48 volt battery bank questions

[rmosborn]

I plan to use 12 - 8 volt golf cart battery’s
I plan to do 6 in series and then the two blocks in parallel
I plan to use 6 inch 4 gauge wire. Is that enough.
Midnite classic 200 controller
Any wire suggestions or confirmation

Thanks

[ClassicCrazy]

I plan to use 12 - 8 volt golf cart battery’s
I plan to do 6 in series and then the two blocks in parallel
I plan to use 6 inch 4 gauge wire. Is that enough.
Midnite classic 200 controller
Any wire suggestions or confirmation

Thanks

What you want to do is not the best plan.
It is difficult to keep two parallel sets of batteries in balance like what you are talking about.
here is some info http://www.smartgauge.co.uk/batt_con.html
You wiring question really depends on your loads and what is recommended for the size inverter you would be  using ( it's surge rating is important to wire for )
You should consider lithium batteries which are much more cost effective these days.
You would most likely get better performance with a smaller AH lithium pack than using lead acid.
For best longevity you only want to take 20% out of your lead acid AH capacity.
There is also needed watering, equalization, and hydrometer testing needing to be done with flooded lead acid batteries.
Larry

[mike90045]

A few things to consider
Golf Cart ( GC ) batteries also come in 6V 200ah versions.  Is 48V 200ah enough for your purpose ?

4 ga wire is only good for 70A and you have to consider voltage drop.  70A @ 48V is about 3Kw of inverter output max.

What size wire fits in the inverter terminals ?   Can you get 4ga lugs that fit your battery bolts ?

  Li batteries are no good when cold and cannot be recharged below freezing.  If you can keep them above 40F, they work great

  Li batteries are UNFORGIVING.  Discharge them too deep or recharge too high, they are toasted.  I suggest you use a FLA battery bank first, work the kinks out of your system, and then in 3 years when they fail, make the move to Li.   And in those 3 years, find out all the quirks about Li batteries, and your whole system.

Li battery BMS systems.  All are different, some have cold recharge lockout.  Some have cell-cell balancing.  Some have fuses, some have relays, some have SSR's / FET's for shutdown.
Does overvoltage shutdown disconnect the battery and fry your Solar Charge Controller, or does it have a relay contact that can shut down the solar CC ( much safer for the CC )

Lots more research needs to be done on your part before you buy anything.

[ClassicCrazy]

Mike,
I think some of the new lithium systems also have self heating batteries . I think what they will do is if there is enough PV they will turn on a heater to warm up battery first until it is above freezing and can take a charge. I am sure that lithium is pricier.

Regarding the controller - I saw an interesting thing at my neighbors place. He had me put in a simple small PV system in his shed just to run lights and a few small AC loads like tool battery charging. And he didn't want to pay too much for it. I sourced everything budget off of ebay. Found a decent PV that would ship UPS and was 12v. That let me get a simple controller. I bought a chinese one that also said it had temp compensation.  He insisted on using a used AGM battery I had. That was a couple years ago and it has been serving his needs. But he told me recently that his inverter ( a small 400 watt harbor freight one ) was giving an error alarm.
I went over figuring that battery had failed - it was already old when he got it and we just had about a week of very overcast days.
When I looked at the battery it was all bulged up on top. I have seen small AGM's bulge when they are bad . Although I thought they should vent before they build up enough gas to bulge like this one was.
Took me awhile but I finally noticed the controller was in 24v instead of 12v . I think what happened was that when the inverter sucked too much juice out of the cold low voltage battery , it shut down the controller for a bit. The controller is supposed to automatically detect 12v or 24v system and set the charging defaults. So when the controller shut down , it was a sunny day , and when it came back on the PV voltage was high enough that the controller defaulted to 24v. So then the controller charged it up way too high and boiled the battery too much and that is what made it bulge. That is my theory of what happened. 
My neighbor is only slightly tech savvy and I can't fault a smart guy at 84 years old for not catching that ! But in the future if I do a favor for a neighbor I won't try to do a simple system on their $600 budget and tell them it is going to cost more because it is not worth using a $25 cheap controller like that instead of something much more quality.
Larry