Mountfield cordless mower

[ajh]

The mower just stopped working, it has an good 80V lithium battery, a PCB which is on a substantial heat sink and covered in resin but I can make out what look like 7 IGBTs, a few capacitors and a relay. No apparent overheated or bulging components.

There is no movement when the control is squeezed and it gives out a double bleep when activated.

The 80V brushless motor cogs as one would expect, has 8 permanent magnets on the rotor and probably 7 pars of coils on the stator.

A replacement PCB is listed at over half the cost of a replacement mower at £340.

I think the motor is probably alright but cannot think of a way of testing it, It has 3 power wires and a ribbon of 7 control wires.

The Q code on the motor shows:

GGP Code:;Power:1500W;Voltage:80V;RPM min:3000;RPM max:4000;Order number:5010009578;Q.ty pcs of order:1098;Serial number:151225-U10;Supplier Code:30001334;.

I wonder if there is any chance of finding a cheap generic motor control PCB

Stiga-Mountfield-Greenworks say return to dealer (out of warranty) and dealer says it is unserviceable.

I guess I can use it as a wind generator if I can find a propeller :-)

[Theo]

Is there a microcontroller?

Any documentation to say what that means?

Have you removed the battery for a few hours/days and tried again?

Measure resistance between each pair of power wires. Should be fairly low and roughly the same. I imagine the control wires are for the hall sensors to feed back the motor position. As the shaft spins different combinations are activated:

It is unclear whether those are analogue (give out positive and negative voltages when it spins) or digital (require being powered up before they are energised, or even has some electronics inside the motor). Probing with a multimeter on voltage mode while spinning might be instructive.

Is it possible to take the motor apart and see where the control wires go?

I wonder who makes the motor? Any indications?

(digging around Alibaba for something similar-looking might be worth a shot)

Brushless DC motor controllers (BLDC) are all over ebay, Aliexpress etc. They are quite common for ebikes for example. The main issue is working out relations between the three phases and the hall sensors.

(with an ebike controller there might be a 'speed limit' due to ebike laws, but it may be possible to derestrict it)

The mower blade is a good start :-)

Theo

[The Natural Philosopher]

From model plane experience you probably have a blown controller. Motors don't usually let go without letting out a lot of magic smoke...

Are there just three fat wires into the motor? If so a model plane controller might work...

..ish there would be no sane RPM stabilisation though.

Almost certainly (some of) the MOSFETS are blown...

[Andy Burns]

A 15.5mph lawnmower might be quite exciting

(yes, yes, i know).

[ajh]

Not yet for fear of breaking it

It has: Globe 9940

381011299 80V DC 151224-U2

but a search doesn't yield much other than a site that has been hacked

Far too complicated for me, I have already fouled up the brushed motor controller for the ebike I was attempting to repair.

I don't think so, the cogging is quite strong so will need a bit of torque to overcome, then it would need to reach 3000rpm (rated speed as a motor)

[ajh]

On 18/10/2022 15:01, The Natural Philosopher wrote: r if I can find a propeller :-)

That is what I am hoping

Yes

I can probably scrape off the resin on theit three connections but can they be checked when still in circuit? The opposite side of the PCB is totally embedded.

[ajh]

I have now measured the resistance between all three power leads, about

0.5V.

Also the open circuit voltage when spun up about 2k rpm is near enough the same 26V between each pair.

[Chris Green]

I hope you mean 0.5 ohms! :-)

[ajh]

0.5Ohms

[ajh]

Yes corrected that after I posted

[The Natural Philosopher]

But I rechecked and you said there were 4 thin ones as well? Think it was 4...

I suspect that the way its constructed its gonna be a new PCB assembly.

The are reasons to encapsulate - like it still works after being rained on - that will preclude it being fixable

All in all, don't buy another mower like this as it is patently non-reparable at economic costs

[The Natural Philosopher]

Very high. Probably the resistance of the test wire. I have expected

0.05 ohms more like for a motor in that class.

I think its clear that its the controller is blown, unfortunately it seems to be a sensored one

[Brian Gaff]

I used to use hall effect sensors many years ago to make cassette auto stops work better. Most relied on some kind of rotating switch from the take up spool, but these wore out, and basically a tiny read relay operated by a hall effect sensor and a small magnet glued to the clutch made them more reliable. You listening Akai!

Brian

[Theo]

OK, so it sounds like the motor coils are OK. It's possible the hall sensors are broken, which would prevent it being able to sense motor position.

Are there any other mechanical components? eg I had an ebike motor that went into a similar sulk and had a similar potted control board. It turned out it had a torque sensor which was just a pot with a spring. The pot had worn its carbon track and wasn't reading correctly. It was easy to replace (once I'd got the part from Japan). Anything like that?

Theo

[ajh]

Nothing else that I can see, the pricing of the controller makes the mower un repairable. No loss to me but something to be wary of if one is in the market for a cordless mower but it is 6 years old.

[ajh]

Yes, sorry I missed the "only"there are three power wires plus a ribbon of thinner ones. I have re checked and the ribbon has 5 wires

That's right, it is such a shame as the rest is in very good condition. I might see if I can take the honda engine out of another one that has a rotten deck and fit that.

OR

Mount the motor and deck upside down under the honda engine and make a generator

[Animal]

Strong cogging is a deathblow for motors for wind generation. They need to get going easily.

[Animal]

You can't find a used one on ebay? And one last long shot: replacing the motor with a 240v brushed jobbie, no controller.