Converting to dual motors

[David_ski]

Originally Posted by Nature Ist

David,
Were you able to determine the total Amp draw when both motors are lifting together compared the Amp draw with the single motor when it is lifting both legs together as was the original factory set-up? Though not an electrical engineer, I think both motors lifting the same weight would be only a small amount more than the single motor.
I'd love to know from someone who has made this conversion, or from someone who knows the draw from two motors each lifting half the weight.

I will be able to comment on that after I complete the conversion. I believe your assumption that there should be only a small amount more current required than a single motor is correct. The total energy required for lifting is the same, and will now be divided between the two motors. The additional overall energy required will be just from the less than 100% efficiency of the motors.

I have the wiring completed. New fused 30A circuits after the main power disconnect switch have been wired in. Along with a second extend/retract switch. I am awaiting on the motor, gearbox, and lead landing gear repair kit to arrive by next Friday. However due to commitments, it will be a couple of weeks before I will have a day to make the changeover.

I will take and log current measurements of the single motor before changeover and with the dual motors after changeover.

[David_ski]

Originally Posted by Nature Ist

David,
Were you able to determine the total Amp draw when both motors are lifting together compared the Amp draw with the single motor when it is lifting both legs together as was the original factory set-up? Though not an electrical engineer, I think both motors lifting the same weight would be only a small amount more than the single motor.
I'd love to know from someone who has made this conversion, or from someone who knows the draw from two motors each lifting half the weight.

I am in the process of converting to dual motor. After doing a rewire for the landing gear circuits I did some current measurements. I will summarize the results after the dual motor setup is complete. I started thinking about DC voltage losses over a distance run. Using the Southwire Calculator (https://www.southwire.com/calculator-vdrop)

Single Motor Currents
No load = 3-4A
Retract under load = 9-10A
Extend under load = 21-23A with an occasional 25A

12V wiring Path
6 AWG Wire
Battery -> Main switch -> Progressive Industries PD4500 AC/DC power distribution panel
~ 12 Feet the voltage drop is 0.84% = 100mV. Negligible loss and it will be ignored.

10 AWG Wire
PD4500 DC Distribution panel -> 20A auto reset circuit breaker -> back of RV to wireless transmitter/receiver panel -> to landing leg extend/retract switch -> landing leg motor.
10 Feet to back of RV from the 20A breaker + 7 Feet up wall to wireless transmitter + 7 feet down wall + 22 Feet back to front of RV to landing gear switch = ~46 feet. A 46 foot run of 10AWG wire consuming 22A DC will see a 17.3% voltage drop = 2.0V. If the 10 AWG wiring from the DC Panel to the wireless transmitter and back to the front of the RV is routed in the attic there will be a couple of more feet required for the overall run.

The new 8 foot run of 10AWG wire (fuse -> switch -> motor) consuming 22A DC will only see a 3% voltage drop = 360 mV.

With a 20A circuit breaker in the path and consistently getting lifting currents between 22-25A explains why the circuit breaker would keep popping every minute when I am lifting. As the current goes up, the voltage drops at the motor, the motor has to work harder which causes more current to be consumed, and then auto reset circuit breaker would pop.

After rewiring the landing gear circuits, and reducing the wire run distance from the battery to the lift motor by 82% the lift motor operation is much better. Looking at the voltage drop on the factory wiring was an eye opener.

[Nature Ist]

David, Thanks for the detailed report of your findings. It's something a lot of people will benefit from when trying to make the conversion.
On my 2020 30.5 CKTS I do not have the remote wireless set-up you have, so the length of run from the battery to my landing gear is only a matter of few feet. I have virtually no voltage drop.
I determined that my landing gear failure was not the motor or the gearbox; it was the threaded rod (jack screw) and the threaded collar on the lead landing jack; the follow landing jack threads were also very close to failing.
Not long after taking delivery of my new unit, I learned of the well-known lack of grease on the gears and threaded jack screw. At that time I installed angled grease Zerks and added two additional Zerks. I greased the living daylights out of the entire assembly.
When I removed the failed lead and follow landing gear I took them apart and found the entire jack screw was very well greased, as were the collar and the gears at the top of the jack. My unit is not loaded heavily, and comes in under it's gross by a good margin. I found crescent moon shaped slivers of metal imbedded in the grease of the screw as I wiped it clean. This comes down to insufficient grade metal on the collar in particular.
What I found led me to believe that I would not avoid this same problem again by switching to dual motors. I opted to replace both jack legs with the only available components - which are exactly the same as the OEM.
I do find the new jacks, with the same original motor and gear box, much smoother and quieter, and the motor does not labor much when lifting.
I would feel better if the dual motor option would prevent another such failure. I believe, if the threaded collar (which was only about 1" long) were made longer with more thread contact, it would not have failed.
I am now contemplating methods of reducing the strain on the landing gear to get better longevity out of the jacks.

