How do you build a battery, exactly?

tdiggs

100 W
Joined
Jun 25, 2012
Messages
135
Location
Glendale, CO
Hi,

I am interested in building a 72v or a larger setup, like a 100V. Something that can reach and sustain 40mph, at least, using ebikes.ca's NC26RD_Fast (9C 2806 hub wheel). I will upgrade the controller to the 40A one (I guess the best one on their site).

My question is, how do you build a battery exactly? Are they user friendly to charge? I know people buy RC lipo cells and put them together, but I do not know which ones to get or how to wire them (and with what do I wire them).

Thanks guys.
 
tdiggs said:
Hi,

I am interested in building a 72v or a larger setup, like a 100V. Something that can reach and sustain 40mph, at least, using ebikes.ca's NC26RD_Fast (9C 2806 hub wheel). I will upgrade the controller to the 40A one (I guess the best one on their site).

My question is, how do you build a battery exactly? Are they user friendly to charge? I know people buy RC lipo cells and put them together, but I do not know which ones to get or how to wire them (and with what do I wire them).

Thanks guys.

You need to learn a lot before you put together a 100v battery and put it on a bike at 40mph+.
And while your at it take out a good insurance for accidents like Aflack. Your gonna need it!

Dan
 
Ha, so you're saying I should stick with pre-built 48volts? Well, can you direct me to some resources that will help explain everything for me? I am willing to learn as much as possible about battery-building and all that goes on with batteries.

Is there any vendor that makes dummy-proof 72v batteries at least?
 
tdiggs said:
Ha, so you're saying I should stick with pre-built 48volts? Well, can you direct me to some resources that will help explain everything for me? I am willing to learn as much as possible about battery-building and all that goes on with batteries.

This is the place for ebike knowledge. Just read everything here. Use the search function with Google.

tdiggs said:
Is there any vendor that makes dummy-proof 72v batteries at least?

I don't know of any that are foolproof. All need care and feeding. If not careful, bad things can happen.

[youtube]u_y27m4Q8b4[/youtube]

Lastly, 100v and 40mph is very ambitious for a first build. Start modestly and build up from there. You'll learn a lot more and have a lot of fun.
 
It might not be your first build, but going for the stars is a big jump.

There are plenty 72v LiFePo builders out there.
As for the 40mph that is the biggest concern for all of us. 30/35 is almost no problem, it's that 40+ that is always a big jump. Most bikes are not built to take the pounding and I mean most!
You need a good DH bike to be safe and not just a FS MTB from WallyWorld. Quality is a must for that kinda speed. I'm not saying you can't or shouldn't, but be careful as to what you use for a platform.

As I said and others, read as much as you can about batteries and what to and not to do. the battery is what will decide if you can do 40+ so spend your money once if that is what you are going to do. A good bike is also not cheap so once again think before you buy the wrong thing. Most of us have done thant and learned from our mistakes. Some have read these stories and did it right the first time.

the old saying SPEED COST MONEY! HOW MUCH DO YOU WANT TO SPEND?

Dan
 
You might try a headway DIY pack on ebay. Search for "headway battery." The headway batteries offer very high c-rates, so they can put out a lot of power fast. I think they're what you want if you want to go 40+ mph.
 
Build a lipo battery pack is the simplest thing there is. Want a 24s pack (88.6V nominal, 100.8V charged)? Buy 4 6s lipo packs, or 6 4s packs, Line them in a row. Split the end pack connector and start connecting the packs in series, leaving a positive red lead on one end and a negative black wire on the other. Time required is 1-5 minutes. maybe a diagram would help.24s3p.jpeg
 
If you have ability and are careful, 40 mph and 20 or 24 s (100v) LiPo pack is OK for a newbie. I had never touched e-bikes before, or used LiPo, and I have survived over 2 years and 7300 miles..

But conversely, i have seen two people f u c k up their batteries by not being careful, even after I have laboured the point of how delicate LiPo is....and how dangerous it can be.

