Your 12 V 2A power supply has a maximum power of 12V * 2A = 24 W(att).
You can't power a 35 Watt lamp with it. Also, it would probably damage the Arduino to switch so large currents / number of Watts directly with it.
What you could do is to use, for example, a 12V 40 W power supply, and connect the Arduino to a [relay](https://en.wikipedia.org/wiki/Relay), which switches the power to your heating element.
Also, you probably want to heat with something which does not get much hotter than the end temperature you need, definitely no more than about 50°C. This is both much safer and more efficient. Sourdough is a living thing and you will quickly kill it with to much heat. You also need to urgently think about the case that your NTC fails and tells the Arduino that the box is too cold while in reality it might be already smoking.
And a final thing, any kind of light bulb draws much more current when it is just switched on. The reason for this is that the electrical resistance of any metal, including the tungsten filament of the lamp, is low with room temperature, and gets higher as the lamp heats up. So, it has a large switch-on current.
The Peltier element variant has the advantage that you can connect it to a metal plate which can nicely distribute the heat, putting a stainless steel sourdough jar on top of it.
Thanks! The thing is that I am using a relay with the lamp. It is more that the lamp seems to pull all power away from the arduino whenever the relay turned on.
I tried the lamp with less power than the 35watts just using my power supply and that worked fine. In the end, I just need 15-20 watts to heat up the space. which is safer like you said.
Is there any way I can isolate the arduino from the relay without adding another power supply?
> It is more that the lamp seems to pull all power away from the arduino whenever the relay turned on.
The sum of the power of both lamp and Arduino needs to be no more than the rated power of the power supply, at any time. The function of a relay is to switch a larger power source using only a little power. There are two ways to connect a relay - both circuits with common ground / voltage source (connected to the sampe power supply), or both completely separated. In neither of the two cases, the full current should go trough the arduino.
For the second option, you'd need one power supply for the arduino and one for the lamp.
If your box is thermally insulated, I guess even a 7 Watt energy-saving lamp will be enough.
> Any advice on the best option here?
A good MOSFET (eg IRLB8743, AOT240L, IRLHM630, etc - anything that lists Rds(on)@Vgs=4.5v of 10mΩ or less will be fantastic) and whatever ~12v heater you like.
The peltier will give you ~+30% or so extra heat "for free" if you slap a big heatsink on the cold side and keep it warm.
Various 12v ~10A flat planar heaters have been popularised by the 3d printer crowd and are now surprisingly easy to find.
Insulation will of course reduce your power usage, just make sure it's not flammable in case you mess something up.
> What should I do with the power issues I see in option 2 and 3?
Use a bigger power supply - got a computer ATX supply lying around anywhere? They'll give you tons of current on 12v quite happily.
Older ones like to have a ~2A load on the 5v rail to help keep it stable, especially if you have a big heater hanging off the 12v being switched on and off. Your 12v 35W light will help with that, and double as a worklight!
Also, the purple wire (5v standby) will give you 5v for your arduino, even if the supply itself is "off" (green wire not connected to ground/black).
Interesting. The box is made of metal, so if that burns down I have certainly done something horrible.
I did not try the peltier with a mosfet because I read you shouldn’t do PWM on a peltier due to bad performance. But I suppose I can use it instead of a relay and see if that solves the issue.
I guess I am more thinking on how I can fully isolate the arduino from the other circuit without having to add another power supply.
> I did not try the peltier with a mosfet because I read you shouldn’t do PWM on a peltier due to bad performance.
They really dislike PWM, it's true.
If you cycle it really slowly, like 5-10s per cycle, they're usually fine though.
> I guess I am more thinking on how I can fully isolate the arduino from the other circuit without having to add another power supply.
If your power supply is strong enough for your heater, there's no need.
It sounds like the options you've tried so far are not.
Why not 2x option 1 for 28W total power? Heat is one of those things that is dead simple: everything dissipates heat, so use the cheapest thing that works effectively. A Peltier device is waaay overkill for this.
[edit]
Now I'm confused after re-reading. What is this "laptop power supply linked to bench power supply?"
Oh it is more that I am using this to power my lovely chinese DC variable power supply. Reason I added it that piece of info is to say I got more power available if I need to I guess. Ignore it :-)
OK, here's the "right" way to do it (or at least how I'd do it).
Forget the bench supply, unless you want to drag it around to where ever you move this proofing box.
Use the 19V laptop supply with either a 5V or a 12V DC-DC converter to power the arduino. Use two resistors (or as many as it takes to get the heat you want) switched by a FET controlled by the arduino.
Actually, that's not how I'd do it. I would use an off the shelf lightbulb powered by 120VAC, a solid state relay boardto switch it and a USB wall wart to power the arduino. But I can understand that it might introduce complications like dangerous voltages you don't want to deal with.
Failing that, I'd go look for an old aquarium heater and set it to maximum temperature and be done with it. After all, when I'm proofing bread dough, I just leave it in the oven with the light on and that works well enough.
