[Spider-man]

So, I am doing an experiment with my EV conversion. I have a BUNCH of lithium batteries taken out of laptops. They are the same kind used in Tesla vehicles. Which charger would be best for me to use? I plan to use the batteries on a moped I am converting. The pack will need to be between 12v and 24v to work with an inverter. I have an AC motor I am using for the build. I have everything planned out except for the charger. I need one that is priced reasonably but doesn't take 20 hrs to charge...

PLEASE HELP!!!

 

[frodus]

WHAT kind of laptop cells are they? Lithium cobalt?

 

[Spider-man]

Yes. I can post a picture of them if you would like. they just look like overgrown AAs. Similar to the A123 cells in all of the photos.

 

[frodus]

They're a completely different chemistry and it's almost a REQUIREMENT to have voltage/temperature monitoring on your pack. These are the kind that don't take kindly to overcharging or overdischarging and can cause fires.

DO NOT charge them with a current above what the datasheet recommends, don't overcharge, and don't overdischarge. If they get hot, discontinue charging immediately. You might want to just use the original laptop charger for these.

Now, a 12-24V pack, going to an inverter, I assume you're wanting to use a single phase AC motor and a normal 12-24V to 120VAC inverter?

1phase ac motors have very low starting torque, so you'll run into that issue.

 

[Spider-man]

I am actually not sure if my motor is single phase or not. I ran it with a voltage regulator to test it out and it has a lot of power. Granted it had no load, so I kept it at a low voltage, but it still seemed to reach its max speed in a short amount of time. it maxes out at 8Amps I believe so that should be plenty of power to get me to 50 Mph with 120v.

I have thought about using a laptop charger but there will be a lot of batteries hooked up in parallel so... it may take a long time to charge with only a laptop charger...

I know a higher voltage is better so the closer to a 24v pack I can get, I definitely will strive to do so. Do you think maybe a charger that only charges to a max voltage of 20ish with a cut off would be sufficient? I might be able to build my own charger but if there is one out there that would work, I would rather have that.

 

[frodus]

Easy way to tell if it's single phase or not. Does it have 2 wires (not including ground)?

Now when you say 24V, talk in cells in series. Are you thinking 6 in series? 8?

20volts will not charge a 6 or 8 cell pack.

 

[Spider-man]

apparently I have a lot to learn...

I plan to have individual battery packs consisting of batteries placed in series and parallel. (6x20 for example) so it will make a pack act like one battery of 24v at 40 Ah. <-- this is just for an example. I have no numbers set in stone yet.

So it would not be possible just to charge them at 20v? Would I have to charge it at 24v~26v ish and just cut it off when the pack reaches 80% max voltage? I don't plan to charge to 100% for safety reasons.

There are 4 contacts on the motor (2 are connected for clockwise/counterclockwise rotation) so I guess it would be single phase.

 

[frodus]

You have a ton to learn, about motors and batteries..... be careful with these batteries.....


It won't be 24V, it'll be 6s20p, with cell voltages around 3.7V and a nominal pack voltage of 22.2VDC

You won't charge them with an input of 20V... it's got to be above nominal for them to charge fully. You need to look at the datasheet for your cell, figure out what the charge voltage is, and multiply by 6 cells to get your charge voltage.

Your motor isn't likely an AC motor per se. It sounds like a Series Wound DC motor. It'll work with AC... depending on the voltage spec of the motor.

What does the nameplate say on it? Where'd you get it?

 

[Karter2]

. it maxes out at 8Amps I believe so that should be plenty of power to get me to 50 Mph with 120v. .

Prepare to be (very) disappointed !

 

[frodus]

I missed that!

8A and 120V at the motor is 960W, or ~1.3horsepower.... that's not much power and you'll have trouble getting to 50mph, if at all.

 

[Karter2]

That 960w wont even get you to 30 mph on the flat.
Throw in a head wind or a slight incline and you wont make 20 mph.
50 mph on the flat would need 5kW+

 

[Spider-man]

It is an AC motor and the reason I say it will do what I think it will is because it is over 2x the size of the engine that the moped had before.

The numbers I gave for the exact pack design were only for an example. it's not set in stone. I got the motor from a guy at a garage sale. It is similar in design to a pool motor. I have a picture attached.

I need 5kW just to get 50 mph on a moped? that seems a bit high for something so light...

