Electrical question: Will this work? Is it safe?
Discussion
… Will I blow something up?
I think it will work, but yes I can think of a safety issue. I want someone to tell me how much of an idiot I am for even considering this!
So I have a newly set up aquarium. It has a temperature controller, an STC-1000, very common little unit that can drive both a heating output when the detected temperature is too low, and it has a cooling output for when the temperature is too high. I currently have the aquarium heater connected to the heating output, and an air pump connected to the cooling output to provide emergency water circulation if it gets too warm.
I am slightly worried about oxygenation during the “lights out” period when the plants aren’t photosynthesising. So I’d like to run the air pump on a timer during the night for additional circulation. But I’d also like it to be driven by the temperature controller so it also comes on at any time if the water gets too warm.
So here’s my crazy idea: Wire the air pump into BOTH the output of an electronic timer, AND the output of the temperature controller. I’d simply have a three-way junction, with all three lives connected together, all three neutrals together and all the earths (though I think the air pump is double insulated and has no earth).
Everything is on the same household circuit, so the RCBO won’t see a current imbalance in normal operation - except, of course, if there actually is a fault in which case it would trip as normal I think.
A very real problem is that if you unplug the air pump from either the timer or the temperature controller but leave the other connected, the live pin of the plug you’re holding could well be live. This is “not ideal”. All of this is enclosed in a cabinet that only I ever open, and I could fit a lock to enforce this. And as mentioned, we have an RCBO on the circuit. But it’s not great; is there a better way of doing this?
Other potential problems I’ve thought of… Firstly, is there any chance that the timer and/or the temperature controller have an effect on the phasing of their outputs, so when they’re both energised and connected together the phases would interfere?
Secondly, is it likely that the timer and/or the temperature controller will take exception (or be damaged) by having their outputs live when they “should” be off?
So, that’s what I’d like to achieve, but my proposed solution has at least one problem (and please tell me if you can think of other problems). Can this be done “correctly”?
Actually, there is a bleedin’ obvious solution: buy a second air pump and plug it into a timer. Is that what I have to do?
I think it will work, but yes I can think of a safety issue. I want someone to tell me how much of an idiot I am for even considering this!
So I have a newly set up aquarium. It has a temperature controller, an STC-1000, very common little unit that can drive both a heating output when the detected temperature is too low, and it has a cooling output for when the temperature is too high. I currently have the aquarium heater connected to the heating output, and an air pump connected to the cooling output to provide emergency water circulation if it gets too warm.
I am slightly worried about oxygenation during the “lights out” period when the plants aren’t photosynthesising. So I’d like to run the air pump on a timer during the night for additional circulation. But I’d also like it to be driven by the temperature controller so it also comes on at any time if the water gets too warm.
So here’s my crazy idea: Wire the air pump into BOTH the output of an electronic timer, AND the output of the temperature controller. I’d simply have a three-way junction, with all three lives connected together, all three neutrals together and all the earths (though I think the air pump is double insulated and has no earth).
Everything is on the same household circuit, so the RCBO won’t see a current imbalance in normal operation - except, of course, if there actually is a fault in which case it would trip as normal I think.
A very real problem is that if you unplug the air pump from either the timer or the temperature controller but leave the other connected, the live pin of the plug you’re holding could well be live. This is “not ideal”. All of this is enclosed in a cabinet that only I ever open, and I could fit a lock to enforce this. And as mentioned, we have an RCBO on the circuit. But it’s not great; is there a better way of doing this?
Other potential problems I’ve thought of… Firstly, is there any chance that the timer and/or the temperature controller have an effect on the phasing of their outputs, so when they’re both energised and connected together the phases would interfere?
Secondly, is it likely that the timer and/or the temperature controller will take exception (or be damaged) by having their outputs live when they “should” be off?
So, that’s what I’d like to achieve, but my proposed solution has at least one problem (and please tell me if you can think of other problems). Can this be done “correctly”?
Actually, there is a bleedin’ obvious solution: buy a second air pump and plug it into a timer. Is that what I have to do?
I don't follow the plug bit but regardless of who is touching what never never never wire in a situation that a plug could be live. Don't rely on a rcd to save your life. Cut off the plugs and wire it properly.
You can join two lives together but really only if the outputs of the two systems are controlled by relays. They must also be on the same phase which you say is the case.
If not relays but circuits then the output is supposed to be made live by the electronics but would have a reverse current and this may damage one controller or the other.
You can join two lives together but really only if the outputs of the two systems are controlled by relays. They must also be on the same phase which you say is the case.
