# Tiller Conversion - Circuit Check



## TigerNut (Dec 18, 2009)

Your drawing is fine, but check the power rating of the engine that's currently on that tiller. I don't think that a 1/3 HP electric motor is going to help you very much, other than to turn a fan which will cool the motor that will actually do the work.

If your tiller is like this one
http://www.youtube.com/watch?v=uoeAtnT2zvM

then it has about a 3.5 HP engine. You're likely to need something that has a similar continuous power rating - at the very least you should be looking for a commercial treadmill motor in the 3HP range.


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## Dennis (Feb 25, 2008)

hoowahfun said:


> Hello everyone, new to the forum but I've been browsing through and reading many of your posts for a while now.
> 
> I've decided that my first EV build will be a conversion of an old gas tiller to a corded AC electric one. Thought this would be simple enough to get my feet wet.
> 
> ...


A 10 amp switch may not be enough because of inrush current. Typically you will see switches rated for higher current than the AC motor's full load current, but on the switch it will tell you what size HP AC motor it is rated for which from calculation to find current from power will be less current than what you would think based on the switch's current rating.


The motor might work if the tiller was a Mantis or Honda FG 110, but a full sized model needs at least a 3 HP AC induction motor. Since this is a variable cycle type load then a 3 HP AC induction motor will replace up to a 4.5 HP gas engine. For such a motor you will need a double pole contactor, 230 volts AC (+-10%), at least 10 AWG if you plan to run 50 foot drop cord for reduced voltage drop, and a 30 AMP double pole circuit breaker in your breaker box. I assume you know how to wire up a 240 volt type outlet. Fuses are NOT needed however. Thermal overloads are what protect motors, not fuses or circuit breakers.


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## hoowahfun (Jun 28, 2012)

TigerNut said:


> Your drawing is fine, but check the power rating of the engine that's currently on that tiller. I don't think that a 1/3 HP electric motor is going to help you very much, other than to turn a fan which will cool the motor that will actually do the work.
> 
> If your tiller is like this one
> http://www.youtube.com/watch?v=uoeAtnT2zvM
> ...


When I first had the idea I did a little browsing online and found this video:

http://www.youtube.com/watch?v=3M3y_IAJs3U

States it was a 4 HP replaced with a 1/4 HP AC motor. The info I gathered on mine said it was a 4 HP motor as well and I thought since my electric motor was larger than the one in the video I would be okay. It seems there are many conflicting opinions on how to match gas HP to electric (HP is HP, but the way HP is measured on gas engines can be skewed). Seems to be an educated guess unless you have any practical data.



Dennis said:


> A 10 amp switch may not be enough because of inrush current. Typically you will see switches rated for higher current than the AC motor's full load current, but on the switch it will tell you what size HP AC motor it is rated for which from calculation to find current from power will be less current than what you would think based on the switch's current rating.


I didn't see a motor HP rating on the switches I had selected. Is there a way to calculate the inrush current for a motor at startup? I'll have to look for a HP rating on motor switches in the future.



Dennis said:


> Fuses are NOT needed however. Thermal overloads are what protect motors, not fuses or circuit breakers


Thanks for the tip. In researching this idea I did see that a circuit breaker wouldn't be sufficient due to slow response time. Good to see a confirmation on that. With this being alternating current would you recommend having a thermal overload on each side of the motor? Or does it matter?


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## TigerNut (Dec 18, 2009)

Well that does look pretty encouraging. Part of it is all about having the right pulleys so you get the speed reduction you're looking for; that will also multiply the torque accordingly.

You can see they used a standard indoor electrical switch in a metal box. Good idea from a robustness and current handling point of view - not so good for inclement weather. If you can find an exterior-rated switch then that might be a way to go. Other idea is a mushroom type safety switch (pull out and turn to switch on, push to turn off).

Make really sure your house supply circuit is protected by a GFCI breaker.

Your mileage is going to vary according to the rock and clay content of your local soil... I live on what pretty much amounts to a gravel pit and any soil breakup that I have to do usually starts with a pickaxe.


