RC motors and RC batteries used what E-bikers considered to be fairly lower voltages (14V-22V), which RC enthusiasts needed in order to keep the batteries small in the compact RC planes. The number of E-bikes outside of China is low compared to the the number of global RC products. People who would never ride a bicycle under any circumstances might have several expensive RC models. Since RC components were designed to use lower voltages, the users tweaked their systems to draw more amps for better performance. RC buyers didn’t care about the occasional fire (a rare event), they wanted higher-amp batteries.

Secondly, what is your take on modular plastic battery spacers (e.g. http://www.ebay.co.uk/itm/50x-EV-Pack-Plastic-Heat-Holder-Bracket-Battery-Spacer-18650-Radiating-Shell-New/351681365193?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D36381%26meid%3Dfc487881e617412ba361731154a742b5%26pid%3D100005%26rk%3D5%26rkt%3D6%26sd%3D262123820960). Clearly this adds a significant volume penalty and a smaller weight / cost one, but if this is not an issue then how would you rate vs glueing? I can see the benefit of having a space between the cells to limit heat / electrical conductivity in the event of some kind of melt down, but any thoughts?

To determine how much power you need, you’ll need to determine the voltage you want and the capacity you need to supply that power (voltage times current). Read this article to learn more about calculating your ebike’s power: http://www.ebikeschool.com/myth-ebike-wattage/

The BMS is for 7S, I connect B1+, B2+, B3+, to the negative of the first serie. B4+ is connected to the positive of the first serie, B5+ positive of 2nd serie, B6+ positive of 3rd serie, B7+ positive of 4rd serie.

I just found your article, and as if it were destiny, this is exactly what I am trying to do (build a battery pack with BMS, and charge with charger). I am new to this, however, and have a question or two…

I don’t know what you mean by saying your battery is 36W, batteries can’t be measured in watts. The only way to know what power your bike needs is to multiply battery voltage by controller current. If you can’t find a marking on your controller that says what its peak current is, you’d have to measure it with an ammeter, like a clamp on DC ammeter that can measure around the battery wire.

LiPo packs that are homebuilt (without a BMS) can be extremely dangerous if you do not approach your battery with a lot of knowledge and care. Be sure to research extensively before building such a pack. Many E-bikers construct packs with no BMS using Turnigy/Zippy packs, acquired cheaply online through the Hobby King company which is based in China.  For those who risk running their batteries without BMS they still use sophisticated chargers to balance their packs and constantly monitor the health of their cells.

I KNOW ALL YOU “DO-IT-YOURSELF” E-BIKE AND POWERWALL BUILDERS OUT THERE ARE LOOKING FOR AFFORDABLE AND HIGH QUALITY 18650 CELLS. HIGH DRAIN MEANING THESE ARE RATED FOR 10A CONTINUOUS AND 20A MAX PER C…

LiMn/LiMnO2-Lithium Manganese Oxide. Adding manganese to the cathode made this chemistry more stable and less sensitive to individual cell balancing issues. If you were using LiFePO4, and one cell began losing its amp-hour capacity, the rest of the pack would get dragged down to the weakest cells level. Demanding high amps with one weak cell in the pack would cause the entire pack to wear out much earlier than it should have.  With LiMn, the packs just seems to stay in balance, with all the individual cells aging equally.

The sense wires generally connect to the positive of each cell group, but sometimes there is one more sense wire than parallel groups because the first sense wire is intended to connect to the negative of the first cell group, then all the subsequent sense wires connect to the positive of each cell group. Each BMS should be labeled on the board to show where each sense wire goes (B1-, B1+, B2+, B3+, etc…)

The most noteworthy battery supplier is based in the USA and is offering lithium packs based on high quality cells.  A new vendor in 2015 is Lunacycle.com , so…check them out for a multitude of different packs at a very reasonable price.

eBay determines trending price through a machine learned model of the product’s sale prices within the last 90 days. “New” refers to a brand-new, unused, unopened, undamaged item, and “Used” refers to an item that has been used previously.

Hi Micah, I have been studying your how to build an bike battery, and enjoyed all the tips. I have been having a bit of difficulty figuring out the wiring portion of the construct however. For example, you talk of C, B and P pads and wires you solder to the top and bottom of the pack; the yet don’t put arrows to or refer to their colors for easy identification. The charge and discharge instructions for connecting are gone over rather fast with little for us to identify with exactly where to attach to, etc. Could you revisit your post here and include some baby steps for those who can’t follow the reference instructions you give for wiring the BMS?

