The cells are stacked 2x8. Heat pads on the outer edge of each cell. No way mine will see 140F.I assume you only have them on one side of the cells, and not the other?
I am more concerned about an unusual cold snap with inadequate heat.
The cells are stacked 2x8. Heat pads on the outer edge of each cell. No way mine will see 140F.I assume you only have them on one side of the cells, and not the other?
I'm not sure how to interpret what you are saying. Are the pads actually heating to 140°? Is that 140°F, or 140°C? Either way, if you are actually getting them that hot, then yeah, you shouldn't put them in contact with the cells. I would actually never recommend that something that hot be used to keep LiFePO4 cells warm.I am using the silicone @140 degrees, I still think it is too hot for direct contact.
Just that I am using the pads but to heat the air around the batteries, i never measured the temperature. I don’t care how hot they get. My system is different in I will never let the batteries get cold soaked, the air is always around 50 degrees and that is all the temperature the batteries will see. And I agree low and slow. I was just using the 60c figure in your post as I never measured temperature on mine.I'm not sure how to interpret what you are saying. Are the pads actually heating to 140°? Is that 140°F, or 140°C? Either way, if you are actually getting them that hot, then yeah, you shouldn't put them in contact with the cells. I would actually never recommend that something that hot be used to keep LiFePO4 cells warm.
My point above was that it is a better strategy to heat low and slow: Lower temperature, and for a longer time to allow the thermal mass of the cells to absorb the heat the whole way through. What @time2roll did was to put 4(?) pads in series, effectively reducing the pads heating to 25% of their rated watts.
I've not heard the term "cold soaked" but I think I get what you mean. My thermostat is set to keep the cells between 50°F and 60°F. My cells never get below 50°F either, so maybe your system isn't that different?Just that I am using the pads but to heat the air around the batteries, i never measured the temperature. I don’t care how hot they get. My system is different in I will never let the batteries get cold soaked, the air is always around 50 degrees and that is all the temperature the batteries will see. And I agree low and slow. I was just using the 60c figure in your post as I never measured temperature on mine.
I work in HVAC and radiant floor heating, so a cold soaked slab is something I deal with which has high mass. It takes more heating capacity to bring a mass up to temp rather than just having to satisfy the heat loss.I've not heard the term "cold soaked" but I think I get what you mean. My thermostat is set to keep the cells between 50°F and 60°F. My cells never get below 50°F either, so maybe your system isn't that different?
That's interesting! I had Googled it and almost all the results were about aviation, or food. Wings of planes are cold soaked after a flight because of the fuel still stored in the wings, or having been parked overnight in very cold temperatures with fuel in the wing tanks, etc. I had assumed you must be in aviation!I work in HVAC and radiant floor heating, so a cold soaked slab is something I deal with which has high mass. It takes more heating capacity to bring a mass up to temp rather than just having to satisfy the heat loss.
My logic to keep my cells in the range of 50°F-60°F was driven by a few things.50-60*F (10-15*C) degrees or 35-45*F ( 2-7*C)?
Set mine at 2-7*C.
Wondering if there is that much difference, what do you think?
I don't think I've mentioned it here anywhere, but I made some changes to my insulated box, and got some happy results.My thought on the temperature range is that 5° F is too small. Besides the heating system coming on more frequently, perhaps the batteries are not getting thoroughly warmed. I use a 10° F spread. Would 15° F be even better? Maybe. To really answer that question, I would need a lot of temperature sensors in different locations on the battery. I will say that the temperature probe on the surface of the battery between cells two and three (4s battery) reports a value that is very similar to the temperature probe on the positive post of the battery.
My batteries are not in a sealed container. I tried to isolate my temperature probes from the ambient air but I've noticed that the temp drops a bit after the warming system shuts off. I suspect that my temperature probe needs a bit more isolation and I need to seal up the insulation around the batteries better. A warming system wasn't part of my initial battery fixture design, so the insulation is retrofitted in as best I could. I don't have much room to work with and that greatly limits my options.
I don't use my batteries hard when they're at the lower temperature ranges. When I'm camping at cold temperatures the furnace is cranking and the batteries are usually sitting around 60° F due to having a furnace duct running through the same compartment where the batteries are located.
I don't think I've mentioned it here anywhere, but I made some changes to my insulated box, and got some happy results.
I was changing the heater-control electronics, and decided to pull the cells out and change some of the bus bars and such. In the process I decided to seal up the box more. I already had a big roll of mastic-lined foil tape for sealing heat ducts, so I used that to seal up all the seams in the XPS and between the XPS and the plywood inserts in the box. I also put a good amount of weather stripping between the box and the lid to prevent air flow when the lid is on (I knew I had a leak there).
When I reassembled the battery with the new electronics and ran a test last weekend (really cold temps from 31-Jan until the morning of 3-Feb) I was pleasantly surprised. The change was not huge, but it was obvious. Temperature fell more slowly between heat cycles than I would have expected, and it took a bit less time to arm the cells back up to 60°F than before.
So @HRTKD, I get the impression (from here and other posts you've made) that you are going mostly all-in on upgrading your system to Victron? I've been helping someone do that for their boat, and I have to admit I like Victron stuff.
Those do look nice, but for most of us using 120VAC would require firing up the inverter, which would be counterproductive. My little 12V 12W heating pads fit my needs better.Coming from a gardening perspective of keeping delicate seedlings at just the right temp makes all the difference. These mats are cheap, durable and come in all sizes. This size only consumes 17.5 watts. If you have 120vac close by this might be an option?
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I sure don't disagree since I haven't taken a survey, but in my case, as in the case of anyone coming from a grid connected world, there has always been a 120vac outlet in my shop close to where my DIY back-up system will be set up so it's just a no brainer in my case. I already own these and most of the time they just lay in a drawer unused. My batteries will remain snug and warm, plus that way they can also serve double duty when gardening time arrives. I'm just trying to keep it in the true spirit of DIY?Those do look nice, but for most of us using 120VAC would require firing up the inverter, which would be counterproductive. My little 12V 12W heating pads fit my needs better.
My situation and use is similar. I had a seed starter heating pad and figured, why not.I sure don't disagree since I haven't taken a survey, but in my case, as in the case of anyone coming from a grid connected world, there has always been a 120vac outlet in my shop close to where my DIY back-up system will be set up so it's just a no brainer in my case. I already own these and most of the time they just lay in a drawer unused. My batteries will remain snug and warm, plus that way they can also serve double duty when gardening time arrives. I'm just trying to keep it in the true spirit of DIY?
Those do look nice, but for most of us using 120VAC would require firing up the inverter, which would be counterproductive. My little 12V 12W heating pads fit my needs better.
I sure don't disagree since I haven't taken a survey, but in my case, as in the case of anyone coming from a grid connected world, there has always been a 120vac outlet in my shop close to where my DIY back-up system will be set up so it's just a no brainer in my case. I already own these and most of the time they just lay in a drawer unused. My batteries will remain snug and warm, plus that way they can also serve double duty when gardening time arrives. I'm just trying to keep it in the true spirit of DIY?
Well, well...maybe I should take a survey?My situation and use is similar. I had a seed starter heating pad and figured, why not.