50 Amp Receptacle to Inverter

[avarusbrightfyr]

Hello all!

Ok, so backstory is I'm doing research on installing a 3000w inverter in my travel trailer, and rather than go through a super complicated and expensive direct to panel wire install, I'm planning using the jury rigged solution of wiring a receptacle to the high output terminals on the inverter and plugging my standard shore power cable into that to power the AC appliances on battery.

The obvious (at least to me) solution is to use a 30 amp receptacle since it only has three wires and that's what the inverters typically come with. Then use a standard 30-50 amp adapter to get my shore power cable plugged in.

Being the efficiency minded person that I am, though, I think it would be nice to avoid using an adapter at all, if possible. I'd like to use a 50 amp receptacle and wire both hot sides together with some sort of bridge, sort of like how they do with the 50-30 amp dog bones. That way I still have just 3 wires coming out of the outlet box but get both legs of the 50 amp cable powered, and I can just plug my 50 amp surge protector straight into the outlet without anything else in the way. My uneducated intuition says maybe another wire spanning from one terminal post to the other, but I'm not sure how safe it is to have current hopping from one side of the outlet to the other.

Any suggestions?

[pianotuna]

https://dakotalithium.com/product/dakota-lithium-24v-100ah-deep-cycle-marine-trolling-motor-battery/...

[avarusbrightfyr]

pianotuna wrote:
There are 24 volt LI battery packs.

https://battlebornbatteries.com/shop/50ah-24v-lifepo4-deep-cycle-battery/

Much appreciated. However, the max continuous amps is 60, which would still require 2 batteries to handle the expected loads.

[pianotuna]

There are 24 volt LI battery packs.

https://battlebornbatteries.com/shop/50ah-24v-lifepo4-deep-cycle-battery/

[2oldman]

Yes, minimum 2 batteries for your planned use. Those lifepos will do a lot better under a heavy load than acids.

[avarusbrightfyr]

2oldman wrote:

avarusbrightfyre wrote:
At 24 volts, the amps are all cut in half.....
Since I'd need 2 batteries anyway, it is starting to make sense to do a 24v system. Does this sound right?

Keep in mind the 24v isn't any magic where it nets you any more wattage or battery life. It simply means you don't have to size your wire to carry the huge 12v amp loads.

BFL13 wrote:
Your problem seems to be that you need 440 AH of bank like the rest of us who do a lot of 12v stuff and you don't want to carry that much weight. .

He's talking about Lifepos.

Yeah, I understand that. Just trying to figure out the minimum system I need to safely run everything in the trailer without damaging anything. If my numbers are correct, it seems like I need 2 batteries minimum to either spread the load in parallel or reduce the amps in series. Or just having to constantly remind six other people not to use the microwave if anything else is on.

[2oldman]

avarusbrightfyre wrote:
At 24 volts, the amps are all cut in half.....
Since I'd need 2 batteries anyway, it is starting to make sense to do a 24v system. Does this sound right?

Keep in mind the 24v isn't any magic where it nets you any more wattage or battery life. It simply means you don't have to size your wire to carry the huge 12v amp loads.

BFL13 wrote:
Your problem seems to be that you need 440 AH of bank like the rest of us who do a lot of 12v stuff and you don't want to carry that much weight. .

He's talking about Lifepos.

[BFL13]

A "900w" MW will want more like 1200w input--check its label.

Inverter to 12v divide by 10 for the amps draw. So that 900w MW will pull about 120a via inverter.

24v means buying a 24v inverter and then you are stuck with that. IMO stay with 12v unless you have a special reason to go 48.

Your problem seems to be that you need 440 AH of bank like the rest of us who do a lot of 12v stuff and you don't want to carry that much weight. Too bad so sad, you have to make choices. We carry 440AH ok, but we also don't carry whatever else.

[avarusbrightfyr]

Ok, let me see if my understanding makes sense.

At 12 volts, assuming a 3000w inverter, at max load that would be 3000w/12v for a total of 250 amps. However, other than my air conditioner, I believe my 900 watt microwave is the highest load I'd have, which would be 900w/12v for a total of 75 amps. The only other appliances would be the fridge and water heater on gas, my TV and sound bar, lights, and other miscellaneous low power items. Let's say no more than 1500 watts total at any given time for a max amp draw of 125. Might be a low estimate, but that's still over the 100 amp continuous limit for one battery, so I would need a minimum of 2 batteries to spread that load safely.

At 24 volts, the amps are all cut in half. Max amps of 125 under full inverter load, which I don't think I'd ever reach without running the air conditioner, and 63 amps at the more reasonable 1500 watt level.

Since I'd need 2 batteries anyway, it is starting to make sense to do a 24v system. Does this sound right?

[pianotuna]

avarusbrightfyre wrote:
Buying one battery at a time will also allow me to figure out how much capacity I need in reality rather than how I live right now. I use a lot of power when on the grid, but that's with the fridge and water heater on AC power, and my big gaming computer on several hours per day. Starting to live on one battery will let me know what I am willing to live without and increase the system size from there as desired.

You could always do a "direct measurement" to find out the capacity needs.

Plug the RV into a 15 amp outlet using a kill-a-watt meter set on watts.

shore power-->kill-a-watt-->rv.

Run everything as you would when boondocking for 3 days.

That would determine the size of battery bank needed in watt-hours.

[pianotuna]

Itinerant1 wrote:
This is why it's advisable to be able for individual cell monitoring not just the battery as a whole.

I believe this an essential feature with any LI chemistry.

Apparently, heat kills LI batteries. leading to lower and lower capacity over time.

[pianotuna]

MrWizard wrote:
PT
How do you draw over 2400 Watts with MW, is it plugged into a 20 amp 120v outlet

It draws about 1570 watts running (measured by a kill-a-watt meter)--but overhead and voltage drop cause the amps to be 210 (measured by the "head" of the remote). I've been told by Magnum that is some what of an approximate figure.

I've not measured the microwave for a while--and the turntable motor is burned out. It may be that it now draws less.

I go a couple of places where I can only draw about 1000 watts, so I use the hybrid feature of the inverter to do load support.

[avarusbrightfyr]

Itinerant1 wrote:
"Lifepo4 chemistry"

I have read that some folks have and it was no big deal, most seasonal campers aren't cycling them a whole lot in the season.

I have also read of folks that have batteries that are like mine made up of individual cells (not pre-made dropins) that have had a cell start to go south after a few years of heavy use and replace that individual cell with no harm.

This is why it's advisable to be able for individual cell monitoring not just the battery as a whole.

I had originally considered building a battery, but once you factor in the BMS the overall cost savings wasn't enough to offset the additional effort required to put it all together. If I could get quality cells for like $100 each and a decent BMS for around $100, then it would definitely be worth the effort to go that route.

[Itinerant1]

"Lifepo4 chemistry"

I have read that some folks have and it was no big deal, most seasonal campers aren't cycling them a whole lot in the season.

I have also read of folks that have batteries that are like mine made up of individual cells (not pre-made dropins) that have had a cell start to go south after a few years of heavy use and replace that individual cell with no harm.

This is why it's advisable to be able for individual cell monitoring not just the battery as a whole.

[avarusbrightfyr]

BFL13 wrote:
Can you add Li batts over the years? Not a good idea with lead-acid batts. You want them all to be in the same condition--usually achieved by buying them at the same time.

I'm not sure, but I would imagine it depends on the battery chemistry. My understanding is that lithium iron phosphate batteries are very different from lithium ion batteries.