Replacement motor focus handset for less than a fiver

[andyboy1970]

Disclaimer - Obviously as a DIY project it is at your own risk

[Owmuchonomy]

I think mine is on it's last legs so thanks to you I will have a go at making one.

[JamesF]

That's a very neat idea

James

[DIYASTRO]

Andy,

Nice !

Just be careful that your LED dimmer (PWM unit) has a diode on the output. (something like a 1N4001 is best) These units are good for what they are designed for but when using them for coils eg. motors / relays you run risk of EMF feed back and that does damage to lots of equipment.

Why manufacturers don't put them in the output side is beyond me, they are only a few pence but to save costs they are frequently left out of the circuit. Worth a look!

I actually make my own PWM circuits, and regardless of what they are used for either motor control, light dimmers, dew heater control, I always put the diode in the output and always use components that exceed the wattage required, capable  up to 14Amps.

Kind regards

Boyd

[andyboy1970]

Cheers Boyd I hadn't considered that.

Had to replace a few diodes across the coils of relays on aircraft I work on.

With the motor being reversible should I put the diode between one of the dimmer unit output wires and the DPDT switch?

(I'm not great at circuit design). 

[DIYASTRO]

Andy,

It is usually ok to simply place the diode across the output terminals, cathode to + anode to - use a !N4001 if you can. A 1N4007 is just as good and more easily obtained. Its simply a bridge in circuit to prevent the EMF damage to the transistor/ mosfet or whatever is used within the circuit to control the power/speed. A1N4148 diode is better than nothing but I prefer the specs of 1N4000 series.

What an interesting job you seem to have! What aircraft?

Boyd

[andyboy1970]

I'm a Licensed avionics engineer, but these days its all systems maintenance with wiring checks getting less and less.

I work on narrow body commercial jets (Orange and white ones) and in the dim and distant past I spent 2 years working on the Concorde fleet.

This is were circuit design gets away from me as I haven't really done it since college 24 years ago!

[DIYASTRO]

Andy,

That sounds really great, although I am sure that like everyone else who works 'grass may seem greener elsewhere'.

Sounds very interesting though.

You have made me think... I was last at college 41 years ago! Thinking recently of going back to solidify my ideas of what is going on!

Kind regards

Boyd