Is my maths correct?

Thurlow

Finding my (electric) wheels
Dec 3, 2019
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500 X 'lg m29' 18650s at £1.64 each (for sale in the uk at fog)
They are 2850mah and I'm building a 48volt battery.

Just over 800 quid for a 100ah monster.

That cant be right can it?
 

Thurlow

Finding my (electric) wheels
Dec 3, 2019
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Oh, it's actually for a solar setup, this forum was fantastic when I built my ebike and hope no one will mind if I just run the numbers past someone smarter than me.
 

vfr400

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Jun 12, 2011
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How are you going to balance it? The BMS alone will probably cost £800.

Assuming 12S for 48v, 500/12 =41.67, so you can build a 12S41P battery.
41 x 2.85 = 116.85 Ah or 5047 watt-hours.

If your charging system can cope with 13S, you get 13S38P for 5068 watt-hours because you're using 494 cells instead of 492.

Wouldn't lead batteries be a lot cheaper and simpler?
 

Thurlow

Finding my (electric) wheels
Dec 3, 2019
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13s was the thinking, the mttp solar charger would charge it and if I'm honest I didnt consider the BMS would need to be anything more fancy than the one in my ebike, it was 40 quid!!

Much much more research to do before shelling out I think!

Lead acid would be simpler but I like the life span of lithium.

Thankyou
 

Nealh

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Just had a look at their prices and some cells like VTC6 are way cheaper then Nkon and other cells also cheaper, cheaper cells could be inferior graded cells.
Cell price is ex vat but even factoring in vat they are a good £1 or so cheaper then Nkon. Makes 40T a more interesting option.
One thing I can't see is delivery charges ?

 
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Thurlow

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Dec 3, 2019
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Yes.. delivery is probably 20 grand.

Regarding the BMS, I think a decent 48 volt solar charger with enough panels and a high amp Bms could balance these over night without mega expense, what issues were you thinking of with the potential for spending 800 on a bms?
 

Nealh

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Samsung 40T 21700 is £2.20 cheaper then Nkon !!!!!.
Depending on delivery they would make a viable choice.
 

Nealh

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Just emailed them to ask.
 

vfr400

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Yes.. delivery is probably 20 grand.

Regarding the BMS, I think a decent 48 volt solar charger with enough panels and a high amp Bms could balance these over night without mega expense, what issues were you thinking of with the potential for spending 800 on a bms?
You should so some research on BMSs for solar. I'd be pretty sure that they're substantially different to ebike ones.

The problem is the balancing. 100mA bleed currents are OK for a 4P cell-pack, but, even for an ebike battery, you're going to need something substantial for 38P.

An ebike BMS with top-balancing is not going to work because ebike batteries are charged and discharged, and the balancing happens at the top end of each charge cycle on the basis of a little and often, while as your battery will spend much of the time held at maximum voltage.

Also, you'll probably want to keep your pack below the voltage at which top balancing occurs otherwise it won't live very long. I'm not an expert on lithium batteries for solar, but I'd say that you'd want to use a maximum of something like 4.05 to 4.1 volts per cell compared with 4.2 for an ebike, where the balancing happens somewhere above 4.15v.

Check out the Electrodacus. It combines a charge controller with BMS up to 7S and 40 amps. There are probably similar products that can cope with larger installations.
 

Thurlow

Finding my (electric) wheels
Dec 3, 2019
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Thanks for that reply you are correct actually am looking at 3.75 to 4.05 for longevity, never even occured to me where in the volt range the balancing occurs.

Maybe I might be advised having a simple monitor system and taking it offline at intervals and manually balancing.. if i go brand new on the cells that might be feasible.

Il have a look around at solar and BMSs

Very interested in seeing if delivery is free on the above cells.. crazy prices.
 

soundwave

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soundwave

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his vids are worth a watch if you want to diy one.

 

Nealh

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P & P is UK £8 +vat, and EU £15 + vat.
If the cells are genuine and good grade an alternative to Nkon.
 

Nealh

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As VFR has mentioned solar monitoring dosen't seem to come cheaply esp for 48v.
 

Nealh

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Nice Smifee, the endorsement sounds good.
Looks like I will use them next time I spot a battery together and thinking of using 20/21700 format.
 

Thurlow

Finding my (electric) wheels
Dec 3, 2019
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Unless you are like me.. if yer in the market to buy everything is expensive the second you dont need it.. boom everything's a bargain!
 

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