Homemade Low Temperature Disconnect for LiFePO4

[Short_Shot]

Sorry but qhat do you need a shunt for? Monitoring current?

Current, yes. But more importantly state of charge, and thus remaining capacity.

You cannot just use a cheap voltage based "battery life meter" on lithium batteries.

 

[Don B. Cilly]

I just keep mine inside the house

 

[HRTKD]

I have a three prong approach to handling low temperatures.
1. Victron MPPT solar charge controller - it understand that charging below (the default of) 32° F is not allowed.
2. Battery warming pads - I keep the batteries between 35° F and 45° F at all times.
3. A smart BMS - it will not allow charging below 32° F.

I am confident that my LiFePO4 batteries will never be harmed by charging at low temperatures.

 

[Taytus]

I have a three prong approach to handling low temperatures.
1. Victron MPPT solar charge controller - it understand that charging below (the default of) 32° F is not allowed.
2. Battery warming pads - I keep the batteries between 35° F and 45° F at all times.
3. A smart BMS - it will not allow charging below 32° F.

I am confident that my LiFePO4 batteries will never be harmed by charging at low temperatures.

What MPPT and battery warming pads would you recommend?

 

[Wetcoast]

I just stumbled onto this thread in search of a solution to this problem. I had bought a few of the "Big Battery" LiFePo4 batteries and have just noticed that they do not come equipped with Low temperature disconnect either, though in saying that, it's probably a good idea not to have it since disconnecting the batteries (load) on some of these MPPT chargers can cause damage to the charge controller. Yikes!! I think that somebody did mention that cutting power at the Solar panel would be the better solution, I have to agree, I just don't know where to find such a thing.

 

[HRTKD]

I just stumbled onto this thread in search of a solution to this problem. I had bought a few of the "Big Battery" LiFePo4 batteries and have just noticed that they do not come equipped with Low temperature disconnect either, though in saying that, it's probably a good idea not to have it since disconnecting the batteries (load) on some of these MPPT chargers can cause damage to the charge controller. Yikes!! I think that somebody did mention that cutting power at the Solar panel would be the better solution, I have to agree, I just don't know where to find such a thing.

A good quality solar charge controller will have the ability to cut off charging when the temperature is below a certain threshold. My Victron MPPT gets the temperature at the battery post.

 

[Wjm1964]

I have a fogstar lifepo4 that has a heating function and my Victron mppt and smart battery sense are pre set at 5⁰ cut off but the app for the battery heat function is at 0 degrees I can change this but it says will invalidate warranty. So instead of using pre set parameters on victron I would have to set a custom charge profile to change the charge cut off setting. Are other heated batteries all set at zero degrees before heating kicks in? I personally don't want my battery to ever reach zero degrees.

 

[HRTKD]

I have a fogstar lifepo4 that has a heating function and my Victron mppt and smart battery sense are pre set at 5⁰ cut off but the app for the battery heat function is at 0 degrees I can change this but it says will invalidate warranty. So instead of using pre set parameters on victron I would have to set a custom charge profile to change the charge cut off setting. Are other heated batteries all set at zero degrees before heating kicks in? I personally don't want my battery to ever reach zero degrees.

You're going to want to change the Victron to a much lower threshold. If the Victron cuts off charging, the battery warmer will never kick in.

I rolled my own solution for battery warming, so my experience isn't quite what you're looking for. My batteries are never allowed to go below 35°F.

 

[Wjm1964]

Looks that way I just didn't want to change things, I could change the battery preset to 6 degrees, just one degree above the preset but then warranty is no good least that's what the app says.

 

[SeaGal]

Might be worth contacting @Ben@Fogstar - I can understand lowering the temp would be a warranty concern, but not raising it. Plus a heater will take time to warm up the cells, so better to not let them get that cold in the first place or you might be waiting hours for them to get back to a safe temperature.

Aiming not to let mine go below 15degrees, but obviously there are different scenarios for grid-connected vs camper-van situations.

 

[Wetcoast]

Here's my scenario in more detail. The solar system is 10 hours away in a remote cabin which includes a few bodies of water to get across. the cabin has about 60 watts worth of drain in the form of electronics (in winter setup) which allows a satellite link and and a weather station plus a half dozen ip cameras to keep an eye on the place while we are gone for winter. It rains there weeks at a time, unless it snows and so, the power that comes off of the solar panels into the battery bank are sometimes quite rare at this time of year. So to add a battery heater that wants 50 watts may be out of the question. Right now the temperature there is hovering within a few degrees either way of freezing. Anyways, thanks for your help guys, funny thing is that all of the literature on the Solar charge controller is in the cabin in the battery room and I can't even remember the brand name of the device. Lol

 

[32 volt boater]

I'm going to replace my kaput Pb (lead acid) batteries with LiFePO4 soon. One thing that was holding me back was finding a low temperature disconnect to prevent charging ( nd destroying) the batteries below 0 degrees C. The few commercial devices I found seemed pretty expensive and overkill ( I don't need Bluetooth on it thank you very much). Witha temperature sensor, 200A relay, an RC snubber circuit to suppress arcing, and a Zener diode and power resistor to regulate the temperature sensor power voltage this will do the job. And I spent $35 and that is enough to make two units with spare parts left over.

