The nimh battery build...

I still don't have all the batteries and won't for a while. They were ordered in three sets because I wanted to test them a piece at a time before I jumped into the build. Hey a hundred bucks is a hundred bucks.

Phase one did come in. Ten aa nimh batteries. I combined them into one 12v cell. It is only 2.5 ah but it does work for a couple of minutes on a 24v motor with a drive wheel attached. So once it worked I ordered enough to make one 12v 12ah battery. It was my plan to co-mingle it with sla batteries and evaluate it. Then someone pointed out that batteries tend to act like water and level out on the surface so I couldn't get a real good feeling that way. That is when I ordered the rest of the batteries.

At this time I have only the one 12v 2.5 cell ready, but I do know how to construct the battery now, so what the heck I can give you that information. I expect you all know how or have better ideas so feel free to share.

Step one.... lay out a piece of duct tape about six or seven inches long. You will get a feel for it.

Step two.....Lay six batteries on the tape but alternate the ends one pos one neg then a pos again. This step is very important

Step three... wrap the tape around and make a packet of it. One long flat battery

Step four.....Get a piece of your wife aluminum foil.Tear of a piece just a little smaller than the width of two battery ends. Remember one pos one neg ends are side by side. You want to connect them.Wrap it over the end of the battery and secure it with a piece of duct tape cut to fit just over the foil but not touching the batteries beside connection.

Step five .....continue repeating step four until you have only one positive and one negative battery end uncovered at each end of the string.

Step Six.......at this point you should have a six volt cell. use your tester and be sure you have continuity at this point. If it reads six volts at this point everything is connected correctly if not try pressing down on the tape connections between batteries to make better connections.

Step seven... Lay the six volt cell aside and begin again. Repeat steps one through six. When you have a second cell tape the two cells together.

Step eight.... At this point use your foil connector to connect the two cells pos to neg on one end ... Your tester should read 12volts when applied to the other ends,.

Step nine....... Attach wires to the ends which have no tape. I use washer with the wires wrapped around the washer and soldiered to hold them... then I duct tape them.

step ten...... I use bands cut from inner tubes to cover each of the tape battery ends to add some spring action to keep the foil connection tight.


Here is where we might part company. I Plan to make 12v cells of 12 ah so I will just make more of these and connect them in parallel. I then connect the 12v cells into series to make my 36v pack. That is because I charge them in 12v increments. i can balance them that way. I suppose you could combine them in series at this point to make 24 or 36v 2.5 ah cells then combine them in parallel with other cells to make your own pack.

The question now isn't whether I can make a 36v 12ah pack it is how it will perform. If you can come up with an easier way I am all ears.

Ps.. A couple of after thoughts. Yes you can get batteries with solder tabs that would be easier.... yes you can get d cells that are 10ah but I chose to go with the very least expensive method. I might have sprung for the others, if I knew in advance how this would perform. So you might want to go one of the other routes after we know how they will perform.

Deacon, What about putting your batteries end to end like torch batteries and stick them inside a plastic tube - ie sink waste pipe?



An example in this link - http://buildthebismark.proboards.com/index.cgi?board=rc&action=display&thread=1370&page=1

Tom

I had actually considered that but couldn't find a tube that fit laying around the shop. If pvc water pipe was the right diameter that would be ideal. You can get end caps, small springs all that stuff and make them but I just couldn't find anything the right diameter.

Besides I think tinfoil and duct tape is how the chinese do it LOL...

Question for ya deacon... simple tho it may be

How are ya gonna recharge this 12v nimh cell?

I have a piece of cardboard with the 12v pos and neg wires hooked to nuts and bolts on the board. I will use a walmart sla battery tender to charge them separately. I have three tenders. I plan to experiment with the times to figure out how long to charge them at different levels of charge remaining after a ride. By doing each 12v battery pack individually I hope to keep them in some kind of balance charge wise.

