splobucket
Well-Known Member
Any ideas where to get a cheap 110VAC to 12VDC transformer? I have a feeling I could just easily rip this one apart and rewire it...
Transformer at Amazon
Transformer at Amazon
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Cell chargers and things like that are low voltage, 3-6V range. You need something from like a laptop.
how much power do you need? I can assume this is for a fan or something small? You should be able to pick something up cheap at a hobby shop or Radio Shack.
True cell phones will be lower, but I wanted to just bring the point across that the wall plug-in was his best bet in case he didn't realize those were transformers.
Edit: well now that you've mentioned that, you'd better figure out just how much current you need. If you're talking about the big 1/2" NPT eBay solenoid valves, those have a coil current rating of 1.4A - if you ever need to energize more than one of those at a time, you're going to need a more beefy power supply (the ebay seller I linked does carry bigger ones). I don't think you'll find many wall warts that will give you more than about 1.5A at 12V...I just ordered some 12VDC solenoid valves for my herms system and will need to power them.
I just ordered some 12VDC solenoid valves for my herms system and will need to power them.
I just ordered some 12VDC solenoid valves for my herms system and will need to power them.
...and come to think of it I do have a laptop charger laying around somewhere. I've got some digging to do.
Well they draw 1.4 Amps when running... I plan on hooking two up at once... now you got me thinking. Do I need a transformer rated for 2.8 amps or 1.4 amps?
Can I hook them up in series or parallel? I figure parallel... this is where my old circuitry knowledge wanes...
First off, wire them in parallel...series is a bad idea.
This is good advice. They are meant to draw a certain amount of current under a certain voltage. If you put them in series could wind up drawing more current than you intended because they're only seeing half the voltage.
2.8 amps is a lot of current for a consumer electronic power supply. You'll be looking for a physically large supply. How about a small battery charger? Get yourself a large 10uF capacitor to put across the output to smooth the waveform. It will be an electrolytic capacitor and they are polarized, so watch your positive and negative terminals.
Just throwing it out there: would an old computer power supply be appropriate for powering something like this?
I turned an old ATX supply into a general-purpose power supply (I use it for my stirplate, among other non-brewing things), and looking at the sticker on the side, the 12V rail is good for 15 amps. So if you gang all the yellow wires together (or enough of them to handle the expected current anyway), then yeah, it should work, just check the sticker on the power supply for the 12 V current rating.
I"m not sure how they respond to wacky loads like solenoids, you'd probably want to be at least a little careful snubbing the line and so forth, but it should be very doable.
Sorry, wouldn't work that way. In series, not only will each solenoid see half the voltage, but also half the current. The current is the working variable here, and likely the solenoid would not work.
Although a cap is a good idea, I wouldn't mess with that unless you had problems with the solenoids retracting. 25V for electrolytic. Also, just make this as hard as possible, I'd also throw a diode in there to handle the negative spikes when the solenoid is released and the electric field collapses in the coil.
I think you guys might be thinking to much. The pull in current is only going to be for a second so stick with the 1.4 amp number. Why are you talking about caps?? Are you worried about powerfactor on two little loads like that?? Keep it simple. Another idea you can go look at door bell transformers ,I don't know what the current rating are but they are only a couple of bucks.good luck.
The link in that thread is broken since the auction's from months ago, but I did find another one by searching for "astrodyne" on ebay. $10 plus $9.99 for shipping is a little lame, but $19.99 total is still fairly decent. I'll keep it in mind when I need more power.http://www.brewtroller.com/forum/showthread.php?t=412
Check this thread out, this power supply will work and its only $10
It is not a momentary current draw. There is an electromagnet in the relay and the current need to supply the electromagnet is not momentary.
He should also think about putting some reversed biased diodes across the solenoid coils so a back emf pulse does not do damage to the power supply when the solenoids disengage. Some 1N4007's should do the trick. It is just good design.
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