LifePO4 BMS selection

[geem]

Thinking about a lithium battery build. How do you choose a BMS to deal with things like a 3kw inverter and a windlass inrush current? My windlass is 1700w at 24v. My watermaker uses a 1500w motor and a 250w motor that would be run through the inverter. The inrush current won't trip the inverter but the inverter can take a load up to 6kw briefly. Obviously wouldn't want the BMS to fry when running either of these loads.
You never have to think about this stuff with lead

 

[gregcope]

Oh. Interesting.

Choices that I can think of;

• Use Lead for those (like an AGM Engine start battery for the inverter).
  
  
• No BMS (!) here be dragons.
  
  
• A contactor/Relay based BMS (123, DIYBMS or others e.g QUCC) can deal with these assuming the contactor/Relay can handle the load. I would go with these with high continuous loads.
  
  
• Mosfet BMS, however only very few can handle those loads. Check the datasheets carefully. For example a JBD-SP04S034-L4S-200A-200A-BU, as 12V BMS can do 480A for 500msecs according to the datasheet (ie around 6kw). I would avoid a Mosfet BMS if running high continuous loads. Mosfets can last ages, but not if hard pressed as they will heat up and start failing.

Worth noting i have zero real world experience of high induction loads. The above is theory!

 

[vas]

+1 on what Greg says (except I wouldn't dare without a BMS)
I wouldn't touch a Mosfet BMS either

IF you have a victron ecosystem, a contactor based BMS like 123 or diyBMS will "talk" to a victron controller (raspberrypi or their own more expensive kit) and current control in both charging and discharging will be setup automatically from the BMS to the devices. That's the approach I'm following. Once I get the last chip for my shunt, I'll move the lot to the boat and can confirm that the 1800W watermaker works as does the fin stab oilpump.

V.

 

[vas]

mind if you start adding everything up, total is not pleasing:
classT fuse,
500A contactor (Bluesea?)
cells
BMS+shunt
rpi or Cerbo
cables, etc

 

[geem]

Oh. Interesting.

Choices that I can think of;

• Use Lead for those (like an AGM Engine start battery for the inverter).
  
  
• No BMS (!) here be dragons.
  
  
• A contactor/Relay based BMS (123, DIYBMS or others e.g QUCC) can deal with these assuming the contactor/Relay can handle the load. I would go with these with high continuous loads.
  
  
• Mosfet BMS, however only very few can handle those loads. Check the datasheets carefully. For example a JBD-SP04S034-L4S-200A-200A-BU, as 12V BMS can do 480A for 500msecs according to the datasheet (ie around 6kw). I would avoid a Mosfet BMS if running high continuous loads. Mosfets can last ages, but not if hard pressed as they will heat up and start failing.

Worth noting i have zero real world experience of high induction loads. The above is theory!

I see you can get a 500amp rated Daly BMS for 8s configuration 24v. I don't know the inrush current if my windlass but assuming the circa 70amp @24v run current, I would have an allowance of 7 times for inrush with a 500amp BMS

 

[geem]

mind if you start adding everything up, total is not pleasing:
classT fuse,
500A contactor (Bluesea?)
cells
BMS+shunt
rpi or Cerbo
cables, etc

Yep, I guess that is why a lithium install done properly costs a lot more than just the cells. The ancillaries probably cost as much as the cells

 

[vas]

well my cells (8X304 EVE) were say 1100euro
all the rest are probably another 700 but I had already a fully victronised setup!

 

[gregcope]

I see you can get a 500amp rated Daly BMS for 8s configuration 24v. I don't know the inrush current if my windlass but assuming the circa 70amp @24v run current, I would have an allowance of 7 times for inrush with a 500amp BMS

Is that a 500A BMS or one that will do 500A for a spike?

 

[geem]

Is that a 500A BMS or one that will do 500A for a spike?

I don't know. My running load won't be more than about 100 Amps worse case lifting the anchor with fridges running and electronics etc.

 

[gregcope]

I don't know. My running load won't be more than about 100 Amps worse case lifting the anchor with fridges running and electronics etc.

Got a link to the 500A bms?

 

[geem]

Got a link to the 500A bms?

All the ones I can find are out of stock. Maybe better to go with a BMS that will switch a 500 amp relay instead?

 

[vas]

All the ones I can find are out of stock. Maybe better to go with a BMS that will switch a 500 amp relay instead?

my understanding is that a mosfet BMS will have constant "losses" and will heat up at the 80A you'll need for your w/m How much for half/one hour, no idea.
I really dislike the concept of mosfets and resulting heat on large loads as a solution to a non-existing problem == you drag all the power of your system constantly through a series of chips so that if and when a problem arrises these chips will block output and save your bank/boat. Flawed to the bone (imho) get a bistable contactor (ok for 300usd for a BlueSea) and be done with, no losses, no heat 24/7 and if and when something fails, just a split amp to disengage the relay!
something like this:
https://www.bluesea.com/products/7702/ML-RBS_Remote_Battery_Switch_with_Manual_Control_-_24V_DC_500A

V.

