# Small Diesel Tractor Conversion



## remy_martian (Feb 4, 2019)

Operating power of 15hp on a tractor is at ~1800 engine RPM with a 540 pto rpm.

That defines the torque you need at that RPM.

The HP of the electric motor is irrelevant unless you do not do direct drive to the transmission input shaft.


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## electro wrks (Mar 5, 2012)

Model number, gear or hydrostatic, engine or transmission driven hyd pump, loader, other attachments, type of use? Pictures would help. Is the operating RPM based on the PTO 540-600 RPM as indicated on the tach?


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## ratchet6900 (11 mo ago)

Hi, thanks for the replies. The 2650 engine RPM gives the standard 540 PTO RPM. Not sure why anything else is relevant as I just need an electric motor that would approximately equal the power input of the diesel engine (the other stuff such as attachments & type of use would however affect battery size requirement).. It could be a direct drive or maybe something geared down to increase torque/reduce RPM to more closely match the diesel.

I realize there is a direct relationship between HP and KW (15 HP = 11.25 KW) but as I understand it, KW ratings often assigned by sellers to their electric motors are not realistic or are hard to interpret (too high; confusion between "rated" KW and "maximum" etc) so I'm wondering what a real world, ballpark solution might be.


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## electro wrks (Mar 5, 2012)

Rarely are conversions as simple as just dropping in a supposedly equivalent motor to replace an ICE. The more info we have, the better we might match a motor for your needs. Possible, other people have done conversions close to what you have and your needs. The experiences of these people would be valuable as to what motor might or might not work in their(your) application. But, if you don't think the info requested is relevant, I won't waste my time trying to help you.


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## remy_martian (Feb 4, 2019)

You need to calculate the torque at 2650RPM that gives you 15HP. I'm not going to do it for you.

Then you need to find an electric motor that makes at least that much continuous-rated torque at 2650 RPM, whether delivered as direct drive (preferred) or through a gearbox (meaning the motor torque can be lower if you're reducing speed).

"KW ratings often assigned by sellers to their electric motors are not realistic or are hard to interpret (too high; confusion between "rated" KW and "maximum" etc) so I'm wondering what a real world, ballpark solution might be."

There's no "ballpark". You need at least 11kW at 2650RPM, or simply put, the torque at that speed that creates 11kW of power. Put in too much torque and you'll bust the driveline. Ballpark is a hot dog. This needs to be engineered.

While Chinese or unscrupulous eBay sellers might "assign" power ratings, manufacturers specify them, along with the conditions that power rating may be run....zero confusion.

You never said why you are doing this expensive project.


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## SimonRafferty (Apr 13, 2009)

I would look at it from the point of view of Max Torque & Max rpm, rather than the rated power output. You might be able to find (online) a torque figure for the diesel engine, or a similar one - and you will probably have an idea of the max rpm your engine runs at.
If you drop in a motor with roughly the same figues, it will have similar capability in terms of torque for running implements / acceleration and speed.
It's difficult to directly compare an engine to an electric motor as the power / torque curves are very different.


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## ratchet6900 (11 mo ago)

OK, 15 HP @ 2650 RPM = 29.7 ft-lbs or, 40.3 N-m. 15 HP also = 11.2 KW. So, an electric motor of about 11 KW should be in the "ballpark", no? Using more realistically available values, a 10 KW motor would suffice(?). Now, ideally a motor that chugs out 10 KW power at around 3,000 RPM (again using "ballpark" numbers) would be pretty close to what is needed. If such a motor cannot be found, maybe one that does the same at 6,000 or so RPM with a 2/1 gear down (use a 2/1 roller chain/sprocket arrangement?) should also work.

Simon, you mention power/torque curves which is perhaps the nuts of the matter here and is what makes me hesitant to simply order a 10KW motor for example and hope it works. Diesel engines tend to develop torque at lower RPMs compared to a gasoline engine, and electric motors of the type applicable here do the same so, maybe the match would not be too bad. As you point out, a motor with roughly the same figures, will have similar capabilities.

There are as well manufactures who supply electric tractors of a similar size range and I suppose one could see what type of motors they use (KW rating, BLDC or PMSM etc.).

As to why BTW I am doing "this expensive project", I have access to a YM155D with a clapped out engine (and all else pretty good) and, since the advantages of electric over fossil fuel are many, going electric rather than trying to source a replacement engine might make sense as well as being an interesting project.


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## SimonRafferty (Apr 13, 2009)

Something around 10kW is going to be about right. 

