Another apu problem :(

Jenny · Sep 29, 2014

We have a Carrier Proheat apu. It is now randomly charging the batteries at 14+ Volts. Other times around 13.6ish. There is no rhyme or reason to it either. Sometimes while the microwave is running it is charging 14+ others it goes to 13.3. Anyone ever have this issue? If so, how'd you fix it?

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davekc · Sep 29, 2014

I'm not sure there is anything to fix. You are showing a charge at those numbers. Numerous things affect that number. Condition and charge of the truck batteries, ambient outside temperature, draw on the system for other components etc. If it only showed 12v or under while on, then you have a alternator out, bad wiring, or bad batteries. If running the ac, between the compressor and the external condenser fan, they both are pulling some juice off the system.

Jenny · Sep 29, 2014

But why would it show charging 14+ using the ac or microwave and 13.5ish not running it?

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Dynamite 1 · Sep 29, 2014

because of the different load being taken from the batteries. also could have a regulator on the apu alt. going bad. loose connection ?

tknight · Sep 29, 2014

alternator demand will vary with load, also you ma have corroding connections, requiring the alternator to output more, as loads increase.

davekc · Sep 29, 2014

Could be several things. I would check it with a meter at several points to see what readings you are getting. Since many don't have one, I would get a confirmation another way.
With truck engine off, turn the key to activate just your dash gauges. Turn generator on and monitor readings off of your dash. Turn off and monitor again to see if the readings are the same as your gauge on the unit. Some will give you different numbers if you are reading from the inverter rather than the unit itself. By using the truck gauge, you are bypassing the information supplied by the unit.

Turtle · Sep 29, 2014

Voltage is pressure through the wires, like water pressure through pipes. There is a direct correlation between temperature and voltage pressure needed to charge the batteries - the lower the temp the higher the required voltage. There is also a correlation with resistance (not just colder means more resistance), both in the cables and connections but with the internal resistance of the batteries themselves. Throw in another variable like a high amp draw and you need higher voltage pressure to put the amps back into the battery. The state of charge of the battery (above or below 90% charged) and the age and condition of the battery (sulfated or not) will play a role.

When associated with these cause and effect variables, "randomly" is not the word I'd use to describe it.

Anything above 13 volts is charging. Closer to 13 volts is more of a maintaining or float charge, and closer to 14.4 volts is bulk charging. If it drops below 12.9 for extended periods of time (and it's not 100+ degrees outside) or if its bouncing between,say, 13.0 and 14.6 volts every few seconds, then you might have a connection of alternator problem. Otherwise it's mostly normal what you are seeing.

Jenny · Sep 29, 2014

Thanks turtle.I understand that a bit better. I had just never noticed it doing that before today.

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iceroadtrucker · Sep 29, 2014

Jenny I got one your good. PS if you want to run your Microwave do some justice turn the truck on. If you run your Comfort Pro but don't have the heavy duty Alt then Id turn the truck on. When it does go out do yourself a favor live alittle and get the heavy duty one. Alt only last short time maybe 2 years if you got a good one maybe longer. Depends on how much the APU is used and what kinda loads u put on it like Big Power Microwaves. A 700 watt not so bad but I know a few that use 1500 watt and larger and woof there go the Batteries and the Alt. Have a nice day.

jamom123 · Sep 29, 2014

Jenny said:
We have a Carrier Proheat apu. It is now randomly charging the batteries at 14+ Volts. Other times around 13.6ish. There is no rhyme or reason to it either. Sometimes while the microwave is running it is charging 14+ others it goes to 13.3. Anyone ever have this issue? If so, how'd you fix it?

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Hi Jenny, where are you reading your voltage from? Inverter, control module, truck dash, voltage meter etc.

Jenny · Sep 30, 2014

Inverter read out

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jamom123 · Oct 1, 2014

Jenny said:
Inverter read out

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Does the apu display ever read under voltage?

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Jenny · Oct 1, 2014

Nope

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davekc · Oct 1, 2014

On the surface, it sounds like your unit is ok.

jamom123 · Oct 1, 2014

I would check the wiring, I wouldn't think it would be your altenator simply because you said you can run the microwave and it doesn't show low voltage. Do you know if your inverter has a direct connect to a single battery or pulls from all batteries?

Jenny · Oct 2, 2014

I believe it is all of them, but not sure, nick would know. I personally think it is a battery issue due to something that happened during a pm on the truck.

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guido4475 · Oct 2, 2014

iceroadtrucker said:
Jenny I got one your good. PS if you want to run your Microwave do some justice turn the truck on. If you run your Comfort Pro but don't have the heavy duty Alt then Id turn the truck on. When it does go out do yourself a favor live alittle and get the heavy duty one. Alt only last short time maybe 2 years if you got a good one maybe longer. Depends on how much the APU is used and what kinda loads u put on it like Big Power Microwaves. A 700 watt not so bad but I know a few that use 1500 watt and larger and woof there go the Batteries and the Alt. Have a nice day.

That is why I have always preferred and bought an APU that are a "True" generator. Not one that uses the trucks batteries as a power source for powering an inverter. I like the idea of a completely "stand alone" unit with the exception of the fuel to feed it, and a wire to start it, and keep the truck batteries up to charge when needed.That way, wear and tear on the trucks electrical system is kept to a minimum, and put on the generator instead. Plus, if you are broke down and immobile, a generator that is using the trucks electrical, or heating and a/c system may not be able to be used as well because of the breakdown cause. Just a thought.

jamom123 · Oct 2, 2014

Jenny said:
I believe it is all of them, but not sure, nick would know. I personally think it is a battery issue due to something that happened during a pm on the truck.

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I'm not 100% sure but i'm thinkin it's either wiring or battery problem like you said. The apu seems to be fine if it wasn't putting out enough voltage it would let you know. Good luck.

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