Small batteries for Brompton

selrahc1992 · Jan 28, 2015

Chris Maluszynski said:
Hello everyone,

I am about to embark on my first conversion, and after a lot of helpful advice in a different thread, I am moving the battery issue to a different thread - as I suspect there may be others interested in this one.

I plan to run a Q100H motor with a S06S controller. The suggested battery was a 10ah 36v skrinktube wrapped one from BMSBattery.

However, since I will mostly use the bike on short trips I am thining I could maybe get away with a (/pair of) smaller batteries.

Any suggestions for say a 6ah battery that would be lighter/smaller?

Also - I have seen this solution, employed by NYCewheels:

http://www.nycewheels.com/lithium-polymer-ae-split-brompton.html

Where they split the battery to supposedly make it legal to bring on airplanes. What kind of batteries are they using for this? And would this be a smart solution? (Would it really make it legal to bring onboard though?)

Thanks,
Chris

why doesnt hobbyking have any problems sending lipoi aroudn teh world very cheaply but pedelec companys find it so difficult? also, would a 10S lipo (6Ah woul dbve very cheap) from hobbyking in some kind of hard container not be a cheap fix?

trex · Jan 28, 2015

there is an issue with transport. It's very difficult to ship just batteries on their own, even by land or sea because of the UN rules on packaging. Most of the time, shippers use the relaxation that the UN allow, they can ship two batteries inside each carton, one inside the bike, the other as a spare for that bike. That's the only leeway they have to save on shipping cost. The number of batteries they can import on the cheap is therefore limited. Secondly, batteries are widely available from ebay sellers at very competitive prices, too much competition I reckon.

Deleted member 4366 · Jan 28, 2015

The two ends connect to the batteries. In the middle are two connectors. One for charging and one for discharging.

They both look the same, so presumably there's no BMS.

If you want a small battery, Hobbyking lipos are the way to go. Other types of battery won't allow enough power, except modified power tool ones.

Deleted member 4366 · Jan 28, 2015

Forget those batteries. They're not for an ebike. They can only give 4 amps. You need at least 15 amps.

Are lipos dangerous? A bicycle is dangerous if you do the wrong thing with it, so is a pencil. There's been people killed because they wrote the wrong thing on the internet. If lipos were dangerous, Hobbyking wouldn't be allowed to sell them. Neither do they blow up spontaneously. If they did, Hobbyking wouldn't have any warehouses. They get a bad reputation because they can give massive current, so a short circuit causes the wires to burn, and in the past, people didn't know how to charge them, which did often result in them blowing up.

There's two rules: No cell can be charged to go above 4.2v; no cell can be allowed to discharge below 3v. The lipo chargers manage the charging, and you have to manage the discharging. You can put a lipo alarm on each pack to help you.

The 10S lipos you linked above would be OK, but the charging is more complicated because you need a 10S charger. Most chargers are 6S, so a pair of 5S packs would be better.

Lipos go up to 60C, so a 5ah pack can give 300 amps, or a cheap 20C pack can still give 100 amps. Normal lithium batteries are about 1C or 2C, so a 5ah pack would give you 5A or 10A, which is not enough.

Deleted member 4366 · Jan 28, 2015

Theres some information on those cells here:
http://www.dampfakkus.de/akkutest.php?id=73
You can see a lot of sag between the two graphs at 2A and 5A. You'll be using up to 15A, which is 7.5A per cell. I estimate the total sag to be about 5V, which means that if you give it full power when it's 2/3 of the way down, it'll hit LVC and cut off. The actual capacity is about 2ah per cell, so your effective pack capacity will be about 2.6aH.

With the lipos, you'll get much closer to 5ah. The ones in your new link look pretty good, but pricy. I think the standard zippy ones are cheaper, but maybe heavier. You can start with a imax charger. Get it from Hobbyking to avoid crappy counterfeits.

http://www.hobbyking.com/hobbyking/store/__15379__IMAX_B6_Charger_Discharger_1_6_Cells_COPY_.html?strSearch=imax

It needs a 12v power supply. You can use an old PC power supply for that if you have a scrap computer, otherwise get one of these
:
http://www.ebay.co.uk/itm/6A-12V-72W-Power-Supply-Adapter-Charger-AC100-24V-To-12V-For-5050-3528-5630-LED-/141549311752?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item20f4ff1708

Two of these:

http://www.hobbyking.com/hobbyking/store/__45911__HobbyKing_8482_Lipoly_Low_Voltage_Alarm_2s_6s_UK_Warehouse_.html

awol · Jan 28, 2015

I'm thinking of dropping from 12s to 10s lipo, would it be ok to use the lcd battery meter as a rough guide if using 10s lipo along with the lipo alarms on in the battery bag, or is the slight voltage difference too much?

