building a booster pack, where to start?

[patpatbut]

Thanks. It seems there is a slightly difference in C rating

From BMSB, my 36 12AH battery is 1.5C continuous and 3C burst
This cell is 1C continuous and 2C burst..

I am running my bike 15amp max. Would that be a problem?

Pat

 

[patpatbut]

Luckily I am able to cancel the headway cells order.

Dave can you help me with my quesiton?

Thanks
Pat

 

[patpatbut]

So for being so annoying

I wish I can order the battery this weekend

Anyone can help me I am really appreciated

Pat

 

[patpatbut]

Anyone?

Thanks
Pat

 

[Deleted member 4366]

There'll be no problem at 15 amps. If the cells are different to your existing ones, what's the advantage over the Headways?

 

[patpatbut]

Headways have a higher C rating (more than 15Amp). The polymer one is only 1C continuous with 12AH capacity so I might not give 15amp.

I have been told, In order to give 15amps from this polymer cell, I need to increase the capacity like 2s2p so 24ah. It means I need to get four of this cells.

It seems getting two headway cells is easier.

Hope it makes sense.

Pat

 

[Deleted member 4366]

The ideal situation is to use identical cells. People have used 12v SLA batteries to boost their lithium one, although I've never heard anything other than the first test ride. Only Kirstin has used one long term, and he uses similar cells. When you use different cells, you're really in the realms of the unknown. We can say that it'll probably work OK, but we won't know for definite until you try it.

 

[patpatbut]

Thanks Dave.

Do you know I really need to get 4 of this polymer cells to achieve continuous 15amps output?

Pat

 

[Deleted member 4366]

In the past many (probably most) ebikes were using 15 amp controllers and 1C batteries of 8 to 10 aH. those cells are 1C continuous, which is 12 amps, and 24 amps max. Your controller will give about 7 amps continuous and 15 amps max.

 

[patpatbut]

Does it mean I can just need two polymer cells considering I am using S06S?

Pat

 

[Deleted member 4366]

There's no exact answer to your questions because nobody has done it before. We can only spout theories and guesses. Currentwise, those cells should be OK, but if I were doing it, I'd take a chance on the Headways because they're easier to handle, unless you already have an idea where you can stick those pouch cells.

 

[patpatbut]

I have two different capacity of headway cells to choose

Should I get 12A or 15Ah (which is higher than my 36v 12aH pack)?

PAt

 

[patpatbut]

Hi Dave,

Do you know the answer?

Thanks
Pat

 

[Deleted member 4366]

There isn't really an answer. The 15aH ones are bigger and cost more, but have more capacity. If all goes according to plan, they will never run out. The 12aH ones are smaller,so easier to install somewhere, but might go down before your others. As long as you have a monitoring system, it shouldn't be a problem other than losing a couple of potential miles from your main pack; however, with the booster pack, you should be going further anyway because you'll be using less current a lot of the time.

 

[patpatbut]

Thanks Dave so much. I have finished the booster pack and it works beautifully. Details to follow if someone is interested. Pat

 

[Deleted member 4366]

Of course we're interested.

 

[patpatbut]

I am charging both of the them now probably need more run to test how good it is.
I will try to post some info next week.

Pat

 

[patpatbut]

Promised the update.

First of all, the reason of doing this is to improve the total distance by running both batteries at 15.5mph. For testing purposes I de-restricted to the check the performance

To recap, my main battery pack is 36v 12ah lifepo4 battery from BMSbattery

The booster pack is from eclipse cycle headway 38140 12ah (2S)

I made the pack using Dave’s diagram (with balance wire and lipo alarm) and the nominal voltage is around 6.8

When connect them together I get around (41.2v+6.8) 48v and the running voltage is around 46v

I have two bikes (ebrompton 36v 340rpm front wheel and a hybrid Bafang CST 36v 250w around 221rpm on 700c wheel) to test.

Ebrompton before the booster pack, I get around 16.5mph flat full throttle with moderate of wind. After connecting the pack, I get around 19.5mph for the same condition

The hybrid bike before the booster pack, I get around 19mph flat full throttle with moderate of wind. After connecting the pack, I get around 22mph for the same condition

If doing full throttle, the total distance is reduced even I have more juice (wind drag possibly)

I charge and balance the headway cells using accucell 6 charger. Charging at 6A in 2S does not cause any problem. It takes around 2 hours to fully charge the pack.

If anyone is interested, I can post some photos.

Pat