Help with 12v DC Power

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blackheart

blackheart

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We have a brew system we are attempting to automate via 12v DC solenoid valves.

s29.jpg


These are connected to a PC Power supply thats 400w. Each of the 10 valves pulls 1 Amp, and if you do the math, the PC power supply can theoretically support all of them on at the same time.

We custom wired the PSU into our system to get the 12v out of it and it measures and test as working fine. It cannot however, power any of the valves. An older and much smaller PSU has no problem powering any of the valves, and does so with a solid *thunk*

After talking to an EE friend of ours he suggested that the PSU is both nice and new and has current limiting protection. Since the valves are demanding ~1A all of a sudden it trips the protection and we have to unplug the PSU and wait for it to reset, hence strange results in metering with a multimeter.

So here is where we need help from others here who might have experience with 12v power supplies, how can we best get a 10A PSU in our current system or modify the existing PSU so that it works with the current setup?

s24.jpg
 
Look for the largest electrolytic capacitor you can stuff in there to take the current hit when a solenoid is switched on. The instantaneous current for the solenoids might be more like 3-5 amps until internal slug is in position, then it drops to 1 amp to hold.
 
I guarantee your valves draw more than 1A when energized. Like kladue said, it's probably 1 amp holding, but more like 6-10A pull in current. I agree the cap would help, but the current limiting circuit might still kick in when trying to recharge the cap.

the dedicated power supply you linked should do the trick...just don't energize more than one valve at a time.
 
I have been searching else where and I might be able to use the 12/24v AC transformer already in use in the system to create a powerful and dirty DC 12v supply that the solenoid valves will like.

12vdcpsu.png


Basically I only need to buy a $4 bridge rectifier and $5 caps. Waiting for confirmation on this as it means I can ditch the computer PSU all together.
 
Judging from the size of the transformer in your picture, you're going to need a bigger transformer. A 10amps@12vdc transformer is BIG. You should probably take a look at how much switch current will be pulled from your transformer. Your filter caps will take most of the switch current but you will need some headroom on your transformer so that you don't let the smoke out....
 
Running 10x lines of 120v ac didnt seem like a good idea and seemed like over kill. I figured it would be easier and safer to go with 12v DC. The coils come off so I guess we could replace them with 120v ac... Also, triggering 120v ac means 10x more SSR's which are about $20 each.... found some on ebay for $8... still... extra $80 vs $5 for a bag of transistors that can do 12v
 
blackheart said:
Running 10x lines of 120v ac didnt seem like a good idea and seemed like over kill. I figured it would be easier and safer to go with 12v DC. The coils come off so I guess we could replace them with 120v ac... Also, triggering 120v ac means 10x more SSR's which are about $20 each.... found some on ebay for $8... still... extra $80 vs $5 for a bag of transistors that can do 12v
Click to expand...


Do you really need SSR's? I bought a tube of 25A 250VAC mechanical relays for pretty cheap off digikey... (like 1$ a piece or so).
 
Vaevictus said:
Do you really need SSR's? I bought a tube of 25A 250VAC mechanical relays for pretty cheap off digikey... (like 1$ a piece or so).
Click to expand...

+1 It's really expensive to use SSR's to switch solenoid valves when relays would work as well for much less money. IMHO it would have been much easier to have purchased 120 volt solenoid valves and bought a relay board like the one pictured below:

493b015f11ad9_87933n.jpg


http://www.ecrater.com/p/3528455/fp08-8-relay-board-kit-for-pic

They are $18.99 and contain (8) 10 amp relays with drivers. They switch with 12 volts. The whole board would draw less than 2.5 amps. I use two of these boards in my control panel.

Electronics_Plate_2.jpg
 
^correct! you don't need SSR's for a solenoid. Small relays are good enough and are probably cheaper and more reliable than the transistor/heatsink combo you need to handle 1A.

the 120Vac setup is the same number of wires, but requires no power supply. Saftey isn't an issue if everything is wired correctly and protected properly.

hope everything works out. good luck :mug:
 
Is the computer power supply a multi output model?, if it is like the multi output Sola power supplies I use, about 80% of the output is in the lowest voltage with the remaining 20% spread among the other voltages. If so then the results you have are to be expected and an external power supply will be needed. As to the use of 120V solenoids in the brewing system, the 12 -24V models will be less likely to be causing GFI trips when there is a spill and some of the wiring connections get wet. The 24V models would be easier to power as current demand would be lower than the 12V models and a 24V/10 Amp power supply is fairly easy to find.
 
How clean of a suply do you need... We are talking about solenoids here, right?

I'm for pulling off the existing 12/24 VAC xformer. Use a CRCRC filter, burn a few volts with filtering and pull your ~12vdc. I doubt the solenoids will mind a little ripple anyway....

bk
 
For $40 on ebay you can get a 12vdc 30AMP PS which will handle plenty of therse, controller and anything else. I sitll like DC over AC any day since this is a hobby and there is too much metal and liquid to start with. My opinion though.
 
Sawdustguy, I saw your web site, I like your setup. This is our first attempt at an all grain brewery, basically the beta version, we are trying not to screw our selves by going with all stainless and 1/2" everywhere, weldless fittings so we can reconfigure the system if needed. In a future version we may go with all 120v for simplicity. but right now we are going to have to stick with what we do have, and thats 10x 12vdc valves.

If one of the 12v dedicated PSU's from ebay can do the job we will go with that. As it stands, I am hearing the 40VA transformer we have is not 40VA != 40A, so I doubt it can handle more than 2-3 valves at the same time. So it looks like building our own PSU is not the best idea.

The only thing I am worried about with buying the the dedicated PSU is, A) It will have the same modern protection to make it not work like the current one (though an older PSU we have does work so I know it is possible) B) The new PSU will be two large to fit in the current project box we have.

Sawdustguy, That looks like a nice sized PSU you are using? What are the specs on that?
 
After some expermenting I think I have solved my problem. I tried a few different power supplies and tried connecting them directly to the valves. I found that the PSU worked but not when connected to my transistor circuit. I replaced one of the 500ohm resistors on the base of the transistor with a 100ohm and then it worked great. So I replaced all of them. Then they all worked.

I also found out they all over heat quickly when left on for more than 20 seconds. Like over heat enough to melt their own solder and start sinking into the PCB melt....

So I am hearing that transistors might be the wrong choice for this type of thing. I might just have to go with mini relays like these.
http://www.sparkfun.com/commerce/product_info.php?products_id=100

and etch a new board to use 10x of those instead. at $1.76 each that wont be so bad.
 
blackheart said:
Sawdustguy, I saw your web site, I like your setup. This is our first attempt at an all grain brewery, basically the beta version, we are trying not to screw our selves by going with all stainless and 1/2" everywhere, weldless fittings so we can reconfigure the system if needed. In a future version we may go with all 120v for simplicity. but right now we are going to have to stick with what we do have, and thats 10x 12vdc valves.

If one of the 12v dedicated PSU's from ebay can do the job we will go with that. As it stands, I am hearing the 40VA transformer we have is not 40VA != 40A, so I doubt it can handle more than 2-3 valves at the same time. So it looks like building our own PSU is not the best idea.

The only thing I am worried about with buying the the dedicated PSU is, A) It will have the same modern protection to make it not work like the current one (though an older PSU we have does work so I know it is possible) B) The new PSU will be two large to fit in the current project box we have.

Sawdustguy, That looks like a nice sized PSU you are using? What are the specs on that?
Click to expand...

It's 12 volts @ 6 amps. It's overkill for what I need but it fits nicely. If you send me your schematic I will help you with your transistor circuit. I am an EE.
 

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