How to delay the relay

[tristanlee85]

This title is pretty generic and likely not the solution to my issue, but it at least describes my thought process.

I am working on a solution for my truck that lets me switch electronically between my 2 fuel tanks. I am using the following device:

http://products.pollakaftermarket.c.../light-truck-6-port-motor-driven-valve/42-302

PDF for the wiring of the motor: http://products.pollakaftermarket.c...light-truck-6-port-motor-driven-valve/42-300#

To summarize, the motor is in the position for the front tank when pin E gets 12v and pin D is grounded. If the polarity is switched (pin E ground and pin D 12v), then the motor position is changed. I have confirmed this functionality by placing the wires directly on the 12v battery then swapping the wires to change the motor's position.

In the vehicle, I have this wired on a DPTP relay. By default, 12v goes to pin E. When a switch on the dash is toggled, then the relay coil is energized and polarity to the motor is switched. I have confirmed this using a multimeter. At the motor, I read +12v. When I flip the switch, it reads -12v.

As per the diagram of the motor, this should engage the motor to change its position. However, this is not the case. What I believe to have narrowed this down to is the fact that the relay is switching too quickly for the motor for whatever reason. My confirmation for this is that when the meter is reading -12v at the motor, I expect it to switch, but it doesn't. If I disconnect one of the wires on the motor then reconnect it to the same position, because there was a bit of a disconnect of the voltage, then the motor is engaged and moves to the correct position.

If you've followed along so far, do you have any thoughts with what I could do to cause a complete disconnect from the motor whenever polarity is changed? This seems to be my observed solution to the issue.

 

[Bluejets]

Both links go to the same place....cannot see any wiring diagram

 

[tristanlee85]

Sorry, looks like they used a different method of linking to the PDF. Here it is: http://products.pollakaftermarket.com/Asset/42-159 IS_41-revdd.pdf

 

[tristanlee85]

"Delaying" the switch isn't really inline with what I think will solve the issue. The problem is that the circuit seems to need to be opened for ~3 seconds between switching polarity in order to get it to function correctly. If polarity is switched instantaneously, then the motor does not extend/retract the valve as it should. However, if I go from +12v, open the circuit for a few seconds, then connect the wires back up for -12v, then the motor functions. I don't know if this is specifically an issue with my wiring or a fault in the motor's behavior. I've even removed my relay from the equation and switched the wires by hand against a 12v source. If I don't wait in between switching, it does not function.

 

[Bluejets]

You don't need to delay anything. I'd say offhand you have a wiring error. Best to draw up exactly what you have and we can comment more accurately from there.

 

[Kiwi]

This might help.





[ MOD Note: got rid of that annoying pdf file ]

 

[AnalogKid]

Replace the DPDT switch with a DPDT center-off switch. This has a third detent position in the middle where no contacts are closed. You can count the three seconds in your head.

To do this electronically requires a timer circuit driving two relays, so there can be a condition where neither is closed. Not hard, but more work that replacing a switch.

ak

 

[Alec_t]

Are you sure you allow enough time for the motor to travel to its limit position before reversing it? I would guess it has a leadscrew drive and could take a second or two to shift the spool. Maybe the internal limit-switches allow reversal only after the limit position has been reached.

 

[tristanlee85]

The problem with changing out the switch to use an on-off-on is that it would then require me to have 2 switches in the dash to switch my tanks: the stock switch which controls powering the fuel pumps and fuel level sender, and then another switch just to switch the valve. The point of using the stock switch and a relay is so that I can invert the voltage that goes to the selector motor while maintaining my stock wiring for powering the pumps.

Rather than creating a diagram (which I can later create if needed), I will link you to the video I created that I sent to the manufacturer describing the issue:

For what it is worth, I did just test with a DPDT on-off-on switch that I just got from RadioShack. Using that switch, it works so I don't understand what is mechanically different about using the relay vs the switch. When the contacts on the relay change to invert the polarity, there is a complete disconnect there, though the change in the position of the relay is much quicker than I am able to do with a switch, but I would be surprised if that is the main issue here.

As for making sure I wait the 3 seconds, I am coming to find out that now since I used the switch, it works when I flip the switch as fast as possible so timing is no longer seems to be the culprit, but I do not understand what would be different here. Voltage read at the motor when comparing the switch vs relay is exactly the same. And yes, I am ensuring that the motor is completely cycled (though it only takes a fraction of a second to happen). I could wait 10 mins, flip the switch while using the relays and the change would still not happen.

