what bms to use ?

[Bobby T]

im running a 6000 watt gs inverter and lipo4 byd batteries and was wondering what bms to use,currently using a daly 200 amp and it is crap 

[Sid Genetry Solar]

It probably doesn't like surge loads from the inverter, right?

Or could you be more specific as to what the issue is?  (I know their balancing is pretty much useless on anything larger than R/C equipment batteries!)

[Bobby T]

 the daly bms isnt really big enought to handle my discharge load and since im using a seperate heltec balancer because of dalys poor balancing capabilities im wondering if i couldnt just use a anl fuse for overload protection and maybe some form of disconect being that the gs inverter has a low voltage shut off ?

 

 

 

 

[Bobby T]

1 hour ago, Sid Genetry Solar said:

It probably doesn't like surge loads from the inverter, right?

Or could you be more specific as to what the issue is?  (I know their balancing is pretty much useless on anything larger than R/C equipment batteries!)

the daly bms isnt really big enought to handle my discharge load and since im using a seperate heltec balancer because of dalys poor balancing capabilities im wondering if i couldnt just use a anl fuse for overload protection and maybe some form of disconect being that the gs inverter has a low voltage shut off ?

[Sid Genetry Solar]

24 minutes ago, Bobby T said:

the daly bms isnt really big enought to handle my discharge load and since im using a seperate heltec balancer because of dalys poor balancing capabilities im wondering if i couldnt just use a anl fuse for overload protection and maybe some form of disconect being that the gs inverter has a low voltage shut off ?

That is what I would personally do.  Instead of an ANL fuse, I'd suggest a properly rated DC-rated breaker (200A should be sufficient), as if for whatever reason it trips, you don't have to buy new fuses!  And if you need to disconnect power to the inverter, just flip the breaker off--no tools required.  You can search eBay for GJ1 or GJ1P; those used breakers can often be found for a pretty good price.  They are usually rated to 80vDC, which is sufficient for a 48v nominal system.

As long as the batteries are well balanced (and not regularly being deep-cycled), a properly set low voltage shutoff on the inverter should be decently sufficient safety.  I personally don't have a "BMS" on my house LiFePo4 battery bank.  As long as you know what you're doing, and are aware of the battery limits, you should be fine with a breaker and inverter configuration.

[Sid Genetry Solar]

200A assuming you're at 48v?  I guess I never clarified...are you at 48v or some other voltage?

[Bobby T]

1 minute ago, Sid Genetry Solar said:

200A assuming you're at 48v?  I guess I never clarified...are you at 48v or some other voltage?

24 volt

[Bobby T]

ive got a 24 volt system

[Sid Genetry Solar]

Ah, 24v...200A is way too low to run serious loads there!  You'd need a 400A disconnect for continuous full load operation on the inverter.

Worth noting that most AC rated breakers are DC rated to 32vDC--so you could basically use any 300-400A breaker that you could find.

Also: do NOT use the cheap little breakers that have overrun eBay and Amazon like the flies:

These little pieces of junk are pretty well guaranteed to trip far sooner than expected--or even not at all.  They probably would make your Daly look good by comparison.

 

So for mathematical purposes, 6,000W * 1.1 (90% efficiency) = 6,600W input load / 24v = 275A RMS at full load. 

Note that a thermal breaker will trip by RMS current; a magnetic breaker seems to trip by peak current.  To calculate peak current, take the 275A RMS * 1.414 (square root of 2) to get the peak amperage = ~390A peak.  So a 300A thermal breaker, or a 400A magnetic breaker should be sufficient.

...yeah, that's a lot of amps at 24v!

[Bobby T]

yip looking at 300 amp anl fuse and a heavy duty 300 amp disconnect for now thanks for your input and i have seen those cheap chinese black and red breakers you posted and i wouldnt even use those on a car lol

 

[Bobby T]

found a 300 amp breaker for $80 bucks think i will go with that

[Sid Genetry Solar]

As long as your batteries are rated for the current, you should be OK.

 

BYD cells...how many amp-hours of capacity do you have?  (A 1C discharge rate is generally pretty safe for most batteries.)

[Bobby T]

i have 6 byd 24 volt batteries and believe they are probably 280 ah 

 

[Sid Genetry Solar]

Ah, OK...so if 280Ah sets are 6 in parallel, that's 1,680Ah total--meaning that a 1C discharge for your bank would be 1,680A...yeah, you'll be just fine with full load on a GS inverter 😉.

40kwh of battery, that's a very decent size.

[Bobby T]

slowly adding more solar and saving for more batteries

[Sid Genetry Solar]

I've only got ~12kwh of batteries so you're well ahead 😉.  At some point I would like to double that to 24kwh--but personally don't see any real reason to go further than that.

[NotMario]

40kwh of LiFePO4... wow.
I got 10kwh. Eventually i'd like 30kwh... basically 72 hours of normal power use...

I did now know you could use any [basically] AC breaker for 24v... I've been using fuses instead. (never blown one, thankfully...)
A bit weird... would one use a double-pole breaker? Or single pole on positive?

Now i see some cleanup in my future...

[Sid Genetry Solar]

12 minutes ago, NotMario said:

I did now know you could use any [basically] AC breaker for 24v... I've been using fuses instead. (never blown one, thankfully...)
A bit weird... would one use a double-pole breaker? Or single pole on positive?

Whatever works.  Issue with higher DC voltages is the arc--which if the breaker isn't specifically designed to quench said arc, the breaker will literally start a fire when you trip it or turn it off.  But more often than not, an AC-rated breakers will have a 32vDC rating (when listed).  It could be safe to assume that an AC-rated breaker with no DC rating would also be safe for 32vDC.

You could use a double-pole breaker and double it up for double the amperage rating...maybe? 

I don't see any benefits to disconnecting DC negative honestly.  Risks of disconnecting DC negative would include "floating" equipment...or the worst being alternate unexpected ground paths (like RS-232 or USB cables) that aren't rated to carry significant current.  If one of those got blasted with power due to an open ground, you'd have fried cables and blown electronics very quickly!