Jethro_uk wrote:
>
>> 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) ?
>
> 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?
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.
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.
Why the requirement that 'switch instantaneously between them, so that to a connected monitor, the draw appears consistent (i.e. no spikes or troughs)'
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.
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.
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.
I was just curious ... in the ongoing smart meter debates (e.g.
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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 ....
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.
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. ;-)
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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Do you have control over the switching between loads, or does some one simply turn off a switch, or worse, pull a plug?
Either mechanical OFF will take anywhere from 5 to 20mS to accomplish and during that time the inductance in the supply wiring will be complaining about the changes in current.
Bottom line, yes it is possible to accomplish what you want but your problem needs to be better stated. Take EVERYTHING into account.
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