Chargery BMS now with Low Temp Cutoff

[DW SD]

@Steve_S - thanks for the info!! I'd consider adding a fan. But probably won't. I think I'll just charge to a slightly lower SOC and call it good. The issue only comes up @ >98% SOC.
I don't need to eek out that last bit of capacity.

Doug

 

[Craig]

If I lower the balance voltage threshold, it will exacerbate the issue. below 98% charge, my balance is <20mV.

Probably, I should just leave it and just not charge to the top. I don't need to eek out any extra capacity.

Thank you,

Doug

You have to realize that once you get in the high charge area that very little energy can make the cells go way out of whack. Your strategy to stay below 98% is probably best. Personally I only start balancing above 90% capacity as its pretty much useless to try and balance the large amounts of energy in the cells below that.

 

[Bob B]

@ craig is right ... If you are only having the problem at the very top it is probably not worth messing with. If you ever decide you want to try to get it balance above the knee it is also possible to do manually with a power resistor.

 

[DW SD]

You have to realize that once you get in the high charge area that very little energy can make the cells go way out of whack. Your strategy to stay below 98% is probably best. Personally I only start balancing above 90% capacity as its pretty much useless to try and balance the large amounts of energy in the cells below that.

OK. Seems like we are on the same page. That's why I set the balance threshold so high. But since I have one cell low and the 3 high, it seems there is a lot of energy to give off.

I had wanted to do one top balance using Chargery and then pretty much leave it. Since I have new cells, charge mostly with solar and have low (C, < .5) loads, I believe it should stay balanced.
If I had a bench top power supply I'd have done a top balance.

Thanks for the insights!

Doug

 

[Steve_S]

@Steve_S - thanks for the info!! I'd consider adding a fan. But probably won't. I think I'll just charge to a slightly lower SOC and call it good. The issue only comes up @ >98% SOC.
I don't need to eek out that last bit of capacity.

Doug

I think that with bigger cells, that top 5% is where you'll get the most fluctuations like the others have said. I think that generally between 3.5 to 3.65 is the "zone" from consensus. By that time too, charging amps "should" be getting much lower due to resistance changes which affects the cell's charge rates. You have a "12V/280AH" pack, assuming you want to save %5 at the Top & Bottom giving you 90% pack capacity (*1) Then you'd likely want to set your High Volt to 13.87 (3.45v per cell) Low Volt to 10.5v (2.62 per cell)

(*) some people have noted that with the cells like the 280AH "EVE's", they have come up with actual higher AH ratings for individual cell tests. In some instances though, some cells have come in lower than specified within an "all good" batch shipped. That will of course have an effect at the top level as some cells may actually be able to take more charge being that they have more physical capacity to do so. The main reason for this is because the cells we receive at the discount rates are Voltage Matched but not properly IR matched. To properly IR match the cells, each cell must go from deep discharge to full charge and back down again in a test cycle, while having the IR monitored along the way. This is a long process and adds a significant cost, hence why when you see advertised "Matched & Balanced" cells or similar and the price is X2 or more, well there's the answer. Also, that creates a certain percentage of "rejects" from the acceptable "batch" limits which can be packaged as Verified Matched cells.

 

[DW SD]

@Steve_S
Ahhh. that also makes sense.
I noticed battle born and others suggest using 14.5V for CC/CV.
I had been using 13.8 with balance staying in tact. When I went to 14.0V, it worked, but not without a lot of balancing time.
Going to 14.2V seemed to blow up the voltage difference and without much progress.

I'll drop back to 13.9 or 13.8 and call it a day.

Thanks for the info!
Doug

 

[diysolarman]

I'll ask here before submitting a claim since Jason couldn't help me with my problem. Jason asked me to go online for a solution. I have 4 of the BMS8T. 1 of the 4 doesn't want to save the configuration and is defaulting to values I had set in the past. Any thoughts:

 

[Craig]

I would reinstall the software and or try to reset factory defaults

 

[diysolarman]

I would reinstall the software and or try to reset factory defaults

Funny thing is that I have reset 4 times (and yet the values go back to my old values; ie 650mV of cell diff). Haven't reinstalled the software though.

 

[diysolarman]

Okay, I have tried using the same LCD and cable on two different BMS8T modules:

The second module saves just fine. First unit is refusing to save settings

 

[Bob B]

I'm not sure if it's going to make any difference, but I did notice that your LCD is at version 4.0 ..... not the new 4.01.

 

[diysolarman]

I'm not sure if it's going to make any difference, but I did notice that your LCD is at version 4.0 ..... not the new 4.01.