In other words: say I leave the house at 13.5v for my ride. When I get back the cells are like 12.9-12.8 -13.2 I hope to make a chart that says 13.2v charge 1 hours. I would then charge each battery individually for the time it needed.. That is the kind of experiments I am planning to make next. When I finish if one cell needs a little more charging, I can do that too. I have no idea if it will work or not, but the nimh cell seems to be a little more forgiving than the lithium. I expect to eventually get a feel for the charging times. You know ride five miles charge six hours kind of thing.

oic - not so "simple" then lol

Reason I ask is I've considered makin' a 6v nimh batt w/D cells just to power my lights when I slow to a stop (gen hub), I've got the nimh cells, even a nice box... but I've refrained 'cause I've been at a loss on how ta charge 'em as a battery... and worried the nimh won't like the gen hub.

My demands far simpler than yers, I outa jus' take 'em and stick them in their charger as individual cells lol but I'm kinda lazy and forgetful when it comes to stuff like that

six volts try the white wire I would just to see... to charge the batteries I mean...

deacon said:

I have no idea if it will work or not, but the nimh cell seems to be a little more forgiving than the lithium. I expect to eventually get a feel for the charging times.

Click to expand...

Charging wise , they are more forgiving (in a some way). You can get "a feel" , but use your multimeter frequently. Not a proper way, but , what a hack, they are (relatively) cheap. BTW , I hope that you've ordered a few extra cells (just in case). Cells in a middle of string/pack (middle two ones) , tend to go south first (something with a way that current travels), co check them more often (after some time , of course, not right now). Charging cells individually (ones that don't have the right voltage), should help to prolong pack life; I admire you in a many ways, but this is something else - you are a very patient guy (referring to a individual charge of cells) - if it was me in question , I would have, probably, set fire to the darn thing (pack).
Now , for packing the cells together (my two cents, experience and something you can do when weather is to bad to ride, if you want). When I was making a pack (in a similar way), first I would get some plywood for a box(1/6" ~ 4 mm where I live), some metal sheeting (galvanized steel for roof drains) and some thin foam (sponge ?) and duct tape. It's hard for me to express myself on English, so bare with me. First two steps are the same , but temporary. When I tape cells together, I measure that pack. Then I form the box out of plywood, with inner dimension 1/2" larger on the battery tab side and on the "cover" sides. Corners are glued and duct taped. Than I cut metal strips to fit the length of the box and screw (or solder if metal allows) wires (one black , one red) onto them. Cut the foam (foam thickness is about 1/2 ") to fit walls of the box and put it (glue it) in place. Metal strips (with wires on them) goes over the foam on the battery tab side. Two little holes on a box are needed for wires to go trough. Metal strips could be fastened to the end walls of the box , but that isn't necessary, because batteries hold them in place. Marking strips with + and - provides some orientation when stacking cells. Remove the tape from cells and put them in the box (between metal strips) in the same order. I used to mark the dots where cell tabs go and with hammer and a nail , make some dents in the strips (to mimic the "real" battery holder). With some more foam fill the remaining space in the ends of pack. Put the cover (last wall of the box) and duct tape it (or make some metal clips to hold it in place). Foam is used instead of springs (preventing movement of cells) and should be , somewhat, well compressed. It should take about 1/2 hour to put that together (or less if you are skillful) , if you have all the materials. Box provides rigidity and easy access to the pack or cells (individually). Now , I hope that I used right words (terms) and that this is understandable. Unfortunately , I have no pics of making this nor finished boxes (gone with a bike). Maybe someone will find this useful.

Sounds like a good idea. I have already found that when the cell gets warm the duct tape gets soft. I will give this some more planning I might just buy some cheap plastic battery holders and hook them together one six cell and one four cell. then again maybe not.

I have been thinking about why I think a 36v system gets more range than a 24v. All other things being equal which I'm sure they aren't really. I see it like dipping water from a two buckets or three buckets. Bare with me here now.

Okay lets say the motor takes 25amps to pull a hill. in a twenty four volt system it would be pulling 12.5 amps from each battery. With a 36v system it would be pulling 8.3 amps from each battery more or less. i would think that one could expect at least 20% better range from a 36v system. Now that is just intuitive reasoning, it could be wrong intuitive reasoning often is.

