Small DIY Battery Inverter Setup -Wires

[Baby Billy]

I had this idea. I wanted to be able to run my pellet stove, or maybe some lights, in the event of a short power outage. I already had a marine battery, so I got a 12 volt 2000w/4000w peak inverter to go with it. A bit larger than what I need right now, but the price was right and it gives me some flexibility.

Then I was looking at batteries. Seems like LiFePo4's are pretty popular, and the prices have gone down quite a bit. Cool, I'll get 2.

Now I need some wires to connect the whole thing. Googles tells me I need 4/0 wires. I figure 2 x 1 foot wires to connect the 2 batteries in parallel, and another 2 x 2 foot wires to connect from the batteries to the inverter. That's when the sticker shock sets in. $107 for those wires from batterycablesusa. And it doesn't seem like it would be much cheaper to buy the wire and make them myself.

Is there any cheaper way to do this, or maybe I'm missing something?

 

[pastera]

That's why people run higher voltages - much cheaper cables and better efficiency.

 

[walter62]

Do you possibly need to install some diodes or other one-way between the batteries?

Figure out your current draw and base your wiring on that.

 

[ToddDubya]

Those wires sound way overkill and probably very difficult to work with. Assuming 100% efficiency, 2000w (output I assume) is gonna need 166.67A from those batteries. They'll be dead in no time. I'd come up with a reasonable expectation of what you'll want to power and work from there. And find out what the actual efficiency of that inverter is. That'll make a big difference.

I don't think you want to wire a marine battery together with LiFePO4 batteries. They're not the same chemistry and they're going to lose voltage at a different rate. LiFePO4 batteries tend to hold a full voltage until they're nearly discharged. They have a large capacity, but can't source the kind of current the marine battery can.

 

[Palladin]

this is still a shooting forum, right?

 

[Kevin_NH]

I don't think you want to wire a marine battery together with LiFePO4 batteries. They're not the same chemistry and they're going to lose voltage at a different rate. LiFePO4 batteries tend to hold a full voltage until they're nearly discharged. They have a large capacity, but can't source the kind of current the marine battery can.

Good point -- paralleled batteries must be identical lest bad things™ happen.

Now I need some wires to connect the whole thing. Googles tells me I need 4/0 wires. I figure 2 x 1 foot wires to connect the 2 batteries in parallel, and another 2 x 2 foot wires to connect from the batteries to the inverter. That's when the sticker shock sets in. $107 for those wires from batterycablesusa. And it doesn't seem like it would be much cheaper to buy the wire and make them myself.

Is there any cheaper way to do this, or maybe I'm missing something?

For your current and distances, 6 gauge cable should suffice (it's what you usually see in a (non-EV) car for the battery connection).

Do you have a nearby makerspace? They'll usually have the big wire terminals and the tool to crimp them, might even have appropriate sized wires.
You could get a month at my makerspace for less than those cables

this is still a shooting forum, right?

If it makes you feel better, we can talk about 4/0 cable using the other name for it -- "quadruple ought"

 

[Palladin]

Good point -- paralleled batteries must be identical lest bad things™ happen.


For your current and distances, 6 gauge cable should suffice (it's what you usually see in a (non-EV) car for the battery connection).

Do you have a nearby makerspace? They'll usually have the big wire terminals and the tool to crimp them, might even have appropriate sized wires.
You could get a month at my makerspace for less than those cables

If it makes you feel better, we can talk about 4/0 cable using the other name for it -- "quadruple ought"

it's four ought

 

[teamRR]

I run into this a lot with wishful thinking on boats.

Short answer - get a generator. It's cheaper and much more capable.

You need a lot of battery to generate even 1000 watts for long - is about a 100 amp draw at 12v (ie volts x amps = watts and inverters are not completely efficient).

Inverters and battery banks are good for a serious off the grid setup. I'm not debating that, but it requires a real investment of thousands. For simple powering when you happen to end up off grid, even those setups can't hold a candle to a < $1000 generator and some jugs of fuel. There are $300 generators to do what you are talking about, possibly less $$ even.

 

[pastera]

Pellet stove is usually less than 300 watts except for running the igniter.

Lights as long as they are LED are insignificant for the two or three you might actually need.

A cheap small generator should be enough.
Or add a double conversion sinewave UPS to cleanup the power.

 

[Fritz the Cat]

it's four ought

Chotyry nulya

 

[tinhorn]

Aught, not ought, fellers.

Several years ago I wired an electric boat. Needed some huge wires and found the best price at a local boat dealer/marine supply store. Had to buy the tool for mashing the lugs onto the ends from Amazon. Almost cheaped out and used jumper cables until I discovered that all mine were copper-plated aluminum.

I also once bought an inverter thinking I could easily connect it to my rig's battery for an instant backup generator. Because I don't understand electrical stuff very well, I never did complete the project. I lost the scent when trying to figure out if my car alternator would keep up with the demand, and what size fuse I needed to protect the whole mess.

 

[whatluck]

Consider making bus bars to connect your batteries

Copper pipe hammered flat and drilled to fit ur battery terminals

 

[Baby Billy]

Those wires sound way overkill and probably very difficult to work with. Assuming 100% efficiency, 2000w (output I assume) is gonna need 166.67A from those batteries. They'll be dead in no time. I'd come up with a reasonable expectation of what you'll want to power and work from there. And find out what the actual efficiency of that inverter is. That'll make a big difference.

I don't think you want to wire a marine battery together with LiFePO4 batteries. They're not the same chemistry and they're going to lose voltage at a different rate. LiFePO4 batteries tend to hold a full voltage until they're nearly discharged. They have a large capacity, but can't source the kind of current the marine battery can.

I don't, you are correct. I got 2 LifePos. The marine battery won't be part of the equation, it is kind of what lead me down this path.

I wouldn't expect to be able to draw 2000 watts constantly, but I wanted a bit of headroom.

Inverter specs say 90% efficiency.

 

[Baby Billy]

Do you possibly need to install some diodes or other one-way between the batteries?

Figure out your current draw and base your wiring on that.

Not that I can tell. You are supposed to be use "identical" batteries, and they (through a built in battery management system) kinda figure it out I guess.

 

[Baby Billy]

Consider making bus bars to connect your batteries

Copper pipe hammered flat and drilled to fit ur battery terminals

I have considered this, and it might be the way to go (to save some money on wiring). They sell the already flattened copper relatively cheap. Much cheaper than the wire. Would just have to drill holes and maybe add some insulation (heat shrink).

 

[Baby Billy]

Pellet stove is usually less than 300 watts except for running the igniter.

Lights as long as they are LED are insignificant for the two or three you might actually need.

A cheap small generator should be enough.
Or add a double conversion sinewave UPS to cleanup the power.

I do have a small generator (1000 or 1500 watts can't remember which) and a larger one (7500 watts). I was thinking this could be used for something short term, possibly portable, or if the generators don't work for some reason.

I've never really had a long term power outage (more than a few hours) so this might never get used. But I figured the batteries could still be useful for running a trolling motor, or maybe something else down the road. Supposedly good for 10 years and >4000 cycles.

 

[Baby Billy]

this is still a shooting forum, right?

That was hurtful

 

[ToddDubya]

this is still a shooting forum, right?

Maybe this is actually for a rail gun

 

[Seedreaper]

this is still a shooting forum, right?

It's dabbled into the being prepared part