Building a pack from LiPo cells

I have an electric kick-scooter that runs off 4 SLA batts. (4*12v9aAh).
I have been wanting to replace the SLAs with LiFePos or LiPos for a while know, but have been reluctant because of the difference in price.
SLAs run for about 0.25$/Wh where I live.
I found a seller on eBay that offers LiPo packs at an attractive price (0.45$/Wh):
http://cgi.ebay.com/2x-14-8v-4000mAh-15C-Li-Po-LiPo-RC-Battery-14-8-WF_W0QQitemZ250340720438QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item250340720438&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A0|293%3A1|294%3A50
So last week I made the step, and placed an order for 8 packs that I plan to disassemble and reconfigure as one 7S4P (24v16Ah).
At first I will not connect any BMS or LVC, just rely on the fact that I am connecting 4 cells in parallel that will help the cells to remain balanced, and I will not discharge the pack too deep so non of the cells will go bellow 3v.
I hope these cells are any good, and that I will see an improvement in performance (and that they will not die on me after a few charges). I will also be shedding around 30Lbs of lead from the scooter, and that is an added plus.
The question is, how should I go around building the new pack after disassembling the packs I received? just connect 4 cells in parallel, and then 7 of these new cells in series to create the new pack? Or should I equalize the cells, or find cells that have similar internal resistance? Any advice would be appreciated.

I'd take a 4s and a 3s pack and solder into a 7s 4000mah pack, dont disassemble the pack, just make into a single pack and put on a 7s balance tap and solder + - from each pack together/heatshrink and the other two + - to a deans connector etc, and then put a new heatshrink cover over the pack. I make 6s packs from 2 x 3s packs all the time, its easy.

so now you will have 4 x 7s 4000mah packs,

next make a charging harness that connects (if a duo charger) 2 packs in parallel, both main leads and balance taps in parallel, (or if using a single 7s charger) make a harness for connecting your 4 packs in parallel, and a series connector to hook them up with on your bike, Deans connectors are what I find the best, but Andersons are also good, and there you go

This is a good duo 7s balancing charger http://store.modelpower.co.uk/graupner-ultra-duo-plus-50-296-p.asp

Thanks. Since I've only ordered 4S packs, I will have to disassemble A few packs to get a 3S and a 4S.
So I might as well disassemble all the packs and build a 4P cell and then serialize 7 of these cells.
The charger you suggested costs more than the batteries I ordered. There are cheaper chargers on the market.
This charger is also limited to 7S, so if I want to raise the voltage to 8S or 10S this charger will no be adequate.
I will be charging the pack with a 24v SLA charger I own. It charges at CC of 3A then CV of 28.8v.
28.8/7 = 4.11v/cell meaning I cannot over charge the cells, unless one of the cells is defective, and does not charge to it's peak voltage, thus the other cells might overcharge.
I also plan on building a PIC based BMS that will monitor each cell's voltage and that will give a beep if one of the cells overcharges or over discharges.

Dave-s said:

Thanks. Since I've only ordered 4S packs, I will have to disassemble A few packs to get a 3S and a 4S.
So I might as well disassemble all the packs and build a 4P cell and then serialize 7 of these cells.
The charger you suggested costs more than the batteries I ordered. There are cheaper chargers on the market.
This charger is also limited to 7S, so if I want to raise the voltage to 8S or 10S this charger will no be adequate.
I will be charging the pack with a 24v SLA charger I own. It charges at CC of 3A then CV of 28.8v.
28.8/7 = 4.11v/cell meaning I cannot over charge the cells, unless one of the cells is defective, and does not charge to it's peak voltage, thus the other cells might overcharge.
I also plan on building a PIC based BMS that will monitor each cell's voltage and that will give a beep if one of the cells overcharges or over discharges.

Click to expand...

What kind of SLA charger are you planning to use? I've been eyeballing a BatteryMINDer, but what concerns me is that "...The BatteryMINDer® automatically dissolves harmful power-robbing sulfation using safe, patented high-frequency pulse technology..." I'm trying to figure out what impact that "high frequency" technique would have on LiPo or A123s.

http://cgi.ebay.com/A123-Lipoly-Nicd-NiMH-PB-Super-Charger-TP1010C-TP-1010C_W0QQitemZ220368176667QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item220368176667&_trksid=p3286.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A1%7C293%3A1%7C294%3A50

I got one of these.. works great !

Ypedal said:

http://cgi.ebay.com/A123-Lipoly-Nicd-Ni ... 7C294%3A50

I got one of these.. works great !

Click to expand...

