Having problems with new lift device power control and delivery

Thread Starter

DevineDesign

Joined Oct 22, 2023
11
Recently I designed a machine that uses a 48vDC brushed motor and uses a 24vDC electromagnetic brake for holding in the off position. Normally Our company uses a push button DPDT pendant for the forward and reverse motion needed. However I'm struggling with a finding a suitable power supply and B how to engage the motor power and the brake power simultaneously. Additionally I would like to add a backup battery and switching the device so this unit can operate in case of a power outage. I'm really struggling with the best way to deliver the power for the motor/brake, And also the best way to arrange the components needed.

1. Is it safe and is it efficient to run a buck converter to lower the voltage for the brake from the power supply?
2. What would the ideal power circuit look like?


This machine is only ran for a maximum of two minutes in either direction. At a maximum of three times a day. So the usage is very minimal.

motor is 48vdc @ 250watt

I am new to this and am not asking for the answers simply some good advise for a good start. Thank you from Iowa.
 

crutschow

Joined Mar 14, 2008
34,047
Since you want battery backup, you could use four small 12V sealed lead acid batteries to get the 48V power and keep them on a trickle charge when power is available.
That way the power supply (charger) can be small and you don't have to do any switching for operation with a power outage.
how to engage the motor power and the brake power simultaneously
I assume you mean not at the same time(?).
Is it safe and is it efficient to run a buck converter to lower the voltage for the brake from the power supply?
Should work fine.
What current does the brake require?
 

Tonyr1084

Joined Sep 24, 2015
7,777
Recently I designed a machine that uses a 48vDC brushed motor and uses a 24vDC electromagnetic brake for holding in the off position.
I assume you mean not at the same time(?).
The way I read the TS is that powering the 24VDC brake releases the brake when powered. In other words, when motor power is applied so is "Brake Release" power, enabling the machine to move.

You say you recently designed a machine. If you're still in the design stage and haven't built or invested capital in the project you might consider using something like a worm drive and a lower voltage motor. I recently designed and built a home made freight elevator using a 12 volt wench made for mounting on your vehicle and pulling your car out of a stuck situation. With worm drive it's very unlikely your project will move when the motor is not powered.
1. Is it safe and is it efficient to run a buck converter to lower the voltage for the brake from the power supply?
2. What would the ideal power circuit look like?
1) I would assume it's safe as long as you don't exceed the amperage the buck is designed for. The closer you come to the max current the buck is rated for the more heat it will generate. Exceed the rating and you could burn it up. So allow yourself anywhere from 33% to 50% headroom. In other words, if your project will draw 10 amps when operating then the buck should be rated for at least 13.3 amps to 15 amps. That "headroom" acts as a safety to insure the machine won't fail prematurely. Wouldn't recommend double the amperage, you're just spending more money than you need to. However, others here are from the "Double the Amps" camp; and that's fine. You can double the capacity of the buck if you want. So with my example, requiring 10 amps but having a buck that can handle 20 amps isn't going to break the bank. It's long been MY opinion that 33 to 50 percent headroom is sufficient. In the industry, commercial electronics are generally rated for 33% headroom whereas "Mission/Life" critical electronics are built with 50% headroom. NASA, Military, Medical all use the 50% rule. So does the automotive industry because you're operating a potentially dangerous machine. But things like kids toys barely design to meet the need.

Years ago my mother-in-law (MIL) ((not MILF)) bought a new washing machine. It suffered a failure in just two years. To fix it was going to cost anywhere from $330 to $400. A large part of the bill was for the ENTIRE MECHANISM when all that was needed was a new "Mode Shift Coil" (MSC). Her decision was to scrap the machine and buy a new one. Before she could do that I took the machine and pulled the MSC out. It failed because the Fusible Link, (FL) a fuse that will burn out if a certain temperature is exceeded, thus preventing a fire. Did the math and found the FL was rated for 106% of normal operation. No wonder why it failed. It was designed to fail. Looking on line I found MANY complaints about that particular failure. So for $1.98 at Radio Shack I bought a new FL rated for 146% of normal operation. It's got to be close to if not fully 10 years since that repair. The machine is still running fine. No problems whatsoever. So headroom is important. Your approach is "Designers Prerogative". YOU get to decide what meets your needs.

As for question #2; again, the circuit you choose is up to you. We can probably come up with several different approaches. Knowing more about what you're doing will hone in on the best solution. But at present - you're just asking for free engineering. I'd like to help, but I don't know enough about what you're trying to accomplish. I don't even know if you've spent any money yet, and there may be a better approach.

