New guy with question about over-Volting vs the magic smoke

[Watermelon Wine]

Hello all!

Paul from Australia here, pretty new to the electric scene but definitely a convert!
So it's a bit of a long story, but background info can be important for understanding intended use...

Maybe 6 or 7 years ago I went to China to catch up with some friends from earlier times. (Shaoguan, Guangdong province)

Whilst there I bought a brushless hub motor (48V 800W) and controller (48V 600W, the only one they had available). (You can see it starting to go off the rails already...)

In the shop they asked 'what size wheel?' ...I knew I wanted torque so kept asking for smaller and smaller, eventually the light struck someone's eyes and they appeared with a scooter motor with a 10" rim welded directly to the 9" magnet ring. When I saw it my eyes lit up too and it was; "Sold!"

When I got home I put it in a 26" soft-tail pushbike with the front wheel still at 26"... It looked terrible but performed better than expected. From there it went into a dead 125cc pitbike frame with 4x 12V 7Ah "alarm batteries" with the little 6mm spade terminals Surprisingly, I was still happy with it and used to tootle a few hundred yards back and forth down the street to my friends' places. Range on flat ground would have been about 2 kms.

My wife and I had kids and bought a farm out of town with an average gradient of about 5:1. ...That's when I started doing really terrible things to it like riding straight up the hill with a flat battery until it stopped and the controller stopped giving me power, (all you have to do is let the throttle off to 0% aim 45 degrees off the slope to get started and you're good to go again... :wink: :lol: )

Anyway, I got sick of it, decided I wanted to convert it to a mid-drive to take advantage of the joys of adjustable gearing ratios and put it in the lathe to chop all the unnecessary bits off. Halfway through the conversion I got busy with other things and it gathered dust.

That was a few years ago and I've now learnt a little bit more about electricity via investigations into running an off-grid solar power supply in the shed that's on the farm. (8kW continuous, I can weld with it! )

After thinking about how to solve some of the problems I had created for a few years I recently got back into it...
Here's where it's up to:



To keep everything strong and straight, but still allow servicing, I ended up buying a 20-19mm (id) collet from an ER32 collet chuck and turned the 8 degree and 30 degree cones required to clamp it onto the shaft.

If I had have had any sense at all I would have bolted a 30 tooth back sprocket onto the side of it, run it to a 50 tooth, and been done with it. Having done it the hard way however, I now have the ability to drive a lot more things with it... The top shaft is from the original motor and will be used for the first testing, but the bottom shaft is a 'precision' ground 20mm straight hollow shaft with an ER20 collet chuck already in the end of it. ($11 on eBay) This, I'm hoping, will let me power all manner of prop shafts for boats/canoes/catamarans/lawnmowers/milling machines/whipper-snippers etc. just by choosing the collet that matches the shaft.

After having had so much time to think things through, I've realised that using any 'normal' sort of motorcycle gearing will leave me travelling slower than walking pace and drawing absolutely zero amps. To combat some of this, (but still keep the torque increase I was hoping for) I've bought an 18T front and 37T rear sprocket. This should let me climb trees, at around walking pace, whilst still drawing nearly zero amps.

This would keep me happy, but 20-30km/hr top speed of arm-stretching torque would just add that little giggle factor. (My last two motorcycles were the GSX1400 and ZX12R, neither of them required much use of the little gear-shifting thingy...)

So! My questions: (Does anyone know the name of this type of motor?!? It is dot matrix printed: "BC48V800W1106085")

I understand kV, (even though I don't know what the kV is for this motor) and would like to make it go around faster! Just how many volts can I send through a motor such as this before I run into limitations? Some of the limitations I can see (through using the search function) might include; the ability of the controller to switch fast enough, spark jump for lack of insulation properties, simply frying it from heat, which I can understand, and many other things that are well above my head to do with efficiency losses through back EMF, eddy currents etc.

What limitations will I crash into first? Is it only amps that causes heat? wattage? some combination of the two? Can increased voltage, (without increasing wattage, thus reduced amps) EVER cause heat?

No doubt I could have saved a lot of work by buying a bigger controller a few years back, at the moment I'm looking at buying something like this: (Wide voltage 48-72V 1500W)

http://www.ebay.com.au/itm/48V-72V-1500W-Electric-Bicycle-E-bike-Scooter-Brushless-DC-Motor-Speed-Controlle-/201744222866?hash=item2ef8e48a92:g:cOkAAOSwnHZYSgT-

There seem to be two types, one with a voltage selector, and one without. Is there a difference? Should I shunt-mod this one? Should I shunt-mod my old one?

Should I cut cooling slots in the rotor bell?

Eventually I can see that I'm going to smoke this motor and re-wind it, and that's okay. I'm even considering building a whole new rotor with stronger magnets, more steel, and smaller air-gap (or whatever you guys recommend! :lol: )

Help me get the smoke out of it.

School me.

Cheers!

Paul.

 

[LewTwo]

Someone else can probably offer a better, more technical explanation but from my limited comprehension:
. Pressure (voltage) = Speed
. Current (amps) = Power (aka torque)
. Work (watts) = Heat (amps * volts)

Most common ebike motors today are rated at 36 volts but many people push them to 72, 96 volts or beyond. The controller (as its name implies) limits the voltage and amperage that you can send to the motor. Electronic components have limits to the voltage and amperages that they can handle. You will find that 48 volt controllers generally have 64 volt capacitors. While you can modify the shut (reduce the resistance) in your controller the FETs also have amperage limits beyond which they will blow up. Per what I have read some older controllers had difficulties when the motor pulse frequency got too high but that problem has largely been eliminated in the newer designs. There are higher end (more expensive) controllers that allow you to program the voltage and amperage limits. Some of these allow you vary timing parameters as well. The one that comes to my mind is the Grin Technologies "Phase runner". it also has provisions for adding heat sink capacity. I believe the Infineon units sold by EMV3EV are also programmable (see links below). The ones that you find on EBAY are a 'crap shoot' because everything depends on the quality of the documentation and/or support. Frequently both of these are non-existent and in rare cases they are both excellent. Best course of action is to ask the vendor to send you a link to the documentation. If they fail to do that or the documentation is inadequate, then move on.

