kenkoh
Solar Enthusiast
Scrap that found the answer.
LiFePO4 heating pad for cold temperatures
- Thread starter Will Prowse
- Start date
SCClockDr
Solar Enthusiast
& the answer was...?
kenkoh
Solar Enthusiast
Yes you can hook it up to the battery you're warming. Didn't give details about the power draw I have to go back to charts and work that one out.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
A few points:
- If you have a well insulated box, it does not need very much energy to keep it warm. I would shy away from high wattage heat pads.
- For an external temp sensor, be sure to set the off point a couple degrees above the min temp you want to allow charging. It is possible for the internals of the battery to still be low even if the box is above freezing.
- You want to gently heat the battery. You don't wan't a really hot spot in the battery.
- I personally would try to avoid the heat pad all together if I can.... even if it means not being able to charge sometimes.
Looks like my idea has stuck at the costs. I couldn't find NC-Relays for about 200A permanent load so I researched contactors and solenoids. Which I could find, but they are to expensive. Looking at the cost I could just sell my BMS and buy one with low-temp cut off included.
Just to fulfill the informations, these are the two contactors would work:
SPST 400A max: https://www.aliexpress.com/item/33029880210.html (1NC)
SPDT 400A max: https://www.aliexpress.com/item/33001649024.html (with 1NO and 1NC) [auxiliary contact at 24VDC]
I also found this solenoid, but I'm not sure about the quality of the product. Amazons reviews aren't the best for these.
SPST 200A max: https://www.aliexpress.com/item/33007969754.html [not even sure here, 'cause on amazon the same is a NO]
Up to 100A there is a lot available on the market, even NCs that are much rare than NOs. And it's very cheap. But above it's a crap.
I also thought about some MOSFETs that switch very fast and are available for high current. They even can be connected in parallel, but the internal resistance seems to be the problem here which would consume lot of power on high current.
Just to fulfill the informations, these are the two contactors would work:
SPST 400A max: https://www.aliexpress.com/item/33029880210.html (1NC)
I also found this solenoid, but I'm not sure about the quality of the product. Amazons reviews aren't the best for these.
SPST 200A max: https://www.aliexpress.com/item/33007969754.html [not even sure here, 'cause on amazon the same is a NO]
Up to 100A there is a lot available on the market, even NCs that are much rare than NOs. And it's very cheap. But above it's a crap.
I also thought about some MOSFETs that switch very fast and are available for high current. They even can be connected in parallel, but the internal resistance seems to be the problem here which would consume lot of power on high current.
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FilterGuy
Solar Engineering Consultant - EG4 and Consumers
I was wondering about that.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Not off hand. Sorry!
I am not sure about putting several smaller SSRs in parallel. I would be a little worried about one of them taking more of the current than the others...but it might work. Be very carefull about start-up currents. If one is a little faster to turn on than the others, it will take the whole load for a moment. If one blows out with an open, the others will try to take up the load and you could have a cascading failure that takes them all out.
Also, be particularly careful when you first hook the circuit to the inverter. The large capacitors in the inverter will have a very high in-rush if you do not pre-charge them. Use a resistor to pre-charge the capacitors before hook-up. (You should do this in any case)
(The Victron Battery Protect is a fancy SSR and they specifically state that it should not be used between the battery and the Inverter. My understanding is that this is because of the potential in-rush current))
Ok, I just found this:
400A:https://www.aliexpress.com/item/4000295716219.html [NOT NC]
200A:https://www.aliexpress.com/item/4000295498163.html [NOT NC]
Didn't know there are so big SSRs. They should be able to handle any in-rush current, and they aren't very expensive. They also should have no realizable delay because of missing mechanical components.
Only problem, they get really hot. Above a current of 60A you need to install not only a heat sink, but also a cooling fan. Just thinking about the heating pads again.
EDIT: Ok, don't know if the others are NCs, when it comes to NC I just found 100A https://www.aliexpress.com/item/4000521371702.html and of course it is more expensive. So, just forget it again.
400A:
200A:
Didn't know there are so big SSRs. They should be able to handle any in-rush current, and they aren't very expensive. They also should have no realizable delay because of missing mechanical components.
Only problem, they get really hot. Above a current of 60A you need to install not only a heat sink, but also a cooling fan. Just thinking about the heating pads again.
EDIT: Ok, don't know if the others are NCs, when it comes to NC I just found 100A https://www.aliexpress.com/item/4000521371702.html and of course it is more expensive. So, just forget it again.
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This one seems to be even programmable. I think I have to take a look closer into it, thanks.
Ok, it seems I'm stuck here for now.
Relay is not an option jet, nevertheless if its a classical relay, contactor, solenoid or SSR. It's just to expensive.
Another BMS is not an option jet. There is not much on the market for now with a low temp cut off, and I need 200A. Installing two of them in parallel or switching to 24V is not an alternative for now.
The programmable battery protectors with a relay inside are to expensive and programming of the voltage is limited. (This may work on the Victron using bluetooth and being able to set the low voltage restart lower than low voltage shutdown e.g. 12,8V restart and 14,6V shutdown, but I don't know)
It may be also possible to use the BMS itself as a relay by just cutting the power off from the negative balancing line with a very lightweight and cheap nc-ssr, but this may also damage the BMS itself. Nevertheless I hope this can work, because I like this hackish idea.
