The nimh battery build...

[zabac70]

There's a number of factors that can influence on the poor performance with this(mixed) setup. Connections (for example) and (my bet) the very nature of different bat. chemistry's and conditions. You just can't see (or measure) what happening in NIMH pack or SLA pack separately , while they are connected and you riding a bike. One damaged cell in SLA can quickly discharge NIMH pack. Proper test would be to compare 12v SLA battery (that is , if you can make the controller and motor to work on that voltage) and 12v NIMH pack. Or (better yet , I just remembered that you have 24 V controller) you can repack NIMH in parallel to get 6.25 AH /24 V pack and compare it to your 7 AH SLA pack (24 V). That should do the best job for comparison (in the given circumstances , without packs with same characteristics AH/V). You should see the difference in range (driving in circles near your house) and in acceleration (well , this one you can only "feel" , without proper instruments ). Let us know what you did (although, I know results in theory).

 

[deacon]

Okay what we need first is a common language.... Since It is my thread (lol) I get to choose the terms... not scientific at all.

STRING... five 1.2v batteries in series to make a 6v battery pack.
subcell... two strings in series to make a 12v battery pack
battery... sub cells in parallel to make a 12v with the correct ah configureation

Battery pack combination of batteries to make the correct voltage pack.

Now, i tested the nimh battery again and discovered that it was killing the charge on the sla batteries. I took it apart to reconstruct it in an easier to work with package. I found two bad subcells. One just wasn't connected I think but the second had a string with three bad aa batteries... Most likely it was something I did while testing. I remade the pack and fixed the aa batteries I think. Anyway 12v 12ah battery is charging as we speak.

If you are not a patient person, I would forget this project all together. I think I can whip it eventually, so I'm hanging in there waiting for my other batteries to arrive,

With the 24v controller i could get the bike home okay, but it was tough going. When the battery is charged again, I am going to hook it up with the 12ah I had it with and give it another shot. I might end up making a smaller battery to get rid of those aa batteries I'm not sure of. I wish I had marked that string.

Here is what i think will happen if the nimh battery (12v) comes in with significantly lower voltage than the sla, it is because there is a bad connection of the subcells or bad aa batteries in a string. having both happen at the same time was actually a good thing. I have an idea what that kind of failure will look like in the future.

 

[zabac70]

OK , I'll adopt your terms My suggestion was to connect two sub cells in series to make 24 V battery (6.25 Ah), in order to compare it with your two 7 AH SLA batts (wired in series for 24 V). In that way you'll get direct comparison between NIMH and SLA (similar AH). And I suggested that you ride it in circles near your house in case of the failure , just to COMPARE performance of SLA and NIMH. Further testing is all up to you (including charging , connections aka battery box/tube, combining etc...). My bet was (and still is) , if you connect and charge properly NIMH pack , that you'll get significantly better range (and , somewhat acceleration, but hardly noticeable on the system of such low voltage). And I still thinking that your chargers aren't "very nice" to NIMH batteries and that you'll need (at ultimate pack , which is still sailing over the ocean) balancers (or BMS , or whatever). However - it is interesting to follow your experiments .

 

[deacon]

When I get finished with the other two, it is my plan to put the 36 12ah sla pack up against the new 36 12.5 nimh batteries and see what is what. I am not actually trying to do a direct comparison except to see if the batteries have a marked difference at this point. They did when the two subcells that were almost totally drained down to zero. I hope that problem is fixed I should know tomorrow. The make a ten cell battery case. The only problem is that I would need 15 of them.. that adds 75 dollars to the build totally unacceptable. I am going to home depot tomorrow to pick up some duct tape and wire not to mention a few wing nuts so I will check on water pipe to see if there is anything available. So that I can make them cylinders i think they would do better. But if I have it fixed this way I would prefer it. So I will just have test the batteries tomorrow.

On the charger I'm hoping not to overheat the battery pack otherwise I'm using the swag system. Scientific wild A** guess

 

[deacon]

I got what I would term my first minor success. I took off to test the bike with a combination sla and nimh battery pack. A wire on the sla pack broke before I got more than a block, but when I got home the nimh battery charge appeared to be about where it should have been. In other words there was no great drain as I had experienced earlier, but then I didn't get very far. i decided that it was an omen so i decided to hold off on the next test until tomorrow.

 

[BossCat]

Cant wait for tomorrow - but I also said that yesterday

When you goto home depot to check on pipe remember to take a battery with you to check on the fit.

Regards
Tom

 

[deacon]

Very Very good news.... I took the battery I made apart first thing this morning before I fooled around with it. I checked each of the subcells for voltage. I charged it all day yesterday a little at a time. The complete battery read 13.71 this morning, but it could do that even if one of the sub cells was totally out of whack. I took it apart to be sure all the sub cells were actually being charged. If they were then I knew I had wiring continuity. If they were all close then I expect that I have a pretty good charging ability to get them balanced within the battery. Which would in theory mean I just had to charge each of the three home made batteries separately to balance them.

