Anyone tried running a RC low-Kv 6374 or 6354 motor on 12V?

[turbo1889]

Would like to do a build using a 12V power system running off of 4s LiFePO4 prismatic cell pack (3.2V per cell = 12.8V). Reason being that then I could direct wire big bright full size LED tail lights, bright LED 12VDC track light bulb(s) as head lights, and maybe even a horn directly to the main pack without a DC/DC converter for reliability (lots of night commuting where I take the bus with the bike in the rack to work and coming home late at night with no bus available) not to mention the ability to charge off of any 12V power source and use a lead acid type 12V battery charger (like available in the shop at work) on the lowest charge setting to top off the bikes battery.

So, Anyone tried running a stock wound RC low-Kv(130-200) 6374 or 6354 motor on only 12V? RPM's should be low enough to only need a one step gear reduction to reduce to mesh with the main drive chain and synchronize with pedal power. The specs. on some of them say that that they can go down to 4s Li-Po cells which would be 14.8V (3.7V per cell = 14.8V) so is dropping another 2V below that enough to brown out to burn out or should it be good to go? Plan would be to use the new CA to provide throttle signal to an RC brush-less motor controller and to limit current down to a max of 40-50A or so and run as a 500-600 watt mid-drive. Probably do a simple contact button throttle and program ramp up and ramp down in the CA to smooth out the on/off simplicity (which is all I need for a low wattage low voltage set-up since I pretty much use my current low wattage bikes as basically on/off for the motor assist).

 

[Whiplash]

Hmm interesting idea. I wonder if it could work? Would be cool cuz you could carry a ton of ah easily!

 

[nieles]

a motor doesn't really care how much voltage is applied to the windings.

it will overheat if you apply to much current, but you stated you will limit the current. so that should not be a problem.

 

[Miles]

It will probably only be around a 250 Watts drive, though..... Unless you're aiming to drive the chain?

 

[turbo1889]

. . . Unless you're aiming to drive the chain?

Yes, jack-shaft between the crank and rear wheel sprockets. Three chain loops, one from the crank to the jack-shaft, one from the motor to the jack-shaft, and finally one from the jack-shaft to the rear wheel sprocket spool cluster with derailer for changing gears.

For example:

With a 130Kv wound 12V motor (lowest I could find for a 6374 motor) a bike could be built with something along the lines of a 13t-34t eight speed rear cassette with a 16t output sprocket on the jack-shaft and a 48t to 16t chain up-step ratio from the crank to the jack-shaft and then a 11t to 60t chain reduction ratio using smaller size 1/4" pitch chain from the motor to the jack-shaft so that when the motor is running at full power at the top of its RPM range under load on 12V (1500-1600 RPM) and the rider is pedaling at a pedal cadence of 95-RPM such that both the motor and rider are topped out together and in sync the resulting jack-shaft RPM would be 285 RPM which translates to a ground speed range of approximately 10-27 mph across the eight rear gears with 26" wheels when both the motor and rider are topped out together. Or in other words, climbing a big hill holding strong at 10mph geared down for maximum torque in the lowest gear or pulling 27 mph top end speed on the flats in the highest gear and everything in-between. For a bike with 20" wheels (what I'm contemplating) just use a 21t output sprocket on the jack-shaft to increase the rear wheel RPM to adjust for its smaller size and you get practically the same resulting speed range of 10-27 mph from lowest to highest gear on the rear sprocket spool cluster when both rider and motor are topped out together with torque multiplication in the lower gears at lower speeds for climbing hills and/or hauling/towing cargo.

As to amps at least for RC use most of the 6374 motors are rated for 90A-100A or there about and the 6354 for 70A-80A or so. So with limiting the amps down to half or less of what they are rated for in RC use it shouldn't be too much through them.

 

[Miles]

That seems ok. Running at less than 2000 rpm will reduce the air drawn through the can, of course...

Have you given up on your dual concentric BB design?

 

[turbo1889]

That seems ok. Running at less than 2000 rpm will reduce the air drawn through the can, of course...

Have you given up on your dual concentric BB design?

No, haven't given up. It's just that I've had a few close calls as of recent commuting home late at night and know that I either need to upgrade one or more of my current motor assisted bikes substantially in the lighting department or do a fresh build that is built for night time commuting and is the best lit up thing on the road that is better lit up then cars are with just as good of lights if not better then full size vehicles. That means a lot of watts of light especially in the headlights and unless I use automobile 12V technology that also means a lot of money. Yes one could use a DC-DC converter to pull power from the main pack and convert it down to the lower voltage but that adds expense, weight, complexity, and an additional failure point that could literally leave me in the dark. Could pull power from just one 12V section of a higher voltage series pack but that leads to an unbalanced pack especially when pulling a lot of power for accessories and using a drive motor on the lower end of the power scale both working together to making the unbalancing significantly higher on the margins, or I could carry an additional 12V pack to run just the lights seperate from the motor pack but then I have the extra weight and don't have the flexibility to pedal only for everything but the uphill sections and use only a minimal amount of the main pack wattage for the motor drive and save most of it for the lights on a longer then normal ride at night.

The best solution as far as I can see is to figure out a motor set-up to drive at 12V with the entire system being a 12V system (actually 12.8V since I'll probably use a 4S3P prismatic 20Ah LiFePO4 pack set-up. I've already located multiple controllers that can do the job at the lower voltage and higher amp levels. The real stickler so far, the monkey wrench in the plans has been the motor. Finding an appropriate motor that will run an e-bike on 12V at the wattage level I'm looking for has been the problem.

However, I was able to locate a year old thread in another sub-section of this forum which may hold the answer and be a better option then using a 6374 at the bottom of its voltage range:

http://endless-sphere.com/forums/viewtopic.php?f=30&t=42377