Connecting batteries up

Brilliant John many thanks...

Would a 550 Ah battery bank power a 5000 Watt interter?

Steve

Steve,

550AH will power a 5000 Watt inverter.  A 100AH battery bank will power a 5000 Watt inverter.  BUT! You won't be able to get 5000 watts out of it at 12 volts.  And as Dennis said, you wouldn't want to draw that kind of current from your batteries.  It'll destroy them. 

At 12 volts, to get 5000 watts, you'll be drawing over 416 amps.  Even 4-0 wire won't carry that safely. 

To get 5000 watts, you'd be better off wiring them in series to get 48 volts.  5000/48 is a little over 100 amps.  #2 wire can safely carry that. 

Read.  Read.  Read.  Next time, we'll have a quiz on why we should keep the current through our wires as low as possible. 

Good luck,

Tom

Steve, it is really a power issue so the same rules will apply. Now remember Power = Volts x Amps.

Most houses in North America will have two 110V (actually anywhere from 110V up to 130V) feeders into the mains panel. These 110V feeds are 180 degrees out of phase with each other, so 220V is available by going across the two phases.

For large loads in the 5000 watt range, like big air conditioners or electric ranges, it is normal for them to be wired for 220V operation, thus reducing the current and wire size.

If you have a 5000 watt 12V/230V inverter, the current at 230V is 5000/230 or 21.7 amps which can be carried by normal household wiring. But assuming that the inverter is working at full capacity, 5000 watts at 12V requires 5000/12 or 416 amps of current flow from the batteries.

Ignoring for the moment that such a current flow would quickly destroy most batteries, it would require a very large guage wire for the connection between the inverter and batteries.

An inverter greater than 3000 watts at 12V is quite unusual, so you might want to take another look at the specs on your inverter.

Some cheap inverters, with no disrespect to your inverter, will be advertised as 2000 watts in very large letters on the packaging. But on closer examination, and in much smaller lettering, it says rated at 1000 watts continuous power, and further explains that it can operate at 2000 watts for 5 seconds.

Are you asking if it will power the inverter, or if it will power a 5wk load?

How much constant load will you have (how much current will you be drawing at any one time).  What about surge current (like starting a power tool)?

Also, larger inverters tend to have larger constant (phantom) loads, even when they're just sitting there waiting for work to do.

You can power a pretty large workload for a SHORT TIME on a farily small battery array.  The problem is that you'll drain the batteries quickly.

Out of curiosity, what kind of inverter do you have?  If it has two (+) and two (-) connections, it is important to know if they are in series or in parallel.  My guess is that they're parallel, and done so you can use a reasonable size wire x2 instead of twice the wire size x1.  Are those connectors holes with set screws made for 2/0 cable?

My guess, then, is that the batteries are so small that there is significant voltage drop when a large load is applied.  Have you hooked up a voltmeter and then attempted to apply various loads to see how much the voltage drops?

That's probably the culprit.

I'm using a bank of four 12v Trojan J185H batteries, each of which has a 215AH capacity (@ 20hr).  I've been able to run a Craftsman drill press, which is the largest single device I have in my garage, without issue.

It's not "just" the size of the batteries, but possibly also combined with loss at the connections.  As is said previously, the amps on that draw would be outrageous. How are the batteries connected to each other (wire size and the connectors/lugs themselves)?  How are they connected to the inverter?  Have you charged each battery individually to full state of charge with a regular household battery charger, so you know they're all full and equally charged?

So many quetions, eh?

My recommendation would be to trade in the 12v inverter on a 24 or 48v version.  The inverter/charger I use is 24v, and I don't expect to draw more than 3kw at any one time.  If I did, I would have opted for a 48v battery bank and inverter input voltage, to keep amperes lower.
 Even with my 24v setup, the batteries are connected to each other and to the inverter with 2/0 "welding cable" and double-crimped bolt-down lugs.

If the batteries were all equally charged, of equal state (that is, newness, ability to hold a charge, capacity), and well-connected electrically, they should all be showing the same voltage.  barring differences between meters (which might be up to 0.2v or so) it seems you either have bad or undercharged batter(y/ies) or bad connections between them.

bad == not able to handle such high amps without severe loss

You are drawing lots of amps.  I'm building an electric truck (the 2nd electric vehicle I've dabbled with) and can tell ya- it's really easy to make ONE crappy electrical connection and lose an incredible amount of usable power.
Same with batteries - one bad one (or just undercharged) can really suck the life out of the rest of them, especially when you're applying a large load (like 350amps @ 120v like the electric PT Cruiser I owned).

Hope some of this helps!

Hi All
Batteries all reconnected after charging each. Now the bank is all equal whichever battery is checked.

Will be doing some load testing in the coming few days. Have done a small load test, this was 3-400 watts for an hour, the bank dropped from 13.8 to 13.2 under load but soon recovered after the test returning to 13.5 or 6 then recovering quickly with the panels/charger replacing the loss in a very short time.

More to follow...

Steve