Lawn Tractor - questions about controllers

Hey everyone, I've about finished converting my Snapper mower to electric. It's propelled by a 24v battery+motor and 1000w controller. Nice lifepo4 battery, and solar charging.

It's just about ready for paint..... Except...

The weak point is the controllers. For the life of me, I can't find a decent controller that won't burn out. My motor, batteries, wires, etc are all fine (not hot). But every controller I get burns out. Some even "burn out" with the circuit closed, so the mower just keeps trying to go forward until I turn it off. Sometimes sparks shooting out of the controller, lol. No joke. I haven't blown my 100a fuse..... Yet.


Here's some ideas I've had:
- Find ways to cool the controller? Fans? Liquid cooling like for a pc? But I don't think it'll be enough to cool the inner mosfet or whatever is generating the heat.

- Go with a contactor. Would this make acceleration too jerky? I have a 24v 40a and 80a contactor here... I mean I could test it, but I've never used one on anything that I ride. I could also do a contractor and add in variable speed with pulleys or something but I've never done anything with belts/pulleys yet.
Edit: top speed with these controllers is 5-10 mph? Like jogging speed. Maybe too fast for mowing using just a contactor (?).

- Dual motor, dual 40a controller. Dead axle with 2 single drive wheels. Maybe this will help take the load off the single controller?

- Golf cart controller? But they're usually super high current from that I've seen. That and my battery cells are made for 115 amps (?) with a 100a fuse, 100a BMS. I guess I could go with a 2nd battery in parallel (2nd BMS)?? This option is probably the most expensive, by far.

Any tips or ideas would be great.

PS. If you're curious about budget (like most EV groups are), I'm way beyond my original budget now, HAHA!!

Brushed motor? If so, it's not uncommon for them to fail stuck-on. (common FET failure mode from overheating or from overvoltage (brush or switch arc, etc, or flyback (like regen) voltage from motor coil voltage collapsing at shutoff).

What specific controllers are you using?

How much current does the system actually draw in use? (usually very little when not loaded, but can be quite high during mowing, especially if the same motor drives the wheels as the blades). If you haven't measured this, and don't have an ammeter or multimeter that goes up to at least a hundred amps, I recommend getting a wattmeter to do so, like this type:
https://www.amazon.com/dp/B013PKYILS
(I got one but haven't used it yet; I usually use a Cycle Analyst for this but you don't need anything that complex).
and test the battery-current to the system in worst-case conditions. The wattmeter will also show you the voltage, so you can see how much it sags under load, which tells you something about how well your battery is handling the load as well. And it shows you system watts, which is a factor of the two above: max current, and max voltage (including loss from sag)




Speed: You need to use a motor that spins at the correct "unloaded" rate for the application. If you've basically replaced an engine with a motor, the motor's shaft speed needs to be the same as the engine's shaft speed was, to do the same job efficiently. If the motor's shaft speed is higher, then when it's loaded down it will be a lot less efficient than it should be, and overheat. If the motor isn't heating up then this is probably not an issue.


Contactor: You can use one to help prevent the "stuck on" syndrome, so that when a controller does fail you can easily shut it down by switching off the contactor to cut all power. You'd still use a controller in that case, with the contactor just being a power switch. The contactor does need to be rated for at least the worst-case highest voltage the system would ever see during any switching event, so at least 30vdc; higher is better (if it isn't, it may not turn off the power as the arc may continue across contacts and weld them). It also must be rated at least the worst case current under worst-case normal load, or it may overheat contacts and damage the contactor.

You could use a contactor in place of the controller, but it would need to be rated much higher than one that is just used as a power switch, because it will have to turn all of the load on and off every time you start and stop, not just in an emergency. It must not only handle same high voltage as above, it must handle worst-case current of even a stuck blade/rotor, or jammed wheel, which could be hundreds of amps (whatever the motor's stall current is), or else ensure your fusing is setup to below the contactor's rating to protect it from that.

Dual controllers--if you have separate motors for wheels vs blades, it will lessen the load on the one when the other is demanding more power, which will help each of them handle things better. But you still have to size them for the actual load on them, which sounds like it is higher than your present system has allowed for...so you still should test the actual current draw from the battery under worst-case conditions.


Golf-cart controllers: some of these are programmable to limit their current to whatever your system (battery, wiring, etc) can actually handle, but are still able to handle the load a higher demand from the motor would require.

chriswfoster said:

Hey everyone, I've about finished converting my Snapper mower to electric. It's propelled by a 24v battery+motor and 1000w controller. Nice lifepo4 battery, and solar charging.

It's just about ready for paint..... Except...

The weak point is the controllers. For the life of me, I can't find a decent controller that won't burn out. My motor, batteries, wires, etc are all fine (not hot). But every controller I get burns out. Some even "burn out" with the circuit closed, so the mower just keeps trying to go forward until I turn it off. Sometimes sparks shooting out of the controller, lol. No joke. I haven't blown my 100a fuse..... Yet.


Here's some ideas I've had:
- Find ways to cool the controller? Fans? Liquid cooling like for a pc? But I don't think it'll be enough to cool the inner mosfet or whatever is generating the heat.

- Go with a contactor. Would this make acceleration too jerky? I have a 24v 40a and 80a contactor here... I mean I could test it, but I've never used one on anything that I ride. I could also do a contractor and add in variable speed with pulleys or something but I've never done anything with belts/pulleys yet.
Edit: top speed with these controllers is 5-10 mph? Like jogging speed. Maybe too fast for mowing using just a contactor (?).

