Help with DC motor

[Donald]

In the diagram #5 is a DC motor the size of a starter. It can run in either direction. Solenoid K1 or K2 are activated to run the in either direction.

When neither solenoid K1 or K2 are activated I think the NC contacts act to " brake" the motor.

I applied 12 negative to A2 and 12 positive to D1 and then tried D2. A1 was unconnected. The motor did not run either way it was connected.

I thought most DC motors you just reversed positive and negative but this seems different.

I left A1 unconnected in my testing thinking it was only needed for braking.

 

[Jetronic]

you need 2 magnetic fields acting on each other, you only supplied the stationary field. it's a serial dc motor, same current goes through both windings. the field coil d1-d2 gets polarity switched to reverse direction

 

[Dave Sherman]

Nothing to do with braking. The NC contacts are to complete a path for the field to go through the armature windings to ground. By leaving A1 disconnected, the armature had no excitation so nothing happens. Jetronic is correct, it's reversing by changing the polarity of the series field winding.

 

[Donald]

So both A1 and either D1 or D2 need 12V positive?

 

[zzyzzx]

Is this gate related?

 

[Jetronic]

So both A1 and either D1 or D2 need 12V positive?

not quite, you NEED to put both in series or you will burn up or overspeed the motor. The motor pulls a lot of current when it's low speed, so the exciter gets a lot of current, but as speed increases the current drops and there's less excitation. if you put 12V on both there's no end to the rpm it will try to run

 

[mk378]

Haven't we been through this before?

It's a series wound motor. The current from battery + goes through the field coil first (D terminals) in either direction depending on the reversing relay. Then the current leaving the field circuit always goes to the armature brush A1, through the armature, and returns to the battery minus from A2.

The D terminals happen to be shorted together when neither (or both) relays are engaged-- but that is just a byproduct of this implementation with simple relays. Shorting the D circuit while off is not necessary for operation and has no braking effect.

If you want to test the motor without the relay box, jumper either D1 or D2 to A1 (your choice determines which way the motor will spin). Connect the battery to the open other D terminal and to A2.

Actually it does not matter what polarity the battery has-- the torque comes from the relative direction of current flow through the two parts of the motor. Also of course you could reverse A1 and A2 would reverse the direction again the same as swapping D.

If you didn't understand that last paragraph, the takeaway is that the only thing that has to happen is that the D and A circuits are connected in series. Connecting in parallel will result in very high current flow and potential damage.

 

[Donald]

Is this gate related?

No. I have many things that don't work.

 

[Donald]

Haven't we been through this before?

It's a series wound motor. The current from battery + goes through the field coil first (D terminals) in either direction depending on the reversing relay. Then the current leaving the field circuit always goes to the armature brush A1, through the armature, and returns to the battery minus from A2.

The D terminals happen to be shorted together when neither (or both) relays are engaged-- but that is just a byproduct of this implementation with simple relays. Shorting the D circuit while off is not necessary for operation and has no braking effect.

If you want to test the motor without the relay box, jumper either D1 or D2 to A1 (your choice determines which way the motor will spin). Connect the battery to the open other D terminal and to A2.

Actually it does not matter what polarity the battery has-- the torque comes from the relative direction of current flow through the two parts of the motor. Also of course you could reverse A1 and A2 would reverse the direction again the same as swapping D.

If you didn't understand that last paragraph, the takeaway is that the only thing that has to happen is that the D and A circuits are connected in series. Connecting in parallel will result in very high current flow and potential damage.

Ok. That's simple enough

 

[Donald]

This is a question my Dad would have readily known the answer.

I need to test the motor and relay independently.

 

[Donald]

Well the motor by itself works. I no need to test both directions. If it works on way it has to work the other.

The solenoid is next to test.

 

[Donald]

Above #12 (thermal cutout) are the K1 and K2 relay coils. There is a diode around each coil? I know what a diode is. But why is there a diode around the relay coils?

 

[mk378]

The diode shunts out "inductive kick" which would otherwise cause arcing at the control switch when it is released. Note that the diode is reverse biased and does not flow any current while power is applied to the coil. It only goes into forward conduction for a moment to dissipate the energy stored in the relay coil after the switch is opened.

 

[Donald]

The diode shunts out "inductive kick" which would otherwise cause arcing at the control switch when it is released. Note that the diode is reverse biased and does not flow any current while power is applied to the coil. It only goes into forward conduction for a moment to dissipate the energy stored in the relay coil after the switch is opened.

My Dad told me it was much easier for an AC contact to release (less arcing) than a DC contact to release. I assume this is kind of related.

 

[nomas]

What type of device is this ? Just curious ..

 

[Donald]

What type of device is this ? Just curious ..

It's a boat bow thruster motor the size of a starter. It can run a few minutes in either direction. Has a dedicated battery a few feet away. It's accessed through a a small access panel with much difficulty. After many attempts over the past two years to get it to work, I decided to pull it out of the boat. It would not fit through the small access panel with the solenoid attached. So disconnected the solenoid and now have both in my garage. Motor works so next to test solenoid by itself using a DVM to check the contacts. I am guessing it's the solenoid. Since the solenoid is sold on Amazon obviously they fail. About $275.

By spring it will be working with the joystick control panel in my garage.

 

[nomas]

It's a boat bow thruster motor the size of a starter. It can run a few minutes in either direction. Has a dedicated battery a few feet away. It's accessed through a a small access panel with much difficulty. After many attempts over the past two years to get it to work, I decided to pull it out of the boat. It would not fit through the small access panel with the solenoid attached. So disconnected the solenoid and now have both in my garage. Motor works so next to test solenoid by itself using a DVM to check the contacts. I am guessing it's the solenoid. Since the solenoid is sold on Amazon obviously they fail. About $275.

By spring it will be working with the joystick control panel in my garage.

It should be easy enough to test the solenoid . Apply 12v and monitor the contacts to change state .

 

[Donald]

It should be easy enough to test the solenoid . Apply 12v and monitor the contacts to change state .

If the contacts show zero ohms with DVM could they still be burned and not be able to carry the high current for the DC motor?

 

[nomas]

If the contacts show zero ohms with DVM could they still be burned and not be able to carry the high current for the DC motor?

Zero ohms is about as good as you can get . Burned ? No .

 

[Donald]

So I have the motor in the garage and the solenoid pack next to my TV chair. I have tried the motor by itself and the solenoid pack by itself and also with the solenoid pack connected to the motor. Using wire jumpers and the actual control joystick. It always works as expected.

Yet it did not work on my boat. Testing with the same battery as used in the boat.

The boat has an older joystick control but I am pretty sure I tested with the new joystick control at the boat and the now thruster did not work.

I cannot install the now thruster motor with the solenoid pack attached. The access cover is too small. Have to place the motor into the area below the access cover, then attach the solenoid then attach the motor to the now thruster housing and then the wiring.