Switching between heaters/theromostats when up to temp.

Thread Starter

slowbutsure

Joined Feb 12, 2024
5
HI

I live in the Philippines and am making a storage water heater. It will have two heating elements, one at the top, and one at the bottom of the tank. I want the one at the top to come on first and the one on the bottom to only come on when the one at the top has switched off (with its thermostat). Can anyone help me with that? Either a ready made product or the simplest way to do it? Appreciated. thanks.
 

crutschow

Joined Mar 14, 2008
34,452
You could detect the current in the top element, such as using something like this, to control the bottom element.

Where do you buy electronic or electrical hardware?
 
Last edited:

Thread Starter

slowbutsure

Joined Feb 12, 2024
5
You could detect the current in the top element, such as using something like this, to control the bottom element.

Where do you buy electronic or electrical hardware?
Thanks, im in the Philippines, and find it difficult to source things. I can get things delivered from Amazon US.
 

Thread Starter

slowbutsure

Joined Feb 12, 2024
5
You could detect the current in the top element, such as using something like this, to control the bottom element.

Where do you buy electronic or electrical hardware?
Actually, just found one of these here in the Philippines. Great help, thanks! One question, would i need a normally open or normally closed one?
 

crutschow

Joined Mar 14, 2008
34,452
Actually, just found one of these here in the Philippines. Great help, thanks! One question, would i need a normally open or normally closed one?
The one I reference only can control 0.3A maximum, so you would need to have that control a relay for the bottom element.
Either normally open or normally closed can work, depending on the characteristics of the relay you get for the bottom element.

Note that you run just one wire (not the wire pair) from the top element through the opening in the sensor to sense the current.
If you run both wires, the magnetic fields from the wires cancel each other, and the sensor cannot detect the current.
 

Thread Starter

slowbutsure

Joined Feb 12, 2024
5
The one I reference only can control 0.3A maximum, so you would need to have that control a relay for the bottom element.
Either normally open or normally closed can work, depending on the characteristics of the relay you get for the bottom element.

Note that you run just one wire (not the wire pair) from the top element through the opening in the sensor to sense the current.
If you run both wires, the magnetic fields from the wires cancel each other, and the sensor cannot detect the current.

Thanks. Just to make sure. the description on that product says 0 - 50amps. So no relay needed?
 

ThePanMan

Joined Mar 13, 2020
793
Just a word of caution; if I read the opening question right, you want to heat the water at the top of the tank to a particular temperature. When the temp is reached you want that upper element to shut off and switch on a bottom element. If that's what I'm reading then at all times the water will be heating via one or the other element. At some point the temperature is going to reach either the safety valve opening or the tank can explode. If you're not familiar with boiler explosions try searching on YouTube for such video's. They can be quite spectacular.

OK, so at some point both elements need to shut off. Otherwise you risk a catastrophic failure of the tank. And possible personal injury. Be careful when messing with boilers.
 
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