If not relays but circuits then the output is supposed to be made live by the electronics but would have a reverse current and this may damage one controller or the other.
Yeah, I think I’ve answered my own question with the bit in small print at the end!
The correct solution is to buy a second air pump and plug that into the timer. I can join the airline outputs of both pumps together using a Y-piece so I only need one airline going into the tank, and have non-return valves to prevent each pump blowing air back down the line through the other pump (as well as preventing back-siphoning of water from the tank).
Writing this thread helped to marshal my thoughts, and made me realise that the idea was moronic!
The correct solution is to buy a second air pump and plug that into the timer. I can join the airline outputs of both pumps together using a Y-piece so I only need one airline going into the tank, and have non-return valves to prevent each pump blowing air back down the line through the other pump (as well as preventing back-siphoning of water from the tank).
Writing this thread helped to marshal my thoughts, and made me realise that the idea was moronic!
xstian said:
Can you not just wire the timer into the feed to the temp controller. So they both run off the same supply/plug top.
If you mean plugging the temp controller into the timer, that would mean that when the timer is off, the temp controller is off. The tank would either cool down, or could overheat. The temp controller needs to be permanently powered up.Or, if you mean plugging the timer into the cooling output of the temp controller, that would mean that the temp controller can’t override the timer and demand cooling if the water temperature goes high when the timer is off.
Dr Mike Oxgreen said:
xstian said:
Can you not just wire the timer into the feed to the temp controller. So they both run off the same supply/plug top.
If you mean plugging the temp controller into the timer, that would mean that when the timer is off, the temp controller is off. The tank would either cool down, or could overheat. The temp controller needs to be permanently powered up.Or, if you mean plugging the timer into the cooling output of the temp controller, that would mean that the temp controller can t override the timer and demand cooling if the water temperature goes high when the timer is off.
You need to use the inputs not outputs.
I guess this could work safely if I could hard-wire everything, a bit like a central heating system is wired, as GasEngineer says.
I can certainly hard-wire the air pump into the cooling output of the temp controller, because it has screw terminal outputs. But electronic timers tend to have plug-in outputs so I’m still left with a “widow-maker” plug going into the timer, where the live pin could still be live when it’s removed from the timer (because it’s also connected to the output of the temp controller).
Maybe electronic timers with hard-wired outputs exist, but I was hoping to use timers that I already have. And rather than buying another timer, I might as well buy a second air pump instead and use a plug-in timer that I have lying around.
I can certainly hard-wire the air pump into the cooling output of the temp controller, because it has screw terminal outputs. But electronic timers tend to have plug-in outputs so I’m still left with a “widow-maker” plug going into the timer, where the live pin could still be live when it’s removed from the timer (because it’s also connected to the output of the temp controller).
Maybe electronic timers with hard-wired outputs exist, but I was hoping to use timers that I already have. And rather than buying another timer, I might as well buy a second air pump instead and use a plug-in timer that I have lying around.
Dr Mike Oxgreen said:
I guess this could work safely if I could hard-wire everything, a bit like a central heating system is wired, as GasEngineer says.
I can certainly hard-wire the air pump into the cooling output of the temp controller, because it has screw terminal outputs. But electronic timers tend to have plug-in outputs so I m still left with a widow-maker plug going into the timer, where the live pin could still be live when it s removed from the timer (because it s also connected to the output of the temp controller).
Maybe electronic timers with hard-wired outputs exist, but I was hoping to use timers that I already have. And rather than buying another timer, I might as well buy a second air pump instead and use a plug-in timer that I have lying around.
I’m assuming this is all 240v equipment?I can certainly hard-wire the air pump into the cooling output of the temp controller, because it has screw terminal outputs. But electronic timers tend to have plug-in outputs so I m still left with a widow-maker plug going into the timer, where the live pin could still be live when it s removed from the timer (because it s also connected to the output of the temp controller).
Maybe electronic timers with hard-wired outputs exist, but I was hoping to use timers that I already have. And rather than buying another timer, I might as well buy a second air pump instead and use a plug-in timer that I have lying around.
xstian said:
No I mean, if you wire the timer and the temp controller to the same supply/plug top. They will then work independently of each other.
So what would the air pump be plugged into?xstian said:
You need to use the inputs not outputs.
I don’t understand this bit.xstian said:
I m assuming this is all 240v equipment?
Yes. The temp controller’s outputs are 240V AC.trashbat said:
Have a look at Shelly microcontrollers. This would give you your safe, hardwired capability and you can set timer schedules on them via an app. They're not expensive. You just need to think carefully about inputs and how it's going to come together.
Thanks, I’ll take a look.Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff