12VDC shutoff in event of overcurrent

Thread Starter

K8uhn

Joined Jan 7, 2024
4
Can anyone help me with a circuit? I have an ATV winch, 12 volts DC. It will be used to raise and lower an antenna on a small tower. Normally it should draw about 45 amps. However I want it to shut off it it meets an obstacle or resistance as it’s raising or lowering. The current should increase if the winch comes under more load. I’d like to be able to set it shut off at a predetermined current, say 48 amps.
 

LowQCab

Joined Nov 6, 2012
4,052
The "Start-Up" Current-Surge may be big enough to cause problems
with the Power-Supply going into "Self-Protection-Mode".
This may, or may not be, adequate protection against breaking something very expensive.

Having this setup operate automatically could be extremely hazardous,
I would NOT recommend automatic operation.

Go outside, and visually observe, and manually control, the raising of the mast.

A Hand-Cranked Boat-Trailer-Winch would be much safer, and a lot cheaper.
.
.
.
 

Thread Starter

K8uhn

Joined Jan 7, 2024
4
Thanks. Friend is using this winch and same power supply with no problems. Winch would be operated with me in sight of the tower using a remote IMG_9845.jpegI just wanted if the “Hazer”(the elevator that winch is pulling) meets resistance to shut off so I could look at the issue. Not interested in a boat winch due to old age. LOL
 

MisterBill2

Joined Jan 23, 2018
18,425
OK, and I was guessing it would be a HAZAR package. The cheating trick would be to get an old three-coil voltage regulator to have the DC current relay to open the contact on overload. To sense over-current use a reed relay and a one or two turn coil of #8 solid wire. You will need to experiment to get the reed to operate at the desired current. Use an NC reed switch so that it releases the run enable relay at over-current. The starting current problem is eliminated because the start button bypasses the overload switch. There must also be a series stop button to release the latched relay. Both of the controls need to be on a long cord because you do not want to be close to the tower while things are going up and down. N8QVS
 

Thread Starter

K8uhn

Joined Jan 7, 2024
4
OK, and I was guessing it would be a HAZAR package. The cheating trick would be to get an old three-coil voltage regulator to have the DC current relay to open the contact on overload. To sense over-current use a reed relay and a one or two turn coil of #8 solid wire. You will need to experiment to get the reed to operate at the desired current. Use an NC reed switch so that it releases the run enable relay at over-current. The starting current problem is eliminated because the start button bypasses the overload switch. There must also be a series stop button to release the latched relay. Both of the controls need to be on a long cord because you do not want to be close to the tower while things are going up and down. N8QVS
Hi there. Thanks for the reply. Yes I have a Hazer but not the original Glenn-Martin version since they are out of business. A guy in Florida is building them out of all aluminum (picture in earlier post)

Could you send me a schematic or drawing of the solution you propose? I’ll be using a 12 VDC ATV winch, 2500 lbs, from Harbor Freight.
Thanks
73
Eric
 

voelew

Joined Jan 25, 2024
3
Can anyone help me with a circuit? I have an ATV winch, 12 volts DC. It will be used to raise and lower an antenna on a small tower. Normally it should draw about 45 amps. However I want it to shut off it it meets an obstacle or resistance as it’s raising or lowering. The current should increase if the winch comes under more load. I’d like to be able to set it shut off at a predetermined current, say 48 amps.
The achieve overcurrent protection for your ATV winch, use a current sensing circuit with a shutoff mechanism. Incorporate a current sensor in series with the winch power supply, connected to a comparator. Set the comparator to trigger a relay when the current exceeds 48 amps. The relay should interrupt the power supply to the winch, cutting it off in the event of overcurrent.
 

MisterBill2

Joined Jan 23, 2018
18,425
A current sensing circuit could consist of an ammeter shunt in the winch motor supply line. For the most convenient implementation of the electronics, that would be the negative 12 volt supply side of the motor circuit.
The voltage developed across the shunt will be in direct proportion to the current, With a 100 AMPS= 100 millivolt shunt , the signal will be one millivolt per amp. So a simple voltage comparator circuit set to switch at 48 millivolts can provide the signal to release the power switching circuit. Voltage sensing comparator circuits are a very mature area and a lot of information is available on the design and operation of them.
A more expensive but much easier scheme is to purchase a digital meter with a setpoint digital switch as part of the package. Digital meters for displaying the shunt voltage in amps are available from a number of sources. I recommend RED LION brand controls because the quality is very good and the customer support has been excellent.
 

