Converting a Lawn Tractor to Electric Power

[surfsup]

TL;DR

48V lith battery running two 40v deck motors

So I am converting an old gas lawn tractor to electric. I have a 48v 2000w motor to drive the axle. For the deck, I sourced two 40v old Ryobi deck motors (I don't have them yet). Since my power supply will be a 48v lithium battery, I wanted to run the two deck motors off the controller running the rear tires.

I don't have specs for the smaller deck motors. They are used off ebay, so not much info is available. Looking at datasheets for the Ryobi mower there's no info on the motor aside from an item# which the internet doesn't really add much info to. So, I assume the 40V motor can handle 48V since it is designed to spin the blades. The motor does supposedly have an rpm of 2500 or 2800 (per controller) which if voltage is 48 I assume will be roughly 3000-3300rpm which should be ok.

Figuring a 20 minute run time, what do you guys think? I realize there's some assumptions here. Could I drop the voltage on the line a bit with a couple high-current diodes?

 

[Vanadium 50]

Is a 20 minute run time realistic?

 

[anorlunda]

2000 w for 20 minutes is 667 watt hours. Every battery has a useable watt hour rating. What is the rating of the 48v battery you have?

The 2000 w number may be pessimistic. You probably use less than maximum power for most of the 20 minutes. 300 watt hours rather than 667 may be more realistic.

But remember, that is just a guess. Do you want to be guaranteed 20 minutes, or would 10-25 minute range be acceptable?

The word useable is also significant. The voltage of the battery changes as it is discharged. That may make the last 10% to 15% of the battery life not useful to you.

Edit: 48v 2000 w for 20 minutes is 667 watt hours is sometimes expressed as 667/48=13.9 amp hours.

 

[surfsup]

Sorry, that statement I made was confusing. I meant I expect to only need to run the mower for 20 minutes to completely mow my lawn. The battery is 48v 35Ah and I figure I will be able to run the mower for around 40-50 minutes based on the weight (200lbs for me and 150lbs for the mower) WITHOUT the added load of the two deck motors, which I don't think will draw too much. I figure I should still get 30mins mowing with the blades running. I did not think about the battery voltage curve, nor did I realize how the curve collapses. Since much of the time I will be running the mower on somewhat flat ground, I should still be ok. I can always do the front one day, then the back on a different day, so it's not a deal-breaker. Anyway, back to original question of running the two 40V motors from the same 48V controller?

 

[anorlunda]

What is a deck motor?

 

[surfsup]

The two 40vdc electric motors I purchased to drive the cutting deck blades. Electric motors mounted to the deck.

 

[anorlunda]

OK, so you have three motors. Add up the amp-hour draw of all three and compare that with your battery rating.

 

[surfsup]

I don't have the amp hour rating of the two 40vdc motors. Looking at the 20inch ryobi mowers which these motors came from, there's 40m of cutting time for a 5aH battery but that also includes being self-propelled. So I should be fine on run-time. But, the run-time is not my question.

The question is whether I can hook all three DC motors up to the same controller. Or do I need to get a separate controller for the two 40vdc motors mounted on the deck for each blade? I thought I would just hook them all to the controller (in parallel) but with a switch and slo-blo fuse upstream of the two 40vdc motors which would also be connected in parallel. So I could just drive the tractor, and hit the switch to control the blades cutting on/off when I want to mow or not mow. The motor propelling the lawn tractor is a 48V 2000w.

 

[anorlunda]

The question is whether I can hook all three DC motors up to the same controller.

To answer that, we would need to see the nameplate info of all the motors.
Even then, I'm not sure. A controller might use motor RPM in the feedback, and in your case all three motors might have different RPM. So I guess we need the details of the controller also. It probably means you won't get a really good answer here because it depends on so many details.

 

[surfsup]

Ok so then I could get a second controller to control the two identical 40vdc motors. I suppose that should be fine since they are the same, yes?

 

[hutchphd]

Ok so then I could get a second controller to control the two identical 40vdc motors. I suppose that should be fine since they are the same, yes?

