Simple BLDC controller

[Jeremy Harris]

It'd work OK, gwhy, but getting short gate drive connections might be challenging. The gate drives are as challenging as the power bus when it comes to getting good signals with as little ringing as possible, as the driver is trying to charge and discharge the gate capacitance as quickly as it can. I've got the gate drivers just about as close to the gate connections as I can get them, although even then I've got track length that are a bit longer than I'd like (the track length from the driver to the gate resistor is around 16mm). The gate drivers are on the power board, rather than the brains board, for this reason. Using a multilayer board would allow your option to be used fairly easily, perhaps, with surface mount drivers on the top layer. (Edited to add: I see Ricky came to the same conclusion and posted while I was scribbling this!).

I doubt my layout is optimum, but it seems to be OK and allows room for distributed commutation capacitors (which take up a lot of the board real estate) which is probably better than having then grouped at the ends of the power bus.

Jeremy

 

[gwhy!]

This was my thinking. It would be possible to put the gate drivers onto this board, but I was thinking on the bottom layer, The caps can be spaced along the bus bars on the top of the board, I was also thinking using 1or 2 mm copper bar on top of the top layer copper. Thanks guys for the input I may just have to put it together and give it ago..

 

[Jeremy Harris]

One option I thought of, using a layout a bit like yours, gwhy, was to use a couple of big copper bus bars (maybe 20mm x 3mm) to both clamp the FETs down and form the power bus, then just have a circuit board down the centre, with the drivers on it.

Jeremy

 

[MitchJi]

Hi,

It might be a good idea to design the boards to fit in a specific case or enclosure. Gary and Richard's BMS is designed to fit in "Hammond extruded aluminum boxes".

I'm not sure which size or model they are using, but something like this:
http://www.alliedelec.com/search/productdetail.aspx?SKU=8061513

Enclosure; Extruded Aluminum; Watertight; IP65; CLEAR, 3.15 X 2.32 X 1.21 - $16.57 (Each)

This heavy-duty watertight aluminum extruded enclosure is IP65 rated and designed for tough environments. House your P.C. boards for equipment interfacing by sliding horizontally into internal slots extruded into the enclosure body. End panels are rugged, yet easy to machine and are black in color. (Flanged versions also available - please contact your local Allied sales representative).

Key Features:

• • Watertight - Heavy-Duty Extruded Enclosures Designed to House P.C. Boards or for Equipment Interfacing
  • Sized for Standard Eurocards
  • P.C. Boards Mount Horizontally By Sliding into Internal Slots Extruded into the Enclosure Body
  • Rugged Body Constructed from One Piece, Extruded Aluminum with a Minimum Thickness of 0.06” (1.5 mm)
  • Extruded Aluminum Body Includes a Recessed Area for Labels or Membrane Keypad
  • End Panels Are Rugged - Yet Easy to Machine - Diecast Aluminum with Full Perimeter Self-Adhesive Gaskets
  • Designed to Meet IP-65 Ratings.

Includes:

• • Two Diecast Aluminum End Panels - Painted in a Durable, Black Satin Powder Paint
  • Extruded, Aluminum Body in Clear Anodized Finish
  • Two Closed Cell Polyethylene Foam - End Plate Gaskets & Rubber "O" Rings for Assembly Screws
  • All Hardware and Self-Adhesive Feet

 

[amberwolf]

That controller looks interesting. My guess is that you're right, the upright boards do look like drivers. The hi side needs inverting, so it may be that the board with the IC on it is just inverting the three hi side drives.

I had planned to trace the circuits out, but so far have not had time. I'm pretty sure I can make this thing work again just by replacing the FETs and putting in shunts (0.1mohm x 2p), and replacing the failing caps. I just need a reason to do it, and time.

It looks as if the magic smoke well and truly escaped from this controller.

That it did. Only one of the FETs is not actually blown apart, with case pieces rattling about, and even that FET is a dead short on all three leads. The LM317 isn't blown, nor do any of the other parts on the board appear dead, except for a couple of swelling caps (which is probably totally unrelated to the FET failure). I forgot what Ianmcnally said happened to this particular controller, but I *think* it was that the bearing in the hubmotor siezed during a ride...you can imagine the next sequence of events.