MisterBill2

Joined Jan 23, 2018
18,425

Hymie

Joined Mar 30, 2018
1,282
The Red Wolf 50A breaker device may work for you, but I doubt it will trip at 50A or thereabouts. Fuses can normally pass around 1.6x rating for a considerable time, therefore I would not expect the device to trip until the current reached at least 75A.

A simple comparator circuit with the output driving a contactor would appear the optimum solution, you could add a smoothing capacitor to the current sense allowing a higher current for short periods (such as start up). You could then fine tune the component values to give the required performance. If necessary you could include a manual override (to the overcurrent protection) allowing for the initial stalled start current.
 

MisterBill2

Joined Jan 23, 2018
18,425
The Red Wolf 50A breaker device may work for you, but I doubt it will trip at 50A or thereabouts. Fuses can normally pass around 1.6x rating for a considerable time, therefore I would not expect the device to trip until the current reached at least 75A.

A simple comparator circuit with the output driving a contactor would appear the optimum solution, you could add a smoothing capacitor to the current sense allowing a higher current for short periods (such as start up). You could then fine tune the component values to give the required performance. If necessary you could include a manual override (to the overcurrent protection) allowing for the initial stalled start current.
I suggested a comparator and a shunt earlier but I did not give any details. A "Meter RElay", either mechanical or digital/electronic is another choice. A digital current display would be very useful for tracking the condition of the lifter assembly.
 

voelew

Joined Jan 25, 2024
3
A current sensing circuit could consist of an ammeter shunt in the winch motor supply line. For the most convenient implementation of the electronics, that would be the negative 12 volt supply side of the motor circuit.
The voltage developed across the shunt will be in direct proportion to the current, With a 100 AMPS= 100 millivolt shunt , the signal will be one millivolt per amp. So a simple voltage comparator circuit set to switch at 48 millivolts can provide the signal to release the power switching circuit. Voltage sensing comparator circuits are a very mature area and a lot of information is available on the design and operation of them.
A more expensive but much easier scheme is to purchase a digital meter with a setpoint digital switch as part of the package. Digital meters for displaying the shunt voltage in amps are available from a number of sources. I recommend RED LION brand controls because the quality is very good and the customer support has been excellent.
A current sensing circuit for a winch motor involves placing a 100-millivolt shunt in the negative 12-volt supply line. The voltage across the shunt is directly proportional to the current, making it easy to measure. A voltage comparator circuit, set to trigger at 48 millivolts, can signal the power switching circuit.
 

MisterBill2

Joined Jan 23, 2018
18,425
Probably there would need to be a way to avoid tripping the jam-detection part during startup. But that could be rather simple.
Even with overload protection, an ammeter in the power lead will be able to show just how much load is on the winch as the HAZAR is pulled up. That could be handy to spot a bit of binding before it becomes an issue or a serious problem. I am not familiar with Harbor Freight 12 volt powered winches, but their AC powered ones also have an electric brake that engages when the motor stops and disengages when it is started. That might affect the starting current as well. In many instances the supply wire resistance tends to limit the starting inrush current a bit. If the DC power supply for the motor is regulated that might not help at all.
 
Last edited:

voelew

Joined Jan 25, 2024
3
Probably there would need to be a way to avoid tripping the jam-detection part during startup. But that could be rather simple.
Even with overload protection, an ammeter in the power lead will be able to show just how much load is on the winch as the HAZAR is pulled up. That could be handy to spot a bit of binding before it becomes an issue or a serious problem.
A gradual startup sequence for the winch could prevent tripping the jam-detection during initial operation. Additionally, incorporating an ammeter in the power lead would provide real-time load monitoring, allowing for early detection of any binding issues before they escalate.
 
Top