If you are careful and accurate there is no more difficulty in building a 48 v or 96 volt pack.

All the info is here on the forum. Start in the battery subsection Stickies
 
@ambroseliao
It isn't my first build. I made a yescomusa 48v 1000w kit with a sun-thing28 (eBay seller) 48v 15ah bike before. I did post some photos about it here (it has changed a little since then though), but I don't think anyone commented on it so it drifted down the thread list. Thank you for that video though!

@DAND214
I have been a mechanic at my local bike shop for just over 4 years now, so acquiring a quality bicycle at a good price isn't a problem and neither is repairing them 8)

@Beagle123
I am unfamiliar with the headway packs. I found some on ebay, but they are 48v or less. I honestly wouldn't mind 72v at least though. 40mph would be awesome, but 35mph would be sufficient.

@wesnewell
You have been a great help for me on my other posts and this is wonderful. Now I googled "6 4s lipo packs", but what came up is a few links to the hobbyking website showing 5000mah 6s lipo packs, but they have another value attached, which is 20C, 25C, etc. What is this value? I am still unsure what to buy exactly. With those packs, I just use the red and black wire, correct? Is there an online calculator, of sorts, to determine how many packs and how you should wire it for what voltage and Ah rating you want?
The BIGGEST question is; How fool-proof are they to charge? Must I charge each one individually and monitor it or could I plug the ends of the whole pack and walk away and let it do it's thing?

@NeilP
I hope to be as successful at you are with the diy battery packs. What kind of speed are you getting from your 100v 20ah Lipo Mongoose?
 
Well I once, and only once saw a peak of 55mph on the Cycle analyst stats page that was running at 100 volts, fully charged, just off charger, with controller tweaked up for max speed.

i did not see the speed myself, only saw it afterwards on chckng the CA. generally run at 20S, 83.6 volts and with the controller tuned down to give a max of about 30
 
Neil is one of the guys that can do anything right on the first try. He's got the right stuff, like many pilots.

Your first place to go read is the battery section FAQ thread. Some links there for threads that make things clear for newbies.

Lots of 40 mph bike threads in the pics section. I'd say start with either 18s or 20s, and a 72v controller. That should get you into the 40 mph club.

I don't advice much more power on cheap ordinary hubmotors. Once you get a monster motor, you can graduate up to 100v or more.

Good stiff frame, Ideally with some good suspension, and body armor. 40 mph slides are much more comfy in leathers. Skinny bike tires slip easier than big motorcycle and scooter tires, so laydowns happen.
 
A small reserve RC Lipo pack can be a great way to introduce oneself to this discipline. 2qty 6S bricks can form 12S1P 48v replacement along with an RC Charger and connectors, wiring. You'll learn more with a small starter setup and reading than jumping in over your head (big high volt pack) with little understanding of the nuances of RC Lipo care & feeding.
 
72V is ambitious. As someone who is new to this it may seem like 72V sould be the same complexity as 36V, but it isn't.

I recommend you series two 36V packs. Its an added complexity (and slightly more expensive), but if you are statistically likely to fry something (being new), theres a better chance you might fry ONLY one of the 36V packs. When you screw up something, 72V is a very expensive mistake.

"KFF" stands for Kentucky Fried Fingers", and it happens to even experienced E-bikers, so...also, even though LiPo is the chemistry that requires the most diligence to prevent a disaster, even LiFePO4 can set your house on fire.

36V doesn't have much of a spark when connecting the pack/charger, 48V is a noticeable POP, and 72V has been recorded as something so large that it can ignite any nearby vapors so, keep away from gasoline/propane storage...
 
tdiggs said:
...Now I googled "6 4s lipo packs", but what came up is a few links to the hobbyking website showing 5000mah 6s lipo packs, but they have another value attached, which is 20C, 25C, etc. What is this value? I am still unsure what to buy exactly. With those packs, I just use the red and black wire, correct? Is there an online calculator, of sorts, to determine how many packs and how you should wire it for what voltage and Ah rating you want?

