I have a low end espresso coffee machine and I want to autofill the water resevoir with RO. I have a 120VAC solenoid with the fittings needed to fill the tank. Ideally, the solenoid would open under two conditions, 1) the coffee maker is turned on, and 2) the float switch indicates level is low.

I would like to use a 12VDC relay (or similar) to control the solenoid. I was thinking that I could put it inline with the float switch and the switch that turned on the coffee machine, converting it to 12VDC. I would like to supply 12VDC converted within the machine, if possible. It would need very low amerage for the relay so I believe I could get away with the smallest transformer. What circuitry would I need to build to accomplish this?

If there happened to be a 12VDC supply in the machine, that would make it simpler, but I would still like to know the circuit needed to build the 120VAC to 12VDC.

Thanks

 

OK, so you turn the machine on, it senses low water, fills itself, makes coffee, senses low water, fill itself while still making coffee, keeps making coffee, senses low water, fill itself while still making coffee, spills out of the pot, spills over the floor, your wife leaves you and your landlord tosses you out.

Running a controller off 12V makes sense. You need a power supply for that, it goes in parallel with the coffee maker and it's power witch so the same switch turns them both on.

DO try to rethink your control logic to keep your happy home happy.

 

I'll throw out a different idea.
Another way to handle this is with a float valve (you can find really small ones at your local hydroponic store).
If your primary chamber is large enough the float valve can be placed directly in it.
If your primary chamber is too small, you can use a secondary chamber, put the float in it, and connect the two chambers with a small rubber tube (at the bottom of each).

The secondary chamber can be placed in a position so that the float valve is at the same level you want the water in the primary chamber to be.

I've done a lot of this stuff myself in the greenhouse, and it works just fine.

I'd like to make a sensor and have containers auto-fill, but I think good-ol' physics without electronic sensors works just fine.

 

This should address both ErnieM's and SPQR's posts. Thank you, btw.

I will be using a float valve going into the chamber. The problem with those it that they are not very reliable. And if it fails, I don't want water everywhere, as Ernie states. I've done something similar with my aquarium, but not integrated into another unit. Basically, I have a float valve that a solenoid controls the water to. That solenoid is on a timer that turns it on for 1 minute every 3 hours to add makeup water from evaporation. The solenoid protects me from failure of the float valve so I don't have water overflowing for hours before it is stopped.

A timer doesn't really work out for what I need in this case, but with this method I would have a backup float switch to the float valve and this also doesn't need to allow water flow unless the coffee machine is turned on, so people would be present. I've attached a diagram. I just need to get 12VDC to the relay, preferably from power supplied to the machine. I believe the relay needs ~ 30mA.

How would one build a circuit for that?

Thanks

 

Hmmm...I was thinking that some of the internals would run on <120V, but if you look HERE, it looks like most of the pumps and valves are 120V operated.

What kind of espresso machine do you have?

 

Saeco Vienna Plus

 

Ok, so HERE is the parts manual.

The pumps and motors seem to be high voltage.
But I note that there is an electric board, and sensors, which most likely are lower voltage.

HERE's the wiring diagram. It's in Italian, but decipherable.
Given the sensors, and electrical board, I'd guess there's some low voltage there somewhere...maybe just grap a meter and find out.

 

I came across that schematic in my search as well. I don't know that there is any low voltage in the machine, but I'll check it when I open it just to be sure. Assuming there is not, here is the circuit I came up with to supply the DC voltage needed.

I think the only thing critical is that I maintain >9V for the relay to turn on. Based on this, I calculated 15K uF for the smoothing capacitor to give a max voltage drop of .5 volts. That gives me 2 volts above the minimum I need, but I don't have enough understanding of circuits at this point to know if this is adequate.

Is this appropriate?
Would a voltage regulator be needed?
Would it be better to put out 14V or 16V from the transformer and use a a 12V regulator?

Thanks

 

How about just using a 12V wall wart, and you don't have to make the extra circuitry.

 

Or perhaps something simpler:

1. Coffee on/off controls wall wart.
2. If wall wart ON and float valve closed, water valve opens
3. If wall wart OFF or float valve open, water valve closes

 

That would certainly work and it's something I would consider. My preference is to try my hand at building the circuit first to help me learn how to do it. It's mainly for my edification. If this turns out to be an abismal failure, I'll probably fall back to the wall wart.

I'd really like to get some feedback on the circuit I'm trying to build to convert AC to DC.

Thanks

 

I still think you need some sort of 'start' button that starts the fill, but prevents filling once the brewing process commences.

 

Filling of the water reservoir is completely independent from the brew process. As it is now, the reservoir has a cover that is removed for manual filling. It can be filled while the machine is running. It grinds the beans and dispenses a single cup with the amount of water selected by a dial.

With this setup, it would refill the reservoir as it makes the coffee when it pumps water from the reservoir. When the machine is off, the solenoid would be closed. When the machine is on, the solenoid would only be open when the level is below the float switch.

But I still would like help with the circuit if anyone is able to provide feedback on that. Or have I posted in the wrong section?

Thanks

 

Let's see what we have:
Here is an analog of your circuit, with calculations for each stage of the power supply.

The capacitor value = (Amps * delta time) / Ripple
= (1 * 0.0083ms) / 1.4 = 5,950 uF

I'm not sure of the resistor

Let's get some expert input here.

 

Thanks SPQR. This looks pretty good, but I have some questions.

I'm assuming you have a specific transformer in mind that yields 15.34 Volts. What transformer is that? How much current is it passing?

