# will it damage a 7.5 volt AC device running it off a DC adaptor? **URL:** \ **Category:** Factual Questions\ **Created:** [January 14, 2010, 6:29am UTC](https://boards.straightdope.com/t/will-it-damage-a-7-5-volt-ac-device-running-it-off-a-dc-adaptor/524904 "2010-01-14T06:29:40Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\ **Post date:** [January 16, 2010, 11:09pm UTC](https://boards.straightdope.com/t/will-it-damage-a-7-5-volt-ac-device-running-it-off-a-dc-adaptor/524904/21 "2010-01-16T23:09:49Z")
> [@beowulff](#): > > It’s a simple half-wave rectifier, one for positive and one for negative. Brings back memories of the exam for my electrical license. Had to know to change from rms to peak voltage for the PIV of the diode. They also like to draw the schematic with the diodes connected so that it would actually be a short circuit and ask whether the circuit is acceptable. I haven’t worked on one since though. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [January 17, 2010, 6:17am UTC](https://boards.straightdope.com/t/will-it-damage-a-7-5-volt-ac-device-running-it-off-a-dc-adaptor/524904/22 "2010-01-17T06:17:52Z")
well unfortunately they don’t work. ☹ the lights come on but it doesn’t put out a valid VGA signal, I guess it does rely on the AC timing signals for generating the VGA output (it’s an active matrix). So I’m going to have to either buy a 240/120 volt convertor box to use the existing adaptors or track down a 240 volt AC AC adaptor with 7.5 volts AC output… crap ---
**Author:** ![foolscap](https://avatars.discourse-cdn.com/v4/letter/f/e9a140/32.png) [@foolscap](https://boards.straightdope.com/u/foolscap)\ **Post date:** [January 17, 2010, 5:05pm UTC](https://boards.straightdope.com/t/will-it-damage-a-7-5-volt-ac-device-running-it-off-a-dc-adaptor/524904/23 "2010-01-17T17:05:53Z")
> [@coremelt](#): > > well unfortunately they don’t work. ☹ > > the lights come on but it doesn’t put out a valid VGA signal, I guess it does rely on the AC timing signals for generating the VGA output (it’s an active matrix). > > So I’m going to have to either buy a 240/120 volt convertor box to use the existing adaptors or track down a 240 volt AC AC adaptor with 7.5 volts AC output… crap If it is using the ac as a timing function, you might have a problem with a U.S part wanting 60Hz, and getting 50Hz from a step-down power supply. You might have to buy an inverter with the correct frequency:smack: ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 17, 2010, 5:13pm UTC](https://boards.straightdope.com/t/will-it-damage-a-7-5-volt-ac-device-running-it-off-a-dc-adaptor/524904/24 "2010-01-17T17:13:51Z")
> [@foolscap](#): > > If it is using the ac as a timing function, you might have a problem > with a U.S part wanting 60Hz, and getting 50Hz from a step-down > power supply. > You might have to buy an inverter with the correct frequency:smack: This reminds me of a problem I solved for a friend a few years ago. He had a cool European-made “light sculpture” that cycled through a rainbow of colors. Unfortunately, it didn’t work right - it would have a weird “glitch” at the end of each fade-out. I realized that the microprocessor was getting it’s dimming sync. signals from the powerline frequency, and it was 60/50 (1.2x) too fast. So, I opened it up and changed the crystal for a faster one I had in my parts bin, and it worked perfectly after that. Sadly, I don’t think it’s going to be that easy in this case - it’s probably time to look for a new device. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [January 17, 2010, 11:10pm UTC](https://boards.straightdope.com/t/will-it-damage-a-7-5-volt-ac-device-running-it-off-a-dc-adaptor/524904/25 "2010-01-17T23:10:55Z")
> [@beowulff](#): > > Sadly, I don’t think it’s going to be that easy in this case - it’s probably time to look for a new device. well according to the box there is an option for shipping with AC-AC 240 volt adaptor and Australian plugs, theres a checkbox for which type of adaptor is included. So it should be able to get timing from 50/60 hz. I’ve contacted the sell (ebay) to try and obtain the right adaptor. [Previous page](https://boards.straightdope.com/t/will-it-damage-a-7-5-volt-ac-device-running-it-off-a-dc-adaptor/524904.md?page=1)