Power tool lithium-ion batteries for a 48V E-bike system -- suggestions?

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Forsea1491
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Power tool lithium-ion batteries for a 48V E-bike system -- suggestions?

Hello.

I recently bought a Crystalyte RoadRunner 48 volt, 20 amp bike kit, with which I converted a mountain bike. The kit's stock SLA batteries are getting to be a bother because they weigh 30 lbs.

I'm thinking about replacing the SLA's with power tool lithium-ion batteries, but I have a few questions.

1. Although my system's four 12 volt SLA's should equal 48 volts when fully charged, they actually read 54 volts when fresh off the charger. My Crystalyte motor and 4820 controller don't seem to have a problem with this higher voltage. So would I be safe in assuming that three 18 volt lithium-ion power tool batteries (3x18=54) are equally safe for my motor and controller? I've searched, but there don't seem to be any lithium-ion power tool batteries in 12 or 24 volt sizes, which would make that 48 volt total I'm looking for easy to configure. Suggestions, anyone?

2. My present batteries are rated at 10 amp hours. What configuration of 3 amp hour 18 volt batteries would come close to equalling this performance?

3. Are there better, and/or more affordable lithium-ion battery solutions for my particular system other than power tool batteries?

Thanks in advance for your help.

reikiman
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Re: Power tool lithium-ion batteries for a 48V E-bike system --

Um, a fully charged battery registers as a higher voltage than it's rated voltage. I don't understand why the "nominal voltage" for a battery is lower than the voltage you read when it's fully charged, just get used to it because that's the way things are. A fully charged 12 volt SLA battery will read, if I recall correctly, around 13.5 volts. Or maybe it's 13.2.

This general rule isn't universal, however. The DeWalt 36 volt battery packs read 36 volts when fully charged. Then as soon as any load is on them they drop to 33 volts. They're actually 33 volt (nominal) packs but for some reason DeWalt ignores convention and reports the fully charged voltage as the pack voltage. Sigh.

Controllers are built assuming the same thing, that the fully charged voltage is higher than the nominal. The other factor in the controller is what the rating of the FET's are. In the case you're suggesting the fully charged voltage for the pack might be 60 volts (or more) (3x20). FETS in a 48 volt controller might not be rated so they handle 60 volts, and could well blow.

That said, crystalyte MOTORS are known to work well at 72 volts (??or higher??) but I think you have to get an higher voltage controller.

To equal 48 volt 10 amp-hour ... well, as you said it won't exactly equal because the voltage is off ... but you'd require 9 power tool packs. They'd be done in a 3S3P configuration.. that is, three packs in parallel, with three groups of those in series. You'd have 56 volt 9 amphours.

Many of us are fond of DeWalt 33 (er.. 36) volt packs. I'm interested in them 'cause they're built using A123Systems cells.

- David Herron, http://davidherron.com/

jdh2550_1
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Re: Power tool lithium-ion batteries for a 48V E-bike system --

Hi,

1) I would expect that three 18V LiIon's when freshly charged will have a voltage greater than 54 volts. Just as your four 12V SLA's have a voltage greater than 48 volts. When discussing voltages of battery packs one is quoting the "nominal voltage" - which is a convenient figure to compare batteries by but is not the exact voltage delivered. Will the actual voltage output by the LiIon's be too high for your controller - sorry, I've no idea...
2) To increase voltage connect batteries in series. To increase capacity (amp hours) connect batteries in parallel. So, to get 54V with 9Ah you would need 3 strings of 3 batteries in parallel with one another. A "string of three batteries" means three batteries in series. Or you could make a string of three packs with each pack being 3 batteries in parallel. I'm not sure which is preferable (long strings in parallel or parallel packs in series). Does that make sense? Here's my attempt at a diagram:

This is (supposed to be) a diagram of three strings of three batteries in parallel

&nbsp;&nbsp;&nbsp;&nbsp;|- Batt1 - Batt2 - Batt3 -| <---|- Batt4 - Batt5 - Batt6 -|-------> &nbsp;&nbsp;&nbsp;&nbsp;|- Batt7 - Batt8 - Batt9 -|

This is (supposed to be) a diagram of a string three packs with three batteries in parallel in each pack

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;| Batt 1 | | Batt 4 | | Batt 7 | <----- | Batt 2 | --- | Batt 5 | --- | Batt 8 | -------> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;| Batt 3 | | Batt 6 | | Batt 9 |

In both these (bad) diagrams series connections run left to right and parallel connections run up and down. In the top configuration Batts 1, 2 & 3 give you 54v and 3Ah. In the bottom configuration Batts 1, 2 & 3 give you 18V and 9Ah.

3. If you find an affordable source of Lithium based batteries - please let me know! :-)

I hope this helps

John H.
Blue XM-2000
Ann Arbor, MI

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

jdh2550_1
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Re: Power tool lithium-ion batteries for a 48V E-bike system --

Mr reikiman beat me to the punch while I was messing around with ASCII art. :-)

David - is 3P3S better than 3S3P or vice-versa? Or does it not matter? Thanks.

John H.
Blue XM-2000
Ann Arbor, MI

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

NickF23
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Re: Power tool lithium-ion batteries for a 48V E-bike system --

Tricky voltage to make up with powertool packs. You might be better off with a purpose made ebike lithium phosphate pack.

here's a few suppliers

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3796

http://www.lifebatt.com/

http://www.falconev.com/batteries.html

http://www.skeuter.com/Foxx%20Details.htm

Brett White also sells a 48 volt lithium phosphate at http://www.users.bigpond.com/solarbbq/bikesale/bsale.htm but you have to ask for them.

reikiman
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Re: Power tool lithium-ion batteries for a 48V E-bike system --

David - is 3P3S better than 3S3P or vice-versa?

Actually I'm not real clear on what the exact difference is. I do remember on the old instantiation of visforvoltage Aerowhatt explained how, for lithium-ion, you want to put batteries in parallel, and string those in series. This way the parallel batteries can keep themselves balanced. I think he used a charger setup which charges all the batteries in parallel, and then sets up the pack for discharge as I described.

- David Herron, http://davidherron.com/

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