Brett V
Mad Scientist
Super nice work! I need to quit being so lazy and start documenting my build with some decent photos.
Horsefly's Cabin Solar LiFePO4 Upgrade
- Thread starter Horsefly
- Start date
Horsefly
Solar Wizard
For yourself, if not for all of us!
Horsefly
Solar Wizard
I realized I didn't post the pic of the board holding the BMS and the Active Balancer. As discussed earlier, this board was not attached, but is held in place by some window screen latches.
I have a ton of little plastic offsets that I used for the BMS and the Active Balancer, as well as the thermostats on the top panel.
I have a ton of little plastic offsets that I used for the BMS and the Active Balancer, as well as the thermostats on the top panel.
Daddy Tanuki
Solar Wizard
Great documentation. one of the things I am not that great about. . I was really digging your posts up until this point..... but those feet.... are your toes prehensile? are the digits opposable? Are you the next evolution in mankind? Damn Bro... Inquiring minds want to know!
Horsefly
Solar Wizard
Yeah, you should see me swinging in trees using only my feet! Funny thing is, I almost edited my feet out of the shorts where they snuck in. I also didn't post the picks that had way more of my ugly feet!Great documentation. one of the things I am not that great about. . I was really digging your posts up until this point..... but those feet.... are your toes prehensile? are the digits opposable? Are you the next evolution in mankind? Damn Bro... Inquiring minds want to know!
Daddy Tanuki
Solar Wizard
Bro, seriously though, good job. looks like mine minus the wood. My box is simply the insulating foam only and with the local temp drops I will soon be able to figure out how well the heating pads and temp controllers actually work. sorry folks too busy converting ethanol to methane to take photos of anything.Great documentation. one of the things I am not that great about. . I was really digging your posts up until this point..... but those feet.... are your toes prehensile? are the digits opposable? Are you the next evolution in mankind? Damn Bro... Inquiring minds want to know!
Daddy Tanuki
Solar Wizard
the controllers you used??? got a link? (if i missed it i was drunk and thats my story).
Horsefly
Solar Wizard
Not sure which controllers you are talking about. The thermostats? Or do you mean the solar charge controllers I installed in 2017?
Brett V
Mad Scientist
Your photos and documentation style inspired me to try... It's just not one one my talents.
Horsefly
Solar Wizard
I think I saw your heating pads (although I can't find the post now), and they look pretty similar to mine. I've done a couple of tests of them on the aluminum plate and it doesn't get too hot too fast. I'm hoping 2 of the 12W pads is enough.Bro, seriously though, good job. looks like mine minus the wood. My box is simply the insulating foam only and with the local temp drops I will soon be able to figure out how well the heating pads and temp controllers actually work. sorry folks too busy converting ethanol to methane to take photos of anything.
Horsefly
Solar Wizard
I don't think I have any particular talent for this. In my case, the partners in owning the cabin (my brother and my sister) spend more time at the cabin than I do, but don't know what all the equipment is for or what to do with it. In addition, we are all over 60 now so the next generation will at some point have to assume responsibility for everything in the cabin, including the solar. So when I did the design of the solar in 2016 and installed it in 2017, I ended up writing a 46 page design document that walks through all the load analysis, NREL data, solar panel temperature coefficients, and everything else that drove us to the particular design that was installed, as well as how to do the settings on the SCC and Inverter.
So this time I need to do a similar document about the LFP upgrade. So once again I need to document all the temperature sensitivities of LFP and what I built to hopefully last the next couple of decades up there. That meant I needed to take a bunch of notes and pictures to help me put together the document.
Daddy Tanuki
Solar Wizard
yep the thermostats.
Daddy Tanuki
Solar Wizard
mine will get their first real test in the next couple of weeks. the real question is will the temp controllers I am using cycle in a way that prevents overheating? I use two of the cheap controllers in series, one actually measures and cycles the pads, the second set is a high temp cutout in case the first one does not work properly. trying to avoid the old battery catching on fire routine that seems to be making the rounds by us third tier DIYers. We read all the stuff on forums like this and think we know what we are doing... (me included)
Horsefly
Solar Wizard
The ones I ended up using were two of these:
https://www.amazon.com/gp/product/B076YD8H19
It's the 24V version of the thermostat that I think I've seen several people here on the forum use, but most use a 12V version.
Earlier (mid-2020) I bought one of these:
https://www.amazon.com/gp/product/B07GQPT9VG
That one would have worked fine and had some additional features, but because it worked in Celsius I figured that would add more complexity for anyone trying to deal with it. So I still have it, maybe for some future project.
Horsefly
Solar Wizard
Your two thermostats in series is almost exactly what my system is set up to do. One thermostat sensor is on the aluminum plate the pads are attached to. The other one is measuring the temp on the top of the cells. You are right that if one thermostat fails, the other should prevent the batteries from getting too hot - Or at least that is the hope!
Daddy Tanuki
Solar Wizard
the ones I am using are enclosed in a plastic box. a little prettier for the not quite so gifted like myself,
when i tested the system with a glass of ice water, and then various levels of heat, it seemed to work, but until it actually runs in the conditions I intended it to work in it is a gamble. It would not be so bad if the cabin was not 3-4 hours away through the week, or if I could monitor things remotely.
