Heltec (JK) 200A Smart BMS with 2A Active Balance

[UV-PWRD]

All good.

As for the flashing, I can't remember if it does that when it's booted, but not discharging/charging or if it does it when it's connected via bluetooth or something, but it's obvious you can do a thing and the light changes i I just can't remember what it is, but it's not a fault condition.

 

[Sanwizard]

All good.

As for the flashing, I can't remember if it does that when it's booted, but not discharging/charging or if it does it when it's connected via bluetooth or something, but it's obvious you can do a thing and the light changes i I just can't remember what it is, but it's not a fault condition.

Thanks. I was concerned when I could not connect. This is the first power up after top balancing, and building out the battery box, heaters, 48v to 12v converters, heat switches, etc. So half the box is now connected and ready to go. Once my Feb cell order arrives, I can complete, and then start on the AC side.
Thanks for your help.
Once I get connected in the AM, i will work on the correct settings. You dont have a cheat sheet do ya?

 

[UV-PWRD]

For what setting?

Your upper and lower disconnects, balance trigger voltage difference, and recovery times are all personal preference.

Take a look at the below and decide how high and low you want to push the cells. Notice how tight the upper and lower knees are. Lots of people treat 3v as the LVD, just remember that a big load applied when the capacity is low can cause a voltage sag below that point so set it accordingly.

I tend to set my lower disconnect a bit beyond where I should have already taken action, so while it's set to 3v, I almost never trigger it because I'll already have switched back to my grid system, as I don't like the inverter powering off late in the evening when there's no other power source because then you have to do the pre-charge resistor stuff etc I monitor my system fairly constantly to avoid that.

 

[Sanwizard]

For what setting?

Your upper and lower disconnects, balance trigger voltage difference, and recovery times are all personal preference.

Take a look at the below and decide how high and low you want to push the cells. Notice how tight the upper and lower knees are. Lots of people treat 3v as the LVD, just remember that a big load applied when the capacity is low can cause a voltage sag below that point so set it accordingly.

I tend to set my lower disconnect a bit beyond where I should have already taken action, so while it's set to 3v, I almost never trigger it because I'll already have switched back to my grid system, as I don't like the inverter powering off late in the evening when there's no other power source because then you have to do the pre-charge resistor stuff etc I monitor my system fairly constantly to avoid that.


View attachment 48925

Good advice. I like the work Andy is doing on off grid garage with his tester. My LV6548 settings will be more conservative than my BMS settings, as I would rather the inverter shut down before the BMS does.
So low probably 2.8 in the BMS, and 3.0 on the inverter. High in BMS would be 3.6, but 3.4 in the inverter.

 

[UV-PWRD]

Just sure to allow for voltage diff at each end, my 7248 and BMS always show a slight difference between the voltages in the apps and at the terminals.

 

[Sanwizard]

Just sure to allow for voltage diff at each end, my 7248 and BMS always show a slight difference between the voltages in the apps and at the terminals.

So thanks to DIY-Dan and Gmx, I was finally able to get the BMS connected via bluetooth! I am using the ENJpower app also. I set the number of cells to 16, and the type to Lifepo4. Would it be ok to compare the other settings with you guys? Any thoughts on what is shown in the pics?

 

[UV-PWRD]

If your inverter is set to LVD sooner, why have your BMS LVD set so low?

Also power off voltage of 2.5 means your battery will be dead flat and in the damage zone if you don't step in and catch it for any reason.

HVD of 3.4 will cut off a little capacity, remember voltage rises above true cell voltage (at rest) when charge is applied so you need to be sure there's enough head room to allow it to charge smoothly and not repeatedly cut off charging and reconnect it because it keeps hitting 3.4v.

Why is charge current so low? Lifepo4 1C rate is equal to the AH capacity of the battery, so on a 280AH cell, a 0.5C charge rate is still 140a. The other side is low charge current gives a slower and slower more even charge with less voltage rise so this can be good it just depends on how many hours of sun you have to charge and what your bank capacity is.

I can't remember if yours was a a 12 or 48v system? You have a 100a discharge rate though, so why the big discrepancy?

Your balance trigger voltage means it will run 24/7 depending on the voltage difference trigger point set higher above, just check that.

 

[Sanwizard]

If your inverter is set to LVD sooner, why have your BMS LVD set so low?

Also power off voltage of 2.5 means your battery will be dead flat and in the damage zone if you don't step in and catch it for any reason.

HVD of 3.4 will cut off a little capacity, remember voltage rises above true cell voltage (at rest) when charge is applied so you need to be sure there's enough head room to allow it to charge smoothly and not repeatedly cut off charging and reconnect it because it keeps hitting 3.4v.

Why is charge current so low? Lifepo4 1C rate is equal to the AH capacity of the battery, so on a 280AH cell, a 0.5C charge rate is still 140a. The other side is low charge current gives a slower and slower more even charge with less voltage rise so this can be good it just depends on how many hours of sun you have to charge and what your bank capacity is.

