Whole Coach Inverter?

[WileyOne]

Originally Posted by Soppy

So if the converter will charge the batteries , and the inverter will supply power to the converter there would be no need for shore or generator power cause the batteries would always be charged. What a great idea!! If it was only that simple. I didn't go into enough detail and forgot to mention to turn off the converter breaker.

I went down to the US Patent Office in Alexandria with this idea, but they told me they don't allow "perpetual motion machines". I guess I need to find another way.

[WileyOne]

I am officially giving up on the idea of ever touching the A/C when the Inverter is running. I knew the A/C would be a massive load, but I had no idea how fast it would deplete the batteries or how long it would take to recharge them. In fact, I love the idea of somehow locking out the A/C when the inverter is running.

But, I still have a pile of 120vac devices that need inverter power:

0300 Fridge
0180 two laptops
0100 WiFi router & 2.4 Ghz directional antenna
1500 Coffeepot or Iron or Fry pan or toaster
0100 Sewing machine
0110 LED TV
0010 Blu-ray Player
0050 Battery Charger for handivac or hand tools
1350 Microwave (short bursts only)
===
3700 watts Total

Obviously, we wouldn't run all this stuff at the same time. I suspect our sustained power draw might be around 700 when driving and 500 when parked. When boondocking, we would use a manual switch (or the breaker) to kill power to the fridge, forcing it to use propane in AUTO mode. I would like to find a way to make this automatic with some sort of relay that monitors the truck ignition.

I think a 3500 watt inverter is the perfect size, but I suppose we could get by with something as small as 2500 if we are real careful not to run two high-current devices at the same time.

Our camping style is to drive a few hundred miles until we get tired then pull into a Walmart or Cracker Barrel. Unless it is really hot, we try not to disturb our neighbors by running our generator all night. An inverter is silent. We generally turn on the generator in the morning, just long enough to heat up a sandwich and make some coffee before hitting the road again.

While moving, the batteries will be charging from the truck's alternator. Does anybody know how much power I can expect to get from the E450 Triton standard electrical system? Will it charge a little more rapidly when the headlights are off?

I guess I'm hoping for a little better than one-to-one charging time. If we draw 500w for 8 hours while we're parked, can we expect the two batteries to fully re-charge in under 6 hours of highway driving?

And that brings up another question. If you drive down the road with your 4KW generator running, will your batteries charge faster than with just excess alternator power?

[Searching_Ut]

Two lead acid batteries aren't going to be able to keep a 3500 watt inverter running at full load. To put out 2000 watts of ac power you're going to be pulling somewhere around 190 amps if the batteries can hold at 12 vdc. When looking at your battery demands you have to remember to add 15 percent or so for inverter efficiency losses. Then you have to factor in the Peukert effect when figuring what you batteries will be able to supply. In a nutshell, as the demand goes up, the batteries ability to deliver rapidly starts dropping at some point and the voltage will get low enough to trip the low voltage shutdown system of your inverter. I picked 2000 watts for the math because that in practice tends to be pushing it for a dual battery system.


I'm not familiar with the alternator in you vehicle so I have no input there. That said, you also need to factor in the acceptance rate of the batteries you're looking to use. You'll want to look up the datasheet on the batteries to see what the recommended charge rate is..

[Sbrownstein]

You are going to run your genny to recharge anyway, if you take out the coffee pot, microwave and fridge, you are left with 550 watts. Much more reasonable. You can use that stuff when running down the road since the alternator will make up what you use in short order anyway.

[WileyOne]

Originally Posted by Sbrownstein

You are going to run your genny to recharge anyway, if you take out the coffee pot, microwave and fridge, you are left with 550 watts. Much more reasonable. You can use that stuff when running down the road since the alternator will make up what you use in short order anyway.

I think you guys missed the part where I said the driving draw would be under 700 and the parking draw would be under 500. Of course it can be done. The only question is whether I can fully recharge, without running the generator, before the next night.

All this theory is making my head hurt. I think I just need to try it and see what happens. The worst that can happen is that I have to run the generator a little to take up the slack. It beats running it all night.

[Soppy]

If you draw 500 watts for 8 hrs , that would work out to 333 amp hrs @ 12 volts. So at minimum you would need a 600 amp hr battery bank. To fully charge the battery bank , you have to put in an extra 25% , or about 400 amp hrs. So to charge them in 6 hrs would require 66 amps from the alternator for 6 hrs. It will actually take much longer as the batteries will not take the full charge once they reach 80% charged.
For the fridge ,the easiest way would be to turn off the breaker.

[Sbrownstein]

A lot longer than 6 hours...

This is for a converter and your alternator is like the boost mode, but still, 6 hours isn't going to get you there. However, doubtful that you will draw 500 watts all night either.

[WileyOne]

Originally Posted by Sbrownstein

A lot longer than 6 hours...

This is for a converter and your alternator is like the boost mode, but still, 6 hours isn't going to get you there. However, doubtful that you will draw 500 watts all night either.