The BIGGEST question is; How fool-proof are they to charge? Must I charge each one individually and monitor it or could I plug the ends of the whole pack and walk away and let it do it's thing?

A "20C or 25C" rating is the maximum discharge rate of the pack. The maximum discharge rate of a 1C 5 AmpHour (Ah) battery is 5 Amps. If the battery is 5Ah and has a 20C rating then it can discharge at 100 Amps. Of course, drawing 100A from a 5Ah pack will drain it very quickly, but it is has been specified to do this. Of course, overdrawing current from a battery with a low C rating will damage the battery and have perhaps other consequences like cell puffing or possibly fire. Over charging batteries can also cause puffing or fire.

There are some very fundamental things to know about series/parallel operation of batteries. For identical batteries, you can connect the red and black wires together (red to red and black to black for parallel operation). You can also put red to black on one of the leads of each pack to put them in series. Parallel operation keeps the voltage the same but doubles the Ah rating. Series operation doubles the voltage but keeps the Ah rating the same.

As for your biggest question, most folks here are very careful with LiPO batteries because of their volatility and history. If you take them for granted, you risk damage to your pack, your bike, your garage, your house, etc.

See here:
http://endless-sphere.com/forums/viewtopic.php?f=6&t=36375&start=1275#p716486
http://www.youtube.com/watch?v=dree0rTr1HM&list=FLRMitiF4LS1XwhID2Gybtdg&index=64

There is so much more to learn about batteries and motors for ebikes. You have come to the right place!
 
Would the Nine-C 2806 hub from Grin be able to handle 72v no problem?

I will be heading to the battery forum straight away.

So you are saying I could take two 36v LiFePO4 batteries and wire them in series and it would be a (fairly) foolproof 72v setup? I have been using a 48v LiFePO4 setup for a few months now and since I have a buyer at a price I cannot refuse, I figured it's upgrade time!
 
Yes, the 9C can handle 72V at 20-30A fairly easily.

As for your second question, yes you could use two 36V LiFEPo4 batteries wired in series as long as they have a safe margin higher capacity than you plan on drawing from them. In other words use a controller that doesn't overdraw from the battery pack. You could then either use a bulk charger and balance afterwards or use a balance charger that does the job all in one sitting.
 
tdiggs said:
@wesnewell
You have been a great help for me on my other posts and this is wonderful. Now I googled "6 4s lipo packs", but what came up is a few links to the hobbyking website showing 5000mah 6s lipo packs, but they have another value attached, which is 20C, 25C, etc. What is this value? I am still unsure what to buy exactly. With those packs, I just use the red and black wire, correct? Is there an online calculator, of sorts, to determine how many packs and how you should wire it for what voltage and Ah rating you want?
The BIGGEST question is; How fool-proof are they to charge? Must I charge each one individually and monitor it or could I plug the ends of the whole pack and walk away and let it do it's thing?
C rates are simple. C rate times pack ah rating = max amp draw from pack. Your controller will have a max amp spec. Just make sure your battery pack can put out twice that rate and you'll never have a problem. Assuming my drawing was using 20C 5000mah 6s packs it would be 15ah times 20, which would be 300A max. If you built a single (row) 5ah pack, it would spec to 100A. Most common controllers draw 40A or less. To charge 10ah 24s2p pack, I unplug the middle connectors making 4 banks of 12s and charge it as 12s4p. There are several 12s-14s chargers on the market from $89 up. Each 6s pack is 22.2V (6x3.7). If you need an online calculator to determine how many to put in series for the voltage you want, you should probably not have an ebike.
 
Again, read some threads on lipo batteries. Lots of good info there. Lots of charging strategies, but I prefer to use RC chargers designed for this kind of battery. You can charge more than one pack at a time with those using paralleling harnesses or paraboards.

