Capacity testing 48v 200ah 16s pack

[JoeyJibJab]

Hey guys, I'm a little confused on the best way to go about capacity testing some lithium cells. I've purchased 16 200ah lithium cells with the intention of creating a 48v pack for an off grid shack. What is the easiest and most cost effective way of capacity testing this battery pack? Thanks.

 

[Samsonite801]

Try this one for starters, and see what you think:

 

[JoeyJibJab]

So I'm unsure of the best way to go about this with a larger pack, I've watched the video.

1. Top balance cells in 16p configuration
2. Arrange the 48v pack in 16s with 150a BMS with low voltage cut off.
3. Attach a battery monitor to the battery to record battery Wh consumed etc.
4. Hook up an inverter and run a 2000w appliance to discharge battery in 5hrs for a 0.2c rate.
5. Analyze results

Will this suit? Thanks

 

[Samsonite801]

So I'm unsure of the best way to go about this with a larger pack, I've watched the video.

1. Top balance cells in 16p configuration
2. Arrange the 48v pack in 16s with 150a BMS with low voltage cut off.
3. Attach a battery monitor to the battery to record battery Wh consumed etc.
4. Hook up an inverter and run a 2000w appliance to discharge battery in 5hrs for a 0.2c rate.
5. Analyze results

Will this suit? Thanks

The battery monitor you describe is usually in the form of a shunt with multimeter display, or hall-effect sensor with multimeter display. Same kind of thing Will was describing in the video...

Get the Wh figure and calculate it into Ah:

Ah to Wh. Wh to Ah.

Convert Amp-hours (Ah) to Watt-hours (Wh) and vice versa

convert-formula.com

Yeah something like what your steps indicate. You basically might want to run it all the way down to the lowest voltage you might do in real life (if you want a real-life, real use, Ah figure), but if you are testing to see how well a cell stands up to published spec, you shoot to try and simulate the same kind of test the manufacturer would do, like maybe test each single cell from 3.65v down to minimum low like maybe 2.50v (whatever the spec sheet says the maximum and minimums are. I've never done a cell bench test yet though, I only know it in theory. I don't know the 'proper' methodology to bench test a single cell to simulate how factory does it (like what ambient temps, what low and high voltage they start and finish from, clamp it to a certain pressure, etc, others here could explain that better)...

On a whole battery though, you may want to focus more on real world spec (in a real world cycle), just so you know what it is capable of. But in Will's video, more his point was to pre-test each individual cell you buy, so you can determine if they actually provide the published spec, so you confirm you are getting your money's worth. Any other measurement you take for real world testing, is just for your own understanding about what you can really expect out of it, so you have an initial baseline documented, and can understand how the performance may be diminishing over cycles and time.

When I say real world spec, I mean like what a normal maximum spectrum cycle will be for you. Like below is an example of a 'long-life' cycle where green shows what a cycle would look like to get max life (which is not so extreme as a full 2.50v - 3.65v cycle)... That might be where you set your inverter shutoff and charge cycling around.

 

[JoeyJibJab]

The battery monitor you describe is usually in the form of a shunt with multimeter display, or hall-effect sensor with multimeter display. Same kind of thing Will was describing in the video...

Get the Wh figure and calculate it into Ah:

Ah to Wh. Wh to Ah.

Convert Amp-hours (Ah) to Watt-hours (Wh) and vice versa

convert-formula.com

Yeah something like what your steps indicate. You basically might want to run it all the way down to the lowest voltage you might do in real life (if you want a real-life, real use, Ah figure), but if you are testing to see how well a cell stands up to published spec, you shoot to try and simulate the same kind of test the manufacturer would do, like maybe test each single cell from 3.65v down to minimum low like maybe 2.50v (whatever the spec sheet says the maximum and minimums are. I've never done a cell bench test yet though, I only know it in theory. I don't know the 'proper' methodology to bench test a single cell to simulate how factory does it (like what ambient temps, what low and high voltage they start and finish from, clamp it to a certain pressure, etc, others here could explain that better)...

On a whole battery though, you may want to focus more on real world spec (in a real world cycle), just so you know what it is capable of. But in Will's video, more his point was to pre-test each individual cell you buy, so you can determine if they actually provide the published spec, so you confirm you are getting your money's worth. Any other measurement you take for real world testing, is just for your own understanding about what you can really expect out of it, so you have an initial baseline documented, and can understand how the performance may be diminishing over cycles and time.

When I say real world spec, I mean like what a normal maximum spectrum cycle will be for you. Like below is an example of a 'long-life' cycle where green shows what a cycle would look like to get max life (which is not so extreme as a full 2.50v - 3.65v cycle)... That might be where you set your inverter shutoff and charge cycling around.

View attachment 27480

Thanks for that! I see what your saying about testing each individual cell. I think though, testing it as a 48v pack will be more practical in my scenario. Testing each individual cell sounds like a pain and very time consuming.

