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Electric Horseless Carriage Rework

 I recently purchased an electric horseless carriage based on the design in the following link - http://www.szott.com/carriage/carriage.html.   I knew it would need some rework, but now I am thinking I may need to replace the motors and controller.

The cart uses 2 of your 24v (MOT-24450G) motors and a Curtis PMC 24-36v, 275 amp controller.  On level hard ground it scoots along very well at about 10 mph pulling less than 20 amps but when it has to climb a hill, especially on grass, it jumps to 100 amps and blows an 80 amp fuse between the batteries

Using your gear ratio calculator, the gear ratio is 16.78 with a top speed of 12.45 mph.  The empty cart weighs 460 pounds.  On jack stands, the wheels spin freely with 1 finger.

I am wondering if I need to go to 2 - 36v 1000 watt motors and controller(s) or can a cart this big and heavy be powered electrically with your products?

A cart as big and heavy as that can easily be powered with two 1000 Watt motors and they would provide a little more than twice as much power as it has now with the two 450 Watt motors.

Since carriage's the existing Curtis controller is rated at 24-36V and 275 Amps it provides an ample amount of power for the vehicle and would not need to be replaced if upgrading to more powerful 24 or 36 Volt motors.

If the two MOT-24450G gear motors are demanding 100 Amps of current from the battery pack when going uphill then that is quite a bit of power for them to use. Most electric bikes that have one of those motors use a 40 Amp circuit breaker so the 80 Amp circuit breaker is a perfect size for the two motors.

Since the carriage currently uses gear motors they would need to be replaced with gear motors to keep the total gear ratio near the same as it is now.

We have a 48 Volt 1000 Watt gear motors item # MOT-481000PL available, however, since the existing controller is rated for 24-36 Volt then it would need to be replaced in order to use these motors.

We also have 24 Volt and 36 Volt 650 Watt gear motors available which are item # MOT-24650PL and item # MOT-36650PL. These 650 Watt gear motors are around 50% more powerful than the existing 450 Watt gear motors and unlike the sealed design of the 450 Watt gear motor, they have a ventilated design with a built-in fan which cools them during peak loads such as when traveling up hills.

If two 24 Volt 650 Watt motors were installed then the circuit breaker could be upgraded to 120 Amps so it could better handle the demands of driving the carriage uphill.

Please let us know if you have any questions.

Thanks for the quick reply.  Sorry but I copied the wrong model number for the motors I have.  They are actually MOT-24500X2500 non-geared motors.  The drive train for each wheel is, motor gear 11 Teeth, jack shaft input sprocket 60, jack shaft output sprocket 13, and final drive sprocket at the wheels, 40.  Overall gear ratio 16.78.

Another question: is there a way to limit the power so it will not blow a fuse?


That is great news about the motors because then you could use two 36 Volt 1000 Watt motors such as item # MOT-361000B and not need to purchase a new the speed controller.

The only way to limit the power, other than through a blowing a fuse or tripping a circuit breaker, is through the size of the speed controller. For example, if a 100 Amp speed controller was used then it would limit the power output and consumption to 100 Amps and if used with a 125 Amp circuit breaker then the circuit breaker would not trip unless there was a short-circuit in the electrical system.

Since the vehicle already has a 275 Amp controller though, and the motors it is and will be used with are rated for less than 275 Amps, then the circuit breaker is presently the only way of limiting the power.

For two a speed controller wired to two 36 Volt 1000 Watt motors we recommend using either a 100 or 125 Amp circuit breaker.

Please let us know if you have any questions.
I am going to take your advice and go to 2 36 volt motors, MOT-361000B, and probably 3 22 Ah batteries.  To prevent blowing fuses as stated above, what controller(s) would you recommend?

Fantastic weekend service!


We carry a heavy-duty 36 Volt 2000 Watt controller item # SPD-362000 which has a 60 Amp current limit. This controller could be used with an 80 Amp fuse and since it has a 60 Amp current limit it should not blow the fuse unless there was an electrical problem.

We also carry a heavy-duty 36-48 Volt 1000 Watt controller item # SPD-481000D which has a 35 Amp current limit. Two of these controllers would be required, one for each motor. They would provide a combined current limit of 70 Amps which makes two of them a more powerful than the 60 Amp controller so they would provide more power to the motor.

We also carry a standard-duty 36 Volt 1000 Watt controller item # SPD-361000B which has a 30 Amp current limit. Two of these controllers would also be required. They would provide a combined current limit of 60 Amps. I only recommend this controller for use on flat ground though since it does not have very much cooling capacity.

One throttle can be wired to two controllers. Most Curtis controller work with 5K Ohm throttles and our speed controllers work with hall-effect throttles so if the original throttle is a 5K ohm type then it will need to be switched over to a hall-effect type throttle to use with our controllers. 

Please let us know if you have any questions.

