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alternator fail light


 Jim McGarvie
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This morning right after start the alternator fail light came on and stayed on except for a few brief periods. I checked the dash voltmeter and it was reading 14V, higher than its usual 13.5V. When I came to a stop a few miles later I turned off our new solar system, thinking maybe there was some kind of conflict. Sure enough, on the way home the alternator fail light never illuminated and the voltmeter was reading as usual.

We recently installed the solar system so I’m not accustomed to it yet. Is this behavior normal? Should I turn the solar system off when driving?

Thanks.

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32 minutes ago, Jim McGarvie said:

This morning right after start the alternator fail light came on and stayed on except for a few brief periods. I checked the dash voltmeter and it was reading 14V, higher than its usual 13.5V. When I came to a stop a few miles later I turned off our new solar system, thinking maybe there was some kind of conflict. Sure enough, on the way home the alternator fail light never illuminated and the voltmeter was reading as usual.

We recently installed the solar system so I’m not accustomed to it yet. Is this behavior normal? Should I turn the solar system off when driving?

Thanks.

Jim, I'm not sure how you connected your solar system.  Most connect to the house batteries only.  Unless you have added something to your Knight, they didn't charge the chassis battery from shore/generator/solar power.  What you are describing is a known phenomenon with Monaco coaches when there are two different charging sources, one being the main engine alternator.  Usually this is reported by people who are running their generator at the same time while motoring down the road.  It is not something to be concerned about, once you confirm the second source.  It seems you have done that, and it is solar.  I'm wondering if you intended to connect the solar to the chassis battery, versus the house battery.  Or do you have some additional way to charge both the house and chassis batteries from shore/generator/solar? 

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3 minutes ago, waterskier_1 said:

Jim, I'm not sure how you connected your solar system.  Most connect to the house batteries only.  Unless you have added something to your Knight, they didn't charge the chassis battery from shore/generator/solar power.  What you are describing is a known phenomenon with Monaco coaches when there are two different charging sources, one being the main engine alternator.  Usually this is reported by people who are running their generator at the same time while motoring down the road.  It is not something to be concerned about, once you confirm the second source.  It seems you have done that, and it is solar.  I'm wondering if you intended to connect the solar to the chassis battery, versus the house battery.  Or do you have some additional way to charge both the house and chassis batteries from shore/generator/solar? 

Hi Rick. I did connect the solar system to the house batteries. But when the engine is running aren't the house batteries connected to the engine batteries so that the alternator can charge the house batteries?

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2 minutes ago, Jim McGarvie said:

Hi Rick. I did connect the solar system to the house batteries. But when the engine is running aren't the house batteries connected to the engine batteries so that the alternator can charge the house batteries?

Yes, but that is a one-way connection.  That is, the alternator can charge the house batteries, but the house batteries can't get back to the chassis system (so they won't drain the chassis battery).  The higher end coaches did have a bi-directional system (BIRD) that basically did connect the two banks together, once one of the banks exceeded a specific voltage (around 13.5 volts).  That gave priority to charging the battery the charging source was connected to first, then once that battery was charged, it would allow charging of the secondary source.  But I don't think your coach came with that system, unless you have modified it.

 

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5 minutes ago, waterskier_1 said:

Yes, but that is a one-way connection.  That is, the alternator can charge the house batteries, but the house batteries can't get back to the chassis system (so they won't drain the chassis battery).  The higher end coaches did have a bi-directional system (BIRD) that basically did connect the two banks together, once one of the banks exceeded a specific voltage (around 13.5 volts).  That gave priority to charging the battery the charging source was connected to first, then once that battery was charged, it would allow charging of the secondary source.  But I don't think your coach came with that system, unless you have modified it.

 

Interesting. I was thinking it was a simple relay connecting the two battery banks when the engine is running, but it sounds like I was wrong. I will check it out.

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13 minutes ago, Jim McGarvie said:

Interesting. I was thinking it was a simple relay connecting the two battery banks when the engine is running, but it sounds like I was wrong. I will check it out.

Jim, I don't have any wiring diagrams for your era model coach.  I've been looking at some older ones, and I can only find the battery boost relay. That should only connect the batteries together when the boost switch is pressed.  I don't see anything about the alternator charging circuitry in the drawings I have. 

 Do you remember seeing a solid state isolator?  It would have 3 heavy red wires, one from the alternator, one from the chassis battery and one from the house batteries.  

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My 2000 Endeavor has a circuit that energizes the boost relay whenever EITHER system gets above a set voltage. That way, either charging system keeps both house and chassis batteries charged. If both systems drop below a high state of charge it drops out, preventing a load on one system from killing both sets of batteries.