So now for the results. Each cell was within 5/100s of each other. I figure with my swag system that is close enough. I wired it back into the 12ah sla battery pack and will test ride it today. I am much more optimistic today than I was yesterday.

I can't wait for the other batteries to arrive. This is the last big challenge for me

at least until the neutron bike...

I found a canvas bag, it came with the piece of excrement hub motor kit, which will hold all 36v 12ah components. I was surprised that it will all fit in the space they made for a 10ah sla battery. I can drop it into the front basket, and remove it to the shop if I want to store the bike in the shed. God I hope this works out. I have a decent system which allows me to carry any number of sla batteries on the trailer but it would be sooooo much easier to bring the battery in to charge, and not have to deal with getting the trailer in and out of the shop. If the Nimh battery just mimics the sla performance I will still consider it money well spent.

My original sla batteries are over a year old but still holding up. Im not so sure about the 7ah but the 12 which I bought for the hubber bubber are still holding their own I think. The 17ah definitely are doing just fine thank you very much. I only got them lower then 13v twice, so they haven't been stressed much. I am going to leave the trailer hitch on even if the nimh batteries are a success. That way I can put the trailer on to easily add 17ah more power for range.

 

[deacon]

The test ride was only slightly better today.After about half a mile it was dragging bad. It didn't even start out like a 36v battery pack. It read 40v but dropped quickly I mean with fifty yards it was running down. The voltage on the nimh battery was almost down to 12 so it failed much faster than the sla, but in fairness one of those was much lower than the other one.

Since I know that all the subcells were hot, I am beginning to wonder how accurate the ah rating of the aa batteries were. I am going to put the testing on hold until I can test with a full nimh pack. At that point I can test for ah rating maybe. I do know this we can build the pack and have it work. The batteries we buy to make the pack from, may be the problem.

One thing I did notice and since I have mixed battery types I'm not paying too much attention to it yet, is that the nimh battery pack is over heated when it comes in. Could be they are not up to the heavy drain. or it could be that the sla batteries are pushing too much current through the nimh pack. I'll just wait till the other batteries arrive to make more tests. Sorry guys no immediate results.

I have to admit that the combo pack (sounds like McDonalds) did do pretty good for a half mile though. With the difference in weight I could probably add more subcells to the battery but pretty soon I would be up to a lith battery in cost. I'm hoping that it is a mixed chemistry problem. But I doubt it....

This build is a lot like a roller coaster.

 

[zabac70]

NIMH discharge rate (and few other parameters) are very different than SLA. That is what I was babbling about in a few recent posts. There is difference between NIMH and NIMH cells also (regarding discharge rate). Now , I was trying to explain earlier , but that includes lots of physics , so I gave up. And that is why I mentioned BMS and proper chargers and comparison with (approximately) same rating SLA battery pack.
If you get your hands on some lap top battery (NIMH) , you'll see that there is much more in it , than just a cells in a box and that is for reason. BTW , you should provide (among said things) some cooling to a NIMH pack. Try to find something on the net about TESLA roadster - they use (used) NIMH batteries for propulsion , so give it a look see.

 

[BarelyAWake]

Try to find something on the net about TESLA roadster - they use (used) NIMH batteries for propulsion , so give it a look see.

Tesla Motors - High performance electric vehicles. Available now.

 

[zabac70]

Thanks for the link BarelyAwake . Since TESLA Motors uses LiIon chemistry , they don't have information's about their first models with NIMH batts. However , I'm sure that it could be found on the internet somewhere (any application for E vehicles), if anyone is interested.

 

[deacon]

Thanks for the heads up guys. At least I know that the batteries can indeed stand the drain. Okay now I have verified that it does make a difference if you mix battery types in the same pack. It's a valuable lesson and that is how I learn, reading it just doesn't teach me because I still have to see what happens.

And don't worry it isn't that I don't listen to you, I just have to see it for myself. I'm not good with theory. I need to experience it to really understand it.

Believe it or not I did understand that there is a difference between battery types. And i understood what you were saying about how they might not interact well. I believed you but I still wanted to see it for myself.

It isn't that the batteries act differently from each other in a pack, they also interact with each other for better or worse and that is a good thing to know. If the battery isn't ruined no harm no foul if it is ruined it was still a cheap lesson.

 

[deacon]

This is the charging method I am trying to use working on the timing now.

The cheapest way to charge a nickel metal hydride battery is to charge at C/10 or below (10% of the rated capacity per hour). So a 100 mAH battery would be charged at 10 mA for 15 hours. This method does not require an end-of-charge sensor and ensures a full charge. Modern cells have an oxygen recycling catalyst which prevents damage to the battery on overcharge, but this recycling cannot keep up if the charge rate is over C/10. The minimum voltage you need to get a full charge varies with temperature--at least 1.41 volts per cell at 20 degrees C. Even though continued charging at C/10 does not cause venting, it does warm the battery slightly. To preserve battery life the best practice is to use a timer to prevent overcharging to continue past 13 to 15 hours. Examples of this kind of charger are shown at Wall mount power supplies for low cost applications. This charger uses a microprocessor to report the state of charge via an LED as well as performing the timing function.

