Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed) - Page 50

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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drgary
Team HB

#491: Post by drgary »

Here's my proposed circuit diagram. Comments are invited (not on the artwork, please, but on the concept).

Image
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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orphanespresso

#492: Post by orphanespresso »

In general you circuit should run:
I am assuming your power switch (very spiffy by the way) is a single pole single throw....a DPDT would be better but single will work, although the switch will be in a sense ON at all times on alternating current with a SPST....anyway...
black (hot) to power switch....to pstat...to element...the element is the load in the system so the second terminal of the element begins the neutral side of the circuit. A thermal safety fuse, pilot light, and anything else you are going to wire in goes on the neutral side of the circuit, the only things you want between the main breaker switch and the load are the contol functions, in this case the pstat.

Diagnose your plug/power wire by looking at the plug and your wall socket...the neutral wire corresponds to the bigger slot on your receptacle so then use the meter to see which wire of the power cord corresponds to which slot on the outlet.

15 ohms reading indicates a wattage of less than 1000 assuming 120 vac...does this seem in the ballpark?

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yakster
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#493: Post by yakster »

Agree, in the US, you always switch the hot, not the neutral so the hot should run through the P-stat.
-Chris

LMWDP # 272

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drgary
Team HB

#494: Post by drgary »

orphanespresso wrote:15 ohms reading indicates a wattage of less than 1000 assuming 120 vac...does this seem in the ballpark?
The element is supposed to be 1000W.

Thank you, Doug and Chris. Looks like this is ready to be wired up! I'll redraw the circuit diagram and may be able to complete this phase tomorrow. :D

Oh ... and Doug ... I got that SPST switch as you suggested. Does it make any difference in how this will function? Should I source a different switch?
orphanespresso wrote:As far as the electrical, there is nothing special here as far as wires or strain relief although I have the feeling that the frame hole would be better used for a switch and just enter the wire under the machine and cable tie it down....13mm sounds a lot like a toggle switch hole size (the La Cara Prestina I have has one hole in the frame which contains a switch). Just a single pole single throw toggle rated for 15 amps, 20 better, but calculate your amp load see what you need.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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RayJohns

#495: Post by RayJohns »

Hi Gary,

What Doug is suggesting on the SPST vs. DPDT switches is that (with a single pole switch) half the "switch" is still technically considered hot, because it's connected to the wall. In some circuits, that could be an issue. However, in your application here it's not anything to lose any sleep over I don't think.

As long as you are breaking the incoming power from the rest of the circuit (which the SPST switch does just fine), then you are okay.

With regard to your wiring, I think it would be better to have the P-stat kill the hot side of the power to the boiler, not the return side. Having it wired as you currently show leaves the boiler connected to the hot side of the circuit constantly. That's a little too much like sticking the hot lead from your wall socket into a bath tub full of water; it could create several potential problems, as well as a potential shock hazard.

It would be better (and safer) to have the heating element of the boiler placed at the end of the line, with just a simple (and direct) return path to common (i.e. the white wire in your wall socket or power cord). The black wire is hot, the green is ground.

Here's a schematic I drew for you, showing how I would wire everything up:

Image

You might also give some thought to wiring in a power light (if you don't have one already or don't feel like using a switch with a built in light). If it were me, I would also wire up a "boiler on" light I think - this would be a lamp or LED which would only be on when power is actually applied to the boiler. This would give you a nice visual indication of when the heating element is on vs. off due to the P-stat (or PID) controlling power to the circuit.

Ray

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RayJohns

#496: Post by RayJohns »

orphanespresso wrote:A thermal safety fuse, pilot light, and anything else you are going to wire in goes on the neutral side of the circuit, the only things you want between the main breaker switch and the load are the contol functions, in this case the pstat.
The thermal safety fuse (which is also a control function in the circuit) should be on the hot side, not the common side. If it's on the return [common] path - and blows - you could inadvertently setup several potential problems.

First there could be a shocking hazard created in the boiler, due to the conductivity and capacitance of the water (a lot like throwing your toaster into the sink). Second, if there was any sort of small compromise in the insulation of the heating element in the boiler - and a sudden disconnection (due to the thermal fuse going out) occurred - this could result in that now becoming the easiest path back to ground. If that resulted, it could allow power back through the chassis ground (resulting in a short or tripping your GFCI breaker). Even without a short, the heating element is always in direct contact with the water - so that's a concern.

The thermal fuse's job is to terminate power arriving at the load (in this case the boiler/heating element), just like the power switch's job is to terminate power; its job is not to remove the return path for the electrons in your circuit, which is what would be occurring should it be placed down stream of the load [on the common side of the circuit].

The pilot light (i.e. a light indicating when the heating element is in operation) would be wired in parallel along with the boiler.

Ray

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drgary
Team HB

#497: Post by drgary »

orphanespresso wrote:... black (hot) to power switch....to pstat...to element...the element is the load in the system so the second terminal of the element begins the neutral side of the circuit. A thermal safety fuse, pilot light, and anything else you are going to wire in goes on the neutral side of the circuit, the only things you want between the main breaker switch and the load are the contol functions, in this case the pstat.
Guys:

The first part of Doug's instruction agrees with Chris and Ray, which is to connect the incoming hot lead to the power switch to the PSTAT.

Ray's diagram shows the safety fuse also between the PSTAT and the heating element. Since Doug and Chris are suggesting that switches are on the hot side of the circuit, the thermofuse is also a switch, albeit one that would open only once. That logic and Ray's explanation about stopping power to the boiler upstream make the most sense and lead me to put it on the hot side too. Does anyone still disagree?

Otherwise am not sure where to wire pilot lights, a green one for Power On and a red one for Boiler On. Reading through this I am guessing the Power On light would be between the On/Off switch and the PSTAT and the Boiler On light would be on the neutral side of the circuit so if there's a malfunctioning PSTAT or heating element it would not light. There are two screw holes in the front of the frame where a missing nameplate would otherwise fasten in. Can you suggest specs for such lights? Is my reasoning correct for wiring them?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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yakster
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#498: Post by yakster »

Since the power, p-stat, and safety are in series, current would flow only when all three are closed so a power on indicator in series would not work (and in series would drop the current).

Normally you connect power indication between hot and neutral after the power switch, but needs to be current limited. Not sure if you have neon bulbs or LEDs. A boiler on light would likewise connect between neutral to the hot after the p-stat (and probably the safety as well, as close to the boiler as possible).

Maybe someone can verify neons or LEDs that can be wired that include current limiters in the circuit, they probably come wired in the bulb kit.
-Chris

LMWDP # 272

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RayJohns

#499: Post by RayJohns »

drgary wrote:Otherwise am not sure where to wire pilot lights, a green one for Power On and a red one for Boiler On. Reading through this I am guessing the Power On light would be between the On/Off switch and the PSTAT and the Boiler On light would be on the neutral side of the circuit so if there's a malfunctioning PSTAT or heating element it would not light.
Let me draw it up. I was going to do it originally, but I didn't want to confuse things if your intent wasn't to have indicator lights.

Ray

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RayJohns

#500: Post by RayJohns »

Here you go:

Image

When you turn power on, the power indicator lamp will illuminate.

When the P-stat allows current to the boiler element, the heating element lamp will illuminate. When the P-stat cuts the power, the element lamp will go out.

The lamps need to be 120 VAC lamps, not LED's. Since you are dealing with A/C power, you couldn't really use LED's unless you found some that were internally rectified or something - lamps would be more straight forward and would tend to go better with the vintage look of the machine.

Ray