[David_ski]

Originally Posted by Nature Ist

David, Thanks for the detailed report of your findings. It's something a lot of people will benefit from when trying to make the conversion.
On my 2020 30.5 CKTS I do not have the remote wireless set-up you have, so the length of run from the battery to my landing gear is only a matter of few feet. I have virtually no voltage drop.
I determined that my landing gear failure was not the motor or the gearbox; it was the threaded rod (jack screw) and the threaded collar on the lead landing jack; the follow landing jack threads were also very close to failing.
Not long after taking delivery of my new unit, I learned of the well-known lack of grease on the gears and threaded jack screw. At that time I installed angled grease Zerks and added two additional Zerks. I greased the living daylights out of the entire assembly.
When I removed the failed lead and follow landing gear I took them apart and found the entire jack screw was very well greased, as were the collar and the gears at the top of the jack. My unit is not loaded heavily, and comes in under it's gross by a good margin. I found crescent moon shaped slivers of metal imbedded in the grease of the screw as I wiped it clean. This comes down to insufficient grade metal on the collar in particular.
What I found led me to believe that I would not avoid this same problem again by switching to dual motors. I opted to replace both jack legs with the only available components - which are exactly the same as the OEM.
I do find the new jacks, with the same original motor and gear box, much smoother and quieter, and the motor does not labor much when lifting.
I would feel better if the dual motor option would prevent another such failure. I believe, if the threaded collar (which was only about 1" long) were made longer with more thread contact, it would not have failed.
I am now contemplating methods of reducing the strain on the landing gear to get better longevity out of the jacks.

Thanks this is also great information. I bought a lead landing gear repair kit.
That will not address the jack screw and threaded collar failure. I don’t believe my unit is near its rated load. It is a 24.5CKTS with a pin weight less than 2k lbs. if the weight on the legs is double that at 4k being closer to the axle, that is still only 2k per leg. 2k leg load is less than 50% of its rated capacity. The first owner of my unit had health issues shortly after he bought it, and the RV spent most of its time the last four years in storage. I lubed them well when I bought the unit, but they could of been used dry in the past.

I will fully disassemble my unit to inspect its integrity and determine if I need to replace the entire landing legs. I was planning on adding some additional grease zerts while I had the leg off the 5th wheel. The existing grease zert for the screw threads is difficult to access and interferes with the door frame. Putting in an angled and a second and third zert will eliminate the interference.

[David_ski]

Originally Posted by David_ski

I am in the process of converting to dual motor. After doing a rewire for the landing gear circuits I did some current measurements. I will summarize the results after the dual motor setup is complete. I started thinking about DC voltage losses over a distance run. Using the Southwire Calculator (https://www.southwire.com/calculator-vdrop)

Single Motor Currents
No load = 3-4A
Retract under load = 9-10A
Extend under load = 21-23A with an occasional 25A

I completed the dual motor conversion yesterday. I had a few challenges throughout the day. When I was lowering my unit the bolt holding the tie bar between lead and follow leg snapped at the lead leg side. It took a while to get the remaining bolt out and I am not exactly clear on what seized to cause the bolt to snap. Whatever caused the bolt to snap would be in the follow leg. After disassembly and examination of the follow leg, there was nothing obvious to cause the binding. The screw gear ran smoothly the entire length from extend to retract.

I took out the old bevel gears and cleaned and inspected everything. I thoroughly greased the screw shaft and added grease to the threaded nut. As I went to install the new bevel gears from the lead gear repair kit, I noticed that the horizontal bevel gear hole that mounts to the threaded screw shaft was not large enough to fit onto the shaft. The old and new bevel gears were shaped slightly different. I used the new lead drive shaft and new bushings, but I used the old bevel gears. After I got it all together, I packed the gears well with new grease and assembled the landing gear leg.

The new motor and gearbox easily went onto the landing leg and after tightening up all bolts. the job was complete.

