Brushless E-bike hub motor questions. / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Brushless E-bike hub motor questions.

previous 1 2 3 4 next

Move Thread

LAN_403

Ash Small

Fri May 01 2015, 10:08AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thanks for the input.

I can get smaller controllers in UK, just no-one has the 48V 1000W ones in stock. Maybe I should try a 24V 500W one or something?

I have read a bit on the commercially available controllers, and realise it's 'pot luck' whether I get lucky or not.

The other options are a simple logic drive (18 transistors for each wheel for each direction, 36 transistors per wheel, or a microprocessor.

I'm tempted by the transistor array. Using this I simply need to implement the chopped PWM, which is pretty staightforward, a couple of 555's would do it, or I could get more complicated.

It also occured to me to incorporate a 'smoothing capacitor' after the chopper PWM bit, to smooth the current (and give a 'ramp up' effect), If this PWM/capacitor is placed before the 'logic gate', and the relevant switches are 'open' the current will just be directed to the correct coils, with no further switching losses in the main switches.

That's the simplest solution I can think of. Simplicity equals reliability, in my mind.

I'm still open to suggestions, though, I've not made my mind up yet, and may try a few alternatives to see which works best. As long as I use plenty of suitable fuses I shouldn't have any catastrophies.

First thing is to get the wheels built up and mounted.

I'm thinking of starting initial testing/evaluation using 12V, just to see how much torque is available at 12V, then working up to 24V, 36V and 48V if necessary.

No real plan with the electronics yet, still considering all the options

Sulaiman

Fri May 01 2015, 01:22PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

the torque available from any particular motor of this kind
does not significantly change due to supply voltage,
the torque is proportional to the current.
So you can test everything except high speed using 12 V.

Ash Small

Fri May 01 2015, 05:29PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Sulaiman wrote ...

the torque available from any particular motor of this kind
does not significantly change due to supply voltage,
the torque is proportional to the current.
So you can test everything except high speed using 12 V.

I was beginning to suspect that that might be the case. Presumably something to do with back EMF?

As I don't need high speed, presumably all I need is 12V

I think some of the 24V controllers run on 12V. Maybe I should look into getting a couple of high amp 24V controllers?

I'm certainly planning on using 12V initially.

Ash Small

Tue May 12 2015, 11:30PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I ask because I tried turning one and it was pretty reluctant to turn. Would it be better to power them up during rim truing?

(EDIT: Most of this post disappeared, but Neil was able to answer before it did so, I assume)

Dr. Slack

Wed May 13 2015, 04:23AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Shorting the windings would make it hardest to spin up, loading them with bulbs would still be harder than leaving them open circuit.

Resolve the reluctance to turn before you invest in the time to build a wheel from it.

Bjørn

Wed May 13 2015, 05:52AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Ash Small wrote ...

I ask because I tried turning one and it was pretty reluctant to turn. Would it be better to power them up during rim truing?

Have you opened one, maybe it is the geared type?

Ash Small

Wed May 13 2015, 10:11AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Not sure what happened with my last post, most of it disappeared, but Neil seems to have answered the complete post.

Looks like it will be best to wait until I can power them up to build and true the wheels.

As long as I won't do any damage by spinning it up 'open circuit' I should be ok.

EDIT: I'm pretty certain there are no gears. I'm certain it was advertised as such. It feels like the reluctance you get with any other type of motor/generator, just like a stepper motor, for example. I will open one up at some point. I want to have a look inside anyway

I realised after I'd ordered the controllers that they don't support 'reverse', so It looks like I'll have to build my own after all. I can still use the ones on order to 'spin them up' and I can measure all the various voltages and currents, etc. which will give me an idea of what's required if I build one.

I've been looking at the various BLDC motor control IC's on the market, and they still scare me so I've drawn up a 'logic controller' using Op Amps, Opto-couplers and 2N2222 NPN BJT's and 2N2907 PNP BJT's. I know I need to sprinkle a few resistors on it as well, but I wanted to get the basic logic sorted first before starting to 'guesstimate' resistor values.

1431635136 3414 FT170865 Bldc Motor Controller

The six 'logic states' are three digit binary numbers between 1 and 6. I've put them in in bl;ue. You read them vertically, but that's probably obvious.

I think the 'forward' and 'reverse' bit is pretty self explanatory.

From what I've read about Op Amps, and I'm pretty sure that's what is required to amplify the Hall Sensor output, they need an isolated supply, same as the high side switches, so the simplest solution seems to be to wind an SMPS with multiple secondaries so the three high side switches have isolated supplies and the Op Amps have isolated supplies as well. I might even use the same system for the low side switches, even though this isn't necessary, just to keep everything nice and neat.

Any tips on biasing Op Amps will be greatly appreciated.

The opto-couplers seem ideal for getting the right signal to the right switch. It seems to be a completely different sequence in reverse to what the forward sequence is. Two switches, one high side, and one low side need to be on at any one time. I'm pretty certain I've got the logic covered, and six quad opto-couplers for each motor should do the trick.

If anyone can see any problems with the circuit (apart from the missing resistors) I'd appreciate any comments.

I'll post details of the three phase full bridge part of the circuit over the next few days, along with the PWM 1-5kHz driver, which will probably be based on the 556 flyback driver circuit I've been working on recently.

I'm still open to fresh ideas and info regarding alternatives. I'm not commited to any particular design yet

[Edit: Double post before 48 hour limit]

Bjørn

Fri May 15 2015, 05:02AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

You can reverse it by switching phases with a relay.

Ash Small

Fri May 15 2015, 10:21AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

BjÃ¸rn wrote ...

You can reverse it by switching phases with a relay.

Can you elaborate please, Bjorn?

Do you mean by putting a relay on each of the outputs from the controllers I've ordered (which arrived this morning), I can change output polarity from +ve to -VE?

Apparently these operate at ~5kHz.

It did occur to me to try something like this using power transistors, but wouldn't I still need the high side isolation, etc?

Or did you mean something else?....Using relays in the above schematic, for example?

I also received a throttle control this morning, so I'm pretty much ready to start taking some measurements, etc.

Am I likely to damage these 24V controllers if I try them on 12V?.....Some apparently work ok, but there was no documentation with these at all. Most of the commercially available IC's seem to run from less than 5V to close to 50V (at least high 30's), so I can't see it being a problem, but I thought I'd ask here first.

EDIT: I have three output states for each of the three motor feed wires from the controller. These can be represented as +1, 0 and -1 (+1 being a positive output, 0 being neutral and -1 being negative output). At any one time, one should be high (+1) one should be low (-1) and one should be floating (0). I presumably just need to change the +1's to -1's, then feed this information to the six switches on the three phase bridge......Or is there a simpler solution that I've missed?

Bjørn

Fri May 15 2015, 01:38PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Swapping any two phase wires should reverse the motor, easily done with a suitable relay. If you use the sense wires you need to do the corresponding swap there too.

previous 1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob