I am trying to find a cheap power supply to provide + and - 9V DC out (wall wart would be great). This is to replace two 9V batteries. I don't want to build one or buy a unit that needs a case (like this one https://www.jameco.com/z/JE215-Dual...MIm7LT_ISN2gIVi4zICh1F9gGUEAQYASABEgLRwfD_BwE) if I don't have to do so - I just want to click "buy". I thought these were relatively commonplace - maybe they were at some time, but I can't seem to find anything.

Any one know where one can be had?

 

Dual supplies are not common.
Just use two 9V wall warts and wire one with its minus to common and the other with its plus to common.
Their outputs are totally isolated so there's no problem with doing that.

 

Have you checked out www.digikey.com, www.mouser.com, www.alliedelec.com?

 

I thought I remembered one at Adafruit, but maybe I remembered wrong. All I see now is +/-12, not 9.

Anyway, maybe this product, or its datasheet or manufacturer, can point you in the right direction:

https://www.adafruit.com/product/2591

 

Do you need an 18V supply, or a +9 0 -9v?

 

Dual supplies are not common.
Just use two 9V wall warts and wire one with its minus to common and the other with its plus to common.
Their outputs are totally isolated so there's no problem with doing that.

I never thought about that. I also mean, I never thought that it could work for some reason. It is a possibility.

What about converting a 9v AC adapter as shown here on the right. (from https://electronics.stackexchange.com/questions/2734/9v-dc-power-supply).

I am trying to resurrect a frequency generator that was given to me ~20-25 years ago. It was probably given to me because it was broken, I really don't remember. This is the model http://www.ecgsimulators.com/products/model-220-biomedical-function-generator at least that is the one currently being sold. Mine looks exactly like that on the outside but not necessarily the same on the inside.

It uses two 9V batteries. I actually have the schematic, which has no copyright notice. I wrote the company and asked if they would mind if I post it in a help forum (i.e., here). They were not crazy about it but did agree that it was ok (I told them I wouldn't if they had big problems with doing so).

The idea was to get a power supply rather than to go through 9V batteries while I try and figure out what is what with it. Then, I would try my hand at fixing it and if/when that failed, I would post the schematic here and ask for guidance.

Now, I am asking for help just to get the power supply

It may be another ~20-25 years

 

Do you need an 18V supply, or a +9 0 -9v?

+/- 9v see other post for a better description.

 

I thought I remembered one at Adafruit, but maybe I remembered wrong. All I see now is +/-12, not 9.

Anyway, maybe this product, or its datasheet or manufacturer, can point you in the right direction:

https://www.adafruit.com/product/2591

*dagnabit* THAT is exactly what I was looking for but in a +/- 9V

 

For quick down and dirty way I would go with @crutschow's method.
Max.

 

Have you checked out www.digikey.com, www.mouser.com, www.alliedelec.com?

I have checked the first two - maybe I missed it but I do not see one. They used to have a ton of these kind converters https://media.digikey.com/pdf/Data Sheets/Recom Power Inc PDFs/RAC15-S_D_TB.pdf with +/- out but I don't even see anything available now.

 

What about converting a 9v AC adapter as shown here on the right.

That will work just fine. With a 6.3 V transformer secondary (a common value from olden days), the peak voltage across the filter caps will be approx. +/-8.2 V. With the transformer lightly loaded, such as 20% or less of its rated output current, the output voltage will be higher, probably a bit over 9 V.

ak

 

Dual supplies are not common.
Just use two 9V wall warts and wire one with its minus to common and the other with its plus to common.
Their outputs are totally isolated so there's no problem with doing that.

They're USUALLY double insulated and totally isolated - types with a moulded plastic earth pin absolutely guarantee this.

 

http://www.phcenterprise.com/index.html

If you can't find it listed on their site, call and tell them what you want. You only need 10W or so (+9V @500mA & -9V @500mA).

By the way, it's likely that the unit would work fine on ±12V.

 

Have you checked out www.digikey.com, www.mouser.com, www.alliedelec.com?