 

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20 minutes ago, Harvey Babb said:

My 2000 Endeavor has a circuit that energizes the boost relay whenever EITHER system gets above a set voltage. That way, either charging system keeps both house and chassis batteries charged. If both systems drop below a high state of charge it drops out, preventing a load on one system from killing both sets of batteries.

 

Thanks for that info, Harvey. Interesting how many different configurations there are.

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Same thing happened to my 2007 diplomat after installing a solar system. I charge the house batteries through a charge controller and when driving in sunny conditions I get the same alternator fail alarm (an annoying buzzer). I've since installed a disconnect switch between the solar panel feed and my charge controller which corrected the problem if I remember to switch it off before driving.

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7 hours ago, gary_van_dyke said:

Same thing happened to my 2007 diplomat after installing a solar system. I charge the house batteries through a charge controller and when driving in sunny conditions I get the same alternator fail alarm (an annoying buzzer). I've since installed a disconnect switch between the solar panel feed and my charge controller which corrected the problem if I remember to switch it off before driving.

Thanks for the input, Gary. It is sounding increasingly like this is normal given the way our coach is wired, so I will do the same as you and turn off the solar system while driving.

3 hours ago, hitechpete said:

Have you set your solar charge controller to the correct battery type, eg: AGM, SLA, Lithium etc.

Yes I did, to correspond to our new AGM batteries. Would that make a difference in the appearance of the alternator fail light? Maybe because the charge voltage is higher for AGMs?

2 hours ago, Bob Nodine said:

This is a common problem and can happen if the inverter/charger or a solar system is charging at the same time the alternator is charging when the house and chassis batteries are connected together.

 

Thanks, Bob. I guess I'll just try to remember to turn the solar system off when driving.

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3 hours ago, Jim McGarvie said:

Thanks for the input, Gary. It is sounding increasingly like this is normal given the way our coach is wired, so I will do the same as you and turn off the solar system while driving.

Yes I did, to correspond to our new AGM batteries. Would that make a difference in the appearance of the alternator fail light? Maybe because the charge voltage is higher for AGMs?

Thanks, Bob. I guess I'll just try to remember to turn the solar system off when driving.

Jim, if you have a system similar to what Harvey describes, then I can see how the solar would effect the Alt Fail signal.  I think you have confirmed that you have no problems with the actual charging and monitoring system that needs attention, by disconnecting the solar when running the main engine.  Another thing that may have done to eliminate this false error is to turn on the headlights.  That additional drain will usually fix the false error, without having to disconnect the solar.  I haven't experienced this problem with my coach, even though I have one 100 Watt (the original Monaco) solar panel connected only to the chassis battery.  But, I also have a way to isolate my chassis and coach batteries so that the alternator does NOT charge (or over charge) my coach batteries.  Remember that I have 1400 Watts of solar, 1300 Watts just for the coach, so I don't need 14.2 Volts from the battery playing bulk charging for 8 hours while driving down the road.  You likely don't have to worry about this, just trying to explain what's going on.  So, if you chassis and coach batteries are not 80% or more charged, when you start the main engine, the solar charger may be in bulk (trying to charge as much as possible to 14.4 Volts) or in Absorption (where it holds 14.4 Volts until current drops below around 1-5 Amps).  That would present 14.4 volts to the alternator regulator, which is trying to drop it down  to below 14.2 volts (Note: this values are representative, not actual for your coach).  This will lead to the Alt Fail circuit falsely detecting an engine alternator problem.  Again, this is more often seen with people who are running their generators down the road to run roof A/C, but that generator also powers the inverter/charger, and, again depending on both batteries state of charge, may provide more voltage to the chassis battery than the engine alternator regulator wants to see.  

I went into more detail than you probably wanted to know, but did so for other reading this so they might know the why behind the mysterious ALT FAIL signal error and what causes it.  I really don't recommend bypassing (removing the ALT FAIL Relay from the FRB) as a solution.   It's better to either turn on the headlights (driving lights if you have them) or, as you say, turn off solar when driving.

 

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1 hour ago, waterskier_1 said:

I went into more detail than you probably wanted to know, but did so for other reading this so they might know the why behind the mysterious ALT FAIL signal error and what causes it.  I really don't recommend bypassing (removing the ALT FAIL Relay from the FRB) as a solution.   It's better to either turn on the headlights (driving lights if you have them) or, as you say, turn off solar when driving.

Thanks Rick. I didn't think about turning on the headlights; I'll give that a try the next time. I agree with you about not bypassing the relay.

BTW, I looked today and I don't appear to have a solid state battery isolator, just a plain, old-fashioned, White-Rodgers relay. There are two trigger wires going to it, and I assume it is used to parallel the battery banks both for charging from the alternator and for the battery boost function.

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