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Upgrading from SLA to LiFePO4

Some of you have been following my project to upgrade my little 180W ebike.
I have all ready posted on upgrading the hub motor from the 180W 36V system to the 1000W 48V system.
I promised to post on the performance when I got my new battery, and it finally came in.

I ordered a 48V 15Ahr LiFePO4 battery pack with BMS and charger from China off ebay for ~$250 shipped.
I hooked it up to the charger after unwrapping. I found the charger shut off after only 10minutes, so that means it did not self discharge during the 6 week boat trip it took to get here. Thats good news.
Another note is how they made it. Its simply duct taped together, but over all looks fine. IF I want to change the shape, I should be able to remove the tape and change it how I like.

In just a few minutes, I had it in the scooter.
P1010375.JPG
There is nothing under the seat. That silver cube is the whole battery.
OK, its not pretty, but I will clean it up as time allows.

I finally got to go on a real test ride.
Here are the results:
Top speed is ~20MPH using a GPS.
It goes about the same speed up or down hill, so the speed must be governed by the controller.
It has plenty of torque. If I put my feet on the ground and pull the throttle, the front wheel will come up (but no, it wont wheelie while moving).
I can go up pretty steep hills with out loosing speed.
So far, I have gone about 8miles on the battery, and there is no noticeable drop in performance.
I pulled over and checked, and nothing (motor, controller, BMS or battery) was hot.

The only downer is that some times when accelerating from a stop (and pointing up hill) the current shuts off and then back on and off making a jerking motion. Since it did not do the same with the SLA batteries, I am sure that this is the BMS which came with the LiFePO4 system. It is protecting the battery from over current, or under voltage.
This tells me that I should have bought the 20Ahr battery, not for the additional range, but for the increased supply current under heavy load. Still, this issue is not common, and over all the bike is very ride-able, and I do not feel the need to order a larger battery.

So, the verdict:
Fun little scooter. Since I started with such a small frame, it is really light and maneuverable. The small LiFePO4 battery in the floor does not weigh much. The whole scooter weighs 32kg. It seems like is has plenty of range, and is fast enough to be usable. Also it is an e-bike, not a scooter. Only need a bike helmet, not license or registration. I am happy enough with it to want to finish off all the details like new lights and key switch. Get the regenerative breaking working and so on.
-Mark

moveon70's picture

Laptop batteries for my scooter

At my work, we have a recycle tub for used batteries. I decided to try to make use of the used laptop batteries for a little stand up electric scooter by sorting through them and finding the cells that were still in good shape.

There are many types of Li-ion rechargeable cell chemistries. (scroll down this link)
http://en.wikipedia.org/wiki/Li-ion

Typically, laptops (and the tesla roadster) use Li-ion cells with the CoO2 cathode. LiMn2O4 cathodes are used in the "X-treme" Li-Ion bike. LiFePO4 batteries are quickly gaining momentum as the battery of choice for scooters because they are inherently safer. LiPo (lithium polymer) is some of the most powerful, but also the most dangerous.

OK, so, the most common size of the CoO2 cathode Li-Ion cells is called an 18650 which is simply the dimension of the cylindrical cell (18mm diameter x650mm in length). Here you can see how they are laid out in a laptop battery.
Laptop1.JPG

laptop2.JPG
These cells do not last for ever. Their capacity diminishes over time even with out going through charge cycles.
That said, some cells will degrade faster than others, so in each laptop battery, there is likely some cells still in good shape. You can see that to make this work, you would need to start with a lot of cells.
laptop3.JPG
These cells had to be taken apart one at a time and remove the BMS. If the voltage of the cell was below 2V, dont bother trying to salvage the cell. It has probably become defective. Any of the cells that have over 3V have a good chance of recovery.

A new 18650 cell has ~2Ahr capacity, and can discharge 4Amps.
http://www.alibaba.com/product-gs/235681810/Li_ion_Battery_Cell_for_SAMSUNG.html

I decided to put 6 in parallel so that I can discharge as much as 24A, and if the cells were new (which they are not) I would have a 12Ahr battery pack.

I did not have a spot welder, so I decided to solder the cells into a 6 cell parallel battery.
laptop4.JPG

I then used 8 batteries to make a pack.
laptop5.JPG
Now for the safety part.
I found a really cool BMS by ecity power to use for the pack.
You can order them off ebay for $40 shipped. (search for BMS li-ion)
Software and diagrams can be found here.
http://www.ecitypower.com/index.php?option=com_weblinks&view=category&id=59%3Abms&Itemid=93

It can handle 8-12 cells, up to 40A, and the voltages can be programmed by the computer for your specific battery chemistry. For the CoO2 Cathode, the cut off voltage should be 4.2V.
laptop6.JPG
Unfortunately, I had trouble getting the BMS to recognize all 8 cells. While messing around with it, some wires touched and zap-pop, melted the wires. So now I am ordering another one.

Until then, I charged up each of the 8 batteries separately and hooked it up and rode it around.
laptop7.JPG
None of the batteries got hot, nor did the voltage seem to drop on hills. When I get my new BMS in, I will be a little more brave on how hard I push it, and update the blog at that time.

