Topband Navitas Prismatic at BH

[snoobler]

My project got simplified by the decision to actually add more cells but split into two separate batteries. These are repurposed plug-in hybrid Lithium LMO/NMC cells, so they're a different beast altogether.

Since the BMS is usually your limit on current, breaking it up into smaller batteries each with their own BMS simplifies each individual battery, adds total current capability and offers redundancy should you have a problem cell.

 

[DiyMegs]

I'm honestly both excited and terrified of NMC chemistry after seeing thermal runaway videos ?.

But I'm so glad to hear you say that scenario snoobler!! Because that's the exact same thing I'm hoping to do! Individual daly bms for each 48v battery and stringing two completely separate batteries for two separate inverters.

 

[snoobler]

There's no crime in feeding two inverters from the same battery bank. makes charging a lot easier.

 

[DiyMegs]

There's no crime in feeding two inverters from the same battery bank. makes charging a lot easier.

?Hmmm

Now comes the redesign ?. Just take my ? jkjk

Thus far it'll be an ~11.5kwh battery with 3500 watt peak draw capacity.? Correct me if I'm wrong.? I was going to go with 3k growwatt inverters.

 

[snoobler]

144 * 3.2V * 25Ah = 11,520Wh, yep.

3500W peak?

Why two separate inverters?

 

[DiyMegs]

3500 watts at 48 volts is just shy of the 3C; right???

So honestly the thought was to have this with my 680watts of solar (test array) and run my emergency home based items as a first attempt at raw cell design. But eventually get 2x 8s6p A123 lifepo4 from big battery for whole home backup on my 6.5kw array being installed later this year ?

 

[snoobler]

If you're just going to string a wee tiny 16S pack, then 75A * 48V = 3600W, but that's not anywhere near 11.5kWh. You have enough for 9 of those.

Let's say you build 3X 3P16S packs. EACH pack would be capable of 225A on a cell rating basis, BUT you'd be limited by the BMS - typically 100A.

You'd tie the packs together in parallel as you would any other 3 48V batteries. Those 3X 3P16S packs each at 100A would provide 3 * 100 * 48 = 14kW, and you're only running the cells at less than 50% of their rated peak current.

 

[DiyMegs]

So then I did mess up on my math ?. I was only expecting the 75 amp draw (for the 3C rate). So how did you extrapolate the EACH pack capability of 225A?? And yes I got 100A 16s daly bms's for the 48v strings.

Goodness I still have plenty to learn! I'm Soo excited!!!

 

[DiyMegs]

Oh wow I see now where I messed up ?

Thank you for pointing this out to me!!! I didn't add the total of the 75amp x 3 together. I'm glad you showed me my error ?

Oh and yes I was planning to do a charging bandwidth modification to get as many cycles as possible!

 

[beetlefan]

Oh wow I see now where I messed up ?

Thank you for pointing this out to me!!! I didn't add the total of the 75amp x 3 together. I'm glad you showed me my error ?

Oh and yes I was planning to do a charging bandwidth modification to get as many cycles as possibS

The cells are sold out,

bus bars - I was going to drill holes in copper stock I bought from Grainger.
milled bus bars will the cat's u know what,
post some pics bro.

Saw BH front page showing few remaining will be available in about two weeks. Buying option single piece only w/o cheaper by box option which is $11/pc

 

[sshibly]

yeah they are back in stock, FYI: I found a thread on endless sphere where a guy in TX had a pallet full of these and selling it for $6/cell

 

[DiyMegs]

yeah they are back in stock, FYI: I found a thread on endless sphere where a guy in TX had a pallet full of these and selling it for $6/cell

Sadly they haven't been active since November. But thanks for the heads up ?.

Now that I've learned from my earlier mistakes (thank you again snoobler!!) I'm thinking about one more bank in parallel ( so 4 total ) will fulfill my ultimate goals ?

 

[ssgtgleason]

I purchased 16 of these modules and trying to decide the best configuration for a 12v system in my RV. Originally I was thinking 4s4p but looking for suggestions.

 

[snoobler]

How much current do you need to draw?

 

[ssgtgleason]

How much current do you need to draw?

The plan for now is to replace the deep cycle lead acid with this one which runs the 12v lights and at times the furnace blower. About the biggest draw is the electric leveling legs. None of these are high amp draws for long periods. Eventually I plan to add solar and if these work out expand the pack to provide a large part of the A/C needs.

 

[snoobler]

How much current do you need to draw for as long as 2 seconds?

 

[ssgtgleason]

How much current do you need to draw for as long as 2 seconds?

I need to test the draw to confirm.

 

[snoobler]

Without knowing the current, you can't establish a configuration. Your biggest limitation is going to be the BMS.

 

[ssgtgleason]

Without knowing the current, you can't establish a configuration. Your biggest limitation is going to be the BMS.

I agree, and will get the expected draw. I do have 4 100amp 12v BMS modules on hand.

 

[snoobler]

Oh. New info. Then you've just established your configuration and likely made current not matter much.

4X 4S individual batteries each with their own BMS. You'll be limited to 75A/battery due to cell limitations, but that's 300A for the parallel battery bank.