Burnt out start capacitor on car ramp

[Lucien Nunes]

You may find the single phase ramp you saw actually had different internal gearing or a finer pitch on the drive screw than the 3-phase version even though they looked identical at a glance.

I'd agree this is very likely the root cause. If I were making lifts I certainly wouldn't ask a 2.2kW single-phase to lift at the same speed as a 3kW 3-phase from a standing start, even with less than max lift load. I bet the switch never opened because the motor couldn't get up to speed, and AC electrolytic start caps are only short-duty rated. Inverter sounds the way to go, if you've got the old motor and it can be connected for 230V.

 

[LeeH]

Have you also check on how many poles the original motor had?

 

[j_mcvic]

I'm not sure if you'll find a single phase input to three output drive as big as 3kW but it would work if you can.

The single phase motor being undersized would cause what's known as excessive slip which leads to very high run current and excessive heat in the rotor and the windings. Hence the rapid demise.

As Rob says you've installed a smaller output motor and the double whammy is that single phase is far less efficient and less starting torque than three phase. You may find the single phase ramp you saw actually had different internal gearing or a finer pitch on the drive screw than the 3-phase version even though they looked identical at a glance.

The other ramp with the 2.2KW motor was a 3ph as well. It was all connected up to the same supply in the dealership.

6SL32105BB230AV0 / 6SL3210-5BB23-0AV0 - Siemens V20 - 3 kW / 13.6 A (FSC), Filtered

3kW is about as big as they go Marvo.

Although without checking, I'm not sure if this particular model is allowed for domestic use, without extra filtering. Not that anyone would notice.

Thanks for the link... If I had known such a thing existed for so cheap I would probably of gone down this route in the first place. Everything that I found was massively expensive.

Hi,mostly covered above^ i would add,a check on your supply to this ramp,with regard to voltage drop,etc,would be in order,before souping up an already struggling motor!

The change to single phase,will give issues,as the ramp has not been designed for such.

Lowering the gearing,at the motor,used to be quite common. It could be a simple ratio change by pulley size (although problems can occur due to a smaller driving pulley having insufficient contact on the belt),or fast and loose,or idler set-ups...but a brief read of the legislation regarding LOLER and PUWER,will indicate to you,the responsibilities,of undertaking such alterations or modifications,to the original design.

To the extent,that as bizarre as it may sound,if such mods were carried out,and an intruder broke in to your garage,operated the ramp,and injured himself in the process - you would have a degree of liability.

Exasperating,but true.

Interesting that you mention a supply check... Its actually running off a 6Kva generator which is rated to 26.1 amps at 230V. When I ran the ramp the first time with no load on it there was no noticable drop on revs from the genny as if it was struggling. Even with the car on it didnt sound like it was struggling or starting to stall.

I'd agree this is very likely the root cause. If I were making lifts I certainly wouldn't ask a 2.2kW single-phase to lift at the same speed as a 3kW 3-phase from a standing start, even with less than max lift load. I bet the switch never opened because the motor couldn't get up to speed, and AC electrolytic start caps are only short-duty rated. Inverter sounds the way to go, if you've got the old motor and it can be connected for 230V.

Yea I still have the old 3 phase motor says it can run off 240AV and 415YV. I can post a picture of the plate if needed!

Have you also check on how many poles the original motor had?

I dont know how many poles it is but I have a picture or all the pins and connections that I can post up if you could tell me?

Thank you all for the help so far... some good foor for thought and it looks like the inverter that Rob posted up could be a winner! Any more advice would be muchly appreciated!

Thanks
Jamie

 

[Lucien Nunes]

Its actually running off a 6Kva generator

This is important. Induction motor loads are notoriously difficult for small generators and they often cannot output their full kVA rating without the voltage drooping badly, no matter how well the engine handles the kW (real power) load. How badly depends on the type of regulator and how it reacts to low power factor etc. But you might have a compound situation where the motor is trying to run up against an overload due to the lift gear ratio being designed for a larger motor, whilst running on a voltage at or below its minimum, plus if the output waveform distorts with motor load and/or the frequency is a little off, the phase shift of the capacitor winding may be incorrect, further reducing available torque.

Number of poles indicates the ratio of shaft speed to frequency. On 50Hz, 2-pole runs just below 3000rpm, 4-pole near 1500 and 6-pole near 1000rpm. If the replacement motor was rated for a higher speed (e.g. 4-pole instead of 6) then its torque would be reduced in proportion for the same kW rating.