diy solar

diy solar

BMS Needs?

If you have 16 cells why not get a 48v charger/inverter - that would be my first question. for 24V you would want to get 2 8S 24V BMS's for your two parallel banks of 8 cells each. The 24V system will somewhat limit the inverter output, thats why 48V systems makes way more sense.
Probably because he implied he already had a 24v inverter and purchased a 24v BMS?
 
I thought the 24V guy was the trailer guy, this is the 12V balancer guy. Yeah these message boards can get confusing, lol
I get confused myself, and agree that he would be happier with a 48v system, but he has already purchased equipment.

He could get close to running the 2400 watt inverter with a 100 amp at 24v BMS, but better to have two of those since he has 16 cells.
 
If you have 16 cells why not get a 48v charger/inverter - that would be my first question. for 24V you would want to get 2 8S 24V BMS's for your two parallel banks of 8 cells each. The 24V system will somewhat limit the inverter output, thats why 48V systems makes way more sense.
Well, I already bought a hybrid inverter and all the other components for a 24v system. I'm just trying to learn as I go and asked questions along the way. This suggestion never came up, so here I am. LOL.
 
I thought the 24V guy was the trailer guy, this is the 12V balancer guy. Yeah these message boards can get confusing, lol
I am a 24v guy and have a fifth wheel trailer. Hahaha. Yeah, the group for cells was frustrating trying to keep up. I appreciate everyones help though! The inverter I have is 2400w, so maybe I'll order another BMS just to be safe. So I would need two 8s BMS's? What happens if I try to make due with what I have, and if it didn't work, just add another with a little reconfiguration?
 
I'd buy that second 8s BMS and make two 24v batteries.
Redundancy is nice. If one of the batteries in parallel goes down for some inexplicable reason you still have one to rely on.

Also any load would be shared by the 2 batteries. A single "parallel pair" battery using one BMS is limited in the amps it can deliver. If I remember right the BMS you bought is a 100a discharge. If you pull the inverter's max 2400w you would actually be drawing over 100a due to the inverter's efficiency. (2400w / .9 (90% efficiency) = 2667w / 24v = 111a

That's more than the rated discharge of the single BMS
with 2 batteries/ 2 BMS you would only be drawing 55a or so.
 
I am a 24v guy and have a fifth wheel trailer. Hahaha. Yeah, the group for cells was frustrating trying to keep up. I appreciate everyones help though! The inverter I have is 2400w, so maybe I'll order another BMS just to be safe. So I would need two 8s BMS's? What happens if I try to make due with what I have, and if it didn't work, just add another with a little reconfiguration?
It just complicates the setup. After you setup 2 series strings of 8 cells each, tie the pos masters together and to the inverter/charger pos, then hook up one bms to each 8s banks' master negative and then tie the bms outputs together and to the negative of the inverter/charger. Make sure the cell banks are at the same state of charge before you tie the two BMS outputs together, and don't forget to use a resistor to charge up the caps in the inverter charger, those sparks can damage the threaded terminals on those prismatic cells.
 
I'd buy that second 8s BMS and make two 24v batteries.
Redundancy is nice. If one of the batteries in parallel goes down for some inexplicable reason you still have one to rely on.

Also any load would be shared by the 2 batteries. A single "parallel pair" battery using one BMS is limited in the amps it can deliver. If I remember right the BMS you bought is a 100a discharge. If you pull the inverter's max 2400w you would actually be drawing over 100a due to the inverter's efficiency. (2400w / .9 (90% efficiency) = 2667w / 24v = 111a

That's more than the rated discharge of the single BMS
with 2 batteries/ 2 BMS you would only be drawing 55a or so
Thanks guys! I ordered another BMS from Overkill. I'll have it here before I leave to TX to pick up my cells in a week or so. I'm a bit nervous hooking everything up and making sure the state of charge is the same and all the other technicalities. Is there a good resource that explains in layman's terms? Will goes pretty fast and I find myself getting lost even when it's his "beginner" series. Maybe I'm too focused on elk hunting right now, but I've had a serious mental block on this stuff.
 
It just complicates the setup. After you setup 2 series strings of 8 cells each, tie the pos masters together and to the inverter/charger pos, then hook up one bms to each 8s banks' master negative and then tie the bms outputs together and to the negative of the inverter/charger. Make sure the cell banks are at the same state of charge before you tie the two BMS outputs together, and don't forget to use a resistor to charge up the caps in the inverter charger, those sparks can damage the threaded terminals on those prismatic cells.
Is there somewhere that explains this process in detail, such as the resistor and such?
 
Thanks guys! I ordered another BMS from Overkill. I'll have it here before I leave to TX to pick up my cells in a week or so. I'm a bit nervous hooking everything up and making sure the state of charge is the same and all the other technicalities. Is there a good resource that explains in layman's terms? Will goes pretty fast and I find myself getting lost even when it's his "beginner" series. Maybe I'm too focused on elk hunting right now, but I've had a serious mental block on this stuff.
If you're getting new cells they usually ship about half charged, mine were 3.29 volts each. Just check each one when they arrive. Basically you're building two entirely separate 8S 24v paks (obviously the s tands for series), wiring the BMS is pretty simple, once you put on your buss bars pos to neg, confirm 24V(26.3V) between your master pos and master neg. Then get your multipin bms connector (unconnected) black wire to master neg, red wire to master pos, and your 1-8 wires go to the pos of each cell. Check its wired properly with a multimeter on the pins. 3.29V, 6.58V, 9.87V all the way to cell 8 at 26.32V. Once confirmed hook up the bms to the master NEG and plug in the multi pin connector, get app going and you should see all the data for each cell and the whole 8s pak. To combine the two paks I would disconnect each BMS's multipin, then just tie the two master positives together through a fuse and a switch to your inverter/chargers pos DC input then tie your two bms outputs together and then to the inverter/chargers DC negative input. With the pos side switch and fuse closed (connected) you can do the resistor trick to charge up the caps on the Inverter/charger through the negative side (if you like,) but in reality I'd hook it all up with the pos switch off (open) and use the switch to make the final connection. Once that's done plug in the BMS's. I've read manuals on these hybrid units and not once have I seen them suggest the resistor trick, even when hooking it up for the first time. Best of luck! :)
 
If you're getting new cells they usually ship about half charged, mine were 3.29 volts each.