They have FETs all over the place on that board. I'd be willing to bet that the gate drive rings like like crazy...might even be why this thing is burned up...

I wouldn't be surprised if the drive has that extra board on there (the doublesided one) just to help with that problem. AFAICT the reason the FETs are like this is that they wanted a shorter controller to fit some specific space, but needed more distance between the FETs on the heatsink for some reason, or else had too much heatload on one side and had to put some on the other. So it has two 4-FET phases on one side, and the other phase on the other side along with the LM317. I'm going to bet that this uneven heating causes some small differences in Rdson between phases, and possibly inefficiencies in motor operation for that reason, possibly leading to failures both mechanical and electronic later on if the differences are great. They're 75PF75 FETs I think (hard to read thru the burn marks); from what I've read a very common FET in ebike/scooter BLDC controllers.

All the "afterthought" caps across the power rails on the underside of the board are another indication that they had problems with power rail spikes after the design was finalised.

My guess is that the combination of poor layout and cheap, high ESR caps on the power rails may have limited what this thing could do quite seriously.

Probably. I never did trace it out, but I wouldn't be surprised to find that paths were mostly autorouted and not optimized, though there are some odd things on there that I don't understand the reasons for. That odd "squiggly" trace, for instance.


Hopefully seeing the flaws and problems they ran across in this design will help you with yours.

 

[BatteryMooch]

...though there are some odd things on there that I don't understand the reasons for. That odd "squiggly" trace, for instance.

Typically, a trace like that is used to adjust (slow down, in this case) the time it takes for a signal to travel between two points. This is done to equalize the time two or more signals take to travel, where one trace is long and relatively straight and the other is short so it has to be extended somehow.

Other uses for weird traces similar to that are PCB-trace antennas.

 

[amberwolf]

I've seen the antennas on stuff, but was pretty sure this wouldn't have one.

I should've thought of the delay line myself, though, as my dad used to have to do something similar with calculating out specific coils of wire lengths for old mainframe computer setups, when he was doing the layouts for the rooms, and had to make sure signals from each cabinet would reach the others in sync. That was when he was Site Project Engineer back at Honeywell Bull and before the Bull , and similar stuff back at Xerox and Control Data, etc.

 

[Gordo]

I've seen the antennas on stuff, but was pretty sure this wouldn't have one.

I should've thought of the delay line myself, though, as my dad used to have to do something similar with calculating out specific coils of wire lengths for old mainframe computer setups, when he was doing the layouts for the rooms, and had to make sure signals from each cabinet would reach the others in sync. That was when he was Site Project Engineer back at Honeywell Bull and before the Bull , and similar stuff back at Xerox and Control Data, etc.

AW;
Are you try to lay the blame for your electrocentricty at your father's feet??? :lol:

 

[texaspyro]

The squiggly trace could also be an inductor. What makes no sense at all is why it is there. It provides a tiny amount of inductance/delay... something appropriate to VERY high frequency (100+ MHz) digital logic, not a simple PWM controller.

 

[Arlo1]

I've pretty much worked out how to put together a small test dyno, so that I can do some proper load testing. I need to get some more LiPo's, too, as testing will need a fair bit of current, more than I can drive from any of the power supplies I've got.

I'm torn between using a friction brake (essentially just a disc brake with a fine adjustment on the brake force applied) or an eddy current brake. It seems that folks building small dynos have used both with success. The eddy current brake seems a better approach, as I think it'll be easier to get smooth control of braking torque using it. I have a suspicion that any friction brake is going to suffer from changes in torque as the disc/pads get hot and so need constant adjustment.

Jeremy

Hey jeremy I built a RC car dyno which is great for testing ebike stuff. But mine is only inertia. It is super easy to build and mesures power as an engine is trying to accelerate so it is very usefull info. Just a thought that you could build a inertia dyno and add a brake to that....

 

[Alan B]

A water pump might make a good load. Easy to regulate the actual load with a valve. Lots of cooling capacity with a 50 gallon bucket full. Measure temperature for a rough energy estimate.

 

[Jeremy Harris]

Hey jeremy I built a RC car dyno which is great for testing ebike stuff. But mine is only inertia. It is super easy to build and mesures power as an engine is trying to accelerate so it is very usefull info. Just a thought that you could build a inertia dyno and add a brake to that....

