Designing new battery + inverter setup/system

[ependydad]

Before we traded the old rig, I yanked out the batteries, battery monitor, inverter, and related accouterments (battery disconnect, catastrophic fuse, and circuit breaker).

The old setup was fairly simple:

• wired 4 batteries in parallel
• added the battery monitor + inverter
• and tied into the camper's 12v system

To use the inverter, I would run an extension cord and backfeed the camper by plugging it into the shore power receptacle (with an adapter).


The new camper has a built-in generator and an automatic transfer switch. I have a few goals in mind with the new setup:

1. get rid of the hokey extension cord + backfeeding of camper
2. be able to provide power to most outlets in the camper
3. better protect each individual battery
4. be able to isolate down to a single battery (for yearly charge maintenance)
5. provide an upgrade path for the future:
   • adding solar charging
   • adding a larger inverter
   • make it easier to add additional 12v loads (TPMS repeater, basement lights, and USB outlets to the living room slide are on my immediate "to do" list)
   • adding a subpanel for inverted vs. not inverted breakers

The idea is that I can parallel the batteries using bussbars for positive and negative. This will aid in better charging of each battery. I'll put a fuse onto each battery in order to protect each one and to be able to pull the fuses in order to isolate individual batteries.

I'll use either the Xantrex 15amp Automatic Transfer Switches or the KISAE 15amp Automatic Transfer switches.

For the future 12v loads, I'll introduce a fuse block that I'll be able to add and protect new 12v needs.



My specific questions:

1. are there specific recommendations you would make with all of this design?
   
2. for the battery fuses, how many amps should they be?
   
3. I previously opted for 1/0 between the batteries, 2/0 between the rest of the components, and 2awg to the inverter (just because it came w/ the inverter). Are these wire sizes sufficient for now and the future?

[BandJCarm]

Great Googly Moogly.

You're way too smart.

[ependydad]

Originally Posted by BandJCarm

Great Googly Moogly.

You're way too smart.

Thanks, but I don't *feel* that way. The sizing of wiring and fuses completely elude me.

I don't understand how you figure out amps based on what the needs are.

[prairiecamper]

The first thing I see is the line from between the shore power and generator, both those power sources are 50 amp split phase ( I.e. 2 lines of 110 volt power) and I believe should go directly to the AC distribution panel first. Then the desired circuits from there could be power sourced from either the inverter or the AC distribution panel through a transfer switch. Maybe I’m not understanding your intent and not interpreting your schematic as you intended. Good luck with your mods.

[ependydad]

Originally Posted by prairiecamper

The first thing I see is the line from between the shore power and generator, both those power sources are 50 amp split phase ( I.e. 2 lines of 110 volt power) and I believe should go directly to the AC distribution panel first. Then the desired circuits from there could be power sourced from either the inverter or the AC distribution panel through a transfer switch. Maybe I’m not understanding your intent and not interpreting your schematic as you intended. Good luck with your mods.

I couldn't come up with a clean way of showing that. But basically, where the 2 circuit breakers are that I'll be inverting, you disconnect the power to each and wire each up to a mini-automatic transfer switch (just 15amps).

I'm not tapping into the 50amp split phase, I'm just modifying 2 individual breakers.

[prairiecamper]

If you want to power only a couple of circuits off the inverter, you could just install a couple of residential 3 way light switches. I did just that with 1 circuit for our entertainment system and real inexpensive less than $20. You need to install an electrical box with a 3 way switch in a wall somewhere convenient ideally near your AC distribution panel. Now determine which circuit you want powered from your inverter by switching breakers on and off. After identifying the breaker you will work with remove the wire attached to that breaker ( safely remove power first). Now place that removed wire to one side of the 3 way switch you installed in the wall. Now another piece of wire 14/2 from the inverter to the other side of the 3 way switch.
Now you have the ability to select either power source, it’s not automatic but if you select your inverter manually you will probably remember to switch the power source manually. Good luck. Obviously you wouldn’t do this for the whole trailer but 1 or 2 circuits is feasible especially for a small 1000 watt inverter.

[Skyliner]

My only comment is to consider switching to a 1500 watt inverter instead of a 1000 watt one. This will give you sufficient capacity to run your microwave for a bit and your lithium batteries should handle it.

[ependydad]

Originally Posted by Skyliner

My only comment is to consider switching to a 1500 watt inverter instead of a 1000 watt one. This will give you sufficient capacity to run your microwave for a bit and your lithium batteries should handle it.

I might do that because with the “portable generator and switching cords”-thing on my last one, it quickly got old for a < 2 minute run of the microwave. It’s a little easier now with the built-in generator and automatic transfer switches in the design, but still.

I have thought that if I upgrade my inverter at this point that I’ll go all-in on an inverter/charger. But we’ll see.

[gastan]

I suggest you visit some boating/yaching/live-aboard forums and read and ask questions there. Boaters - especially live-aboards - deal with 12V issues all the time. If you have any type of "cabin cruiser" and want to spend a week-end or more "on the hook" in some secluded anchorage, a viable battery/inverter setup is a must.

Google amazon for some books on the subject. David Smead has written several very good books on this subject. I have his "Wiring 12 Volts for Ample Power" and it is a life-saver.

[CedarCreekWoody]

All of this from the guy that is afraid of electricity? Lol

[garbonz]

I tried the Pd lithium charger but didn’t like it. One step charger, with no float. Went back to the 9245 and added a charge wizard remote which allows you to force bulk charge and also allows you “storage” mode at 13.2 volts which is perfect for lithium’s.

I am now cutting off charging at 13.8 volts which gives a 96 % SOC and maybe give a longer like span. Probably overthinking it, but thes bb’s art spensive.

