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could a 24v 8" hub motor scooter wheel be run off 2 18v 4ah cordless drill batteries?

if so, how long might it roll at a fairly constant average walking speed (3mph) on one charge?

example wheel: http://www.uumotor.com/250w-sensorless-hub-motor-8-inch-brushless-with-tyre-24v-36v-48v.html

example drill battery: http://www.dewalt.co.uk/attachments/productdetails/catno/DCB182/

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ambientvoid (author) 2 years ago

oh i forgot to mention that its not going to be a scooter, more of a go kart shape. im intending on using 2 hubmotor wheels (1 mounted either side of me) with castor wheels for balance, i want to end up with something like the steering of an electric wheelchair (2 motors forward for forward, 2 back for reverse, 1 forward 1 back for turn on the spot)

You may need more battery capacity.

Agreed, a second motor really pushes it.

ambientvoid (author)  Wired_Mist2 years ago

so two 4ah batteries per wheel wouldn't be enough?

Price alone, works to nearly $80us for each batt. You said 2 per wheel so, 4x80 = $320 in batteries, Ouch ! I found a local dealer selling a DEEP CYCLE 12v,70ah for $105. Just one should do fine. if you are willing to drop that much on batteries, you could buy two. call it your mobie car booster :D lol Just be sure to use deep cycle for the best results.

ambientvoid (author)  Wired_Mist2 years ago

thats for brand new, i already have 2 drill batteries and I found some with a nice low starting price on ebay which could be worth a shot. Most of the reason I'm leaning towards drill batteries is because they're fairly small and light, if you know of a better alternative that's as lightweight and compact as possible I'm totally fine with that instead. How weighty is this deep cycle battery?

The Deep cycle I looked at were 75Ah and 40-50 lbs, Each. Or a pair of sealed 12V 18Ah like this at 15 lbs each. The second should give you some decent batt life for the weight.

Wired_Mist2 years ago

A second thing to consider is Voltage / Amperage requirements. Yes you can run a 24v motor with the battery you listed, but it will turn much slower and pull more amps. I see the Batt you listed is a 4Ah. I have a old lawn mower engine that is 500w @ 24v. I had to use a pair of sealed 12v 10Ah batts in parallel. without a load, I lost significant power within a hour. Can you find the rating in Watts or amps?

Sorry to contradict Mist, but the scooter and any rolling electric machine running on a single battery will NOT Pull more current.

In fact with a single battery opposed to two, the whole vehicle will be lighter and draw even less current.

And with a single battery the motor scooter will run slower doing exactly what author wants, a walking gate. Low friction well lubricated bearings and high tire pressure are also primary effective features.

Then when you learn the range the system can deliver its easily doubled for an extra 0.61 Kg.

Check these out, let me know what you think :)

http://www.motorsanddrives.com/cowern/motorterms12...

http://ecmweb.com/design/highs-and-lows-motor-voltage

Thanks for pointing out that two batts would weigh more, I totally forgot!

Took a look at your article, here is a confusing bizarre quote ;

"when voltage gets low, the current must get higher to provide the same amount of power "

THIS IS TOTALLY WRONG !!

Only two ways to increase motor current ..... [1] Raise the voltage ..... [2] Increase the motor mechanical load ..............................

Again sorry to yell but there is lots of bad information out there :)

.

BTW Ohms law P = V x I .... or .... A = B x C

Given any simple equation like above if you decide to keep A constant while lowering B then mathematically C must increase.

That has no bearing on how a motor responds because when you lower the motor voltage you also lower the motor power and if the load friction does not stall the rotor then the current will also drop.

I'll tell you what, later today I'll set up a bench test. I have a similar 18v battery and a 24v 500w motor here, and I'll do it freespining, loaded and stalled. Could you provide an article or two for reference?

Stalled, it will take the motor resistance/supply voltage amps. Freerunning, it will run as fast as it can, before the friction in the bearings becomes signficant, and loaded, it will fall in the gap, plotted linearly, between zero and stalled. The terminal voltage of a DC motor = back EMF+ IR, where I is the motor current, and R is the terminal DC resistance. You can get picky and add a term for the winding inductance L too, so B= E+IR+L di/Dt.

+1

Excellent way to go. Not everyone knows about a bench test.

Use an easy fan load based on your machine speed.

I do like to help, but searching the net to let you believe, is lots of work.

Steve and I are the reference because we both actually did time in a machine lab back in our school days.

My references are experience and rare hardbound no longer available books.

rickharris2 years ago

Do you mean in series (36 volts0 or in parallel (18 volts but more current)

W=V * A so you can do your own calculations. Assume the 250watts to be the draw of the motor although it will be less on average. Your battery will have an Amper/hour rating. Work out the current your motor draws and use the A.hr to see how long it will run for.

iceng2 years ago

BTW at this lower speed I would by-pass any speed controller to improve battery efficiency and simply use a mechanical stop start switch.

18V * 2A = 36 Watts for 2 hours

..........................or

18 watts for 4 hours.

iceng2 years ago

How heavy are you and your scooter togethr ??

ambientvoid (author)  iceng2 years ago

the scooter doesn't exist yet so im not sure how much it will weigh but im trying to keep the weight to an absolute minimum so it can be carried fairly easily, 20kg maybe? im about 14 stone (89kg)