Charging inverter batteries off the alternator

Please clarify-- do you have the "normal" two sets of batteries (HOUSE and CHASSIS) or do you have a third set just for the inverter (very rare)?

Again, if just house and chassis with inverter running off house bank, both should charge from the alternator-- set up this way from the factory.

Mr Wizard, I am NOT running my A/C off the inverter. All I want to do is be able to charge my inverter batteries while driving, Plain and simple. Not being electrical savvy I am just looking for a simple way to do that. I had a Monaco LaPalma that would do that and I am sure that when my MH was new it would do that too, somewhere along the way it must have gotten disconnected. (I bought it in 2009, used) I have the standard setup with 4 six volt batteries to power my inverter. Pianotuna, would you recommend I disconnect the battery isolator to prevent any damage to the inverter?

RoyB wrote:
I have found you CANNOT use a "DIODE BASED" BATTERY ISOLATOR. Those high current diodes have a 0.7VDC voltage drop across them.

Roy Ken

True, But (big but)many/most coaches with diode-based isolators use an alternator with external SENSE WIRE that is connected to the chassis battery terminal of the isolator. So the sense wire is reading post-isolator voltage.

Said another way, the alternator may be putting out 14.9 and the batteries ("downstream" of the diode-based isolator) receive 14.2.

Hi,

If the alternator is 160 amps the most you want to "send" to the inverter batteries, on a continuous basis, is about 40 to 50 amps. I'd suggest a continuous duty solenoid in series with a 50 amp automatic circuit breaker. Use appropriate wire size.

I'd far rather replace the circuit breaker than replace the alternator.

I prefer to be "in control" so I have toggle switches that activate my solenoids. By doing that I have a "poor man's boost system for the chassis battery. It also allows me to "give the alternator a rest" if I feel it is working too hard.

Nascarcruzin wrote:
I had a RV shop wire it for me earlier, but the only used a 100 amp isolator which did not last long. (alt. is 160 amp) I have it hooked up now with a 200 amp battery isolator, but sometimes my inverter goes into a default mode. I am scared it could do permanent damage to the inverter.

I have found you CANNOT use a "DIODE BASED" BATTERY ISOLATOR. Those high current diodes have a 0.7VDC voltage drop across them.

Battery science and my own experience tells me you need around 14.4VDC at around 20AMPS available to charge a deep cycle battery in as little as three hours time. Having this large 0.7VDC voltage drop when using diode based battery isolators drops the charging voltage down to around 13.6VDC and this according to battery science takes around 12 hours to re-charge a deep cycle battery back up to its 90% charge state.

If this is what you are looking to do then the diode based type battery isolator will work for you. To get the deep cycle batteries re-charged any quicker then you must use a SMART MODE RELAY CIRCUIT to switch the batteries into the charging circuit.

No expert here - just what I read and have been playing with over the past many years with my JEEPs camping off the power grids and more recently with the RV Trailer off the power grid camping...

Inverters are very power hungry and you have to respect that... My PSW 1500WATT Inverter requires a 175AMP in-line fuse with the DC Voltage source. Thats alot of power to work with from a battery system.

Roy Ken

your inverter goes into 'Fault' mode?
so what is the fault code ? low voltage ?

how big is your battery bank?

what are you doing? running A/C from inverter while driving?

thats going to overload the alternator and charging system and No it does not save 'gas'

better off to run the generstor to power tne A/C

i know i'm making wild guesses , but you did not provide much info

I had a RV shop wire it for me earlier, but the only used a 100 amp isolator which did not last long. (alt. is 160 amp) I have it hooked up now with a 200 amp battery isolator, but sometimes my inverter goes into a default mode. I am scared it could do permanent damage to the inverter.

A battery combiner like THIS will charge your house batterys from the chassis charging system.

This would be my choice for using my Truck Alternator to also charge my deep cycle batteries. Please read up on how the BLUE SEA SI-ACR smart relay works and see if this may fit your application. The idea here is to NEVER discharge your truck start battery in the process... In the old days we would use diode based BATTERY ISOLATORS but the large DC VOLTAGE drop using high current diodes prohibits proper charging of deep cycle batteries. The difference in 13.6VDC verses 14.4VDC in DC charging voltage is crucial in charging deep cycle batteries in a short time three hour frame.

BLUE SEA SI-ACR SMART RELAY

This is what I was planning on doing for my unique situation of keeping a separate set of deep cycle batteries sitting in the back of my truck to run some high wattage two way radio equipment and also support my OFF-ROAD POPUP trailer operations when camping off the power grid. My battery requirements now is to use 150AH capacity batteries verses the 110AH shown in the drawing.



This is as far as I have got with this project with my worries being will I do harm to my truck alternator system. Never have looked up what size truck alternator I have or asked around if this is a good idea or not.

I see from the BLUE SEA APPLICATIONS this drawing I have is workable but I sure don't want to destroy my truck alternator in the process...

Just food for thought
Roy Ken

Virtually ALL motorhomes charge both HOUSE and CHASSIS battery from the alternator.

So, I would start by troubleshooting the system you already have.