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18s

ArthurEld

Solar Wizard
Joined
Aug 3, 2020
Messages
2,271
Location
Palm Harbor, Florida
I know some people are creating higher voltage 17s and 18s batteries.

My inverter can handle up to 63V so I am wondering about making an 18s battery and never setting my upper charge limit over 63V or 3.5V per cell.

This isn't anything I plan to do soon but the subject interests me.

Are there any downsides?
 
I am thinking of doing this also. My MPP LV6548 inverters can handle 62.0V.
1618
SOC48V setup LiFePO448V+ setup LiFePO4
100.00%58.40065.700
99.50%55.20062.100
99.00%54.00060.750
90.00%53.60060.300
80.00%53.20059.850
70.00%52.80059.400
60.00%52.40058.950
50.00%52.20058.725
40.00%52.00058.500
30.00%51.60058.050
20.00%51.20057.600
14.00%50.40056.700
9.50%48.00054.000
5.00%44.80050.400
0.00%40.00045.000

Not only would this make a higher voltage battery requiring fewer amps to invert to the AC system, but it would also have the added storage of the two additional cells. I also think inverting 60VDC to 120VAC is more efficient than 53.5VDC to 120VAC. I'm not too sure about the effeciency part though, but it "seems to make sense to me".

PS - I quit using any BMS's two years ago.
 
Last edited:
I did this with my mpp
Solar 5048mg for some time until I acquired 14 additional cells. Then I rebuilt it as 16s2p.
I have 4 more cells coming so that I can go back to 18s2p. There is no
Problem with doing this.
 
I am thinking of doing this also. My MPP LV6548 inverters can handle 62.0V.
1618
SOC48V setup LiFePO448V+ setup LiFePO4
100.00%58.40065.700
99.50%55.20062.100
99.00%54.00060.750
90.00%53.60060.300
80.00%53.20059.850
70.00%52.80059.400
60.00%52.40058.950
50.00%52.20058.725
40.00%52.00058.500
30.00%51.60058.050
20.00%51.20057.600
14.00%50.40056.700
9.50%48.00054.000
5.00%44.80050.400
0.00%40.00045.000

Not only would this make a higher voltage battery requiring fewer amps to invert to the AC system, but it would also have the added storage of the two additional cells. I also think inverting 60VDC to 120VAC is more efficient than 53.5VDC to 120VAC. I'm not too sure about the effeciency part though, but it "seems to make sense to me".

PS - I quit using any BMS's two years ago.
Why did you quit using BMS's?
 
Why did you quit using BMS's?
I set the inverter to never go over 95% and never go under 5%. The spaces that the BMS would sound the alarms and thus do the only thing a BMS can do is turn off the battery. So, if my battery is never in the voltages that the BMS can do anything, the only thing the BMS can thus do is observe and report. I've watched many off-grid users use old BEV battery cells with nothing but the voltage settings of the inverter get by just fine for many many years.

I used 4 different BMSs and have come to the conclusion that they are just not worth what they cost. Especially will all the "setting" up you have to do. In the end, all I was doing was looking at cell numbers. It didn't matter what the BMS can do, the cells get back in balance all on their own just by charging them and letting them sit.
 
I currently use 16s regular old lithium. I charge it up to 4.0v per cell. 2 of my inverters have a 45-90v operating voltage. The 16s allows the inverter to use less amps therefore less stress. Also smaller wires due to less amps. I’ve been thinking heavily about going to 18s LFP.
 
I set the inverter to never go over 95% and never go under 5%. The spaces that the BMS would sound the alarms and thus do the only thing a BMS can do is turn off the battery. So, if my battery is never in the voltages that the BMS can do anything, the only thing the BMS can thus do is observe and report. I've watched many off-grid users use old BEV battery cells with nothing but the voltage settings of the inverter get by just fine for many many years.

I used 4 different BMSs and have come to the conclusion that they are just not worth what they cost. Especially will all the "setting" up you have to do. In the end, all I was doing was looking at cell numbers. It didn't matter what the BMS can do, the cells get back in balance all on their own just by charging them and letting them sit.
I noticed you have a JK BMS. And I was wondering if JK would work correctly with 18s. I am curious about using 18s and I like using BMSs.
You say they beep and turn off. Is that because you can't set it correctly to use 18s?
I know a lot of people don't use BMSs and it doesn't bother me.
 
