The Ebike Project

As anyone who has been following my blog knows, I’ve been working on an ebike that I purchased just before the winter rolled in. After taking it all apart, and refurbishing it, so to speak, there was only one major change that I wanted to make. The SLA(Sealed Lead Acid) batteries that came with it would not give me the range that I wanted, so I decided to build a lithium battery to power this ebike.

I’m certainly no expert when it comes to electronics, even though I worked in the power electronics industry for 35 years, my job was mostly mechanical rather than electrical. I was exposed to a lot of the electronic side of the job too though. But I always like to say that I’m not an expert at anything. I know a bit about a lot of things, and I like it like that.

Anyway, I’ve done a lot of research on the things I might need to know to complete this project. The internet has all kinds of information on any subject you’d like, but you do have to filter through a ton of stuff to find exactly what you need. I have been frequenting an electric vehicle forum called http://endless-sphere.com/forums/

Here I can find everything I need to know in order to build my lithium battery. However, it’s not that easy. You really have to filter through a lot of misinformation, and over-information. In other words, there are people on this forum who don’t know what they’re taking about, and there are also people who are tech gurus, and they tend to get into things in a bit too much detail, and it’s very hard to follow them.

I just wanted to know the basics that I needed to know in order to build my battery. Now, some tech gurus would say that I need a B of A in electronics to do the job properly, and there are a few gurus that will take the time to explain things in clear English too. Most of the time, I will just do my own searching, unless I come to a point where I really need a question answered that is critical to my build.

Anyway, I had ordered some equipment that I needed from China, and I’ve been waiting for that slow boat to arrive. Since I had stripped all the lithium cells that I needed from the laptop battery packs, I needed to fully charge them, to see which ones would be good to use.

I started off with a small charger that plugs into the wall outlet, like this;

IMG_0005

Of course, something like this will take a long time to charge 120 cells, which is what I needed for my ebike battery. I could only fully charge two batteries a day with this setup. I had always intended to buy a larger charger, but I have to do these things in increments, so that it fits into my budget.

Last week, my larger charger arrived from China. It is a specialized charger commonly used in the RC(Radio Controlled) market, and it is designed to charge lithium batteries.

IMG_0004

This is the iMax B6AC charger I purchased. I got it on ebay for $34. with free shipping. It is a dual power input charger, which means that I can power it either by AC 120volt, or DC 12 volt. However, when I received it, I found that the AC input mode did not work. I contacted the seller, and they told me to send pictures and they would find out, from the manufacturer, what could be the problem.

Well, I didn’t want to wait for all that back and forth communication, so I did a simple continuity test myself, and found that the AC cord was the problem. Once I knew this, I knew that I could make it work by either getting a new cord, or by fixing the present cord. I informed the ebay seller of my findings.

To their credit, the ebay seller got back to me and offered me a $5. refund. I did some calculating, and decided that $8. would be enough to offset the existing problem, and I informed the seller. Keep in mind, buyers on ebay are in a much better position than they used to be. Positive feedback is a highly valued commodity on ebay now, and sellers want positive feedback desperately.

The seller agreed to an $8. refund, and I have received that refund. In return, I gave the seller positive feedback, which they deserved. I then opened up the charger and hard wired the AC cord right to the circuit board, where the incoming power wires connect, and after that, all is working well. So, in actual fact, I only paid $26. for this charger.

It’s working fine now, and I built a special jig which holds 12 lithium cells, in parallel, so I can charge 12 at a time. Much better than charging only 2 at a time. It takes all day to charge those 12 cells, but this charger will not be used as my final ebike charger. I’ll eventually need a ‘bulk’ charger for that job. This charger only puts out 50 watts, and it would take too much time to charge my finished battery, which will be a 31.2 amp hours or 1123.2 watts.

IMG_0006

This is the jig I built to charge 12 cells at a time. It will make the charging job go much more quickly. The completed battery, will have 10 of these 12 cell groups, to make 120 cells. However, due to space restrictions, I will need to build my battery in two blocks of 5 x 12 cells, or what the ebike industry calls 5S12P. Five cells in series, and twelve cells in parallel.

Cells in series increase the voltage, and cells in parallel increase the amps. So, these cells are 3.6 volts each, and when I put 10 cells in series, I will have 10 x 3.6, which is the 36 volts I need. These cells are also 2.6 amps each, so when I put 12 cells in parallel, I will have 12 x 2.6, which is 31.2 amps.

One thing about lithium cells that complicates things a bit, is the fact that each of the cells needs to be ‘balanced’, when you hook them up in series. All the cells in parallel are seen as just one cell, but cells in series are seen as separate cells. So, in my battery, I will have 10 cells, and each of those cells will need to remain in balance, or at the same voltage.

This will require some extra wiring, because each of the 10 cells will need it’s own separate charge wire, in order to be able to charge just one cell, or group of 12 in this case, at a time. This is another reason that I purchased this iMax B6AC charger. It is also a balance charger, and will automatically keep the 10 separate cells in my battery balanced.

From what I’ve read, these cells shouldn’t go out of balance too often, so I’m expecting that I will only have to use this charger maybe once a month or so, to balance the complete battery, but this will take longer, so in between balance charges, I will be using a ‘bulk’ charger, which will have more power, and will charge the complete battery much faster.

Anyway, I haven’t decided on which type of bulk charger I’m going to use yet, there are a number of options. I won’t need that for a while, so I’ll just keep doing more research on that subject.

After I finish charging and sorting all the lithium cells I have, I can start building the enclosure for the battery pack. I do have some ideas as to how I’m going to do this, but I’m just taking one step at a time. My next ebike update might have some more information on the enclosure.

Note; When using lithium cells harvested from laptop battery packs, it’s important to check the pack voltage and amperage on the outside plastic cover of the battery pack, so that you can determine, exactly, what type of cells are inside the pack. Some battery packs use cells that are 3.6 volts each, and some use cells that are 3.7 volts each. Typically, battery packs which are marked as 10.8 volts, have cells that are 3.6 volts each. Packs that are marked as 11.1 volts, have cells that are 3.7 volts each.

You need to know which cells you have in order to be able to charge them properly. The 3.6 volt cells can be charged to a full charge of 4.1 volts, and the 3.7 volts cells can be charged to a full voltage of 4.2 volts. However, there is enough evidence to suggest that not charging to full voltage can extend the life cycles of the completed battery considerably. We are likely talking ‘years’ here rather than just a few weeks, or months.

If you choose to charge to the full voltage, then that’s fine, but charging over the full voltage can do damage to the cells. This is why you need to know what the nominal voltage is to start with.

This fact is not made very clear in all of my research. Many times these laptop cells are just seen as 3.7 volts, but that is not the case, and many times the voltage difference is seen as ‘not that much’, but if you constantly charge a 3.6 volt cell over the recommended 4.1 volts, you are probably slowly killing those cells.

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