Wiring in new bank of batteries?

[wilfor03]

I've got one bank (original)of 3-12v Interstate batteries hooked in parallel with a 2500w inverter hooked up for backup power when the grid dies (very often here). My question is: I want to get another 3-12v group just like the original ones and hook it up to a new 5kw inverter for the backup bank. I'd like to be able to switch between the two banks, both for charging from the charge controller, and for using separate banks to the inverter? That way if one bank has a bad battery (or whatever), I can switch to the other bank and still have my back up power. To me, I get confused when trying to think of a way to do this safely? Could I just use a couple 4-way battery switches (one for the input and one for the output)? Like this one: "http://www.amazon.com/Marine-Battery-BSS-9001E-Position-Selector/dp/B002MYI4CI" Just want to do this the right way, the first time. Thanks folks, we appreciate all the help...Bill
 

[Rover]

A switch on the battery  output would be fine, its how it handled on boats (including mine) . I'm not so sure about the cutting the current from the charge controller to the batteries as you operate the switch. I really don't know (I have a dual bank charger on the boat so I don't need to) , might be able to do it if the switch is "alternator safe", in other words there is never an open connectiion when switching, its a big deal for some us that have older diesel engines and older alts.

On the output side of the switch just remember to NOT, leave it in the "ALL" position .... or you defeat your battery bank seperation

Obviously make sure the switch is rated to a level that excedes your max potential (Input and Output)

[wpowokal]

A few things come to mind here firstly the KISS principle, your post does not reveal the charging source if solar then switch every thing off, then change over. I question if the batteries as shown could support a 5Kw inverter at anywhere near full load, do the maths on the potential currents a Kw @ 12v is around 80 amps. Therefore same simple solution applies to changing battery banks, simple cheep and possibly foolproof.

allan

[wilfor03]

Hey gang..thanks for the replies.....its solar powered input to the battery's. When I have to switch over to the backup, I currently have a 2500w inverter hooked up and when I have my "necessities" on, I figure I'm close to the max on the inverter when the freezer and refer start up, as well as a 42" TV, a couple CFL's, and a ceiling fan or two. That's why I'm up-sizing to the 5000w inverter and wanting to install another bank of 12v battery's with switches on the input and output of the banks. I have a shutoff switch on the panel before the charge controller, so switching banks wouldn't be a problem. the switches are rated at 200 working amps.

[wpowokal]

Bill if you must use a switch like in your link try to find one that does not have a "both" position because unless both banks are at near equal voltage there will be a large transfer of current if it is switched to Both.

What is the amp hour of your batteries?

allan

[wilfor03]

Bill if you must use a switch like in your link try to find one that does not have a "both" position because unless both banks are at near equal voltage there will be a large transfer of current if it is switched to Both.

What is the amp hour of your batteries?

allan

I guess they'll be about 1155cca or 1445amps each (x3 - soon to be 6). They came out of an electric forklift piece of equipment and are still hot as ever (holding a good charge). Yeah, its sorta scary with that much amperage(sp) thinking what could happen if ya don't do something right, eh? That's why I'm trying to seek some answers afore I do something that will hurt!! Maybe I'll  just hook em all up in parallel after all, and if I have a bad one, I'll just disconnect it out of the bank. Keeping it somewhat simple. Appreciate the input there, wpowakal.....and everybody else.....Bill   

[wooferhound]

Those look like 8D batteries, I have 1 of these in my solar system. They are somewhere around 220-250 amphours each.

[wpowokal]

5 Kw on a 12v system is asking for problems, probably the reason you seem to be getting away it is that they are auto batteries able to give high current, but their longevity will be limited. If you plan on buying a new 5Kw inverter why not go to 24V, I run a cool room on a 24v system from a 3Kw inverter that's 1.5Kw running. Do you realy need that many Kw, what does the battery voltage dip to when under your normal load? you say you figure you are close to max on the inverter with necessities but are you? what is your current inverters surge capability?

