View Full Version : Battery Pad-Heater Installation Tips Please
November 24th, 2009, 18:41 PST
When we arrive at our cabin, it can be as cold as 0* f inside (it is often ten degrees colder inside than out). Our two twelve volt, AGM batteries, while fully charged, are anemic at these temps and since they are under the stairs, take forever to warm up. Since we usually start the Honda EU 2000 on arrival, my plan is to heat the batteries at the same time for a couple of hours. I bought two orange silicone battery heater pads today. 60W each. Not thermostatically controlled.
The batteries now sit on 2" blue foam. I plan to cut a piece of that grey, cement board (used for a thermal barrier below woodstoves, etc.), sit that on top of the blue foam, put the battery heaters on top of that, then the batteries. I will plug the two heaters into the outlet dedicated to running the battery charger (and thus on generator power only).
Any thoughts or suggestions?
Next question: will heating my batteries enhance battery life as well as performance?
November 24th, 2009, 18:55 PST
I think the reverse will be true, that heating will shorten battery life rather than lengthen it, depending on how you draw it down. As a rule of thumb, battery capacity goes down (short term) with temperature, but battery life goes up:http://www.batteryfaq.org/
While I don't think that putting 60 watts under the batteries is going to hurt them, I'm not sure it is going to do much good. I might also be concerned if the battery warms at the bottom, but is still quite cold near the top. I don't know what the result might be but my intuition is that it might be a problem.
I also think that depending on the the thermal mass of the batteries, it is going to take a long time to draw out the cold. When we are away for a while, things take days to thaw. Try spreading peanut butter that has been -40 for a couple of weeks.
Depending on what you need the batteries for, I think I would use them, and let them warm up naturally. If you have them in a foam box, they will generate some heat from charging, as well as from discharging.
November 24th, 2009, 21:07 PST
A cold battery will have less capacity. Running a cold battery down to low state of charge is worse for damage then the little bit of heating you are planning. Did not do calculations but gut feel is 60 watts will take a long time to warm up 100 lbs of lead.
AGM's are pretty good for cold weather use. What is the open circuit battery voltage when you first show up before putting any load on them?
How long are you leaving the cabin unattended and are you sure you don't have any loads on the battery? Just to be sure I would put a switch in-line to disconnect them from inverter before you leave.
Make sure you fully charge the batteries before leaving.
November 25th, 2009, 8:34 PST
I agree with RCinfla as far as it goes. [B]if[B] you run the battery down below ~50% soc it will get drawn down faster. If the battery is allowed to sit un-recharged it would be subject to sulphation just as any battery would be. The 50% discharge would not be measured in % of AH capacity as you might do with a warm batter, but with a hydrometer, (or more probably, intuitively).
If the battery were drawn way down, and it was still cold, there is a risk of freezing it, but I think in the real world that would be pretty unlikely, as the battery will produce some heat as it discharges, and you are beginning to heat the building.
Here is my take. If you are going to run the genny anyway, why do you care if the battery has some more limited (short term) battery capacity. Since you are going to run the genny, use it to power your loads for a while to keep the battery loading down. Save the trouble (and money) for a bigger battery bank going forward.
(On the other hand, it isn't going to do any harm, I don't think)
November 25th, 2009, 11:17 PST
Up in the frozen Cariboo where Winter temps can dip to -40, my batteries are in a box insulated with 2" of polyfoam on all sides. The MX60 & panels stay hooked all year 'round, and the batteries have never frozen nor been discharged/unusable upon Spring arrival - despite the interior cabin temp being a good 10 degrees below outside (logs hold cold as well as heat). Frankly, your batteries shouldn't be suffering like that if they remain on controlled charge all Winter; enough current should be going in to keep them warm and happy.
As Tony says, if you're going to run the generator anyway ... My choice would be use a battery charger and 'warm them from the inside out' rather than sticking them on heating pads. Those pads, btw, were designed for automotive applications in cold climate where there is no charge source or insulation.
November 25th, 2009, 11:39 PST
Thanks, as always, Gentlemen.
To respond to your questions: (1)Before we leave the cabin which is 91 airmiles north of Anchorage and 62 degrees lattitude, I always charge the batteries with my Vector charger until it says "FULL". This time of year, there may be a tiny bit of solar charging as well by my single PV panel.
(2) I just installed my new Morningstar 300 inverter last weekend. We put a breaker between it and the batteries and of course wired an on/off switch as well. So, it should be isolated from the batteries when the breaker is OFF.