My internal danger meter is pinging as this is my first set of lithium's. the AGM's I had before I had plenty of experience with. never had to worry about temps as inside the battery shed it never got below freezing even when it was -15c outside. the inverter, batteries and SCC controllers made enough heat to keep it at about 3-5c most of the time. as I can get up to 100 amps while charging at 48 volts (measured this recently while bulk charging) thats either .25c with current bank, or .15c when i get the last set of batteries in.
your system looks pretty squared away though... I like the looks of it. I still have to finalize the routing on all of my cables but am waiting until i get the last 16 cells in and commissioned to shorten, and tie down all the cables. its safe enough, just look's like azz to me. hence no photo's of the complete system yet. I have no desire to be clowned yet... figure I will wait until its final configuration has been set and then you can all laugh at me and poke fun of my work.
Horsefly
Solar Wizard
Yeah, when I started seeing people post that their LFP cells caught fire I almost set down my tools and stepped back from this project. The fact that my heater system could fail and wreck the cells is bad enough, but catching fire is much worse. Our cabin has no one ever in it from about mid-November until generally early May. If something isn't right the place could burn down and we would never know. We have no Internet up there, else I would put in some additional smarts to log everything and maybe send an alert if stuff is out of normal range. But all of that plus a full time Internet connection would cost more than the new cells.
Daddy Tanuki
Solar Wizard
my cabin is in range of cell towers (thank you Mt. Fuji for being a tourist magnet) and I have been asking questions about how to use a "wireless" router in reverse... IE use a wifi hotspot into the router and then a ethernet cable coming out to my inverter and SCC's and BMS. neither my inverter nor my SCC's support wireless. just ethernet, and a couple of other patch cables. so i am trying to figure out what to buy router wise so that I can use a prepaid wireless hotspot and then feed the signal into the gear with ethernet. that would make me feel much more comfortable if I could monitor via the internet. and both items can be shut down via the internet so I could set warning alerts and if XX parameter is being reached I could shut down the system until I get back. much better than fire i think. or maybe I am just too paranoid....
Horsefly
Solar Wizard
Mt Fuji?! You are in Japan? There must be an interesting story there.
Years ago I took and old Linksys router and flashed it with a freeware firmware image (Tomato, I think) which allowed it to do kinda what you are wanting. You could plug wired ethernet into the four ports on the back of the Linksys, and the Linksys would connect with your WiFi, so that wired devices that were not close to your regular router could get on the Internet. I think that is called a wireless bridge. You might want to look into it. I just checked and my just retired Netgear Nighthawk R8000 can be put in wireless bridge mode, so it may be you have an old router laying around that can do it.
Daddy Tanuki
Solar Wizard
got any more info on that Bro?
Horsefly
Solar Wizard
Not really. Have you tried to Google "wireless bridge"? That explains it pretty well, and I am more certain now that it would give you what you want. If you can find a wi-fi router that supports wireless bridge, you could have it connect to your pre-paid hot spot via wi-fi, then plug your SCC's and Inverter into the back of the router. Then you would have them all on the Internet.
Looks like this one supports it: https://www.amazon.com/NETGEAR-AC1200-Wireless-Access-WAC104-100NAS/dp/B01LFSDZCU
It's got 3 ethernet ports you can use.
I'm sure there are others that can switch from router mode to wireless bridge mode. Like I said, my Netgear Nighthawk R8000 supports it. Maybe Netgear supports it on most of their routers.
Daddy Tanuki
Solar Wizard
I actually did but I am a menonite when it comes to all most anything other than specific programs on computers. years ago (pre/early pentium) I used to build my own PC's gave up even that minor task soon after the pentium 133 chips came out. too many options that I did not have time to track down and research so now I am pretty much computer illiterate unless it is handed to me on a platter. should have seen me trying to get the bluetooth dongle to work on my bms with my phone.... not a pretty site
Horsefly
Solar Wizard
I thought I should post an update on test results using the new battery box and heating system.
I bought two temperature loggers that recorded the temperature every 30 seconds in two places in the box. The first logger measured the temperature on the top of the cells, representing - I hope - the overall temperature of the cells. The second temperature logger measured the temperature on the top of the aluminum plate under the cells. This second logger was to give an indication if the heaters were warming too hot and too fast, in which case the aluminum plate would rise to a potentially dangerous level before the temperature on the top of the cells reached the target 60°F.
I also bought a voltage logger that would be connected to the leads of the heating pads, registering simply when the pads were ON or OFF. This logger was also set to register every 30 seconds.
Here is a test that ran from the evening of 9-Dec-2021 until around 8:00am on 11-Dec-2021. The outside temperature during this time ranged from around 30°F down to 20°F. I believe this temperature range may be pretty close to what the system will experience over the winter in the basement of our cabin.