Are these brushed or brushless motors??

.

 

[anorlunda]

Ok so then I could get a second controller to control the two identical 40vdc motors. I suppose that should be fine since they are the same, yes?

Not necessarily. If one motor controls one blade, the thickness of the grass makes one blade have heavier loads than the other. Sometimes, one blade will be closer to the ground than the other. Sometimes, one blade might strike the ground, but not the other.

It depends on what the controller is controlling. Is it just voltage, or is it RPM?
The motor nameplates should tell you the type of DC motor. Can you photograph them and post the photos?

Modern BLDC motors often come with a controller included in the motor price. The controllers are the inexpensive portion of the price.

 

[surfsup]

I don't have the motors yet, I got two used motors from ebay that used to be in Ryobi 20inch electric mowers to run the blade. I don't know if they are brushed or brushless. I assume RPM, there is a controller on ebay?

 

[anorlunda]

I don't have the motors yet, I got two used motors from ebay that used to be in Ryobi 20inch electric mowers to run the blade. I don't know if they are brushed or brushless. I assume RPM, there is a controller on ebay?

In that case your question is premature. When you get them, post the photos of the nameplates.

 

[surfsup]

The controller for them says 2500/2800 RPM on it. The markings are minimal, chinese stuff...unfortunately.

 

[Averagesupernova]

It's a guarantee the motor on the discharge will be loaded heavier.

 

[surfsup]

So I'm not sure what specifically to look for in a controller, I see they are somewhat inexpensive:

https://www.amazon.com/gp/product/B086JYJDYN/?tag=pfamazon01-20

If I were to buy two controllers for the two 40vdc motos used for the two mower blades, what should I look for?

 

[DaveE]

So many unknowns here. I'm afraid you're not going to get a useful answer, I think you'll just have to try it and see what you get. The key thing you'll want to watch for is motor overheating, especially if you run it at excess voltage.

In the real world of product design, no one works this way. We specify what we need and find parts that have documentation to match our requirements. The DIY/eBay path is often the reverse of this. The hardest question to answer in engineering is "I'm going to do something slightly wrong (or unknown), will it be ok?"

 

[surfsup]

The motors have zero markings on them but I know the electric mower made by ryobi is 40v. Not sure still if they are brushless or brushed. I assume brushed since the OEM would likely cheap out every other could. Heres a pic, they just arrived. Yes I know there's some unknowns which is why I am seeking help. After searching forever to source parts and wanting to save some cash I found these two motors. Basically I just need a controller (or two) to hook them up to a 48v battery. Just wondering if there's a good source for controllers.

 

[anorlunda]

Basically I just need a controller (or two) to hook them up to a 48v battery. Just wondering if there's a good source for controllers.

Impossible to answer without knowledge of the motors. Controllers are specific to a motor type. It is like asking about a new carburetor without knowing the make and model of the car you own.

Is there an ad or something that you saw to buy the motors? If so, can you post a link.

 

[hutchphd]

Looking at the Home Depot ad, new Ryobi mowers claim 40V brushless motors. If the motors have three wires coming out (and probably not colored green or red or black) my guess is brushless. Which really means 3 phase square wave AC is provided by the controller to these wire at the appropriate frequency to make them spin synchronously. But it would certainly be far better to have some specs. What mower model did they come from??
You will need to know the amps to get a controller at very least.

 

[surfsup]

They supposedly came out of a ryobi 20inch electric self propelled walk behind single blade mower. Seems to be only one model. Yes it looks like three wires and the ad says brushless

https://www.homedepot.com/p/RYOBI-20-in-40-Volt-Brushless-Lithium-Ion-Cordless-Battery-Self-Propelled-Lawn-Mower-with-5-0-Ah-Battery-and-Charger-Included-RY40190/300402757

The motors are out of two different mowers, I bought two to put in my 42inch riding lawn tractor. They don't need to be synchronized I can get two controllers. Just want to make sure I get the right controller. Again 48v battery will be the power source. Never realized wiring up a couple electric motors would be so complex. Thanks for all the help so far!

