Electrical Issues: Hatch Lift - Battletech Pod - Tail Gate Lift Motor

[PL1]

How about using a bridge rectifier to drive a relay.

Connect the bridge rectifier inputs in parallel with the motor voltage and the outputs to the coil of the relay.



The circuit is usually used to convert AC to DC, but will work for this purpose as long as you use the right diodes.

Regardless of the polarity, when a voltage is applied to the motor, it applies power to the relay coil, closing the contacts which applies the 12v operating voltage to the clutch.


Scott

[kahlid74]

How about using a bridge rectifier to drive a relay.

Connect the bridge rectifier inputs in parallel with the motor voltage and the outputs to the coil of the relay.



The circuit is usually used to convert AC to DC, but will work for this purpose as long as you use the right diodes.

Regardless of the polarity, when a voltage is applied to the motor, it applies power to the relay coil, closing the contacts which applies the 12v operating voltage to the clutch.


Scott

Awesome idea!  I did however figure out what the issue was.

The clutch is not the culprit and if not energized, the arm doesn't move even though the motor does.  So here's what I found out, my PS, an Antec 600 Watt was too smart.  Something in the power supply didn't like the DPDT configuration.  I then grabbed a cheapo PS 300 watt no name from the corner of shame, wired it up without the clutch and it works like a SOB.  Sweetness.

So what do you think my Antec PS was seeing that caused it to kill the PS when power was sent through the DPDT.  I also used my Killowat meter and only 1.4 amps were running through the system at the time of the motor running.  So it can't be an amp thing can it?

[PL1]

Maybe the Antec PS interpreted the sudden jump in current as a short and shut down to "protect" the system.   


Scott

[kahlid74]

Perhaps it's the motor?  I hooked up a 10A 12VDC DPDT Relay.  The trigger switch works and I can see it work.  Everything is happy except when I try to draw power through it via the motor.  Without the motor I get 12V in either regular or reverse polarity.  So now I'm not sure what's going on.  Is my relay really unable to power the motor?  It's the weirdest thing.  Doesn't make any sense.

[PL1]

Perhaps it's the motor?  I hooked up a 10A 12VDC DPDT Relay.  The trigger switch works and I can see it work.  Everything is happy except when I try to draw power through it via the motor.  Without the motor I get 12V in either regular or reverse polarity.  So now I'm not sure what's going on.  Is my relay really unable to power the motor?  It's the weirdest thing.  Doesn't make any sense.

IIRC you mentioned previously that you had measured the no-load current draw at about 2A -- I assume that means that the motor works when connected directly.   

When in doubt, draw it out.

A diagram showing how you've got everything hooked up might help clarify things.   


Scott

[kahlid74]

So it's basically the motor.  It's shorting for some reason.  I proceeded to hook it up to an ac adapter which provides 12v 7 Amps and basically it's tripping out.  It sounds like it's clicking or something else weird.  I'll try to take a video and see if I can isolate it but I'm at a loss.  Did the motor burn out or die?  Did I brick it somehow?  Is there a way to un-brick it?  What could I have done to mess it up?

[danny_galaga]

Thanks for the replies guys.  The DPDT is rated for 12V at 20 AMPS so I know we're good to go on that front.  The clutch is DISCONNECTED which is where I'm guessing this is breaking down.  When I power on the PS I hear the clutch activate but the motor obviously doesn't turn on.  I'm thinking of trying the motor with the clutch connected to the UP switch and seeing if it works.  If it does, how do I wire the clutch into the DPDT while preventing it from ever reversing polarity?

I know you've advances somewhat in the troouble-shooting, but bear in mind there is no 'polarity' for a clutch coil- it will work the same no matter which way it's wired (",)

[kahlid74]

Thanks for the replies guys.  The DPDT is rated for 12V at 20 AMPS so I know we're good to go on that front.  The clutch is DISCONNECTED which is where I'm guessing this is breaking down.  When I power on the PS I hear the clutch activate but the motor obviously doesn't turn on.  I'm thinking of trying the motor with the clutch connected to the UP switch and seeing if it works.  If it does, how do I wire the clutch into the DPDT while preventing it from ever reversing polarity?