(3) As for the "open circuit battery voltage" I don't know exactily what that is but when we arrived, it was 2* f inside the cabin and 12* f OAT (so the batteries were colder than Hillary's heart after she heard about "that woman, Ms. Lewinsky"). Before we turned anything on, my Morningstar controller (top LED number) read something above 13 volts and the green 'fully charged' light was flashing. As I said, I'd charged them up almost 2 months before, there had likely been some PV charging and we'd pulled the defunct Xantrex 1000 inverter and unplugged my small backup inverter.
I appreciate your good comments on my battery heating scheme. I paid $36 for the both of them so it will be a cheap experiment (I hope!). I'll watch the batteries to make sure nothing gets too warm.
Happy Thanksgiving to all.
November 25th, 2009, 11:45 PST
2 cents from sunny California...
Do not charge (or use) batteries that may be frozen. Use of an electric heater to get the batteries in operational range (~70-80F) with a smallish heater (60 watts should not kill a battery for short term use) operated with a genset seems like it would be OK.
Once the battery bank is in the optimum temperature, a foam box and normal cycling should be good enough to keep things working well (what do I know of -40F/C).
Get a cheap remote thermometer to monitor the core battery bank temperature will ensure that you don't go thermal run-a-way (a possibility with an insulated box and lots of charge/discharge current). If you can find a remote thermometer with an alarm setting (say at 90+F) would give you plenty of warning if things get out of hand.
Once you have time on the installation--you will quickly figure out what works best for you.
November 25th, 2009, 11:55 PST
I'd cut a aluminum plate, to place between the heater pad and the battery. Unless the pad is the same footprint as the battery, it may, when warm, try to warp the heavy battery around the lump in the middle. And the alum. plate will spread the heat to the entire base of the battery, in addition to distributing the weight load.
November 25th, 2009, 12:01 PST
Thanks Mike and BB.
To followup: when the controller says 12.2 volts with no load on the batteries, I fire up the Honda generator and charge them up to "FULL" with the Vector charger. That's what my installer-electrician suggested. Does that sound like a good, conservative approach? And after dinner when I run the Honda to power the halogens to light the sledding hill for my kids, I charge them up, whatever the voltage indicates.
From reading this forum, I get the idea that as long as the charger doesn't overcharge the batteries, you really can't charge them too often.
Ok, thanks again. I really like my new Morningstar 300 inverter; no noisy fan, and it definitely has the appearance of a quality unit. By the way, the first one we got did not power up. My guy called the factory and they got on their horse, UPS'd a new one up in time for us to install it last weekend. Very happy with the excellent customer service.
November 25th, 2009, 12:16 PST
Really depends on the charger and setup... Yes, it is very possible to overcharge a battery bank... AGM and Sealed batteries are very susceptible to overcharging (overcharge once and vent them-kill them... Long term high voltage charging can cause loss of lifetime).
Read the Battery FAQs that Tony "Icarus" linked to in his earlier post. And look up the charging instructions for your brand and model of batteries. Basically, you will charge them with maximum current until they reach the recommended set voltage (something like 14.4 for AGMs at 77F, note is temperature sensitive, cold batteries need higher charging voltage). When 14.4 volts is reached, then keep the charging voltage on the battery banks until the current reduces to xx% x Capacity... Or something like that.
In general, with short term charging (AC generators, solar panels, and daily energy usage from bank)--you probably do not need to crank down to 13.x volts for day to day usage while you are there. However, when you leave for weeks or months at a time, having the battery charge controller crank back down to 13.x volts will maintain the charge and lessen the risk of over charging (.e., entering float stage earlier when you are away from the cabin).
November 25th, 2009, 21:17 PST
I'm not familiar with vector chargers, but if it is anything like the Vector inverters that Canadian Tire sells, I would consider looking at a different charger, something like the Xantrex TC series (new gen has come out) A proper 3 (or 4) stage charger with temperature compensation will go a long way to keeping your batteries up to snuff.
I'm glad you like the Suresine 300. I love mine.
Also happy Thanksgiving to all those in the USofA. We did ours a month ago when the weather was nice.
November 29th, 2009, 17:59 PST
Maybe I am misunderstanding it, but you plan to put the battery warmer under the batteries? I wouldn't do that having used the battery warmers in cars. Even if you put something on top if them to spread out the weight it will still rock and likely pinch the warmer. Now if you can somehow add 4 or more spacers to create a space under the battery then maybe. If it were me I would just wrap the warmers around the exterior of the batteries and let them do their thing. I would do as your suggesting and just let them run when ever the genset is running to warm up the batteries a bit, but 60w seems like it might get warm so I would check it when you first hook everything up to make sure you don't overheat the batteries.
Powered by vBulletin® Version 4.1.10 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.