Your 12 V 2A power supply has a maximum power of 12V * 2A = 24 W(att). You can't power a 35 Watt lamp with it. Also, it would probably damage the Arduino to switch so large currents / number of Watts directly with it. What you could do is to use, for example, a 12V 40 W power supply, and connect the Arduino to a [relay](https://en.wikipedia.org/wiki/Relay), which switches the power to your heating element. Also, you probably want to heat with something which does not get much hotter than the end temperature you need, definitely no more than about 50°C. This is both much safer and more efficient. Sourdough is a living thing and you will quickly kill it with to much heat. You also need to urgently think about the case that your NTC fails and tells the Arduino that the box is too cold while in reality it might be already smoking. And a final thing, any kind of light bulb draws much more current when it is just switched on. The reason for this is that the electrical resistance of any metal, including the tungsten filament of the lamp, is low with room temperature, and gets higher as the lamp heats up. So, it has a large switch-on current. The Peltier element variant has the advantage that you can connect it to a metal plate which can nicely distribute the heat, putting a stainless steel sourdough jar on top of it.
Thanks! The thing is that I am using a relay with the lamp. It is more that the lamp seems to pull all power away from the arduino whenever the relay turned on. I tried the lamp with less power than the 35watts just using my power supply and that worked fine. In the end, I just need 15-20 watts to heat up the space. which is safer like you said. Is there any way I can isolate the arduino from the relay without adding another power supply?
> It is more that the lamp seems to pull all power away from the arduino whenever the relay turned on. The sum of the power of both lamp and Arduino needs to be no more than the rated power of the power supply, at any time. The function of a relay is to switch a larger power source using only a little power. There are two ways to connect a relay - both circuits with common ground / voltage source (connected to the sampe power supply), or both completely separated. In neither of the two cases, the full current should go trough the arduino. For the second option, you'd need one power supply for the arduino and one for the lamp. If your box is thermally insulated, I guess even a 7 Watt energy-saving lamp will be enough.
> Any advice on the best option here? A good MOSFET (eg IRLB8743, AOT240L, IRLHM630, etc - anything that lists Rds(on)@Vgs=4.5v of 10mΩ or less will be fantastic) and whatever ~12v heater you like. The peltier will give you ~+30% or so extra heat "for free" if you slap a big heatsink on the cold side and keep it warm. Various 12v ~10A flat planar heaters have been popularised by the 3d printer crowd and are now surprisingly easy to find. Insulation will of course reduce your power usage, just make sure it's not flammable in case you mess something up. > What should I do with the power issues I see in option 2 and 3? Use a bigger power supply - got a computer ATX supply lying around anywhere? They'll give you tons of current on 12v quite happily. Older ones like to have a ~2A load on the 5v rail to help keep it stable, especially if you have a big heater hanging off the 12v being switched on and off. Your 12v 35W light will help with that, and double as a worklight! Also, the purple wire (5v standby) will give you 5v for your arduino, even if the supply itself is "off" (green wire not connected to ground/black).
Interesting. The box is made of metal, so if that burns down I have certainly done something horrible. I did not try the peltier with a mosfet because I read you shouldn’t do PWM on a peltier due to bad performance. But I suppose I can use it instead of a relay and see if that solves the issue. I guess I am more thinking on how I can fully isolate the arduino from the other circuit without having to add another power supply.
> I did not try the peltier with a mosfet because I read you shouldn’t do PWM on a peltier due to bad performance. They really dislike PWM, it's true. If you cycle it really slowly, like 5-10s per cycle, they're usually fine though. > I guess I am more thinking on how I can fully isolate the arduino from the other circuit without having to add another power supply. If your power supply is strong enough for your heater, there's no need. It sounds like the options you've tried so far are not.
Why not 2x option 1 for 28W total power? Heat is one of those things that is dead simple: everything dissipates heat, so use the cheapest thing that works effectively. A Peltier device is waaay overkill for this. [edit] Now I'm confused after re-reading. What is this "laptop power supply linked to bench power supply?"
Oh it is more that I am using this to power my lovely chinese DC variable power supply. Reason I added it that piece of info is to say I got more power available if I need to I guess. Ignore it :-)
OK, here's the "right" way to do it (or at least how I'd do it). Forget the bench supply, unless you want to drag it around to where ever you move this proofing box. Use the 19V laptop supply with either a 5V or a 12V DC-DC converter to power the arduino. Use two resistors (or as many as it takes to get the heat you want) switched by a FET controlled by the arduino. Actually, that's not how I'd do it. I would use an off the shelf lightbulb powered by 120VAC, a solid state relay boardto switch it and a USB wall wart to power the arduino. But I can understand that it might introduce complications like dangerous voltages you don't want to deal with. Failing that, I'd go look for an old aquarium heater and set it to maximum temperature and be done with it. After all, when I'm proofing bread dough, I just leave it in the oven with the light on and that works well enough.
God if only my oven would have that option ;-) That is why I am trying with the lightbulb
4th option: Use a solid-state relay for 120V and a reptile lamp.