# Heating Pad not hitting max temperature
**URL:** https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382
**Category:** Sparkfun
**Created:** [5 July 2024 02:11 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382 "2024-07-05T02:11:07Z")
**Posts on this page:** 20
**Page:** 2
### Author:  [@Jeff105671](https://forum.core-electronics.com.au/u/Jeff105671)
#### Post date: [26 July 2024 01:31 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/21 "2024-07-26T01:31:46Z")
> [@Dion267210](#):
>
> so I have to work out why the current through the mosfet drops to 35mA when I attach 5V to VIN.
VIN is the input to the regulator. It is designed for 9V, not 5V.
[Powering Alternatives for Arduino Boards | Arduino Documentation](https://docs.arduino.cc/learn/electronics/power-pins/)
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### Author:  [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)
#### Post date: [26 July 2024 01:35 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/22 "2024-07-26T01:35:54Z")
> [@Dion267210](#):
>
> not sure why it needs 10V to open?
I did not say that. I said it needs close to 10V to be FULLY ON. That device says the threshold voltage (when it STARTS to switch) could be up to 4V and the graph says at 5V it is only partially on. Too marginal for my liking but if you continue to use it be my guest. It is so close that anything could upset it.
> [@Dion267210](#):
>
> Agree it is not ideal but for prototype purposes it works
Where is that coming from. It is during the prototyping phase that you want everything to be spot on. The last thing you want is potential built in problems while still experimenting. That is why you are at the position you find yourself in now.
If this is your thinking I don’t think much of it. You would be better if you could guarantee everything to be spot on before you went much further.
Cheers Bob
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### Author:  [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)
#### Post date: [26 July 2024 01:38 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/23 "2024-07-26T01:38:49Z")
> [@Jeff105671](#):
>
> VIN is the input to the regulator. It is designed for 9V, not 5V.
Missed that little gem. You are quite correct of course. The 5V input should go to the pin marked “5V” on Arduino (I think)
Cheers Bob
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [26 July 2024 02:21 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/24 "2024-07-26T02:21:26Z")
> [@Jeff105671](#):
>
> > [@Dion267210](#):
> >
> > so I have to work out why the current through the mosfet drops to 35mA when I attach 5V to VIN.
>
> VIN is the input to the regulator. It is designed for 9V, not 5V.
> [Powering Alternatives for Arduino Boards | Arduino Documentation](https://docs.arduino.cc/learn/electronics/power-pins/)
Thanks. Looking at the datasheets the inputs for VIN for Uno and Nano are 7-12. The load I am looking to power is specified as 5V, so if I use anything higher than that to power the microcontroller I would then need a voltage divider to get the voltage down to where I need it for the load if I am powering both with a single power source. Perhaps going into the microcontroller via the 5V output pin is the way to go?
I am assuming if I only have 5V going to the 5V output pin and nothing going to barrel jack or VIN it should be ok?
### 3V3/5V Pin
**Avoid this option** since the risk of damaging the onboard voltage regulator is high. It can be done safely if the applied voltage to the 3V3 or 5V pins is not higher than the input voltage of the voltage regulators.
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [26 July 2024 02:34 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/25 "2024-07-26T02:34:43Z")
> [@Robert93820](#):
>
> Where is that coming from. It is during the prototyping phase that you want everything to be spot on. The last thing you want is potential built in problems while still experimenting. That is why you are at the position you find yourself in now.
>
> If this is your thinking I don’t think much of it. You would be better if you could guarantee everything to be spot on before you went much further.
What I mean is that although the orange terminal is designed for a PCB, it also works on a breadboard well enough to ascertain whether a circuit is working or not. The short pins does however make it unsuitable as a longer term solution as it can easily be knocked loose. For that I would transition to a soldered PCB.
