diy solar

diy solar

LiFePO4 Battery Warmer Install

Right, it puts out 12v. But what is the input volt range? It sounds like it's expecting a minimum of 15v. If I give it 13v, what's going to happen?
 
Your setup is looking really awesome @HRTKD - If you get some info on the pads you used being available on-line, please post!

Where (approximately) are you located? Do you expect to have somewhat long periods of below freezing while your unit is mostly unattended? (If it isn't obvious, I'm selfishly trying to compare to my situation with a cabin in the mountains.)
 
Your setup is looking really awesome @HRTKD - If you get some info on the pads you used being available on-line, please post!

Where (approximately) are you located? Do you expect to have somewhat long periods of below freezing while your unit is mostly unattended? (If it isn't obvious, I'm selfishly trying to compare to my situation with a cabin in the mountains.)

Colorado front range. It's supposed to get below 0° F this week. If things work out, I'll check the trailer during that period.
 
The specs for the board says the input power is 12v +/- .5v. That's certainly not in the upper range at which a LiFePO4 battery can be charged. My boards are wired off the common bus bars in my system. They're seeing pretty much whatever the solar charge controller or converter is pumping out, so a voltage as much as 14.4v is likely. So far, it's working.

However, it is a concern. Maybe run thinner wire so you get some voltage drop? Normally, I wouldn't recommend such a thing.



I thought I answered this already, but I don't see my post. :(

My thermostat is active 24 hours a day. It, and the warming pads, will use solar when it's available, otherwise, it's battery power. So far, I haven't seen my state of charge drop below 97% on my 560Ah of battery capacity. A system that only warms the batteries when power from solar is available could be done, but it increases the complexity of the system.

There are parasitic draws on an RV's electrical system. Some of these are hard to control. The gas detector is hard wired into the 12v system from what I hear. You can turn off the trailer's 12v disconnect but the gas detector will still be on.

Yes, the thermostat works below freezing. My thermostat board is going to be the same temperature as the unheated trailer. I've been working on the trailer when it's below freezing, so I know the thermostat is still going in those conditions.
I've ordered one of the PTC heating plates from Amazon. Just one right now 12VDC, 70C PTC, just to try it out. I want to understand how much power I'm using trying to heat LiFePO4 Batteries, just to charge them. I may prove that AGM or flooded lead may be the best for my use

https://www.amazon.com/gp/product/B07RS3HQKS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I believe I could feed this either with the solar panels before the controller, Also with a 12V transformer off the 120V generator supply if I happen to arrive at night with no solar. After this hits temperature, the heat load would shut off, restoring the solar power to the controller for charging the batteries.

I was looking for a way to fix the poor installation of the cold temp sensors in the purchased batteries. Will has been busy proving almost none of the purchased batteries are correct. SOK and Big Battery mounted their sensor either in the air, or on the case. I would have to open up the batteries (void the warranty) to properly place the sensor in the middle of the battery cells. I have one Big Battery on order. I'll make my own instead of buying more. I'll put the OverKill BMS sensor in the correct spot, along with a few thermocouples and a controller for the heater.

On parasitic loads, I've surveyed my trailer. By pulling the fuses and putting a multimeter (current meter) across the fuse mount, I could pull the fuses that I don't need. The biggest load was the radio/satellite amp. Others were the fridge, CO and Propane detector. I believe I'm down to about 17W constant. (408Wh/day usage or 34AH/day). With the 600W of solar only putting out 120Wh every three days (40Wh/day), it looks bad. If the batteries shut down they will kill power to the solar converter, I'll have to manually restart the batteries. They say never to leave the solar on and disconnect the battery power. Things could get damaged.

My #1 reason for leaving the battery on is I have humidity issues in the trailer. The Adirondacks has high humidity. With the camper under the pavilion, it stays cooler than the outside air. The sun comes up and gathers moisture from the moss and trees and blows under the pavilion. The cold sides of the camper, along with any air infiltration inside the camper condenses the moisture like a cold drinking glass in the summer. I have paralleled the heating thermostat with a PID temperature controller, with 2 thermocouples in series, reversed, creating a differential thermostat. One TC is outside, the other inside. I set the temperature to about 3 degrees. If the inside of the camper is colder, it turns on the heat. This only happens in the mornings when the sun come up. This is only needed above freezing as moisture can't be transferred below that. Heating a camper 3 degrees above ambient is just a few minutes each time, just in the mornings when the sun comes up. Afternoons and night the camper is naturally warmer than the outside.

So I really don't need power until it's a warm day in spring. I'll have more solar power when it's sunny, snows melting, high humidity. It's a great correlation. I could add a snap disk temperature switch in few fuses I have for the heat controller, bringing my parasitical loads to zero.

Thanks for the info on the temp controller. I'll look into it.