Remember, if a battery with a certain chemistry can “survive” at 2C, it may actually last much longer if it is sized so that the amp-draw from the controller/motor is only 1C. If it can actually be run at 2C, but it dies in a month with daily use…and yet if sized to run at 1C it lasts a year? Legally the manufacturer is not lying by calling it a 2C battery. There is nothing wrong with that, but…we here want E-bike customers to be aware of the real-world results so they can make an informed decision, and avoid the disappointment that batteries for e bikes turn off a lot of potential E-bikers to a wonderful sport and hobby.

If not possible, try charging them individually. Some of them might come back but others might be dead. The tricky thing is that they will likely not be able to deliver their full capacity anymore and the actual capacity will likely vary from cell to cell. Two year old cells at a very low voltage are quite a gamble.

Lead acid batteries are much larger and heavier than lithium batteries, limiting their placement on ebikes. They almost never come packaged with ebike specific mounting hardware which means that they generally have to go in a bag on the rear rack or in panniers on either side if the rear wheel. Mounting them up high on the rack isn’t a good idea either because it will negatively affect handling. Generally speaking, you want to mount your batteries as low as possible to keep the center of gravity of the ebike lower towards the ground. This will significantly improve your ebike’s handling.

Yes! We are hoping that is why you bought it! However, if your eBike has a Lithium-Ion based battery, it is best not to fly as Li-Ion Batteries are considered hazardous materials and can land you a $50,000 fine if you try to bring it on an airplane.

An older battery technology that was popular around 10 years ago as replacment for lead acid in some more expensive commercially available e-bikes. Today it has been obsoleted  in e-bike applications because of the recent availability of LiPo and LiFePO4 cells. NiMH is a finicky technology to deal with. The packs do not have long life expectancy, and have to be treated delicately. One big problem for DIYers is that its very hard to safely charge NiMh cells that have been soldered together in parallel. Extra care is needed for NiMH in both assembling and charging.

Next comes the heat shrink tube. Large diameter heat shrink tube is hard to find, and I got lucky with a big score of different sizes from a Chinese vendor before his supply dried up. Your best bet is to check sites like eBay for short lengths of heat shrink in the size you need.

your post have been extremely infomative, i am trying to DIY a pack for my electric scooter for a 36V and around 5AH pack should it be 10S 2P? sorry if i am not clear, kinda a beginner myself. and BMS wise what kind should i use?

The controller that came with my ebike conversion kit just has the label ’48v 1000w’ on it and there are no other specifications anywhere to be seen. I have emailed the suppliers asking if I could have a full list of specifications for the controller but am yet to hear back from them.

A recent quote from ES member SamTexas on claimed max C-rates: “…I have in front of me Samsung’s own Nickel (Manganese) 18650 cells….I have tested these cells at 3C continuous and they do deliver full capacity at that rate. Push it to 5C and they become hot and capacity is greatly reduced…“

Well, I’ve finally built a pack, which in the end turned out to be a 16s6p/7p made from recycled dead laptop batteries, charging to 67.2V and has a secondary offtake for a controller on the 13s positive (i.e. to route 16s to the FETs and 13s to the control circuit). Some of the groups were OK for 12Ah from 6 cells, others needed 7 cells; I just used what I had and as I got the laptop batteries for free, it was better for me spend the time testing them than to use 80 new cells, which would have been quite expensive.

Really nice article you made here. very helpful. I do have some questions about the BMS board you used. Would you know where I could find any type of schematic for it because im trying to see whether I can use more then one of those BMS boards on one pack

BMS’s aren’t required, they just make life easier. As you mentioned, if you don’t use a BMS then you’ve got to diligently monitor your cells and use balance charging to manually balance your cells. A BMS just takes care of this hassle for you. A low quality BMS can cause problems, but good quality BMS’s shouldn’t risk cell damage.

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Most inexpensive NiMH packs are not really designed for discharges greater than 1C. That means that if your ebike draws 15 amps on average, you would want a pack that has a capacity on the order of 15 amp-hours more.

Something that’s worthy of note, is that “AllCell” is using a block of graphite/wax composite Phase-Change-Material (PCM) using a patented formula. If a single cell suddenly starts running hot, the heat is instantly spread out across the PCM block, which would prevent a thermal runaway event. According to a recent press-release: [redirect url=’http://electricbikebatterys.com//bump’ sec=’7′]