I can't remember if yours was a a 12 or 48v system? You have a 100a discharge rate though, so why the big discrepancy?

Your balance trigger voltage means it will run 24/7 depending on the voltage difference trigger point set higher above, just check that.

See, this is why I shared my settings! All good advice. My charge setting are low for thw time being as my ac input is currently an extention cord on a 20amp circuit, so I dont want to blow the breaker.
Mine is a 48V 16s Lishen 272ah system on an LV6548. When my other cells finally arrive, it will be a 544ah system.

I want the BMS to be the final guard for my cells, and use the inverter with more conservative approach.

 

[UV-PWRD]

Similar setup to me then, more battery though.

I'm 4.5kw PV, MPP7248, ETC 277AH Cells.

I also have an old grid connect system with 5kw PV and the ability to pull in another 30a DC from that system into the battery as required.

 

[ArthurEld]

If your inverter is set to LVD sooner, why have your BMS LVD set so low?

Also power off voltage of 2.5 means your battery will be dead flat and in the damage zone if you don't step in and catch it for any reason.

HVD of 3.4 will cut off a little capacity, remember voltage rises above true cell voltage (at rest) when charge is applied so you need to be sure there's enough head room to allow it to charge smoothly and not repeatedly cut off charging and reconnect it because it keeps hitting 3.4v.

His high voltage disconnect is 3.6. 3.4 is has high voltage disconnect recovery so it will turn back on after it disconnected.

 

[UV-PWRD]

Yep misread, Cheers

 

[Sanwizard]

His high voltage disconnect is 3.6. 3.4 is has high voltage disconnect recovery so it will turn back on after it disconnected.

Thanks guys. Your input has helped me immensely, and it is much appreciated!

Now on to the MPP settings!. That tiny frigging manual is making me blind.

 

[UV-PWRD]

I've got a PDF version for the 7248 if that helps?

 

[GXMnow]

Also with LFP cells, you should set it to cut off charge at 0C and cut back on at 2 or 3C. You should not allow LFP to charge below freezing.
Charge UTP is the turn off temp, currently -20C, and Charge UTPR is the recover, turn back on temp, currently -10C

I would also set the balance start voltage higher. Most people recommend only top balancing LFP while charging. One way to do this would be to set the Balance Start voltage to abut 3.3 volts per cell. Then it will only move power between cells when they are close to fully charged. If you will not be charging them this high up, then just set it 0.05 to 0.3 below your absorb charging voltage. The lower you set it, the more time it will have to try and bring the cells into balance while the cells are in bulk charge as well as the whole time the charger is in absorb charge. In your current settings, the balance start voltage is only 1.5 volts. It will keep balancing all the time, even when the cells are fully discharged. That is not good. Even though it transfers charge from the high cells to the low cells, it is only about 90% efficient, so it is still throwing away some power each time it moves some. I am running NMC cells, not LFP, so they do act a bit different. My setting are quite different due to the different cell chemistry, but I have looked into LFP.

 

[Sanwizard]

Also with LFP cells, you should set it to cut off charge at 0C and cut back on at 2 or 3C. You should not allow LFP to charge below freezing.
Charge UTP is the turn off temp, currently -20C, and Charge UTPR is the recover, turn back on temp, currently -10C

I would also set the balance start voltage higher. Most people recommend only top balancing LFP while charging. One way to do this would be to set the Balance Start voltage to abut 3.3 volts per cell. Then it will only move power between cells when they are close to fully charged. If you will not be charging them this high up, then just set it 0.05 to 0.3 below your absorb charging voltage. The lower you set it, the more time it will have to try and bring the cells into balance while the cells are in bulk charge as well as the whole time the charger is in absorb charge. In your current settings, the balance start voltage is only 1.5 volts. It will keep balancing all the time, even when the cells are fully discharged. That is not good. Even though it transfers charge from the high cells to the low cells, it is only about 90% efficient, so it is still throwing away some power each time it moves some. I am running NMC cells, not LFP, so they do act a bit different. My setting are quite different due to the different cell chemistry, but I have looked into LFP.

So what voltage do you guys let your Lishen 272ah cells sit at? Mine are at 3.53V, but I think thats too high. I think its the float voltage I need to change to let that drop down a bit right?

 

[GXMnow]

I am not familiar with your charger, but yes, sort of, is my answer.