The amount of power that you can push through a given motor depends on how much heat it can dissipate before damaging the windings. Some people have increased this by boring holes in the case and even by adding small fans to increase the airflow. Others have sealed their motors and filled them with liquid coolant.

Best of luck

P.S.
That motor resembles a scooter motor that Goldenmotor used to sale. Their programmers are also programmable but their archaic software requires MS Windows (and is really designed for Windows XP) which is a total deal killer as far as I am concerned.

Grin Technologies "Phase runner": http://www.ebikes.ca/c-phaserunner.html
EMV3EV Infineon controllers: https://em3ev.com/shop/?product_cat=ebike-motor-controllers
Goldenmotor: https://www.goldenmotor.com/

 

[amberwolf]

The motor itself doesn't have a practical voltage limit (200-300v lower limit for the winding insulation, maybe; you wouldn't wanna be dealing with a battery that high voltage anyway).

So your practical limit is the gearing ratio vs kV of the motor and the price of the controller and battery you need for the higher voltage you want to run it at.

 

[Watermelon Wine]

Thanks for the replies guys! I'm pretty confident now that 72V isn't too over the top for a version 2.0 :lol:

...and that the gear reduction should keep the heat at bay for a while... that is until I start sneaking the gearing back up!

Any controller I get will be competing with this one:
View attachment 1

One of my DIY over-volting experiments included putting 24 Volts through this little bad boy, with the intention of making a tiny electric motorbike for the kids to play on.


At 24V it spun up to, oh, about a million...
Would it handle 48 do you think? (12V DC brushed motor)

I'm still not confident that I understand the heat thing, most of the things I've (very slowly!) figured out about carrying energy around the shed points to the same amount to work (watts) being done with far smaller cable if the voltage is increased...

Of course, smaller cable isn't necessarily the same as heat, but adds to my confusion...

For example, in the early days I thought I wanted to run a 12V DC 'backbone' system through the shed to run lights, until I discovered that I would need $1000 worth of copper cable to run 10x 10W lights... Now, a few years on, I can run a welder drawing 3kW+ through 2.5mm^2 (about 13AWG) but only at 230v AC 50Hz. The amount of copper required to run the 100W of lightbulbs reduces to the thickness of a human hair...

BUT! There is a change from DC to AC thrown in there to confuse matters...

What am I missing?!? :|

 

[amberwolf]

What am I missing?!? :|

Work (watts) = Heat (amps * volts)

thus:
increase volts, decrease amps
decrease amps, decrease wire size

 

[dogman dan]

Pretty clear to me that that motor core is a generic 28mm wide magnet motor, commonly called 9 continent type, but also made by about a zillion other factories in china.

Its practical limit for very reliable use is around 1500w, but pushing it to 2000w tends to work ok. At 3000w, typically meaning a 72v 40 amps controller, it runs real nice, but will tend to overheat if pushed hard for 40 min or so, or about 10 miles. In winter, let er rip at 3000w works fine in the cold air. In summer, you can risk melting it down.

But since its in that tiny wheel, it will take more, the above is for 26" wheel bikes. My own experience has been that drilling a few very small holes in the cover will let you smell when its really hot, and back off. Bigger holes often used to cool it faster, but many things tend to make that work less than you may think. It WILL definitely help the motor cool faster once you stop, and convection cooling can really start happening. This helps for sure, because often when you stop, the motor will keep climbing in temp. With the cooling holes, you burn up hall sensors less often. But again, a few tiny holes lets you smell it when you are stopped, and stop before that happens. Ride a bit, take a short stop for a sniff, ride some more. As it heats, you will smell hot motor. Stop before you smell burnt.

 

[Watermelon Wine]

Cheers for the info Dan!

I've heard of a 9C motor, but had no idea what mine might actually be.

I had a closer look at the windings in it and there are *approximately* 6 turns of 8 strands of .64mm (appears closest to AWG# 22) in star/wye (ends twisted together) configuration.

I tried the multimeter between the three phase wires and came up with 1.1 ohms resistance between all the phases. (Not sure what this means... this is about where my understanding of electrickery currently ends... get it!?! ) I plugged this figure into an online calculator and came up with; (input) 50V 1.1 ohms = (output) 45.45 amps , 2270 Watts... but again, I have no idea what this means...
http://www.sengpielaudio.com/calculator-ohm.htm

I think I got to the bottom of the heat thing... After finding this: https://en.wikipedia.org/wiki/Joule_heating

For some reason I always wanted to simplify the formula to: Watts/Volts = Amps . ...and thus leave the heat 'mostly' tied to the amperage, (since the wire size in my motor is fixed) but eventually realised that it depends entirely on which aspects of the system one views as 'fixed', a controller fixed at a voltage is certainly as valid, and ties the heat quite correctly to the wattage as expected.

I choose to blame it on my OCD! :lol:

As far as cooling goes, I was sort of planning to keep one side of the motor open, as per the hobby king 'donkey' that looked like a good idea at the time... So should be able to smell the trouble brewing!

The first time I assembled the motor, the magnet ring managed to find (and attract) every last piece of ferrous swarf that had worked its way into the windings of the stator, which made a horrible grinding noise and made me doubt my machining skills... (Two hours of 'tweezering' later... )

I wondered about putting an air-filter type mesh-screen thing over the vents, but I'd better get it running before I worry too much about the minor details!