I cannot determine what my throttle is so lets replace it.  Need a foot pedal throttle for use with your SPD-362000, 2 MOT-361000B motors and 3 22Ah batteries.  Can you make this into a package, with wiring diagrams, connectors, etc?
We can make those parts into a kit which will have matching and labeled connectors on all of the parts so all you have to do is plug them together. We can also supply a wiring diagram for the kit after it is made upon request.

Also, if you would like, we could add a heavy-duty reverse relay and direction switch to the kit for around $50 extra. This reverse relay would have a parking brake feature that would stop the motors from spinning when the direction switch was in its middle park position. When the switch is in its park position the motors could still very slowly move if the carriage was on a steep hill but would hold the cart at a complete stop under most other conditions. The direction switch would be an old-fashioned style panel mount toggle switch that looks like this.


22Ah batteries are rated for a 7 minute maximum discharge current of 66 Amps and a 30 minute maximum discharge current of 46 Amps. Since the SPD-362000 controller has a 60 Amp maximum current rating this is something to consider. If the carriage would be used to go up steep hills for a maximum time of 7 minutes at a time then the 22Ah batteries will be suitable, however, if the carriage needs to travel up steep hills for more than 7 minutes at a time then larger batteries should be considered.

I do not see a 36 Volt battery charger on your list so I am not sure if you already have one or need one included with the kit.

I can go ahead and start making the kit but I need to ask a few questions first.

Would you like the kit to have reverse?

Will the 22Ah batteries be suitable or do you need larger batteries?

Do you need a battery charger included with the kit?

Please let us know if you have any questions.

I hope you can assist me with some trouble shooting. On a rare occasion my cart will only move in one direction when turned on. If I turn it off and back on it will work fine in both directions. Turn it off and back on again and only one direction. There is no rhyme or reason to which direction will work, sometimes it's both, some times its only one, sometimes it's neither. It is not a mechanical issue because the motor doesn't spin when the issue happens. Do you think this would be somewhere between the throttle/direction switch and the power from battery?
Hi Brad, from your description the problem sounds most likely to be the relays. The relay contacts carry the full power of the motor so they are the most stressed switching part on the wagon and the most likely to wear out. The original relays in your kit are 36V 40A and we recently added a more powerful 36V 60A relay to our lineup which is our item # RLY-3660T.
Would relays act this way? I would think they would either be good or bad. Why would they work sometimes and not other times. Would they have symptoms of resetting themselves like these are doing?
Would you like the kit to have reverse?
Yes.  There is a reversing switch installed but if I am going with new electronics, lets replace it

Will the 22Ah batteries be suitable or do you need larger batteries?
From your description, I will probably need larger batteries.  What I want to be able to use this cart for is driving around campgrounds, sometime on hard surface and sometime on grass, parades and outdoor events, that will have varying degree of hills but no real off roading.  Currently I have 2 deep cycle batteries that came from a telephone switch sub station.  The area that they set in is approximately 13 1/5 x 13 x 1/2.  I can go to 13 1/2 x 19 3/4 if need be without too much modification.  Larger areas would require more modification.

Do you need a battery charger included with the kit?
Yes.  It would be better to use one charger instead of 3.

Currently, there is a large relay connected to and on/off switch.  I thing this can be eliminated if there is an on/off for the controller.  I also have a keyed disconnect between the batteries that I will keep to prevent the cart from rolling away at night.

Again, thanks for all your help!  Wilson

Hi Brad, It is common for a malfunctioning relay to operate randomly and intermittently. One of the relay's contacts could be sticking and then unsticking from the vibration of the other relay turning off and on. The next time the problem occurs you could try tapping on the relays with the handle of a screwdriver or something similar to see if they start working. That is a good way to test the relays to see if they are malfunctioning.

Hi Wilson, The SPD-362000 controller requires a heavy-duty 36 Volt power relay connected to the on/off switch. If we make the kit with the heavy-duty reverse relay then we will need to wire the on/off switch and the reverse switch together in the wiring harness. The carriage's original 24 Volt power relay would not work for long before it burned out on 36 Volts so it will need to be replaced with a 36 Volt power relay during the conversion.

The next significant size up from 22Ah batteries are 35Ah batteries. 35Ah batteries can handle 84 Amps of continuous power draw so they are suitable for continuous hard or uphill driving of the carriage. Under light use on flat and hard ground, three 35Ah batteries are estimated to provide two or more hours of ride-time, and under heavy use such as continuous steep uphill driving closer to 1 hour of ride-time.

Would 35Ah batteries be suitable for the kit or are you looking for more ride-time than they are estimated to provide?

Lets do the heavy duty 36 V power relay and switches so everything matches up.

I would like the longest drive time I can get and some campgrounds can be quite hilly.  After some measuring, with some modification, I can get 3 of your BAT-12V75A batteries in my battery space if you feel these batteries would work.

When this project is complete, what kind of horsepower would this package produce?

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