A123 newb...will this work?

[KTP]

Hi guys,

I would like a small battery to power a 400 watt Kollmorgen brushless motor geared down to drive the cranks at around 80 to 100 rpm. I have read a lot about the different battery types available but for a quick and dirty solution, would purchasing this Dewalt Nano 28V 2 battery + saw kit be totally stupid?


http://www.toolking.com/DeWalt_28v_cordless_reciprocating_saw_with_nano_technology_DC315K.aspx

Actually having the saw itself would be an added bonus, and I could use the flashlight base as a quick connect for the battery on the bike.

Is this a fairly good deal, and can a unmodified 28V Nano battery pack run a geared down Kollmorgen motor for a few minutes? Are the included charger and the BMS in the battery halfway decent?

I am fairly certain the Kollmorgen built in controller can handle up to 28V, and I believe the 28V Nano packs are a bit less than 28V right off the charger (from what I read).

Thanks!

 

[Electricdirtbiker]

Not a stupid idea at all. Conceptually it should work for some distance.
Besure 28v is ok for your motor and controller, they will be working fairly hard. Monitor the current.
2 or more batteries will give you more useful range and the pack will have a longer life.
The pack output wiring may not handle the current you need.
The motor is about 90% efficent, so 10% of your power will be heat in the motor windings, besure it gets out.
Aircraft motors have little mass (weight) to sink some of the heat away, its the props job, which you won't have.
If your motor is designed say 10-20k rpms. Thats a lot of gearing down to reach 100rpm. 100-200 :1 ratio.
A robust light weight gear box is a challenge to build. Do you machine or know some one?
Some model motors have light weight front bearings that are for axial loads (props), radial loads (gears) will wear out fast.
Outrunner motors are nice, but harder to apply.
The "nonhub e-bikes" form has lots more info on this.
Good luck

 

[KTP]

Oh, I guess you are not familiar with the Kollmorgen 400 watt motors. No big deal, neither was I 2 weeks ago

They are rather large scooter type brushless motors with a controller epoxied into the back plate. I think a ton of them were dumped on the surplus market a couple of years ago. I got two brand new ones for $50 each, which still seems a decent price. They look to be ok quality, probably at least as good as a chinese hub motor. I have to think they have better cooling than the RC motors which as you mentioned are meant to be behind a prop (except maybe the heli type motors?) Oh, and I believe this motor turns full speed no load at only 3500 rpm. Much slower than the RC motors. Gearing 30 to 1 should be plenty by the time there is a slight load on the motor.

28V is right at the borderline for the built in controller I believe (I seem to remember reading that somewhere). I read that an 8 cell A123 pack would be around 28.8 volts right off the charger but would quickly drop to 26.4 volts and flatline there for most of it's life. I am guessing the controller *probably* can deal with 28.8V for a few seconds (I hope). Otherwise I could drop 0.7 volts across a beefy diode or something for a quick fix. A waste of power though.

28V at 2.3AH is around 60 watt hours. So 2 batteries would give me about 120 watt hours, or running the motor at 400 watts for about 15 minutes. Enough time to do some tests and maybe get up a steep hill or two.

The advantage? I get a returnable warrantied battery and charger without having to wait 2 or 3 weeks for one to come over a boat from China and then possibly have a defect. The disadvantage? If you consider the portable saw to be worth $0, then I am paying $240 for 120 watt hours, or $2 a watt hour. I think the PING batteries everyone uses are around $1 or a bit less a watt-hour. Of course it looks like they can only deliver 2C

Argh, why is there never an easy solution that doesn't require days of research...

 

[Electricdirtbiker]

Sorry, the Kollmorgen I've heard about makes large brushless motors for rc aircraft.
400watts rating is likely a continous nominal power. Its closer to 3 x that on a hard take off, 43 amps.
My concern would be the bms fuse in the dewalt pack will pass some 15-20 amps, not sure, but its not up to 70 amps that these calls are good for.
So the more packs you parallel the less likely to blow the fuse. Sounds like you have no interest in opening the cases and adding heavier wires.

Good Luck
Wes

 

[KTP]

Thanks. Well, the big advantage to not opening the cases is you get full warranty, just send it back to DeWalt. Much easier than dealing with a company in China.

I know the A123 batteries themselves can do at least 10C if not more, so a 28V 2.3AH pack ought to be able to supply at least 600 watts. The question becomes what does the wiring look like inside the pack and are they limiting the current to some lower value. I think I read something about a 20 amp limit?

It might not be possible to do this, unless maybe you could parallel two unopened 28V packs? Unsure if they would discharge equally...

 

[Electricdirtbiker]

The packs will discharge evenly enough as long as they all get the same charge and the paralleling leads/cables to them are all the same length.
The current drain limitation is either the internal wiring or most likely the fuse. Because the packs are in parallel, if one fuse blows, the rest will follow right after, in a split second.
Using the oem charger is a huge convience.
Wes

 

[MitchJi]

Hi,

http://endless-sphere.com/forums/viewtopic.php?f=14&t=7051&hilit=+milwaukee

Tool Packs, Series or Parallel?

DeWalt Cells are better. Milwaukee packs are probably easier. Check this excellent Tutorial by Jondah:
http://mitchji.home.comcast.net/EbikeMisc/jondoh_milwaukee_howto.mp4

Also try searching for Tool Packs, Dewalt, Milwaukee, Makita and Bosch.

 

[kishigo]

If you use the flashlight as the connection, you will have to modify the circuit as the flashlight limits the voltage out of the battery to 18V. There are lots of threads on this topic out there. The battery furnishes both a switched and unswitched negative output. The unswitched one is not suitable for use as it has a built in 15A fuse. The switched one can drive up to around 20A before the BMS (onboard the battery) switches out.