[RE-wrenches] Wintertime battery maintenance charge rate?

[Ronald Paredes]

Hello Dan,

The electrolyte’s freezing point at 40⁰F below is about 1.230, which translates to about 85% SOC for the T-105 batteries. Ideally, however, you should try to keep the batteries at 100% SOC.  At 40⁰F below, the T-105 battery will self-discharge at a rate of .15 Amp-hours per day. Since you will have a battery bank of 4 strings, the total self-discharge rate will be about .60 Amp-hours per day (7.2Wh per day) for the whole system. The important thing to keep in mind when batteries will experience extreme temperatures is that the electrolyte cannot be stratified, or the above calculations will not apply. A good starting point is to fully charge and equalize the batteries prior to storing them. By the way, the equalizing voltage for a 12V system should be 15.5V. To answer your question, the 24 Watts should do the job. 

Hope this helps and please feel free to contact me.

Best Regards,

Ronald Paredes
Technical Product Manager – Renewable Energy
Trojan Battery Company

12380 Clark Street 
Santa Fe Springs, CA 90670
Tel: (562)236-3000 Ext. 3066
Fax: (562)236-3279
rparedes at trojanbattery.com
www.trojanbattery.com

Trojan Battery Company - Clean Energy for Life™


-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Dan Fink
Sent: Tuesday, July 13, 2010 1:56 PM
To: RE-wrenches
Subject: [RE-wrenches] Wintertime battery maintenance charge rate?

Hello esteemed Wrenches;

I'm currently at a remote job site in far Northern BC, float plane and helicopter access only. My system install was a success, as I am using satellite internet to ping the list here!

There is a main lodge, and a remote camp, and neither are occupied from November thru May. The remote camp gets ZERO sunlight for 3 months of the year, while the main lodge is on a lake and gets some sun each month. Both PV arrays must be stowed indoors for the winter, as they are on ground racks and the Grizzly bears and moose will rip them to shreds when nobody is at the camps during winter, and snowdrifts can be 10 feet deep or more.

My plan is to move the small battery bank box (2 Trojan T-105s in a
cooler) to the Lake by helicopter each  fall, parallel it with the batteries there all thru the main DC fuse (6 Trojan T-105s wired for 12v), and run a small winter maintenance PV panel into all for the winter. Total of 880 amp-hours capacity.

My question is, how much winter charging is needed to keep the batteries charged and prevent freezing? We have an existing Unisolar roll-up panel on site that is showing 24 watts on my meter, and can be mounted on a tall pole. Is that enough? Temps can reach 40 below F.

Your input is appreciated!
DAN FINK
Buckville Energy Consulting LLC
_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org



This e-mail message and any attachments that accompany it may contain 
information that is confidential, privileged, or protected from disclosure.  
It is intended solely for the use of the individual(s) to whom it was intended 
to be addressed. If you have received this e-mail by mistake, or you are not 
the intended recipient, any reading, disclosure, copying or other use of this 
communication is strictly prohibited.  If you have received this communication 
in error, please immediately advise the sender at their phone number listed 
above, or by electronic mail, and also permanently delete the original and all 
copies of this e-mail and any attachments from all locations. Thank you.