I know you've advances somewhat in the troouble-shooting, but bear in mind there is no 'polarity' for a clutch coil- it will work the same no matter which way it's wired (",)

Good to know, thanks!

So does anyone have any ideas on the motor?  Did I destroy it somehow?

[BadMouth]

So does anyone have any ideas on the motor?  Did I destroy it somehow?

Did it smoke?
Does it turn freely by hand?

Maybe that sucker does draw more than 10A and is overwhelming the relay.

[kahlid74]

So does anyone have any ideas on the motor?  Did I destroy it somehow?

Did it smoke?
Does it turn freely by hand?

Maybe that sucker does draw more than 10A and is overwhelming the relay.

No smoke, I can move the slider back and forth freely, which is what the motor is connected to, so it should be good there.

That's what I was thinking too, more than 10AMP wise but wouldn't my Kilowat plug see that?  When someone spikes it shows on the kilowat..  Could it be similar to the draw of an HDD that has a high peak start-up and then settles down?  The issue now is I can't even get the motor working plugged directly into a power supply.  I'm at a loss.

[lilshawn]

the problem with a kilowat plug is that you are only seeing the input side of the power supply. you aren't seeing any of the work being done.

take my ridiculous welding transformer for instance, going in is only ~1000 watts (~10 amps) but it outputs ~1300 amps.(~3000 watts) where did all this extra crap come from? ohms law that's where.

you need to actively measure the motor draw. Your motor is drawing more than the power supply is designed to output. I'm not even going to get into rail load requirements for proper voltage regulation.

yah, yah, yah i know it says 30 whatever amps on this rail and that rail but seriously, that ish is made up. hit up some power supply test reviews. hardly a single power supply now a days can hit the rated wattage listed on the label without blowing up or catching fire.

go get yourself a car battery (or take it out to your car) and hook 'er up. you will know in 2 seconds if your motor works or not.

[kahlid74]

the problem with a kilowat plug is that you are only seeing the input side of the power supply. you aren't seeing any of the work being done.

take my ridiculous welding transformer for instance, going in is only ~1000 watts (~10 amps) but it outputs ~1300 amps.(~3000 watts) where did all this extra crap come from? ohms law that's where.

you need to actively measure the motor draw. Your motor is drawing more than the power supply is designed to output. I'm not even going to get into rail load requirements for proper voltage regulation.

yah, yah, yah i know it says 30 whatever amps on this rail and that rail but seriously, that ish is made up. hit up some power supply test reviews. hardly a single power supply now a days can hit the rated wattage listed on the label without blowing up or catching fire.

go get yourself a car battery (or take it out to your car) and hook 'er up. you will know in 2 seconds if your motor works or not.

Thanks for more info man.  I'm not super familiar with this stuff, only the basics, so any place to start troubleshooting is good to go.  So from a high level, why would it work before with the PS and now not work?  Perhaps the PS is no longer able to supply the power it needs?

[DaOld Man]

Maybe Im missing something here, but does the clutch maybe have a diode across the coil for snubber control? If so, if you reverse the current on the clutch you could be shorting out the power supply.
(This may have already been discussed, I havent intensely read every post.)
If this cant be the problem, if you can remove the brushes on the motor, take them out and see if one is broken.
Do you have a 10 amp auto battery charger? You can try the motor on it.

[kahlid74]

Maybe Im missing something here, but does the clutch maybe have a diode across the coil for snubber control? If so, if you reverse the current on the clutch you could be shorting out the power supply.
(This may have already been discussed, I havent intensely read every post.)
If this cant be the problem, if you can remove the brushes on the motor, take them out and see if one is broken.
Do you have a 10 amp auto battery charger? You can try the motor on it.

I have a battery charger yeap.  I'll go grab it and try that.

[kahlid74]

Lilshawn you are right.  The draw of AMPs is above 10 so the relay is failing, but are relays supposed to give an indication of when they fail?

Thanks DaOld Man, I hooked up my Lanmower charger which is supposed to be 6AMP at 12volt and the amp gauge went way off the side over 8 AMPs and the motor ran.

So I need a stronger relay and I need a solid PS that's 12volt 20AMP.

Thanks again guys!

