Lithium Battery Pack - Build or Buy?

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Lithium Battery Pack - Build or Buy?

Post by Mad Professor » Feb 25 2013 12:30pm

Good day all.

As per the title I can't yet deside if it's better you build a pack or just buy a prebuilt pack ready to go.

This is not for my self, but for my father.
He build his own e-bike, and had been using 3x 12v 7ah SLA batteries.
But the SLA batteries have now had it, so my father brought a prebuilt DIY pack from a UK eBay seller, but this pack has failed within 3 months, and the seller and ebay are not intrested in helping, but I will save the details on that for another post.

So my father wants to get a new battery pack for his e-bike, but I keep on putting him off buying anything else, as I don't want him wasting any more money on bad battery packs.

His current setup is some unknown make 250w brushless hub motor, and an unknown make controller, Peak current load seems to be around 9Amps.
He mostly uses his e-bike in pedal assist mode, but does use the thumb thottle from time to time.
Most return trips are around 20-25 mile, and is out on the bike for aprox 2 hours.

I am guessing that my father will need a battery pack around the 15 to 20Ah Capacity.

I have been looking at building him a battery pack using laptop 18650 battery cells, but after reading SamTexas "Info on Laptop 18650 LiCo cells" post, it seems that the laptop cells are only rated for 0.5c continuous discharge, so a 2200mAh cell is only really good for 1100mAh continuous discharge.

So if I was to use the 18650 battery cells I would be needing at least a 136+ cells to make a 15Ah pack. and 180+ cells to make a 20Ah pack.

I have also been looking at the Turnigy 5000mAh 20C Single Cells.
Once again I would be looking at 30 Cells for 15Ah, and 40 Cells for 20Ah.

With both setups I will need a suitable BMS, and charger.

But I am still unsure what would be best, if we was to build or buy.

The other problem we have atm, is that alot of couriers within the UK, are very picky about shipping lithium cells.

So I would really like to know what other people suggest we should do?

Thanks for your time.

Best Regards.

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Re: Lithium Battery Pack - Build or Buy?

Post by Kingfish » Feb 25 2013 12:37pm

If it were me, I’d want to know the operating voltage. What can be gleaned by “3x 12v 7ah SLA batteries”: Is it 36V @ 7Ah or 12V @ 21Ah?

Any extra Ah is gravy, but knowing the voltage would help. :)
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Re: Lithium Battery Pack - Build or Buy?

Post by Mad Professor » Feb 25 2013 12:40pm

Yes, sorry.

It's a 36v system.

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Re: Lithium Battery Pack - Build or Buy?

Post by 999zip999 » Feb 25 2013 12:42pm

Going with the ease of a plug and play prebuild pack verus the work of triing to get and balance the cells before a build. Do you want a father and son hobby of building a pack. Or spend your time riding ? Building a pack takes alot of time.
There are a lot of choices of Lifepo4 packs with BMS's plug and play. To get quaity you can't get the cheapest pack on ebay.
Plus what DIY pack did you buy ?

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Re: Lithium Battery Pack - Build or Buy?

Post by wesnewell » Feb 25 2013 12:59pm

I don't understand why he will need 15-20ah of lithium if he only had 7ah of sla. 10ah of lithium will come close to triple the range of 7ah of sla. And if the controller is truly only 10A max, then 10ah of 1C batteries is all you need to meet the current draw. Personally, I use 20C lipo from HK. For him, I'd start with 10ah of 12s made up of 4 6s packs and a 12s charger. If he needs more range than that you can always add on to lipo. Not so easy with lifepo4 packs. If he just needs the same range as the sla gave him then 2 6s packs will do more than that.
BTW, building a 12s lipo pack takes about 30 seconds.
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Re: Lithium Battery Pack - Build or Buy?

