Battery stuff

deacon · #1 01-15-2010, 08:13 AM

We need a place to put our experiences with batteries of all types. The reason is that the information is pretty scattered. So maybe we can keep this thread around so that we can find the latest information someone finds, either information or first hand anecdotal information.

I found something interesting this morning. I have no idea what is going on. I will have to do some experiments to verify it but here is what I found.

Situation background.

I have three 12ah 12v batteries setup in series but I needed 48 so I wired two 7ah batteries in parallel then wired them in series to the three 12ah batteries. It works just fine and does indeed put out 53volts from the pack.

What happened:
After a short ride I put the pack on to charge. Since I use battery tenders, three of them, I set up the 12ah batteries to charge while still in the circuit. It always works just fine. So this morning I went to move the battery tenders to the two 7ah batteries that had not been charged. I found that the charge lights would stay green. I should have read the charge on the batteries but I had already hooked them up and walked away when I began to wonder. Did the charge leach back into them from the ones being charged. It should not have I think, but I don't really know.

deacon · #2 01-15-2010, 12:09 PM

I rode the bike to the mall did my one hour walk and then rode it home. All the batteries were fully charged. I should have read them each before I left but I only decided to check them out when I got back. I also wish I could have started with all new matched batteries but alas I have what I have.

let's just assume they all left the starting gate at 13.25 volts which is full charge. When i got back I read each of the five batteries.3 of them are 12ah and two are 7ah strung together to make a 14ah battery. I will hence forth refer to it as one battery.

so battery one read 12.67v battery two 12.89v battery three 12.47volts and battery four 12.87 volts. I think the two batteries batteries with lowest voltage are over a year old maybe even close to two. I think they are the original two from the hub motor when I first started e bikes again about two years ago. Battery two is about 9months old I think. Battery four, the combo battery, is probably a year old. That would explain the significant difference in the drain. The combo battery has a little more juice to begin with so that would explain it's holding up better.

I think I have pretty much decided to replace batteries as they wear out with 17ah units. That size seems to fit my needs plus about 30% reserve.

jdcburg · #3 01-15-2010, 04:00 PM

Deacon - I have 4 12v 12ah SLAs, all the same model. I bought them in pairs, one pair 6 months ago and the other pair 2 months later. They usually come off the charger at around 13.5 each. After they set overnight they drop back to 13.25-13.43. I use them in pairs in series so I have a 24 volt 12 ah pack plus a backup pack. After a 7-8 mile ride, I usually find one at 12.4 and the other at 12.8 regardless of which pack I use. This is just a casual observation at this point - I haven't started documenting all the variables, but it's interesting they discharge at different rates while hooked in series under the same load. Maybe when I start riding again (after the snow is gone) I'll start keeping records - jd

deacon · #4 01-15-2010, 04:08 PM

I thought that I had noticed that the position in the line made a difference. The last battery in the string seems to have a high voltage after a ride. I wonder if the draw is not constant but goes down from one battery to another.

deacon · #5 01-16-2010, 02:02 PM

One thing I learned today is: What happens when one of your battery charges is set for 6 volts instead of 12... 1' The bike is lethargic after a few yards... 2.It gets to the point quickly so that it won't pull even the smallest hill. 3. You get a lot of exercise pedaling and pushing a bike with a trailer full of sla batteries. Forget all my previous findings. I haven't had a fully charged battery pack in no telling how long.

Tonight I am going to concentrate on charging and evaluating my batteries. I rewired my trailer with the 16" bike wheels. It is running 36 volts again. I am going to get a full charge on that set of batteries tonight. Then tomorrow I am going to see how much they fell over night. After that evaluation I will decide what combination of batteries to buy next.

deacon · #6 01-17-2010, 10:13 AM

After the battery charger's wrong setting debacle I began testing again. I have two sets of sla batteries. One set is 3 12v 17ah in series for a 36v 17ah pack, the other is 3 sets of 12v 12ah and a 12v 7ah wired in parallel then wired in series for 36v 19ah pack.

the first thing of interest so far is that no matter the age difference both batteries in the parallel legs have exactly the same charge at all times. However each of the parallel sets have different charge levels after an hour or so. They vary a few tenths of a volt but all are above the 13.25 max charge level that is recommended. Since it is raining I plan to keep charging both packs alternately all day.