[pmsherman]

I assume that you'll be installing a split phase transfer switch between the existing transfer switch and the distribution panel. This will supply power to everything in the RV, including the microwave, electric element in the water heater, air conditioners and the converter. This won't work because the converter will be trying to recharge the batteries from power being supplied by the inverter.

If you want to have power available for all of the AC devices, even if you don't intend to use the air conditioners and water heater electric heating element, you'll need to power the inverter directly from the generator - shore power transfer switch which will require installing a separate breaker for the converter. This new breaker cannot be connected to anything in the existing breaker panel. You might also have to build a checklist of breakers to turn off when running on the inverter to prevent overloading it.

Phil

[Murbella7]

Originally Posted by ependydad

Before we traded the old rig, I yanked out the batteries, battery monitor, inverter, and related accouterments (battery disconnect, catastrophic fuse, and circuit breaker).

The old setup was fairly simple:

• wired 4 batteries in parallel
• added the battery monitor + inverter
• and tied into the camper's 12v system

To use the inverter, I would run an extension cord and backfeed the camper by plugging it into the shore power receptacle (with an adapter).


The new camper has a built-in generator and an automatic transfer switch. I have a few goals in mind with the new setup:

1. get rid of the hokey extension cord + backfeeding of camper
2. be able to provide power to most outlets in the camper
3. better protect each individual battery
4. be able to isolate down to a single battery (for yearly charge maintenance)
5. provide an upgrade path for the future:
   • adding solar charging
   • adding a larger inverter
   • make it easier to add additional 12v loads (TPMS repeater, basement lights, and USB outlets to the living room slide are on my immediate "to do" list)
   • adding a subpanel for inverted vs. not inverted breakers

The idea is that I can parallel the batteries using bussbars for positive and negative. This will aid in better charging of each battery. I'll put a fuse onto each battery in order to protect each one and to be able to pull the fuses in order to isolate individual batteries.

I'll use either the Xantrex 15amp Automatic Transfer Switches or the KISAE 15amp Automatic Transfer switches.

For the future 12v loads, I'll introduce a fuse block that I'll be able to add and protect new 12v needs.



My specific questions:

1. are there specific recommendations you would make with all of this design?
   
2. for the battery fuses, how many amps should they be?
   
3. I previously opted for 1/0 between the batteries, 2/0 between the rest of the components, and 2awg to the inverter (just because it came w/ the inverter). Are these wire sizes sufficient for now and the future?

An elegant setup. I appreciate that the transfer switches swap power from inverter to mains, etc, but what prevents you from overloading the inverter?
Do you flip the breakers on circuits that have devices that might cause an overload or do you remember to not uses those things?

[aircommuter]

You could get an inverter that has a transfer switch built in and has input connections for generator and shore power. Some also have relays that can auto start the generator if the battery voltage goes below a set value for a set time.
Just a possibility.

[ScottBrownstein]

Originally Posted by ependydad

...
I'm not tapping into the 50amp split phase, I'm just modifying 2 individual breakers.

Although your neat diagram shows power from the main transfer switch going directly to the two 15 amp inverter transfer switches, I assume you mean that power from the two inverter assisted panel breakers goes to the inverter transfer switches and then continues out to the original load that was attached to those breakers.

These would be the two Kisae transfer switches that you Googled the other day...right?

I also agree with other posters that I would up the inverter to 1500 or 2000 watts. Just because you have it doesn't mean you use it and the idle current will be about the same between a 1000, 1500 or 2000 watt PSW inverter.

Even with the 1000 watt inverter, I would up the breaker amperage to 100 amp as well.

[ependydad]

Originally Posted by ScottBrownstein

Although your neat diagram shows power from the main transfer switch going directly to the two 15 amp inverter transfer switches, I assume you mean that power from the two inverter assisted panel breakers goes to the inverter transfer switches and then continues out to the original load that was attached to those breakers.

These would be the two Kisae transfer switches that you Googled the other day...right?

Yes, I need to rework the diagram to show this better.

[tomkatb]

I would opt for a 2000 watt inverter. That would power most anything except the A/C.

Use a 400 amp breaker or fuse from the battery and 4/0 cable to the inverter. 12 volt line loss is awful at 12 volts. Difference between operating the microwave or not. My son has been testing this. He is building a stelth camper.

$500 buys four six volt batteries. 230 usable amps. Lithium ion would be a lot more expensive.

Your system seems quite detailed and would be super but, defies the KISS principal. I would worry about fire.

[ScottBrownstein]

4/0 is overkill for a 2000 watt inverter. Max amperage is in the 170 amp range and even #2 would be OK if the run is under 5 feet or so.

That being said, it is not defensible to fuse even 4/0 at 400 amps. NEC ampacity of even that much copper is only 260 amps. You wouldn't be protecting anything. 200 amps is fine for a 2000 watt unit and it drops from there.

Don't understand the fire comment either. Everything is correctly protected. Transfer switches are fully rated...what am I missing? It really is simple, automatic and straightforward.

Of course, the very low internal resistance on lithium batteries can be an accident waiting to happen, but that goes with lithium and they do have some internal protection.

[ependydad]

And, I already own the 4 lithium batteries... so it makes that part of the decision easy.

[ependydad]

Originally Posted by ScottBrownstein

4/0 is overkill for a 2000 watt inverter. Max amperage is in the 170 amp range and even #2 would be OK if the run is under 5 feet or so.

That being said, it is not defensible to fuse even 4/0 at 400 amps. NEC ampacity of even that much copper is only 260 amps. You wouldn't be protecting anything. 200 amps is fine for a 2000 watt unit and it drops from there

Scott, how are you figuring out the amps needed? And I assume the wire size is a direct correlation from them (and run length)?