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Transforming the Voy

This morning I received my hub motor and accesories from Golden moter.
It was a big day for the little Voy.
Today my new motor came in.
getting started.JPG

I ordered the 48V 1000W 16" brushless hub motor with a smart controller, throttle grip, and a button attachment.
Open the box.JPG
Before ordering I did a lot of research. I was concerned about the new motor fitting in the scooter and being able to attach my existing chain sprocket and rear drum break. I looked at the detailed drawings on the web site and called the distributor in Arizona. The distributor said that if I want the one on the web site, then I would need to order from the site to make sure I got the right one...well, I did, and my fears were realized when I opened the box and found the motor dis not have accomodations for a chain or rear break.
Also, the axel was too short.
axle.JPG
I had to make a decision to use the motor I got, or to try and get the one that was advertised. I decided to use the one I got even though I was dissipointed. The whole purpose of this project is to learn how these systems work, and so I could still do that with the motor that was provided even though I would loose the chain for pedals which makes this no longer a bike in the state of California.
First issue was trying to fit the wheel on the bike. The swing arm was too wide for the new motor.
After thinking about all the clever things that could be done, I decided to try and just bend it.
If you ever want to feel strong, try to bend cheap steel. I was able to bend it mostly by hand. My modified swing arm came out pretty good and the suspension still worked.
Bend the swing arm.JPG

Next, I decided to put a tire on it and instantly saw a problem....there is not enough clearance to fill the valve stem with air.
Valve stem.JPG
I used a 7/16" end mill in a cordless drill and elongated the hole.
Valve step hole.JPG
After that the valve stem could come off at and angle and be filled.

Finally, the wheel was mounted.
wheel mounted.JPG

Shortly after that, I just plugged the motor into the new controller. The plugs were all ready matched to the motor, so it was easy. Since my new LiFePo4 battery is not delivered yet, I just used some lead acid ones for now. With in 10 min, I was ready to take my first ride.
First ride.JPG
Nothing on the head set works, and I dont want to try the lights since I switched from a 36V to a 48V system, its likely that many of those bulbes will burn out.
I decided to just remove the head cluster and eventually replace it with my own lights and gauges.

Even though I was using half charged used 7ah SLA batteries...that little scooter really woke up.
The spedometer is not working, so I do not know how fast it goes, but it must be close to 20MPH. With fresh batteries, Im pretty certain it will be better. The motor has good torque as well. Once I get the battery situation improved, I will bring a GPS with me and report on its preformance.
For now...though I had to loose some features, I am really impressed with how powerful and quiet the motor is.
There are some features that I will be experimenting with:
Regen breaking, which will effectively give my a rear break again.
Cruise control (a feature built into the controller) which I tested, on the center stand, but not on the road.
Reverse, built into the controller. NOt sure what value it has, but I will try it out.
Security system and Alarm. The controller has a vibration alarm wich will lock up the motor. I want to see if I can get that working.

It was a big day today. I will update when I have more info.
-Mark

moveon70's picture

Running two battery sets in parallel

Just learned how to insert pictures.
This is the schematic for dual battery sets.

Once again, if you wire your batteries together with out the diode, they will work, but as the batteries age, the worst one will pull down the whole system.

Series parallel battery pack big.jpg

I bought the bridge rectifier from Frys for $7. It is an NTE5340 and can handle 40A.
The two battery sets go in on the two "AC" lines for the rectifier. The Chager connection goes on the DC- line, and the motor controller goes on the DC+ line. It worked great!

moveon70's picture

Upgrading my Electra Voy Bicycle

I bought a used ebike purely for the experience of upgrading it.

I stared with a Electra Voy bike/scooter which I found on Craigslist and boght for $150. It has a 36V lead acid battery set which feed a 180W hub motor.
My ultimate goal (and I have all ready ordered parts) is to upgrade it to a 48V, 1000W, LiFePo4 system with regen breaking.
I ordered the motor and controller (with regen breaking) from "Golden Motor" ($400), and the LiFePo4 battery with Battery Management System from a Chinese distributor through ebay($400).

It will take a couple months for my new parts to come in, so until then I thought I would mess around with the current system. The 3 12V, 12Ahr batteries were shot. I picked up some used 12V 7Ahr batteries from a surplus house for $5 each and decided to see if I can make them work.

This scotter has allowances for two sets of batteries. When one set dies, you can switch to the other set. I was interested in putting two sets (a total of 6 batteries) but do not want to switch between them. If the two sets are simply wired in parallel, then one weak battery brings down both sets. Instead I decided to use some diodes to seperate them out. After drawing the schematic I realized that it was actually the same diode lay out as a bridege rectifier. (see attached file for schematic).
I bought an NTE5340 40A bridge rectifier from Fry's for $7 and it all ready has push on blade connectors, so it was easy.

So far, it works great. I can charge all 6 batteries with the 36V charger, and as I ride, the controller pulls the most current from the set with the most voltage. They basically drain together. Fantastic!

Next posting will be once I get some of my new parts in.
-Mark

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