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## PStechPaul (May 1, 2012)

I watched the video and the motor looks larger than a 1/4 HP, more likely it's 3/4 or 1 HP. Also the number of poles and the type of AC motor are important. A fan motor may be shaded pole, which has very poor starting torque but is fine for fans and is "impedance protected" so that a locked rotor will not cause a major overload. It may be a PSC type, which is permanent split-phase capacitor, and these are good all-purpose motors. Capacitor start motors have even higher starting torque for loads like pumps.

For tilling, the speed of the blades is probably important, and will be determined by the size of the pulleys and the rated motor speed. If you can provide the nameplate data for the fan motor it will help determine if it is OK, and if you can find out how fast the tiller blades should turn, that will be needed as well.

The wall switch in the video (which the woman called a "plug") may not be suitable for the motor, but you can get high capacity switches that will do the job. Rather than an E-stop button, I think you will be safer to use a spring-operated handlebar lever switch such as are standard on mowers, so that if you should trip over a rock and fall toward the blades they would at least stop moving before you landed on them.

Here are some ideas, but you can probably get a switch from almost any power tool with a guarded pushbutton, such as a circular saw or chainsaw, or you might find an old electric mower. A pushbutton would work, but it might be difficult to hold in while tilling, But it should be easy to rig up a handlebar lever like a bicycle brake.

http://www.digikey.com/product-detail/en/3832510MG/1091-1007-ND/2747838
http://www.digikey.com/product-detail/en/C7001AFBB/1091-1040-ND/2747871

http://www.automationdirect.com/adc...inated_Pushbuttons_Flush_-a-_Extended/GCX3102
http://www.automationdirect.com/adc...ated_Pushbuttons_Flush_-a-_Extended/ECX1702-5

Here is a good 18A motor starting contactor. If you use this, you can use a much smaller switch to control the coil:
http://www.automationdirect.com/adc...ctors_-z-_Overloads/9_to_25_Amp/SC-E04-110VAC

You can also get cable-pull-operated safety switches which might work for you. These will handle a motor directly, 30A at 240VAC, although only 6.5A 120V breaking rating. But that's 1 HP at 120 VAC.
http://www.automationdirect.com/adc...witches/Cable-Pull_Safety_Switches/SDM2K96X11


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## hoowahfun (Jun 28, 2012)

PStechPaul said:


> I watched the video and the motor looks larger than a 1/4 HP, more likely it's 3/4 or 1 HP. Also the number of poles and the type of AC motor are important. A fan motor may be shaded pole, which has very poor starting torque but is fine for fans and is "impedance protected" so that a locked rotor will not cause a major overload. It may be a PSC type, which is permanent split-phase capacitor, and these are good all-purpose motors. Capacitor start motors have even higher starting torque for loads like pumps.
> 
> For tilling, the speed of the blades is probably important, and will be determined by the size of the pulleys and the rated motor speed. If you can provide the nameplate data for the fan motor it will help determine if it is OK, and if you can find out how fast the tiller blades should turn, that will be needed as well.
> 
> ...


Yeah I'm not a big fan of the wall switch, I'd rather have something a little more finished looking/operating than that. The nameplate data for the attic fan motor is on the wiring diagram in the first post. As for the rotation speed of the tines or pulley's on the tiller...that's anyone's guess lol.

Here is a pic of the motor:









As for ON/OFF operation I was thinking of a selector switch like the one below. I also liked the orange since it kind of went with the original paint job:

http://www.galco.com/buy/Idec/HW1F-2F10QD-A-120V

Naturally if a 10A switch is not large enough another will have to be selected. FYI it was wired in my house on a 120V, 15A tandem circuit breaker (assuming single pole). Any suggestions on amperage rating I should look for in an ON/OFF switch? Maybe 15A would be sufficient?

The tiller also has a clutch to engage the tines so I'm not terribly worried about it riding off into the sunset. You can see it here on the left handle:


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## hoowahfun (Jun 28, 2012)

TigerNut said:


> Make really sure your house supply circuit is protected by a GFCI breaker.
> 
> Your mileage is going to vary according to the rock and clay content of your local soil... I live on what pretty much amounts to a gravel pit and any soil breakup that I have to do usually starts with a pickaxe.


