Finally found a LiFePO4 BMS with Low-temp Charging Protection

[HRTKD]

My current plan is to create a 2p4s battery with the 280 ah cells from Xuba. Will this be a good use case for the @OverkillSolar BMS? I don't need the battery bank for high current draws. I camp in cold weather and need a battery set that will last all night running the furnace and still have enough juice to run the coffee maker in the morning.

 

[Sgt Raven]

My current plan is to create a 2p4s battery with the 280 ah cells from Xuba. Will this be a good use case for the @OverkillSolar BMS? I don't need the battery bank for high current draws. I camp in cold weather and need a battery set that will last all night running the furnace and still have enough juice to run the coffee maker in the morning.

What is the max amperage you think it will draw? I'm using a 120A with a 4S XUBA 280AH battery, but I haven't pulled out more than 10A at a time. I did try a 300W inverter I bought a couple of years ago, but never used and it blew up on the first try.

 

[HRTKD]

What is the max amperage you think it will draw? I'm using a 120A with a 4S XUBA 280AH battery, but I haven't pulled out more than 10A at a time. I did try a 300W inverter I bought a couple of years ago, but never used and it blew up on the first try.

My spreadsheet says the max draw is 129 amps. But that would be turning on just about everything in my trailer at once, which is very unlikely. I included the four tank heaters in my calculation, but I rarely run them and most likely would only run the two on the 120 gallon fresh water tank if I had enough spare power. In a day, I calculated that the total draw would be 3302 watts and that is figuring an expected runtime for each item.

I have a 1000 watt MSW Xantrex inverter that is usually used only for the coffee pot. I didn't factor in the standby draw for that, just the known draw when it is active.

 

[Sgt Raven]

My spreadsheet says the max draw is 129 amps. But that would be turning on just about everything in my trailer at once, which is very unlikely. I included the four tank heaters in my calculation, but I rarely run them and most likely would only run the two on the 120 gallon fresh water tank if I had enough spare power. In a day, I calculated that the total draw would be 3302 watts and that is figuring an expected runtime for each item.

I have a 1000 watt MSW Xantrex inverter that is usually used only for the coffee pot. I didn't factor in the standby draw for that, just the known draw when it is active.

Max on your inverter looks like 145A, but that's a real short pull when it peaks. I think you might want to get Overkillsolar's 8AWG wire upgrade for the 120A version. That would give a little more fudge factor in it. IIRC, mdare pulled 147A on his 120A with the 8AWG upgrade he did. But that wasn't a long term test, either. Again, IIRC it was around post 400 or so in this thread.

 

[OverkillSolar]

Max on your inverter looks like 145A, but that's a real short pull when it peaks. I think you might want to get Overkillsolar's 8AWG wire upgrade for the 120A version. That would give a little more fudge factor in it. IIRC, mdare pulled 147A on his 120A with the 8AWG upgrade he did. But that wasn't a long term test, either. Again, IIRC it was around post 400 or so in this thread.

A 150a surge is no problem for the BMS. Long term at that level heat builds up regardless of what size wires are on it.

 

[NEWYORKHILLBILLY]

A 150a surge is no problem for the BMS. Long term at that level heat builds up regardless of what size wires are on it.

What would be the recommended long term draw of this BMS . I know its rated for 120 amps but many say to be conservative in that draw. what would you recommend?

 

[OverkillSolar]

I am comfortable with 120a at 100% duty cycle as long as it gets some air to stay cool.

The BMSs that I ran for extended load testing at 125 amps all got up to around 50 Celsius just sitting flat on the table. In a tight enclosure they got up to 90c and started melting the plastic box.

No need for a fan, just some free air for convection is enough.

 

[Sgt Raven]

I am comfortable with 120a at 100% duty cycle as long as it gets some air to stay cool.

The BMSs that I ran for extended load testing at 125 amps all got up to around 50 Celsius just sitting flat on the table. In a tight enclosure they got up to 90c and started melting the plastic box.

