Burnt out start capacitor on car ramp

[j_mcvic]

Hi,

i recent bought a 2 poster screw type car ramp. Changed the motor for a 2.2kw motor. Wired it up and tested it with nothing on it and it went up and down no bother.

Put my 1 tonne Clio on it and it lifted about 1ft off the ground and then ground to a hault. It went back down no bother.

I I took the cover off the motor and tried to raise the ramp and smoke came out the start capacitor. The start capacitor is a 250 micro farad and 300 VAC. My question is - can I fit a larger capacitor? Would it be worth fitting an in line switch as like a second centrifugal switch as I think this is why the original capacitor burnt out.

Any advice would be much appreciated!

thanks
Jamie

 

[GMES]

Hi Jamie and welcome to the forum.

 

[j_mcvic]

Hi Gmes - thanks for the welcome!

 

[Marvo]

If this is your own personal car ramp then it's one thing but if this is for a customer then I'd advise extreme caution, there would likely be a jail sentence if something went wrong and someone got injured.

It sounds to me like the new motor wasn't the same spec as the old one, maybe it's a different rotational speed or maybe a different type of motor with different starting torque characteristics such as CSR instead of CSCR for example.

You can't just introduce a switch to the capacitor to make one type of motor behave like another, they're constructed differently from the ground up and they're wound differently.

I'm not sure on your level of motor experience but the next step is to test the windings to see if they've survived the overload condition, replace the burned out cap and bench test the motor. If it survived then you'd need to start figuring out if it's a different spec to the original motor or whether there's a mechanical issue somewhere causing the overload.

 

[j_mcvic]

Hi All,

First off I want to apologise for my horrendous grammar in my first post. I wrote it tired and in a rush last night - big mistake!

I also missed out some vital information. The ramp was originally a 3 phase ramp. When I went to buy it it had a 3kw 3 phase motor on it. The guy also had an identical ramp for sale with a 3 phase 2.2kw motor on it. So I bought a 2.2kw single phase cap start and cap run motor.

I must add that this ramp is purely for myself as a hobbyist mechanic. If there was going to be other people involved I would be purchasing new and having professionally installed. I will be honest - my electrical knowledge is not extensive. However, I do have a good practical ability and a good ability to follow instructions!!

The old motor (leroy - Somer) that came off was a 3kw, 11.3A @ 240V and 6.5A @ 415V.
The new motor (techtop) 2.2Kw, 12.6A @ 230V.

As always - any advice is much appreciated.

Thanks
Jamie

 

[Bobster]

There lies your problem.

You've fit a smaller motor with less torque.

 

[j_mcvic]

Hi Rob,

Even though the ramp right next to mine which was identical was running off a 2.2Kw motor?

Thanks
Jamie

 

[Bobster]

Hi Rob,

Even though the ramp right next to mine which was identical was running off a 2.2Kw motor?

Thanks
Jamie

That was 3 phase though correct?

 

[j_mcvic]

That was 3 phase though correct?

Rob, this is correct. I know that single phase motors are not as efficient as 3 phase motors so appreciate that these 2 motors are not on a par. However these ramps were in a Renault main dealership so would be up and down multiple times a day 5 days a week including much heavier vehicles than my Clio! I assumed the 2.2Kw single phase motor would be enough to raise my Clio on the occasional weekend. So that was my thinking behind getting a 2.2Kw motor. However taking a step back and looking at it again a too small motor makes perfect sense sadly. If it's too small then it's lifting but not getting up to speed to open the centrifugal switch therefore burning out the capacitor. Is this correct?

So realistically I have 2 options. The most feasible and probably the best would be to change the motor for a 3Kw version. The second option would be to get a bigger driven gear on the top of the ramp to reduce the torque required from the motor.

Thoughts?

Thanks
Jamie

 

[Bobster]

Rob, this is correct. I know that single phase motors are not as efficient as 3 phase motors so appreciate that these 2 motors are not on a par. However these ramps were in a Renault main dealership so would be up and down multiple times a day 5 days a week including much heavier vehicles than my Clio! I assumed the 2.2Kw single phase motor would be enough to raise my Clio on the occasional weekend. So that was my thinking behind getting a 2.2Kw motor. However taking a step back and looking at it again a too small motor makes perfect sense sadly. If it's too small then it's lifting but not getting up to speed to open the centrifugal switch therefore burning out the capacitor. Is this correct?

So realistically I have 2 options. The most feasible and probably the best would be to change the motor for a 3Kw version. The second option would be to get a bigger driven gear on the top of the ramp to reduce the torque required from the motor.

Thoughts?

Thanks
Jamie

Whilst efficiency comes a little into play here, it's the starting torque a 3 phase motor gives out over a single phase one that is most likely to be your issue.

This is probably why the capacitor has burnt out, it's not got enough guts to get it to a speed where it is taken out of circuit.

Mechanically altering the gearing is a solution. Or a larger single phase motor.

Edit: if the motor has burnt itself out, it raises the question of is the motor protection suitably rated.

 

[Darkwood]

Why not put the 3ph motor back on and fit a VSD single to 3phase drive but you will need to know your regulations regarding lifts and ramps as adapting and/or altering the controls in any way can have a knock on effect as to the safety of the equipment .... even for personal use, I would think long and hard about doing any alterations and consider the possible safety implementations in doing so.... your safest bet is return it back to 3 phase and use a 1ph to 3ph power inverter thus assuming the ramp/lift is safe to use then you haven't done any changes.

 

[LeeH]

That ^^^^^^

 

[Marvo]

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.

 

[Bobster]

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.

 

[PEG]

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.

 

[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.