: Warm alternator when engine is cold

Reply #9 – July 28, 2020, 09:59:04 am

Make sure your sense wire is connected to the S post on the alternator.

Re: Warm alternator when engine is cold

Reply #10 – July 28, 2020, 10:05:30 am

Unfortunately, the person that recommended the 28si didn't give you all the information needed to use it in an RV with a diode isolator. Here is my post from 3 years ago with the Delco tech bulletin instructions to use a 28si with a diode isolator.

DelcoRemy 28SI alternator

Re: Warm alternator when engine is cold

Reply #11 – July 28, 2020, 10:15:02 am

Here are some suggestions I put together. I wonder if your '91 originally had the ignition diode like mine did. Do you know if there is an "excite" wire near the alternator, maybe no longer connected?

Leece Neville Alternator went---again

Re: Warm alternator when engine is cold

Reply #12 – July 28, 2020, 10:16:55 am

Here is how I connected the alternator.

Positive / Negative / and sense wire

Re: Warm alternator when engine is cold

Reply #13 – July 28, 2020, 11:33:34 am

We need to verify if your 3rd wire is sense or excite. On my '91 there was no sense wire, I had to add one.

Maybe JohnFitz a fellow '91 owner can comment on his alternator wiring.

From what I can tell, Foretravel wired some '91 U300s to use a "Delco" type truck alternator, and used the excite diode as shown in my schematic, with no sense wire.

If it is wired as a sense wire, it will have 12v with key off. If it only has 12v with key on it is an excite wire.

Re: Warm alternator when engine is cold

Reply #14 – July 28, 2020, 11:35:58 am

Here is a 200 amp zero voltage loss isolator with connections to power the alternator when ignition comes on. ~$120.
Victron Argofet Battery Isolator

You lose about 3/4 volt going through the diodes on the OEM isolator.

Re: Warm alternator when engine is cold

Reply #15 – July 30, 2020, 05:32:05 pm

Just measured the voltage. When engine is off, positive measured at 12.6V. Sense wire measured at the same 12.6V
It is not that warm as I last touch it. Just barely.

Probably going to be another shop visit

Re: Warm alternator when engine is cold

Reply #16 – July 30, 2020, 08:47:43 pm

Think that you need to do what P Fleming said get the correct isolator.

Re: Warm alternator when engine is cold

Reply #17 – July 31, 2020, 12:37:30 am

I hope my addition to this thread might help.

Our coach broke down just north of Las Vegas. Flat bedded into the Cummins dealer in North Las Vegas.

Required a ECU x change. We left the coach and drove back to Orange County.

Shop finished the repair while we were home. Then moved the coach week ago into their storage lot.

No hookups. Parked.

We are not able the get back to get our coach till next week.

Two weeks without power.

With an isolator the engine batteries could be discharged if something was a unexpected draw on the engine side.

Ah this is the advantage of a combiner and a solar panel system.

When they moved the coach outside the solar will auto combine both banks and keep both banks up fully charged.

Rare stuff but reality strikes.

Should have two fully charged battery banks on our retrieval next week

Re: Warm alternator when engine is cold

Reply #18 – July 31, 2020, 11:11:08 am

Solar does not need a combiner to charge both the house and start batteries. Lots of smart ways to make this happen without a combiner.

Re: Warm alternator when engine is cold

Reply #19 – July 31, 2020, 11:36:26 am

Separate solar systems for the battery banks would work with separate charge controllers.

All new coaches come with combiners.

I like the combiner also for its starter lug option that if it is wired in when it gets a signal from the adjacent starter relay during cranking it disconnects the banks automatically to show the start batteries true condition.

The combiner bolts in where the isolator was. And it's operating switch replaces the boost switch.

No wiring needed. But the lights do not work that confirm it's actions this way but it is audible when it works.

I killed three different chassis battery chargers and 2 sets of chassis batteries before the solar and combiner

Oh and it consumes no power when engaged versus the 3amp load from the boost solenoid.

Yes it's more money than a isolator.

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