Single Motor Currents
No load = 3-4A
Retract under load = 9-10A
Extend under load = 21-23A with an occasional 25A

Dual Motor Currents
Retract under load = 10-12A
Extend under load = 20-22A

I was surprised that the overall dual motor current required for lifting was slightly lower, but it was more consistent than with a single motor. I chatted with my son (also an electrical engineer), and we talked about motor torque/current charts in general. Running each motor under less load have the motors operating in more efficient portion of torque/current curve.

The new motor tends to run just slightly slower than original motor. For $110, I might change out the original motor so that both motors will be from the same manufacturer.

Today I will pull the original lead leg and do a full a disassembly, inspection, and re-grease the gears and screws.

[Nature Ist]

David, I guess it makes some sense that the current demand could be lower for 2 motors working much easier than one working hard. It's an outcome you won't regret! I hope your tie bar bolt shear wasn't a result of what I experienced. I did have some previous binding before my lead leg jack screw stripped. When I removed my follow leg, I could not see anything wrong until after replacing it with the new follow leg. It was at that point that I destroyed the old leg to get the jack screw out and discovered the slivers of metal from the collar and jack screw threads that were embedded in the collar. They seemed to be loose enough to cause an intermittent binding.

When researching the dual motor option, and when looking at replacement motors, I had noticed the replacements were a slightly different RPM and wondered about how noticeable that would be. I think you now know. My only concern with dual motor, or different motor speeds, is raising the front sides unequally, the front frame a bit or putting too much lift on the one side that is lifting sooner than the other. The concern with that is: putting more weight on one of those jack screws that we know are prone to failure.
I guess I'll be keeping my hydraulic bottle jack in my truck while traveling!

[David_ski]

Originally Posted by Nature Ist

David, I guess it makes some sense that the current demand could be lower for 2 motors working much easier than one working hard. It's an outcome you won't regret! I hope your tie bar bolt shear wasn't a result of what I experienced. I did have some previous binding before my lead leg jack screw stripped. When I removed my follow leg, I could not see anything wrong until after replacing it with the new follow leg. It was at that point that I destroyed the old leg to get the jack screw out and discovered the slivers of metal from the collar and jack screw threads that were embedded in the collar. They seemed to be loose enough to cause an intermittent binding.

When researching the dual motor option, and when looking at replacement motors, I had noticed the replacements were a slightly different RPM and wondered about how noticeable that would be. I think you now know. My only concern with dual motor, or different motor speeds, is raising the front sides unequally, the front frame a bit or putting too much lift on the one side that is lifting sooner than the other. The concern with that is: putting more weight on one of those jack screws that we know are prone to failure.
I guess I'll be keeping my hydraulic bottle jack in my truck while traveling!

Today I took the lead jack leg apart and lubricated everything. The elevation screw did not operate as smooth as the follow leg. I have a new lead jack leg on order that will be here on Tuesday. I put it all back together to get the kingpin off of my truck. The passenger side (formerly follow leg) operation with the motor is smooth. The driver side motor wobbles back and forth as the lead screw catches and releases. It will only need to retract one more time.

I watch the legs as I raise and lower landing gear. I don't let it get more than 3/4 inch off from side to side. After raising and lowering the jacks a couple of times, I now have a operating pattern going between: raise both simultaneously, raise the passenger side only to catch up, and then back to raise both simultaneously.

[David_ski]

Originally Posted by David_ski

Today I took the lead jack leg apart and lubricated everything. The elevation screw did not operate as smooth as the follow leg. I have a new lead jack leg on order that will be here on Tuesday. I put it all back together to get the kingpin off of my truck. The passenger side (formerly follow leg) operation with the motor is smooth. The driver side motor wobbles back and forth as the lead screw catches and releases. It will only need to retract one more time.

I watch the legs as I raise and lower landing gear. I don't let it get more than 3/4 inch off from side to side. After raising and lowering the jacks a couple of times, I now have a operating pattern going between: raise both simultaneously, raise the passenger side only to catch up, and then back to raise both simultaneously.

New lead leg arrived yesterday and I swapped out the old one today My landing leg needs to extend 19-3/4" to get to level in my driveway. I marked my leg extension with a scribe, and permanent marker every 2 inches to 18", 19" and 19-3/4". The dual motors run at slightly different RPMs. This allows me to visually watch each side extend and retract so I keep them close to equal.