I found several small transformers that will give 12.6V in series. A couple at 90mA and one at 200mA. Bumping up to 14V parallel puts me at 170mA. I could also do 16V series at 70mA. Each of these around $5 on DigiKey (a pretty good deal). (They also have a dual 5V +-12V transformer that would be a great addition for bread boarding.)
​

I'm also guessing it doesn't matter where the resistor is in the circuit since my purpose was to limit the current to the coil on the relay. Is this correct?

I had the resistor sized in my diagram to remove 60 mA of current (I think). I'm also thinking of adding a 12V switch with an LED. That will drop voltage and reduce current further, so I'll need to recalculate for the resistor. I'll measure the resistance and current draw on the switch when it arrives. The switch is to provide an easy mechanism for turning off the water makeup portion in the event of a problem, while still allowing the unit to operate.
​

Concerning the 7812, it would provide consistent 12V. Is maintaining 12V critical? If I'm running at 10.5V or 11V would there be any adverse effect on the circuit from an operational or longevity perspective? Essentially, could I rely on the transformer's ability to maintain voltage? Should I, or would it be necessary to increase the voltage output from the transformer and add the 7812?

Thanks

 

I think I would work the problem backwards.

How much voltage and current do you need to turn on the solenoid? 12V @ XmA.
You can do that right now. Just connect your solenoid to a 12V power supply and measure the current when the solenoid is "ON"

I don't think you need to limit the current, because the solenoid would only draw what it needed to work, and no more.

You would need to "limit the current" to an LED so it doesn't blow - so an appropriately sized resistor is important.

In terms of maintaining the 12V - play with your solenoid, and see how it works.
If it works fine at 11V, then you're OK. I doubt that "wires" and a "piece of metal" (the solenoid) would be negatively impacted by slilghtly low voltage.

I looked in a couple of books, and at a variety of websites for the calculations at each stage of the power supply. So if that is the type of supply you will build, then you're going to need about 15V. To be honest you probably won't need much current, but as I said above, you can measure that today.

I just went to Jameco and found THIS transformer
Primary 110V
Secondary 18 V at 2 amps

You can probably find something cheaper at a local surplus store.

So think backwards. Figure out how your solenoid works, then go from there.

 

The relay draws about 30mA when I measured it at 12V. I'll check its operation at lower voltages.

That transformer seems big for what I need. I was thinking of this one as a 16V option at 70 mA, or if I can stick with 12.6V this one. They both put out low current (I need very little) and are pretty inexpensive. I'll check the local surplus store and see what they have too.

The LED in this swtich draws 20mA with vf=2.2V. What would be the best configuration to put the LED into the circuit and what size resistor would it need to still allow the current and voltage necessary at the relay? I calculated 490 ohms.

I was able to get inside the machine and check voltages. There is a 9V 2VA transformer that appears to be connected in series, so it's putting out 18V. Based on my calculation it is producing 111 mA of current (2W/9V/2=0.111). I found connectors coming off the PCB that are 5V supplied from a 7805 VR, but I don't know what it is powering. If I went that route, the relay I'd need is 80 mA. that only leaves 31 mA for everything else if I cut out the LED. This is probably too much strain on the system. My guess is I'd be better off making my own 12V power source. Let me know your thoughts on that.

I'm including some options on the circuit. I'm thinking the 3rd might be the best choice. Option 1 drops the voltage at the relay to 8.8 volts, but that might still work too.

Thanks

 

Now you're narrowing things down quite nicely.

You know your relay draws very little current at 12V.
Your LED draw even less, so you could get away with an reasonable transformer, let's say 14-20V on the secondary, with 150 mA - "extra".
You pick.

Your local surplus, I bet, has myriad possibilities.

If you choose 12V as your supply, and your LED should not get more than 20mA, the R=E/I,
R = 12/0.020 = 600 ohms
You can also play with the value of that resistor a little. If you already have some 470 ohm resistors, then try those.
I've played with a few LEDs and was able to crank up the current a little and make them brighter.

The 7812 can handle up to 35V on the input, so you have some flexibility.

If I had to bet, your relay would work fine with quite a lot of ripple, but the size of the capacitor would change little, so it's reasonable to add it.

So now put it together on a breadboard, and see how it goes!

PS - What software are you using to draw your schematics? They look nice.

 

Thanks for the feedback. I'll see what I can do with 12.6V straight out of the transformer first and go from there. I'll let you know how it goes.

I'm thinking I should also include a 1A fuse on the AC side of the circuit to make sure my project doesn't cause irreparable damage to the machine or the new major components.

I'm using MS Visio to build the schematics, 2 different versions. I'm on Visio 2000 at home and it doesn't show a jump on the traces when they cross other pathways like newer versions. I think the other version I used was 2007 for the earlier designs in this thread. 2007 has a few more features that are nice. I also created some custom stencils like the 7812, relay, transformer, and added symbols to the bridge rectifier they had.

Cheers

 

...to make sure my project doesn't cause irreparable damage to the machine or the new major components.

This line got me thinking, and I'll free-associate for a while (I'm in California, I'm allowed). I don't propose this to you, but I present it as an intellectual exercise.

Is it possible to set up a system that has little or no contact with the espresso maker?

What do you need?
1 - you need to know when the machine is ON.
2 - you need to know the water level

How could you tell if the machine is ON?
1 - have something connected to the on/off switch/ use the on/off switch
2 - have a light sensor attached to one of the lights that come on
3 - have a current sensor on the plug that knows when current is flowing and when it is not.

I'd vote for number 3.
There are ferrite current sensors like THIS, and there are IC current sensors like THIS.

Then you need to know the water level.
1 - connect to the float/sensor already inside
2 - make your own mini float/switch that is off/on at a particular level

In that way you could have a box that plugs into your wall socket. The espresso machine plugs into it, the water sensor put in the reservoir along with the tube.

I may try one of those for my espresso maker!