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Electrodacus SBMS0 or Chargery 8S?

DZL hit most points dead on so I really don't have anything to add regarding SBMS vs Chargery. Another BMS that does active Balancing is REC BMS but ONLY on their ActiveBMS and that's only on 12V. I've asked them about a 24v model as there larger units still only do passive balancing.

I will give my two cents on Dacian's claim on MPPT (stages) vs CCCV charging with lifepo4 and balancing. CCCV charging is perfectly fine with lifepo4. There really is very little to be gained by an absorption charge with lifepo4 in terms of capacity. The benefit of a multi stage charging is when it comes to balancing. At the top end of your charge cycle, lifepo4 voltage is going to spike quickly so any imbalance will really rear it's head at the top. No amount of balance current is going to offset a fast charge for shore power or a large PV array if you have a imbalance. Balancing during absorption and to some extent float is where the battery can "catch up". During the absorption phase, the current will drop giving the lower balance current time to catch up. You won't be able to get in perfect balance with one charge cycle, but over time, the battery will be balance.

Now with Dacian's CCCV method with the DSSR20s, like I said before work perfectly fine for charging. However if you end up with an imbalance and you cut off charging after the bulk phase (which is how the DSSR20s work), you are giving very little balance current when you are charging at high current. As long as you have a well balanced and matched cells this shouldn't be a problem. Any minor imbalance for differences between the cells should be minimal and even the smallest balance current over time should be able to keep in check.

Even though my bank has 1amp balance on each cell (oldschool MiniBMS v7), I still yearly do a top balance and capacity check just to be safe. This is probably over kill, but I like to know what's going on with my cells. If something like this is done, you can really get by with the CCCV charge method. You aren't harming anything by doing CCCV charging, you might just end up with less capacity if the cells drift about of balance as the BMS will disconnect prematurely.
 
At the top end of your charge cycle, lifepo4 voltage is going to spike quickly so any imbalance will really rear it's head at the top. No amount of balance current is going to offset a fast charge for shore power or a large PV array if you have a imbalance. … You won't be able to get in perfect balance with one charge cycle, but over time, the battery will be balance.

Now with Dacian's CCCV method with the DSSR20s, like I said before work perfectly fine for charging. However if you end up with an imbalance and you cut off charging after the bulk phase (which is how the DSSR20s work), … Any minor imbalance for differences between the cells should be minimal and even the smallest balance current over time should be able to keep in check.

Even though my bank has 1amp balance on each cell (oldschool MiniBMS v7), I still yearly do a top balance and capacity check just to be safe. This is probably over kill, but I like to know what's going on with my cells. If something like this is done, you can really get by with the CCCV charge method. You aren't harming anything by doing CCCV charging, you might just end up with less capacity if the cells drift about of balance as the BMS will disconnect prematurely.

1 amp balancing current? That's amazing. But unnecessary, hopefully? since most BMSes only do 100-200 mA?

If it's true that the SBMS doesn't have the option of a float mode, then that's a good point about the inability to automatically balance the cells by floating at 3.65V, with active balancing, I essentially get a top balance every time, right? I thought it was highly programmable. If you're right, occasional top balancing would fix it, WOW, what a chore. This is DEFINITELY, not going to happen… I already ruined 4 battery lead acid bank by not topping them off with water for a few years. I have a job and a family and I'm very involved at church and my RV storage place is half an hour from my house. I need a set-and-forget setup!

I'm starting to think the "ideal" setup (6P w/ DSSRs) for me is the LEAST ideal setup in terms of maintenance. Maybe my best bet is to use a S2P3/Victron SmartSolar to give me everything I want EXCEPT shade tolerance (Victron interoperability & monitoring, minimal maintenance).
 
1 amp balancing current? That's amazing. But unnecessary, hopefully? since most BMSes only do 100-200 mA?

If it's true that the SBMS doesn't have the option of a float mode, then that's a good point about the inability to automatically balance the cells by floating at 3.65V, with active balancing, I essentially get a top balance every time, right? I thought it was highly programmable. If you're right, occasional top balancing would fix it, WOW, what a chore. This is DEFINITELY, not going to happen… I already ruined 4 battery lead acid bank by not topping them off with water for a few years. I have a job and a family and I'm very involved at church and my RV storage place is half an hour from my house. I need a set-and-forget setup!

I'm starting to think the "ideal" setup (6P w/ DSSRs) for me is the LEAST ideal setup in terms of maintenance. Maybe my best bet is to use a S2P3/Victron SmartSolar to give me everything I want EXCEPT shade tolerance (Victron interoperability & monitoring, minimal maintenance).

I wouldn't call it unnecessary. Most BMS' only do small current because they are doing it internally. My BMS has external balance/monitor boards so you can fit larger resistors. Even so, 1 amp isn't that much if you are charging at 120amps.