Allan

[dave ames]

 hi bill,

 been watching this thread for a couple days thinking you might pop back in and say "just kidding"....cuz when i saw those itsy bitsy teenie weenie inverter cables your using i said to myself "he's gotta be kidding"

 those cables are what? something like awg 6 or so? might be good for a 500 watter' but we can't possibly think we can send over 200 amps through those. that inverter must be screaming with the low voltage alarm and shutting down at less than 1000 watts?

 i bet if you got yourself set up with a proper set of cables (4/0) and gave the system a chance to run you might be surprised!

 afraid the 5kw inverter will be a problem. it's hard to move that much current around at 12v. could do two 2500 watt inverters at 12v with a bit of work..would have to set up a dc buss and feed each one separate.

 i would steer clear of two battery banks unless i had a really good reason.

..just one guys thoughts.

it's all good fun!

cheers, dave

 

[rossw]

I question if the batteries as shown could support a 5Kw inverter at anywhere near full load, do the maths on the potential currents a Kw @ 12v is around 80 amps.

I hate to be argumentative, but 80A @ 12V, even with a 100% efficient inverter, is only 960 watts.
I run a 48V system and have 200A fuses which should blow if my 5KW inverter tries to deliver it's rated peak of 10KW.
(It's not a problem for me, because I should have 2 banks switched in at any given time, so have 400A of fuse)

5KW out with a 90% efficient inverter will take 460 amps off a 12V supply.... if your volts drop (and they WILL) - you will require even more amps!

[img width= height=]http://house.albury.net.au/13sep2010/thumb.100_4591.JPG[/img] and
[img width= height=]http://house.albury.net.au/13sep2010/thumb.100_4592.JPG[/img]
 are pics of my battery "isolators". They're rated at 350A continuous, 500A peak. The fuses are 600V DC rated, 200A HRC.

[wpowokal]

Ross errr what I said was and you quoted it, a Kw @ 12v is 80 amps, sometimes it is sufficient to be near enough for the purpose of explaining, you should know that if you have the correct fuses which I am sure you have they will be rated for the surge that you inverter can provide, ie  without quoting a specific fuse, motor start rating. With respect what is your point??

We all seem to be saying the same thing albeit some seeking to score brownie points, we are trying to help Bill understand his system and hopefully make informed decisions.

a bad day made worse

allan

[wilfor03]

   Whoa, everybody...First off, thank all of you who have responded to the initial question of adding more battery's (a new bank). The system I've shown in these pictures was a TEST system with stuff I've had laying around here. I'm updating from the battery's to the inverter with 4/0 wiring, and have decided to add the other 3 12v battery's in parallel (no switches) with the original 3 (a bigger bank). The 2500w inverter I've been using was borrowed from a neighbor, and I want to get my own, and got a good price on the 5,000w inverter, so that's the reason for the bigger install. I'm only powering an icebox (5amps), an upright freezer (5amps), a 42" inch LCD TV (1.7amps), DirecTV (1.3amps), 4 CFL's (at the most) (52watts), and a ceiling fan (60watts) on backup power (about 14 amps, I think) . With the way the system is right now, I've run it for 4 1/2 hours and NOTHING has heated up in the wiring, inverter, batteries, etc (not that I could tell, anyway @95deg weather). Battery voltage at the end of the  4 1/2 hours did drop to 12.4v (close to the shutdown voltage for me) when I shut it down. I just want to expand the capacity of the back up a wee bit more cause I can get another 3 battery's for about $200. Can't pass that one up, eh? Again, thank you guys.......Bill   

[rossw]

Ross errr what I said was and you quoted it, a Kw @ 12v is 80 amps, sometimes it is sufficient to be near enough for the purpose of explaining
...
With respect what is your point??

To be honest, I missed the "*A* kilowatt, and saw the 5KW and 80 amps and thought you were trying to say a 5KW/12V system will only pull 80A.

My bad

[TomW]

My bad

I am so glad I do not make any mistakes. Whew.

 
 
 

Accuracy is very important.

Tom