I know I'm missing something since this seems too easy, but if I have a motorhome, and install a second alternator via a third party bracket (namely a 360 amp one), I can feed that alternator's output directly to the house batteries for not just charging, but for inverter use when the engine is running?The alternator has protection against overcharging, so it will run until the batteries get to 14.7, then start floating.Assuming I have the proper wire gauge, are there any issues that might pop up?

sure you canyour going to need multiple strands of "2 aught" cable or maybe something largerunless you fuse the cables near the alternator, for the max rating, of the smaller cable runissue number one will be power you rob from the engine to drive this humongous load your thinking about, the strain on the belts and the additional load the engine cooling system and pulleysnothing that can't be solved, IF you throw enough money into all the heavy duty OTR parts needed for the job

The theory sounds workable to me, in general. I might think about rejiggering the battery isolator system so that the house and chassis batteries are not tied together while the engine is running, though that's probably not essential. I'd also make sure that the new alternator is rated for continuous heavy-duty use; many are really only designed for intermittent heavy loading, and that's not what you're proposing.Do make certain the regulator sense wires are connected to the batteries that the respective alternator outputs are going to. It would not be good to have the alternator sensing the chassis voltage while powering the house system."Proper wire gauge" is going to be quite heavy.

What is wrong with the system now?I would be more inclined to put 500 watts of solar on the roof. Will still charge on the road but more importantly the battery will tend to stay at a higher charge level before you even roll.

Since the house batteries are one alternator, the chassis on another, they have no contact with each other. I plan to keep them this way, just so an electrical fault with the RV part won't affect the engine or drivetrain.Catastrophic fuses go without saying. I like having those on all the main paths, just so that a short doesn't mean a swath of pure destruction.00 wire makes sense, I was even thinking of 000 wire, just so voltage losses are minimized.As for load, at idle, the secondary alternator sits at 160 amperes, so it isn't too much drag. It is present, but it isn't anything out of spec for the engine.This is for a custom class "B" motorhome, and 500 watts of solar will be difficult to place on the rig, unless I go with a portable solar rig, which I don't really have room for.

mlts22 wrote: I can feed that alternator's output directly to the house batteries for not just charging, but for inverter use when the engine is running?I guess I'd be wondering.. when do you expect to use an inverter with the engine running?

Using an alternator to feed your house batteries?

34 Replies

time2roll
Nomad
Feb 23, 2015
Harvey51 wrote:
I can't imagine these high currents! If I needed that much power i would be looking for a higher voltage to reduce the current. What voltage do electric car batteries use?
Traction battery is close to 400 volts.
They still use a small 12v to run the computer, maintained with a 3 stage DC/DC converter.
Fubeca
Explorer
Feb 23, 2015
Anecdotal alert:

I lost my alternator after towing 9 hours with two depleted gc2s. I don't know if it was just it's time or if the extended draw trying to charge the house batts back up contributed. The truck had ~115000 miles - but I don't know if the alt. was original.
Harvey51
Explorer
Feb 23, 2015
I can't imagine these high currents! If I needed that much power i would be looking for a higher voltage to reduce the current. What voltage do electric car batteries use?
time2roll
Nomad
Feb 23, 2015
MEX, I think they are 200 each for 600 total.
And most likely they will derate 50% at continuous load.
MEXICOWANDERER
Explorer
Feb 23, 2015
rtz549 wrote:
Put triple 600 amp alternators on it. It should be good.

http://www.nationsautoelectric.com/gmtriplet.html

I am aware of ZERO alternators in that frame size whose rectifier heat sink can withstand more than 180-amperes continuous. Rectifiers are rectifiers and they dro X amount of voltage. Most of the people doing the R&D in those specialty shops can't find their --- with both hands and a flashlight. They didn't like it back when I was doing research and evaluationand had to tell them - no way Jose.

There are no free lunches with alternator design. Wind enough ampere-turns in the rotor and it'll fry any OEM voltage regulator. Hand wind a stator to the max using quarter-gauge wire sizes and it's four hour each job which means getting them wound in Tijuana. Trash the original stator laminations and use laser cut Tempel Temcor steel. Then an EXTERIOR rectifier has got to be utilized.

Who are these idiots trying to kid?
time2roll
Nomad
Feb 23, 2015
pnichols wrote:
MrWizard wrote:
i have said in many posts, i think RV's should come with two independent alternators for the two different DC systems in the RV
Off topic ... but when one comes to think about it, many motorized (ClassA/B/C) RVs kindof do have two different DC systems.

Valid discussion as the OP expressed concern that an issue of one system could affect the other.

I don't think this is a real issue to worry about as there should be some isolation. Alternators are pretty reliable these days. Mine only lasted 184,000 miles and 13 years. Plenty of other stuff that could go first including trading the entire RV.
DrewE
Explorer III
Feb 23, 2015
JnJnKatiebug wrote:
I don't know about your setup but my chassis batteries and house batteries are in the same compartment. Lot's of knowledgeable people here so why can't you just make a short heavy duty jumper cable out of welding lead and connect the two sets of batteries while you were driving. This looks like a way to charge them from time to time when power was not available.

That's essentially what a standard battery isolator does. The solenoid version, in particular, is pretty much exactly that: a suitably heavy connecting cable, with a switch that turns on when the engine is running, connecting the house and chassis batteries together.

Actual jumper cables with clamps and such would not be a wise idea because of the potential for human error (forgetting to remove them, installing them incorrectly, etc.); because of sparks when removing them which could be very dangerous if there was any hydrogen gas buildup in the battery compartment; and because of the possibility of them vibrating loose and grounding out, causing a high-current short circuit.
JnJnKatiebug
Explorer
Feb 23, 2015
I don't know about your setup but my chassis batteries and house batteries are in the same compartment. Lot's of knowledgeable people here so why can't you just make a short heavy duty jumper cable out of welding lead and connect the two sets of batteries while you were driving. This looks like a way to charge them from time to time when power was not available.
pnichols
Explorer II
Feb 23, 2015
MrWizard wrote:
i have said in many posts, i think RV's should come with two independent alternators for the two different DC systems in the RV

Off topic ... but when one comes to think about it, many motorized (ClassA/B/C) RVs kindof do have two different DC systems.

For example: Our Class C has it's chassis battery and coach batteries directly connected together (all three in parallel with each other) whenever the main engine is running. Hence, the main engine's - and only - alternator could completely fail and the coach batteries could then backup the chassis battery, with these batteries in combination supplying all of the motorhome's 12V DC power needs. The built-in motorhome generator could be left running while driving to keep all the batteries charged when underway.

With this kind of systems setup, a failed alternator need not leave an RV stranded.
rtz549
Explorer
Feb 22, 2015
Put triple 600 amp alternators on it. It should be good.

http://www.nationsautoelectric.com/gmtriplet.html