Thanks for that, Arlo, very timely, as I've spent the afternoon in the workshop machining up a disc brake. In my junk pile of bits I found a 120mm diameter disc brake from a pocket bike, so I machined up a hub to mount it directly on to a 12mm diameter shaft. This will fit directly on to the Colossus/Turnigy shafts. To take the caliper, I made up and arm with a 12mm bearing that slips over the remaining length of motor shaft. To this I've added a cable hooked up to an old friction type dérailleur gear shift, the sort with the adjustable friction knob in the centre. This seems to work well, I can wind up the friction and use the lever to make fine adjustments to the brake pad pressure.

Next I just need make up a mounting plate for the motor plus a load cell to fit under the disc caliper arm and measure torque. I can measure rpm using the Hall signal, so when hooked up to a power meter I should be pretty much ready to go. I've ordered another 12off 5S, 5Ah packs so that I can deliver enough current whilst testing.

I did look at making an inertial dyno, but I need to be able to get around 10N-m of torque, which meant using a pretty big/heavy flywheel. It turns out that I'd need a flywheel with a moment of inertia of at least 0.05 kg m² to be able to get a reasonable acceleration time. I wanted to make sure that the flywheel moment of inertia was much greater than that of the motor to get a better chance of getting a decent measurement, and to cut down on the jitter on the instantaneous angular velocity measurement. Unfortunately 0.05 kg m² equates to a pretty big and heavy steel disc, bigger than anything I had lying around.

A water pump might make a good load. Easy to regulate the actual load with a valve. Lots of cooling capacity with a 50 gallon bucket full. Measure temperature for a rough energy estimate.

I did seriously look at making a water brake, too, as they are fairly easy to build. Essentially the classic dyno water brake is just a very inefficient Pelton wheel water pump, where you vary the load by varying the level of water inside the pump housing. You do need to keep the water temperature fairly constant, though, as its viscosity changes with temperature, altering the braking effort as it warms up. I also looked at making an eddy current brake. There are some examples on the net of ones that people have made for testing model engines, using alloy discs and arrays of neodymium magnets on movable arms. If the disc brake isn't smooth enough then I plan to have a go at building an eddy current brake instead.

I'm out tomorrow, so it'll be Thursday before I get back to making up the load cell etc. I've dug out some strain gauges from the spares box and have a few of INA122 instrumentation amps somewhere, so all I really need to do is work out the dimensions for a load cell that will measure up to about 100N and get machining.

Jeremy

 

[Thud]

Jeremy,
I would love an afternoon to ferrit around in your junk boxes LOL!
I bet you have some cool stuff.
(of course everyones stuff is cooler than the stuff in ones own "junk/someday" project boxes)

 

[Jeremy Harris]

Everyone else's junk is ALWAYS much better than the stuff you have yourself, it's an immutable law of the universe............

Anyway, here's a photo of the disk brake and moment arm mounted on the Colossus 7kW motor:


Not a lot to show for the best part of an afternoons work..................

Jeremy

 

[liveforphysics]

Did you get the calipers torque arm mounted in freely pivoting way so you can use a load-cell to brace it and get torque readings?

 

[Jeremy Harris]

Did you get the calipers torque arm mounted in freely pivoting way so you can use a load-cell to brace it and get torque readings?

Yes, the arm is pivoted on a ball race fitted to the motor shaft. This means that the torque arm will measure both the brake torque and the bearing drag, so it'll give a true reading of total torque applied to the motor shaft. I'm going to leave it floating, just constrained by resting against the load cell, so that I can't accidentally introduce any other forces to it (side loads, for example) that might hinder free movement.

Jeremy

 

[bigmoose]

Jeremy, I was starting to look at an automotive alternator rotor as the field generator for an eddy current dyno design. Basically allow the test motor to spin an alloy cylinder around the rotor, vary the energizing current to the rotor, and measure the reaction torque of the rotor...KF helped me start to understand FEMM to analyize the magnetic circuit, then my wifey who is a professor at a local college asked the engineering department if they had a motor dyno... I received the loan of the following for a few weeks to play with. I think it will be under-rated for our uses in speed and power however. I don't want to return it with the rotor shattered!