 

[tristanlee85]

And for what it's worth, the manufacturer of this valve has a switch they recommend (on-on) which is already wired to have the leads reversed: http://products.pollakaftermarket.c...alves/toggle-switch-d-p-d-t--1156/34-592-1814 I just happened to test with an on-off-on because it's all that RadioShack had to offer me. However, my goal is to not have another switch here. This should be possible with a relay.

 

[Alec_t]

I've even removed my relay from the equation and switched the wires by hand against a 12v source. If I don't wait in between switching, it does not function.

As for making sure I wait the 3 seconds, I am coming to find out that now since I used the switch, it works when I flip the switch as fast as possible so timing is no longer seems to be the culprit

In view of that inconsistency, this is beginning to look like a poor (high resistance) connection somewhere. Are the relay contacts adequately rated for switching heavy DC current (many are not)? Is your wire gauge man enough for the job?

 

[Bluejets]

As previously mentioned,if you were to supply a diagram of what you have, it might be possible to detect any problem area. Other than that, everyone is just taking stabs in the dark.

 

[tristanlee85]

The diagram to best show what I am doing is what Kiwi posted above earlier:

The switch in the diagram represents the switch that already exists in the truck. When in the down (rear tank) position, 12v runs through the switch to energize the relay coil, which inverts the polarity. The motor draws little current. The manufacturer recommends 18awg wire and in my application I am using 16awg. Even though, my bench test is using something much smaller for demonstration (24awg solid) and that is more than enough to move the motor.

Perhaps the issue lies within the relay itself. The DPDT relay I was using seemed faulty. The coil was rated for 12vdc and when I applied this to it, I could see that the magnet was attempting to latch, but it wasn't strong enough. I ruled out that relay being bad (even though brand new) because my SPDT relays would easily latch on the same power source. So, I have a new DPDT relay on order to see if that issue gets resolved. That is the reason I switched from a DPDT relay to (2) SPDT relays in my video to demonstrate the same effect.

It very well could be a resistance issue with the relays. Both are identical and I don't believe have been used before. All relays are rated at 30A and this motor pulls no where near that.

 

[Bluejets]

Use a decent power supply as i suspect the current one is shutting down or at least limiting the current to an unusable level. For example, try using a car battery. Diagram is ok and unless relay is 24v instead of 12v then i'd say it's ok also.

 

[tristanlee85]

I get the same behavior using the vehicle battery as well.

After long communication with the manufacturer, it appears I may have acquired a model of their valve that works off momentary voltage rather than continuous. Removing my relays from the equation and going back to the simple on-off-on switch, if I toggle the switch quickly, it works. If I toggle on, wait 10 seconds, then toggle to the other position, then the valve does not move. I need to keep it in the off position for a few seconds.

Their comment to that was:

It looks like you have a 42-115 type valve and the instructions for a 42-159 style.

The -115 requires a momentary 12 Vdc to move the mechanism. It has a PTC to cut the power in case the power is left on too long. The three seconds off is probably enough to allow the PTC to cool off to run the motor.

If that's true (and there are no markings on the unit for me to see if it's the old style), then that would explain everything. The question now would be, would it be effective for me to implement a way to have voltage applied to the motor momentarily (~5 seconds) vs spending additional money ($80) to buy a new unit that hopefully is the right model...

 

[Bluejets]

Quite simple to switch a relay on for a few seconds using say an npn transistor biased off and with a base series capacitor sized to give whatever time delay pulse. Maybe 2 are needed to cover the 2 different directions. Also relay might be able to be done away with if is just a high signal pulse required. I'd sketch you up a simple arrangement but am away from my home base presently and a bit beyond me to do on the mobile.

 

[Alec_t]

Here's one option:

(Not shown are the 9V supply regulator, transient suppression components and supply decoupling arrangement).

 

[tristanlee85]

Thank you both for the feedback and schematic above. I appreciate the effort you put into this. It turns out that all along the motor that I was trying to work with was not as advertised. There were 2 different models which are identical in their appearance with no stamping to differentiate the 2. One motor was for GM vehicles which used an momentary on-off-on switch and the other being for Ford which used an on-off-on. The motor for the momentary switch was not designed for continuous voltage and has a protective circuit inside to prevent it from overheating should voltage be applied longer than a couple seconds. This would explain the reason why removing power source from the motor for 3 - 5 seconds allowed the motor to function, because this was likely enough time for the motor to cool off (according to the manufacturer). They had sent me another motor which exhibited the same behavior so I assumed it was something I was doing wrong.

After being fed up, I decided to purchase one from a different manufacturer and it works correctly when voltage is always applied to it using my DPDT relay setup.