Newbie from NZ

[Doddy]

EDIT:
One very quick question to OP - are you confident that the wiring/polarity to the battery was correct?, it's the easy way to destroy a controller if reverse connected.

I was going to suggest also adding a TVS across the motor but this article https://www.modularcircuits.com/blog...fety-features/ adds some interesting information. For reference, the h-bridge is essentially the output from the controller.
END-EDIT:

Rambling reply alert

In theory, nope, you're not missing a lot, apart from understanding the stall-current of the motor.

Before we get too involved, can I ask you to characterise how the controller failed? Did it fail immediately in a puff of smoke?, or did it fail after prolonged use? Was the motor output under significant load at the time, or just turning air through the gearbox? If it was under heavy load was the motor straining, or stalled? All this may help to understand what may have gone wrong with your first controller.

Before I forget to include this: sometimes s**t happens and a device will fail very quickly after initial power-up/test. Particularly power-devices such as those in your controller. I had this with a Seig mill brushless motor controller and a IGBT exploded within 20 minutes of operation on a brand-new mill - an otherwise expensive repair which was fortunately covered by the supplier. So, yeah, particularly with Chinese-sourced boards s**t sometimes does happen. Anyway, back to the main thrust of this reply...

The motor will often be described with two ratings for current draw (I noticed that with the earlier 90W motor). The lower of the two (around 1.5A?, from memory) would be the no-load current, and the higher value (6A?, from memory) would be the current draw under a quoted load (so many Nm... I think around 4, from memory?). Beyond that load the motor will draw more current. As the load increases, it will slow the speed of the motor and the current will increase. At the point that the motor stops (stalls) the current will be at a maximum, the stall current. That will be (significantly) higher than the rated power under load and will likely result in damage to the motor coils if power is not quickly removed. At the same time it's presenting more of a load to the speed controller which may be similarly stressed.

There's a slightly confusing labelling on the motor in the attached image, with V=12V, I=13A, and P=120W. I expect that the "P" output here is the mechanical output power at the rated voltage, current and RPM, somewhat lower than the computed 12*13 = 156W and the ratio to the rated power indicates the motor efficiency (120/156 = 77% efficient). Be warned, there will be further losses through the gearbox.

What you can do is measure the resistance of the rotor winding of the motor isolated from any supply - i.e. just on the bench-top. This is likely to be a rather low number of Ohms, but if you can measure this then that allows you to calculate the stall-current (it's essentially I(stall) = 12V / R(static)). This would tell you the maximum possible load that the motor would present if you stall it... or on start-up. Normally, of course, the motor would quickly come to speed and the current drawn would drop from the stall-current to the current appropriate for the mechanical load presented to the motor. For this reason a poorly designed, or under-specced speed controller may fail at the instant of turning the motor on. But, it must be expected that the motor has to start from stationary position in all but a few cases, and the speed controller should be designed to handle this instantaneous current surge.

So, the controller that failed is described with two primary ratings, a Voltage range 0-55V and a Current rating off 60A. Read through the advertising blurb and immediately you find that the 60A is a peak rating, and the continuous rating is 40A. So, a little bit of optimistic headline advertising there - to all intents that controller would be designed for 40A operation. But that doesn't explain the failure. What you might uncover if you stripped the controller down is that the rated current capacity is that in the manufacturer's data sheet for the power control devices (the output MOSFETS, or whatever devices are chosen), whereas the rest of the design could be poorly designed (for example, PCB traces could be too thin [localised heating, vaporisation of the PCB foil], inadequate heat sinking [the power devices would get too hot under load, overheat and fail], or inadequate protection from back-EMF from the motor [with PWM drives the motor will generate large voltage spikes which can damage semiconductors if not clamped]). All this comes under the banner of fitness for purpose. And, without wishing to appear too xenophobic or casting stereotypes, Chinese advertising. But, let's not kid ourselves, most of the electronics will come out of China and we, the consumer, drive the quality down by the price we want to pay.

Enough of the hypothesis, posturing and blame. Let's get practical.

I'm surprised that you managed to burn out the controller, but possibly not for the reason that you might expect. I'm going to throw some random numbers together to explain why...

*** ALL NUMBERS BELOW ARE PLUCKED OUT OF THIN AIR FOR EXAMPLE PURPOSES ONLY ***

Let's make a bold assumption on that motor. Rated 12V, an average of 12A, I'm going to make a rough-arsed guess that the rotor resistance (including brushes and terminals) comes out at 0.5 Ohm. That would give you a stall current of 24A. Still way below the maximum current that the controller is advertised as capable of sustaining, even under the stalled (or starting) condition.

But, the motor is only one component in the whole drive chain here. We need to consider the internal resistance of the battery, the resistance of the cable from the battery to the controller (both positive and negative supplies) and the resistance of the cable from the controller to the motor (again, both lengths). And in amongst that lot, the resistance of the terminals/connectors being used, and the internal resistance of the controller. Some not unreasonable numbers....

R(motor-stalled) = 0.5R
R(bat) = 0.05R
R(2m cable) = 0.2R. Imagine that you have four such lengths - source/return battery->controller, and controller->motor
R(controller) = 0.15R
R(terminal) = 0.0 - unrealistic, but it's just drawing out the numbers unnecessarily a this point

Your overall resistance would be 0.5 + 0.05 + 4x0.2 + 0.15 = 1.5R, and so the current draw from the battery would be 12V/1.5 = 8A (thereabouts). Definitely well within the advertised rating of the controller.

Further, you might expect the controller to be suffering under the short-load of 8A at 12V (around 100W of dissipated power), but it's not. Because of the internal resistance of the battery the battery terminal voltage has dropped...

V(terminal) = V(cell) - I * R(bat) = 12-8*0.05 = 11.6V

and then you have the voltage drop across the supply wires to the controller...

V(controller) = V(terminal) - I * R * (R(2m cable) * 2) = 11.6 - 8 * (0.2 * 2) = 8.4V at the controller, so the maximum power dissipated by the controller/motor/cables-between-these would be only 8.4 * 8 = 70W.

What I'm getting at here, is that with low voltage, high current designs, you get significant parasitic losses throughout the system that tend to degrade the performance significantly but in the same breath tend to be self-protecting.


I'm rambling now, and not coming to a conclusion...

My thoughts are with the advertised controller and motor, on paper they should work fine, and you've either been unlucky with a unit destined to fail due to manufacturing flaw, or that its design is either flawed, or underrated for the advertised specification. I'd approach the Chinese supplier for a refund or replacement.

For the new controller and motor... tread with caution. If you use a long supply wire from the battery to the controller (increasing the resistance) you should introduce a level of protection that you can use to test, and then start to reduce in length as you gain confidence that the controller isn't overheating etc, with the motor under load. Ultimately you do want that cable length to introduce as low an electrical resistance as possible to allow you to attain the power through the motor that you expect.