But it might give some ideas for others who may attempt to build one. Simple generator caged with open ball bearings, the reaction torque is measured with a reaction arm, a deadweight and a simple spring scale.
View attachment 1

 

[liveforphysics]

Did you get the calipers torque arm mounted in freely pivoting way so you can use a load-cell to brace it and get torque readings?

Yes, the arm is pivoted on a ball race fitted to the motor shaft. This means that the torque arm will measure both the brake torque and the bearing drag, so it'll give a true reading of total torque applied to the motor shaft. I'm going to leave it floating, just constrained by resting against the load cell, so that I can't accidentally introduce any other forces to it (side loads, for example) that might hinder free movement.

Jeremy

Perfect. Knowing you're brilliant, I figured you would, just wanted to make sure.

 

[liveforphysics]

Jeremy, I was starting to look at an automotive alternator rotor as the field generator for an eddy current dyno design. Basically allow the test motor to spin an alloy cylinder around the rotor, vary the energizing current to the rotor, and measure the reaction torque of the rotor...KF helped me start to understand FEMM to analyize the magnetic circuit, then my wifey who is a professor at a local college asked the engineering department if they had a motor dyno... I received the loan of the following for a few weeks to play with. I think it will be under-rated for our uses in speed and power however. I don't want to return it with the rotor shattered!

But it might give some ideas for others who may attempt to build one. Simple generator caged with open ball bearings, the reaction torque is measured with a reaction arm, a deadweight and a simple spring scale.
View attachment 1

Very cool Dave! Throw the big Turnigy motor on there and see how deep you can embed parts of the rotor into the case.

 

[Arlo1]

Did you get the calipers torque arm mounted in freely pivoting way so you can use a load-cell to brace it and get torque readings?

In his responce to me he says he did!!

Very cool Jeremy!!! Simple and a food scale will give you readings if wanted!

 

[Alan B]

Looks like a good approach, Jeremy. Can that disk take 7kw for long?

 

[MitchJi]

Hi Jeremy,

Not a lot to show for the best part of an afternoons work..................

I don't think I know anyone else who could build most of a dyno in part of an afternoon, using parts from their scrap pile.

But thinking "not a lot to show" gives some idea of just how capable you are.

 

[Jeremy Harris]

Thanks for the kind words, folks. I'm with family most of today, so won't get a chance to do any more work on the dyno until tomorrow.

I doubt that brake disk will take 7kW for long, Alan, but it should be OK for short bursts at that sort of power level. It shouldn't take long to take a reading, then the brake can be let off to let it cool down a bit before taking the next reading. My guess is that the brake should be up to absorbing quite a lot of power for short periods, based on the amount of energy that a bike disc brake can safely absorb without overheating.

Thanks for the info on the "proper" dyno, Bigmoose. I have a couple of old car alternators lying around and might look at using one as a brake if the disc doesn't do the job.

Jeremy

 

[markcycle]

You guys have given me some good ideas on how to get my Dyno calibrated. It's been so long in this uncalibrated state that I've stop calling it a Dyno and just been calling it a test load fixture

 

[otas]

Nice job, Jeremy!

What software do you use for layout?

Thanks, Alan.

You probably need to be sitting down and promise not to chuckle, but the layout is done by hand, using an old version of Autocad (Autocad 2000) that I'm just used to working with for other mechanical stuff. It didn't seem worth going through the learning curve with another package when I have around 25 years invested in Autocad's quirky user interface, although I'm sure some of the other packages, like Eagle, would do the job more quickly and with less errors. I keep promising to sit down and learn to use Eagle, but it does things so differently to Autocad that I end up just reverting to what I know through impatience to get something done. There's also something therapeutic about doing manual track layout, like solving a good crossword puzzle.............

Jeremy

Jeremy, my confession: I used the MS Publisher in the past!!! more reason to chuckle, but I have reluctantly learned the EasyPC using it in manual mode, which I find reasonably user friendly and therapeutic. I have been using the laserjet method iron on PCB prototype manufacture, but using the acetate film. I succeeded only on a small PCB's, and I had a problem with the film sliding on the PCB and peeling off the toner from the PCB, so I had to do a lot of retouching with a felt tip permanent marker pen. I am grateful for your mention of the coated paper method and soaking it off. I will try it soon, if I have the right inkjet coated paper.
Happy New Year!
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