Post by Mad Professor » Feb 26 2013 5:31am

999zip999: The prebuilt pack my father brought from uk eBay is still a sore subject, And I will be putting up a Rant / Warning post at some point regarding that, The pack was made from 60x 18650 laptop cells, there was no built in BMS, no overvoltage protection / undervoltage protection, and the charger sold with the pack was a SLA charger.

wesnewell: My father's old 3x 12v 7ah (36v 7ah) SLA pack, could only do about 10-12Miles on a good day, but now lucky to do 5 miles.

Building a pack would not be an issue for me.

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Re: Lithium Battery Pack - Build or Buy?

Post by dogman dan » Feb 26 2013 6:44am

If you have the funds, you might consider a good prebuilt pack from a reputable vendor. 36v 15 ah lifepo4 from pingbattery.com for example. Pings got a 5 year track record for good customer service, but likely it won't be needed anyway. There is a growing list of folks that got 4 years life out of Li Pings batteries. You can run up to 25 amps controllers from a 15 ah ping pack.

RC lipo is still a definite option, but lifepo4 has about double the expected lifespan. If you go lipo, 6 of the 5s 5ah packs would get you 36v 15 ah. To charge, get a reasonably high wattage RC charger, 150w, 200w, something like that. But not a quad charger that is 4 cheap 50w chargers in one box. Get a voltmeter or better still a wattmeter to monitor voltage on the bike, and a cellog 8 for checking voltages of individual cells from time to time.

Charge that lipo only in a fire resistant place. Charge a ping nearly anyplace.

Which ever way you go, definitely no more buying from ebayers who don't have a good track record. At least, try to get some 2c or better cells from a trusted vendor. You might look into cells Dr Bass sells here from time to time. He's got a source for decent cells that go fast when he has enough to put em on sale.

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Re: Lithium Battery Pack - Build or Buy?

Post by 999zip999 » Feb 26 2013 11:11am

I still triing to find out what motor and controller you have. This will tell you what battery you need.You need to match the battery to the motor and controller so the battery will last.

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Re: Lithium Battery Pack - Build or Buy?

Post by knoxie » Feb 26 2013 1:48pm

yep Ping is the only pack I would trust for family members, hobby packs are only for the technically aware members of the family IMHO unless they are of course hobbyists, kinda goes in hand in hand :lol:
Electric KMX 72V Lipo, USPD drive unit. BMX 72V, Puma BMC,
Raleigh 26 inch MTB Puma 50V Turnigy 25C Lipo 10AH, Trek MTB, X5 48V NIMH. Electric BMX
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Re: Lithium Battery Pack - Build or Buy?

Post by SamTexas » Feb 26 2013 4:39pm

Mad Professor wrote: I have been looking at building him a battery pack using laptop 18650 battery cells, but after reading SamTexas "Info on Laptop 18650 LiCo cells" post, it seems that the laptop cells are only rated for 0.5c continuous discharge, so a 2200mAh cell is only really good for 1100mAh continuous discharge.

So if I was to use the 18650 battery cells I would be needing at least a 136+ cells to make a 15Ah pack. and 180+ cells to make a 20Ah pack.
A few corrections first:
1) "so a 2200mAh cell is only really good for 1100mA continuous discharge". It seems you are thinking that only 1100mAh can be extracted from a 2200mAh cell. If so, it's not true. ALL 2200mAh can be extracted.
2) "So if I was to use the 18650 battery cells I would be needing at least a 136+ cells to make a 15Ah pack". 136 x 2.2Ah x 3.7V = 1,107Wh. 1,0107Wh/36V = 30.75Ah. This corresponds well with 1). You did misunderstand. For a 36V, 15Ah pack, you only need 68 2200mAh cells.

I'm not trying to convince you (or anyone else for that matter) to use laptop cells. But for me, nothing can beat laptop cells for a European 250W pedal assist ebike. They let you build the smallest, lightest pack. Nothing else comes close. And the power (even at 0.5C) is more than sufficient for that application. A 36V, 15Ah pack will allow you father to forget "range anxiety". In pedal assist mode, it can easily do 50 miles.