The 12v 17ah batteries were all bought at the same time from the same dealer and yet they also vary significantly from battery to battery. I think that is why they use 13.25 as a benchmark.

by switching the chargers/tenders from pack to pack, I hope I am going to be able to saturate them without over charging them. I have no idea if it will help or not but at least I will have two hot packs for tomorrow when the sun is supposed to shine and the temp is supposed to be in the high fifties at least maybe low 60s. I would like to convert at least one of those packs to 48v. I'm trying to decide the best way to do that at the moment.

36v is perfectly satisfactory, but 48v just has more umph...It's not about tip end speed, it's about the feeling of having enough power to climb those nasty hills without any help at all, and at a decent speed with a little help.

deacon · #7 01-21-2010, 01:14 PM

One of the buggaboos with making a diy kit for the consumer has always been the battery charging thing. Today I took a crack at it head on.

I began with my standard battery pack. three 12 volt batteries in series. I wanted to go with one car battery charger. That would make it simple and easy for the customer to find. So the first thing is you can not hard wire the battery pack in series, The thing I did was to hard wire both posts of the center battery in the pack and put alligator clips on the other end of the wires. They can be easily removed for rewiring the circuit parallel for charging then rewiring it as series for use with the bike.

All the elements are in place. I have an easy to build motor and drive system, an easy to build battery trailer, and an easy to build charging system. Should I ever get ambitious, I can build a kit or more likely write a DIY instruction CD again.

deacon · #8 01-26-2010, 01:35 PM

Ok I had way too much time on my hands today. So what do we know about recharging NiMH batteries. It looks as though we could build our own NiMH pack for about half or less the price of Lithium./

My question is recharging the pack. I'm thinking set it up in 12v 8 or 10ah blocks. String them together to make 36v pack but charge them in 12v bricks.

Looks like a 36v 20ah pack would run about 250 that would be an interesting build. I think I might hold off to see if anything better comes along though. two hundred for that pack would be better.

deacon · #9 01-27-2010, 11:06 AM

If your ebike doesn't perform exactly as it should, check your battery connectioins.Mine left me padaling most of the way home. The motor ran just not very well. When I got home I read the combined battery and it read 33v. then I checked each battery and got over 13v each. That is 39v not 33. Then I checked one of the clips that makes the series ciruit. It was fine but it was clipped to the bolt that goes through the terminal. The problem was that the bolt wasn't tight. The bolt wasn't making continuous contact so the battery wasn't at full capacity at the time of discharge. Now I have to go back and re-evaluate the small wheel bike because it is the same pack I used for the evaluation of it. I will try to get to that this afternoon.

deacon · #10 01-30-2010, 10:03 AM

I'm sure everyone here knows this, but I'm going to bore you anyway. If you have a scooter brushed motor by Currie, you can overpower it. I just burned up a heavy duty controller which is the third one I burned up. I really am sick of controllers in general so i did some quick experimenting before the snow came in.

I have a 600 watt motor at 24 volts and it does pretty well just like it is. First of all I reduced my battery pack to 24volts and found that with my Rhino drive, which is friction and slips on the tires rather than choke down and blow a fuse, I could run it on 24v with no problems. I use a twenty amp household wall switch taped to the handlebars. I also use a 40amp fuse inline. I would rather blow a fuse than melt the switch and have a run away bike.

So then I had to try it at 36volts. It blew the fuse whenever I tried to start it. The problem was that the motor pulled too many amps at start up. Not to mention it lifted the front wheel off the ground.

I almost gave up on the 36v even though I need it on long even moderately steep hills. Then I racked my pudding soft gray matter and came up with an idea. The idea was simple super charger. I figure out how to use two switches on the same battery pack. I'm sure you all know how to do it but here is a quick explanation anyway.

The gray terminal wire hooks to the motors black wire. The blue wire from the red terminals carries 36volts and goes to a fused line to the switch on the handlebars. The green wire goes from the second battery in line and goes along a fused wire to a second switch on the handlebars. it delivers 24volts. Both switch wires hook up to the red wire of the motor.

The green wire will start the bike off at 24v and run along just fine. When I get to the point where I see the big hill I will switch to the 36v switch and pulse it up the hill or just let it run up the hill wide open. At the top of the hill I can turn it off and go back to 24volts. Or I can just use the 24volt to start the bike and then switch to 36v when it starts to hum.

I just have to carry a pocket full of fuses. Just in case I get my right and left hand confused.

I haven't had a chance to test this bike yet with both switches but it has worked for me before and i do know that the voltage is right on the switches. I just don't know what will happen when I switch over. I do not expect any trouble with it. I have bench tested it.

Since there is 6inches of snow on the ground and it is still snowing, it might take a day or two before I can do the real world test...