Good point. I just put a new one our bathroom last week where my wife hung a necklace off of the plug at the outlet...she pulled the plug and her necklace melted in two  Serves her right lol.

As for soil condition it's mostly hard red Georgia clay!


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## Dennis (Feb 25, 2008)

hoowahfun said:


> Yeah I'm not a big fan of the wall switch, I'd rather have something a little more finished looking/operating than that. The nameplate data for the attic fan motor is on the wiring diagram in the first post. As for the rotation speed of the tines or pulley's on the tiller...that's anyone's guess lol.
> 
> Here is a pic of the motor:
> 
> ...



I did not see a capacitor on your motor. So I assume it is a split-phase motor as those used in washing machines or dryers. This type of motor is notorious for burning out easily if it is stalled. 

Fifteen amp switches usually have 1/2 HP rating stamped on them at 115 VAC. So yes, a 15 amp switch will handle your 1/3 HP motor.

I still stand by the fact that you should use a 3 HP motor, but it is your project. If you really want to stick with a 1/3 HP motor then you need to make sure to have a very low ratio reduction of final speed. With a 2-pole, 3 HP motor you could keep your speed performance and have zero risk of stall when tilling up red clay dirt.

I own a Leeson 3 HP motor, catalog number: 120341. It's for woodworking applications. The reason I use this motor is because of the very high breakdown torque of 300+ % (13.5 BD / 4.5 FL) which is beyond a general purpose 3 HP AC induction motor which usually have 200+%, but a general purpose AC induction motor should work fine for your application. 

Breakdown torque is the torque that the AC motor will produce when you apply more and more load beyond full load until which point the motor can no longer produce more torque, but instead the torque will start to decrease. So the maximum is the breakdown torque. This is not a DC motor you are dealing with in which torque just goes up and up until the current limit is reached either from passive electrical resistance limiting the current or from electronic current limit of a motor controller.

I just want your project to work well. Start up torque is not a major issue here because the tines are not under load at start up or you will have the motor up to speed first, then apply the clutch. If you hit a hard spot and have low breakdown torque then the motor is going to stall unless you gear it very low in which case if time spent tilling does not bother you then by all means use the 1/3 HP motor.


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## PStechPaul (May 1, 2012)

The melted necklace is one reason why most outlets are now wired with the ground pin up. That way it is usually the first pin that will be cointacted by a metal object such as a neclace or clothes hanger. If the current goes through the object to the hot blade, it should trip the GFCI. But if the object strikes the hot and neutral, it is seen as a normal load by the GFCI and it won't trip. The main breaker will probably trip eventually, unless the load burns up or melts first, as in this case.

I couldn't find the part number for the motor but it looks like a 1/3 HP HVAC belt drive blower motor something like this:
http://www.grainger.com/Grainger/AO-SMITH-SplitPhase-Motor-4UE63?Pid=search

A split phase motor has an auxiliary starting winding which has less inductance than the main winding and creates a rotating field that starts the motor. Then a centrifugal switch removes it once it reaches close to its design speed of 1725 RPM. The 6.5 amp rating indicates it may not be very efficient. 120V at 6.5A is 780VA, while 1/3HP is about 250W, so you are losing almost 500VA which is probably about half reaactive and half resistive (or actual power wasted as heat). The motor listed above is rated only about 60% efficiency. 

http://www.grainger.com/Grainger/AO...cm_sp=IO-_-IDP-_-RR_VTV70300505&cm_vc=IDPRRZ1
This motor is 1/2 HP and is about 65% efficient, with a full load current of 7.2 amps. About the same current as your motor but twice the power. It is also split phase.

http://www.ebay.com/itm/ELECTRIC-MO...601?pt=LH_DefaultDomain_0&hash=item3a698c7029
This motor is 1/2 HP, 120/240V, and 5.2A. It is capacitor start and run, and is rated at 86% efficiency, which is excellent.

http://www.ebay.com/itm/Genteq-5SME...260?pt=LH_DefaultDomain_0&hash=item336d8c8714
That's a 1HP 1050 RPM motor which is higher torque, but it is not sealed so maybe not good for outdoor use.

