Looking for an AC adaptor

Jim Smith · Post by **Jim Smith** » 18 Dec 2000 8:42 am

I need some 7-10 VAC 1500 mA adaptors. Not even Radio Shack lists anything with that much amperage. Any ideas where to get them?

I was at a used electronics store and some some that listed the amperage as 20 VA. Does that mean 2000 mA, and would that be too much amperage for my needs?

Jim Smith · Post by **Jim Smith** » 18 Dec 2000 5:37 pm

A lot of rack effects use these wall warts. Does anyone know where to get replacements, other than the overpriced factory ones of course?

Donny Hinson · Post by **Donny Hinson** » 18 Dec 2000 7:06 pm

Jack Stoner, our resident electronics guru might know if the 20-VA would work. I know that some of the old electronic keyboards used to have a pretty husky power supply....also some of the old computer game systems. You might try a local thrift store, or flea-market too.

Jim Smith · Post by **Jim Smith** » 18 Dec 2000 7:11 pm

Thanks Donny. I'm hoping to get an answer before Christmas. I plan to give this unit to my son and don't want to burn it up. Seems like everyone has gone for the holidays. Yours is the first post in the whole forum in almost two hours!

Jack Stoner · Post by **Jack Stoner** » 19 Dec 2000 4:37 am

I'll have to dig into my books (read the f.... book) and see about the VA rating. I haven't done any of those conversions for years and forgot the formula. I'll check this evening and see if I can find the forumula (unless I get lucky and someone else posts what it is before I get to it). I have to leave in about two hours for my weekly Tuesday (noon) gig.

Jim Palenscar · Post by **Jim Palenscar** » 19 Dec 2000 6:14 am

Maybe have Gerry Walker build you one?

Bill Terry · Post by **Bill Terry** » 19 Dec 2000 7:36 am

http://www.vabiomed.org/documents/tech0003.htm

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bterry.home.netcom.com

Jim Smith · Post by **Jim Smith** » 19 Dec 2000 8:00 am

Thanks for the link Bill, although it's talking watts instead of amps. Since VA is Volt-Amps, does that means it's Volts x Amps? Would a 10V 20 VA power supply provide 10/20 or .5 amps? I should have paid more attention in electronics class!

Bill Terry · Post by **Bill Terry** » 19 Dec 2000 10:46 am

Jim,
I'm a little rusty on that stuff too

... but here's the way I understand what I read on that link. Power is I*V, which is measured in Watts. So if your device requires 10V at 1500mA, it needs 15 watts.

If your load is purely resistive, (which yours is probably not), then VA = Watts. In that case your 20VA supply = 20Watts and would be fine for a load requiring 15W.

Since your load probably has some reactance, you have to convert the power requirement from Watts to VA. We don't know the actual power factor of your device, so we can use the generic 70% the author recommends. The conversion is:

required VA = required Watts / power factor

VA = 15W /.70
VA required = 21.42

Based on that, looks like the 20VA supply wouldn't provide enough power. Anybody else that REALLY knows this stuff jump right in....

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bterry.home.netcom.com

Jim Smith · Post by **Jim Smith** » 19 Dec 2000 11:05 am

Velly intellesting Bill.

Since my unit requires 7-10 VAC @ 1500 mA, if we take the low end of 7 V x 1500 mA = 10.5 watts. Then 10.5/.7 = 15 VA which would be enough. Does that sound right? Guess I need to revisit the store to see exactly how those adaptors are marked and see if the clerks at the second hand electronics store know that much about what they're selling!

Bill Terry · Post by **Bill Terry** » 19 Dec 2000 11:42 am

Yeah Jim, that seems reasonable to me... Good luck.

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bterry.home.netcom.com

Donny Hinson · Post by **Donny Hinson** » 19 Dec 2000 5:27 pm

Jim, check out this link...
http://www.kingdatron.com/ac.html

They make a lot of power supplies, and I think the table displayed will help you! (1500 ma=1.5amps)

The KWM020-1509 should be what you're looking for...and the reason I'm the only one around is I have no life!

<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Donny Hinson on 19 December 2000 at 05:31 PM.]</p></FONT>

Jim Smith · Post by **Jim Smith** » 19 Dec 2000 6:19 pm

Thanks for the link Donny, but the 1509 is 9V/1.7A. I think that's too much amperage, plus that company is in Taiwan!

Donny Hinson · Post by **Donny Hinson** » 20 Dec 2000 12:53 am

Jim...no problem there, your device will only use the amperage it needs!

Also, a company called EBATTS claim to carry any power supply you need!

Their toll-free number is
1-877-4EBATTS