Now invent something to shut the water off so if the pipes freeze the house does not flood.

"Many people think frozen pipes are a limited problem and will affect only a few homes and offices each year. Actually, insurance industry studies have found the amount of water damage generated by frozen and broken water pipes ranks second, only behind hurricanes, in the number of homes damaged and the amount of insurance claim costs in the U.S. each year. This means an average of over 250,000 homes each year will suffer damage from frozen and burst pipes. The damage is estimated to be in the $400-500 million each year."

Frozen Water Pipes — AFTERDISASTER

The most recommended disaster remediation team in the Southeast—trusted by homeowners, businesses and government agencies for decades.

afterdisaster.com

I was no angry after I listened to a relative who insisted I unplug my electric heaters before leaving the house for a week in the winter.

Well the stupid furnace did fail and my house flooded.

It was my fualt, I knew there was NO WAY a modern electric heater thats UL listed was starting a damn fire when I placed it on the stone in front of the fireplace!

Ya sure UL listed electric heaters just breath damn fire like majic dragons the instant you leave them unattended. Ya sure.

I just wanted the relative to shut up but I knew better. The weather almanac said the temp went to 27 degrees. 1500 watts electric heat would have saved all my stuff. Walls carpet ceilings belongings all trashed. Lost 70% of everything I owned.

 

[32 volt boater]

Here's my scenario in more detail. The solar system is 10 hours away in a remote cabin which includes a few bodies of water to get across. the cabin has about 60 watts worth of drain in the form of electronics (in winter setup) which allows a satellite link and and a weather station plus a half dozen ip cameras to keep an eye on the place while we are gone for winter. It rains there weeks at a time, unless it snows and so, the power that comes off of the solar panels into the battery bank are sometimes quite rare at this time of year. So to add a battery heater that wants 50 watts may be out of the question. Right now the temperature there is hovering within a few degrees either way of freezing. Anyways, thanks for your help guys, funny thing is that all of the literature on the Solar charge controller is in the cabin in the battery room and I can't even remember the brand name of the device. Lol

View attachment 122789

The maximum frost line depth is 100-inches as seen near the tip of Minnesota, North Dakota, and Alaska, all the way to zero inches in Florida.

Just bury the battery box below the frost line.





Might be a bit of digging and wiring

 

[32 volt boater]

This is bullcrap !!




Cant I ever think of something first?

Just once!

 

[SeaGal]

LOL.. not the first... see this posting where a chap in Alaska put his 6 foot underground...

Pylontech - The Right Buy for Me?

The lead acid batteries I bought seem to be almost junk after 1.5 years of regular use and some hundreds of cycles. I was thinking of replacing them with a lithium Pylontech UP5000; 4.8kWH (or maybe a Pylontech US3000C; 3.5kWH). (EDIT Feb 16th: I bought US2000C x 2 as it was what was...

diysolarforum.com

 

[Ben@Fogstar]

I have a fogstar lifepo4 that has a heating function and my Victron mppt and smart battery sense are pre set at 5⁰ cut off but the app for the battery heat function is at 0 degrees I can change this but it says will invalidate warranty. So instead of using pre set parameters on victron I would have to set a custom charge profile to change the charge cut off setting. Are other heated batteries all set at zero degrees before heating kicks in? I personally don't want my battery to ever reach zero degrees.

Hi @Wjm1964

It won't invalidate the warranty. We previously had the settings unlocked and some customers changed high voltage disconnect to 24V to 'try and make a 12V battery a 24V battery'....I wish I was joking. So we put a scary message. But we're not going to not honour a warranty for useful tweaks customers make. I'll pm you the settings password!

 

[Rbertalotto]

Where are you going to read the temperature to "cut off".....How will you know that the core of the battery is warm enough to resume charging. That's the main problem with all the external temperature control schemes. The only way to be sure is an internal, BMS that reads internal battery temperature or even better, never let the batteries get below freezing. I recently built two battery heating systems that cost about what you paid and are keeping the batteries at 35+ degrees no matter outside ambient temperature. You can read all about it here: www.rvbprecision.com

 

[Wjm1964]

Hi @Wjm1964

It won't invalidate the warranty. We previously had the settings unlocked and some customers changed high voltage disconnect to 24V to 'try and make a 12V battery a 24V battery'....I wish I was joking. So we put a scary message. But we're not going to not honour a warranty for useful tweaks customers make. I'll pm you the settings password!

It reminds me of someone who complained about solar panels they self installed and had zero output, turned out they were mounted upside down.. That's Humans for ya Thanks for the PW

 

[curiouscarbon]

This is bullcrap !!

View attachment 122880


Cant I ever think of something first?

Just once!

great minds think alike ??️

 

[curiouscarbon]

Hi @Wjm1964

It won't invalidate the warranty. We previously had the settings unlocked and some customers changed high voltage disconnect to 24V to 'try and make a 12V battery a 24V battery'....I wish I was joking. So we put a scary message. But we're not going to not honour a warranty for useful tweaks customers make. I'll pm you the settings password!

haha... holy crap. i wish you were joking? wow!

when i modify settings on my ESS systems, it feels essential to like triple check the modified parameters against my internal model of potential failure modes.....