Author Topic: A complete failure to understand the task at hand  (Read 1972 times)

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Offline IanB

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A complete failure to understand the task at hand
« on: December 05, 2021, 06:02:45 am »
I just watched this video segment about how to discharge a capacitor for safety.

Can anyone spot a tiny flaw in the demonstrated method?

https://youtu.be/ozOhWeIk_Hs?t=45
"Listen to your favorite playlists and podcasts on your thermostat" -- ecobee

I'm a chemical engineer -- I know all about the flow of fluids.
 
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Offline bob91343

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Re: A complete failure to understand the task at hand
« Reply #1 on: December 05, 2021, 06:27:14 am »
First of all his manual start procedure is dangerous, as it risks his fingers getting caught in the blades as the motor starts.

Second, a direct short on the capacitor with a screwdriver is not a good idea.  Better to see, with a voltmeter, if there is a charge that needs removal.  If so, a resistor is better than a screwdriver because you might get a big spark, but frankly I have done this without a problem.

Switching it off before sticking your fingers in may not be safe enough; better to disconnect it entirely from the power line/mains.
 

Offline IanB

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Re: A complete failure to understand the task at hand
« Reply #2 on: December 05, 2021, 07:08:00 am »
There's something else, that is a bit more fundamental.
"Listen to your favorite playlists and podcasts on your thermostat" -- ecobee

I'm a chemical engineer -- I know all about the flow of fluids.
 
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Online james_s

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Re: A complete failure to understand the task at hand
« Reply #3 on: December 05, 2021, 08:06:29 am »
Switching it off before sticking your fingers in may not be safe enough; better to disconnect it entirely from the power line/mains.

The switch mounted to the side of a furnace is the service disconnect as far as code is concerned. It's very typical to just switch it off there when servicing rather than going to the service panel and shutting off the breaker there.
 

Offline JackJones

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Re: A complete failure to understand the task at hand
« Reply #4 on: December 05, 2021, 09:12:13 am »
Quote
take an insulated screwdriver

Wait a second..
 

Offline IanB

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Re: A complete failure to understand the task at hand
« Reply #5 on: December 05, 2021, 09:29:11 am »
Quote
take an insulated screwdriver

Wait a second..

 :-+
"Listen to your favorite playlists and podcasts on your thermostat" -- ecobee

I'm a chemical engineer -- I know all about the flow of fluids.
 
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Online tom66

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Re: A complete failure to understand the task at hand
« Reply #6 on: December 05, 2021, 09:48:54 am »
Is it not an AC start/run capacitor?  The charge across the start capacitor should be pretty close to zero once the centrifugal switch re-engages, which would happen reasonably quickly (and the motor wouldn't spin, and the cap wouldn't charge, if the switch was defective.)  The run capacitor (if present) should be discharged nearly immediately.  Both are effectively shorted out by the windings of the motor.

Still, using an insulated screwdriver is pretty special...
 

Offline eti

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Re: A complete failure to understand the task at hand
« Reply #7 on: December 05, 2021, 10:21:17 am »
“Furnace”? It’s a boiler. You’re boiling water not melting pewter.
 

Offline nali

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Re: A complete failure to understand the task at hand
« Reply #8 on: December 05, 2021, 10:26:05 am »
“Furnace”? It’s a boiler. You’re boiling water not melting pewter.

If yours is boiling water you need to get it looked at!
 

Offline nali

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Re: A complete failure to understand the task at hand
« Reply #9 on: December 05, 2021, 10:33:41 am »
I wonder if he's overlooking the obvious technical detail by concentrating too much on his YT script or if he's just ignorant? Either way it's a  :palm:

Mind you a couple of hundred volts on the fingers never hurt us as kids, we learned pretty quick ;D
 

Offline tooki

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Re: A complete failure to understand the task at hand
« Reply #10 on: December 05, 2021, 01:55:04 pm »
“Furnace”? It’s a boiler. You’re boiling water not melting pewter.
In USA it’s common to refer to the hot-air-maker in a forced-air HVAC system as the “furnace”. I don’t know what they’re called in the UK. Either way it’s not a boiler since it’s for forced air. (In USA, we refer to boilers for radiator systems as “boilers”. A furnace is a different device. Radiator heat is comparatively rare in USA, found mostly in old buildings, sadly.)

However, the device to create hot water we generally call a “hot water heater”, and not a boiler, at least in the residential context.


“Furnace”? It’s a boiler. You’re boiling water not melting pewter.

If yours is boiling water you need to get it looked at!
Steam heat is a thing, too. My first apartment in Maryland was heated with steam heat from a central boiler.
« Last Edit: December 05, 2021, 01:57:20 pm by tooki »
 

Offline nali

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Re: A complete failure to understand the task at hand
« Reply #11 on: December 05, 2021, 02:10:30 pm »
So, in the US you have furnaces that boil water and in the UK we have water heaters we call boilers. It's a funny old world...

