My 72v lion battery build and charging options Q&A

[maadgaftler]

Hello, this is my first post and I would appreashate any input you gurus have.

I have been working on an ebike also and I was hoping if you can be kind to help me out with some questions on my battery build and a charging system. I have bought this about a year ago,
http://www.ebay.com/itm/48V-1000W-Electric-Bicycle-Kit-Scooters-Brushless-Hub-Motor-Cycling-DISC-26Air-/181006189568?pt=UK_Sporting_Goods_Scooters_LE&hash=item2a24cf4400

Installed it with some handmade torque arms and bought these...
http://www.ebay.com/itm/GENUINE-DELL-INSPIRON-1100-1150-5100-5150-5160-14-8V-96WH-6T473-D0093-TESTED-/190719939697?pt=LH_DefaultDomain_0&hash=item2c67cb5471

Just like a lot of you, I want my battery to fit into the front triangle of a hardtail frame. I built the batteries into 12s 12p for a total of 144 batteries at 48v, pretty much all I can fit into the frame.
The rating of the batteries are 6450 mAH and 96 WH

I have also ordered 3 of the little 1~8s buzzer alarms and hooked them up as some sort of a monitoring system. I am thinking of buying 3 BMS boards to switch between the buzzer alarms and BMS for charginng.

I am suspect of having some dead cell(s) in my pack because it didnt have any speed, mabe 10 mi/hr at the most and it was cutting out more and more frequently.

Q could this be from too much juice, bad cells or too low a charge?

I am planning on installing a this latger controller unit soon.
http://www.ebay.com/itm/72V-1500W-Brushless-Speed-Controller-Electric-Scooter-E-Bike-/251141519996?hash=item3a79337a7c&item=251141519996&pt=Other_Vehicle_Parts&vxp=mtr

I am having a hard time on configuring a charging system for it that isnt way expencive.

I plan on reconfiguring the batteries into something like (8p6s x 8p6s x 8p6s)s = 75.6v at full charge. I dont think the extra 3.6v will do any harm. I found these,
http://www.ebay.com/itm/BMS-PCB-PCM-for-24V-25-2V-7S-Li-Ion-Battery-Pack-50A-10A-limit-With-Balance-/150978287352?pt=LH_DefaultDomain_0&hash=item232701d6f8

The new configuration will allow me to use old lion power tool chargers, 24v lion chargers that are cheaper and more common that a bulk 72v charger that are very expensive and to keep my options open and to be able to single out dead cells much easier as time goes by.

Q If that works, I will have to switch the 3 cellpacks back and forth from parellell into series to create 72v for travel and charging. Can you give me an idea of anything else that is less complicated?

Q Can you give me an estamated speed and range of my current battery pack and the new, higher powered configuration? I weigh 220# the bike is a 25# xc race bike I built from scratch. The bike weighs about 100# now.

I have been having a hard time trying to figure out a charging and bms system. Before I built the battery, I charged each set of 3 parrelell (what I cut all the puter batteries before building the large cellpack) on an aftermarket 4.2v cellphone smart charger that you just fit the battery into. It took days to charge all the parelell sets.

I would appreashate any input you guys have to keep me on the right track on building something that is badass.
When I install the new controller, I plan on taking some pics and a video for you guys.

 

[dogman dan]

I'm a bit confused by the info on your cells. 144 cells of 6.45 ah each? 78 AH of 48v fits in your triangle? Something is not adding up right to me. 78 ah of 48v ought to a bit bigger. 6.45 ah laptop cells? Or are they 645 mha? Is each string of cells 6.45 ah?

10mph and cutting out all the time makes no sense for a battery of that size. Move a decimal point, and 7.8 ah of a low c rate cell would be garanteed to sag and engage your lvc in the controller. 8 ah x.5c = 4 amps of power.

 

[maadgaftler]

The first is correct. They are 18650 from 12 dell laptop with 12 cells in each one. 144 total cells at 6450 mAh 95WH, they are currently configured 12s 12p to 48V total, well actually 50.4v.

I do think the lvc in the controller is doing the cutting out, I plan on installing the new 72v controller soon. I probably have some dead cells, I bought another lot of the dell batteries that I have charged to full capacity and have been sitting for about a month now. I am going to test them with a meter to see if any of them had dropped and I will set them aside.

As for the battery pack, im going to break it apart and charge each individual string of three parelell batts with my aftermarket smart cell phone charger and do the same with the meter. then I plan on making three 24v batteries and tie them into series for 72v, am i on the right track? would this allow me to use 3-24v chargers

 

[SamTexas]

The first is correct. They are 18650 from 12 dell laptop with 12 cells in each one. 144 total cells at 6450 mAh 95WH, they are currently configured 12s 12p to 48V total, well actually 50.4v.

Using the data you provided above:
95Wh/6.45Ah = 14.7V.
So each of laptop battery has 12 cells in 4s3p configuration. Therefore each cell is 2150mAh. 6450mAh is the capacity of 3 cells in parallel. 95Wh is the total energy of 12 cells.

I read your first post twice and still have difficulty visualizing your battery configuration. If you can, post of pictures of the battery pack you built using those 12 Dell laptop batteries.

 

[dogman dan]

That makes more sense. I hadn't heard of 6 ah laptop cells. Even I could figure out that 144 18650 cells fits in a bike triangle, but 144 6 ah cells sounded huge.
So if it's 144 cells, at 12s that's 12 p strings.

