Hello, I have a micro lathe that runs on 24V DC. The motor is 150W. I have an Amazon power supply for 24V rated for 25A. I had it burning in the past when the motor would stall. Are there any electronic devices for low voltage DC that can protect the power supply when the motor stalls? My electrical knowledge is very limited and I would like to know If there are such devices, like a magnetic contactor but for low voltage
Protection to Micro lathe power supply?
- Thread starter Igor_toko
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I have specified protection relays in motor control center buckets, and they have a donut current transformer on the, and provide tighter control than just the standard old-style starter overloads.
With DC operation, the current transformer will not work, but I would guess there must be a DC-rated overcurrent protection relay.
You would want it adjustable, ie: with a dial or something.
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With DC operation, the current transformer will not work, but I would guess there must be a DC-rated overcurrent protection relay.
You would want it adjustable, ie: with a dial or something.
.
While a fuse is not really a motor overcurrent element in my opinion, if the problem is drawing more than 25A and 24VDC, than perhaps install a DC-rated fuse, with a current rating of perhaps 20 amps.
150W at 24VDC is 6.25 A normal rated amps.
Motor stall amps I think for AC inductions motors is six times normal current; not sure about DC motors.
The problem with fuses are they are not resetable like many overload devices, and also a fuse would have to act fast enough to protect the power supply.
Some electronic devices can't withstand even momentary over voltage or overcurrent.
I don't really have a good solution; just sharing some thoughts.
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150W at 24VDC is 6.25 A normal rated amps.
Motor stall amps I think for AC inductions motors is six times normal current; not sure about DC motors.
The problem with fuses are they are not resetable like many overload devices, and also a fuse would have to act fast enough to protect the power supply.
Some electronic devices can't withstand even momentary over voltage or overcurrent.
I don't really have a good solution; just sharing some thoughts.
.
Hello, thanks for the response. I googled and found a few of these type of devices, perhaps it could work https://www.aliexpress.com/i/3256804496411752.html?gatewayAdapt=4itemAdapt
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Slow-blow fuses have been used for many years for motor protection. They are a time-delay fuse that will tolerate the normal in-rush current of the motor, yet still give some overload protection to the motor. There ARE many better ways of overload protection, but a fuse is always the simplest. A 1/4"x1-1/4" fuse will have no problem handling the ampacity of your load and the fuse holders are available in multiple styles: panel mount, in-line, pc board mount, with many different flavors of each type.
Fuses ARE a one-time use item. But if you keep blowing a fuse, either you've got a problem or you ARE the problem. Either there is something physically wrong, or you are trying to force the motor to handle more load than it was designed for. If you've got something wrong then you need to find, and fix, the problem.
A good rule of thumb for fuse size is to multiply the full load amps by 1.25 to find the approximate fuse size. In your case with a 150W motor we can use the 6.25A that GreenTwin listed, 6.25 * 1.25 gives us about 7.8 amps. So a slow-blow fuse in the 7.5-8 amp range should protect both the motor and the power supply.
Fuses ARE a one-time use item. But if you keep blowing a fuse, either you've got a problem or you ARE the problem. Either there is something physically wrong, or you are trying to force the motor to handle more load than it was designed for. If you've got something wrong then you need to find, and fix, the problem.
A good rule of thumb for fuse size is to multiply the full load amps by 1.25 to find the approximate fuse size. In your case with a 150W motor we can use the 6.25A that GreenTwin listed, 6.25 * 1.25 gives us about 7.8 amps. So a slow-blow fuse in the 7.5-8 amp range should protect both the motor and the power supply.
yes, all kinds of devices. When the motor stalls its the same as a dead short similar to locked rotor current. Look for a circuit breaker or a fuse block. Hunt down someone who can size it for you. Another type of circuit would be a crowbar circuit but that should be built into the power supply.
ACS712 (appropriate range possibly the 30A device) and Arduino.
You can do with it whatever suits.
Principle: when the fuse explodes, always check the device and circuit behind it.
You can install an additional Relay as shown in the picture.
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Being more at ease with mechanics than with electronics I'm not sure whether this experience is relevant: after I had a new mains board for the workshop installed with highly sensitive trippers the system shut off random and often. I could narrow it down to my 60-70 year old Schaublin 102 VM lathe. After installing a frequency control system between the mains and the machine I experienced no further troubles.