So, it sounds like you are suggesting that I just go ahead and try it.
We are definitely going to need a power monitor to analyze our usage. I just wasn't expecting to pay $200 for a thing like that, plus the cost of a shunt.

If we are diligent, we can manage the two batteries by doing a few simple common sense things:

>select an inverter with a low idle current
>replace all incandescent bulbs with LED's
>unplug anything that isn't needed, especially charging bricks
>avoid using household surge protectors on the output side of the inverter. they do draw a small amount of current
>use 12 volt devices where possible. a car USB charger will be more efficient than a house USB charger. a 12vdc TV is more efficient than a 120vac TV. a tiny 12v fan will draw much less than a household fan
>turn off anything that isn't being used at night, like the WiFi router
>run the fridge on propane when the truck engine and generator are off
>turn off any lights that aren't needed
>only use the microwave for short jobs like a sandwich or a cup of coffee. No turkey roasting.
>turn off the inverter when it isn't needed

What have I missed?

[Sbrownstein]

Originally Posted by WileyOne

So, it sounds like you are suggesting that I just go ahead and try it...What have I missed?

Not much. BTW, don't buy from Amazon, you can get a Trimetric, including a shunt and shipping for $175 from a lot of solar energy sites. Nothing special about the wire, just use light gauge hookup wire.

All of this math will go away when you have an SOC meter. Figure out what you can and can't do and adjust accordingly.

Microwave is going to be a killer, but only for a minute or so. Make sure you size your leads and fusing to handle it. I used Xantrex Prowatts, have a 1000 and a 2000 watt as well. Very low idle current. get the remote on/off switch as well. Get is Kisae transfer switch. It is available on 20 and 15 amp variety and is simpler to wire than the Xantrex version, about the same price.

With your SOC gauge installed you will rapidly figure out what you can do and what you shouldn't do since you will always know how much you are drawing and where you stand with the batteries.

I can't stand to run a 5000 watt generator to watch a 100 watt TV! In addition, it is nice to have 120 volts all the time when driving down the road.

[Uncleslatty]

Newmar Canyon Star. Every morning I have battery default message on magnum energy inverter. No power to coach. Running generator to recharge. It has battery disconnect switch. I am a rewby who needs help. Dealer gave me a 45 minute walkthrough. I am 71 so much of what they told me was lost. Dealer tells me to go to YouTube for help. Newmar tells me to read manual. So I am sitting in my driveway until I figure how to run the power.

I have a beautiful view of the Costal marsh of Georgia if somebody wants to boondocking and help me.

[Sbrownstein]

Originally Posted by Uncleslatty

Newmar Canyon Star. Every morning I have battery default message on magnum energy inverter. No power to coach...

OK, first thing. What does no power to coach mean? No lights or no outlets?
Are you connected to shore power? Are your batteries turned on (disconnect switch)?

Does running your generator cure all of this?

[WileyOne]

Originally Posted by Sbrownstein

You can get a Trimetric, including a shunt and shipping for $175 from a lot of solar energy sites.

I found a Victron 700 for $128 including a 500A shunt and cables.
No tax. Free shipping.

www.marinepartssource.com/

I decided I didn't need the 702 because I'll never put two batteries in series and I don't appreciate the value of temperature monitoring. I can always add Bluetooth later, so I'm not ready to spend extra $$$ for the 712.

Now I need to find a way to keep my new shunt clean and dry. It will be mounted under the steps of my MH, exposed to road splash and grime.

[WileyOne]

Before I joined this forum, I thought it would be a great idea to install a second marine battery in my little 24 foot Class-C and connect them through an A/B/A+B switch. Man, have I learned a lot in the past couple of months.
.
The battery that came with my coach is a
...........Group 27DC (575 CCA, 705 MCA, 23A average, 200 min).
The battery that I added is a
...........Group 29DC (675 CCA, 845 MCA, 210 RC, 85 RRC).
.
I now realize that I need to connect them in parallel to act as one double-capacity 12-volt unit, otherwise my new Victron BMV-700 won't be able to monitor both of them simultaneously.
.
Victron doesn't have the greatest support system. Their main office is in the Netherlands and they rely on their distributors to answer end-user questions. I am betting that I can get better answers here.
.
Questions:
> Am I likely have any problems because these two batteries aren't perfectly matched?
> What AWG size cables should I use to make the connections?

[Sbrownstein]

Originally Posted by WileyOne

Questions:
> Am I likely have any problems because these two batteries aren't perfectly matched?
> What AWG size cables should I use to make the connections?

Yes, you need to connect them in parallel to create one 12 volt battery bank. You will need 2 short battery jumper wires, best to make them the same size as the battery wire you already have...or larger. Put the coach red on one battery and jump over to the new positive post and put the coach black on the other battery and jump over to the old negative post. Victron won't care how you do this but if you want to get the best capacity out of your bank, that is the way it should be done. Not the best idea to have batteries of different capacities since one will dominate for both charge and discharge, but why throw out a perfectly good battery?