Your motor might do the job for you, but if not, there are many available at reasonable cost on eBay or Craigs List. Good luck with your project.


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## hoowahfun (Jun 28, 2012)

PStechPaul said:


> The melted necklace is one reason why most outlets are now wired with the ground pin up. That way it is usually the first pin that will be cointacted by a metal object such as a neclace or clothes hanger. If the current goes through the object to the hot blade, it should trip the GFCI. But if the object strikes the hot and neutral, it is seen as a normal load by the GFCI and it won't trip. The main breaker will probably trip eventually, unless the load burns up or melts first, as in this case.
> 
> I couldn't find the part number for the motor but it looks like a 1/3 HP HVAC belt drive blower motor something like this:
> http://www.grainger.com/Grainger/AO-SMITH-SplitPhase-Motor-4UE63?Pid=search
> ...


I'm not very familiar with various motor types (split phase, capacitor, etc.) or their uses, but this is good information. My biggest concern now is having an undersized motor and even the possibility of ruining the motor if stalled. Although it's free I hate to let something go to waste due to bad planning. The other part of me is eager for first hand practical experience. I'll have to think about this as I may put the tiller on hold and use the motor for another conversion of some kind.


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## rwaudio (May 22, 2008)

hoowahfun said:


> Hello everyone, new to the forum but I've been browsing through and reading many of your posts for a while now.
> 
> I've decided that my first EV build will be a conversion of an old gas tiller to a corded AC electric one. Thought this would be simple enough to get my feet wet.
> 
> ...


If I was going to tackle a project like this I would probably look for an old table saw motor, (Ideally the belt driven style) it has good torque but a stall won't damage it. Find a saw with other problems and the motor might be virtually free. It also has a suitable switch and wiring to simplify requirements, even if they have to be replaced you know what you need. Some models are loud, but the older ones I've used are fairly quiet.


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## Dennis (Feb 25, 2008)

The motor catalog number I posted is used in table saws. Hence, the reason it's for woodworking applications. It is a capacitor-start, capacitor-run motor that if stalled for a short bit will not damage it, unlike a split phase motor. I would not use a motor from an old saw because it could be a universal motor which are not very powerful and are very unreliable since they have brushes.

The motor I selected for you also has very good speed regulation under load in that its full load speed is 3512 RPM and at 1.5 times overload the speed drops to 3455 RPM which is an overall speed change of just 1.6%. Just to prove that I know what I am talking about and am not some fake internet expert. I will BUY this motor for you and have it shipped to you. I know what I am talking about and am willing to put my money where my mouth is, that if this motor fails then you can tell the this whole forum that I should not be listened to for advice.

You know you are dealing with someone who knows their stuff if they are willing to spend their own money to prove it.


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## hoowahfun (Jun 28, 2012)

Dennis said:


> The motor catalog number I posted is used in table saws. Hence, the reason it's for woodworking applications. It is a capacitor-start, capacitor-run motor that if stalled for a short bit will not damage it, unlike a split phase motor. I would not use a motor from an old saw because it could be a universal motor which are not very powerful and are very unreliable since they have brushes.
> 
> The motor I selected for you also has very good speed regulation under load in that its full load speed is 3512 RPM and at 1.5 times overload the speed drops to 3455 RPM which is an overall speed change of just 1.6%. Just to prove that I know what I am talking about and am not some fake internet expert. I will BUY this motor for you and have it shipped to you. I know what I am talking about and am willing to put my money where my mouth is, that if this motor fails then you can tell the this whole forum that I should not be listened to for advice.
> 
> You know you are dealing with someone who knows their stuff if they are willing to spend their own money to prove it.


So just to make sure I read this right, you're willing to buy a motor and send it to me for free to make your point?


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## Dennis (Feb 25, 2008)

hoowahfun said:


> So just to make sure I read this right, you're willing to buy a motor and send it to me for free to make your point?



The advice you receive must be accurate or else we will lose members from our advice being wrong and a disgruntled member will spread the word to others that the members here do not know their stuff and thus as a result we will not gain more members. I do not want that to happen and so I want your conversion to be successful so that you can spread the word to you friends to come to this forum so it can grow as the #1 source for information on EV related information.


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