Well , your intuition is right. It's all chewed up in Ohm's law and few other electricity (general physics) lows for very long time (Tesla also has something to do with that).
However , it's kind of cool that you came up with that conclusion only by driving the bike and thinking about it.

It how I learn lol.... I used to teach photography with an illustration that film is like a bucket that holds exactly a gallon of water. To fill the bucket you turn on the faucet and it runs for a minute... So increase the volume from the facet and it take less time to fill the bucket. That is the rule of f stop and shutter speed

you had to be there.

Deacon, forgot to mention while looking into batteries for my powabyke I followed a post on a fourm to a battery site. I ended up finding they had an ebay site and seen this.

36 VOLT 9 AMP NIMH ELECTRIC BICYCLE BATTERY PACK *NEW* on eBay (end time 29-Apr-10 16:22:00 BST)

You could be onto a winner with your pack, fingers crossed.

Tom

You know, he is using the most expensive per ah battery I saw, when I was looking. It was $120 for 20 batteries. You need thirty batteries to make a 36v cell like that. he is probably clearing something like a hundred bucks US on that pack. It isn't a bad hit for him and not an exorbitant mark up. But I would rather build my own and save the bucks.

The first shipment arrived. I spend a couple of hours building a 12v 12.5 ah battery. I have it on he charger now. I Think to keep from messin up my two good battery packs, I will mate it with a couple of 7ah batteries just to test it. I am not really satisfied with my construction. Its not the batteries its that last connection with wires to make the connect of each 12v 2.5 unit together to create the 12.5 ah battery pack. It doesn't seem very secure. Still I think it will hold enough to test anyway, I might try to find something to make a tube for them.

Anyway I'll start collecting data tomorrow on the new batteries.

I found that electrical conduit is the right inside diameter but the batteries are 2 inches long and it take ten to make a 12v battery cell. Best I could do would be five to a run and that is ten inches a little unwieldy, The pack the way i have it set up now is 6" long and two inches wide more or less. that is 12v 12.5 ah. I haven't weighed it yet but it is way lighter then an sla battery. How it performs is yet to be seen.

So , camels made it over Gobi desert..Cool! Find a tube (plastic plumbing with right inner diametar?) or build a box(es). It's all in preparations...

for me its find out if it is worth the effort first. I want to test this sloppy first, then I will build it purdy.... Well not pretty I don't build pretty. At least more functional. And this is only the first order from a month ago the one I mentioned last time is still weeks away but at least now i can test the first battery for charging,

my homemade battery register 12.78v when I put it on my 2amp charger, It ran for three hours and I took it off still cold. It read 14v but I know it will drop over the next hour or so. I'll update this post with the correct battery reading in an h our or so. If im still awake that is.

after one hour 13.93

After eight hours 13.77

I will be test riding with this battery today so my guess is 13.6 or so. Thats a respectable sla starting reading.

well it didn't work out too well on the first try. I mated the Nic with two 7ah sla batteries. The bike didn't even make it a block. I have no idea what happened but it drained very very quickly. I put my big pack on it an it acted funny as well. I found one of the cells in it way under voltage. So maybe one of my chargers is bad. I'm going to have to check that out when i finish this cup of coffee.

The cell on the big battery in question is the same voltage as it was when I got home last night. 12.4 which is too low to run the bike. I have it on a charger now along with the batteries I plan to match to the nic this time. I'm curious to see what it will do matched with two 12 ah sla batteries.

I will say one things it is smaller and much lighter than the sla battery. That alone will make it worth the money if it will just match the performance of the sla. That remains a question in my mind. I know everyone says it is better... we shall shortly see. also I can fit the whole 36v pack in the little basket on my handlebars. If I make it work no more trailer to drag around. Of course I may still have a trailer for the stability factor, but it will be much lighter and smaller for sure.

Oh while in bed last night I figured the better way to hook the cell connect wire to the battery. All I have to do is skin back an inch and a half or so of the wire covering. Then just fold it up in the alum foil to me a square about a 1/4 inch. That can be duct taped the top of the battery, It will be covered with an inner tube cutting to give it the tension to hold it in place.

That will be much easier and better than what I'm doing now. I may have to go back and redo the battery sub-pack I have now.