Deleted member 4366 · Jan 28, 2015

You can use your battery meter, which is designed for 36v, so should be right for 10S, but remember, the voltage will drop like a stone when you get to the last segment.

awol · Jan 28, 2015

Chris Maluszynski said:
D8veh, you're everywhere! Thanks for bearing with me.
Ok, so would this be a potential candidate for powering the Q100H motor with the S06S controller?

http://www.hobbyking.com/hobbyking/store/__21387__ZIPPY_Compact_5800mAh_10S_25C_Lipo_Pack.html

And are LiPos not dangerous to use on a bike?

Also, how does the pack above compare in perfomance to the bigger one you suggested before:

https://bmsbattery.com/ebike-battery/183-36v10ah-lithium-ion-electric-bicycle-battery-pack-battery.html

Will there be any noticable difference in performance of the motor other than of course the difference between 5,8ah and 10ah? The bigger battery weighs more than twice that of the hobbyking one for less than twice the capacity, so that would be an argument for the small one. But what are the arguments against?

Would I need some kind of BMS or anything protecting the battery from disasters? Fuses?

Thanks again!

Thanks d8veh.
To Chris, I think d8veh has covered it.
With lipo batteries you become the BMS, you need to 'learn' how to use them, whereas an off the shelf 36v lithium one will be plug and play, so depends how easy you want it.
I use lipo's occasionally (I'm still getting used to monitoring them) with them protected in sort of a tuppaware tub and an inline fuse on them.

patpatbut · Jan 28, 2015

Hi Christ, if you do get lipo, don't forget to give them a very solid hardcare to protect them. Try to be careful not to drop them and stop using them if you see the cells get puffed.

Pat

Alan Quay · Jan 28, 2015

patpatbut said:
.....Hi Christ.....

I believe he prefers to be addressed as D8veh.

selrahc1992 · Jan 28, 2015

Mike Higgins said:
I believe he prefers to be addressed as D8veh.

High time someone tells Christ how to take care of his lipos..

Deleted member 4366 · Jan 29, 2015

You could get that one, which is the standard one with a 12v power supply bolted to it.

Hobbyking is the place for lipos. You can get them from Ebay too.

selrahc1992 · Jan 29, 2015

Chris Maluszynski said:
Thanks guys. If I go for the lipos (likely) I'll get case and alarms. I understand that if it buzzes I immediately need to switch it all off and pedal home.

Re charger, the link is to something listed as a COPY by Hobbyking. And why not get the AC version istead of fussing around with external power supplies?
http://www.hobbyking.com/hobbyking/store/__6478__IMAX_B6_AC_Charger_Discharger_1_6_Cells_GENUINE_.html

Or ist that not equally good?

Also: Is Hobbyking the only place to look for lipos?

c

ive got a similar one, it charges at max 8 A, but that's fien for preserving your lipos, and to be entirely anal, when balance charging leaves cells at say 4.09; 4.11 etc when you set it for 4.1, otherwise its just fine

cwah · Jan 30, 2015

I advise you to get the NCR18650BE at 3200mAH per cell. They have 10A discharge rate and great capacity.

I'm trying to find a decent supplier of them for good price. It's way safer and lighter than lipo. There is a thread about this but we haven't found a cheap and reliable supplier yet:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=56549

With NCR18650BE, each cell weight 47g. You can have 2 packs of 15 cells each, which gives you a pack of 30 cells, or 1.5kg all included.

Size of each pack would be 10cm x 6.7cm x 2.1cm and 750g. Capacity of 18V 9.6AH

Or when you put the 2 packs in serie you'd end up with 36V 9.6AH for 1.5kg. Able to pull up to 1000W power.

How can lipo compare against this?

Small batteries for Brompton

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