Battery overwintering unattended

[awirtz]

Hello- I am in Vermont but leaving soon for bigger snowier mountains out west. My battery bank consist of 16 trojan t105 batteries in an insulated plywood box in my basement. It will see freezing temperatures this winter when I am gone. My question is, should I fully charge the batteries then disconnect my panels before I leave or should I leave the solar panels hooked up to charge the batteries all winter? They will have no load over the winter and I won't have any means to monitor or check on the system. Thanks

[crewzer]

Here's a link to Trojan's storage recommendations for their batteries: http://www.trojanbattery.com/Tech-Support/BatteryMaintenance/Storage.aspx

Here's a link to Bill Darden's battery storage recommendations: http://www.uuhome.de/william.darden/carfaq13.htm#store

HTH,
Jim / crewzer

[mike95490]

You need a fancy long term float charger.
Does your regular charge controller provide that?
Do you have grid power?
Is there a heater inside the battery box, and is it vented to the outdoors?

[awirtz]

Hello- Thanks Mike & Jim. I am off-grid with 1050 watts pv and an outback powerstation. I do not know if the outback has a fancy long term float charger but the outback is user friendly with adjustable settings so I think I will leave the batteries hooked up and they can always be charged but set the charge parameters a little lower. Are there any negative effects to having the batteries potentially in a continuous float state for up to six months? My battery box doesn't have a heater but it is vented outdoors with a powervent. Are there low wattage dc heaters out there?-(probably not since heating uses tons of wattage) Thanks- DREW

[crewzer]

Drew,

The MX will only charge the batteries during favorable daytime conditions. Accordingly, they won't be in a continuous float state for up to six months.

I like the idea of setting the MX' parameters for low/short settings. I'd use Trojan's recommendation for the Float setting, but I'd use a short and low setting for the Absorb setting (i.e., 14.3 V for 15 minutes for a 12 V battery)... just enough to stir up the electrolyte, but not quite enough to boiling off much water. You'll need to connect the remote battery temp sensor to compensate for the low ambient temperature.

HTH,
Jim / crewzer

[mike95490]

My battery box doesn't have a heater but it is vented outdoors with a powervent. Are there low wattage dc heaters out there?-(probably not since heating uses tons of wattage) Thanks- DREW


As long as the batteries are fully charged, I think you have to go further north to freeze them.
http://www.uuhome.de/william.darden/carfaq4.htm#freeze_points -35F
If they were going to sit idle, and discharge, I would worry. In the winter, with snow buidup and such, with no loads, you won't likely overcharge. In case the snow shuts the panels off, are there any loads that will drain the batteries, and if the worst happens, and one leaks on the floor, do you have a containment system? What powers the powervent?

What's your climate like in winter: http://www.city-data.com/city/Morrisville-Vermont.html

Maybe try throwing a sheet over your panels, and measure you batt voltage, and then measure again the next day, might give an idea what snow covering them would do. Use a digital meter

[niel]

awirtz,
go ahead and leave the pvs connected through the mx60. as crewzer said you could lower the absorb voltage down to its minimum voltage to 14.3v. this is best for your batteries as all batteries have a self discharge and being cold it is also bad for a battery's capacity. this would prevent the self discharge and being on float it will not harm the batteries, but it will warm them a tad thusly helping in the prevention of the batteries freezing should the temp get that low. i've heard of discharges as high as 7% per month for some batteries, but even if your's is lower that adds up over the course of many months and could put the batteries more in danger of freezing without a float charge on it.