That looks like a great charger for use at home, and for proper/regular battery care. Though I'm looking for something smaller, lighter, and water-resistant, for carrying with me (and maybe even mounting on the scooter).

I wouldn't connect a SLA charger that has the de-sulferication function to a LiPo pack.
This charger looks pretty sturdy:
http://cgi.ebay.com/LiFePO4-24V-5A-Charger-for-Scooter-E-Bike-Battery-Power_W0QQitemZ170303279629QQcmdZViewItemQQptZScooters?hash=item170303279629&_trksid=p3286.c0.m14&_trkparms=72%3A1205|66%3A2|65%3A12|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A50
If you want something a bit cheaper and more portable then this will do the job:
http://www.tncscooters.com/product.php?sku=101138
Forget about having a charger that is water proof. Most chargers have a lot of air intakes to keep the components from overheating.
A sealed charger will be a low current one, and this will take forever to charge your pack.
You might want to put the charger on a timer, or disconnect it when it finishes charging, because most SLA chargers have a float function that might shorten the life of your LiPo pack.

I would have gone for something proven, lipo quality is very errant... I hope they work well for you.
Zippy lipos from hobbycity.com are well regarded.

Thanks.
I too hope that these LiPos are worth the money.
The Zippys are $0.95 per Wh, and the ones I ordered are $0.45.
The 2nd reason I chose these are that after shipping they still come to less than $50.
My country has a high taxation on batteries: %70 + %15.5 VAT, and they include the shipping price when calculating customs. So the $72.65 5S1P 5000mAh Zippy will cost $172 after shipping and tax.
Any package under $50 is exempt from tax, so this was a big motivation for me to order these.
The reason I was willing to order a "No name" LiPo pack was because LiPo technology has come a long way since the early LiPos that needed very strict care and maintenance, and I am hopping that there will not be too great a difference between the hi-end stuff and these.

Yikes, that's some crazy taxes, where are you from? What are you planning to charge them with?

Dave-s said:

My country has a high taxation on batteries: %70 + %15.5 VAT, and they include the shipping price when calculating customs. So the $72.65 5S1P 5000mAh Zippy will cost $172 after shipping and tax.

Click to expand...

...Coming soon to a United States near you!

i am also interested in these packs.. have you done some testing on these batteries?

how did it work out taking appart these packs? i had some chinese lipo packs, and cells were sticked together with double sided tape.

Dave-s said:

I have an electric kick-scooter that runs off 4 SLA batts. (4*12v9aAh).
I have been wanting to replace the SLAs with LiFePos or LiPos for a while know, but have been reluctant because of the difference in price.
SLAs run for about 0.25$/Wh where I live.
I found a seller on eBay that offers LiPo packs at an attractive price (0.45$/Wh):
http://cgi.ebay.com/2x-14-8v-4000mAh-15 ... 1|294%3A50
So last week I made the step, and placed an order for 8 packs that I plan to disassemble and reconfigure as one 7S4P (24v16Ah).
At first I will not connect any BMS or LVC, just rely on the fact that I am connecting 4 cells in parallel that will help the cells to remain balanced, and I will not discharge the pack too deep so non of the cells will go bellow 3v.
I hope these cells are any good, and that I will see an improvement in performance (and that they will not die on me after a few charges). I will also be shedding around 30Lbs of lead from the scooter, and that is an added plus.
The question is, how should I go around building the new pack after disassembling the packs I received? just connect 4 cells in parallel, and then 7 of these new cells in series to create the new pack? Or should I equalize the cells, or find cells that have similar internal resistance? Any advice would be appreciated.

Click to expand...

get the lipos from batteryspace.com there better thay also got a 50ah cell lmao its stupid bit almost like a mouse pad lmao

Still waiting for the packs ... hope to get them sometime this week.
The batteries from batteryspace are much more expensive. They are well over $1/Wh before shipping, whereas the packs I ordered are $0.45/wH inc. shipping.

Picked up the batteries today. The SOB shipped all the packs in 1 package although I paid for separate shipping for each pair.
Luckily I didn't have to pay any customs/tax for the packs.
I measured the voltage of one of the packs, and it read 15.8v. 3 cells voltage is around 3.953v and one read 3.93..v.
This weekend I'll get around to build my new pack. I just need to find where I can buy an 8 pin connector for balancing.

Consider to not take them apart. I desoldered and took apart a Zippy pack. Cells got hot from desoldering which probably damaged them. They were "glued" together with double sided tape which was a big hassle to take apart... I used a food knife and had to bend _hard_. I was as careful as I could but the cells was bent in the process, probably damaged them.