The 20 c lipo is good enough for most, but 30c performs better. Much depends on what you aim for, win a race, or just get from a to b in a fun way. I have preferred the 30 c myself, less sag means you can run them a bit deeper discharge with less worry.

8 5 ah 5s packs makes a good 72v 10 ah pack. But 6s is nice too. 12s is a good starting point, and works with the stock 36-48v controllers. Add one more, and 18s is still pretty fast, but not quite as fast as full 72v. Start with 12s, then 18 is a good plan for many. I see you have been running 48v, so you aren't completely inexperienced,

Two 36v batteries connected in series will get you 72v, but for the hot rod bike you seem to dream of, it can't be something with a low c rate. You need at least 5-10c stuff, to keep the battery light and small and still provide lots of amps. No point in a fast bike, loaded with a huge cumbersome battery. So get a little 12s lipo, learn about it, then start building a hot rod.

The 9c motors can take 72v 40 amps for about 20-30 min, as long as 72v 10 ah lasts. So don't carry more than that much battery. At 20-30 amps, they can take 2000w for quite a long time. Just keep it short if you go to 40 amps.
 
Here is kind of a side question. In my ebike I just sold I used sun-thing28's battery ( http://www.ebay.com/itm/48V-10AH-Li...arts_Vehicles_CarParts_SM&hash=item20cc7c422f ), but it was bulky to fit in the frame. I am thinking of getting the nice Nine Continents motor and CA and then run this basic LiFePO4 battery (which seems to be fairly good and purely plug and play), but in the future (after much more research) build a simple 72v setup that I can swap the 48v with. Obviously I may need to upgrade the controller later too.

Question is; Can that sun-thing28 LiFePO4 pack be untaped and reconfigured in a shape I deem desirable to fit the frame bag and then retaped back up to protect it?

So, to build a simple 72v 10ah pack. I know I need to get 5 ah cells and wire a certain amount of two strands in series (to increase the total voltage) and then hook those two strands in parallel to increase the ah rating to 10 ah. Now as far as what to purchase when I go shopping, I may need some help distinguishing between the whole 5s, 6s, 11.1v, 3.7v and other stuff I have seen. I also do know that I should buy the highest C rating I can afford, 20C being a minimum.

When you say 12s and 18s, I know that it is those cells (12 or 18 of them) wired in series, but how do I know how to wire my cells and how many cells I need to accomplish a 48v or 72v system with 10ah or 15ah, for example?

My typical commute is only aout 10 minutes at full blast and I will keep that in mind, to never go over 20 min of full blast on the 9C motor. I plan on running the stock 20A controller until I gain the knowledge and confidence to build a 72v pack, then I will switch to the 40A controller, which I understand to deliver more power and be better.
 
yes, it is pretty easy to take the pack apart and reconfigure the two sections. you could then stack them one over the other in the center of the frame. nothing changes, you just have to mount it in another configuration with new mounts to hold it and run a new lead out for charging. it is critical that the connection between one section and the other be made by a large wire that is permanently soldered. if that connection is open while the battery is plugged in then it will damage the BMS.
 
I did not plan on unwiring any of the cells, just essentially folding them into another shape and taping them. Is that sufficient.
 
Frame and suspension fork, 2.3 to 2.5 tires, big disc brakes 180 to 203mm, batteries in the center triangle. I would use 1" or 1.25" wide rims minimum. Make sure the frame build up is done well. You are hauling a$$ going 40mph. I'm pretty comfortable at 30mph, but at 40+ I am on my toes concentrating. I've been up to 46mph on mine, and it is wicked....
 
tdiggs said:
I did not plan on unwiring any of the cells, just essentially folding them into another shape and taping them. Is that sufficient.

it depends on what shape you bend it into. if you can keep the sense wires intact without having to patch in extensions to make it work then maybe, but you will have to connect the two sections together where that short piece of 12AWG stranded connects the two sections. you can get some 10AWG and solder it back to connect the two sections when they are mounted in their final positions.
 
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