[DaOld Man]

Yeah I kinda figured that.
The power supply needs to be beefy, but it doesnt have to be regulated for a motor. A 10 amp transformer with a 20 amp bridge rectifier and maybe one beefy capacitor for a filter should be just fine.
The regulated power supplies are probably not good for motors, since they do have a short circuit protection and may see the motors start up current as a short.
Its not like the motor is going to be running constantly, so I wouldnt go overboard, since a bigger transformer means more floor space needed. (A 10 amp battery charger may be all you need.)

[lilshawn]

A Relay will usually end up with stuck contacts if the amperage is too high.

I suspect the power supply output regulator has had enough and is shutting off on you (overload protection)

i wouldn't use that power supply for a computer anymore.

[danny_galaga]

To be REALLY sure what the motor does, you should get a car battery like Lilshawn says, and hook up an ammeter (or an induction loop thingo on a digital voltmeter) so you can see what the true current draw is- loaded and unloaded. Just remember that a DC motor draws STACKS of power at start up (because it has an effectively very low resistance) and at speed draws a lot less. For instance your typical car starter might draw 50 amps or so just free spinning, and say 200 amps cranking the engine but if you lock that bad boy up it will be over 500 amps! More than likely a very short duration spike won't effect things but you should get a handle on what's really going on. I myself would be very surprised if it only draws 10 AMPS, but am happy to be wrong. hook it up to a car battery so you have effectively unlimited amps for the motor and measure the current.

You also have to make sure you have enough amps for the motor because you risk burning it out if the voltage drop is too great, which will happen if you overload your power supply. Again this happens with starters. At 12V, it's fine, motor can spin fast. But if your battery is a bit dead and the voltage drops to say 9V, even though you would think that would mean less current draw (V=I x R), it will actually be more because now the motor is spinning much more slowly, and for a DC motor, speed is proportional to resistance. This is when car starters burn out. I'm only using starters as examples because I used to be an auto-electrician and that is where most of the repairs were done. Smaller motors didn't have as many problems, therefore I can't reliably quote figures for them, but the principles are the same...

[kahlid74]

To be REALLY sure what the motor does, you should get a car battery like Lilshawn says, and hook up an ammeter (or an induction loop thingo on a digital voltmeter) so you can see what the true current draw is- loaded and unloaded. Just remember that a DC motor draws STACKS of power at start up (because it has an effectively very low resistance) and at speed draws a lot less. For instance your typical car starter might draw 50 amps or so just free spinning, and say 200 amps cranking the engine but if you lock that bad boy up it will be over 500 amps! More than likely a very short duration spike won't effect things but you should get a handle on what's really going on. I myself would be very surprised if it only draws 10 AMPS, but am happy to be wrong. hook it up to a car battery so you have effectively unlimited amps for the motor and measure the current.

You also have to make sure you have enough amps for the motor because you risk burning it out if the voltage drop is too great, which will happen if you overload your power supply. Again this happens with starters. At 12V, it's fine, motor can spin fast. But if your battery is a bit dead and the voltage drops to say 9V, even though you would think that would mean less current draw (V=I x R), it will actually be more because now the motor is spinning much more slowly, and for a DC motor, speed is proportional to resistance. This is when car starters burn out. I'm only using starters as examples because I used to be an auto-electrician and that is where most of the repairs were done. Smaller motors didn't have as many problems, therefore I can't reliably quote figures for them, but the principles are the same...

Thanks for the great recommendations!  I'll definitely give this a go.

[kahlid74]

Sooo, it's been a while since I updated this.  Too much stuff going on but i finally got back to this.  While picking up grass seed at Menards I grabbed a car battery charger.  Hooked it up to my Relay/UP-DOWN button/On-Off Button and boom-shakalaka, it worked like a champ:





So I then had to decide whether I wanted an Arduino to power it or a Raspberry Pi.  I had one of these "PiFace" electrical boards that has 8 inputs and 8 outputs and two 10AMP relays built into it.  So I decided what the heck, lets build it on Pi.  So I'm going to use a 3.5" LCD screen as the main login screen and a USB numpad as the keycode enter system.

[lilshawn]

that sounds epic. I can't wait to see that in action!