I'm sure some industrial and/or municipial systems here probably use steam but in a domestic environment we normally heat water to something like 70C. Although that's changing with the move to heatpumps which is more like 40C AIUI.
 

Offline tooki

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Re: A complete failure to understand the task at hand
« Reply #12 on: December 05, 2021, 02:19:23 pm »
So, in the US you have furnaces that boil water and in the UK we have water heaters we call boilers. It's a funny old world...
No, as I said, a furnace makes hot air. A boiler makes hot water or steam for radiator heating, and a hot water heater makes hot water for the faucets, bathtub, etc. (In commercial contexts, I believe “boiler” also encompasses hot water heaters, since they’re often more complex, integrated systems with heat exchangers.)

I'm sure some industrial and/or municipial systems here probably use steam but in a domestic environment we normally heat water to something like 70C. Although that's changing with the move to heatpumps which is more like 40C AIUI.
I don’t think steam radiator heat was ever common in single family homes. But it was certainly used in large installations like apartment complexes.
 

Offline jpanhalt

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Re: A complete failure to understand the task at hand
« Reply #13 on: December 05, 2021, 02:31:23 pm »
In the US residential systems, a "furnace" heats air, which is then distributed throughout the home.  It is probably the most common residential heating and AC method.  A "boiler" is anything that heats water as the fluid. (https://www.servicechampions.net/blog/7-home-heating-system-types/ ) If one refers to it as a "hot-water heater" and calls for service, you are very likely to get the wrong person.  Boiler techs are trained specifically. A tech may do both, but a furnace tech without boiler training would/should not service a boiler system.

Boiler systems that heat water to below boiling (e.g., 180°F), which is then distributed are also called "hydronic" systems.  That distinguishes them from steam systems.  Hydronic systems are quite popular even in new homes.  They offer very constant temperature compared to forced air, but they also recover more slowly when a room gets suddenly cooler.
 

Offline tooki

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Re: A complete failure to understand the task at hand
« Reply #14 on: December 05, 2021, 02:49:44 pm »
In the US residential systems, a "furnace" heats air, which is then distributed throughout the home.  It is probably the most common residential heating and AC method.  A "boiler" is anything that heats water as the fluid. (https://www.servicechampions.net/blog/7-home-heating-system-types/ ) If one refers to it as a "hot-water heater" and calls for service, you are very likely to get the wrong person.
Again, depends on the purpose: if it’s heating water for space heating (or for space heating and hot water), it’s called a boiler. If it’s heating water only to give you got water out of the faucet, it’s typically called a “water heater”.

Hydronic systems are quite popular even in new homes.  They offer very constant temperature compared to forced air, but they also recover more slowly when a room gets suddenly cooler.
They exist, and are growing in popularity thanks to the loveliness of underfloor heating, but they are hardly “quite popular”: this source says only 5% of US heating is hydronic.
 

Offline IanB

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Re: A complete failure to understand the task at hand
« Reply #15 on: December 05, 2021, 05:35:25 pm »
Again, depends on the purpose: if it’s heating water for space heating (or for space heating and hot water), it’s called a boiler. If it’s heating water only to give you got water out of the faucet, it’s typically called a “water heater”.

It's generally the same in the UK. The most common form of central heating is with hot water to radiators, and then the boiler is used both for heating and hot water.

Other forms of central heating do exist, including forced air, in which case there would need to be a separate water heater. In this case it would be called a water heater and not a boiler.

Central air conditioning is not typically found in UK homes, so you don't have "HVAC" systems, you just have "heating" systems.

The big advantage I see with furnace hot air systems in the USA is that they are readily combined with central A/C units for cooling. Warm air circulation in winter, cool air circulation in summer.
"Listen to your favorite playlists and podcasts on your thermostat" -- ecobee

I'm a chemical engineer -- I know all about the flow of fluids.
 

Online james_s

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Re: A complete failure to understand the task at hand
« Reply #16 on: December 05, 2021, 07:13:45 pm »
Is it not an AC start/run capacitor?  The charge across the start capacitor should be pretty close to zero once the centrifugal switch re-engages, which would happen reasonably quickly (and the motor wouldn't spin, and the cap wouldn't charge, if the switch was defective.)  The run capacitor (if present) should be discharged nearly immediately.  Both are effectively shorted out by the windings of the motor.

Still, using an insulated screwdriver is pretty special...

Furnace blowers typically use PSC motors so the capacitor remains in operation whenever the motor is running, I've never seen one with a motor that had a centrifugal switch. The last couple that I've installed have BLDC motors which are much more efficient, especially at low speeds, although I do have some concerns about reliability. The industry calls them ECM motors.

It's possible that he's bridging the terminals with the (non-insulated) tip of an insulated screwdriver.
« Last Edit: December 05, 2021, 07:27:41 pm by james_s »
 

Online james_s

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Re: A complete failure to understand the task at hand
« Reply #17 on: December 05, 2021, 07:18:54 pm »
The big advantage I see with furnace hot air systems in the USA is that they are readily combined with central A/C units for cooling. Warm air circulation in winter, cool air circulation in summer.

