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Adjustable Voltage Wall Warts??? — Parallax Forums

Adjustable Voltage Wall Warts???

idbruceidbruce Posts: 6,197
in General Discussion
Are there any wall warts with adjustable voltage that may fit the following specifications?

6-12VDC, 1.5A

12V max 1A min

Comments

  • LeonLeon Posts: 7,620
    edited 2015-09-18 09:05
    They are mostly switchers, designed to be as cheap as possible, and are difficult to make with variable outputs.
  • PublisonPublison Posts: 12,366
    Radio Shack


    http://www.radioshack.com/enercell-6-12vdc-2-5-amp-high-power-ac-adapter/2730318.html

    http://www.radioshack.com/enercell-universal-1000ma-ac-adapter/2730316.html
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    I did have one that allowed on to set the range, and change a variety of barrel plugs -- kind of a Swiss Army knife solution to wallwarts. It was a tiny transformer with multiple taps on the windings. That link to the Enercell 6-12vdc device may be the same thing.

    Frankly, I got rid of it as I was more afraid of ending up with the wrong setting or the wrong polarity at some point in time. I just felt it was too adjustable. But I do see that they are still available retail in Taiwan.

    Switchers have taken over in this role and some come with numerical LED displays that confirm the voltage output. The tiny adjustment screw is less libel to be tampered with that a switch.
  • RDL2004RDL2004 Posts: 2,554
    Try your local Walmart.


    Powerline 1300 mA Universal AC Adapter

    3-12 volts 1300 mA, 7 tips and switchable polarity
  • idbruceidbruce Posts: 6,197
    @Leon - Yea, I knew it was going to be somewhat of a specialty item, however I see following posts offered a couple of options.

    @Jim - Those RS Enercell's are pricey.... WOW

    @Loopy - Yea, I can see where all the settings and parts could lead to trouble.

    @RDL2004 - Thanks for the link. It's not exactly what I was hoping for, but it has a reasonable price and it may be a solution.

    Instead of having adjustable voltage, perhaps I should be thinking of PWM instead. Perhaps the best solution would be a control board based upon a 555 timer. I basically want to control the speed of 12V fan. So perhaps a 1300 mA wall wart going into a control board, with the fan hooked up to it.

    So how about a control board? Does anyone know of a low priced control board to accomplish this task?
  • JLockeJLocke Posts: 354
    edited 2015-09-19 04:56
    Fry's has several with selectable outputs.
    http://www.frys.com/category/Outpost/Electronic+Components/Electrical+-+Power+Adapters/
  • idbruceidbruce Posts: 6,197
    @JLocke - Thanks.... It is always nice to have options.
  • Peter JakackiPeter Jakacki Posts: 10,193
    If you could crack one open it would probably be easy enough to insert a pot into the feedback resistor and calibrate those voltages that you want. Alternatively just get an old laptop power-pack as these are normally 18 or 19V at several amps and feed that into a common DC switcher that is safe for you to vary the output voltage with a pot of switched resistors. There are plenty of both of these on ebay such as this dc step-down and if you need to buy a laptop supply try something like this. These are just the first ones that popped up.
  • idbruceidbruce Posts: 6,197
    edited 2015-09-19 16:50
    Peter

    I don't know if you have been following along with the discussion about the aluminum metal melting furnaces that I am currently working on, but this thread is an offshoot of that discussion.forums.parallax.com/discussion/161856/robot-parts-and-lost-foam-casting

    I recently found a fan which may be suitable for providing forced air to my furnaces, however the problem of controlling the amount of forced air still remains. As I see it, there are only two options, either control the fan speed or insert a valve within the forced air pipeline.

    If you have been following along with the other thread, you will notice that I gave up on one concept and I am now pursuing the concept of making it more portable.

    In addition to the problem of controlling the air flow, there is also the issue of providing power for the fan. As you know, dealing with extension cords is often a real pain, so I am now considering an alternative power source and plan, which would provide me with another product and further options for the customer.

    With all this in mind, I am now considering the construction of a lawn and garden tractor battery carrying assembly, which would have the fan mounted to it, and a baffle mounted to the fan. The fan can be connected to the battery with aligator clips attached to the fan leads.

    As mentioned in the other thread, I am now pursuing a design of a furnace mounted to a patio block which has handles on each side. With the idea that I am now proposing, it should be a quick and easy setup, that can be fired up just about anywhere.
    1. Carry furnace (Approx. 20LBS) to desired melting location.
    2. Carry battery (Approx. 15LBS) to desired melting location.
    3. Connect forced air pipe.
    4. Load charcoal into furnace.
    5. Ignite charcoal.
    6. Insert aluminum filled crucible into furnace.
    7. Adjust forced air baffle.
    8. Kick back and wait for the metal to melt.

    The following attachment should give you an idea of what I am now considering. However, perhaps the baffle idea may put undue stress upon the fan, thus decreasing life expectancy.
    battery holder.jpg
    431 x 274 - 16K
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    There is always more than one way to skin a cat.