Here the blue line shows the temperature of the aluminum plate where the heating pads are installed. The cells rest on the top of this aluminum plate. The green line shows when the heater was turned ON. The red line shows the temperature measured on the top of the cells. NOTE: One of the problems I had with all my tests is that here in Denver the sun can be intense, and even when the outside temperature stayed in the low 30's, the sunlight would warm the battery box, artificially raising the temperature of the cells. This is the case the afternoon of 10-Dec-2021.
The blue line provided some very useful information. When the heater turned on the aluminum plate warmed up very quickly at first, but then slowed. By the time the cells were warm enough to turn off the heat the plate had only warmed to 68°F both nights. I had included the second thermostat to turn off the heat if the plate got up to 85°F, which seems very unlikely to ever happen.
In this case the heater turned on once per night, running for almost exactly 3 hours each time. The heater pulled around 1.2A when ON, so this test seemed to indicate that about 3.6Ah per day would keep the battery in the target range of 50°F to 60°F.
The second test was much more of a stress test. This was from the late afternoon of 31-Dec-2021 (New Year's Eve) through mid-morning of 2-Jan-2022. The outside temperature began falling early afternoon of 31-Dec, and was in the single digits (°F) both nights (31-Dec and 1-Jan). The high on new years day was only 13°F. The loggers were configured the same as in the earlier test, logging every 30 seconds.
As one might expect, the heaters were ON more frequently, and were on for a longer time as they fought to overcome the heat leaking out of the insulated battery box. Although the first cycle of the heater was only for 2:43, the other three were 3:16, 3:17, and 3:23. The last three cycles all used just about 4Ah of energy to keep the cell temperature between 50°F and 60°F.
I bought two temperature loggers that recorded the temperature every 30 seconds in two places in the box. The first logger measured the temperature on the top of the cells, representing - I hope - the overall temperature of the cells. The second temperature logger measured the temperature on the top of the aluminum plate under the cells. This second logger was to give an indication if the heaters were warming too hot and too fast, in which case the aluminum plate would rise to a potentially dangerous level before the temperature on the top of the cells reached the target 60°F.
I also bought a voltage logger that would be connected to the leads of the heating pads, registering simply when the pads were ON or OFF. This logger was also set to register every 30 seconds.
Here is a test that ran from the evening of 9-Dec-2021 until around 8:00am on 11-Dec-2021. The outside temperature during this time ranged from around 30°F down to 20°F. I believe this temperature range may be pretty close to what the system will experience over the winter in the basement of our cabin.
Here the blue line shows the temperature of the aluminum plate where the heating pads are installed. The cells rest on the top of this aluminum plate. The green line shows when the heater was turned ON. The red line shows the temperature measured on the top of the cells. NOTE: One of the problems I had with all my tests is that here in Denver the sun can be intense, and even when the outside temperature stayed in the low 30's, the sunlight would warm the battery box, artificially raising the temperature of the cells. This is the case the afternoon of 10-Dec-2021.
The blue line provided some very useful information. When the heater turned on the aluminum plate warmed up very quickly at first, but then slowed. By the time the cells were warm enough to turn off the heat the plate had only warmed to 68°F both nights. I had included the second thermostat to turn off the heat if the plate got up to 85°F, which seems very unlikely to ever happen.
In this case the heater turned on once per night, running for almost exactly 3 hours each time. The heater pulled around 1.2A when ON, so this test seemed to indicate that about 3.6Ah per day would keep the battery in the target range of 50°F to 60°F.
The second test was much more of a stress test. This was from the late afternoon of 31-Dec-2021 (New Year's Eve) through mid-morning of 2-Jan-2022. The outside temperature began falling early afternoon of 31-Dec, and was in the single digits (°F) both nights (31-Dec and 1-Jan). The high on new years day was only 13°F. The loggers were configured the same as in the earlier test, logging every 30 seconds.
As one might expect, the heaters were ON more frequently, and were on for a longer time as they fought to overcome the heat leaking out of the insulated battery box. Although the first cycle of the heater was only for 2:43, the other three were 3:16, 3:17, and 3:23. The last three cycles all used just about 4Ah of energy to keep the cell temperature between 50°F and 60°F.
Horsefly
Solar Wizard
For me the key results of these tests (and others I've run) is that with my two small 12W heating pads there is virtually no risk of heating the cells too hot too fast. That would indicate that my second thermostat is not needed, so I may remove it and set it aside as a spare, in case the main thermostat ever fails.
I may use a different method to prevent using the heater if the battery gets to low. I used the PowerMon-5S only because I already had it and it could be easily programmed to turn off the SSR if the voltage got low. I've purchased a separate different low-voltage protection board (here) and will try it out. If it seems to work, I'll probably remove the PowerMon-5S, and maybe the SSR as well (since the device has a relay).
I may use a different method to prevent using the heater if the battery gets to low. I used the PowerMon-5S only because I already had it and it could be easily programmed to turn off the SSR if the voltage got low. I've purchased a separate different low-voltage protection board (here) and will try it out. If it seems to work, I'll probably remove the PowerMon-5S, and maybe the SSR as well (since the device has a relay).
MrM1
I'm Here, But I'm Not All There
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