Dual battery set-up using chassis battery

[ct1500]

Has anyone incorporated their truck's OEM 12v battery with their camper's battery(ies)?

I'm brainstorming a way to do this and would appreciate some input. I'm thinking that if I run large (1/0g) wire from my truck battery to the coach/camper, then I could connect them in parallel, thus turning my truck chassis into a generator.

I think I'd need some sort of D/C to D/C charge manager to put in between the two batteries to make sure the trucks battery doesn't become too depleted.

Any thoughts on whether I could run a large (2000w) true sine inverter using this set-up with the truck's motor running? It'd be nice to run the camper's A/C for short periods of time without buying a Honda 2000Eu.

Appreciate any input! Thanks!!

[pianotuna]

Hi burningman,

Great comments!

For a 440 amp-hour bank

Efficiency

1000 watts demand

88 percent for Pure Sine Wave

1136 watts input to inverter

1136 / 12 volts = 95 amps

based on 440 amp-hour bank, Peukert corrected amps = 147

Run time to dead 3 hours

440 amp hours = 283 available (to dead)

running for one hour may consume 147 amp-hours

battery efficiency is about 90 percent on a new in great shape jar.

147 /.9 = 164 amp-hours to be replaced

164 x 12 = 1968 watt-hours

So those 1000 watt-hours require 1968 watt-hours to be put back into the bank.

The PD converter is only 70 percent efficient so 2812 watt hours are consumed in total to operate a 1000 watt load for one hour.

Overall efficiency appears to be about 36 percent, if the recharging is done from shore power.

Of course, if generator has to be run to do the recharging efficiency becomes even worse.

If you recharge with solar--then things get a LOT more efficient.

[burningman]

I have a Xantrex 2000-watt pure wine wave inverter.
The first thing you need to know about using one is you have to put IN what you get out, plus a bit since things aren't 100% efficient.
2000 watts at 120 volts (the theoretical inverter output) requires about 170 amps input at 12 volts!
The battery specs are one thing, but how much current you get at the other end of the cables is another thing.
Also, a 100 amp-hour deep-cycle battery isn't necessarily good at producing 100-amp sustained output. They're better at producing 1 amp for 100 hours... although in reality you only get about half that because when they're halfway drained they don't make full voltage anymore - plus it's bad for them. So, you need a bank of them, at least two but four is where they start to work well.
You'll need very heavy, VERY SHORT cables.
1/0 gauge long enough to reach your truck battery won't be enough, you really need the inverter to be located right next to the batteries.
I've used 2-gauge, but piled on three sets at once, only two feet long, and it's hard to get much over 1000 watts through them.

The other thing is all that power has to come from your alternator. You'll need somewhere around 100 amps while your A/C is running. That's a lot.

There's usually no such thing as running an A/C for short periods of time. It's gotta be on and stay on if it's gonna actually cool your camper.

I think it's foolish to use your starting battery for any other purpose.

Bottom line, it's really not practical to run an A/C this way. A/C is generator territory.

[pianotuna]

Hi towpro,

Force? Not really. It allows you to select a higher voltage. Unfortunately the design of the whole unit doesn't allow fully amps until the battery bank has recovered some what. But it is certainly better than the WFCO.

If my PD dies I might well replace it with an Iota with the IQ4 module.

[SidecarFlip]

Bumpyroad wrote:

SidecarFlip wrote:
and an inverter genny is super quiet too....

If you care to read the thread about medical equipment in a camper, you'll see I use ac every night to power my CPAP machine. Always on battery, always on a PSW inverter. My ac power needs are small but necessary. .

why not just get a 12 volt respironics CPAP machine and be more efficient?
bumpy

You want to buy me one? I already have 4 machines, don't need another one. My fun money is alloted to other things...

[towpro]

You can also get the pendent button for your built-in charger if you have the progressive Dynamics system. This allows you to force in into higher charge modes when you do start your generator.

[Bumpyroad]

SidecarFlip wrote:
and an inverter genny is super quiet too....

If you care to read the thread about medical equipment in a camper, you'll see I use ac every night to power my CPAP machine. Always on battery, always on a PSW inverter. My ac power needs are small but necessary. .

why not just get a 12 volt respironics CPAP machine and be more efficient?
bumpy

[bka0721]

SidecarFlip wrote:
Usually, 2 hours per day (in the afternoon) is sufficient to recharge my twin 6 volt Trojan's to full capacity using the genny shore powered to the TC and letting the converter charge the batteries. The genny runs in economy (low speed) mode so it's quiet as a mouse. A full tank (1.2 gallons) lasts 3-4 days.

Just a side comment so as not to hijack this thread, but a much more efficient way to charge your battery bank, while using a generator or shore power, is to just use a smart stand-alone battery charger that is plugged directly (appropriately sized power cord) into your generator/shore power. This will charge your battery bank in a fraction of the time a convertor (almost in all cases) takes to charge a battery bank and for less fuel and annoyance to your neighbors no matter what quiet setting you choose. The savings you realize will more than pay for this smart charger.

b

[SidecarFlip]

and an inverter genny is super quiet too....

If you care to read the thread about medical equipment in a camper, you'll see I use ac every night to power my CPAP machine. Always on battery, always on a PSW inverter. My ac power needs are small but necessary.

I camp in the woods most of the time so solar is not an option (no sunlight to speak of). Consequently, I use an inverter genny, in my case a Champion.

Usually, 2 hours per day (in the afternoon) is sufficient to recharge my twin 6 volt Trojan's to full capacity using the genny shore powered to the TC and letting the converter charge the batteries. The genny runs in economy (low speed) mode so it's quiet as a mouse. A full tank (1.2 gallons) lasts 3-4 days.

