Slightly OT:Electronic circuit

Can anyone suggest an electronic circuit which can take 2 400W loads, and switch instantaneously between them, so that to a connected monitor, the draw appears consistent (i.e. no spikes or troughs) ?
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On 13/06/2012 12:27 p.m., Jethro_uk wrote:

Try sci.electronics.design
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Jethro_uk wrote:

what sort of loads (AC or DC, inductive such as motors or resistive such as incandescent lamps or heaters)? are the two loads the same type of load?
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On Wed, 13 Jun 2012 07:20:54 +0100, Andy Burns wrote:

Sorry, should have said for UK AC Mains. Let's say both loads are like a half bar fire - so plain resistive loads. I'm picturing a black box which plugs into the wall, and which has 2 sockets. When the load on one socket is removed, the box switches power to the other socket.
X-posted to sci.electronics.design as previous poster suggested.
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that's simple, just 2 triacs controlled by whatever is making the decision. Triacs would need to be switched at zero crossing to avoid any glitch.
The details of the switching vary depending on whether the load is resistive or inductive.
NT
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NT wrote:

And how fussy the monitor is about consumption spikes. Even with something like a cooker hob element or light bulb, there'll be a short term increase in consumption as it gets up to temperature, and if it's something like a capacitor start motor, the surge as it gets up to speed will be noticeable, to say the least.
Automatically switching from one outlet to another when one load is removed is not too hard to arrange, again depending on how fussy you are about cases where the load is unplugged at, say, peak voltage, and whether you're talking about millisecond current peaks and gaps or not.
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wrote:

If the monitoring device isnt very fussy, a simple relay would do the whole job. If youre using say 1kW plug-in heaters, rewind the relay coil to operate on 4A, and the contacts will switch to load 2 when load 1 no longer draws current. To move back topowering load 1, unplug load 2 and press a button that momentarily connects power to load 1. The relay then latches. Note that the relay should switch the live, and its coil be in the neutral line, otherwise the pushbutton would short the coil.
NT
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We'll see...

But 'whatever is making the decision' gets tricky doing the detection that the first load is gone at the zero crossing point in time. By definition if the first load goes away at other than the zero crossing time, you will see some spike or trough.

He said its resistive.
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Yes. One could switch it fast with a triac, and if necessary even use a big LC or switched mode circuit to smooth the transition.

Yes. Is it safe to assume its totally resistive?
And why does someone need to hide load switching from an upstream monitor?
NT
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On Wed, 13 Jun 2012 02:57:55 -0700 (PDT), NT wrote:

A light bulb is resistive but it's non-linear from switch on...

This has me wondering as well.
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I'd rather use mosfets so there is less to smooth out.
Still gets tricky detecting the removal of the first load quickly enough to avoid any switching glitch unless he is happy with some system where the user effectively has a 'switch loads' button and lets the system switch when it wants to at say the next zero crossing etc.
That would be completely trivial to do.

Doesn't really matter if he's happy with a 'switch loads' button that produces a switch at zero current flowing.
Tho there would still be a problem as John pointed out with the other load being cold initially etc.

Yeah, I asked him that, but he hasn't been back yet.
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very simple. Just detect near zero current, with the detector blanked at times when V is close to zero

Even heating loads normally take more current when cold. Its all solvable, but would take a much more complex control system.
NT

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Why the requirement that 'switch instantaneously between them, so that to a connected monitor, the draw appears consistent (i.e. no spikes or troughs)'
That’s the hard thing to do.
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On Wed, 13 Jun 2012 19:39:21 +1000, Rod Speed wrote:

I was just curious ... in the ongoing smart meter debates (e.g. http:// forums.theregister.co.uk/forum/1/2012/05/24/british_gas_alertme/) it seems some people claim that smart meters will tell energy companies who is growing cannabis, by looking for energy draws consistent with growlamps coming on/off at set times. It seemed to be that a simple way to negate that would be something which gave the *appearance* of a permanently-on appliance drawing 400W. OK, it would add to the cost of such an operation, but it would hide the profile from the meter.
I suspect there's space there for some snake-oil devices ....
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Most of ours appear to just bypass the meter completely so they get free power.
Least that’s what it appears from the fact that those caught usually get charged with bypassing the meter too.

Dunno, my superficial reaction is that that would likely be very obvious, that it isnt turned off when most are sleeping etc.
Not sure what they normally do lights wise tho, whether they normally run them 24/7 for that sort of crop.

Not enough to matter if they are paying for the power used.

Dunno, see above.