 

[Poey50]

I'm not a fan of MOSFET -based BMSs on boats, either and think external relays are the way to go especially in a dual bus set-up where charge and load circuits are separated. For loads of up to 100amps then I've been very happy with these from GWL which will switch loads to 120amps. I haven't explored how they cope with higher inrush currents but I assume they aren't likely to switch in those moments. Quite small footprint and, of course, bistable.
123ELECTRIC BMS123 Smart - Dual Relay | shop.GWL.eu

 

[vas]

I'm not a fan of MOSFET -based BMSs on boats, either and think external relays are the way to go especially in a dual bus set-up where charge and load circuits are separated. For loads of up to 100amps then I've been very happy with these from GWL which will switch loads to 120amps. I haven't explored how they cope with higher inrush currents but I assume they aren't likely to switch in those moments. Quite small footprint and, of course, bistable.
123ELECTRIC BMS123 Smart - Dual Relay | shop.GWL.eu

OP wants 80-100A @24V, this one only does 60A@24V (the two relays in parallel) so not enough. I should also note that I had serious problems sourcing any of their stuff down here, maybe availability in the UK is fine, dunno.

 

[Poey50]

OP wants 80-100A @24V, this one only does 60A@24V (the two relays in parallel) so not enough. I should also note that I had serious problems sourcing any of their stuff down here, maybe availability in the UK is fine, dunno.

Click through to the manual. Each switches 120amps at 24 volts.

 

[vas]

Click through to the manual. Each switches 120amps at 24 volts.

apologies, saw the description which states [in bold] 60A@24V, manual slightly confusing but looks like it will fit OP needs.

 

[Zing]

Thinking about a lithium battery build. How do you choose a BMS to deal with things like a 3kw inverter and a windlass inrush current? My windlass is 1700w at 24v. My watermaker uses a 1500w motor and a 250w motor that would be run through the inverter. The inrush current won't trip the inverter but the inverter can take a load up to 6kw briefly. Obviously wouldn't want the BMS to fry when running either of these loads.
You never have to think about this stuff with lead

I don't protect those consumers with the BMS. They all are fused though. Also the battery doesn't need protecting from overcurrent as it large and has very high peak transient current capacity and even has capacity to run all my consumers continuously. My battery is not fused, but it could easily be.

My BMS (Cell Performance Monitor, from GWL) just monitors voltage. It shuts down chargers if over 3.5v. It activates an alarm if below 3.0v. If under 2.7v or over 3.8v it isolates the battery via a Blue Sea latching contactor. I don't need anything else. I suspect you probably don't either. If you feel you do need current protection, you could buy an ammeter with a relay output at a programmable set point. ABB amongst others do them. You can get also get similar things for buttons on Ebay, ditto for temperature monitoring.

 

[vas]

isn't 2.7 and 3.8 a bit too low/high for disconnects? I've programmed 3.0 and 3.55 respectively (granted bank is still at my office, will move onboard following week).

 

[Zing]

isn't 2.7 and 3.8 a bit too low/high for disconnects? I've programmed 3.0 and 3.55 respectively (granted bank is still at my office, will move onboard following week).

The factory disconnect limits are 2.5v and 3.65v, but I can’t get exactly there with the settings I have. The 2.5v is well outside my settings anyway and 3.8v is close enough at the top. In practical terms it is only minutes away from 3.65v and some lithium batteries have a 4.0v disconnect limit, so I’m sure I’ll be fine. BTW, these are disconnect limits. I will never get there in normal use and have never been there so far.

 

[Kelpie]

Thinking about a lithium battery build. How do you choose a BMS to deal with things like a 3kw inverter and a windlass inrush current? My windlass is 1700w at 24v. My watermaker uses a 1500w motor and a 250w motor that would be run through the inverter. The inrush current won't trip the inverter but the inverter can take a load up to 6kw briefly. Obviously wouldn't want the BMS to fry when running either of these loads.
You never have to think about this stuff with lead

You never have to think about it with lead because you don't tend to run huge inverters off them.

Since you are at 24v your have already halved the problem. All of the main options have already been discussed so not much to add there.

It really depends how much money you have and how idiot proof you want to make the system.
I have gone ultra cheap: a 4S pack with a 120A JBD BMS. Everything currently runs through that, and I just take care not to load it too much. So I don't hoover and cook at the same time.

I do have a plan to install a relay which will activate the remote on/off switch on my inverter, and that will mean it can bypass the BMS. But I haven't got around to setting that up yet, and tbh drawing 250A from a set of 270Ah cells doesn't really sit well with me.
So I think I will build a second pack, with another 120A BMS, and that will solve a lot of problems at the same time.

FWIW I've been living aboard full time with this system for over six months now, and I'm very happy with it. I had to switch back to gas cooking for a day, because we had two days of almost no sun. But given I spent about £1k in total I'm not complaining.