Carl
 
Right, it puts out 12v. But what is the input volt range? It sounds like it's expecting a minimum of 15v. If I give it 13v, what's going to happen?
I'm coming in here kinda late, and I have only skimmed the thread to see this discussion. I think that the stuff you have implemented (electronic thermostat and heating pad) are almost certainly fine across a big operating range of voltage. Inserting a 78x-based regulator is only asking for trouble. A LM7812 requires (as I recall) a +2V headroom, and below that the efficiency goes to hell. You should be fine without it, IMHO.
 
Colorado front range. It's supposed to get below 0° F this week. If things work out, I'll check the trailer during that period.
Hey! We're neighbors! I'm in the suburbia that stretches forever south of Denver. My mailing address says Centennial, but it might as well be Larkspur or Glendale.
 
I have qty 4, 7 watt heating pads (for a total of 28 watts) on my qty 4 280ah cells, with a 1/16 in steel plate for dissipation. Knowing what I know now, I would have used a thicker aluminum plate. Aluminum dissipates heat better. They have 1/2 to 3/4 of XPS foam insulation on each side, except the top. I'm seeing about a 25-30F raise in temp (compared to ambient) at the top of my cells, which I assume to be the coolest part. The bottom of my cells, where the heating plate is, sees about a 40F rise from ambient. I think you will have more than enough heat—perhaps too much. You could easily modulate the heat with a repeat cycle timer, its basically a little circuit board that you can set to 10 sec on, 10 sec off, 10 sec on, etc. You can set the delay to whatever you want. I found one on Amazon for around $10, but ended up not needing it because my heating pads are small enough that they dont raise the temp too much.

When I had it connected and not touching the batteries, the plate got hot to the touch—it would almost burn me. But once the cells were in direct, firm contact with the heating plate—it now doesnt get over about 70ºF.
I know this post was a couple of months ago, so sorry for commenting late. The heat pads you have are smaller than the ones I bought (24V, 30W, quantity 4), but the same basic design. The problem is that the heat pads are spec'd with a maximum temp of 150°C. Mine were something over that, but not lots. The problem is (as you stated) they get very hot. To use these to slowly heat LFP cells will require you to cycle them on and off with a duty cycle that will warm but not cook your cells. Just FYI: Test it before you implement it.
 
I've ordered one of the PTC heating plates from Amazon. Just one right now 12VDC, 70C PTC, just to try it out. I want to understand how much power I'm using trying to heat LiFePO4 Batteries, just to charge them. I may prove that AGM or flooded lead may be the best for my use

https://www.amazon.com/gp/product/B07RS3HQKS/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I believe I could feed this either with the solar panels before the controller, Also with a 12V transformer off the 120V generator supply if I happen to arrive at night with no solar. After this hits temperature, the heat load would shut off, restoring the solar power to the controller for charging the batteries.

I was looking for a way to fix the poor installation of the cold temp sensors in the purchased batteries. Will has been busy proving almost none of the purchased batteries are correct. SOK and Big Battery mounted their sensor either in the air, or on the case. I would have to open up the batteries (void the warranty) to properly place the sensor in the middle of the battery cells. I have one Big Battery on order. I'll make my own instead of buying more. I'll put the OverKill BMS sensor in the correct spot, along with a few thermocouples and a controller for the heater.

On parasitic loads, I've surveyed my trailer. By pulling the fuses and putting a multimeter (current meter) across the fuse mount, I could pull the fuses that I don't need. The biggest load was the radio/satellite amp. Others were the fridge, CO and Propane detector. I believe I'm down to about 17W constant. (408Wh/day usage or 34AH/day). With the 600W of solar only putting out 120Wh every three days (40Wh/day), it looks bad. If the batteries shut down they will kill power to the solar converter, I'll have to manually restart the batteries. They say never to leave the solar on and disconnect the battery power. Things could get damaged.

My #1 reason for leaving the battery on is I have humidity issues in the trailer. The Adirondacks has high humidity. With the camper under the pavilion, it stays cooler than the outside air. The sun comes up and gathers moisture from the moss and trees and blows under the pavilion. The cold sides of the camper, along with any air infiltration inside the camper condenses the moisture like a cold drinking glass in the summer. I have paralleled the heating thermostat with a PID temperature controller, with 2 thermocouples in series, reversed, creating a differential thermostat. One TC is outside, the other inside. I set the temperature to about 3 degrees. If the inside of the camper is colder, it turns on the heat. This only happens in the mornings when the sun come up. This is only needed above freezing as moisture can't be transferred below that. Heating a camper 3 degrees above ambient is just a few minutes each time, just in the mornings when the sun comes up. Afternoons and night the camper is naturally warmer than the outside.

So I really don't need power until it's a warm day in spring. I'll have more solar power when it's sunny, snows melting, high humidity. It's a great correlation. I could add a snap disk temperature switch in few fuses I have for the heat controller, bringing my parasitical loads to zero.

Thanks for the info on the temp controller. I'll look into it.

