Hoist Brake Coil Problem

[creisinger79]

The hoist brake coil is a 48VDC coil. The original electrical system for the coil involved a transformer (480VAC-48VAC), rectifier, and resistors. The components are no longer manufactured and we are attempting to upgrade to using a stand-alone 48VDC power supply. When the brake coil is activated, the 48VDC output from the power supply drops to 26VDC. The brake coil remain engaged for roughly 5 seconds then disengages. Do we need a larger power supply?

 

[timbobelfast]

The hoist brake coil is a 48VDC coil. The original electrical system for the coil involved a transformer (480VAC-48VAC), rectifier, and resistors. The components are no longer manufactured and we are attempting to upgrade to using a stand-alone 48VDC power supply. When the brake coil is activated, the 48VDC output from the power supply drops to 26VDC. The brake coil remain engaged for roughly 5 seconds then disengages. Do we need a larger power supply?

What is the rated output (I) of the DC PSU? Given the safety requirement of the hoist brake, you will not want to get this wrong!

Can you not source the correct like for like anywhere else?


Almost sure that I have seen similar in a Stahl crane control panel manufactured within in the last 5 - 6 years.

 

[snowhead]

I think this needs a lot more thought, as it's potentailly safety related.

The voltage dropping to 26v suggests the supply is too small.
But the fact the coil is remaining engaged suggests the steel / iron core is getting magentised more than with the old power supply.

I suspect that as the old supply was rectified A.C not true D.C. the core was being magnetised at a lower level.
You are using a pure D.C output supply I assume?

You may have to duplicate what was originally there, the brake coil would have been designed around it.

 

[creisinger79]

The power supply is 80W, 1.7A. This is a 15ton rated crane. The brake coil is large and rated at 48VDC...due to its age and poor record keeping, I don't have any more information on the coil. The crane manufacturer couldn't give us anything beyond the voltage. The bridge and trolley brakes, which are considerably smaller, were running the same system and have already been replaced with 48VDC power supplies with success. Operator damage to the crane, including the electrical components for the hoist brake system, has pushed the need for the upgrade. My superiors want to implement a straight 48VDC power supply for both cost and simplicity reasons. I suspected the power supply I had on hand would not be sufficient, but needed to "prove" that before a larger one was ordered. I don't have any science to back my belief that it's not large enough or that a straight power supply system will even work. Until I show that this won't work, going with an updated version of the old method won't be considered...especially since it works with the bridge and trolley brake coils.

That is correct, it was not a true DC system. It was rectified from a 480VAC primary/48VAC secondary transformer. Yes, it is a pure DC power supply.
[automerge]1598442004[/automerge]
Continuing with the rectified AC vs true DC with the power supply...doesn't the DC power supply do exactly what the other components were doing? The DC power supply transforms the incoming AC to the usable AC voltage level, then rectifies that AC voltage level to DC, then passes the voltage through a filter to smooth out the waveform. All this happens inside a single component. What am I missing that makes this process different from the old supply system?

 

[UNG]

Is there no information on the old components of the power supply that may give an indication of the output needed for the brake coil to operate correctly

If you have the resistance of the brake coil can you not do the calculation to get an idea of the size of PSU needed

 

[creisinger79]

I honestly didn't even think of that....

Took a resistance reading on the coil: 7.6 ohms.
Came up with 303 watts of power and 6.3 amps using Ohm's Law.

 

[UNG]

I honestly didn't even think of that....

Took a resistance reading on the coil: 7.6 ohms.
Came up with 303 watts of power and 6.3 amps using Ohm's Law.

I think you have found out why your 80w 1.7A supply didn't work

Now you have worked out what the coil can draw I would allow a bit more to cover the initial in rush current at it energises when looking for a suitable PSU

 

[Darkwood]

I am not too knowledged in crane/hoist regulations here but I would first ask if what you intend to do is compliant as this type of work has its own BS standards that need to be met, even repairing an old hoist that now falls foul of updated regs may mean you need to upgrade the whole control system to comply as you are altering the original control design.
I believe swapping like for like is acceptable but any changes will shoulder the responsibility of it future use and safety And compliance on you, I will assume you are aware of this before I give advice?

Edit ... you are US based so take the above with relevance to your local standards but I have quoted on UK standards and would have thought your own standards would contain similar requirements... ps.. I i can still buy these control voltages here in the UK, seems they are phased out in the US then?

 

[creisinger79]

I am aware as is the company I work for. We have been in contact with the original crane manufacturer and the crane service company and both agree that a properly sized 48VDC power supply should accomplish the same function as the old system (transformer, rectifier, diodes).

 

[Darkwood]

My concern is this is a safety critical device and unless the manufacturer in writing specs a modern alternative then the responsibility is on yourself, this makes it difficult as a forum to comment but yes it does sound your dc power supply is underrated or the brake coil is at fault thus dragging down the voltage.

I would get the brake details if available to correctly spec the dc supply if you lack these details then going overboard with the dc power rating would be advisable to ensure a load related failure doesn't occur, the last thing you want is a heavy load not been stopped because the brake supply was borderline and couldn't match the full load of the crane.

Which ever supply you go for I would push for a crane calibration to push it to its limits and ensure the brake holds under max load following your repair.

 

[SheffSimon]

I am not too knowledged in crane/hoist regulations here but I would first ask if what you intend to do is compliant as this type of work has its own BS standards that need to be met, even repairing an old hoist that now falls foul of updated regs may mean you need to upgrade the whole control system to comply as you are altering the original control design.
I believe swapping like for like is acceptable but any changes will shoulder the responsibility of it future use and safety And compliance on you, I will assume you are aware of this before I give advice?

Edit ... you are US based so take the above with relevance to your local standards but I have quoted on UK standards and would have thought your own standards would contain similar requirements... ps.. I i can still buy these control voltages here in the UK, seems they are phased out in the US then?

Just for your info, there's a version of 60204 applicable to hoisting machines 60204-32. Other than that, it's 12100 risk assessment and then 13849 or 62061 for functional safety. As you say, needs some thought and considered design.

 

[UNG]

Just for your info, there's a version of 60204 applicable to hoisting machines 60204-32. Other than that, it's 12100 risk assessment and then 13849 or 62061 for functional safety. As you say, needs some thought and considered design.

Are these USA standards or UK as the OP is the other side of the pond

 

[creisinger79]

Found a power supply to properly operate the brake coil. Thanks everyone for your help on this.

 

[Megawatt]

The hoist brake coil is a 48VDC coil. The original electrical system for the coil involved a transformer (480VAC-48VAC), rectifier, and resistors. The components are no longer manufactured and we are attempting to upgrade to using a stand-alone 48VDC power supply. When the brake coil is activated, the 48VDC output from the power supply drops to 26VDC. The brake coil remain engaged for roughly 5 seconds then disengages. Do we need a larger power supply?

Yes with DC voltage it is terrible about voltage drop. The inrush current on a coil is tremendous and try putting a snubber across the coil. That could be what’s holding your coil in