I'm still in two minds on the best way to go about top balancing the cells.

Option 1:
- Arrange in 16s with BMS (LV and HV set accordingly) and charge to around 3.5-3.6 with a bench top power supply (60v, 5amp)
- Finish off balancing in 16p or in chunks of 4p etc. to 3.65v

Option 2:
- Arrange in 16p and charge with a 30v, 10a power supply to 3.65v. As per Wills video.

Option 3:
- Arrange cells in packs of 12 or 24v with a separate BMS and charge with either 12v or 24v charger, or a 30v 10a supply.
- Finish top balance with 30v power supply in 16p or in chunks of 4p etc.

Option 3 is the most costly, but I can use the smaller bench top power supply for the final top balance.

 

[Samsonite801]

I wound up just getting a power supply, this kit, an RD6012w (they are up to RD6018/RD6018w now):

60.0US $ 20% OFF|Rd Rd6012 Rd6012w Usb Wifi Dc To Dc Voltage Step Down Bench Power Supply Adjustable Buck Converter Voltmeter 60v 12a - Multimeters - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

I use it also, working with 48v DC motors lately too, so it serves other purposes, I'm building an off grid homestead, and toying with DC motors to drive things like greenhouse fans, pumps, and solenoids, testing temperature switches, PWM controllers, and other stuff running on DC 48v, so a power supply can be a handy thing to have around anyways, depending on your situation.

Here is the RD6018/RD6018w:

72.0US $ 20% OFF|Rd Ruiden Rd6018 Rd6018w 60v 18a Usb Wifi Dc Dc Adjustable Step Down Voltage Bench Power Supply Buck Converter &1000w Ac Dc Psu - Switching Power Supply - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

It requires the main buck converter front panel (the heart of it), a case, and the backend steady-state regulated power supply, lots of You Tube videos showing how to assemble the kit. I bought all 3 components from the Factory RD Store on AliExpress, using the Ships from United States option and they came pretty fast.



As far as balancing, I would just stick with Will's (no frills, no gimmicks) top balancing video:

He basically just connects all cells in parallel, and runs them up to 3.65v, with the power supply set to Constant Voltage (I just set to Constant Voltage to 3.64v, and OverVolt Protection to 3.65v) and call it good once the current goes down to 0.

 

[JoeyJibJab]

I wound up just getting a power supply, this kit, an RD6012w (they are up to RD6018/RD6018w now):

60.0US $ 20% OFF|Rd Rd6012 Rd6012w Usb Wifi Dc To Dc Voltage Step Down Bench Power Supply Adjustable Buck Converter Voltmeter 60v 12a - Multimeters - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

I use it also, working with 48v DC motors lately too, so it serves other purposes, I'm building an off grid homestead, and toying with DC motors to drive things like greenhouse fans, pumps, and solenoids, testing temperature switches, PWM controllers, and other stuff running on DC 48v, so a power supply can be a handy thing to have around anyways, depending on your situation.

Here is the RD6018/RD6018w:

72.0US $ 20% OFF|Rd Ruiden Rd6018 Rd6018w 60v 18a Usb Wifi Dc Dc Adjustable Step Down Voltage Bench Power Supply Buck Converter &1000w Ac Dc Psu - Switching Power Supply - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

It requires the main buck converter front panel (the heart of it), a case, and the backend steady-state regulated power supply, lots of You Tube videos showing how to assemble the kit. I bought all 3 components from the Factory RD Store on AliExpress, using the Ships from United States option and they came pretty fast.
View attachment 27574


As far as balancing, I would just stick with Will's (no frills, no gimmicks) top balancing video:

He basically just connects all cells in parallel, and runs them up to 3.65v, with the power supply set to Constant Voltage (I just set to Constant Voltage to 3.64v, and OverVolt Protection to 3.65v) and call it good once the current goes down to 0.

Awesome, thanks. I might grab one of these. They seem like a bit of a safer option than the really cheap power supplies, especially as I'm dealing with a decent sized battery. I'd like to play it as safe as possible.

I'd love to get more into electronics so I'm sure it'll come in handy eventually. I think I'll charge up the pack in 16s first to 3.55 or so to save some time, and then finish off the balance in 16p. I think this power supply has a HV cut off which is a nice safety feature.

 

[Samsonite801]

Awesome, thanks. I might grab one of these. They seem like a bit of a safer option than the really cheap power supplies, especially as I'm dealing with a decent sized battery. I'd like to play it as safe as possible.

I'd love to get more into electronics so I'm sure it'll come in handy eventually. I think I'll charge up the pack in 16s first to 3.55 or so to save some time, and then finish off the balance in 16p. I think this power supply has a HV cut off which is a nice safety feature.

Yeah it does have CV, or CC, and OVP, and OCP...

I attached the manual for my RD6012w here on this post if you want to review it. Like I said, right after I bought mine, I found out they have a RD6018 / RD6018w, which is 18a instead of 12a...