Why? you are the number 2 trade anyway as a pipe bender
How do I go about this?
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Don't know really. I don’t have a lot of free time to study, I easily lose concentration and would be better suited in a classroom environment. I get these pipe dreams now and again (not just because I’m a gas engineer
).
Yup I think we are pretty much in agreement (or not actually poles apart on that one John) the way I`d put it is :- Bonding, basically is usually a good idea, however there are quite a few instances where it can actually make a "relatively safe" situation less safe than it would be without bonding and this condition should always be considered prior to making a final decision
The one main example I am thinking of is someone touching say an appliance that has become Live (Line or Phase) for one or two reasons and everything else within hand reach is "floating" (electrically), bonding or effectively earthing things within reach certainly increases chances of electric shock and therefore electrocution if not an unintended knee jerk sort of reaction which in itself cause harm. I suppose the flip side is that having that faulty appliance at a potential opposite to the faulty appliance potential could also be said to give us more of a chance of becoming aware of it (if we survive).
It seems to be that cases of things being live for quite some time until some chance happening causes us to become touching something earthed or earth like at some time and we might then decide to investigate or report it (or not).
Again it`s the balance of proballities question and interpreting the so called best answer.
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Seems to me you already have a pretty good understanding on a practical level. Have seen you helping people on a lot of threads with thermostat and programmers, you'd be surprised how many electricians struggle with basic control systems.
Most of the rest domestic wise is just knowing what is and isn't acceptable, and in doubt finding out with the book. Frequency, capacitance, inductance etc for the most part is only important to the engineers well above my pay grade
Three phase domestic appliances? That surprises me
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I suppose it may be more than three-phase, maybe should call it polyphase? But most inverter drive motors are three-phase today, allows better control.
He's not talking about a 3-phase supply. Rather, he's talking about motors which, internally or externally, convert the supply (single-phase AC or even DC) into 3 (or more) phases, in order to enable them to be 'brushless' motors (and, probably, to be 'more controllable'). Even the mini-fans in PCs etc. do that (usually with a 12V DC supply).
OK, with you. I can see that for a washing machine, which uses a wide range of motor speeds, and maybe a drier, but fridge/freezer? If it's not single speed, start/stop on thermostat I'd think it must be a recent development.
I don't know for sure, but I don't think it's anything remotely 'recent' - the fact that a polyphase drive of a motor enables it to be 'brushless' is one of the big advantages. As I said, I think that for as long as I can remember ('decades') little things like the "12V DC" fans in PCs have used this approach.
I believe fridge motors are 1-phase, capacitor start, (so brushless) but I haven't examined one for many years.
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The three-phase motor in domestic fridge/freezers and freezers allow a slower start so less inrush, and less start noise, and using an energy meter you can see when the auto defrost runs as the peak is normally around 70 watt with around 140 watt on defrost cycle.
However, the commercial freezers don't turn on/off but vary motor speed to keep at required temperature.
However, the commercial freezers don't turn on/off but vary motor speed to keep at required temperature.
I can believe that is true of some. Making brushless AC-fed motors is pretty simple, but that is nothing like as simple with DC-few ones. When fridges/freezers etc. have inverter-driven motors, I think it for reasons (e.g. related to inrush currents at start-up_) other than 'brushlessness'!
I don't know a lot about motors, so I'm largely passing on what I've been told, but I'm sure there are people here who know much more.
In terms of the DC-fed computer fan motors I mentioned, I think (but may be wrong!) that there are two main ways in which 'brushlessness' is achieved. I believe that, as I've said, one approach is to use an inverter to create a (usually polyphase) AC feed for the motor, whilst I think that another (perhaps more common) approach is to have multiple stator coils with 'electronivc' switching between them (using Hall-effect sensors) to create a rotating magnetic field. In either case I think that PWM (rather than just voltage variation) can, and often is, use for speed control.
However, as above, this is a field that I don't know much about, so I look forward to 'being put right' by those who are 'in the know'!!
I remember relativley recently (relative by my standards but ancient by some of you - maybe 1990 or a bit later), I odered what was then a speed controller for some industrial single phase fans and at that time it was quite expensive considered to the cost of said fans.
Blimey I exclaimed, it was heavy, I was surprised.
I opened it up to take a peek and exclaimed (sarcastically) "Wow it`s bristling with technology" , indeed my peers and my wholesalers were equally surprised too - no electronics at all save a smoothing cap or three but a large rotary autotransformer wound on a toroidal iron core, all house in a metal case of course and big plastic knob on the outside.
Blimey I exclaimed, it was heavy, I was surprised.
I opened it up to take a peek and exclaimed (sarcastically) "Wow it`s bristling with technology" , indeed my peers and my wholesalers were equally surprised too - no electronics at all save a smoothing cap or three but a large rotary autotransformer wound on a toroidal iron core, all house in a metal case of course and big plastic knob on the outside.
This was discussed at some length here Fridge motor
Looking at it again, I'm not clear where 3-phase, or more, at the motor or supply, in ericmark's #22, comes into the discussion, but no doubt you will enlighten me!
If numbers are imaginary, do they exist?
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