I think, the best I can do for now is to realize the pad heating with a temperature controller. It's not completely secure and it will waste lot of energy, but its cheap and it will work for a while. Meanwhile I'll observe the market for interesting changes. Maybe we'll get new BMS models with low temp cut off, or the SSRs evolve. We'll see.
Relay is not an option jet, nevertheless if its a classical relay, contactor, solenoid or SSR. It's just to expensive.
Another BMS is not an option jet. There is not much on the market for now with a low temp cut off, and I need 200A. Installing two of them in parallel or switching to 24V is not an alternative for now.
The programmable battery protectors with a relay inside are to expensive and programming of the voltage is limited. (This may work on the Victron using bluetooth and being able to set the low voltage restart lower than low voltage shutdown e.g. 12,8V restart and 14,6V shutdown, but I don't know)
It may be also possible to use the BMS itself as a relay by just cutting the power off from the negative balancing line with a very lightweight and cheap nc-ssr, but this may also damage the BMS itself. Nevertheless I hope this can work, because I like this hackish idea.
I think, the best I can do for now is to realize the pad heating with a temperature controller. It's not completely secure and it will waste lot of energy, but its cheap and it will work for a while. Meanwhile I'll observe the market for interesting changes. Maybe we'll get new BMS models with low temp cut off, or the SSRs evolve. We'll see.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
@astronom.... did you ever pursue the Peltier idea? @svConcordia In this thread has a cooling problem that a Peltier might be an interesting solution for (Even with the horrible efficiency it might work well).
Still haven't built the sysytem, but some parts arrived (although only 8 Peltier instead of 10 ordered... figuring out with the AliExpress vendor in progress).
orangeminnie
New Member
- Joined
- Feb 5, 2020
- Messages
- 198
source?
Good points.
Because of charge/discharge efficiencies wouldn't you want to be quite a bit above 0C? With that said, in cold situations with a functioning heating system your batteries would normally be slightly warmer than the ambient temperature inside the box and you're not trying to heat the batteries so much as trying to prevent them from cooling further.
The environmental thermostat in my camper can't be set below 55F(around 13C) why screw around with letting your batteries get below 50F(10C)? It seems to me that you'd spend less energy holding the line at 50F than letting it get to near 32F then warming back up to 50F in the morning.
In other words warming up cold batteries is a lot harder than not letting them get cold in the first place.
I have a koi pond that freezes in the winter. In order to keep an open hole in the ice to vent methane and CO2 I constructed a floating bubble to keep a pocket of warm air over the pond which would prevent ice from forming in one spot. It was nothing more than an upside down plastic tub with floats and a 25w light bulb in it. It worked like a champ for years and this is in Wisconsin winters.
So what do you think about simple enclosure heaters? They've been around a long time and they are designed to keep enclosures for electronics warm. You just need to keep that bubble of air from getting colder.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Yes, it will take longer to get them back up to 55 F, but letting them get down to around 35F and then heating them back to 55F will take less total energy than holding them at 55F. (That is basic thermal dynamics)
Ideally, your temperature control would kick on around 35F or 36F (or whatever your lower limit is) and kick off around 5deg above that (~40F) This keeps the batteries warm enough with the least amount of expended energy.
I just got a notification from this thread and had forgotten about it. The self heating ammo can I posted on page 2 is still in service and we're entering consistent warm weather in Colorado. The temperature was maintained the entire winter including temps below 0*F, snow days, days of minimal solar collection (usually due to snow on panels). I never really thought much about it. I had the temp set to 40*F for months on end and it never dipped below that.
I'm going to install a marine deckplate or something similar in the lid above the BMS, which was 102*F today (78*F outside). It's going to get a lot hotter. The probe wedged between the cells peaked at 85*F today and is still 82*F at 11:30pm. Anyway, deckplate would allow easy summer mode. Probably some sort of filter / pantyhose to limit dust infiltration to ammo can. Silicone heating pad on thick aluminum false floor works great. I didn't even bother with the PID control of the heater much. It's set to max at ~60 watts. I could have eliminated a lot of complexity by just using a 50w silicone heat pad.
I'm going to install a marine deckplate or something similar in the lid above the BMS, which was 102*F today (78*F outside). It's going to get a lot hotter. The probe wedged between the cells peaked at 85*F today and is still 82*F at 11:30pm. Anyway, deckplate would allow easy summer mode. Probably some sort of filter / pantyhose to limit dust infiltration to ammo can. Silicone heating pad on thick aluminum false floor works great. I didn't even bother with the PID control of the heater much. It's set to max at ~60 watts. I could have eliminated a lot of complexity by just using a 50w silicone heat pad.
Is that energy difference enough to justify letting them get into the cold inefficient range to begin with? I guess that really depends on the details of the system and the use case.
Capt Bill
Sailing Options
I would consider one or two of these for a freeze protect switch in a battery box, possibly connected to an older style light bulb:
Senasys Snap Disc Thermostat Switch - Circuit On At 35°F and Off At 45°F - Large Flange, Part Number 2511L002-2132 - Temperature Sensors - Amazon.com
Senasys Snap Disc Thermostat Switch - Circuit On At 35°F and Off At 45°F - Large Flange, Part Number 2511L002-2132 - Temperature Sensors - Amazon.com
www.amazon.com
and another interesting option I cam across was:
I was also thinking of an insulating layer of "Aircrete" (foam injected cement that has microscopic bubbles giving it insulation plus fireproof abilities) around battery bank / inside a battery box idea.
Food for Options ;+)
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