I also recommend Digikey. as a source. They have a good on-line catalog.

 

To follow up on this mini-project:

The type of adapter that I was looking for is unavailable as far as I can tell. I have looked at a lot of sources.

As I thought about it more, I don't even need one like that. The Frequency Generator operates from two 9V batteries and it has two separate 9V battery connectors.




The solution I chose was to just put two 9V battery connectors onto two 9V adapters (wired correctly, of course).

On to the junk box where I find that I have salvaged many AC to DC 9V adapters. The measured output voltage (no load) varied between units from about 11.9 to 14.7 V – not unusual for these old type wall warts.

I bit the bullet and just cobbled together two of the venerable 7809 circuits and included a power on LED (see below). I had several adapters that are + tip on a 2.5mm plug and I used a screw terminal on the output side so that I can change the output connector easily. I have no idea how well regulated the wall warts are and I pretty much guessed on the caps within what I had handy. I also had a couple of cheap plastic cases for housing.



So far, these work very well. In addition to the specific use mentioned, they can serve as a 9V battery eliminator and a general 9V regulated supply.



I also made a breakthrough with fixing the frequency generator and am hopeful to get it up and working.

Thanks for the suggestions.

I am happy.

 

For quick down and dirty way I would go with @crutschow's method.
Max.

That's what I would do also. A pair of wall warts for a few bucks on Amazon and done. If this is replacing a pair of 9V batteries the current demand can't be very much.


Ron

 

From this:

I am trying to find a cheap power supply to provide + and - 9V DC out…I don't want to build one…I just want to click "buy"…

to this:

…I bit the bullet and just cobbled together two of the venerable 7809 circuits…

Fickle much?

 

From this:


to this:


Fickle much?

No.

I appreciate the suggestions, as I have stated. When I reach out for help and people respond, I am always thankful. This is why I felt it was important to provide a follow up post with what I ended up doing. I thought that I explained things in that post, but apparently not to your satisfaction. So, I will elaborate, but I think you are being a bit harsh. Not being able to find what you are looking for and doing it another way does not, in my mind, qualify as being "Fickle much".

As I stated, many years ago, I received, as a donation, a Function Generator. No doubt it was disgarded because it did not work - that was my recollection. But, loving free electronic stuff, I took it happily...and happily stored it away for many years. Came upon it and thought - "I should check this out".

I did and I could not get much of anything out of it that resembled a "function". Of course I was using only a volt meter. As I started to get into it systematically, the batteries wore out. That was the point at which I posted.

All I wanted was a non-battery solution to keep working on it...without having to go to the store and buy a bunch of 9Vs. Having the schematic, I figured I would just wire a +/- 9V adapter to the board and keep going. After all, I had no idea if this thing was ever going to work.

I could not find one. After spending many hours looking, I could not find one. In fact, the very site that you suggested was the final straw. After scrolling through 20-30 pages of wall warts and not finding one, I said enough is enough (I was not about to call them on the phone). I literally had spent several hours searching.

So, I thought WTF, I have built power supplies and I have everything I need right here - definitely have plenty of wall warts. That is when I built the regulated 9V supplies that I posted a schematic and pictures of. Yes, I bit the bullet and it was a rewarding weekend project.

It has paid off as I continued to work on the function generator and I spotted one major problem (an IC that was plugged in backwards and I couldn't believe it and must have quadruple checked the schematic and my meter - it is a TL064 and pins 4 and 11 are + and -....the chip was in wrong (no wonder they gave it to me) and ALL the pots needed a serious CAEON 27 treatment...and the small ones still need another treatment or maybe replacement.

BUT, my efforts have a payoff...armed with my $28.63 toy O-Scope, I took the following tonight.






Hopefully, I can get things a little cleaner and train my brain to be a distortion analyser, or at least a pot-turning machine.

So, thanks for the suggestions (all), I appreciate it,as always

...please forgive me and if I feel like I might change my mind again @KJ6EAD , about anything, I will email you and request a permission slip first .