So 12 cells is 25.8 ah? That shoud be able to put out 12 amps then, but your kit is likely to be pulling 25 or more. So it's still a tad small for a 20 amps controller, and likely it's sagging under load enough to lvc it. That's assuming you have .5c discharge rate cells.

So higher c rate batteries would help, or another 144 of the ones you have if they are cheap enough. What you have might work if you cut one of the shunts on your contoller, to cut the amps in half. You might have a plug on the controller that will amp limit, some do. In fact, maybe it's turned on now, explaining the 10 mph max speed.

I also got around to looking at your motor, and it can run on 72v, but you will have to be careful about ride length if you overvolt it. Melting motors is fun, but not when it's your only motor. If you really want to go 40 mph, I have to say, you need real high discharge rate batteries. 20-50c stuff is the kine.

 

[SamTexas]

Even I could figure out that 144 18650 cells fits in a bike triangle,

It's not that easy unless you want the width of the battery to be 7 to 8 inches wide. My battery width is never more than 4 inches, including the side covers. The most I can fit in my triangle is 72 cells (12s6p) and a small controller.

 

[SamTexas]

So 12 cells is 25.8 ah? That shoud be able to put out 12 amps then, but your kit is likely to be pulling 25 or more. So it's still a tad small for a 20 amps controller, and likely it's sagging under load enough to lvc it. That's assuming you have .5c discharge rate cells.

All laptop batteries should be discharging at 0.5C continuous. But his 25.8Ah battery is way more than sufficient to handle his 20A controller. In fact it can easily handle a 40A controller. 2C discharge for 30 seconds is fine, and that all most people need to speed up from stop. 1C discharge for 10 mins is also fine.

The only problem is when the user CONTINOUSLY pull 1C or higher.

But that's getting ahead of ourselves. 25.8Ah is the capacity when the cells were brand new. I have the feeling he was using recycled laptop batteries.

 

[el_walto]

I think throwing together 144 random cells without a BMS is a really bad idea.

 

[SamTexas]

Throwing 144 random cells together is a bad idea, with or without a BMS. Cells capacity should be determined and grouped together so that all groups have more or less the same capacity. 5% difference is acceptable.

 

[maadgaftler]

Sam, What kind of #'s do you have? yea there used, im testing them further and picking the best ones
Run time?
Range?
Speed?
Charge?

I plan on setting up some pics for you guys, but I want to know how I am going to reconfigure them before I tear into it again.
Dogman, same with you, because I had looked quite a bit for laptop batteries with higher #,s and kept them all the same for integrety and balance.

I have the batteries incased in a "vote for me" sign made out of corrigated plastic and installed into some aluminum from the bottom of a double slider door, bent around into the triangle and bolted onto the bottle cage brackets.

 

[SamTexas]

I don't know how to answer your questions. I don't understand them. Here's my best shot:

Runtime: For any laptop battery, the runtime should be 2 hours or more. This is necessary for a 0.5C or lower average discharge.
Range: Whatever your average speed is, the range should at least twice as much. Ex: 18mph average, range must be at least 36 miles. Same reason as above.
Speed: Average speed is whatever you want, as long as the above two conditions are met.
Charge: Laptop cells should never be charged at more than 0.5C. Ex: 10Ah pack should never be charged at 5A or higher. It's best to charge at 0.3C. Maximum voltage is 4.2V per cell, so 42V for 10s.

The pics (if and when you post) are not for me. They are for me to help you.

 

[maadgaftler]

el_walto,
I have also ordered 3 of the little 1~8s buzzer alarms and hooked them up as some sort of a monitoring system. I am thinking of buying 3 BMS boards to switch between the buzzer alarms and BMS for charginng a 3 pack of (8p6s) . I am thinking of buying some of the chargers for power tools or ebike scooters
Do you have any inexpensive BMS and charging ideas?

 

[dogman dan]

I agree Sam, good new cells in that capacity should be plenty to run that bike. So I also suspect he's got some used cells, perhaps sold as "new".

Sort of familar to me, since i'm the proud owner of some "new" A123 cells that can't handle a 1c discharge rate. New A123's should easily handle 10c. Well, the plastic covers look new.

Till you do some testing, you are cruising for a bruising bro. You have to find out what your fine cells are able to tolerate. It's step one of building a pack ya know. Sort out the shit cells, and don't use em. I'd say you need to discharge test each of your paralell strings, and find out if any of them perform substantially less than the rest. It can be done without complete dissasembly. But the bad news is, you might have to dissasemble the whole thing, to find individual crappy cells. Worse still, you may find like I did, you bought a nice set of used up batteries and none of them are very good.

So you need at least some minimal testing equipment. One way to get it, woud be to buy a decent RC charger. Even if its a fairly cheap one like I have, I was able to put my crap cells on it, set it to discharge at 5 amps, and see that whoops, they can't even do that!!! Trying again with less amps, I was able to see what discharge rate those "new" A123's could take.

That gives you the ability to charge your cells safe as well, including balancing them. Then if you get er going, you can just monitor your depth of discharge with a voltmeter, or idealy a voltmeter and wattmeter.

 

[SamTexas]

Sort of familar to me, since i'm the proud owner of some "new" A123 cells that can't handle a 1c discharge rate. New A123's should easily handle 10c. Well, the
plastic covers look new.

You're too forgiving. I would NEVER let someone do that to me. Just can't stand deception.