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Re: Lithium Battery Pack - Build or Buy?

Post by dogman dan » Feb 27 2013 7:24am

I would say other types of lico cells come pretty close. Lifepo4 like the ping pack I recomended will be larger in size, and weigh slightly more. But compared to lead, he'll be happy with its size and weight.

The real reason for going lifepo4 would be the longer potential cycle lifespan. But NOTHING wrong with the laptop cells for this application, particularly if a very affordable supply of them is at hand.

Correct, you wouldn't have to make the laptop cell pack oversize. It will have to be on the large side already to get really long range, so the discharge rate should allow it to easily provide all it's potential watthours. You just need to make it large enough to go the distance, 10 ah minimum, but 15 ah better so you can make the distance on a less than a 100% discharge.

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Re: Lithium Battery Pack - Build or Buy?

Post by SamTexas » Feb 27 2013 8:56am

Mad Professor wrote: I have also been looking at the Turnigy 5000mAh 20C Single Cells.
Once again I would be looking at 30 Cells for 15Ah, and 40 Cells for 20Ah.
I missed this part. I wouldn't want you for a son. Not in this life time. What kind of son would give his father the most volative, most unstable chemistry, when plenty of safer batteries are available. If you want performance (even when performance is totally unnecessary), go for A123, assuming of course that you do love your father.

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Re: Lithium Battery Pack - Build or Buy?

Post by Mad Professor » Feb 27 2013 9:12am

Thanks for your replies so far, as always lots to think about.

SamTexas: I take it you don't care much for the single turnigy cells, I was just doing a google search and came across the single turnigy cells, but as you seem to feel very stongly about them, I think I will stay clear of them.

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Re: Lithium Battery Pack - Build or Buy?

Post by SamTexas » Feb 27 2013 9:46am

Mad Professor wrote:Thanks for your replies so far, as always lots to think about.

SamTexas: I take it you don't care much for the single turnigy cells, I was just doing a google search and came across the single turnigy cells, but as you seem to feel very stongly about them, I think I will stay clear of them.
Not just single Turnigy cells, but anything that is remotely related to RC LiCo (aka LiPo).

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Re: Lithium Battery Pack - Build or Buy?

Post by 999zip999 » Feb 27 2013 11:09am

A Ping pack is a good choice customer is great plus you have those led's on the bms. How much do you want to spend or have to spend. You already know to cheap on ebay is just to cheap.
There are screw top A123 cells 7-8ah 32157 from OSN battery for a home made build easy assembly and replacement. I would go 2p.
2.jpg
2.jpg (49.36 KiB) Viewed 2413 times
They do have screw tops also about 15.50usd

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Re: Lithium Battery Pack - Build or Buy?

Post by SamTexas » Feb 27 2013 11:37am

Are you getting a commission for every sale from OSN? Nothing's wrong with that, but it'd nice to know if the recommendation is coming from someone who has ACTUALLY used the product or from a saleman.

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Re: Lithium Battery Pack - Build or Buy?

Post by bowlofsalad » Feb 28 2013 11:46pm

SamTexas wrote:Are you getting a commission for every sale from OSN? Nothing's wrong with that, but it'd nice to know if the recommendation is coming from someone who has ACTUALLY used the product or from a saleman.
I've been wondering the same thing, he got upset when I called him out last time.

Pingbattery and em3ev seem to be the stables for battery vendors around here. I can't speak for either personally (yet), but I definitely think lifepo4 (both are lifepo4) sounds excellent on paper as far as value and safety are concerned.

However, I am often puzzled why one chooses ping over em3ev. Em3ev seems to use a superior version of lifepo4. I theorize it's the lack of pack options, which is perfectly reasonable. Not everyone wants a 20ah pack due to it's greater size and weight over something like a 10 or 15ah pack.

