LiPo battery setup: 2 x 4S ? 3 x 3S ? 2 x 5S ? Cyber Monday?

ESK8 Electronics
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Hi there,

While I almost figured out all my parts, I’m still scratching my head regarding batteries.

I’m not looking for very high speed, I just want at least 12km (7.5miles) of range. I’m 70Kg (154lbs). I’ll be running one 63mm motor (which I don’t have yet, not sure what to buy). It’s almost all flat here.

Using http://calc.esk8.today/, I have an approximate idea of what I would need.

  • 2 x 4S batteries with at least 5Ah
  • 3 x 3S batteries with at least 4.5Ah
  • 2 x 5S batteries with at least 4Ah

But then, how do I choose which one is best ? I always see higher voltage is better, but I don’t feel like I need to go for 10S for my use. What about C rating ? Should I go for 20C or 30C ? I guess 30C just to be safe ?

Also, should I order for HobbyKing right now as they have a cyber sale ? I went on the site 2 weeks ago and it seems that they always have sales going on. Not sure if the prices are better for BlackFriday/CyberMonday. There’s a good deal on that 3S 30C 4.5Ah (https://hobbyking.com/en_us/turnigy-4500mah-3s-30c-lipo-pack-xt-90.html).

2

What gearing, wheel size and motor kV do you intend to buy. How fast is not very fast?

3

25/30km/h max If it goes faster, not a problem of course. I’ll be able to limit it using the VESC anyway.

4

Let’s give you a top speed of 40km/hr. So you can build up to it. 10s 16/36 gears. 97mm wheels. 6374 170kv gives you torque and speed for later. Of course you can limit ERPM so you only hit 25-30kph

5

So you think I should directly go for 10S ? I was thinking 3 x 3S is a nice compromise, as I can add a 3S later to get 12S. What C rating should I get ? Is 25C ok ?

6

just go for 10s.

7

10s 5ah would give you 12 mile range easily. It’s always a good idea to over build. More voltage than you really need and more capacity than you really need. You’ll draw less amps and you won’t have to run your batteries all the way down. This way they will last longer. I would go with 2x5s 5ah if you can and get them with the highest C rating you can. The C rating is important to reduce voltage sag and overheating.

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10s 5ah 20c is 100a 30c would be 150a. 10s is a good idea. Higher c rating also better

9

My opinion is better go with 9S so that later on you could upgrade to 12s because with 2x5 or 2x6 you have no room to downgrade or upgrade… I am going (4 x 3s) x 4 for 12s4p

10

If u use x5 2s lipos for a 10s pack, then you ad X1 2s lipos you get a 12s pack…unless I don’t understand what you are trying to define.

11

there is not much 2s packs these days, that’s why I did not mention them :slight_smile:

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9s or 10s are any of those significantly cheaper on HK?

13

Hmm, I don’t have any trouble getting them but I must be a regional thing.

14

I went with these ones https://hobbyking.com/en_us/graphene-6000mah-3s-65c-w-xt90.html saved half k on batteries ;D

15

It depends on what are you looking, I was looking 60C+ because of Chinese C rating I have in mind going maybe 4wd

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16

I can dig that. Have you checked hobbyking.com? They have international shipping and warehouses.

17

I got already the batteries went with 3s packs, europe & UK (get the joke? :joy:) does not allow import lipos from outside so no international warehouses only eu/uk :slight_smile:

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18

I was in need of 3S and at least 5Ah 50C for my spotwelder, found this 7S 5Ah 60C cheaper than I’ve ever seen, got 2, will make two 3S packs, and a flat 8s with the rest :yum: $51.93 - $7.42/1S 5Ah 60C

19

How would you guys sort those batteries by quality ?

  1. Turnigy Nano tech
  2. Turnigy
  3. Zippy

Am I correct ? I might go for those: https://hobbyking.com/en_us/turnigy-nano-tech-4500mah-5s-35-70c-lipo-pack-xt-60.html $12.50 off, looks like a good deal. I know it’s only 4.5Ah but it’s still enough for 12km range.

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I’ve been learning more and more about lipos. Some advice.

  • cheap lipos are overrated on discharge rating. sometimes a LOT. I’d go for the 40c ones minimum. This also helps for braking.

  • charging them to 100% and draining them to empty will greatly shorten cycle life. Maybe by half or more. I would size the pack to use 50-70% and charge to 4.1v per cell

  • bigger mAh packs give you higher charge rates so stronger brakes

  • general consumption seems to be 10-20wh/mile, depending on weight and riding style. If you’re light and go slow on flats, and don’t do stop and go, you might get 10wh/mile. (wh is watt-hour, which is voltage times amp-hours. so 3s 5000mah pack is (3.735.000 = 55.5wh). Its easier to calculate range with wh than ah, as it takes into account voltage)

  • if you abuse the lipos, you might get 50-150 cycles out of them. If you treat them well they might go quite a few more

  • more expensive lipos have better cycle life, sometimes much better. if you treat the Turnigy Graphene packs nicely they might to 1000 cycles, which makes them actually much much cheaper in the long run

  • lipos don’t like to be stored at 100%, cycle life takes a hit

  • lipos don’t like being discharged below say 3.7v/cell. Like, really don’t like.

  • it’s a huge pain in the butt to charge 3 x 3s packs. disconnect everything and parallel charge on hobby charger, then reconnect making sure not to cross wires. Every ride. 10s or 12s is a bit easier as you can find bulk chargers for those voltages (and cell monitors on the balance leads to make sure you don’t overcharge a cell. And balance charge periodically). Sucks bad if you have an enclosure that’s hard to open.

  • you have to babysit them. the cells go out of balance much more readily than 18650s.

  • lipos, especially abused lipos, occasionally catch fire on their own. Sometimes during charging, sometimes during discharging, sometimes all on their own. It’s very unlikely to happen but if it does, you could lose your house. So low risk but high consequence. Careful guys in RC store their lipos in lipo bunkers, and charge only outdoors. If your enclosure is hard to open, sayonara board if it happens.

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