Need to replace my 48V FLA battery bank - should I change technologies?

Riley

I have am off-grid seasonal home. Used mainly in the spring/summer... some fall and one visit in winter. 
3.5 KW of panels and a 12 KW generator. 6KW inverter/charger. 

My system used Rolls L16 6V (S-550) batteries to provide 48VDC with 8 battery packs. 

I was just going to replace with the same but wondering if things have changed. 
What about carbon/lead?

I should say that in the wintertime, they are left fully charged and disconnected when I am not there for months at a time. 
They do get cold (-15C)
Thoughts?

wellbuilt

 I’m not seeing much of a Advantage in going to LC battery’s  
 They do charge faster and they say that last longer ? 

 But if you are not charging with a generator I would just stick with LA .
 They may have some thing better when you are ready for your next set

Saggys

I agree with wellbuilt, in the cold weather unless you have a conditioned space for your batteries, stick with lead acid. How long did your present set last you?

Riley

I got 5/6 years from them and they were still in good shape until I made a mistake in the fall (October). 
Because my panels can get snow covered for multiple months at a time, I usually "mothball" the batteries by fully disconnecting them (open breaker to the batteries from the charge controller and the inverter). In doing so, the parasitic draw of the charge controller will not slowly discharge the batteries. This has served me well.... 

Last October, I didn't open the breaker to the charge controller (due to another reason) and this destroyed my batteries. I figure they were about half way thru their lifetime so that makes me feel a little better (I was hoping to get 10 years from them if I didn't make any stupid mistakes). 

The longer story is why I didn't open the breaker... let me know if interested and I can post that. 

I am glad to hear your guys comments on sticking with old school FLA  batteries as that's what I have on order. 
 

wellbuilt

 Wow killing off your battery’s is a real bummer . 

 That’s why I went with golf cart battery’s for 90 bucks each x16 I have a 430ah battery .
 It’s hard to stay 100% on top of the battery / second home thing. 

 I try to make a list of what has to happen  before I leave but I still miss things  when we are in a hurry. 

  I forget the cooler full of food some times , and I had the door wide open for a few weeks because I did not check it .
   It’s allways some thing .

  

Riley

Its an interesting story that I will write up later for others to learn from. I have been on top of this and didn't really forget anything. 
Long story short, when I opened the breaker for the charge controller to leave the batteries disconnected, the MPPT went into fault due to the sunshine and no battery present. I freaked out and closed the breaker to check I hadn't damaged the charge controller... 

it was ok so I left it as it and figured I would return later to resolve it after researching. 
I did return after 2.5 months... and they were dead... too much snow. 

Oh well, I did get 6 years from them but it still hurts. 

LostinNevada

Riley,
I sent you a PM.

Saggys

We also have an off grid cabin in snow country, I tilt the panels to 65 degrees for winter which helps with snow cover. I am usually up there weekly, some times every other weekend and always leave the inverter off and the CC on for the last 8 years and have not had any problems returning to a discharged battery bank. I guess we have been lucky so far?

Riley

Saggys said:

We also have an off grid cabin in snow country, I tilt the panels to 65 degrees for winter which helps with snow cover. I am usually up there weekly, some times every other weekend and always leave the inverter off and the CC on for the last 8 years and have not had any problems returning to a discharged battery bank. I guess we have been lucky so far?

Well you are checking/visiting often as compared to me. Plus my panels are not on a steep angle so they do get snow covered. 
The other thing to consider is that your batteries are being discharged and charged ever so lightly so that does cycle them a bit..

That's another reason I do a full disconnect. Why wear them for nothing. I would at least open the breaker to the inverter... it will draw some current as well. 

wellbuilt

 I agree in the winter months I just turn every thing off once the battery’s are full . 

 I’m allways above full voltage when I return  51. 5 or so . 

 In the summer months I’ll leave the charge controller on  for a week with 1 or 2 strings of solar panels  just to raise the SG  instead of equalizing equalizing the batteries . 

    This top me up to full and keeps SG good .

javid

I have a snowy off-grid system.  I would definitely be looking at LifePo4 server rack batteries like EG4 for your system.  Either warm the battery above 32 degrees before using it or figure out a battery box with heater - the battery management system won't let you hurt the battery in any case. 

Cold won't hurt them if you aren't using them and they have hardly any self discharge.  They will last forever and perform way better with no maintenance and you can take them to 95% DOD with no issues and they are way cheaper than lead acid when you consider how much usable power you have and their longevity.  

mike95490

javid said:

..... - the battery management system won't let you hurt the battery in any case.

Not always true.   "some" BMS systems will shutdown the battery if too cold.  Some dont.   And then you have the problem of
warming the pack up, and restarting the BMS   What happened to your MPPT controllers when the battery disconnected and they lost V+ and are running +137V and no 48V battery ?

javid

mike95490 said:

javid said:

..... - the battery management system won't let you hurt the battery in any case.

Not always true.   "some" BMS systems will shutdown the battery if too cold.  Some dont.   And then you have the problem of
warming the pack up, and restarting the BMS   What happened to your MPPT controllers when the battery disconnected and they lost V+ and are running +137V and no 48V battery ?

If the BMS doesn't shutdown the battery when it is too cold, it isn't doing its job properly.  A LiFePo4 BMS will typically disable charging at 32F and disable discharge at 15 or 20F.  This would prevent the scenario with the MPPT controller you sketched out.  There are no doubt some compromises, but LiFePo4 batteries have so many advantages.  Heck a 100AH 48 V battery would only weigh 70 or so pounds - you could bring it home with you and bring it back to cabin warm enough to start using immediately....