I've used one of these (not on an EV) electric propulsion outboard,electric propel outboard, hub motor,brushless motor, BLDC motor,electric outboard,GMX motorcycle,Golden GMX,Electric motorcross,electric motorcycle,EZOutboard, EZinboard, EZ Outboard Motor,wheelchair conversion kit,foldable electric wheelchair,gearless wheelchair motor,portable electric wheelchair
I used a fan cooled 10kW 48V motor which produced 30Nm and up to about 5000rpm. https://www.goldenmotor.com/eCar/HPM48-10000Curve.pdf
However, there are loads of other motors in that kind of power range for electric go-karts available.

Electric is more similar to diesel in terms of the power curve than petrol - but it has even more low end torque. 

In my Polaris (technically a tractor too), I replaced a 100BHp Petrol Engine with a 60Hp Electric - and it actually goes better. Better acceleration & fractionally higher top speed. 

There used to be a 'rule of thumb' that replacing a gas engine with an electric with half the power will give a similar driving experience. I would imagine it's similar for a Naturally Aspirated Diesel.


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## remy_martian (Feb 4, 2019)

No, not exactly.

Something that makes 11kW at 2650 RPM. I thought that was clear. Torque curves are irrelevant for a tractor as it generally operates at one propulsor speed.

A 45kW motor, rated at 10,000RPM should roughly make 11kW at 2600RPM for direct drive. Or an 11kW at 2600RPM. Or a 15kW at 5300RPM on a 1:2 speed reducer. Or an 80kW Leaf motor that is torque limited, aka "derated", by its inverter by almost half to produce a max torque 2650rpm in direct drive.

It all boils down to making your "29.7 ft-lbs or, 40.3 N-m" at 2650.


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## ratchet6900 (11 mo ago)

SimonRafferty said:


> Something around 10kW is going to be about right.
> 
> I've used one of these (not on an EV) electric propulsion outboard,electric propel outboard, hub motor,brushless motor, BLDC motor,electric outboard,GMX motorcycle,Golden GMX,Electric motorcross,electric motorcycle,EZOutboard, EZinboard, EZ Outboard Motor,wheelchair conversion kit,foldable electric wheelchair,gearless wheelchair motor,portable electric wheelchair
> I used a fan cooled 10kW 48V motor which produced 30Nm and up to about 5000rpm. https://www.goldenmotor.com/eCar/HPM48-10000Curve.pdf
> ...


Excellent info Simon. Thank you! The Goldenmotor looks good as it operates at 48V which is sorta what I was looking at (I have a small 48V quad BTW for which I installed a BLBC Kelly controller in place of the stock unit - works very well).

Still wondering though if a BLDC or PMSM would be best for this application - I expect either would be OK.


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## brian_ (Feb 7, 2017)

<deleted as redundant>


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## brian_ (Feb 7, 2017)

SimonRafferty said:


> There used to be a 'rule of thumb' that replacing a gas engine with an electric with half the power will give a similar driving experience.


But that was never valid. Look at any production EV - none of them deliver the performance of an otherwise comparable gas-engine vehicle with double the rated horsepower. The 150 kW (200 HP) Chevrolet Bolt performs like other overweight compact vehicles with that same power rating from a gas engine... not like 400 HP cars.


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## ratchet6900 (11 mo ago)

brian_ said:


> Or, you put suitable reduction gearing between a higher-speed motor and the transmission input... either approach works.


An alternative would also be to operate in a lower transmission gear for a high RPM motor. It allows direct drive but spins the clutch assembly a lot faster which may introduce vibration & roughness issues(?).

OTOH, maybe the clutch could be deleted but, the transmission is nonsynchronous and double clutching is sometimes necessary to switch gears so who knows how that would shake out without a clutch?


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## brian_ (Feb 7, 2017)

ratchet6900 said:


> An alternative would also be to operate in a lower transmission gear for a high RPM motor.


At low speed you would not have a lower-than-normal gear, but that might be okay since you don't need to keep motor speed up to produce maximum motor torque.


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## ratchet6900 (11 mo ago)

brian_ said:


> At low speed you would not have a lower-than-normal gear, but that might be okay since you don't need to keep motor speed up to produce maximum motor torque.


I'm not sure I follow that. A "high" RPM motor will have lower torque than a "low" speed motor for the same KW rating.so does that work if I want torque to be similar to the diesel engine? That's why I figured the solution might be to shift the transmission to a lower gear to get the same m/l tractor speed and torque availability.


