hotponyshoes
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Yea if you had a kit of parts it would be ideal as I don't have a clue what I am looking for
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Yea if you had a kit of parts it would be ideal as I don't have a clue what I am looking for
daleyd
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I’ll have a look and see what I’ve got. I definitely don’t have a ct, so you’d need to find one of those. I’m sure I have a phase angle thyristor and a controller that should be suitableYea if you had a kit of parts it would be ideal as I don't have a clue what I am looking for
Would it not be easier to have a small 2nd generator feeding just the hand washer running a 1kw element heating a tank of water.
One of the small camping generators would do and quiet in use. Once the tank is up to temp the generator would be doing very little work.
One of the small camping generators would do and quiet in use. Once the tank is up to temp the generator would be doing very little work.
hotponyshoes
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I have got a small petrol generator that would possibly do that job.
But, its petrol (and we are mostly doing open-flame bbqs so I'd rather not have petrol on site or have anyone refuelling a generator during the day.
The 20a generator is diesel and will do all day on the one tank.
Seems easier to me to carry some sort of controller box (seeing as I have to take power distribution anyway) rather than take an extra generator.
Plus I'd make the use of the 'wasted' power when I'm not using it all.
hotponyshoes
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Existing heater is only 3kw but that's the on-demand one (13a)
It would (i think?) make more sense to make up a tank with an immersion element in.
I'd guess I can use a 5kw or larger element if I can control the power it draws?
daleyd
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Yeah, whatever works I guess. You’d be limited by the size of thyristor available, you would need to size the heating element accordingly.
There’s no real point in getting a heater that can take more power than the thyristor can handle as you’d never use the extra. I have some 40a units but they are logic control (on/off) so wouldn’t be much kop for your application.
hotponyshoes
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I don't know how a thyristor works!
16a max going to the heater.would be fine.
I don't expect there would ever be more than that surplus anyway.
But, I'm confused,
If the thyristor is 16a and I tried using it with a 20a heater will it work because the heater only uses the 16a supplied or will it blow the thyristor by trying to draw too much power?
(Obviously I would fit a 16a breaker but you get the question)
Does the heater need to be rated less than the thyristor?
If yes, how does it work if I used a 13a heater but controlled the thyristor to only supply 8a? Would it still not be trying to pull 13a or is that fine because the 13a is less than the rating of the 16a thyristor?
Maybe just answered my own question?
Kram
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(SCR means thyristor and is easier to type). Its the same as a large light dimmer, works exactly the same way.
SCR's chop up the AC wave form and reduce the time that an item gets power.
It can cause harsh interference and also lowers the power factor, drawing current when the voltage is low.
Yes the SCR needs to be bigger than the load current, however you could possibly parallel up a second SCR and drive it from the modules output to increase the rating.
SCR's chop up the AC wave form and reduce the time that an item gets power.
It can cause harsh interference and also lowers the power factor, drawing current when the voltage is low.
Yes the SCR needs to be bigger than the load current, however you could possibly parallel up a second SCR and drive it from the modules output to increase the rating.
daleyd
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An SCR is a trade name for a specific type of thyristor, but the terms are broadly interchangeable. Typically to control current in both directions you might have 2 SCR back to back, or might use a TRIAC - both of which belong to the thyristor family of devices. The company I work for makes thyristors but we sell than as those, not SCR - though they may contain an SCR inside, if that makes sense.
It’s a semiconductor device, so ideally it needs to be sized larger than the load going through it, you can damage the device if you exceed the rating.
I’ve got some theory on how they work, I’ll see if I can post it up here for info.
It’s a semiconductor device, so ideally it needs to be sized larger than the load going through it, you can damage the device if you exceed the rating.
I’ve got some theory on how they work, I’ll see if I can post it up here for info.
sako243
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An SCR stands for silicon control rectifier (not a trade name, just an abbreviation). It is to all intents and purposes a switchable diode (diodes are silicon devices used for rectifying current hence the name). Diodes allow current to flow in one direction only (within the device limits). Normally you can't turn them on or off, they're just always on.
An SCR is turned on (allows current to flow) when a current is passed into the gate terminal. You only need a pulse, they remain conducting as long as the current flowing through the main anode/cathode junction remains above the holding current. I.e. The only way you can turn them off is to remove the load.
They don't work well for AC because they only allow current in one direction so will inherently rectify the current flowing through them. A TRIAC is another form of thyristor that is effectively two SCRs back to back. This allows current to flow in both directions through the main body of the device. These need a constant gate current to stay on because at some point during the AC cycle the current will drop to zero briefly (50 times a second).
To limit "power" through the device normally you have some electronics synchronised to the AC waveform with a zero crossing detector. You then turn on the device a controlled period after the zero crossing (as it won't turn off until the current flowing through it is zero). The relationship isn't quite linear as @daleyd says because the waveform is sinusoidal but it's close enough most of the time.
An SCR is turned on (allows current to flow) when a current is passed into the gate terminal. You only need a pulse, they remain conducting as long as the current flowing through the main anode/cathode junction remains above the holding current. I.e. The only way you can turn them off is to remove the load.
They don't work well for AC because they only allow current in one direction so will inherently rectify the current flowing through them. A TRIAC is another form of thyristor that is effectively two SCRs back to back. This allows current to flow in both directions through the main body of the device. These need a constant gate current to stay on because at some point during the AC cycle the current will drop to zero briefly (50 times a second).
To limit "power" through the device normally you have some electronics synchronised to the AC waveform with a zero crossing detector. You then turn on the device a controlled period after the zero crossing (as it won't turn off until the current flowing through it is zero). The relationship isn't quite linear as @daleyd says because the waveform is sinusoidal but it's close enough most of the time.
Seadog
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100 times by my reckoning.
Finally someone who knows what he's talking about...
Maybe I should have read further down, but there you go. Something about scr's is that they only work on one half wave, so immediately you halve your power, unless you drive a back to back package.
daleyd
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Care to expand on that? I've tried to keep it in simple terms rather than going into things like gate pulses as that level of details isn't needed at this point.
There's a document above which goes into more detail if needed, but the broad answer is that, yes you can restrict current with the proper components.