This a simple circuit
A resistor for protection of motor. Next current limiting.
Can be as simple a slow blow fuse sized for motor it is Old tech .
They do make motor controllers with adjustable current limiting costly. This tech is used on garage doors for safety.
I like the time delay fuse match to motor. Add a cooling fan {At low speed can over heat because the motor fan is turning slowly}.
Dave
Igor, the 20A-30A Ali express one will work if you can put it between the power supply in the lathe and the fwd/rev and speed control in the lathe. The reason is that the input to that board has a specific + and -. Your controller in the lathe will reverse the polarity to the motor, so the Ali board will have to be installed before that happens.
Your motor is rated at 150w = 6.25A
The power supply is rated at 25A, 24V x 25A = 600w
Look at something like this from Digikey. Much simpler. It is a simple thermal overload breaker with a manual reset button. That means you will have to wait for it to cool off before it will reset. Connect it on the output of your Amazon power supply. Probably about 10 Amps will work. If you look at the data sheet, the 10A version will trip at twice its rated current (20A) in 10 seconds, and at 5 times its rated current (50A) in one second. It can be a bit of a guessing game on what size breaker to buy, because you want it to protect the power supply, but not be tripping all the time. At only $6.18 each, you might order 2 different amperage ratings in case one trips too often.
Lloyd
https://www.digikey.com/en/products/detail/e-t-a/1658-G21-01-P10-10A/659608
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The other option is to put the breaker on the power going into the power supply, but that would be a much lower amperage depending on the input ratings of the Amazon power supply. But that would protect everything, including the power supply. The power supply doesn't have a fuse on its input side??
Lloyd
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............and just what is the relay supposed to do?
It looks like he is trying to use the relay as a circuit to latch the (Low Voltage DC) power circuit to the motor. When the fuse blows the motor is removed from the power supply by the relay. The power supply will still be energize but the motor load has been remove. To restore power to the motor you would need to replace the fuse and push the n.o. push button .
The circuit is called a electrically latch relay.
A latching relay is an electrically actuated electric switch that can maintain its position without power being applied on its coil. Used in motor control centers.
In this Circuit replace B2 with the fuse and you have the same as minh-thanh circuit, minus the nc contact . See here for more info.
https://www.electrical4u.com/latching-relay/
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When the fuse blows, the motor is removed from the power supply by the fuse.
It's just an auxiliary switch that also doubles as a fuse
No it doesn't.....not by the relay...which is why I asked, what is the purpose of the relay?
See here for more info.
https://www.electrical4u.com/latching-relay/
In this Circuit replace B2 with the fuse and you have the same as minh-thanh circuit, minus. the nc contact.
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Even installing additional equipment or circuits to protect the machine's power source is not as effective as using the machine
With small machines: Don't try to force them to work too hard, it will only harm the mechanical part of the machine - not just the power source , and the mechanical part of the machine is what is more important if I need a precise machine for my needs - When the power source or motor burns out: please reconsider how to use it.
With small machines: Don't try to force them to work too hard, it will only harm the mechanical part of the machine - not just the power source , and the mechanical part of the machine is what is more important if I need a precise machine for my needs - When the power source or motor burns out: please reconsider how to use it.
Motor starters are often wired with the sealing contact parallel to the starter coil, allowing a motor contactor to close and latch closed.
If there is a power interruption, or a brownout, the coil will release, and the motor will stop, and the start button has to be manually pressed to restart the motor.
In some situations, the operator may want the motor to restart automatically after a power outage, in which case the control contacts are wired directly in series with the contactor coil. This does not provide brownout protection, but I have seen it done, especially in situations where there process is not constantly staffed by people who could otherwise reset the starter, or it is critical that the process restart immediately, such as after a tranfer to a standby generator.
Either way, the latch function does not provide overcurrent (short circuit) or overload protection.
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If there is a power interruption, or a brownout, the coil will release, and the motor will stop, and the start button has to be manually pressed to restart the motor.
In some situations, the operator may want the motor to restart automatically after a power outage, in which case the control contacts are wired directly in series with the contactor coil. This does not provide brownout protection, but I have seen it done, especially in situations where there process is not constantly staffed by people who could otherwise reset the starter, or it is critical that the process restart immediately, such as after a tranfer to a standby generator.
Either way, the latch function does not provide overcurrent (short circuit) or overload protection.
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