I realized I still have a beginner's question.

allon wrote:If you have a multimeter, measure resistance between the blades of the plug --

Check ground pin on plug to case -- should be 0 ohms
For each of the four power switch states, measure each blade to ground - should be open circuit no matter what.

Here it is: How do I tell if it's "open circuit"?

allon wrote:If you're really ambitious, use a heat gun and thermocouple to gently raise the thermal cutoff switch to 145-150 degrees C or until it opens the circuit, should be around 135 degrees C. If it doesn't open, then replace it.

note: you'd have to be very gentle with the heatgun; I'd consider running it with a variac, and raising the temp slowly; this is only necessary if you don't trust the thermal cutoff and want assurance that it works.

I'll just have to borrow the variable control heat gun and TC from here ...

I'm gonna back away from the testing of the thermal cut-off at the moment....
You'd have to be very careful not to cook anything in the process.

As far as testing "open circuit", when you connect a multimeter measuring resistance, you get infinite ohms for open circuit, which will be displayed as "1." or "0L" on many multimeters. A resistance of 0.0 is a closed circuit. Sometimes there will be a small bit of resistance, like 0.1 or 0.2, but it's still considered a closed circuit, for these purposes....


http://www.ladyada.net/learn/multimeter/continuity.html

Thanks for clarifying, Allon. The thermal safety switch doesn't look fried, so it should be fine. I'll see what progress I can make on this, this weekend.

A few questions for ya:

1. What components do you have here? My understanding is you have a 300W heating element and a 1000W heating element. You also have a thermal cut off switch of some sort (?) - the black block with 6 terminals on it?

2. On the switches, what configuration are they (as far as poles and throws). Can you provide close up photos and information on how the the switches function?

3. What are you trying to accomplish here as far as operation of the machine is concerned? Does one switch turn power on and off? And then a subsequent switch selects the power level?

I think answering these questions will help, as far as wiring the machine up. Myself, I would ignore how it was previous wired and simply stand back and look at what you have to work with and how you want the machine to operate when you are done with the connections. This should help you draw up a schematic and then decide how you can wire everything together.

Ray

Hi Ray, and thanks for posting. Here's a close-up look at this stuff.

RayJohns wrote: 1. What components do you have here? My understanding is you have a 300W heating element and a 1000W heating element. You also have a thermal cut off switch of some sort (?) - the black block with 6 terminals on it?

I think the black item with six terminals only connects wires straight through and has no switching function. I think of it as a junction unit.





The thermal cutoff switch looks like this. It has a steel surface that sits on the bottom of the boiler. It appears to have some rust on it from the collar that holds it to the plate, which fits loosely around it, like a washer. As mentioned above, it is stamped with Elmwood 8 between the terminals. Black letters on the side read 2455RC98-969 L135C 99/40.

RayJohns wrote:2. On the switches, what configuration are they (as far as poles and throws). Can you provide close up photos and information on how the the switches function?

Tell you how they function? Both are toggle switches, either on or off. Both are in the off position per scratched information on the front. They are identical switches with the brand name Carling. But here's vital info. Each is engraved with the following information:

12A 250 VAC
20A 125 VAC
1 HP 120 240 VAC

This is probably too much information, but I want you to have a good look. The first four photos are of the switch marked for the 300 W heating element.









The next three photos, also probably too much information, are of the switch to the 1000 watt heating element:

RayJohns wrote:3. What are you trying to accomplish here as far as operation of the machine is concerned? Does one switch turn power on and off? And then a subsequent switch selects the power level?

I think answering these questions will help, as far as wiring the machine up. Myself, I would ignore how it was previous wired and simply stand back and look at what you have to work with and how you want the machine to operate when you are done with the connections. This should help you draw up a schematic and then decide how you can wire everything together.

Ray

As discussed above with Allon, I think for safety reasons I should wire it as it was as this may help prevent overheating, and I'm not going to PID this old war horse! That would mean wiring according to his second diagram.

drgary wrote:Hi Ray, and thanks for posting. Here's a close-up look at this stuff.

As discussed above with Allon, I think for safety reasons I should wire it as it was as this may help prevent overheating, and I'm not going to PID this old war horse! That would mean wiring according to his second diagram.

No, the second diagram won't work because the 300W switch is *NOT* a SPDT switch like I thought.
With the close up look, I can see that the first diagram is accurate; the wire goes to a terminal on the 300W switch, and from there, from the SAME terminal, to the 1000W switch.

There are three wires on the switch, but only two contacts.

So the first diagram is correct.

Got it, Allon. Thanks for checking those details for me. I really appreciate it.

How to Think Like an Electrician

This rebuild is teaching me that I need to start thinking like an electrician and not just blindly follow the directions of other HB members. It's a great learning opportunity. And again, I'm learning this all at my own risk. Anyone reading this applies these concepts at their own risk, and minors should only work with these concepts under the supervision of a qualified adult. I am not an electrician.

Here's how I understand basic electrical concepts so I can apply them to the circuitry in this simple machine. For those who have been guiding me online, this is to communicate what I do and don't understand. Key terms are in italic type.

Basic Concepts

An electric circuit is a closed pathway through a conductor (a material through which electrons move easily, with little resistance* or impedance*) where a current of electrons flowing from a power source enters with a measurable amount of force (volts or V) that has the potential to do work. The wire bringing electrons into the circuit is called the hot lead. Electric current powers components that convert their potential energy into a desirable form like heat, light, or motion. The amount of energy used by components (measured in watts or W) is called a load (resistance, measured in ohms). The remaining electrons exit the system through what is called the neutral lead, returning to the power source. For safety purposes, an alternate pathway (ground) is provided for electrons to dissipate into the earth itself or where so designed, into the chassis of the device. Hot and neutral leads are typically covered with insulation (material that does not easily conduct current) made to withstand heat and moisture to keep current within the circuit. Conductors and components must have sufficient carrying capacity (measured in amperes or amps), or the wires can overheat and melt, so the device breaks or injury can occur through shock or fire. If current leaks out of its intended pathway, it seeks a path of least resistance (short circuit) back to the source. That pathway isn't designed to carry the current and can overheat, melt, or present a lethal shock hazard if the current passes through you!

* Resistance is the term for direct current (DC), and impedance is the equivalent for alternating current (AC)

When rewiring an espresso machine, it's crucial to understand which wires are hot, neutral and ground. For the following, see the first post in this thread, which has links to online references. Sometimes the machine has its wires color coded according to standards. It's also helpful to draw a circuit diagram as a guide for rewiring. Before powering up the device, one can use a multimeter, which tests and measures circuit components using a small amount of current. Its calculations can be understood by referencing Ohm's Law.

My next post will show the practicalities of how I propose to wire the machine and pre-test it.

Here's my attempt to wire the machine as Allon suggested it in his first diagram, which makes sense. I'm showing it as a wiring diagram and with the connections physically made. I'm using the wiring harness provided by Orphan Espresso, which looks serviceable. I'm also keeping the junction box as this allows me to swap out the power cord without messing with the rest of the wiring.

In the wiring diagram, brown is hot, blue is neutral, yellow/green is ground.



Here's the photo:



Next I'll need to test these connections with a multimeter.

Off topic but relevant, now I can fully service my Microcimbali per Doug's rebuild instructions on OE. See: http://www.orphanespresso.com/La-Cimbal ... 551-1.html

Now THAT'S a clamp! Just scored this vintage Jorgensen clamp off eBay. The Microcimbali and Prestina spring assemblies both easily fit inside its 14 inch jaws. Considering the Prestina's a full-sized commercial group, the Microcimbali spring and lever look pretty hefty.