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### Author:  [@Jeff105671](https://forum.core-electronics.com.au/u/Jeff105671)
#### Post date: [26 July 2024 03:07 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/26 "2024-07-26T03:07:06Z")
> [@Dion267210](#):
>
> I am assuming if I only have 5V going to the 5V output pin and nothing going to barrel jack or VIN it should be ok?
You can power the UNO this way, but it is not recommended and there is a risk of damaging it. The best solution is to use a 9V or 12V power supply, use the barrel jack on the UNO, and a regulator (not a voltage divider) for the device that needs 5V. That also provides good isolation for the power to the two components, which is a problem you have already run into.
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [26 July 2024 03:56 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/27 "2024-07-26T03:56:29Z")
> [@Jeff105671](#):
>
> The best solution is to use a 9V or 12V power supply, use the barrel jack on the UNO, and a regulator (not a voltage divider) for the device that needs 5V
Thanks. I can picture the power source going from the mains to the barrel jack into the UNO, but how do I splice it off to the voltage regulator for the 5V device?
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### Author:  [@Jeff105671](https://forum.core-electronics.com.au/u/Jeff105671)
#### Post date: [26 July 2024 05:30 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/28 "2024-07-26T05:30:16Z")
> [@Dion267210](#):
>
> but how do I splice it off to the voltage regulator for the 5V device?
I presume you mean the DC adapter going to the barrel jack into the UNO, not the mains! You can split the 9-12V DC supply using an adapter like this:
> **[Snap Action 2-to-6 Wiring Block Connector - Clear DF-62](https://core-electronics.com.au/snap-action-2-to-6-wiring-block-connector-clear-df-62.html)**
>
> Snap action blocks are perfect when you have to quickly wire up a bunch of free-hanging components, and you don't want to solder. They're much...
That gives you a three-way split: you only need two, so there’s one spare.
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### Author:  [@Jack](https://forum.core-electronics.com.au/u/Jack)
#### Post date: [26 July 2024 05:47 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/29 "2024-07-26T05:47:23Z")
If you are using a DC power supply you could use an end like this to get 9-12V and power the Arduino through it’s Vin. You can then use the 9-12 with a voltage regulator.
> [@Jeff105671](#):
>
> You can split the 9-12V DC supply using an adapter like this:
I am assuming this was where these came in.
The Arduino has an on-board regulator you can use for 5V but you may want to opt for another 5V regulator such as [this one](https://core-electronics.com.au/lm7805-5v-voltage-regulator.html) to ensure your heating pad can draw enough current.
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [26 July 2024 06:32 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/30 "2024-07-26T06:32:33Z")
> [@Jeff105671](#):
>
> You can split the 9-12V DC supply using an adapter like this:
Yes, that sounds good. I would still need to get a 9VDC mains adaptor with active and neutral wires free to plug into the 2-6 adaptor. I guess I could plug the power supply into a barrel jack mounted on the PCB and then split off into the 2-6 from there? Perhaps that is what @Jack was referring to here? I am assuming he may have meant to post a picture or a link?
> [@Jack](#):
>
> If you are using a DC power supply you could use an end like this to get 9-12V and power the Arduino through it’s Vin. You can then use the 9-12 with a voltage regulator.
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### Author:  [@Jeff105671](https://forum.core-electronics.com.au/u/Jeff105671)
#### Post date: [26 July 2024 06:45 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/31 "2024-07-26T06:45:23Z")
> [@Dion267210](#):
>
> I guess I could plug the power supply into a barrel jack mounted on the PCB and then split off into the 2-6 from there?
Just cut the barrel jack off the adapter and wire it straight into the 2 side of the 2-6 adapter. Wiring power through the breadboard is not going to work well. Give yourself at least 10cm length back from the barrel plug in case you want to use the plug with some other device in the future.
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [26 July 2024 06:54 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/32 "2024-07-26T06:54:23Z")
> [@Jeff105671](#):
>
> Just cut the barrel jack off the adapter and wire it straight into the 2 side of the 2-6 adapter.
