yes, converting to ac will eliminate the problems you're having with the dc motors. i would suggest that you contact the mfg. of your etv's, (seimans, mais, etc.) for the needed conversion pieces which should include updated speed reducers. i assume you're at sinapore airport which should mean your units are mais.

note to the rest of you, not everything discussed here refers to forklift technologies. etv's are more elevator technology than forklift.

AC Motors will eliminate the brush issues but create new issues - like transducer problems the DC motors don't have. Engineering new technology is always a compromise at best.
You can't beat routine & PROPER maintenance (meaning no second level parts) by a knowledgeable, trained & professional person.

I agree with with randal-s.

There must be a means of holding the load elevated, without relying on a motor. A brake on the cable drum (assuming it has one) would make the most sense.

If the load weight is causing a DC motor to run backwards, a AC motor is going to run back wards as well. Does the motor run backwards with the power off?

It would be less expensive to get a new lift truck with AC motors and controls than to try and update an existing truck. Guarenteed.

By the way, I am a proponent of the AC motors and controls.

Has anyone thought of Brakes? It sounds like you have a variation of a cable elevator or in rolling terms a Transtacker such as Raymond Manufactures. I am going to go out on a limb and suggest it would be criminal for any engineer to design a piece of equipment that relied on a motor to hold position and not a brake system to hold the position. The first question should be what is the load and how is the mechanical system maintained. There are great benifits to using AC technology BUT I am not sure they are cost justifyable in revamping an older system.

Please go back to the basics, check the doccumentation. You need to find out what the engineers designed the piece of equipment to do then see what the service provider has bypassed and thirdly check to see what abuse, overloading or missuse the operators are adding to the situation.

A well maintained DC System should last for decades if: properly maintained, supplied the correct voltages ( dying batteries will kill electrical componants mostly Brushes and contactors) and operated within the design parameters.

Hi guys just come across your thread has anyone mentioned a permenant magnet ac motor as this would hold once the current was off assuming the load was not super heavy and when you apply current it would turn,not sure on the details I am relaying this third hand.

Seems to me that is a very strange way of doing things why not revamp your engineering on the Drum side using a clutch & a lock to secure the platform when traveling,- then to lower release the lock & lower -- I am no electrical engineer but it seems that you have already overloaded the electric motor subsequently burning it out & only an electrical engineer could tell you this - ( that is would an AC Motor do this consistently & what horsepower would be required to perform this task & hold the load then from your info i an presuming you reverse the direction of the motor to lower your load.

Having not seen your application but from the information you have sent i would be looking at modifying my drum & cable side
by placing a gear & mechanical lock - you could safely lift to a stopping point then lock - travel - lift & unlock then lower without to much modification.

To change to an AC motor would be very expensive & you would need an DC/AC transducer & some type of software to pulse that current to the motor changing it from DC to AC.

Let me know what you think.

An example of the Cam & lock mechanisms can be found on a simple come along / fence puller type of tool.

Hi Frankie,

We do not have hydraulics on our ETVs. The raising/lowering of platforms is by wire rope (electrical motor turning a wire-rope drum).

The failure was due to the DC motor being unable to provide sufficient torque to hold the wire rope drum. Main cause was the worn commutator brushes and faulty speed drive.

So, someone suggested that the use of AC motor would eliminate this. I just needed some confirmation that this is true before embarking on a major exercise to replace all our hoisting motors.

Hi Singapore.

You have a lowering problem AC motors create electrical power the relationship between the two factors seem irrelevant.

Most units today with advanced electronics have a load holding solenoid or some way to secure the hydraulics in a fixed position - In your case up.

Read the schematic & determine first if you have an Electrical problem or a mechanical one.

If all your electrical is OK - then you need to find out why the pressure is being lost & the unit is lowering by itself.

More information is needed to proceed further.

It is true. There are two inherent benefits of AC motors - one is that they can not "run away", if the system fail they will typically just stop functioning. The other benefit is that there are no wear items other than the shaft bearings, so the AC motor is maintenance free. No brush wear, no brush dust etc.
The downside has been the need for more advanced power electronics to create the AC current from a DC battery, but with reduced costs for electronics this is becoming less and less of a disadvantage.