 

[surfsup]

I did look at part replacement pdf and tried to find the motor specs on the internet but I had no luck.

 

[surfsup]

5Ah batter for 35m run time so since self propelled and that uses some juice probably about 5-7A draw tops?

 

[surfsup]

So here's a link to ebay for a three phase controller 6-60v
https://www.ebay.com/itm/6V-60V-400W-BLDC-3-phase-DC-Brushless-Motor-Controller-PWM-Hall-motor-Control/293878373935?_trkparms=ispr%3D1&hash=item446c841e2f:g:aXQAAOSwmFJfzIV2&amdata=enc%3AAQAFAAACkBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkvjzWOStkxwnlDuxSI1PVVjJc8O%252FzAr5HqsShh8U7L775x2POvvOBPF9zqZfv4vQ1EKk967VlOfRhbAVJ07tVUUmUKPXMMwWMjA%252BomZtEWkxi5OoDs5n4Z7rjO6MKJxg0jo2W8FHjILcUe1oFytKptdZQMlP5xxeyBe4%252FzfLMLNx5QmvMaB3Ivm4fjfu7xSL9Fe4c8zdatRQNYhUuF%252BDe%252BIpX6jSUcuAoXVw2g7mBUV6DwyFzsF4D9hH1TppF4ticuBi%252Ba1DTpHg0%252FkidMvLWAPEDqKmkmd931o7r%252FZfALP2hLpipcYzrXyPP026Na8dFTkxfwYWznof6PBnYX6YSrSzsnMULlJww%252FPP%252FEt8ZMGMXn%252BGs%252FCT4UUTwEGa8zjKzw3TylyXVrCZJzbjNEF7bYhIYR5x%252BGQhxf4DKF4a07uIaFifOB1vW6jvnEpYGsGZ9%252B9avEyzFTrlk%252BoGecD7EqIMlXTt%252BN8mQW3bucEet1%252BjGI2MhauTivPw5gINkMO%252FWNRxCY41tA%252FdT1iYZVByD1xudp6XgMtQE8esiuPDplHt%252BaFcO1NtaXSB9xSpRgg9eAGqsCEgRNzlen51w8UU2Wr8R7Ft0oyt9actmtdrXMuzA%252FBUColqz2zyHnKDa5EuMZeWJdIT12tuq0NdMPcDyk19aM4dl4WB1Ujy58lQUoZ3KKjz%252BDDuxpkHcaqe%252BJCuaVu06LYkZxQEsroiz1M9fNCbwlIWmr4IQe7DUOvGoDau6ml0bXnMGaqGAhp47sRBp4msKj7ov10fS4tlcxxseJFq2k9GM8Y3CRwjKvNSNsIAnS5N8cGtSFWfDHL9VthaC%7Ccksum%3A2938783739354d271648a52f4852a66a8c36b1056a2a%7Campid%3APL_CLK%7Cclp%3A2334524

Would a couple of these work for the two 40v motors?

 

[hutchphd]

5Ah batter for 35m run time so since self propelled and that uses some juice probably about 5-7A draw tops?

That is a an average number. When the blade hits big clump of a grass it could be a lot bigger than that. The controllers for radio controlled airplanes typically are rated for 30 A (and these are brushless motors driving maybe a ten inch propeller). You will need to get a good spec on the motors or be prepared to control a bunch of current (I don' t know how much? How fat are the wires on the motor?...that may tell you something)