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Re: Lithium Battery Pack - Build or Buy?

Post by Mad Professor » Mar 01 2013 2:13am

Once again thanks for all your input.

I think I am going to try and build a pack based around the 18650 laptop cells.

I used to be in the I.T trade, so after a quick phone call I was able to collect 12 old laptop batteries.

8x ICR18650-20, 3.7v 2000mAh.
16x LGR18650P, 3.7v ????mAh.
16x LGR18650U, 3.7v ????mAh.
32x US18650GR-G4, 3.7v 2000mAh.
24x US18650S-H2, 3.7v ????mAh.

I now need to find the datasheets or specifications for the above.

I am also going to be making some more phone calls today, and see if I can get some more laptop batteries.

Then the fun task of testing each individual cell, only then will I know if the cells above will be suitable for use.

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Re: Lithium Battery Pack - Build or Buy?

Post by alban » Mar 05 2013 3:40pm

Hi
You may have decided on the laptop battery route already.
I have had a good experience with using Headways (LiFePO4 cylindrical) bought from Eclipsebikes in the UK. Reasonable price, some warranty. Heavy for Lithium but robust and easily mendable packs. Easy to put together (no welding) with the ready-made stuff. 12X10AH would be good enough for range. 3C discharge.
Use a BMS or balance charge using an RC balance charger ( eg iCharger). For latter option break into 2 groups of 6 cells and charge in parallel using a special board. Link in series for riding. I used Deans connectors as RC stuff comes with them. Have some cheapo RC low voltage alarms to give warning if going too low. Wattmeter or CycleAnalyst too as fuel guage.

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Re: Lithium Battery Pack - Build or Buy?

Post by SamTexas » Mar 05 2013 3:52pm

Mad Professor wrote: Then the fun task of testing each individual cell, only then will I know if the cells above will be suitable for use.
You could do that but it would be very time consuming and quite unnecessary. Most laptop batteries are built in 3s2p configuration. You want to break the series connection but keep the parallel group. So for a 6 cell battery, break it up into three 2-cell groups. Most likely one group is dead or so low in capacity that it's not worth keeping. The idea behind all this is: When one cell dies, it pulls the cell paralleled to it to death too. Otherwise, both cells are healthy.

Of course there are other configuration as well, such as 4s2p, 3s3p, and very rarely 3s4p. The same technique applies: Keep the parallel cell groups.

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Re: Lithium Battery Pack - Build or Buy?

Post by etriker » Mar 05 2013 4:08pm

Sometimes one cell in the parallel pair goes open and the other cell is still ok.

http://www.youtube.com/watch?v=XoIpsuCDkl0

This is a video showing a laptop cell pack that failed like this.

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Re: Lithium Battery Pack - Build or Buy?

Post by SamTexas » Mar 05 2013 4:16pm

etriker wrote:Sometimes one cell in the parallel pair goes open and the other cell is still ok.
Correct. But it's very rare. I just throw both away, but that's may be because I have too many cells to play with.

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Re: Lithium Battery Pack - Build or Buy?

Post by etriker » Mar 05 2013 4:19pm

SamTexas wrote:
etriker wrote:Sometimes one cell in the parallel pair goes open and the other cell is still ok.
Correct. But it's very rare. I just throw both away, but that's may be because I have too many cells to play with.
That video shows the numbers on those packs and this is a common failure for these HP Samsung cell packs.

I don't throw away Samsung cells that test good that is for sure ! :)

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Re: Lithium Battery Pack - Build or Buy?

Post by SamTexas » Mar 05 2013 4:22pm

I disagree. I have worked on over 1000 pairs and I only saw that condition 2 or 3 times.

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Re: Lithium Battery Pack - Build or Buy?

Post by Mad Professor » Mar 05 2013 4:24pm

I know I could just test the cells how they are, but I would prefer to take more time and test each individual cell, so that I know that all the cells I use are good.

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