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Topic: [SOLVED] Homebrew PCB - Puzzle - Laminator Running Backwards After Jam (Read 2461 times) previous topic - next topic

tack

I wasn't sure where else to put this and it is PCB making related...

I use a laminator for toner transfer and the process works well for prototyping or small quantity requirements.

Usually my copperclad goes through just fine but yesterday I had a jam. I pushed the board through in the same direction it was moving but then it reversed and came back out! Now the laminator rollers are running in reverse direction, from rear to front.

I've taken it apart and thought I'd find some kind of jumped cog somewhere but I can't see anything amiss.

Everything is 240V AC with a single phase motor driving the rollers. It looks like a couple of LEDs are driven just with diodes, for half wave rectification, and large value resistors.

I can't provide any imaged until back home but just wondered if anyone had ever come across anything similar?

MarkT

one-phase induction motors can run backwards if forced - they normally use shaded poles to bias the field to elliptical
rotation which at start up should get them moving the right way - however if physically jammed they can run backwards
as the bulk of the magnetic field is simply alternating and once the rotor is running backwards it will respond nearly as well
in the reverse direction.
[ I won't respond to messages, use the forum please ]

tack

The strange thing, Mark, is that it now permanently runs in reverse. If you switch it off and start again it runs backwards. I totally get where you're coming from about forcing a start in a certain direction, but AFAIK a shaded pole start can't be reversed without physically rotating the armature 180 degrees.

I've worked with larger capacitor start machines int he past and built in reversing on oil pumps by using a DPDT relay to swap the capacitor connections, but nothing changed on this at all. It just jammed and started going the other way.

Very odd.

tack

Well, I just took it apart and set a screwdriver under the main cog. As I started teh motor I levered it in the opposite direction and it started going forwards again. Turning off and on and it goes right way, so the problem is solved.

I still don't understand how it continues in the direction it last went. I thought any start method would bias the field in a particular direction, CW or CCW.

Every day is a school day.

outofoptions


fungus


I still don't understand how it continues in the direction it last went. I thought any start method would bias the field in a particular direction, CW or CCW.


Maybe it depends on where the motor stops turning.

Try moving it a bit with no power connected, see if it starts up randomly afterwards.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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