Dual battery set-up using chassis battery

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.

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.

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.

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...

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.

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

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

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.

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.

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.