DC to AC, can it be done / USAT point soleniod.

[Dieseldonkey]

Hi,
Took a complete punt on ebay the other day and won a USAT point motor for a quid plus postage. On reading the instructions it states it requires an 18VAC power source. I know and understand how AC can be rectified to DC with diodes, but can it be reversed so that my 20 volt DC power supply can be used to produce an AC voltage? What would I need to do this? It looks to me like the point is operated by two separate coil solenoids, one for each direction of throw. However it does have some LED's on the control switch box and direction indicator lights on the motor itself, so I'm reluctant to try a DC voltage to see what happens, in case there are polarity sensitive electronics built into the unit. Any help appreciated.
Thanks
Dieseldonkey

 

[spike]

Think they are AC when used with it's own two button switch.
In the switch are a set of diodes the coils will be dc.
Far as I know there are no other electronics inside apart from a small microswitch.

 

[Dieseldonkey]

Thanks for the useful info Spike.
I'll have a play about in that case and see what I can make it do by removing the supplied switch. I take it its just simply a 'push to make' type switch are good for activating the solenoids, with no requirement for a latching switch? Are the USAT point motors any good in the longer term for outdoors. They seem a little harder to source new and aren't cheap compared to other brands. They do seem robust though.

 

[spike]

Thanks for the useful info Spike.
I'll have a play about in that case and see what I can make it do by removing the supplied switch. I take it its just simply a 'push to make' type switch are good for activating the solenoids, with no requirement for a latching switch? Are the USAT point motors any good in the longer term for outdoors. They seem a little harder to source new and aren't cheap compared to other brands. They do seem robust though.

IMO the switch is not upto longtime outside.
Water gets in easy..........they rust around the coils, the small internal microswitch that switches the frog is quite palsy.
The springs rust........etc.
If outside for a long time I would spray with silicon from time to time.
Apart from that the actual point is quite nice.

 

[spike]

http://www.elmassian.com/trains-mainmenu-27/track-mainmenu-93/usat-6-switches

Above is a link to show the inards if you have'nt had the top off yet.

 

[tramcar trev]

There are inverters available to unrectify dc back to ac..... usually in a 12VDC to 240AC though....

 

[Rhinochugger]

If you use a Helmsman controller, it has a supplementary AC output - just like the old 00/HO H&M stuff (not that I have any leccy points - I do it the hard way an' have to get up out of the chair, in between sips of Pimms )

 

[tramcar trev]

If you use a Helmsman controller, it has a supplementary AC output - just like the old 00/HO H&M stuff (not that I have any leccy points - I do it the hard way an' have to get up out of the chair, in between sips of Pimms )

Obviously you are not a "Chap" a Chap would drink G&T...... Gordons of course.....
I'm planning a 1 way layout with sprung single bladed points at the passing loops.......

 

[Gizzy]

I personally think it would be easier and cheaper to purchase an AC transformer and use this instead.

Problem solved and if you need a DC supply for other point motors then rectify this, as you mentioned.

DC to AC is much more complex and not very efficient. It involves chopping up and reversing the DC signal at a frequency to make the AC component.

That's one reason why our mains generation and transmission is AC....

 

[Gizzy]

http://www.elmassian.com/trains-mainmenu-27/track-mainmenu-93/usat-6-switches

Above is a link to show the inards if you have'nt had the top off yet.

Looking at the hand drawn circuit diagram, there is a bridge rectifier to change AC to DC within the motor.

You could drive this with DC but you will need to switch the polarity. This is what the bridge rectifier is effectively doing anyway, rectifying the AC and providing the positive and negative polarity (i.e directional) to move the blades left or right (directional).

Easier to use an AC supply as I mentioned previously and switch with the Gaugemaster GM511 switch http://www.gaugemaster.com/item_details.asp?code=GM511&style=main&strType=g although you wouldn't need the diodes supplied in this case....