Hello Bob,

I'll try updating the LCD software to see if that fixes it

 

[Bluerso]

I'm looking to order a BMS8T-300 plus the required DCCs. The DCC manuals mention that I would only need 1 DCC since they are bidirectional, but I want to confirm that if the BMS disables the charging due to low temperature, it will still allow load so that the SCC/battery heater is powered?

 

[Steve_S]

If you are building your setup as Common-Port then yes, you only need one DCC Contactor.
Yes, the Low Temp function was added into the firmware this spring and it does work as expected. Charging will be disabled if the temps are too low or too high obviously. With a Single DCC is "should " still allow for discharging (LFP can discharge up to -20C temps generally), some lower, depends on specific cell chemistry, Always refer to Cell Manufacturer Documents for your specific cells.

Do note, the BMS is only responsible for managing the cells within its own pack, it's the "Guard Dog" and last-ditch safety system for the cells/pack. The SCC & INverter/Charger systems should cutoff for Hi/Lo Volt conditions on their own BEFORE the BMS forces it off. Depending on SCC / Inverter System, some can monitor temps and act on it, while others cannot. This is NOT like the Temp Sensors used for Lead Acid Battery packs, which serves an entirely different purpose (compensation voltage for temp differentials).

Hope that helps, Good Luck.

PS: I started this thread, which I will be adding to later this week or early next week as I complete a set of builds & installs.

Chargery BMS, DCC (Solid State Contactor) thread.

Good Day folks, I am starting this thread related to the Chargery DCC, so the first post will be a basic "intro". See the following posts for more info. The DC contactor is designed specially to work with the CHARGERY BMS', the following are some features: Bi-directional connection, one...

diysolarforum.com

 

[Bob B]

If you are building your setup as Common-Port then yes, you only need one DCC Contactor.
Yes, the Low Temp function was added into the firmware this spring and it does work as expected. Charging will be disabled if the temps are too low or too high obviously. With a Single DCC is "should " still allow for discharging (LFP can discharge up to -20C temps generally), some lower, depends on specific cell chemistry, Always refer to Cell Manufacturer Documents for your specific cells.

Chargery BMS, DCC (Solid State Contactor) thread.

Good Day folks, I am starting this thread related to the Chargery DCC, so the first post will be a basic "intro". See the following posts for more info. The DC contactor is designed specially to work with the CHARGERY BMS', the following are some features: Bi-directional connection, one...

diysolarforum.com

@Steve_S .... Sorry, but I can't get my head around this ... could you please do a diagram that shows how a single DCC would cut of charging but still allow load? Seems to me that 2 SSR's would be required to do that .... or does one DCC have 2 SSR's?

 

[grizzzman]

You would need two DCCs for separate control.

 

[Steve_S]

As I understand the way it's made but I could very well be wrong, the DCC has a built-in pre-charge circuit and some sort of opto-coupling to handle the job. When it's used in separate-prt with two DCC's, the wire is split so one pair to Charge DCC and one pair to Discharge DCC, as if using two standard type contactors. I opened mine up but with the heat sinks attached you can't see much.

For more specifics, we'd have to get info from Jason directly.

 

[Craig]

@Steve_S .... Sorry, but I can't get my head around this ... could you please do a diagram that shows how a single DCC would cut of charging but still allow load? Seems to me that 2 SSR's would be required to do that .... or does one DCC have 2 SSR's?

I cant diagram for sure but as I see it there is actually 2 directional switches , for lack of better term, inside the dcc one to shut off input and one to shut off output.

But in all honesty I am a skeptic as to how well these will work. I have some on order but do not recommend them as of yet. Personally I do not like the idea of shutting off the connection between the inverter and SCC from battery I would rather shut the device down, use a device that takes 12v input from the Chargery or shut down the between the panels and SCC or inverter and load since the amps at those two points are the least. Even though I am not afraid to shut down SCC with panels attached. I do not think it is a good Idea to have it boot up every time there is an overcharged cell.

 

[Bob B]

I cant diagram for sure but as I see it there is actually 2 directional switches , for lack of better term, inside the dcc one to shut off input and one to shut off output.

But in all honesty I am a skeptic as to how well these will work. I have some on order but do not recommend them as of yet. Personally I do not like the idea of shutting off the connection between the inverter and SCC from battery I would rather shut the device down, use a device that takes 12v input from the Chargery or shut down the between the panels and SCC or inverter and load since the amps at those two points are the least. Even though I am not afraid to shut down SCC with panels attached. I do not think it is a good Idea to have it boot up every time there is an overcharged cell.

That's the approach I'm taking .... trying to avoid switching the battery power.

 

[zacharyk]

This might be a dumb question, but why not use a load-side lockout relay or some kind of disconnect that's triggered by the BMS vs having a NO power sucking relay on the Chargery?