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## remy_martian (Feb 4, 2019)

If your tractor has a PTO, transmission gear lowering is worthless.


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## ratchet6900 (11 mo ago)

remy_martian said:


> If your tractor has a PTO, transmission gear lowering is worthless.


I'm referring to the existing tractor transmission, not gearing down the motor output (unless I miss the intent of your post).


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## remy_martian (Feb 4, 2019)

Yup...you got it wrong if there's a PTO.


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## ratchet6900 (11 mo ago)

remy_martian said:


> Yup...you got it wrong if there's a PTO.


OK, the 540 PTO speed will be affected if the input RPMs to the transmission is not maintained at 2,650. So the electric motor needs to produce sufficient torque at 2650 for direct drive hookup & proper PTO use.

I have noticed that the beforementioned Goldenmotor unit can be "customized", according to their Alibaba site, for operation at 3,000 (vs 5,000 which I gather is the default RPM). I queried them about how that RPM reduction might affect torque i.e. does the output remain at 10 KW but haven't received a reply. So then, 3,000 is probably close enough for government work but 5,000 is problematical w/o a motor gear down. OTOH, I plan on using this machine mainly for snow plowing or towing so maybe it doesn't matter a lot.

I have also noticed a radial flux motor of about the right KWs on Alibaba which IIRC ran at 2500 RPM. Maybe better take another look but IIRC it was too large on diameter to fit between the frame rails.


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## remy_martian (Feb 4, 2019)

Don't trust what any Chinese seller/supplier tells you. The people you interface with are commission sales, some are middlemen operating out of an apartment flat that consolidate orders.

5000 is no problem if it is a >22kW motor at that speed.

Every snow plow/oiader I've seen/used needs a hydraulic pump - which is built into the PTO path, usually, though my POS Massey has a front pump off the crankshaft to run the loader.


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## ratchet6900 (11 mo ago)

I dunno, someone just emailed me a lot of detailed documentation on the 10KW motor I was looking at. According to the specs though, it is a little light on torque (26 N-m) at the rated speed of 3750 RPM whereas the diesel chugs out about 40. 

The docs do however state the RPM is "configurable" from 2,000 to 5,000 RPM. I can't figure out what exactly that amounts to and have asked for clarification. If the motor is configured to a speed lower than 3750, does the torque proportionately increase to maintain the rated 10 KW output? Is this "configuration" done in software in the controller or, is the motor wound or otherwise constructed differently to produce more torque with less RPM?? Or maybe it is just setting an upper RPM limit in the controller.

As for the hydraulic pump, yeah, the existing pump is attached to the engine and would have to be replaced if the 3-point hitch lift is to be used. Haven't looked into that but I suppose an outboard electric hydraulic pump could be added(?).


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## remy_martian (Feb 4, 2019)

You need to look into the tractor systems in detail. 3 point hitch is a gotta have. As is a pto if it has one. Most pto setups use a dual clutch setup...

They may have the pole count of the motor configurable, or a variation of it as a standard model, to change speed. You need to ask about the kW rating at the lower speed.

You have a fair bit of homework to do if you want to do more than just pull a garden cart around.

Look at the David Brown tractor build on here.


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## SimonRafferty (Apr 13, 2009)

brian_ said:


> But that was never valid.


I didn't say it was a good rule of thumb 
For me, it hasn't been miles off - 60-70% of the power to deliver a similar 'driving experience' & usability.


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## ratchet6900 (11 mo ago)

Just checked out the 40 HP David Brown tractor conversion thread. I note he went with only an 8 KW rated & 18 Nm rated motor (a QS-180) for a considerably larger tractor (40 HP) than mine. He has said however that he is not happy with the performance as it does not have much low end torque. The motor does seem awfully small for a 40 HP replacement. BTW, he is using the same Golden Motor 10 KW separate to power unit the PTO.


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## SimonRafferty (Apr 13, 2009)

While my 'power' is 60-70%, the torque is higher than the original ICE. I think that's probably what makes the difference.


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## brian_ (Feb 7, 2017)

SimonRafferty said:


> While my 'power' is 60-70%, the torque is higher than the original ICE. I think that's probably what makes the difference.


Right - it is only power that matters, but drivers often don't shift to get the engine (or electric motor) to the speed needed for maximum power, so they are comparing power at an inappropriate shaft speed, making comparisons "interesting". It's understandable in some cases, because shifting to keep a hyperactive engine buzzing at its peak can be inconvenient at best and overwhelming at worst.

