110 VAC to 12 VDC transformer?

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

Don't you have any old cell phone chargers or wall worst from RC Cars or anything like that?
Search 12VDC Wall Wart on google. Or try mouser.com or digikey.com

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.

Bjornbrewer said:

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.

Click to expand...

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.

Go to a second hand store and find a piece of obsolete electronics that operates on 12V. Keep the supply and throw away the dot matrix printer, AM radio, whatever. You'll probably get it for a couple of bucks.

How many mA of power do you need? There're plenty of them from 400mA to 1,500mA that can be had for a dollar at Good Will or Salvation Army stores.
Everyone has a couple from dead electeronic game toys.

I would go through all those old boxes from your last move. Things like linksys routers, cable modems, wireless phone, etc will all be somewhere between 5 - 12 volts.

You could just build one yourself too! I just designed the transformer for a 15V - 8,000A single phase power supply. I could give you the design....or is that too big?

IrregularPulse said:

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.

Click to expand...

gotcha

Irregularpulse, gimme a little credit! I knew that they were transformers, honestly i just never thought about one of them, I'll have to do some digging... 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.

Are you looking for some kind of wall wart or do you intend to install the power supply inside an enclosure?

I just bought a 12V 2A power supply for the latter purpose from this seller:
http://business.shop.ebay.com/Power...=&_sac=1&_ssn=yallstore&_trksid=p3286.c0.m282

The ventilated metal chassis and screw terminals made it a bit more suitable than hacking up a wall wart - though it's hard to beat the price of a wall wart from a thrift store, or better yet, one you already have

splobucket said:

I just ordered some 12VDC solenoid valves for my herms system and will need to power them.

Click to expand...

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...

splobucket said:

I just ordered some 12VDC solenoid valves for my herms system and will need to power them.

Click to expand...

How much current are those things drawing to open/close? Depending on size, they can be substantial.

splobucket said:

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.

Click to expand...

Be careful. Solenoids tend to have a fairly hefty current draw. Make sure you size your supply to meet the load or you'll get a little brew day excitement. Kill the breaker before you unplug the smoking, drooping mess.

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...

splobucket said:

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...

Click to expand...

First off, wire them in parallel...series is a bad idea. If you're firing them both at the same time, you need to account for the current of both, so 2.8 amps.

Do you have a link to the datasheet on these things?

Indeed I do...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290390771911#ht_1811wt_818

It's basically two of these. One's normally open, and one's normally closed. That way I can power them both and they'll switch position.

"1.4A current draw" is kind of vague. it could be much great for the short time it's actually energizing. There's typically a pull in current and a holding current (that's the terminology for relays anyways) and the pull in current is much greater... 3-10x or more.

It may be wise to check with the seller to try to get that information so there's no surprises.

Just throwing it out there: would an old computer power supply be appropriate for powering something like this?

Bjornbrewer said:

First off, wire them in parallel...series is a bad idea.

Click to expand...

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.

Fingers said:

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.

Click to expand...

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.

ChrisS68 said:

Just throwing it out there: would an old computer power supply be appropriate for powering something like this?

Click to expand...

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.

I should say that I'm a software guy by trade, and while I'd be comfortable doing this and blowing my own stuff up, standard disclaimers apply.

http://www.brewtroller.com/forum/showthread.php?t=412

Check this thread out, this power supply will work and its only $10

goose_on_fire said:

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.

Click to expand...

Great idea - I think it would work perfectly. In fact, while you are canabalizing that old PC, take the fan out, tear the HD open (need a torx set) and remove the magnets for the stir plate build. Save the case for a possible control panel build. If there is a nice big fansink on the processor, save it to cool an SSR later in your electric brewery build. Yowza, now we're recycling!

passedpawn said:

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.

Click to expand...

Ah yes, you're correct of course. Too many beers during the hockey game.

I mentioned the capacitor because battery chargers tend to have a choppy rectified waveform. You might get some buzzing, weakness in the solenoid, and an annoying 120Hz hum. Personally, I don't think you'd need the diode. That's more to protect electronic circuitry from transients and the reverse voltage from the coil. I would think a battery charger would be quite immune to a bit of a spike on the output.

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.

doug1395 said:

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.

Click to expand...

We're not overthinking this. What (almost) everyone is saying is true. the pull in current is actually only for about 5-10milliseconds, but that's enough to clear a fuse, blow out a diode, overload a FET, whatever. The point is you have to account for it and provide for it.

The cap they talk about isn't for power factor correction it's for an additional power reserve. When the load requires a large current draw for a short duration you can put a cap in parallel with it to supply the extra current without overloading the power supply. Just like how a large capacitor helps a car audio system...same concept.

As far as the doorbell transformer, that's 24VAC. He needs 12VDC.

Sorry, not trying to rip apart your post, but please don't tell us we're overthinking it and then give bad information.

pickles said:

http://www.brewtroller.com/forum/showthread.php?t=412

Check this thread out, this power supply will work and its only $10

Click to expand...

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.

Look, he needs a DC Power supply not a transformer. A transformer is a device that transforms an AC voltage to a higher or lower AC voltage. He needs a DC power supply large enough to handle 1.4 amps per device. 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 can not wire them in series. He must wire them in parralel. If only two relays are on at one time a DC power supply like the one pictured below should be used.



It can handle 6 amps and is availabable for $10

http://cgi.ebay.com/12-VOLT-DC-POWE...emQQptZLH_DefaultDomain_0?hash=item20af91cc42

Your right I'm sorry coffee had not kicked in yet

Sawdustguy said:

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.

Click to expand...

There is a momentary and a continuous current draw. Momentary and high while energizing, then continuous and low while holding.

But the power supply in the link does look like it could work. 6A may be enough for this setup, but I think the OP should still try to get the information on the solenoids.

The momentary surge is slight. We are talking DC and the coil looks like a simple resistive load to the power supply. It is not like putting a large electrolytic capacitor across the supply that looks like a short until it starts to charge up. 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.

Sawdustguy said:

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.

Click to expand...

I totally agree with this part.

It is tuff when you buy stuff from china or ebay but, Try and find out who makes the valve. Contact them. I have a servo valve on my rig and it only draws a few hundred milliamps. 1.4amps seems like a huge number. I am only using around 1.2amps to power PID, Valve, and PWM circuit. Unless the solenoid mechanism is a much greedier device I can not see it drawing that much current.

that servo valve has a motor...relatively low current draw. The solenoid is more like a relay which must overcome a spring and react quickly...higher current draw.

Ah I see. I was wondering about that.

Well then disregard my last post.......In that case I would second the idea of using an old PC power supply. You should be able to get the amperage you need and the flexibility of voltages.

Yup, I like the idea of the old PC supply. In that case, I would agree about the protective diodes and eliminate the capacitor on the output. The power supply will already have some.

All in favor, say aye.

Aye, And I already have one laying around... I checked my laptop chargers and cellphone chargers... they're not the correct voltage.