No need for a fan, just some free air for convection is enough.

I guess if the battery and BMS is in a closed box, a vent and a small computer case fan might be of some help. Really the fan part could be a pusher or puller, just as long as the air is exchanged enough.

 

[HRTKD]

A method of air flow is in the works for my project. The location where the batteries will be placed is currently enclosed, but I plan to add a method of inflow and outflow. Supplementing the passive air flow with an active fan, based on temperature, is something I'll have in Phase II of the project.

Can the BMS sent a high temp signal to a relay? That would be an easy way to trigger the fan.

 

[NEWYORKHILLBILLY]

I am comfortable with 120a at 100% duty cycle as long as it gets some air to stay cool.

The BMSs that I ran for extended load testing at 125 amps all got up to around 50 Celsius just sitting flat on the table. In a tight enclosure they got up to 90c and started melting the plastic box.

No need for a fan, just some free air for convection is enough.

Did you do any testing at 1/2 duty cycle 60amps? I wondering if at 60 amps this would stay cool enough to be in a battery case with the cell's

 

[Sgt Raven]

I think mine got to around 30C pushing 35A charging. My Alinco PS's heat sink body was around 72C at the same time.

 

[OverkillSolar]

A method of air flow is in the works for my project. The location where the batteries will be placed is currently enclosed, but I plan to add a method of inflow and outflow. Supplementing the passive air flow with an active fan, based on temperature, is something I'll have in Phase II of the project.

Can the BMS sent a high temp signal to a relay? That would be an easy way to trigger the fan.

This is in the works. I’m reversing engineering the comm protocol so we can run arduino type stuff. A relay module will be no problem.

Did you do any testing at 1/2 duty cycle 60amps? I wondering if at 60 amps this would stay cool enough to be in a battery case with the cell's

I can do that today. I’ll wrap one up in bubble wrap and run it for a while.

 

[OverkillSolar]

I can do that today. I’ll wrap one up in bubble wrap and run it for a while.

Test begins:


Running at 69 amps (nice) for at least 20 minutes unless my battery goes dead first

 

[Sgt Raven]

This is in the works. I’m reversing engineering the comm protocol so we can run arduino type stuff. A relay module will be no problem.


I can do that today. I’ll wrap one up in bubble wrap and run it for a while.

That could be a sticky mess and smelly, too.

 

[HRTKD]

This is in the works. I’m reversing engineering the comm protocol so we can run arduino type stuff. A relay module will be no problem.

Blue Sky thought here: How about a low temp signal too? That way I could turn on a pad heater - or other suitable heater - to keep the batteries from getting too cold.

 

[OverkillSolar]

Blue Sky thought here: How about a low temp signal too? That way I could turn on a pad heater - or other suitable heater - to keep the batteries from getting too cold.

Yea no problem

 

[OverkillSolar]

That could be a sticky mess and smelly, too.

10 minutes in its only up to 35c
...
20 minutes, 41c

 

[OverkillSolar]

@NEWYORKHILLBILLY it ran for 40 minutes at 70 amps and reached 48 Celsius, which is fine.

 

[Sgt Raven]

@NEWYORKHILLBILLY it ran for 40 minutes at 70 amps and reached 48 Celsius, which is fine.

View attachment 13973
View attachment 13974

All i can say, Steve, is you go above and beyond for possible customers.
You are a credit to the DIY LFP world.

 

[HRTKD]

All i can say, Steve, is you go above and beyond for possible customers.
You are a credit to the DIY LFP world.

Agreed. I don't have my batteries yet, but I think I've settled on which BMS to go with. The BMS is inexpensive enough that I may buy what's available now and replace it when helpful new features are available.

As someone else on another thread lamented, picking solar panels and batteries are easy. Finding the right BMS is a lot more work. I would prefer a BMS with more amps, but for what I'm doing right now it's enough.