Don't depend on the cells being anywhere near the same state of charge. 25% of the 16 cells I originally ordered, 4 were within 5 amps hours of 100%, the other 12 were about 50%.

Just check each one when they arrive. Basically you're building two entirely separate 8S 24v paks (obviously the s tands for series), wiring the BMS is pretty simple, once you put on your buss bars pos to neg, confirm 24V(26.3V) between your master pos and master neg. Then get your multipin bms connector (unconnected) black wire to master neg, red wire to master pos, and your 1-8 wires go to the pos of each cell. Check its wired properly with a multimeter on the pins. 3.29V, 6.58V, 9.87V all the way to cell 8 at 26.32V. Once confirmed hook up the bms to the master NEG and plug in the multi pin connector, get app going and you should see all the data for each cell and the whole 8s pak. To combine the two paks I would disconnect each BMS's multipin, then just tie the two master positives together through a fuse and a switch to your inverter/chargers pos DC input then tie your two bms outputs together and then to the inverter/chargers DC negative input. With the pos side switch and fuse closed (connected) you can do the resistor trick to charge up the caps on the Inverter/charger through the negative side (if you like,) but in reality I'd hook it all up with the pos switch off (open) and use the switch to make the final connection. Once that's done plug in the BMS's. I've read manuals on these hybrid units and not once have I seen them suggest the resistor trick, even when hooking it up for the first time. Best of luck! :)

Best to start by top balancing.


Then hook them up in a pack.

Pre-charging the inverter before connecting is VERY MUCH recommended.



Lots of discussion about what value to use. I use this:


I have also used this:


Both worked fine.
 
If you are working with older equipment sure it's a good practice, but modern hybrid charger/inverters use HTC thermistors to protect against in rush current. Like I say I haven't seen it in a manual yet for a new unit.
 
If you are working with older equipment sure it's a good practice, but modern hybrid charger/inverters use HTC thermistors to protect against in rush current. Like I say I haven't seen it in a manual yet for a new unit.
This is a DIY forum. He is talking about a mobile system for his RV. Likely he will choose something like a Victron Multiplus.

A precharge is a VERY GOOD IDEA. We aren't talking $5,000 grid tied inverter.
 
This is a DIY forum. He is talking about a mobile system for his RV. Likely he will choose something like a Victron Multiplus.

A precharge is a VERY GOOD IDEA. We aren't talking $5,000 grid tied inverter.
These protections are built into $500 hybrid inverter/chargers.
 
This is a DIY forum. He is talking about a mobile system for his RV. Likely he will choose something like a Victron Multiplus.

A precharge is a VERY GOOD IDEA. We aren't talking $5,000 grid tied inverter.
Thank you. I purchased an MPP LV2424 hybrid unit. I don't recall anywhere in the manual about precharging anything. However, I wasn't really searching for it neither. Mainly have been focused on getting all the components and what will be needed to rewire the whole cabinet as my OCD will not allow me to move forward with the rat's nest that the factory provided.
 
using precharge on an already protected circuit is safe

there’s safety and money efficiency, definitely two fundamentally distinct design goals

to save money, confirm whether your device has internal capacitor precharge protection and then omit an add on precharge circuit

to ensure safety, use a precharge circuit on inverters and anything that makes a spark the first time it is connected

i plan on implementing current sensor and voltage sensor based precharge circuit on inverter and maybe SCC if i feel like it :geek:

for the average inverter, i would implement it anyways

most people are not implementing per circuit current sensors so this is maybe fringe approach here fwiw
 
Thank you. I purchased an MPP LV2424 hybrid unit. I don't recall anywhere in the manual about precharging anything. However, I wasn't really searching for it neither. Mainly have been focused on getting all the components and what will be needed to rewire the whole cabinet as my OCD will not allow me to move forward with the rat's nest that the factory provided.
I just purchased the baby brother of this for my grandson (the 1000w 12v model). I haven't received it yet, so can’t tell you if it needs it.
You will know if it requires it the first time you hook it up, if there is a loud snap and arc, you need it. Be careful and don't make it on the flat part of a current-carrying connection, or screw threads, or something like that. It can give a large divot/burn mark. If you need it, you need it. If you don't, then you don't.

Let me know how you like it. I assume this is the one:

 
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I just purchased the baby brother of this for my grandson (the 1000w 12v model). I haven't received it yet, so can tell you if it needs it.
You will know if it requires it the first time you hook it up, if there is a loud snap and arc, you need it. Be careful and don't make it on the flat part of a current-carrying connection, or screw threads, or something like that. It can give a large divot/burn mark. If you need it, you need it. If you don't, then you don't.

Let me know how you like it. I assume this is the one:

Bingo, that's the one. Hopefully I can find out these details prior to hooking it up. I'll review the owner's manual again to see what I can find out.
 
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