So here's a link to ebay for a three phase controller 6-60v
https://www.ebay.com/itm/6V-60V-400W-BLDC-3-phase-DC-Brushless-Motor-Controller-PWM-Hall-motor-Control/293878373935?_trkparms=ispr%3D1&hash=item446c841e2f:g:aXQAAOSwmFJfzIV2&amdata=enc%3AAQAFAAACkBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkvjzWOStkxwnlDuxSI1PVVjJc8O%252FzAr5HqsShh8U7L775x2POvvOBPF9zqZfv4vQ1EKk967VlOfRhbAVJ07tVUUmUKPXMMwWMjA%252BomZtEWkxi5OoDs5n4Z7rjO6MKJxg0jo2W8FHjILcUe1oFytKptdZQMlP5xxeyBe4%252FzfLMLNx5QmvMaB3Ivm4fjfu7xSL9Fe4c8zdatRQNYhUuF%252BDe%252BIpX6jSUcuAoXVw2g7mBUV6DwyFzsF4D9hH1TppF4ticuBi%252Ba1DTpHg0%252FkidMvLWAPEDqKmkmd931o7r%252FZfALP2hLpipcYzrXyPP026Na8dFTkxfwYWznof6PBnYX6YSrSzsnMULlJww%252FPP%252FEt8ZMGMXn%252BGs%252FCT4UUTwEGa8zjKzw3TylyXVrCZJzbjNEF7bYhIYR5x%252BGQhxf4DKF4a07uIaFifOB1vW6jvnEpYGsGZ9%252B9avEyzFTrlk%252BoGecD7EqIMlXTt%252BN8mQW3bucEet1%252BjGI2MhauTivPw5gINkMO%252FWNRxCY41tA%252FdT1iYZVByD1xudp6XgMtQE8esiuPDplHt%252BaFcO1NtaXSB9xSpRgg9eAGqsCEgRNzlen51w8UU2Wr8R7Ft0oyt9actmtdrXMuzA%252FBUColqz2zyHnKDa5EuMZeWJdIT12tuq0NdMPcDyk19aM4dl4WB1Ujy58lQUoZ3KKjz%252BDDuxpkHcaqe%252BJCuaVu06LYkZxQEsroiz1M9fNCbwlIWmr4IQe7DUOvGoDau6ml0bXnMGaqGAhp47sRBp4msKj7ov10fS4tlcxxseJFq2k9GM8Y3CRwjKvNSNsIAnS5N8cGtSFWfDHL9VthaC%7Ccksum%3A2938783739354d271648a52f4852a66a8c36b1056a2a%7Campid%3APL_CLK%7Cclp%3A2334524

Would a couple of these work for the two 40v motors?

My guess is that if the motor wires will fit the clamp connectors on these boards you are good to go (and these are pretty cheap so smoke is not a disaster) See how hot they get. I think they will work. Incidentally interchanging any two of the three (3 phase) wires simply reverses the motor direction!

SAFETY SUGGESTION: It is very much easier to inadvertently power up an electric motor than a gas motor. You should have a foolproof simple way to impede the blades when doing maintenance or storage. Just like the BattleBots...really. A couple pieces of rebar that drop through the deck...something. And an easy way to disconnect the battery in addition.

 

[hutchphd]

Also I have no idea what this board expects for control inputs and leave that up to you. It seems likely to me that it will power your Deck motors but the control signal details are unknown to me.

 

[surfsup]

Thanks for the input. Appreciated.

The ebay photos for 40v ryobi motor controller shows the controller's labels with 8A or 10A printed on them. While they are only $15 I'll look around a bit more. I can spend a bit more than that for two controllers. Just want them to work well and not burn up.

To control the deck motors I was just going to wire them both to a switch/fuse. On/off. That's it.

For power up I plan to just wire them up on a bench first and try to dial in the rpms about the same on each controller to get that set. Then install everything in the spring.

 

[Tom.G]

It is mentioned that the controller(s) you propose are for motors with a Hall effect sensor. So far here there is no indication that the motors are so equipped.

If you are on a tight budget you might want to start with a single deck motor and controller. If there is no smoke after several mowing sessions, continue with the full implementation.

A tip about used motors:
Smell them. If they smell burnt they are good only to take up room in the garbage dump.

(although those above several horsepower can be economical to send out for rewinding.)

Cheers,
Tom

 

[surfsup]

I didn't see one without hall sensor. The wires are probably 14-gauge ? The wires in background are for my drive motor controller which are probably about 8-gauge? I think 22gauge wire can handle 10A so the thickness is likely more for resistance vs amp load? The ryobi controllers I saw have 8A or 10A printed on them.