Looking for a way to fast-charge my ebike pack

[CUDAcores89]

Hey folks, I haven't been on here in a really long time but I decided to stop in because well, I have a problem.

Currently I own an ebike. I ride the bike to and from where I work every day. The ride itself is a round trip of 20 miles. My system bike is a 1000w front-wheel drive I bought off ebay that I have been using for about a year now, and it works great. I use a 12S DIY ebike pack I made from Samsung 28A 18650 cells I got for about 17 cents a cell.

The pack itself is a 12S8P 44v 22.4AH battery pack I hand-built from some laptop batteries I got at my local recycling center.

I frequently visit my local computer recycling center and they sell things to me by the pound. One day a company had brought in an entire pallet of NEW in box HP 6-cell laptop batteries that had these Samsung 28A 18650 cells inside, each laptop battery had 6 cells. I asked how much they wanted for them they said "$1.50 a pound" . I went and bought 100 packs and gutted 20 of them to build my battery. the rest I sold on ebay and made a nice profit.

Currently I split the pack electrically into two 6S packs and charge it with a turnigy accucell 6. The problem is charging it this way is veeeerrrryy slow, and it usually takes so long to charge that I frequently wake up in the morning after plugging it in overnight and the pack is still charging. :x

It looks like I will have to find a faster way to charge my pack. Here is what I am thinking:

1. Buy a 1000w lipo charger and power it with server power supplies found at my recycling center.

This option is the most expensive. At my recycling center I find 12v 40-60A server power supplies from working machines all the time and I can get them for roughly $1 a piece. I would buy a very expensive 1000w lipo charger like a icharger 3010b or a cellpro powerlab 8. I then buy 2-3 server supplies for about $3 and run the charger off that. This would allow me to slow charge or fast charge my pack. I could also reduce the cell end voltages to extend the packs lifespan further.

2. Get a meanwell power supply. I could also buy something like a meanwell 48v 10A power supply and adjust the trimpot to my chosen end voltage. This would cost less than the icharger, but it would only be able to bulk charge the pack, and it would be annoying to adjust the end voltage every time I wanted to change it with a tiny screwdriver.

3. buy this DC-DC converter from aliexpress and hook it up to a bunch of server power supplies.

This one would probably cost me only about $25 in parts. I could buy this B900w digital DC-DC boost converter from aliexpress for around $18:

https://www.aliexpress.com/store/product/DC-Converter-High-Precise-LED-Control-Boost-Converter-B900W-Input-8-60V-to-10-120V-900W/2338265_32725667572.html

Then hook up a 48v DIY power supply made form 4 server power supplies. This one would allow me to charge the pack at probably around 450-500w (with these Chinese converters take the claimed number and divide it by two) and I could also easily adjust the end voltage and current. However I would not be able to balance charge the pack. Although that being said, I have measured my ebike pack before and after running it on a full cycle, and the cells do a very good job of staying within about 0.02-0.03v of eachother.

Right now I am leaning towards option 3 because it does almost everything I am looking for, but there might be something I have overlooked.

which one should I do? Or is there something even better I haven't thought about?

 

[Sunder]

Bit risky, but you could get 4 x server PSU and just push unregulated voltage to your packs in 3S configs (avoiding any common ground issues). This will bring them to 4.0v per cell, which is recommended for long life anyway.

When you want a full charge, or need a balance, just do it less frequently using your existing charger.

Only issue I could see is whether the cells could cope with the rate of charge you're giving it. May have to see if you can find some smaller 20A max PSUs.

 

[wesnewell]

They're 4.3V cells with a recommended charge rate of 1400ma (.5C). I'd use a bulk charger at 50.4V 10A for the whole pack (4.2V per cell average). You'd get a full 4.2V per cell charge in a little over 2 hours. A couple of battery medics to balance it occasionally.

 

[spinningmagnets]

You need to buy a digital contact thermometer with a separate probe. Connect the probe to your pack and check on it once in a while to see how warm its getting. Slowly raise the amount of amps you are charging with until the temperature is about warm to your hands' touch (100F?).

The cells that are made to be low discharge (*like yours) are also slow-recharge. If you try to charge them fast, and the cells get hot, the pack will die soon. If you need a fast charge pack, you need high-discharge cells. 25R, 30Q, maybe LiPo (*which I don't recommend to anyone new to battery charging systems and their danger modes)

 

[CUDAcores89]

You need to buy a digital contact thermometer with a separate probe. Connect the probe to your pack and check on it once in a while to see how warm its getting. Slowly raise the amount of amps you are charging with until the temperature is about warm to your hands' touch (100F?).

The cells that are made to be low discharge (*like yours) are also slow-recharge. If you try to charge them fast, and the cells get hot, the pack will die soon. If you need a fast charge pack, you need high-discharge cells. 25R, 30Q, maybe LiPo (*which I don't recommend to anyone new to battery charging systems and their danger modes)

i suppose "fast charge" is a relative term. If I can charge the pack at something like 5 amps just so it is done when I wake up in the morning I will be happy.

Thanks for the help everyone. I ended up going with option 3 + some Hobbyking battery medics for balancing. This gives me almost all the advantages of option 1 at a much lower price point. Thanks for your help.

 

[dogman dan]

5 amps ought to be possible. That's .25c charge rate. not that fast.

Charge that thing outside the house if you can. Might not be that big a risk, but that's what I thought about my battery. Its the safe one, no problem. I was asleep when the house caught fire.

 

[markz]

Asleep and charging?

edit - Well outside is fine, I meant inside.

I like to keep an eye on the charging process, but if it takes too long then outside for sure.
Look at Meanwell Switching Power Supplies. Top quality product. Can connect 2 or more in series to get your voltage.

Mouser.com
Ebay.com
Sager.com

I got some of them Makita's 1.6Ah and I use two Meanwell HRP 24V 16A 300W units to charge. I have another 3 laying around. I can set the voltage to 41.5V for 10S, just below the 42V mark, for longevity purposes. However my downfall is I set LVC to 28V so 2.8V per cell. Its more like 2.9V or 3.0V per cell because with my weight I pull too many watts.

The thing with Laptop cans is that they are low discharge rate, and low charge rate.
BUT
You put enough in parallel, you can increase the discharge rate.

 

[999zip999]

I fast bulk charge my 24s A123 20ah pack as two 12s at 16amp each at the same time. With a meanwell set at 28v and a 12.6v hp 600 power supply times two. So about an hour or less for 18ah.