 

[zabac70]

Wow , I'm amazed Seems to me that you have been doing some serious research . Just kidding. Keep up as you planned. I bore everyone just because someone (sometime) might find it useful .

 

[deacon]

hey keep boring us I don't mind new ideas I can always use them.

Believe it or not I received the second shipment of batteries today. The problem is that the package came open in the post office and 19 batteries are missing. I emailed the seller and if he wont send them along I will buy them from someone. I am so close to having a pack that it is frustrating. i am going to build a ten hour pack with what i have now. I will have to remove one of the subcells from the 12.5 amp hour i have now. But I want to ride this battery pack. Ten hour pack should be enough to evaluate the nimh batteries. When the others come in I will add them back to the batteries if it proves to be worth the effort.

 

[zabac70]

Sorry about that I was sure that (messing with someones shipment) is solely problem with post office in Balkans and third world. There is anecdote about that (this is true event): certain computer magazine journalist (where I live), has ordered new wireless keyboard and mouse (for gamers) by Logitech , in order to evaluate it and to write about it in his magazine (that was new stuff, not yet available in stores , eagerly awaited by gamers and few months till official promotion). So he got the paper to go to customs in post office and he went. He found his package open and the mouse was missing. Of course , he was furious and after some yelling he asked to see the boss/manager (or what such person is called). Boss came up , looked in the package and without moving a muscle on his face said : It has lost weight in the journey, so what!? Just like someone sent some tomato's and they been mashed Sorry about off.

 

[deacon]

Its about the same here. I used to be a policeman long ago and far away. They keep track of crime here, so town with good police departments look like they have the most crime.

The reason is, if you know your police will do nothing. people don't bother to report crimes. So the statistics make it look like the worst police departments have the least crime. Same with the post office here, why bother to complain, if you know it will do no good.

I made two 10ah packs and will just pull a cell off the pack I already made to match them. If and when the replacements arrive, I will raise the level.

I found out why the guy on ebay is using the more epensive d cells. The balance problem comes in on the parralell strings. There are no strings using the D cells. So he doesn't have a blance problem. He sends a smart charger along to solve the over charge problem. Something anyone else building this battery pack should keep in mind.

Just from looking it is possible to build a 10ah D cell pack for about $150 which is a little cheaper than a lith. the good part is that you could have acess to the pack to change out a single cell. The smart charger is about thirty bucks I think. Still its getting close to the lith battery packs from china... Sorry I looked again and it's about half the price of a lith from china not even a ping.

The way to do it and it will be my next battery build if this works at all. Will be easy change 10ah d cell battery packs. They would not need balance circuits at all.

 

[deacon]

Utter and complete waste of time... I charged up the pack and made sure there were all there. 40v on the pack when I pulled out of the drive way. I hit the throttle and the bike whined and moved ahead at a snail's pace. I went about half a block and turned around thinking surely the battery level dropped it was the only thing that could account for the poor performance. Well it didn't. It came in at 39v more than enough to power the bike at a good clip.

I know voltage is no real indication of the amps in the battery but in most cases when the amps fall so do the volts reading. It is performing as if the amps were almost gone, but the voltage reads full. The batteries were not heated at all. i can only assume that the umph is not there for some reason. Maybe it is that level drain we hear so much about. Whatever the reason, when I put the throttle to the wall it just crawled and needed a lot of pedal to increase the speed at all. Could be why they don't make nimh battery packs. you would get a lot of range because you would be pedaling all the time. it would be a good pedal assist but that all.

Also I had the sla weight off the bike there is no excuse for the way it ran, that I can find. I almost offered to give them away but I think I will hold onto them, I might find a way to use them to add to the range of an sla pack. There has to be a way to hi-bred the packs.
I think I will turn my attention to making a better trailer conformation. I think I am stuck with SLA so I better figure out how to make them work better for me.

 

[deacon]

It wasnt the wiring. I wonder has anyone tried the lithium batteries with the currie motor. I wonder if it could be the way the currie processes energy. The bike will run on the nimh battery but very very slowly. I just remembered that the big draw was the steady flow of current in the nimh maybe when the controller calls for power the nimh pack just cant deliver enough of it. The currie is not all that efficient. My motor pulls a lot of amps.

I am going to run an experiment tomorrow. I am going to run the 12ah sla pack to the trail to walk. Then I am going to read the voltage on the pack. Then I am gong to charge the battery again. I will run the same route again but with the Nimh pack as well as the sla pack to see what the voltage drain on each pack is. To see if it worth using the nimh pack to just increase the range of the sla pack.

 

[Gss]

Deacon, why not just save your money for a little while and get a 36v8AH NICD battery at www.ebikes.ca Homepage of the revolution . It's about $240. It's rated 5C so you can be sure it will work on your bike.