BMS vs Growatt 6000T Charger?

[shot428]

I have no experience with bms's and none with Li batteries, so this is new to me. After getting my new system hooked up I have a few questions ?

Initial batt charge was done with modified 10 amp charger (purchased with batt), when charging was done the meter was at 58.4 v. When I turned the charger off the meter changed to 56. At the time, I thought nothing of it but now I'm wondering if that 56v should be my float voltage?

I set the growatt float to 54 because it is what the battery guy said to do and I watched its first cycle yesterday. I used 2 led lights that kilowatt says pull 326 watts each (so totally balanced load) and the growatt said it was doin 661 watts. I ran this for 8 hours and then switched the AC in on, I set the growatt to a 10 amp charge and a few hours in I raised it to 20a, at 10 the fans come on bout every 10~15 min and runs for 2~5 min, at 20 the fans run continuously (nothing to do with my ?, just adding info on the 6000T for others).

As the batt got to 54v I expected to see the charge amps reduce (float) I admit I have no clue what float does which is why I was watching and nothing, just kept charging. But when it got to 56v the charge current dropped to .1a and I am assuming that .1a is float ?

Note: there is no communication between the batt and the growatt.

So does the bms override the inverter ? Or what am I missing? And finally should I change float to 56v ?

Thanks !

 

[Ampster]

Float is a low current Constant Voltage stage. It generally is not good for Lithium batteries but a setting of 54 volts is below the charging voltage of 56 volts so that is just about resting voltage and should not hurt them since your battery guy recommended that voltage setting. Leave float at 54 volts like he recommended, The BMS is a safety device that also can balance your cells.

 

[DThames]

If the unit is trying to hold the float voltage setting there will be some x amps going to the battery, or from the charger. If you increase the load, in order to maintain the float setting, you should see the amps go up on the charger side, making up for the additional load.

 

[shot428]

I just found this post and it seems to apply

Growatt - Odd behavior

I know this is an old post, but I've experience the same issue with my new Growatt 3000w 24v. Battery topped off, solar turned off even though I was still pulling a decent load and the sun was out. Tonight I noticed my charge light was solid Green indicating full charge even though my SOC was...

diysolarforum.com

 

[shot428]

So for the 2nd cycle test I set float to 54v and bulk to 54.8v and when it hit 54 the current dropped to .1a, the shunt reports 99% charge and it just stays there ,,,,,,,,, for several hours.

3rd cycle I set float to 56 and bulk to 56.8 when it got to 55 the current started dropping and when it reached 55.9 charge current went to zero and the voltage fluctuated between 55.80 and 55.96 counting up to 96 then drops to 80 then counts up again does this continuously. Shunt still reporting 99% charge and it stayed like this overnight .

4th cycle float 56, bulk 58 and once again it did the 55.80 to 55.96 thing and now reports 100% charge. I do believe this is now my proper setting but have emailed this info to the battery guy to see what he says ?

The other thing that changed was the shunts report of the kwh's , the battery is rated at 120 AH so 48 x 120 = 5760

1st cycle shunt said 4.9 kwh, 2nd cycle 5.1 kwh, 3rd cycle 5.9 kwh and 4th cycle 6.1 kwh

 

[Kornbread]

I wonder if your SCC is seeing a bit of resistance? The batteries may be at x.xxvoltage but due to resistance between the SCC and battery the SCC is seeing x.xxvoltage + resistance.

 

[shot428]

I wonder if your SCC is seeing a bit of resistance? The batteries may be at x.xxvoltage but due to resistance between the SCC and battery the SCC is seeing x.xxvoltage + resistance.

SCC ?

shunt says int res is 360.6

 

[Kornbread]

SCC ?

shunt says int res is 360.6

Stuby for Solar Charge Controller, which in this case is an AIO, or All In One.

Resistance would be the total of all wires, connections, and anything else between the SCC and Battery.

 

[shot428]

Stuby for Solar Charge Controller, which in this case is an AIO, or All In One.

Resistance would be the total of all wires, connections, and anything else between the SCC and Battery.

2 feet #4 wire from batt to 400a shunt (neg) 150a anl fuse (pos) 20 inches #4 wire to aio ,,, res should be low but will have to disassemble to test with meter

Thanks

 

[Kornbread]

2 feet #4 wire from batt to 400a shunt (neg) 150a anl fuse (pos) 20 inches #4 wire to aio ,,, res should be low but will have to disassemble to test with meter

Thanks

I'd get a t class fuse for the batteries. If something goes south, Li batteries can drop a ton of current in an instant. A class t fuse has a significantly higher interrupt current rating that anl.
Even a so-so connection can impact resistance.
IMO, you might want to consider upsizing the 4awg from the battery buss bar to the SCC.

 

[DThames]

You keep stating the state of charge based on the shunt. One thing to understand, the shut is not very smart, even it is a Smart Shunt. Shut meters work good for a guide but poor to base battery setting decisions on. When the shut says less than 100%, it just means it has not been clocked up to its full setting value. I used the word "clocked" to get attention. The shut doesn't measure state of charge. It is "clocked" in amp hours by amps flowing over time, through the shunt. It (the shunt meter) has no idea the true state of charge of the battery. It is an integration type recorder of what goes in and what goes out.

 

[shot428]

Thank you every one

I do intend to up the wire gauge when I add the 2nd battery, I used #4 because I had it laying around and due to my intended use, which is as a UPS to backup needed medical equipment when the pwr fails with a max draw of 15 amps ( 3 items 1400 watts). So yes, the 6000T was def overkill but if SHTF it would fill our needs (once I get everything put together)

I was not feeling that the numbers from the shunt were sacred but they were verified via multi and clamp meters and shared them because I thought others might interpret the info differently from how I was? I did admit I was clueless

I'm also retired and have lots of free time, so I have now spent several hours learning and as a result I now know that not all info was available as until today I did not know that the dif types have dif voltage requirements. My battery is a A123 20ah pouch cell type 8s6p w/150a bms X 2 for 48v.

A123 cells have a charge window between 3.3v and 3.6v while the blue box china cells are 3.3 to 3.65

A123 recommends that you charge to 80% to extend the life (cycles) of the battery and that for a 48v battery the bulk charge not exceed 57.6v

An 80% charge per cell would be 3.54v with total being 56.6

I am currently at 55.9v which = 3.49v per cell

Hopefully this info helps the next guy