Carl
My home 200W (24V) panels put out 0Wh today, and the last days. 4 days ago, 10Wh, 5 days ago 40Wh, 6,7,8,9 days ago = 0Wh. 10 days = 20Wh, 11 days ago 50 WH. (about 11Wh/day average with 2 100W panels)

I have 600W of panels at camp, Maybe I could go to 800W. That could be about 43Wh/day average, with about 3 days with no power. I'll need to either get really down to the minimums or swap to an autostart generator.

I'm looking into shutting down the battery when there is no solar or generator 120VAC power. Possibly only turning on the battery AFTER the heat has warmed the battery. Also, generating heat with DC battery current is a big load, I can't do it. I may try some other possibilities, like solar heating (black solar air heat collector) that forces heat into the battery box, or using the camper propane heater, or possibly one of the diesel air heaters. I'm thinking the solar air heat collector could work as it would heat when the sun is up, and there would be solar power at the same time. For the 120VAC generator, I'll have to put 120V heat mats inside the battery box.

I have an email with Big Battery to see how the battery is shut down, and woken up. My guess is the switch on the top could be swapped out for a solenoid. OverKill Solar BMS's have a switch also. Other BMS's need the balance wire plug pulled to shut down.
 
I know this post was a couple of months ago, so sorry for commenting late. The heat pads you have are smaller than the ones I bought (24V, 30W, quantity 4), but the same basic design. The problem is that the heat pads are spec'd with a maximum temp of 150°C. Mine were something over that, but not lots. The problem is (as you stated) they get very hot. To use these to slowly heat LFP cells will require you to cycle them on and off with a duty cycle that will warm but not cook your cells. Just FYI: Test it before you implement it.
Yes! My plan was to use a repeat cycle delay timer to cycle the pads on and off to modulate the heat. But I found in real-world application (adhered to a steel plate, and in full contact with the battery cells) it doesn't get near that hot. In fact, only about 80-90ºF. They are currently in use in our van and working awesomely!
 
Yes! My plan was to use a repeat cycle delay timer to cycle the pads on and off to modulate the heat. But I found in real-world application (adhered to a steel plate, and in full contact with the battery cells) it doesn't get near that hot. In fact, only about 80-90ºF. They are currently in use in our van and working awesomely!
That's great! Well then, I may have to get some of those and do some experiments. My 30W @ 24V pads are just too much. I can put 2 of yours in series and maybe it would work better with my 24V pack. Thanks for responding!
 
Since today is the coldest since I installed the warming pads, I made a trip down to the storage lot to check on things. The temperature gauge in my car ranged between 1° F and 4° F. I tried to get a reading inside the trailer. I had brought a thermometer with me but put it in my pocket. It was taking it to dang long to get down the actual ambient temp from being in my pocket, and I was freezing my keester off, so I gave up. I doubt that the trailer and outside temperatures differed much.

In the picture below, the battery on the left is being warmed (red light next to the current temperature) and the battery on the right is on its way down towards 35° F. The Victron battery monitor said the state of charge is 99.7%. That's impressive considering that it has been overcast and snowing lightly all day.

20210213_163642.jpg
 
Hey Jim - I was anxiously awaiting your post on this! Today/this morning was a pretty good test of your thermo design. Seems tomorrow will be an even better test. It's 0°F here right now, and I think it is supposed to be down to -8°F for me (and you).

Anyway, it seems your system is performing absolutely awesome. I can see all the XPS(?) on top. I need to go back and re-read your thread on all the things you did.

Thanks for posting, and I hope this continues to work for you. You are way ahead of me, but thanks for breaking trail. ?

Steve in Centennial
 
Any word on availability of just heater pads you used. I'm in the planning stages, ordered batteries yesterday from group buy guy. I like your results with the Ulta Heat pads.
 
Contact the folks an Annod Industries. They're the distributor for UltraHeat. It's not on their website yet. :(

thanks, sent them messages.
Hey did you ever consider using the relay functions on your

Victron Energy BMV-712 Smart Battery Monitor

As a heater switch?
I have the temp probe on my 712 and seems reasonable to try and use the switching function.
Not sure yet how.......
 
Hey did you ever consider using the relay functions on your

Victron Energy BMV-712 Smart Battery Monitor

As a heater switch?
I have the temp probe on my 712 and seems reasonable to try and use the switching function.
Not sure yet how.......

No, I never considered it. I would be interested to see how that is done though.
 
Hopefully the answer does not start out like this:

>You could build an analogue comparator circuit with hysteresis, driving a suitable relay or switching transistor.

rotfl.gif


I'm laughing hard, because I know the thread/post you're talking about. My reluctance with using the BMV-712 is how granular the control of the temperature range is.
 
Any word on availability of just heater pads you used. I'm in the planning stages, ordered batteries yesterday from group buy guy. I like your results with the Ulta Heat pads.

UltraHeat says the Z-25N60 8 x 11 Proto Type Kit can be bought by contacting their office. You will want to speak with Mike Lewis, (574) 522-6594 ext. 106 or Mike_l@uhiworldwide.com

Mike designs all of the UltraHeat products and should be able to help you with your request.
 
Back
Top