That what I was thinking! Just wondering if there was a non-destructive way around it but I’m ok with that approach. That is how my 5V USB power supply into orange terminal was set up.
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### Author:  [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)
#### Post date: [26 July 2024 10:02 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/33 "2024-07-26T10:02:01Z")
> [@Dion267210](#):
>
> **Avoid this option** since the risk of damaging the onboard voltage regulator is high. It can be done safely if the applied voltage to the 3V3 or 5V pins is not higher than the input voltage of the voltage regulators.
It is OK to input 5V to the “5V” pin. this can be an input OR output.
The 3.3V pin is output only. You CANNOT input 3.3V to this pin.
> [@Dion267210](#):
>
> That is how my 5V USB power supply into orange terminal was set up.
What do you mean by "5V USB power supply. It is not shown in your pics. Is it 5V derived from a computer port or a 5V charging supply with USB outputs. I have been going along the assumption that it is a POWER SUPPLY. If it is a charging sort of thing it could be anything.
Cheers Bob
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [26 July 2024 22:31 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/34 "2024-07-26T22:31:06Z")
> [@Robert93820](#):
>
> What do you mean by "5V USB power supply.
It’s a micro USB cable whereby I lopped off the plug and connected to the orange terminal so I can connect to breadboard and PCB. It is a 5V 1A Apple voltage regulator.
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### Author:  [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)
#### Post date: [27 July 2024 00:52 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/35 "2024-07-27T00:52:21Z")
Hi Dion
As long as it is a SUPPLY as against a CHARGER (phone etc) it should be OK although at only 1A it could struggle running everything given tat the inrush current (published cold resistance of heater 8.3Ω) of the heater is 0.6A if near the limit you could get a voltage sag at switch on with everything connected. This could create a situation where the Mosfet never gets to switch on. Might explain why the heater seems to be OK when connected directly. This would not be helped by using that Mosfet which I think is pretty marginal at best. I still think you would be better using the Mosfet I suggested earlier which should be fully ON at 5V
Can you try a power supply with more current capability like 2A plus. Doesn’t matter how big you go.
Cheers Bob
Add on:
If you are interested this is how I power a breadboard
This is a piece of 22AWG tinned copper crimped with the stranded wire into a bootlace ferrule then inserted into the breadboard holes. Incedently 22AWG (0.71mm) is the maximum recommended diameter for these contacts.
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [27 July 2024 01:47 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/36 "2024-07-27T01:47:41Z")
> [@Robert93820](#):
>
> As long as it is a SUPPLY as against a CHARGER (phone etc) it should be OK
Hmmm, actually it is a charger we used for iPhones. This could be why I struggle to achieve 450mA . I also tried with 2.4A charger this morning and was able to get to 470mA, which is still short of the ~600mA I should be drawing.
Getting a decent power supply and the mosfet you have recommended should go a long way to resolve some of my problems.
> [@Robert93820](#):
>
> f you are interested this is how I power a breadboard
Thank you, that is very helpful.
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### Author:  [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)
#### Post date: [27 July 2024 02:08 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/37 "2024-07-27T02:08:14Z")
Hi Dion
Although they MIGHT be OK chargers may not be particularly “clean” as there is no real reason they should be. Power SUPPLIES on the other hand go to some lengths to make sure they ARE “clean”.
Regarding your orange terminal block. I have some of those so I just tried one. It would not go into my quality “Wish” board at all. I have another “quality” board and the terminal would not insert into this either. Measurement showed the pins to be 1.02 X 1.03mm and the contacts are quoted 0.7mm max. I did find however that I could force it into a “cheapo” breadboard but only about 1mm which is far from ideal. Even if I could force it in further (longer pins) it would probably destroy that contact.
My suggestion still stands. Modify your method of powering while using a breadboard and mark those contacts you have been using as suspect for future use.
> [@Dion267210](#):
>
> Getting a decent power supply and the mosfet you have recommended should go a long way to resolve some of my problems.
