Inverter current levels?

[jdege]

A lot of people seem to run inverters from 12V batteries as if it were no big deal.

But I've been running numbers, and the currents seem extreme.

A typical household outlet in the US provides 20A at 120V. That's 2400W.

So figure an inverter rated at 2500W.

To provide 2500W from a 12V battery, assuming perfect efficiency, would need to supply 208A.

That's a huge amount of current.

I can't see how I might have messed up the numbers, but I've not seen any discussion of the difficulties in handling I'd expect in handling currents like these. I mean, 4/0 gauge wire isn't easy to work with.

 

[sumpower]

I have used the following as a rule of thumb when installing systems for clients. Has always worked out that the customers were happy with this being part of the decision process. This was back when lead acid were the only game in town.

12 volt: 1,200-1,800 Watt Max "usable" AC inverter
24 volt: 2,400 Watt to 3,600 Watt Max "usable" AC inverter
48 volt: 4,800 Watt or larger inverter

 

[OffGridInTheCity]

A lot of people seem to run inverters from 12V batteries as if it were no big deal.

But I've been running numbers, and the currents seem extreme.

A typical household outlet in the US provides 20A at 120V. That's 2400W.

So figure an inverter rated at 2500W.

To provide 2500W from a 12V battery, assuming perfect efficiency, would need to supply 208A.

That's a huge amount of current.

I can't see how I might have messed up the numbers, but I've not seen any discussion of the difficulties in handling I'd expect in handling currents like these. I mean, 4/0 gauge wire isn't easy to work with.

Agree with you - it's always seemed *extreme* to me as well.... and is why even my camper is 48vdc system with 12vdc converter (for 12vdc subsystem) and all works smoothly at much lower amps.

On the other hand, properly sized wiring / fusing / equipment can lead to perfectly safe operations....

 

[HarryN]

It sure is a pain, that is for sure.

It is a good reason to move up to 24 volt when possible.

In the attached sketch, I show wiring dual feed wires to inverters, especially for 12 volt.

Wired this way, most of the wires can be 2 awg, other than the ones connected to the shunt.

Just run the chargers into the fuse block or safety hub as needed for the planned current flow.

 

[TimE]

There is a lot to be said for 24v and 230v appliances. We run 560Ah of lithium with a 3000w inverter providing 230v AC. Our single burner induction hob is 2000w maximum. The electric stove is 2000w maximum. We can run one or the other or both on low settings. All appliances run with the UK standard fuse plug at 13A. The breakers are limited on the AC side to16A.
The inverter is less only 12 inches from the main 24v busbars so short cables as well

 

[OTRwSolar]

A lot of people seem to run inverters from 12V batteries as if it were no big deal.

But I've been running numbers, and the currents seem extreme.

A typical household outlet in the US provides 20A at 120V. That's 2400W.

So figure an inverter rated at 2500W.

To provide 2500W from a 12V battery, assuming perfect efficiency, would need to supply 208A.

That's a huge amount of current.

I can't see how I might have messed up the numbers, but I've not seen any discussion of the difficulties in handling I'd expect in handling currents like these. I mean, 4/0 gauge wire isn't easy to work with.

Space ultimately led us to go 12v in our small camper. Larger 2/0 or 4/0 cables were the least of our concerns.

We feed our 2400w inverter/charger with a 304ah 4s/12v lifepo4 pack that's about the size of a large vehicle battery. We have room for one more 304ah pack, but no more. Yes, we could have gone 24v with two 304ah packs, but that would have necessitated purchasing/building another 304ah pack plus installing (and more $$ for) 24v/12v conversion hardware to feed the 12v devices in our RV. The single 304ah 4s pack supports our ah, voltage, and current needs just fine---it easily powers our air conditioner for hours at a time with zero issues. If we need more ah's in the future we'll simply parallel another 304ah pack and call it a day. For us, going 12v and crimping/installing 2/0 and 4/0 cable was a no-brainer.

If we had a larger RV with lots more space for batteries *and* wanted/needed significantly more ah and current capability, we wouldn't have hesitated going 48v.