Check out my video on the home made freight elevator.
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
A reliable mains source is a suit transformer with 48vac secondary and a bridge rectifier, no Capacitor needed.
Do NOT use a SMPS supply.
 
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MisterBill2

Joined Jan 23, 2018
17,800
Max is correct. And I built a power trailer mover with a gearmotor that had the electric released brake, and it works very well. Use one switch to select motor direction and then switch them both on and off with a second switch. Been using that driver for 20 years with no problems.
The different voltages do pose a real problem, however.
Is the 24 volt brake normally applied? or is it normally released and it requires a voltage to apply? I am hoping that the brake is normally applied and requires the24 volts to release, so that overheating will not be a problem.
IF, and ONLY IF, the brake is released by the application of power, then a series resistor to drop the voltage could work adequately, with the two connected in parallel with the motor. THis should be OK for short operations, at least.

NOTE: using a motor and brake requiring different voltages is a quite poor choice!!
 
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Thread Starter

DevineDesign

Joined Oct 22, 2023
11
Thanks for the input. So the new design is basically a DC version of the only product the company I work for manufactures. The only product. So I have big shoes to fill. The previous unit which is still in production is old iron and hard to beat. Some of the units in the field have never been serviced in 20 years. So I don't want to fail.

The Gearmotor was purchased before I took the position so no choice on the drive otherwise it would have been worm drive. I have attached a image of the unit I will be using. Also the pendant forward and reverse. Thank you everyone.
 

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Thread Starter

DevineDesign

Joined Oct 22, 2023
11
correct...... brake is on when power is removed. No power and it will not move. So I need to apply power to both simultaneously for operation.
 

Thread Starter

DevineDesign

Joined Oct 22, 2023
11
Wow. I'm in over my head I feel. I'm looking at power transformers and I will say this is not easy for me. Toroidal? Is this what I need?
 

Thread Starter

DevineDesign

Joined Oct 22, 2023
11
I would like to be able to have the option of the battery because eventually this will go for FDA approval for use in hospitals. Currently everything up to this point is UL certified. One of the biggest concerns is being able to deliver power to the brake and the motor at the same time. The lift is generally controlled by using a push button pendant for the up and down movement. But to apply power to brake while the up or down button is pushed id my #1 frustration. I'm guessing that I will need some type of
relay to achieve this function.?

Pendant is Schneider electric
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
Surely the PB's do not operate the motor directly, normally you would have a relay or contactor equipped with aux contacts in order to control the brake simultaneously .
 
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MisterBill2

Joined Jan 23, 2018
17,800
Given that the brake must release whenever the motor runs, and must engage whenever the motor is not powered, normally the brake would be wired directly across the motor. How do the previous versions operate?
AND, how does the motor reverse? Separate field and brushes? Or just two wires and a permanent magnet field? If that is the case, then there would be several contacts on the push buttons.
Is it possible that the motor is only running on 24 volts by design? THAT would make it all very simple.
 

Thread Starter

DevineDesign

Joined Oct 22, 2023
11
Ugh. I guess let me ask this. Is it out of bounds for me at this stage to ask if anyone would be interested in arranging a useable, functioning solution. This could be a easy arrangement where I supply pictures, any info needed on the parts and hire this task out. Or am I crazy for thinking like this? PayPal, Cash app, shit I'll have cash mailed to you and personally delivered my a guy dressed as Elvis.... just so this isn't on my plate anymore. I'm a nobody from sales that happened to have a good idea while drinking. Let me know the rules. If interested let me know. Thanks.
 

MisterBill2

Joined Jan 23, 2018
17,800
OK, the motor is a PM reversable brush motor, direction controlled by the polarity of the power. The brake is not polarity sensitive and releases with power applied. So we use a resistor in series with the brake to drop the voltage to 24 volts. Rather inefficient but very reliable if it is done right. And the brake ALWAYS is operated when the motor is powered, without any extra circuitry. We still need to know how much current the brake requires. And the brake across the motor will allow it to apply more gently as the motor coasts to a stop,acting as a generator when the power is disconnected.
And it is not a good idea to use a worm gear for a lift because of the single small load bearing part and the quite high friction. Folks do it when there is some overwhelming reason why nothing else can be done.
 
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Thread Starter

DevineDesign

Joined Oct 22, 2023
11
I landed in the driver's seat after personnel changes. Normally the position doesn't involve this. I believe I've been attached a picture of the brake in the earlier post. Any pictures or any other questions needed from me let me know.
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
Personally I would not rely on the pendant to do the actual switching, which of course would require interlocking contact to prevent dual direction initiation.
A relay set up to take care of both motor and brake would be optimum.
There is the high initial current of a DC brushed motor before it starts to rotate, higher than the stated plate current!
 
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