It certainly wouldn’t be hard to do a system that switched loads with a timer and switched them at the zero crossing with a triac. That would be good enough for the meter to not notice anything much, even tho you would get a measurable spike in the current with the inrush current to the previous off grow lamps.
Maybe not tho if they deliberately check for spikes like that. The switch on surge wouldn’t be trivial with that sort of load.
You could avoid that by not switching the 'off' loads completely off tho. Then you wouldn’t get any spike on switching at all. Very easy to do in fact.
If its not an academic question and you actually are growing them yourself, I'd do it with an X10 system with a dimmer for each load and switch it with a PC.
Not that much harder to do without a PC.
Don’t know what you'd do about having a load that is on 24/7 if that’s whats done with grow lamps tho. Or a load that’s the same in summer and winter, there cant be too many normal domestic situations like that.
Guess you could just grow different numbers of plants in summer and winter and hope they don’t wonder about why there is no time in spring and autumn with no real heating or cooling demand.
Guess you could just not grow much in spring and autumn, but it would likely be tricky to have that in synch with unseasonable weather when everyone else is heating or cooling and they can see that from their other meter readings.
It'd be a lot simpler to just power the grow lights before the meter. You are flouting the law already, so you might as well flout that law too. It isnt likely to make much difference penalty wise if you get caught.
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On Wednesday, June 13, 2012 12:26:45 PM UTC+1, Rod Speed wrote:

That's what I've heard especaally when growing in quantity rather than personal use which could just be one or two bulbs. A hydroponics centre has opened up near me selling such things to grow peppers and the like.

That's a worry as my economy seven comes on when I'm asleep. That's two 2KW heaters and my 3KW water heater, :-{}

I think so but surely with that yuo'd be looking at high useage overall rather than high usage at certain times. Most of tehse places are rented out and seeled up with the air con going too so I'm not convinced monitoring on/off is a sensible way bto detect such things.

I'd have thought the effort envolved in hiding it would be better spent by-passing the meter, it's not like teh growers are overly worried when it comes to breaking laws.

What if it's ramped up with a 'dimmer' tyoe system.

I thi9nk these growers are found by very large monthly bills where the previous tentant had average bills each month/quater.
Then I think it takes under 3 months from start to finish with growing so a person mught up and leave before the first bill arrives.

One of the big problems is air conditioning in places like that as teh smell carries.

I'd have thought if someone was going through all the trouble oif hiding such things they couldn;t hide would then think about doing exactly that.
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Yeah, tho I wouldnt like the prospect of trying to detect small scale personal use cannabis crops by monitoring the meter.

I meant the fact that it doesnt at least go to lower power use when most are sleeping. Plenty do maintain a lower temp at night.
The water heater shouldnt be taking much when everyone is asleep, particularly if its well insulated.

I doubt it, because as we both agree, they'd most likely just take the high usage before the meter.
Not sure how viable it would be to monitor clusters of houses and compare the smart meter readings with the cluster demand to catch those stealing significant amounts of power like that. Not sure what it would cost to measure the total cluster demand and whether that would pay for itself very quickly given that there cant be that many doing it on a commercial scale.

Spose so.

Yeah, specially as most would just steal the power, if only because the power use would be a dead giveaway with a house full of cannabis plants.

Yeah, no argument there.
Not so true with small scale personal use crops tho.

Yeah, that would work fine.

I doubt it. I bet they just steal the power.
That appears to be the case here, they usually do get charged with stealing the power as well as with cultivation here.

Dunno, the one I saw on a doco recently here had one hell of an operation. Non trivial setup effort. I did wonder how that hadn't been noticed by the neighbours when being setup and wondered if the neighbours had dobbed them in an the program didnt say so they didnt get killed etc.
We actually had one of our politicians quite literally executed by the mafia, but that was a massive operation with a vast field crop back in the days before chopper surveillance.
We've just recently had some caught who had actually buried a couple of full size shipping containers in a paddock and were growing the crop under lights in those.

True.
Yeah, me too.
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On 6/13/2012 3:47 AM, Jethro_uk wrote:

It's hard to imagine they track transients. It's gonna be hard to hide the turnon transients. If the transients can't be tracked, just switch 'em at the same time randomly. How about this... Grow twice as much and put the lights on a swivel to point them one way or the other. Might as well put that 400W to good use.
I suppose they use every possible means to locate grow operations. Low hanging fruit is right here on the internet. ;-)
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On Wed, 13 Jun 2012 04:58:49 -0700, the renowned mike

Why would energy companies want to locate grow operations? To target products to them or something? They're paying customers, right?
OTOH, operations where they bypass the meter would likely be more of a priority. Maybe they can correlate smart meters on a sub circuit with monitors of aggregate energy flow and detect 'leakage'.
Best regards, Spehro Pefhany
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On 6/13/2012 5:38 AM, Spehro Pefhany wrote:

They don't. Law Enforcement uses them as a tool.

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