Battery selection - 6 volt versus 12 volt?

[Wdeertz]

I've searched the forum and web and am more confused the more I read. I currently have 4 100Ah wet cell house batteries which I am about to replace with AGM batteries. All things being equal which configuration will give me more peak draw?

4 6 volt 200Ah batteries (2 wired in series and parallel together)
4 12 volt 100Ah batteries (all wired in parallel)

I have a 2000 watt inverter and need peak draw for say 5 minutes to run my 1500 watt microwave. My current wet cell bank will only run the microwave for 1-2 minutes before it throws the fuse. It's my understanding that the wet cell batteries have limited peak draw capacity and I should get better peak draw with AGM batteries.

Thanks

[okcnewbie]

Originally Posted by Wdeertz

I have a 2000 watt inverter and need peak draw for say 5 minutes to run my 1500 watt microwave. My current wet cell bank will only run the microwave for 1-2 minutes before it throws the fuse. It's my understanding that the wet cell batteries have limited peak draw capacity and I should get better peak draw with AGM batteries.

I've never heard of peak draw being a factor in solar setup and design. (other than inverter) I suspect you have voltage drop or some other wiring problem that prevents your current setup from being able to run the microwave for 5 minutes. Have you actually used a kill-a-watt meter or something else to see your max draw with the microwave? I've seen some that were way higher than spec.

I think 200#'s of 12 deep cycle would work just like 200#'s of 6 volt deep cycle. Many installers ( pro and diy) don't use adequate wiring.

I'm no pro and this is IMO.

[twinboat]

First, what size fuse ? You should be running at least a 175 amp fuse. Most recommend 250 amps and 2/0 cables.

6 of one, 1/2 dozen of the other, as far as 6 volt or 12 volt batteries.

At the 20 Hour rate you can draw 5 amps per 100 AH of capacity, so your looking at 20 amps " steady " to meet the 20 hour rating. Of course you can draw much more, but the batteries will discharge faster. There are charts listing the 1, 5, 10, and longer hour rates.

A 15 amp draw at 120 volts is 150 amp draw at 12 volts, plus 10% to 20% losses in the system.

Going with a 175 amp draw, for 15 minutes, that's 43 AH out of your 200 AH of capacity.

As far as a higher rate of drawing down AGMs, I've haven't heard that.

[CountryFit]

Originally Posted by Wdeertz

I've searched the forum and web and am more confused the more I read. I currently have 4 100Ah wet cell house batteries which I am about to replace with AGM batteries. All things being equal which configuration will give me more peak draw?

4 6 volt 200Ah batteries (2 wired in series and parallel together)
4 12 volt 100Ah batteries (all wired in parallel)

I have a 2000 watt inverter and need peak draw for say 5 minutes to run my 1500 watt microwave. My current wet cell bank will only run the microwave for 1-2 minutes before it throws the fuse. It's my understanding that the wet cell batteries have limited peak draw capacity and I should get better peak draw with AGM batteries.

Thanks

as others have already made it clear, the capacity/"peak draw" of these two batteries are very similar. what you are experiencing is not likley caused by the batteries you are using; rather the size of the fuse. 1500w microwave compounded with inverter efficiency, wire heat, modified wave deficiency (if yours is), etc, will demand 150a -170a from the battery pack at 12v nominal; assuming your battery cables are of 2/0 size. if your fuse (type t) is less than 200a, it might be blown especially in summer time. the recommended size is 300a. as for why it blows after 1 to 2 minutes, because the fuse needs time to accumulate heat until to the blowing point.

[Wdeertz]

Thanks for the feedback. Answer to some of your questions are:

1) The 2000 watt inverter has a 250amp fuse which should easily handle a 1500 watt load
2) I stated the microwave at 1500 watts but kilowatt confirmed peak demand was only 1360watts so its slightly less than I had originally used in my calculations.
3) Inverter is wired using double 1/0 cables which according to my calculations should be sufficient.
4) AGM batteries have a lower peukerts exponent and therefore can dispense a charge at a higher rate than wet cell batteries. (seehttp://www.vonwentzel.net/Battery/01.Type/ andhttps://www.batterystuff.com/kb/tools/peukert-s-law-a-nerds-attempt-to-explain-battery-capacity.html for discussion of peukerts law and AGM versus wet cell)

I guess what I'm hearing from the comments so far is that 4 100Ah 12 volt batteries will approximate 4 200Ah 6 volt batteries. I had heard the 6 volt golf cart batteries had larger lead plates which seems to bear out when I compare the weights of 2 6 volt batteries to a comparable Ah 12 volt battery. A downsize I see of using going the 6 volt route is if one battery dies prematurely my capacity will be at 50% while in the 12 volt route I'd have 75% of my capacity available.