Battery size to support 2kw inverter

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Rvliberty

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Nov 5, 2011
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87
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Bellevue, Wa
It was suggested to me that to put in a 2kw magnum inverter one should have at least 440 amphours of battery capacity. Has anyone done this with 220 ah or less? Any issues?
 
If you intend to use anywhere near the 2K output of the inverter you will need at least a 400 ah battery bank.  You will also need a good 3-stage charger if you draw down your batteries very often or expect fast recovery when you do.

Decide what you want the inverter to drive, size it accordingly, then figure out the battery capacity required to make it happen.
 
Lou is right on. Also if you plan to dry camp a lot, you may want to consider 6 volt batteries as opposed to 12 volts. Sixes are better at taking a deep discharge and coming back strong more often than most 12V.

As Lou said, it really comes down to what you plan on powering with your inverter......
 
I am already planning on 6v conversion. I would love to add another set to get 440ah but having a hard time finding room in a winnebago view 24J. Suggestions?
 
I've no idea where you might put the batteries, but to put this in context;

a. Two thousand watts at 12V = 167 amps draw.
b. A 440 AH battery is good for about 50% of that (assuming good golf cart batteries or equal) each charge/discharge cycle or 220 Amps for one hour (0r 110 A for two hours, etc.).
c. This reduces to about 1.4 hours at full drain. Actually, allowing for 90% efficiency in the Inverter, more like 1.25 hours.

The above is why 440 AH is recommended. Obviously, you won't (I hope) try to run at 2,000 W all the time, but if you use any significant part of it, you need the big batteries. Note also that most inverters will be most efficient when producing full power, so it behooves you to properly size the inverter, not oversize it.

Hope this clarifies the problem,

Ernie
 
Even 1000 watts is tremendous load on the batteries - about 90 amps continuous.  That's similar to cranking your engine continuously  and you know you couldn't do that for long on just one battery, so two is a bare minimum. But I suspect your typical use will be more like 300-400 watts, e.g. computer, tv, sound system, satellite, etc.  You can probably manage with two batteries and 220 AH if that's your most common loading. But then, you wouldn't need a 2000W inverter either, and a smaller one will be more efficient at lighter loads.
 
The other problem in trying to draw a lot of current from deep cycle batteries is they aren't made for that kind of use.  Deep cycle batteries have thick plates with limited surface area and are suited for long, slow discharges.  You can't draw out all of their energy over a short period of time.  The plate surface will get depleted and the battery voltage will drop, making the inverter shut down from low voltage long before all of the battery's charge is used up.

Adding more batteries keeps the current drawn from each battery within usable limits.  Most deep cycle batteries deliver their rated capacity over a 20 hour discharge cycle.  Most are also rated for a 4 hour discharge at reduced capacity.  A 2 hour discharge is really pushing them.
 
Still have not decided how to add/change in the spring with ours.  I know the 6V batteries are great, just not sure if it's cost effective for what we need.  I've got what came with the trailer, single car battery, 12V now.  It's not enough to run the 32" flat screen on the inverter, amp draw exceeding even fully charged.  It's either just add another 12V or switch to 4 6V batt's, again, still looking into what's best.
 
Excellent point, Lou! A 220AH battery bank has nowhere near 220AH if the amp rate is high. For example, a 6v golf cart battery that can deliver 220AH over 20 hours is only rated for 185 AH over 5 hours. This example is from the Trojan battery spec tables.
 
Thanks to all for your inputs.  This is a big help.  I was told that Magnum Energy recommends 440 ah for a 2kw system but did not know why.  The input about running the inverter at near peak demand to get the best performance may be why I have seen several people talk about using a couple of smaller, task specific inverters.

Most of the time the draw will be in the 300-400 watt area as indicated, but I do want to be able to run the coffee pot and even the microwave for short periods of time (a few minutes at best) without using the generator.

I would love to go to 440 ah if I can find a place on a 2012 View 24J to stuff the dang batteries.  So far my only choice is an exterior storage area but I think it will need to be reinforced, or the dinette bench in the slide out (and I will have to use AGMs).  I am averse to putting that much weight on the slide as well as constantly flexing the wiring.  I have looked under the coach for a place to build and mount a separate battery box, but I have yet to find one.

Again, thanks for the valuable input.  Further suggestions are greatly appreciated.

 
Using Ernie's posting
a. Two thousand watts at 12V = 167 amps draw.
keep in mind the amperage required for up to 2 kw and select wire size from the batteries to the inverter appropriately.  The further the distance, the bigger the wire size.
 
My best advice is to use a 700-1000W inverter with two batteries and use the generator when you need more power.  There are coffeemakers that will run on 1000W (usually the smaller 4 cups models), or get the type with an insulated carafe and just run the generator while it brews and then turn the genny off.
 
The OP did mention Magnum in his post, so he might be looking at a combo (MS or PS series)to save space. At least on those you can specify the size of the stack, as well as back the charger off to almost anyplace you choose.
 
Sorry... I should have said battery stack. I'm around giant UPS systems and really big battery banks in news and satellite trucks allot and we slang the terms sometimes. I have an MS2012, and installed another 6 in some new news trucks I just bought it's a great unit. But if you really want to know how your batteries are performing , make sure you get the BMK option with it. You will have a much easier time managing your loads with a smaller battery bank.
 
Minimum battery bank to support a 2KW inverter is 200 amp hours (At the 20 hour rate)

Recommended minimum is twice that (400 amp hours)

Suggestion is two pair of six volt golf car batteries in series parallel.  Or more
 
The point is that if it is ever run at anywhere near full load, a two battery bank (180-220 AH) is going to be insufficient. The voltage will fall rapidly and likely will cause the inverter to shut down within a minute or two or three. And doing so will impact the batteries life span as well.
 
The only time a really high draw would be used is the microwave and that would only be for a few minutes. It is a 1000w microwave. The specs say the peak draw is 1500w input for the 1000 w output. I am not sure how long the 1500w draw would be (constant or just start up).  I need to put a kill-o-watt on it to see. I really want 440 ah but still trying to figure out where to put the dang things.
 
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