- Dual motor, dual 40a controller. Dead axle with 2 single drive wheels. Maybe this will help take the load off the single controller?

- Golf cart controller? But they're usually super high current from that I've seen. That and my battery cells are made for 115 amps (?) with a 100a fuse, 100a BMS. I guess I could go with a 2nd battery in parallel (2nd BMS)?? This option is probably the most expensive, by far.

Any tips or ideas would be great.

PS. If you're curious about budget (like most EV groups are), I'm way beyond my original budget now, HAHA!!

Click to expand...

Here the controller that I have right now. Same as my last one lol.
https://www.monsterscooterparts.com/catalog/product/view/id/19483/s/24-volt-1000-watt-1000w-permanent-magnet-universal-speed-voltage-controller/?gclid=Cj0KCQjw852XBhC6ARIsAJsFPN3VIxIX_UbrwyOa8aGaZNvIXZlgYdUwAxfRo_3Remb5TGTI9PWMOk8aAlU-EALw_wcB

I haven't measured the amps or for a voltage drop. I'll get that one you linked, but for now I'll try to get the voltage meter out and check for voltage sag.

Also my blade motor isn't going through the controller. In fact it's been unused while I'm testing.

Where is your controller mounted? Is it getting ventilation?

The link doesn't list a current limit. Their answer to a question I quoted below means there isn't likely any marking on the label for one either, and this is a *critical* piece of information required to find a suitable controller for an application.

This may mean the controller doesn't even do proper current limiting, which makes it really easy to blow up. Some brushed controllers don't monitor current flow and so cant' detect when too much is flowing, so they don't limit anything--only the throttle does any controlling of the amount of current thru the controller to the motor. Without this function, it's very easy for the controller FETs to overheat and fail--it can happen so quickly that the controller as a whole doesnt' even get hot, and when it does it is often spectactular.

There are a fair number of good brushed controllers out there, some programmable (those are more expensive). Even the simple 4QD.co.uk controllers like the 2QD are probably better designed than the cheap brushed scooter controllers. Curtis, even the old simple nonprogrammable ones, are good. (I used both of those on early versions of CrazyBike2 with powerchair brushed motors with gearboxes built in, at different times). The curtis I used was similar to this one
https://www.ebay.com/itm/134176992443
though I don't know if that is suitable for your application (it would almost certainly survive it, however.

Most of the very simple brushed controllers that *do* do current limiting are likely to be easy to modify the current detection circuit to be adjustable, if you find it necessary to get a bigger-than-needed one and turn it down. More complex ones run by MCUs may be a bit more difficult to reverse engineer and modify that detection circuit, but likely still possible. (the mods I have in mind are better and more controllable than a "shunt mod", which is another option but harder to be precise with and more difficult to keep adjusting till you get it right).

How many amps is this controller
Unfortunately, as a parts retailer we do not have access to those specifications from the manufacturer. This controller uses a 3 wire throttle. Although compatible with most 24 Volt products equipped with 600-1000 Watt motors, it is not compatible with 4-wire or Currie 5-pin or 6-pin half grip throttles.

Click to expand...

If the blade motor isn't being run by the controller yet but the controller is failing, I think you're likely to have some serious problems once you do connect it up, if it runs on the same one. I think you will have to use a separate controller for it.

Is your traction motor running at the right speed, unloaded, to match the loaded speed the system needs, at full throttle? Meaning, if you prop the drive wheel(s) up off the ground, is the wheel speed within a small percentage of being the same as when riding it? If it is a lot faster than when riding it, you probably need different gearing between them, so that the motor is kept closer to it's unloaded speed when it is fully loaded, and draws less current.

chriswfoster said:

Here the controller that I have right now. Same as my last one lol.
https://www.monsterscooterparts.com/catalog/product/view/id/19483/s/24-volt-1000-watt-1000w-permanent-magnet-universal-speed-voltage-controller/?gclid=Cj0KCQjw852XBhC6ARIsAJsFPN3VIxIX_UbrwyOa8aGaZNvIXZlgYdUwAxfRo_3Remb5TGTI9PWMOk8aAlU-EALw_wcB

I haven't measured the amps or for a voltage drop. I'll get that one you linked, but for now I'll try to get the voltage meter out and check for voltage sag.

Also my blade motor isn't going through the controller. In fact it's been unused while I'm testing.

Click to expand...

A useful article from 4QD:
https://www.4qd.co.uk/how-to-choose-a-controller/
their stuff:
https://www.4qd.co.uk/product-category/controllers/

Curtis makes a lot of the forklift and golf cart controllers, you can find them used on Ebay and the like, but knowing which one to look for is a bit harder.

Either way, I'd do the load testing to find out current draw under load (and without load), so you have some idea of what the controller has to be capable of, before buying a new one. .


I don't know anyting about any of these cheap things on amazon, but there are a number that specify they have current limiting, some of them adjustable (hackable, I'm sure, at least). The ones with pots instead of throttle connectors, you just disconnect the pot and hook your throttle in place of it (assuming you're using a pot throttle instead of hall).
https://www.amazon.com/s?k=2000W+PWM+DC+Motor+Speed+Controller%2C10-50V+12V+24V+48V+40A+Speed+Regulator%2CCurrent+Limiting+Protection+and+Over-Current+Alarm&i=industrial&crid=1551OZ2BPGJV&sprefix=2000w+pwm+dc+motor+speed+controller%2C10-50v+12v+24v+48v+40a+speed+regulator%2Ccurrent+limiting+protection+and+over-current+alarm%2Cindustrial%2C115&ref=nb_sb_noss