Community Forums

Just4Fun20 · 11-30-2020, 09:12 AM

I do see a few references to this so perhaps it's OK...

When I start the rig (2018 Aspire... 450HP Cummins) I put it in "fast idle". Often, the alternator light is on and the voltage is 12ish volts (normal for 'not charging'). I wait 1-3 seconds and the voltage jumps up to "normal" and the light goes out. Is this normal? ...or is it a sign of an impending failure?

We typically spend a week at a time in a location so, sit a week, then start (just FYI).

Thanks in advance.

wolfe10 · 11-30-2020, 09:15 AM

In cold conditions, the ENGINE INTAKE MANIFOLD HEATER can remain on even after engine start. It is a huge draw and can well exceed alternator output at even high idle speed.

If all returns to "normal" after a few minutes (after the intake manifold heater turns off) all is fine.

dave&ginny · 11-30-2020, 10:31 AM

I've never had that happen. You might want to call one of the cummins service shops and ask them.

twinboat · 11-30-2020, 10:58 AM

Quote:

Originally Posted by dave&ginny

I've never had that happen. You might want to call one of the cummins service shops and ask them.

Same engine ?

twinboat · 11-30-2020, 10:59 AM

What your seeing is normal.

Jose67 · 11-30-2020, 11:21 AM

Not normal. It sounds as if one or more of the rectifiers in the alternator field has gone, not allowing the full 170 amps output from the alternator. If it was my issue, I would remove and rebuild my alternator (new bridge rectifiers, field brushes and voltage regulator) and replace the engine batteries for good measure.

The air horn heater cycles on and off as necessary. So, the voltmeter reading should go down then up as needed then stop and go up to 13 v. DC nominal. Good luck.

Alpine36 · 11-30-2020, 11:32 AM

Engine pre heater is more than likely causing this, normal situation on a cold start.
If this happens on a warm restart then you might have a problem.

brobox · 11-30-2020, 11:48 AM

It is normal. It is the DEF heater and intake manifold heater that draw a lot of amps on startup. The explanation came straight from Cummins when I asked the same question on my 14. DEF heaters and excessive current draw on startup was something new to me.

Hayman · 11-30-2020, 12:11 PM

I agree upon start up there is voltage fluctuation due to manifold heater but I've never gotten an alternator warning light . Just my .02 cents but I would get the alternator tested !

YC1 · 11-30-2020, 01:00 PM

Any chance you are connected to shoreline when this happens?

I agree that the intake heater is a monster draw and just for kicks, hold the aux start button down while starting and for 20-30 seconds after to see if you get the same symptoms. I would not worry a bit about your alt light. I think things are operating normally.

**Lt Dan** · 11-30-2020, 01:32 PM

Is it the alternator light or a low voltage warning? I get the same thing when starting mine but it's a low voltage warning due to the grid heater.

kevinantholt · 12-01-2020, 08:20 AM

It is Normal. I have the same issue since I bought the RV New. (Same Year and Model as you) Your Alternator is fine. It's what the others have said. Intake manifold heater is on. As soon as it turns off you can see your voltage goes back up to charging. Mine usually takes about 30 seconds or so. I live in WA state so no extreme cold, but if you are in a colder state the heater may stay on longer.

HarleySG · 12-01-2020, 10:37 AM

Normal for me as well, and I’m in Colorado.

clyde1949 · 12-01-2020, 07:59 PM

Quote:

Originally Posted by Just4Fun20

I do see a few references to this so perhaps it's OK...

When I start the rig (2018 Aspire... 450HP Cummins) I put it in "fast idle". Often, the alternator light is on and the voltage is 12ish volts (normal for 'not charging'). I wait 1-3 seconds and the voltage jumps up to "normal" and the light goes out. Is this normal? ...or is it a sign of an impending failure?

We typically spend a week at a time in a location so, sit a week, then start (just FYI).

Thanks in advance.

Thats normal