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How to get 75 VAC from 120 VAC

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seeyf

New Member
Hi, I purchased a piece of electrochromic film from smarttint.com which switches from opaque to transparent when a voltage is applied to it. I'm looking for an appropriate inverter to power it using AA or other standard batteries, if possible. The spec sheet is available here (http://shop.smarttint.com/smart-tint-non-adhesive_ep_42-1.html) Mine is the Non-adhesive, low voltage version. The main requirements are:

35-75 VAC
50-60Hz
2.7mA (my sheet is 8 x 5.5 in)

Any idea if there is something that can provide this, or even a wall converter that would work? So far I've asked people at Mouser and Digikey who said they don't have anything for me. They do sell a mobile adapter so it seems like it is possible, but it seems a little overkill as it provides 5A which is much more than I need. I'm using this for an art project with an Arduino that I hope to use to turn the film on and off through a relay.

I saw this post where it was suggested a 220 to 120 stepdown transformer could be used to get 60VAC from 120VAC, does that mean I could use a travel transformer like this?
 

MikeMl

Well-Known Member
Most Helpful Member
What's wrong with a (120V-75V)/2.7mA = 45V/2.7mA = 16.6KΩ resistor? It would need to dissipate 45V*2.7mA = 121mW, so even a 1/4W resistor would work. If shock hazard is a worry, then get a small 120V to 120V isolation transformer, or even a couple of door bell transformers back-to-back.
 

seeyf

New Member
Hi Mike, thanks for your reply, I tried it out and it did work! I thought a more substantial solution would be needed but you're right in that the dissipation is not a lot, since the current is small. I think I will get the isolation transformer to be safe too.
 

MikeMl

Well-Known Member
Most Helpful Member
If it is an objet d'art that someone can touch, best get an isolation transformer of some sort.
 

dr pepper

Well-Known Member
Most Helpful Member
They are not as popular as they once were however you can get transformer kits, where the transformer comes with a prewound mains primary and you design the secondary and wind it to get exactly the voltage you want, its not difficult to work out or do.
Probably the simplest way.
Or if you want to run from batteries you could wind your own transfomer and build a royer oscillator, or maybe a 555/H bridge circuit.
 
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