I talked to a guy once who drove a Mazda RX-8 when it was new, and wasn't impressed by the performance compared to his car. That didn't make sense given his lower-powered car... then I realized that he was running that rotary engine at half the speed it needed to be turning to put out its maximum power (8,250 RPM). Yeah, a Formula 1 car is a slug, too, at its idle speed.


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## ratchet6900 (11 mo ago)

OK, I think I've figured out what Golden Motor means by "the RPM is configurable from 2,000 to 5,000 RPM".

All it apparently refers to is the RPM/torque curve for the motor i.e. if the motor is loaded down or "configured" to operate at 2,000 RPM instead of the rated RPM of 3750, torque will increase from the rated 26 N-m to around 41 N-m (the 41 being very close to the diesel torque). Thing is for a tractor though, how long will the motor operate around the 2,000/41 point w/o overheating?? I suspect not very long but maybe the liquid cooled version would be better(?).


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## remy_martian (Feb 4, 2019)

I think you may be getting confused again. The power and therefore lost power as heat is _about_ the same because that alleged config change is lowering the voltage.

Air cooling for a tractor working dry soil is not a good idea. Motor should be dust sealed.


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## ratchet6900 (11 mo ago)

Maybe. W = I squared * R. I must increase as torque increases and R remains the same (unless there is something particular about a BLDC motor I'm not aware of) so, W must also increase(?).

Why is the alleged config lowering the voltage? Battery voltage wouldn't drop by much unless the battery is low or too small.

It could be air cooled and sealed at the same time (my quad BLDC is) and IIRC, they state the motor is water proof.


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## remy_martian (Feb 4, 2019)

Motors are magic...keep the applied voltage the same, lower the rotational speed by 60%, somehow double the current because you want it to, and HP (V*I/746) doubles.


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## remy_martian (Feb 4, 2019)

You've clearly not been around farm equipment much, or dug through a clod of dirt with your fingers to access grease fittings. 

Air-cooled gets severely derated after getting caked with dust/mud. If you're only running a snow plow, or doing hay rides, air cooled probably would work. plowing, baling, disking, cultivating, not so much.


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## piotrsko (Dec 9, 2007)

Going to go off on a different track. Back long ago everyone here was interested in golden motors. Afaik, only one person got one, tested it and was sorely disappointed. Someone did make a successful swap but also was disappointed over the lack of power versus advertised.

You will notice there's not bunches here on this site if they were as good as advertised. Wonder why?

Torque is kinda a function of case diameter. Bigger motors make more power than smaller motors but don't have an efficiency gain from size.

My 2¢: it's your conversion. Do whatever you want, just don't disappear if it fails, man up and let others know it didn't work.

I have a 13" Kostov. Big russian style brute of a motor, but doesn't make the hp a hitachi does. It does motor along all day for the last 25000 miles so it did meet my design goal.


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## ratchet6900 (11 mo ago)

Thank you for the input. Yeah, that's my uncertainty here as well - it's kind of a craps shoot unless you can find someone who has actually done it successfully. There is another tractor conversion project in progress being discussed here that utilizes a 10KW Golden to drive the PTO with a QS motor to the transmission. He was not happy with the performance of the QS (low torque) and was going to try the Golden in its place (but AFAIK has not tried it yet). The Golden did successfully power his mower however.









David Brown 880 Tractor Conversion


I'm looking do a 40hp tractor conversion. I've managed to find, and have now bought, a David Brown 880 Selectamatic with a tired engine - rest of the tractor is mechanically sound (so I'm told), but it does need some TLC (definitely doesn't look anywhere near as good as the one in the photo...




www.diyelectriccar.com





If I do the conversion I will certainly post progress here, successful or not.


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## remy_martian (Feb 4, 2019)

Just remember that quoted Chinese HP/kW motor ratings are in metric, so divide the numbers they give you by 2.54 😂


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## wscoleman1941 (Oct 27, 2021)

I have a deal for you. I have a D&D SepX DC motor with a Curtis controller, state of charge meter, Curtis controller programmer, wiring harnesses, instruction books; the whole lot. It's rated at about 17 HP with a 48 V wet cell golf cart battery pack. You can make me an offer. I just want to find it a new home. I live in Kirtland, OH. The setup was used in an Urba Electric car which I swapped from DC to AC. It is all clean and in nice condition. Initial cost was over $2,000.


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