I think you might get some results there. Don’t forget the series gate resistor (about ik should do to limit the inrush to 5mA) as to drive it from Arduino or similar it will be required.
Cheers Bob
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### Author:  [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)
#### Post date: [31 July 2024 02:49 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/38 "2024-07-31T02:49:47Z")
Hi Dion
I know this is late and goes back to your original post but!!
I just had a look at that video. What a lot of absolute garbage. That would be the most unscientific scientific experiment I have ever seen.
Not too bad until the fool put his hand on the heater. What sort of an idiot would do that. If the heater had any real grunt he could have well done himself some damage.
His next statement was a classic. How by placing his hand on the heater he “INSULATED” it and lowered the temperature. The temperature lowered because the heater was trying to heat up his hand and did not have enough power to retain its heat. If you covered both sides of the heater with thermal insulating material the heater would get hotter as there would be no thermal path to dissipate heat. But in this situation the heater could not do any real work.
Disregarding that video and back to the heater. 5V @ 0.6A is only 3W. Not a lot of heating power. One suggested use would be as a hand warmer which could be about as far as you would get I am afraid. A Transistor or Mosfet dissipating 3 W would probably not even require a heat sink. If a resistor it would be warm to hot to the touch but would not do much damage.
Try it. Get a 10Ω 5W resistor and apply 5V. This will give you 2.5W. If you can increase the voltage to 5.5V this will produce about 3W. The 5W resistor will get fairly hot, a 10W one will be a bit cooler as it is bigger and able to dissipate more heat into the air but neither one will be really hot.
What I am getting at is that this heater (only being 3W) will not have a great deal of heating power if your area or subject has any volume to speak of. I don’t know what the requirements of a dough proofing box is but I would be surprised if this little heater could cope.
Cheers Bob
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### Author:  [@Dion267210](https://forum.core-electronics.com.au/u/Dion267210)
#### Post date: [31 July 2024 06:04 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/39 "2024-07-31T06:04:11Z")
Thanks Bob, that is the exact thing I experienced even when I did get it to work. It took an hour to heat an empty plastic tub from 16C to 17C! Not much use when I want it to warm a 1.5kg mass to 24-25C! The tub isn’t very big, perhaps 30x40x10cm. It’s plastic so a reasonable insulator but even so the thermal losses were eroding most of the heat generated.
I have a 46.5ohm heating element I have removed from an old toaster oven i am considering connecting to 12V just to see what will happen, but my basic understanding of ohms law tells me it will still be around 3W?
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### Author:  [@Robert93820](https://forum.core-electronics.com.au/u/Robert93820)
#### Post date: [31 July 2024 06:18 UTC](https://forum.core-electronics.com.au/t/heating-pad-not-hitting-max-temperature/20382/40 "2024-07-31T06:18:22Z")
Hi DionI think to have any success with anything you are going to have to minimise thermal loss through the walls and use a thermally insulated container like a fridge or a wall oven.
> [@Dion267210](#):
>
> I have a 46.5ohm heating element I have removed from an old toaster oven
Be a bit careful here. If you measured this as 46.5Ω with a DMM that will be the COLD resistance This will be greater or even considerably greater when the element heats up and won’t necessarily be the operating resistance. The only real way to measure this operating resistance is to measure the voltage and current then calculate it. The wattage is simply the voltage across the element multiplied by the current.
The measurement of current should be ideally non invasive like a clamp meter.
There is a quirk you might not know about with a clamp meter measuring DC. It is residual magnetism in the core laminations interfering with the hall device sensor. You have to continually (between measurements) zero the meter with no current through it or you can end up with a substantial error.
Cheers Bob
> [@Dion267210](#):
>
> it will still be around 3W
That is correct if that is the operating resistance so it is not going to get very hot.
240V at that resistance is about 1240W which is more like it for a toaster. As the element heated up it possibly could settle down to something near 1kW
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