    Perhaps you should just buy a leaf blower at a garage sale.
    http://www.ebay.com/bhp/leaf-blower

    If you want forced air for foundry work, you will want lots of it.
  • idbruceidbruce Posts: 6,197
    Loopy

    I just use the shopvac for my purposes, but at this point, I am thinking about the end user, and just providing them with options.
  • pmrobertpmrobert Posts: 673
    edited 2015-09-20 01:16
    In a similar universe and application, turbocharger compressors do not like having their output throttled, bad things can happen to the compressor wheel. They are perfectly OK with either having their inducer restricted or the exducer diverted if there is a need to reduce output volume to the intended target (the engine usually). Of course, this is usually a very transient condition such as lifting the throttle for a shift, etc. as the turbine stops powering the compressor shortly after a lift. I'm not sure what the ramifications would be for restricting the output of a continually powered centrifugal compressor. If the electric motor driving it relies on air flow for cooling that may not be good either. I very much like your idea of PWM varying the motor speed - I've been using a similar scheme on a smoker air supply/temp control fan for a while without issue though I use an AC powered motor with a triac chopping it's AC as needed. Similar yet quite different from your needs!
  • idbruceidbruce Posts: 6,197
    @pmrobert

    I totally agree that PWM is the way to go for longevity of the fan, and I further believe that a 555 timer circuit would be the simplest solution. There are several simple 555 schematics available to achieve what I want to do, but up to this point, I have been unable to find a packaged solution, which is beyond my comprehension, considering the popularity and history of the 555 timer.

    From a cost perspective, I believe a baffle would be more economical, dependable, and a fan problem would be very easy to diagnose. The fan would most likely give plenty of early warning that it would need replacement, and the fans are relatively inexpensive, compared to circuit board production, enclosures, etc...

    Certainly the easiest solution would be to place a gate valve within the pipeline, but they are fairly expensive and repetitive positioning might be a little complicated.
  • pmrobertpmrobert Posts: 673
    This maybe?
    http://www.ebay.com/itm/like/320979230658?ul_noapp=true&chn=ps&lpid=82

    or

    http://www.ebay.com/itm/NEW-9-50V-40A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller-12V-24V-36V-50V-2000W/231514448333?_trksid=p2141725.c100338.m3726&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20150313114020&meid=921d2c3d28f943ff83e4e4c9ebcabaab&pid=100338&rk=1&rkt=30&sd=320979230658
  • kwinnkwinn Posts: 8,697
    @idbruce

    The attached 555 circuit will provide a 5% - 95% PWM control range. For a motor you would need to add a protection diode.
  • kwinnkwinn Posts: 8,697
    Oops, here's the schematic.
    PWM 5 - 95 percent.png
    376 x 376 - 12K
  • idbruceidbruce Posts: 6,197
    @pmrobert - The first one looks like it might work. Thanks for the lead.

    @kwinn - Yep.... Looks like that would work. Here is one that has gotten some pretty good reviews for controlling fans
    pwmfancontrollerwith555_1241855842.jpg
    and here is a link to the full article http://pcbheaven.com/circuitpages/PWM_Fan_controller_using_a_555/
  • ercoerco Posts: 20,256
    pmrobert wrote: »
    I'm not sure what the ramifications would be for restricting the output of a continually powered centrifugal compressor.

    The downstream static pressure builds up, airflow and power input are both reduced, much the same as restricting the inlet. My Corvair's thermostat is a pair of outlet doors that open & close to control how much air flows over the heads.
    pmrobert wrote: »
    If the electric motor driving it relies on air flow for cooling that may not be good either.

    Ditto, airflow through a Corvair is not optional. :)


  • ercoerco Posts: 20,256
    Bruce: $2 and I think I see an NE555 on board: http://www.ebay.com/itm/Quality-Motor-Speed-Control-Switch-Controller-PWM-DC-6V-12V-24V-28V-3A-/151663604118?hash=item234fdaf196
  • idbruceidbruce Posts: 6,197
    edited 2015-09-21 10:39
    @erco

    At $2.05 and free U.S. shipping, it is certainly worth a try. If it does work well as a fan controller, the biggest drawback that I can see, is the possible huge turn around time from order placement to product receipt. However, at that price, providing they work well and my product sells, I suppose I could place a decent sized order for inventory.

    Anyhow, I will order one, but it is really a drag to know that the soonest I can test it is Oct.9th, and possibly not until Nov. 13th. My test fan should be showing up by the middle of the week and I guess I will just rig something up until then.

    Thanks for the ebay lead :) Now you got me buying one of erco's special deals. Are you trying to corrupt the whole forum? Seriously, if it works well, I will truly be grateful for your lead and input into this matter.

    Bruce
  • ercoerco Posts: 20,256
    edited 2015-09-21 17:15
    idbruce wrote: »
    Now you got me buying one of erco's special deals. Are you trying to corrupt the whole forum?

    You'll feel so much better after you drink some Ebay China Koolaid. Don't forget the 2% commission for my twins' college fund! :)

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