18s Lipo pack for eBike, have I got all my basis covered?

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mbgjt1   100 W

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18s Lipo pack for eBike, have I got all my basis covered?

Post by mbgjt1 » Jan 18 2022 4:24pm

I'm in the process of buying 3 x 6s Turnigy 12,000mAh battery packs to connect in series. These will be used to power my eBike.

I would like to confirm that I am covering all my bases with this setup. I am planning to buy:

3 x 6s Turnigy 12,000mAh battery packs to be connected in series to make an 18s pack.
https://hobbyking.com/en_us/turnigy-hig ... vIQAvD_BwE

2 x XT90 series connectors. First to connect two packs together, then the output of these two packs will be connected to the third pack.
https://hobbyking.com/en_us/xt90-series ... s4QAvD_BwE

1 x ISDT Q8 MAX battery charger.
https://hobbyking.com/en_us/isdt-q8-max ... _analytics

1 x Parallel charging board
https://hobbyking.com/en_us/turnigy-xt9 ... _analytics

2 x server power supply units which I will have to connect in series to output a voltage of 24V

Is there anything else I need to think about? I will also be 3d printing a case for the battery packs, and adding padded foam to absorb all the shocks from off road riding.

Appreciate any advice :)

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motomech   1.21 GW

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Re: 18s Lipo pack for eBike, have I got all my basis covered?

Post by motomech » Jan 19 2022 4:23pm

I think what you are talking about is running 18S and then "breaking the string" to parallel charge 6S. If so, why use a 8S charger?
Even so, what you are proposing is super time consuming and frought w/ problems.
I've found that parallel charging LiPoly bricks doesn't allow one to keep track of what the cells are doing as you are reading an aggregate cell value, one could be quite low, while the other is high and you wouldn't know it. Trying to parallel three is pretty much useless. You would be better off using a "duo" 6s + 6S charger, break everything down, charge 2 6S bricks at the same time and then the third after. Given that you will be doing a "storage charge" initially and a "top charge" before using the bike, be prepared to dedicating lot's of time to the "care and feeding" of your ebike. Not to mention sore fingers from connecting and dis-connecting XT-90 connectors.
I ditched using the RC toy chargers years ago as they didn't last charging big bricks of LiPoly, even quality brand names and I now "bulk charge" using Mean Wells. Of course, top cell count will be limited to 14S(or perhaps an unuseful 15S), but that is enough for me and has the the added advantage of keeping the Voltage low enough I don't get big sparks if I do have to connect/disconnect. In that vein, I have found the leaving the "string" intact helps keep the cells in balance and much of the time I just leave everything on the bike to charge. Do this and obey the Depth of Discharge Rule for LiPoly and very little cell balancing will be needed. When it is, I use "clip-on" Battery Medics, which are low-tech and passive.
I have been using LiPoly bricks on ebikes for at least 8 years and I'm pretty sure what you are proposing would not be maintainable on a daily basis.
Too many time consuming steps with the opportunity for things to go wrong.
'11 Motobecane Fathom team, Bafang SWX02-11T, 14S (54V) LiPoly, PSW Power 9-FET 17A controller. Schwalbe Marathon's, 24 to 25 MPH.

mbgjt1   100 W

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Re: 18s Lipo pack for eBike, have I got all my basis covered?

Post by mbgjt1 » Jan 24 2022 8:52pm

motomech wrote:
Jan 19 2022 4:23pm
I think what you are talking about is running 18S and then "breaking the string" to parallel charge 6S. If so, why use a 8S charger?
Even so, what you are proposing is super time consuming and frought w/ problems.
I've found that parallel charging LiPoly bricks doesn't allow one to keep track of what the cells are doing as you are reading an aggregate cell value, one could be quite low, while the other is high and you wouldn't know it. Trying to parallel three is pretty much useless. You would be better off using a "duo" 6s + 6S charger, break everything down, charge 2 6S bricks at the same time and then the third after. Given that you will be doing a "storage charge" initially and a "top charge" before using the bike, be prepared to dedicating lot's of time to the "care and feeding" of your ebike. Not to mention sore fingers from connecting and dis-connecting XT-90 connectors.
I ditched using the RC toy chargers years ago as they didn't last charging big bricks of LiPoly, even quality brand names and I now "bulk charge" using Mean Wells. Of course, top cell count will be limited to 14S(or perhaps an unuseful 15S), but that is enough for me and has the the added advantage of keeping the Voltage low enough I don't get big sparks if I do have to connect/disconnect. In that vein, I have found the leaving the "string" intact helps keep the cells in balance and much of the time I just leave everything on the bike to charge. Do this and obey the Depth of Discharge Rule for LiPoly and very little cell balancing will be needed. When it is, I use "clip-on" Battery Medics, which are low-tech and passive.
I have been using LiPoly bricks on ebikes for at least 8 years and I'm pretty sure what you are proposing would not be maintainable on a daily basis.
Too many time consuming steps with the opportunity for things to go wrong.
Very good points, in that case I may opt to use 2 x 6s lipo battery packs and use a lipo charger with dual output to charge them at the same time.

The reason I would like to go lipo is it allows me to gauge how much capacity and voltage I would need when building my final battery pack. Once I get that done, I can sell the lipo packs after using them for a month of two.

but yes you're right, i would have to always ensure they are stored at a safe storage voltage, and charge them up before hand.

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