# Need help finding batteries!!



## Amberwolf (May 29, 2009)

Are you building an electric bike? If so, you're easily in the right section. 

At the moment I'm using old powerchair batteries. I've only got two on the bike (in my avatar pic) now, at 23 pounds each I might blow up the tires or break something if I tried four of them, plus hauling the cargo the bike is nominally designed to carry.  The bike by itself weighs around 60 pounds, without motor or batteries--those double it's weight! I have a third to go with the others on a trike once I build that.

They are U1 sized MK-Powered brand gel cells, 12V 31Ah. Each is about 1/2 the physical size of an average ICE car's battery. 

I got them for nothing because they came from someone replacing them with new ones. You might be able to do the same, if you ask around at "mobility repair" places. If not free, you might get them really cheap. They'd be used, and thus no longer full capacity, but it's a good bet they'll be cheap enough and still have enough capacity to be fully worth it.

Mine will move me on that bike about 15 miles at around 16-17MPH in normal traffic, before needing an overnight recharge. I'm using the charger that came with the batteries, as I guess they replaced that too. 

You can probably find used golf cart batteries, too.

I'm not sure of any good ways to get *new* batteries to do what you're after. I'd certainly go local to find them, if possible, simply because shipping alone could cost you a good portion of your budget, especially on lead-acids. 

As for assembling a pack of individual cells, it will depend on what kind as to what you will have to do. If it's a bunch of lead-acid cells, like the Cyclone cells, you just cable them together the same way you would if they were all in one battery, stringing the batteries together. You *can* add balancing circuitry, etc, but it isn't required--just more helpful to extend the life of the pack more, if you manage it's charge and discharge better.

If it's LiFePO4, you really ought to have a BMS for it. You can get small ones for the Chinese-made packs on ebay, but they aren't all that inexpensive despite how cheaply they are made, and they will have a fairly low current limit both for charging and discharging. You can probably fix that if you know electronics well enough to replace the necessary parts.
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## ithinkidontknow (May 14, 2009)

Yes I am building an electric bike, I think you have actually posted on some of my other posts before. It is an electric tadpole trike. Up until recently it has just been all research work but now I am starting to get ready for construction. 

I should probably start a post once I start real work but this is what I am thinking so far:

48v 750w Motor 
Yi Yun 48v controller if I can get my hands on the right one

This is my plan for "bike version" which I plan to build to stay under the Washington laws for electrically assisted bicycles. However, after I build the version with the above components, I plan to try to get a moped registration filed with the DMV so then I will be able to go 30mph on roads and have up to 2hp. At that point I would like to install another 750w motor. 

But as I am sure you know, this will eat up serious amounts of energy! For this reason, I need some bigger batteries. 

Now to respond to some of your suggestions. Unfortunately, I don't know if I have time to look into freebies just because I am on a fairly limited time schedule as I will go back to school in the fall. If anyone in the Seattle area has an ideas of where to get cheap batteries like this, please let me know! I am really just looking to buy something anyway so that I can expect it to last a long time. 

I was looking at a battery manufacturer that makes deep cycles in my area and I can get 12v 85Ah batteries for 80 dollars a piece and they weigh around 40 pounds. Unfortunately, 4 of these is going to be quite a bit of weight (not to mention space) which is not ideal. I remember hearing something about voltage multipliers but this appears to be only for AC to DC conversion but maybe there is something I don't know. 

I would love to stop doing research and start the building but it seems like there is more work to be done


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## Amberwolf (May 29, 2009)

ithinkidontknow said:


> Yes I am building an electric bike, I think you have actually posted on some of my other posts before. It is an electric tadpole trike. Up until recently it has just been all research work but now I am starting to get ready for construction.


Just be *sure* you have it all down and measured out, etc., before you start. I'll tell you from experience that even so you'll end up with lots of lttle things and a few big things that don't go according to plan, and require rethinking--every one of those is going to cost you time and money, but most importantly is going to change *other* things, which will in turn change *others*, and make it feel like planning was worthless. 

It isn't.  Without the planning and research, *every* step would probably go that way, instead of just a few of them here and there. 

I did reply to some of your other threads; I just wasnt' sure if you were still building the same thing (some people's projects change after their first feedback!). 




> 48v 750w Motor
> Yi Yun 48v controller if I can get my hands on the right one


Just remember that you get what you pay for, and those are pretty cheap controllers. 

I don't know anything about them other than a bit of googling on their costs and whatnot, and seeing them for around $30-$35 for a "800-1500W" 48V controller sounds pretty cheap, even with the nice-looking aluminum shell. 

I'll still stand by the 4QD products, though they are more expensive, they seem to be nearly bulletproof in design. I'm building a 2QD right now, using recycled parts except for the PCB from 4QD themselves. Other than having issues with some of my recycled parts (mostly from old power supplies, UPSs, etc.), it's going pretty well. 

Given a few of the parts problems I've had, with shorted transistors, open and shorted diodes, and in one case a capacitor that was sort of marked backwards (the plastic shrinkwrap they use for labelling was loose, and had spun around partway!), I daresay a lot of controllers would have just smoked, probably burning the PCB. Not this one. It just sat there protecting itself, shutdown, until i figured out the problems one by one and replaced parts. 