The SBMS isn't a charger, just a BMS. The DSSR20 doesn't give the option for float. You can still use the SBMS with an MPPT charger but it should have a remote on/off connector (the 100/50 doesn't). You can run the output through a battery protect and use the SBMS to control the battery protect. I drew this up with a complete victron setup that I had BEFORE the sbms was released and before the Cerbo (using a rapsberry pi for the VEnus). I ended up keeping my minibms as it was doing it's job:

1600264859623.png

You see how the SBMS optocoupler output goes through the BMV712? That's to disable charging when below freezing. The SBMS can do this as well, but it will disable discharging below freezing as well. But the optocoupler turns off the output of the MPPT and DC-DC (also before Victons own DC-DC chargers, but I still don't really like them as they are $$$ for the output). Turning off both charging and discharging when there is a temp event is something a lot of people have talked to Dacian about trying to fix with a software update but he won't as he states if the battery reaches below freezing, it will take a long time to warm up plus the IC for the BMS controls it so he would have to write extra code ONTOP of the IC in order to address it. I think he feels it's better to let the IC do it's own thing in that regard but limits users in mobile applications.

And the yearly top balance, you 100% do NOT need to do that. That was just me being anal and wanting to see were my batteries were at every year.
 
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The SBMS isn't a charger, just a BMS. The DSSR20 doesn't give the option for float.

I'm not sure much charging is accomplished during float anyways. Its my understanding that with lifepo4 if you do use a float voltage (which many people don't) it should be set at a lower SOC (3.3v-3.4v?) the SBMS0 can balance at these levels, but many BMS without programmable balance limits don't begin balancing until somewhere in the region of 3.4 to 3.6v. Lack of an absorption phase might have a bigger impact though.

You can still use the SBMS with an MPPT charger but it should have a remote on/off connector (the 100/50 doesn't). You can run the output through a battery protect and use the SBMS to control the battery protect.

The only thing I would add to this is that (I believe all) Victron MPPTs can be switched via the Ve.Direct port, in your diagram this is occupied by the GX connection. I believe @childcarepro will also be using a GX device so is in the same boat. But for others, either (1) a battery protect or some type of disconnect or relay, or (2) a Ve.Direct cable can control victron MPPT's

I drew this up with a complete victron setup that I had BEFORE the sbms was released and before the Cerbo (using a rapsberry pi for the VEnus). I ended up keeping my minibms as it was doing it's job:

View attachment 22888

You see how the SBMS optocoupler output goes through the BMV712? That's to disable charging when below freezing. The SBMS can do this as well, but it will disable discharging below freezing as well. But the optocoupler turns off the output of the MPPT and DC-DC (also before Victons own DC-DC chargers, but I still don't really like them as they are $$$ for the output). Turning off both charging and discharging when there is a temp event is something a lot of people have talked to Dacian about trying to fix with a software update but he won't as he states if the battery reaches below freezing, it will take a long time to warm up plus the IC for the BMS controls it so he would have to write extra code ONTOP of the IC in order to address it. I think he feels it's better to let the IC do it's own thing in that regard but limits users in mobile applications.

Very nice schematic! And some very well thought through design choices from the sound of it. I'm definitely going to use this for ideas/inspiration. What brand DC-DC (battery to battery) charger are you using, haven't seen it before?
 
Very nice schematic! And some very well thought through design choices from the sound of it. I'm definitely going to use this for ideas/inspiration. What brand DC-DC (battery to battery) charger are you using, haven't seen it before?

Thanks. I made a post on the promaster forum about my electrical system but since my BMS was no longer sold (minibms) I drew up how you could use a modern BMS that's available.

The dc-dc is from Australia (enerdrive). It is the same unit as the Kisae DMT-1250 but was released there before it was available here in the US (or at least I didn't know about it). I had a friend that lives in Australia buy it and ship it over here.
 
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I wouldn't call it unnecessary. Most BMS' only do small current because they are doing it internally. My BMS has external balance/monitor boards so you can fit larger resistors. Even so, 1 amp isn't that much if you are charging at 120amps.
Good point, but consensus seems to be 200 mA is enough, I imagine because during charging, if the BMS is unable to prevent one cell from rising too fast, the BMS would disconnect the battery from the solar charger/inverter charger to avoid damaging the high cell. And during discharge, somewhere near 2V would shut off the load side if unable to prevent voltage drop in the low cell for the same reason.

Nice diagram! I'll have to study it to see where mine can be improved.

And the yearly top balance, you 100% do NOT need to do that. That was just me being anal and wanting to see were my batteries were at every year.

I'm super anal too, but only about the research and implementation side, not so much the maintenance side! I've gotta get better about that. :)
 
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