I noticed you have a JK BMS. And I was wondering if JK would work correctly with 18s. I am curious about using 18s and I like using BMSs.
You say they beep and turn off. Is that because you can't set it correctly to use 18s?
I know a lot of people don't use BMSs and it doesn't bother me.
The JK is only 16s, it doesn't have the 18s connections.
 
I set the inverter to never go over 95% and never go under 5%. The spaces that the BMS would sound the alarms and thus do the only thing a BMS can do is turn off the battery. So, if my battery is never in the voltages that the BMS can do anything, the only thing the BMS can thus do is observe and report. I've watched many off-grid users use old BEV battery cells with nothing but the voltage settings of the inverter get by just fine for many many years.

I used 4 different BMSs and have come to the conclusion that they are just not worth what they cost. Especially will all the "setting" up you have to do. In the end, all I was doing was looking at cell numbers. It didn't matter what the BMS can do, the cells get back in balance all on their own just by charging them and letting them sit.
While I understand what you're saying - the hi/low is not the only thing that can happen. It's entirely possible for 1 cell (pack) in a string to go way low or hi but you don't notice the danger because the overall battery voltage seems OK. This could damage or at least wear out a cell way faster than the others.

In other words part of what BMS should do is alert you to a large cell difference so you can take action before it becomes too serious - balance or replace the cell.
 
While I understand what you're saying - the hi/low is not the only thing that can happen. It's entirely possible for 1 cell (pack) in a string to go way low or hi but you don't notice the danger because the overall battery voltage seems OK. This could damage or at least wear out a cell way faster than the others.

In other words part of what BMS should do is alert you to a large cell difference so you can take action before it becomes too serious - balance or replace the cell.
Exactly. Yes some inverters can be set to stop discharge, and the charge controller stops charge, but if any of those fail to do their job then the bms is there to save the day. For example, we had a large lightning storm come thru. For some reason that reset my charge controller. So it was going to charge my batteries up to 68v (instead of 64v) if I didn’t catch the reset. If I wouldn’t have seen it then the bms would have stopped a fire from occurring
 
While I understand what you're saying - the hi/low is not the only thing that can happen. It's entirely possible for 1 cell (pack) in a string to go way low or hi but you don't notice the danger because the overall battery voltage seems OK. This could damage or at least wear out a cell way faster than the others.

In other words part of what BMS should do is alert you to a large cell difference so you can take action before it becomes too serious - balance or replace the cell.
Yea, I get it, with 12-year-old packs (BYD used packs), the "run away" cell only happened when overcharging the entire pack. So, I just limited the entire pack and the runaway cell never happened again. If you want to use a BMS, by all means, go for it.

Now, can we stop talking about using or not using BMS's, and stick with higher voltage setups. :)
 
Yea, I get it, with 12-year-old packs (BYD used packs), the "run away" cell only happened when overcharging the entire pack. So, I just limited the entire pack and the runaway cell never happened again. If you want to use a BMS, by all means, go for it.

Now, can we stop talking about using or not using BMS's, and stick with higher voltage setups. :)
If you don’t want to use a bms then don’t. But don’t expect to not get comments if you just throw a random “PS I quit using a bms” in there.. that might have been when that one particular cell felt like running away, but another cell could start acting up at a lower voltage. Do you at least have individual cell voltage monitoring
A higher voltage setup imo is always best, can’t think of a downside
 
My position on bms use is this, they are useless and unneeded right up until they arent.
I ran my 18s for like 14 months with no bms. I just monitored them very closely and had no issues right up until one went to 4v.

I threw a huge load on my system to drop the voltage across the whole pack quickly, but it was at 4v for a few hours. Now since then I have tested those cells and they still hold full capacity in my bank, but when recharging it is always the lowest voltage cell

Make of that what you will.
 
I just finished getting my jkbms to communicate with Victron VENUS OS on a raspberry pi.
Very cool. Next will be my smart shunt.
Wanna check it out, click on this Victron VRM
I need to get my 5048MG to report to this thing somehow now
 
I don’t see a downside to using 18S, keeping the pack in the knee will dramatically extend their life, as long as you do not discharge below 2.5V per cell… maybe someone can do the math and see what the best lifespan and energy density would be… 3.0 to 3.5 power range… heck, 2.8 to 3.4 would be nearly a full cycle, and a lot of Wh’s….
 
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