Works fine for me, but may not be your ideal.

[d3500ram]

ct1500 wrote:
...
I'm brainstorming a way to do this and would appreciate some input....

...It'd be nice to run the camper's A/C for short periods of time without buying a Honda 2000Eu. ...
.

I like questions like the one you posted because those TC'ers here who know their schnitt chime in with really good information. It is good education for me to read responses from those who know much more than me. That said, here is my opinion:

-there is no such thing as "short periods of time" when it comes to situations regarding running the AC. Where I camp in my neck of the woods I rarely if ever run the AC, but in those few times outside of my region when I need it then I run it... and for more than just a few minutes.

=The fact that you mentioned eU2000 perhaps indicates that you have considered it. The reputation of the Honda's are well earned. I Have a 3000 to be sure that I can run my MW and AC (not at the same time) but having too much power is something I never worry about. I have even charged others' batteries in a pinch... and I take beer in exchange for the appreciation...LOL

I like the conversation of those who are more knowledgeable than I but my opinion is this: if you like hassle free (like me) then get a Honda 2000, plug it in and be done with it. The ability to not only run an AC as well as charging the house batteries off the grid is a wonderful sense of comfort and independence.

JMHO.

[towpro]

RoyB wrote:
I was thinking about using one of those smart relay like the BLUE SEA Automatic Charging Relays SI-Series which will monitor your DC OUTPUT coming out of your Alternator circuit and when it is high (Charge Mode) it will switch in the external Battery to charge it as well.



Roy Ken

the problem with that blue sea relay is if you have solar on the camper, the blue sea sees this higher voltage (on camper side) and closes the circuit to your truck so you solar is now charging your truck batteries as well.

plus most trucks are only wired with 16 gauge wire, which supports 4 amps charge current if your lucky.

[time2roll]

You really need four batteries to drive a 2000 watt inverter.
Not going to run the air conditioner long although some power from the alternator will help.

[bka0721]

RoyB wrote:
One of my golden battery rules is to never do anything to the truck start battery system when I am camping off-grid. This is the only way to get home
Roy Ken

This is the only answer you truly need. Don’t sacrifice your ability to self-rescue. Whether it is because someone was hurt during your watch and you must leave quickly and or to leave to return home or travel to your next destination.

For me, due to my choice to be remote/boondocking exclusively I am hours, I mean hours from a location that could send me a tow truck or a jump of the battery. When my OEM batteries finally gave up the ghost, keeping me from leaving it was a simple solution for me to fix this issue, myself. I gave my truck a jump off of my generator/inverter. Redundancy. Basically I have two of everything, multiple battery banks, two water systems, two power systems, two generators, two heat systems, two inverters, two charge controllers, two solar systems and the list goes on.

While I am able to run my A/C off of my DC, I do it sparingly, off my solar system. I have that much Solar wattage/battery bank and inverter. But, I would never ever put my truck and or battery system in direct line for this type of abuse. Never.

If you continue on this path, be sure you check what your Inverter is rated for surge Amp coverage/capabilities. As this is a critical factor for Inverters. Just because it is a 2000W inverter, like a Microwave, this is not continuous wattage/AmpH use. Also, you must have Catastrophic Fuses in place, off line switch capability, cable matched and size rated to your inverter (basically the thickness of your thumb (male)) and verify the connections are tight, often (heat/cool loosens these). Type of battery dictates what your drawdown (discharge) capabilities are as well, AMP/FWC/LIB). Engine type of your truck dictates whether the engine is safe to operate under long term idle conditions and or high amp output rated for existing alternators.

If you choose to continue, please keep us updated as there have been many successful people that move forward when the best advice says otherwise and are successful with their choice.

But so did Icarus.

b

[kohldad]

I'm not sure if it's feasible to use a dc to ac inverter to achieve similar output to the Honda, or not.

You could, but only for a few minutes before you kill both batteries.

You could put in an isolator that automatically disconnects the truck battery, but I would advise against it. As mentioned, the truck battery is designed for cranking with large amount of amp output for a very short period. It is not designed for slow discharge with a lot of drain.

Plus, too much chance of killing the truck battery and leaving yourself stranded.

[SidecarFlip]

Kayteg1 wrote:
In my bus conversion the only way to run AC on the road was via inverter, but bus had original 8kW alternator.
My new truck has dual alternators, so I am pretty confident I could run inverter with AC on it, but having build-in generator I would rather fire it up.
I am not sure if single cylinder propane generator will use less fuel than V8 diesel, but small engine is way easier to replace down the road.
Coming to batteries, driving truck with dual alternators I am very tempted to wire up truck batteries to camper - instead of carrying another 120 lb of batteries.
The issue is that in case I deplete the truck batteries too low, I will have no power to start generator.
So couple of ideas I am planning to check for the future
1- disconnect 1 of truck batteries and keep it for generator start
2 - check if the new technology gizmo will start my generator with low batteries.
Those cigarette pack sized batteries claim to give 400 amp, what is way more than my generator needs.
My new truck has remote start and I already tried it in February, when overnight my camper heater depleted camper battery.
The remote start will run the engine, turn the external lights on, but will NOT activate trailer charging relay. THAT SUCKS !

You try to draw 400 starting amps @ 12 volts through those pencil wires, what you will have is a stinking smoky melted mess in about 2 seconds. neither the cables nor the internal circuitry of that L-Ion pack will take that much amperage. It may well be capable of delivering 400 amps but not all at once. Never happen.