That is exactly the main advantage, in my case I have both a gas furnace and a heat pump, a so-called "dual fuel" system where the furnace serves as the air handler for the heat pump. Another advantage of forced air is that it can rapidly warm up a cold house, you turn it on and you have nice warm air blowing out of the registers almost immediately whereas with a hydronic system it takes quite a while to get going. On the flip side, the temperature tends to be a lot less even, going above and below the setpoint as the furnace cycles on and off. The thermal mass that makes a hydronic system slow to respond also makes the temperature very consistent and even. The best of both worlds would be hydronic radiant floor heating combined with a forced air heat pump for cooling and supplementary heat.
 

Online james_s

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Re: A complete failure to understand the task at hand
« Reply #18 on: December 05, 2021, 07:23:55 pm »
Again, depends on the purpose: if it’s heating water for space heating (or for space heating and hot water), it’s called a boiler. If it’s heating water only to give you got water out of the faucet, it’s typically called a “water heater”.

It is a little more complicated than that. It is common to use a conventional tank style hot water heater for dual purpose, supplying hot water to plumbing fixtures and hydronic heating loops using a circulating pump. I've been told it's against code in the UK to use potable water in hydronic heating but it is apparently allowed here. We have boilers here too, very much like the ones that are so common in the UK and other parts of the world, my grandparents house was heated by a boiler supplying radiators but they are rare, theirs was the only house I'd ever seen in this region with such a system until maybe 10 years ago when radiant floor heating started to get popular.
 

Offline jonovid

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Re: A complete failure to understand the task at hand
« Reply #19 on: December 05, 2021, 07:43:07 pm »
in the video insulated screwdriver tip was NOT used but the insulated stem of the  screwdriver
also you can use the  screwdriver tip on the gap of the two pins before removing any wires or clips
Hobbyist with a basic knowledge of electronics
 
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Offline SiliconWizard

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Re: A complete failure to understand the task at hand
« Reply #20 on: December 05, 2021, 07:59:53 pm »
in the video insulated screwdriver tip was NOT used but the insulated stem of the  screwdriver

Yes. This is fun. ;D
« Last Edit: December 05, 2021, 08:02:35 pm by SiliconWizard »
 

Offline Cerebus

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Re: A complete failure to understand the task at hand
« Reply #21 on: December 05, 2021, 08:01:21 pm »
I've been told it's against code in the UK to use potable water in hydronic heating but it is apparently allowed here.

Not really "against code", it's just something you wouldn't do. Steel 'radiators' are the norm here and that implies that you want the circulating water to have heaps of anti-corrosion additives in, so of necessity hot water for heating purposes will be inside a closed, self contained system that is completely separate from hot water for washing and bathing purposes. What is "against code" is to return any potable water to the public supply once it has been heated (above 25ºC) and all water heaters, including ones intended to provide potable heated water, will have a non-return check value in the cold supply.

It used to be quite common to have non-potable hot water supplies to sinks, baths etc. but nowadays almost all hot water for washing and bathing is potable. The change comes about with a move from systems that heated potable water in a hot water tank with a heat exchanger fed from the heating system (thus employing boiler water with all the additives etc) to 'combination' boilers that have separate heating and hot water circuits, the latter for hot water 'on demand' only. So now hot water goes from cold potable water to hot tap water in a matter of seconds (thus remaining potable) whereas with a hot water tank water could be held for hours, possibly days, before being consumed possibly going through 'unsafe' holding temperatures for extended periods of time.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline PaulAm

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Re: A complete failure to understand the task at hand
« Reply #22 on: December 05, 2021, 10:20:37 pm »
In the US you can use the same water heater for potable and non-potable hydronic systems, you just need to use a heat exchanger so the nonpotable water is in its own loop.  They can be connected with fill valves and a backflow preventer to keep the nonpotable water separate.
 

Online sleemanj

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Re: A complete failure to understand the task at hand
« Reply #23 on: December 05, 2021, 10:40:44 pm »
In New Zealand, we just put on a coat.
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Offline SpecialK

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Re: A complete failure to understand the task at hand
« Reply #24 on: December 05, 2021, 11:46:16 pm »
in the video insulated screwdriver tip was NOT used but the insulated stem of the  screwdriver
also you can use the  screwdriver tip on the gap of the two pins before removing any wires or clips

Really?  I am have trouble telling is the shaft of the screwdriver is insulated.  It doesn't appear to be. Bad camera work and lighting, not to mention my old eyes.

I think he means to say grab the screwdiver by the (insulated) handle, which he clearly is doing.  I haven't totally wrapped my head around those oil filled motor capacitors.  They are pretty large physically and operate at line voltage.  However, as the motor spins down so too should the voltage across the capacitor IMO.  The windings would look like a DC short once all the fields collapse.  Wouldn't energy capacity be a function of capacitance?  I see these are pretty small in comparison to aluminum electrolytics.  I think 5 or 10 microfarads in my experience.
 


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