Your absorb voltage should be about 3.5 volts per cell for a full charge, or just 3.4 volts if you want to extend the life a bit. That is still very close to truly full on LFP cells. Once the absorb charge stage ends, most just have the charger shut off. But if you have a separate charge controller, or an "all in one" that is charging from the sun, and inverting to power loads, then you want to keep the solar providing the power. This is done by using a float charge setting. The float voltage should be a little below where the cells would rest at a very small load. Most LFP cells seem to drop down about 0.2 volts when the charge current is cut off. So take whatever you set your absorb voltage to, and drop it by about 0.2 to 0.3 volts per cell to get the float voltage. If you charge to 56 volts (3.5 per cell x 16) then you should have the float between 51.2 and 52.8 volts (3.2 to 3.2 volts per cell). When the cells reach a full absorb charge at 56 volts, the charger will switch to float mode and the current will drop to essentially zero. The inverter will start pulling the voltage down, and the cells will also naturally start to drop back a bit as well. When the voltage drops to the Float Voltage setting, the solar charge source should then start outputting current to hold the battery bank at the float voltage. The current to/from the battery will drop to near zero, and the solar charge controller is essentially running the inverter, with the battery just acting like a capacitor, holding the charge with very little current. This is also a good time for the balancer to do it's job as the battery current is very low.

My system can't do this right now as my charger and inverter are the same unit. My only solar source right now is my Enphase system which is AC coupled to the inverter output. The inverter/charger can either take AC current in and charge the battery, or it can take battery current and invert to AC to push into my home, it physically can't do both at once. When I do add some solar panels and a DC coupled MPPT solar charge controller, then I will be able to have it float the batteries and invert like this.

 

[Sanwizard]

I am not familiar with your charger, but yes, sort of, is my answer.

Your absorb voltage should be about 3.5 volts per cell for a full charge, or just 3.4 volts if you want to extend the life a bit. That is still very close to truly full on LFP cells. Once the absorb charge stage ends, most just have the charger shut off. But if you have a separate charge controller, or an "all in one" that is charging from the sun, and inverting to power loads, then you want to keep the solar providing the power. This is done by using a float charge setting. The float voltage should be a little below where the cells would rest at a very small load. Most LFP cells seem to drop down about 0.2 volts when the charge current is cut off. So take whatever you set your absorb voltage to, and drop it by about 0.2 to 0.3 volts per cell to get the float voltage. If you charge to 56 volts (3.5 per cell x 16) then you should have the float between 51.2 and 52.8 volts (3.2 to 3.2 volts per cell). When the cells reach a full absorb charge at 56 volts, the charger will switch to float mode and the current will drop to essentially zero. The inverter will start pulling the voltage down, and the cells will also naturally start to drop back a bit as well. When the voltage drops to the Float Voltage setting, the solar charge source should then start outputting current to hold the battery bank at the float voltage. The current to/from the battery will drop to near zero, and the solar charge controller is essentially running the inverter, with the battery just acting like a capacitor, holding the charge with very little current. This is also a good time for the balancer to do it's job as the battery current is very low.

My system can't do this right now as my charger and inverter are the same unit. My only solar source right now is my Enphase system which is AC coupled to the inverter output. The inverter/charger can either take AC current in and charge the battery, or it can take battery current and invert to AC to push into my home, it physically can't do both at once. When I do add some solar panels and a DC coupled MPPT solar charge controller, then I will be able to have it float the batteries and invert like this.

Thanks guys! My battery is now stable at 54V, with each cell around 3.375. The LV6548 is using around 28W, which is great. Also, the ENJ power app is working great. I am most impressed with thw new watchpower app for android. The LV6548 has built in wifi. You simply register the inverter wifi with your home wifi, and I can now monitor the Inverter from anywhere i have wifi access in the house. If I connect an external IP, I should also be able to use it anywhere on the Internet.
I bought two Raspberry Pi's to load Jblance's monitoring code, but so far so good without it. I may just connect the Pi to the BMS, as that only has bluetooth.
Anyway, now to work on the AC side while I wait for my second inverter from Watts247, and 20 more cells from Mike's group buy.

I just had Dominion energy in South Carolina remove my Grid Tie SMA inverters, and replace the meter with a standard one. Hybrid Inverter DC coupled is the way to go! I plan to buy another two to four LV6548's for the SC house, and another 64 310ah cells to connect those to. That house is loaded up with panels already, so I figure I can do the whole house off grid for less than the previous owner paid for the grid tie system!
I cannot believe how much I have learned from all you guys on this forum! Better than college!

 

[MikeSolarPT]

It is only a shame that this BMS CAN port can be connected to the inverter. I don't know why every manufacturer uses a different communication protocol for CAN port.

 

[upnorthandpersonal]

CAN only defines the physical layer, transfer layer and a small application layer, but does not define any protocols such as application data. There are various other standards that do that for a specific field (like CANopen, DeviceNet, MilCAN, etc.) but even within those it's not just plug and play.

For this reason, I've been working on a system that essentially acts as a 'supervisor' and keeps track of BMS, Inverter, Charge Controller, etc. and is able to take actions based on conditions there are in. For example, reading the temperature sensor on the BMS and use that to control heating pads, or control the inverter, etc. Since I'm already graphing the data with Grafana (see below), this is just the next step.

Off-grid Solar / Battery monitoring and control freeware

Thanks Joe!

diysolarforum.com

 

[GXMnow]

Have you been able to find the data protocol for the JK-BMS? IT would be cool if I could make my PLC read out some of the data over the RS-485 port.