Thanks Larry, I figured you would have some experience in this, especially given your RV retrofit experience. This is generally what I had thought would be the case. I also was browsing that exact controller when your post came in 😊
Good to have my thoughts confirmed on heat generation, that should make this setup feasible. I am going to look for a dual mode controller or 2 controllers for both heating and cooling, a heating mode for the heating pad, then a cooling mode controlling a small vent fan in the battery box to deal with what little heat is generated. The controller you linked to operates such that it has a central temperature setting maybe 65F, and once either heating or cooling is triggered, the respective load will run until the central temperature setting has been hit (i.e triggered the heater at 40F but the heater runs till the battery is at 65F). I’d like to operate in two separate 5-10degree windows, essentially keeping the batteries between 40-45F and 90-95F. With Regards, Daniel Young, NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90 From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Starlight Solar Power Systems Sent: Monday, February 26, 2018 12:14 PM To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Subject: Re: [RE-wrenches] heating a lithium battery bank Hi Daniel, Charging a Li battery below freezing can damage the battery very quickly. Low current, C.05 rate, can be used until cell temperature is above freezing but that can be hard to setup and control. You can store or discharge most Li batteries down to about -5°F. Unless you are using very high current, 1C or more, for long times, the battery temp. will rise very little. Same applies to charging, keeping the rate low will not cause a heat issue. Your best option is build a battery box, insulate and heat it. Very simple with DC silicone heaters. A well insulated box is the key to low power consumption. Make the box so you can vent for summer use. Silicone heaters: https://www.ebay.com/sch/i.html?_from=R40 <https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2057872.m570.l1313.TR0.TRC6.A0.H0.XSilicone+Heater+Flexible+Pad+.TRS5&_nkw=Silicone+Heater+Flexible+Pad+&_sacat=0> &_trksid=p2057872.m570.l1313.TR0.TRC6.A0.H0.XSilicone+Heater+Flexible+Pad+.TRS5&_nkw=Silicone+Heater+Flexible+Pad+&_sacat=0 Temp controller: https://www.ebay.com/itm/Digital-STC-1000-All-Purpose-Temperature-Controller-Thermostat-With-Sensor-D/112145401355?hash=item1a1c63060b:m:mpDAMY9SK0sPRVsidEQ682w Larry Crutcher Starlight Solar Power Systems On Feb 26, 2018, at 9:56 AM, Daniel Young <dyo...@dovetailsolar.com <mailto:dyo...@dovetailsolar.com> > wrote: Hello Wrenches, here is a fun one for you all. The client you all helped me with earlier this year is now considering changing out their AGM off grid bank with a lithium battery bank before the next winter. I looked into this, as we have been eying the various lithium options for 2+yrs now, but not bit the bullet and really designed a bank into a system. The main issue I am trying to consider is this. The cabin is not occupied during most of the winter, and the batteries are in the unconditioned, but attached, garage. They drain the plumbing system and shut off all breakers except the ones that power the internet, chest freezer, and security system. As such, the battery bank has routinely gotten below freezing, sometimes staying there for 1-2 weeks. This is not an issue with AGM’s, within reason. The battery bank has never gotten below 20F over the last 2 winters, where the site has seen below zero temps for brief periods. But the AGMs likely produce more heat during a charge than lithium’s, and they have significantly more thermal mass to ride through the really cold nights. Lithium batteries, to the best of my knowledge, can be below freezing during storage. But to safely charge, they must be above 32F. So the thought was to provide an insulated battery box, and design in some small heating system that is set to 40-45F. The first thought was a low power fiberglass heating pad like is sometimes used for livestock to give them a slightly warmed place to lay down. Then tie that to a thermostat with a sensor on the battery bank. I would of course need to try to account for the extra load in the battery bank sizing. They array is more than is needed right now so I do not worry about it’s ability to compensate when the sun is shining. In theory this could be ok, but I worry about the summer. Will the insulated enclosure cause the opposite issue during the summer, the batteries getting too hot? I have seen the AGM bank go to 110F at one point in Aug 2016. But with the lower internal resistance of the lithium’s, maybe this is less likely to be an issue. Do any of you wrenches have any experience with this unconditioned setup? With Regards, Daniel Young, NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90 <http://www.members.re-wrenches.org/> www.members.re-wrenches.org
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