New here, need some advice.

[Jonnytub]

Hi everyone,

So caught the bug after trying a friends add on kit from ebay. He got it from ebike conversions ltd so i did the same and converted my carrera mtb with it also. The kit is a generic 1000w rear hub with a decent 15ah battery pack consisting of fst 2400mah cells. I get good range but I’m looking to build a separate pack using a set of Samsung Q30’s I got given (brand new, boxed).

I’ve attached a photo of the hailong battery box holder I got from aliexpress with batteries installed (not in any config but stops them rolling off the table). I was hoping to get some advice about how to go about putting the pack together, series, parallel, etc. I can borrow a spot welder and I’m confident in my soldering skills but I’m not sure how to go about setting this up to be a basic switch out for the commuter pack.

Any thoughts or links would be great, i’ve probably watched 100’s of youtube tutorials but not one seems to fit my specific needs.

If this isn’t the right place then by all means delete, this is my first visit so will learn as I go.

 

[Deleted member 4366]

Use pure nickel strip. Cut slots in it where you weld it so that there is no direct path from one electrode to the other.

You have 52 cells in there. Are you going for 48v, in which case you need 13 groups of 4. 36v is 10 groups of 5.

here's a typical 36v one. Obviously, the other side is different because the series connections are staggered. Don't forget that each group of 5 needs to be the opposite way round to the previous group. Your photo shows them all the same way.

 

[Jonnytub]

Yeah going for 48v, what ah would this config run with the sammy cells?

Got my nickel strip ready, just waiting for the spot welder to get dropped off. Thanks for the photo and advice it really helps. I guess the next step will be adding the bms, not sure which one I need to get?

(I just chucked the cells in there temporary to keep them from rolling around).

 

[Deleted member 4366]

I forgot to mention that you should use the cardboard washers on the positive ends because the heatshrink can get nicked during welding, which can cause a massive short.

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR2.TRC0.A0.H0.X18650+insulators.TRS0&_nkw=18650+insulators&_sacat=0

also, you should get some of that special sticky-backed cardboard to cover the the pack and protect the balance leads from touching the cell ends:

 

[Jonnytub]

Thanks, just bought a 200 pc set for future use as well, awesome

I have some sticky back 3mm foam and kapton tape as well, used to tinker with electronics years ago but never really got into batteries so this is a first.

Thanks for the great advice!

 

[anotherkiwi]

Yeah going for 48v, what ah would this config run with the sammy cells?

Got my nickel strip ready, just waiting for the spot welder to get dropped off. Thanks for the photo and advice it really helps. I guess the next step will be adding the bms, not sure which one I need to get?

(I just chucked the cells in there temporary to keep them from rolling around).

4 X 3000 = 12000 so 12 Ah

What is the Amp rating of your controller? A 20 or 30 Amp BMS would be the logical choice.

 

[Jonnytub]

I vaguely remeber 30amp but would have to check for certain, the current battery is supposedly rated at 15ah but i think it uses the same number of cells (fst 2400mah)?

Think I’ll pull this battery out again and recount lol

 

[Deleted member 4366]

I just use cheapo BMSs from Ebay or Aliexpress. BMSs are different than controllers in that their rating is normally continuous power, so a 20A one can give 20A continuous and maybe 40A for bursts. That means that you should choose one with the same rating or higher as your controller.

You need to think about both the thickness and length, whether there's enough room in the case for it. you get single, double and triple-decker ones.

Make sure you get one with balancing function. They don't always say, so you have to look at the picture to see if it has a row of 13 bleed resistors, like this one:
http://www.ebay.co.uk/itm/13S-48V-20A-Lithium-Cell-18650-Battery-Protection-BMS-PCB-Board-Balance-Cable-CE-/292218085702?epid=2181456851&hash=item44098e2146:g:joYAAOSwXz9ZlYVt

Also, look for one that has a separate pad for charge control (marked C-).

 

[Jonnytub]

Thanks d8veh, just bought that one you linked to and thanks for all the advice.

Cheers

Jonny

 

[Jonnytub]

Hi D8veh,

Quick question if your around as I think I'm confusing myself here. The current (old) pack has the same number of cells (FST 2400mah) but is rated 15Ah, how does that work with cell configuration as I can only see 4 rows tabbed if I take a peek under the cardboard?

 

[Jonnytub]

Obviously further up the pack it expands but I can't get to that bit without dismantling and this is where I stumble on calculating it.

 

[Jonnytub]

All welded up. Just waiting on the BMS which should have been here yesterday.

 

[Deleted member 4366]

Hi D8veh,

Quick question if your around as I think I'm confusing myself here. The current (old) pack has the same number of cells (FST 2400mah) but is rated 15Ah, how does that work with cell configuration as I can only see 4 rows tabbed if I take a peek under the cardboard?

Difficult to say without seeing the whole pack. Logic says 6 x 2.4 = 14.4Ah, but that arrangement looks to be in multiples of 4.

 

[Jonnytub]

That was my thinking too so whilst I won’t outright claim ebc ltd are lying about their ah claim I will be dismantling this pack to change it out for 30q’s sometime in the next year or so now that I’ve got the spot welder running. I’ll report back here when the time comes.

Speaking of which, I’ve also managed to fix two dead makita 3ah batteries as well so it’s a win for the cheapo chinese unit so far, I’m sure it will flunk out on me in the future but so far it’s done a grand job, just gotta remember to let it cool down after so many welds....