2 motors pushing an object. 1 motor goes bad... other keeps going... object breaks???

[mjosbesh]

I have two 12V DC motors working together to move an object. If one motor goes bad or loses connection I want the other motor to stop. Currently I use a 4 amp fuse on each motor to achieve this. If one motor has a problem the other motor encounters increased load and blows the fuse. This works but its not ideal because the object gets kinked before the fuse blows.

Any ideas? I want to achieve this goal the most simple way possible.

 

[ramussons]

What you have done IS the Most Simplest way

The not-so-simple way would be to use a Current sensor (shunt) to monitor the motor currents and disconnect the power feed if it exceeds a set value.

You can also incorporate a temperature sensor along with this "electronics" and get a pretty good safety system for your motors.

 

[dorke]

What is the current of motor under normal operation?

 

[duke37]

If they are similar motors and similar loads, have you thought about putting them in series?
Then the current and torque would be the same in each motor.

 

[dorke]

If they are similar motors and similar loads, have you thought about putting them in series?
Then the current and torque would be the same in each motor.

Possible,but 24V PS instead of 12v is needed.

 

[Minder]

Another faster method than a fuse is a slot opto detector on each motor or activated device and a couple 555 missing pulse detectors, a small relay on the output of each in an OR'd fashion would shut the system down.
M.

 

[mjosbesh]

What is the current of motor under normal operation?

Up to 7 amps for each motor

If they are similar motors and similar loads, have you thought about putting them in series?
Then the current and torque would be the same in each motor.

Yes, I was wondering about this possibility. Would the current and voltage be exactly the same for both motors if I wire them in series? Also, If each motor requires 12 V and up to 7 amps would I need to double both the Voltage and the Amps of the power supply?

 

[davenn]

Also, If each motor requires 12 V and up to 7 amps would I need to double both the Voltage and the Amps of the power supply?

yes, 24V and a minimum of 14A, preferably 16 - 20A to take care of the high start up current the motors will require

that is ... 14A will only cover the standard running current requirement
Assuming your stated 7A is for the normal running condition ??


Dave

 

[mjosbesh]

yes, 24V and a minimum of 14A, preferably 16 - 20A to take care of the high start up current the motors will require

that is ... 14A will only cover the standard running current requirement
Assuming your stated 7A is for the normal running condition ??


Dave

These motors are attached to linear actuators and the 7 A is the max when the actuator is fully loaded and nearly stalls.

 

[mjosbesh]

I have two 12 V 7.5 A power supplies. Can I connect them together to get a 24 V 15 A power supply?
If so do I connect them in parallel or series?

 

[dorke]

I have two 12 V 7.5 A power supplies. Can I connect them together to get a 24 V 15 A power supply?
If so do I connect them in parallel or series?

In series,you will get 24V @7,5A.
This is only possible if the P.S are "floating" i.e the "-" is not connected to earth GND.

 

[duke37]

You will need to supplly 7A for the series connection plus some for start up. It depends on the inertia as to how long the start up transient will last.

You will NOT get 24V 15A. You either have 12V 15A in parallel (assuming they do not fight) or 24V 7.5A in series.
As @dorke says, in series at least one of the supplies must be floating since it sits on top of the other.

 

[mjosbesh]

You will need to supplly 7A for the series connection plus some for start up. It depends on the inertia as to how long the start up transient will last.

You will NOT get 24V 15A. You either have 12V 15A in parallel (assuming they do not fight) or 24V 7.5A in series.
As @dorke says, in series at least one of the supplies must be floating since it sits on top of the other.

Thank you for the info but I'm sorry I don't fully understand what you mean by floating. Can you explain a little more?

 

[mjosbesh]

I tried putting the two 12V power supplies in series and parallel. Parallel worked but series didn't. Not sure why

 

[duke37]

Floating means that the power supply has no connection to 'earth'. This means that it can supply its voltage, in this case 12V, from a different reference.
Consider a stool 12 inches high, you can put another stool on top to give a total height of 24 inches but this cannot be done if the top stool is screwed to the floor.

Another consideration is that the series connection needs to be the right way round, one positive connected to one negative and the remaining connections are the output. If you get it wrong you will get 12V minus 12V so a nett voltage of zero.

 

[dorke]

I tried putting the two 12V power supplies in series and parallel. Parallel worked but series didn't. Not sure why

A simple test to check if your p.s is floating :
Check the voltage between the (+) and the chassis(at a good connection point) of your PS .
if there is 12V it isn't floating.

 

[mjosbesh]

I'm sorry, I am still confused and maybe it is because I am calling a power adapter a power supply??? I didn't realize there is a difference but what I have looks similar to a laptop power adapter but it is 12VDC 7.5A with a positive and negative wire coming out the DC side.

 

[dorke]

It is a power supply,it's shape an form doesn't change it's functionality.
So it as a plastic box not a metallic one.

Here is how you should test if is floating :
With the adapter/P.S not connected to power.
Measure the resistance between the DC (-) and the power connector(2 or 3 prongs).
Start with the earth one(if there is one) and than to the others.
do the same for the(+) one.
If you get low resistance it isn't floating.
What do you measure?

 

[duke37]

The motors must be connected the right way round whether in parallel or series to get them going in the same direction.
You can test on 12V when the motors should run but slower.