 

[rmay635703]

It is an AC motor and the reason I say it will do what I think it will is because it is over 2x the size of the engine that the moped had before.

I need 5kW just to get 50 mph on a moped? that seems a bit high for something so light...

??? How do you know it is 2x the size, just by weight?>??

Also AERO trumps WEIGHT everyday of the week, the thing could weigh 5lbs but with its terrible aero it still couldn't go 50mph due to all the wind drag.

Now if you want to do something that would make me proud, build your moped into a multigeared thing with this type of fairing.
http://ecomodder.com/blog/diy-aero-fairings-honda-125cc-motorcycle-214-mpg/

Do that and keep it as light as possible and it may well get up to 50mph but it will still by VERY VERY slow to get there, much like my 5hp 2300lb minivan going 30mph.

 

[frodus]

Size of motor means little. Single phase motors don't make good traction motors. There's very little starting torque, so you'll be very disapointed. The wires inside are also fairly small, and it's likely that the windings are as well, which limits the current you'll be able to draw.

Does it have brushes? (it could potentially be a series motor, that works with AC/DC)

 

[Spider-man]

??? How do you know it is 2x the size, just by weight?>??

I am talking about size as in LxWxH. I don't know what the moped engine weighs. It is only 1 cylinder.

---------
As far as brushes go, I have no idea any other specs on it. I assumed it was AC because it says 115v and 60Hz. DC does not have a Hz rating.

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For achieving the speed I want I was just planning on using a gear ratio that would set it's max speed around 50 mph. is that a bad idea?

 

[Karter2]

Spider-man,
in addition to the above comments, i would suggest you rethink your objectives from scratch.
Do you really need/want 50 mph ?
..and what range (distance) do you want to travel between charges.?
Or are you happy to accept whatever your current components will give ? ( quite likely 20 mph max )
If your objective is 50 mph, then you need to accept that you will need a better motor, inverter/controller, and most likely a much larger/better battery.
For 50mph performance levels you will need to consider higher pack voltages than 24v in order to keep the amps at sensible levels.

There is no gearing changes that will enable a <1kW moped to get to 50 mph....unless it is downhill !

 

[Spider-man]

well the pack voltage would just be for hooking up to a high power inverter. the inverter would convert my voltage to AC and potential of 1k to 2k watts...

I guess I may have missed a zero somewhere in my math.

Ok, so back to my original question: How do I need to charge my batteries? Is there a good set of chargers out there for my battery chemistry or will I have to build one?

 

[Karter2]

Chargers are readily available for various chemistry, any voltage, any charge rate...
EG..( but not necessarily recommended !)
http://www.bmsbattery.com/18-alloy-shell
.... but that is the easy part of your build, first you need to fully understand what what voltage and capacity battery pack you actually NEED to fill your requirements for speed and range.

 

[frodus]

The motor is a bad choice for the conversion, it's going to leave you underpowered. The batteries are a somewhat dangerous chemistry choice, but doable. I HIGHLY RECOMMEND A BMS OF SOME SORT. The inverter you speak of needs to have a low voltage cutoff, otherwise you'll overdischarge the cells. If the inverter does not have one, you will NEED to get a LVC board.

Not sure how you intend to throttle the motor.... hooking batteries to inverter to motor will not work for long, you'll overload the inverter and it'll either shut down, or overheat. The motor is going to use high amps to start. You need something in between the motor and the inverter.

If you're still set on the idea, put together however many cells you can in parallel, then 6 in series and get a 6S lipo BALANCING charger. You can get one at a hobby parts store....

Something like this:
http://www.hobbyking.com/hobbyking/store/__7523__Turnigy_Accucel_8_150W_7A_Balancer_Charger.html
http://www.hobbyking.com/hobbyking/store/__5548__IMAX_B6_Charger_Discharger_1_6_Cells_GENUINE_.html
http://www.hobbyking.com/hobbyking/...0_200W_10A_6S_Bal_Dis_Cyc_Charger_w_acc_.html

 

[Spider-man]

When I say I am connecting an inverter to the batteries that is a serious simplification. I will have a cut off switch in line with that connection so I can turn it off. (rather than just stand by) I also plan to have 2 potentiometers in line going from the inverter to the motor so that one can be mounted onto the bike body and be an extra step for regulating my max power the motor will get. The second will be attached to the handle bar and be the "throttle." So I do plan to have gauges and safety regulators, but I didn't mention those just to save time.