The voltage can probably differ pretty much from your original battery without damage anything. I say use them in 8s4p.

I will be using a 24v 3A SLA charger to charge the pack.
This will charge the battery to 28.8v. A 8S LiPo pack max voltage is 33.6v, so an 8S pack will not get fully charged using my charger.
If I do 7S I will have 4 spare cells in the case that any of the cells in the pack go bad, and the 7S max voltage is 29.4v - closer to the charger voltage.

You should really use a dedicated lipo charger. Hobbycity sells a great 10cell charger from iCharger. If one of your cells goes bad it could still get overcharged(or undercharged) causing the pack to fail, the lipo chargers monitor each cell in the pack preventing any issues.

Those dedicated chargers cost $$$ and you also need a power supply in addition to the charger.
These charger also look very delicate. Drop them once and they will stop working.
I like my SLA charger because it is small, light weight and can be abused and it will still work.

I just don't want you to die.

That's very nice of you ...
I just read Matt's thread about his experience with LiPo packs: http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=9170
If you notice #5: he never had a pack go out of balance before, so a dedicated balancing charger I think is a bit unnecessary.
I will charge the pack at a low current (3A), and I will be discharging well under the 15C rate it is rated for, so it has no reason to heat up.
I will also monitor the pack voltage so not to discharge it too deeply.
And I think I will buy one of these, just to be on the safe side:
http://cgi.ebay.com/M-size-EC-POWER-EC-GUARD-LIPO-Anti-Explosion-safe-BAG-F_W0QQitemZ180336628927QQihZ008QQcategoryZ2562QQcmdZViewItemQQ_trksidZp1742.m153.l1262
This will protect me while charging the pack.

Dave-s said:

I will be using a 24v 3A SLA charger to charge the pack.
This will charge the battery to 28.8v. A 8S LiPo pack max voltage is 33.6v, so an 8S pack will not get fully charged using my charger.
If I do 7S I will have 4 spare cells in the case that any of the cells in the pack go bad, and the 7S max voltage is 29.4v - closer to the charger voltage.

Click to expand...

This is pure insanity, in my opinion. You should not take apart these packs, and you should most definitely not use a cheap SLA charger. You need to use a LiPo-specific charger with individual cell monitoring that cuts off the charge if any one cell gets about 4.25V. If you don't, the question will not be if your pack will explode, just when.

-- Gary

Dave-s said:

That's very nice of you ...
If you notice #5: he never had a pack go out of balance before, so a dedicated balancing charger I think is a bit unnecessary.

Click to expand...

That is because he uses a balancing charger, he said he has never had one go out of balance during discharge. I know it cost more but get a decent charger, or it will end badly(either ruined cells or worse).

This is a very bad idea. I'm not anyones safety ninny, but I would strongly advise against this. You're also going to miss out on half the energy storage potential of your pack by only charging to 28.8v. You would be safer and better off with half the batteries and a good LiPo charger.

Also, LiPo cells stay balanced when you don't have any bad cells, and the packs are made from cells that are all balanced for Ri and capacity. You get this with premium packs, but not with expired on the shelf immature technology LiPo packs. Some of the black shrinkwrap ebay low C ebay packs sold by a variety of different retailers have Ri between 30-90mOhm per cell.... The cheaper the batteries, the more crucial it becomes to use better chargers.

I understand that your safety design element comes in the form of charging 5v under max charged voltage. This would provide some reasonable safety with a controlled current regulated voltage supply, assuming you balanced the cells often. However, an SLA charger is a transformer, a full wave bridge rectifier, a cap or two, and a switch. It is NOT a circuit that can be trusted for much of anything but poking some current into LA batteries.

It's time to blow an extra $100-120, and get a 10amp 10S LiPo balance charger from HobbyCity. You will be so glad you did, and getting the full charge voltage will be a similar effect as getting the capacity of your pack doubled without adding more batteries or weight.

I don't want to see you end up as another one of the LiPo is an evil firebomb horror stories.

I would also avoid cutting the packs apart. It's possible, but it's really not as much fun as you may be thinking it is. I always end up bending the cells, which causes delaminations between the lithium foil and the polymer.

OK OK ... you guys convinced me to buy a LiPo charger.
The 10S 10A charger costs $170 + $15 S/H
I can get this 8S 7A charger on Ebay for $90, inc S/H: http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5606&Product_Name=IMAX_B8_Charger/Discharger_1-8_Cells
The only disadvantage is that the 10S charger is 300W, and the 8S is 150W, so it is half the current charging at 4.5A instead of 9.0A.