I know for sure (from experience) that the cheap ScootNGo controller I started out with before (and modified, repaired, modified, and repaired some more) would have greeted me with clouds of electronic remains....

Now I am just trying to find a suitable LM339 in my junkpile, as the first one I pulled had one of four comparators not responding to any inputs. 


Now, you probably don't want to put a lot of heavy batteries on that 750W version, or you won't get much acceleration out of it. I'd go with a smaller set now, one that will, with that motor, give you the range and speed you want with the estimated GVW you'll have, plus 10% to 20% added as a "oops" factor (because of things you may have to add or beef up on the frame, suspension, etc, as you test it out). 




> This is my plan for "bike version" which I plan to build to stay under the Washington laws for electrically assisted bicycles. However, after I build the version with the above components, I plan to try to get a moped registration filed with the DMV so then I will be able to go 30mph on roads and have up to 2hp. At that point I would like to install another 750w motor.
> 
> But as I am sure you know, this will eat up serious amounts of energy! For this reason, I need some bigger batteries.


True--but I recommend that you do that in two smaller sets of batteries, potentially one for each motor, and possibly a separate controller for each motor, both of which can be run from one throttle (with some tweaking, perhaps). 

That way you can start out with one motor plus a set of batteries sized for that motor to be able to easily pull around, then just add a second set once you're ready.




> Now to respond to some of your suggestions. Unfortunately, I don't know if I have time to look into freebies just because I am on a fairly limited time schedule as I will go back to school in the fall. If anyone in the Seattle area has an ideas of where to get cheap batteries like this, please let me know! I am really just looking to buy something anyway so that I can expect it to last a long time.


Fair enough. It's just difficult at best to get *good* new batteries cheaply, especially since you want to find the lightest ones that give the most power over the longest period.  Even within lead-acids, there are a lot of types, and some are better than others for each application.



> I was looking at a battery manufacturer that makes deep cycles in my area and I can get 12v 85Ah batteries for 80 dollars a piece and they weigh around 40 pounds. Unfortunately, 4 of these is going to be quite a bit of weight (not to mention space) which is not ideal. I remember hearing something about voltage multipliers but this appears to be only for AC to DC conversion but maybe there is something I don't know.


You can do voltage multipliers any way you want, but you'll be cutting the current proportionally to the voltage increase. If you double the voltage, you'll halve the current, since your power source the multiplier is powered from can only produce so much power total. 

This yahoo group is supposed to have a good converter circuit in it's archives, according to Joseph (the circuit creator), though I have not yet tried out any of the circuits there.
http://tech.groups.yahoo.com/group/switchmode/

As for those big batteries, that *is* a lot of weight. 160 pounds, plus battery boxes capable of carrying that weight and hardware to attach them (10-20 pounds?), is very significant in a small EV like this. Your frame, suspension, and tires will all have to handle that, plus anything else on it and it's own weight. Not to mention that 750W isn't much to pull all that with. 

I'll shortly have a ~650W motor on my CrazyBike, run by the 2QD controller. It'll be around 120 pounds total, plus my 150 pounds, and another 10 pounds or so of stuff I usually carry with me. So I can give you some performance data from that once I test it. I am guessing based on my previous ~350W motor that I should get about the same top speed (same end gearing result), but that my acceleration should increase. 

Previously just to get started took much more leg force/pedals than I wanted, so this motor should help. It's also a 4pole motor, vs the 2pole I had before. More torque, less speed. Also more energy consumed, but I need to be able to get started much faster than I can now. 



> I would love to stop doing research and start the building but it seems like there is more work to be done


It can get depressing to do nothing but research and study when just building a project would be more fun and feels more productive. But I not all that long ago wrote a blog post about how I ought to do *more* research before starting something, since so often I end up changing things afterward to the point where I might as well never have done the first two or three versions of something. If I'd researched or even just thought about it a little more, I'd've saved a lot of time and work, but most of all I'd've saved the parts for other uses (which in your case are going to cost you money).
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## sunworksco (Sep 8, 2008)

I would consider buying used A123 DeWalt cordless tool batteries on Ebay or where you can find them.Go for the 36volt 10-cell packs and then reconfigure them after watching the DeWalt battery Youtube videos.


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## ithinkidontknow (May 14, 2009)

What sort of storage capacity do these have? 
And would it really be better to buy these if I could just buy other lithium cells like this and build my own pack?


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## sunworksco (Sep 8, 2008)

Just the voltage you need.Like I said go to Youtube.com and type in DeWalt battteries/bicycle.


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## ithinkidontknow (May 14, 2009)

I understand what the purpose of doing this is. I did look at some of the videos and also looked onto a few websites that show how to take the cells out. However, this does not answer the questions I still have. From what I found these are 2300mAh cells from A123 with 3.2v nominal. 

The question still stands though, why buy these in packs when you can just order A123 cells (and for cheaper) and assemble your own pack? I don't really see any use for the BMS they have in them but maybe I am wrong. Anyone know how to incorporate the BMS they have into a bigger pack?

Also, I need 48v for my motor, not 36, so it would still require me to construct a different battery setup. From my calculations it would cost me $700+ to buy enough of these batteries to make a 20Ah pack. This is not really that much cheaper than packs they have for sale commercially, especially if you take into account the much the labor and other components will end up costing me.


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