10s vs 9s vs 8s vs 7s Li-ion battery configuration

[baikiewheelie]

Hi all,

I would like to build a home made concealed Li-ion battery inside an actual water bottle.

Please advice which configuration should I choose?

I mean,

1. What are the most common BMS available on the market?
2. What are the most common CONTROLLERS available on the market?
3. How does the chosen configuration limit the choice of a motor?

Cheers,
Al.

 

[Nobuo]

Each BMS is made for a specific Voltage, so if You have a 9s battery you must use a 9s BMS

You will have problems to find a 32V controller, and you have the same problem about Voltage .
Decide between 36V or 24V for getting easily the right BMS and controller.

You should take into account that less Voltage is less top speed and efficiency

 

[baikiewheelie]

Hi all,

I am designing a battery pack for an electric bike. It would be "concealed" in a water bottle.

The goal is to estimate what is required number of battery cells (18650) for the optimal pack?

Typically, one can fit roughly 30 batteries inside the water bottle. Then 7s4p or 10s3p arrangement can be used (since there is no way to publish tables here, I have made a blog post detailing the battery pack calculations http://almantas.imakescience.com/2015/03/designing-battery-pack-for-actual-and.html)

So, from the motor power perspective, it is clearly better to use 10s3p. But from battery longevity perspective, it is better to use 7s4p (I plan to use 15A controller which would then drain each cell at 4p with 3.75A and at 3p with 5A).

It that all logic correct?

 

[d8veh]

There's a lot of different 18650 cells. Some can go as high as 10A. 10S3P should be able to give 15A easily if you choose the right cells. Generally, the cells that can give the best current have the lowest capacity, but you should be able to get a minimum of 6Ah.

 

[dogman dan]

Less top speed, meaning more efficiency. Slow is more efficient.

Inside a real water bottle will be a tiny battery in terms of capacity in watt hours. So, you better be using a tiny watts setup. Something slow, like 24v, 200-250w controller. 15 mph stuff.

So the battery would be either 6s or 7s. If you go to 36v, 10s, you'll be too fast pulling 400-600w, and only go a few miles.

If you can cram 200 watt hours into a real water bottle, then a bike running on 200w would run about an hour, vs 20 min or so for a faster run pulling 600w.

Also, if you build for a short fast run, you'd need the very very best, and most expensive cells for them to handle the draw from 5 ah worth of it.

Some bikes have two bottle mounts, so two real bottle batteries is a possibility, for a faster 36v bike with some range.

 

[Nobuo]

Less top speed, meaning more efficiency. Slow is more efficient.

Of course, but I was talking about the build. A BLDC motor runs more efficient at higher Voltages, or I am wrong?

 

[999zip999]

Lots of premade bottle batteries on the market of all different quality. The battery must match the controller's demands. You would be giving yourself a headache. Trying to make a magic battery.
Hard to help without knowing what motor and controller you are using.
More info on what you are trying to power.

 

[baikiewheelie]

Lots of premade bottle batteries on the market of all different quality. The battery must match the controller's demands. You would be giving yourself a headache. Trying to make a magic battery.
Hard to help without knowing what motor and controller you are using.
More info on what you are trying to power.

Could you please give a link where I can buy AN ACTUAL water bottle battery pack or the whole kit? I was not able to find it Those widely available Chinese water-bottle-supposed-to-be-looking-like-ridiculous-designs are no good for me, mate.

I haven't chosen a motor and controller yet. Looking at something 250-360W range for FRONT fork (gear hub at the rear).

 

[DAND214]

What size/capacity water bottle are you planning to use?
Will it really fit in a bottle cage?
Do you plan on mounting the BMS in there too?

As posted above, you won't get much in there and if so you won't go very far.

Dan

 

[baikiewheelie]

So the battery would be either 6s or 7s.

6s? how about the BMS adn controller for 6s? there are not very common, are they?

If you can cram 200 watt hours into a real water bottle, then a bike running on 200w would run about an hour, vs 20 min or so for a faster run pulling 600w.

Yes, I agree. More specifically, with 7s4p config I can push it to 5A per cell easily and still have 9.5Wh per cell capacity (266 Wh total per battery pack total capacity) at those nice 24V*20A = 480W powers. So half hour drive on max power. More than enough for my commute.
But thanks for confirming my estimations
Cheers,
Al.

 

[baikiewheelie]

What size/capacity water bottle are you planning to use?
Will it really fit in a bottle cage?
Do you plan on mounting the BMS in there too?

As posted above, you won't get much in there and if so you won't go very far.

Dan

Hi Dan,
No need to go far I only got 2 hills in my commute, each somewhat average steepness, 200 meter long or so. I drive them up myself in 3-5 minutes by pedaling. So half an hour battery juice is what I need at most because most of the time I use my own bioenergy, hehe. For a weekend rides I plan to pop another (or even two) battery bottle into my backpack. Its a road bike I that I would like to modify - all stealthy and cute.
I am searching for 1000 ml (40oz) bottles. It is not easy to find a nice looking one though. I like this - MSR water bottle, 1 liter. Width 3.5 in / 8.89 cm, height 8.75 in / 22.3 cm. I hope to fit there 12 batteries in levels 1, 12 batteries in level 2 and 4 in level 3. I hope there will be enough space in level 3 to fit the BMS (from ebay), which measures 53*63MM.