The best way to drive a heating element?

[momaka]

Re: The best way to drive a heating element?

I already described the heating element in my first post ...
https://i.imgur.com/LTMVhCw.png
and I posted a cad drawing of what the final heating element is going to look like. I don't have specs because it doesn't exist yet.

I understood that part.

However, to drive even such "heating element", you still need some technical specs. Can't do without them. At all.

Like any science question, step #1 is always: identify the problem... in this case, your heating element (which is not a problem per se... but driving it properly can be a problem if you don't do it right.)

If you don't know the specs on the heating element, then the thread question becomes almost equivalent to asking something along the lines of "what's the best way to cook potatoes?" Now bear with me for a moment here, please, I'm not trying to grill you. (See what I did there? )
But answering such question can yield a 1000 answers (or more), none of which may be relevant to your needs or what you're trying to do. So to help us help you figure out an answer to your question faster, always try to provide as many technical details as you can.

Back to the heating element in question, it looks just like a long trace on a PCB, and my guess is you're hoping to use that as a heating element by passing current through it. Well, that's OK. But if you want to do it this way, then either use proper formulas to calculate the resistance of the heating element, or determine it through experimenting / measurement. Knowing the resistance is really all we need. Knowing the power... that would be useful too, but not 100% necessary. After all, if you don't know the power rating of a heating element and you put too much through it, it will just overheat and likely break/burn out.

The heater spec isn't really technically known other than it has about 1.5 ohms of resistance to it ... this test board that Im using its a piece of home etch copper board that I took the dremmel to and carved out the pattern so that its one continuous line in a snake pattern over the whole board, but Im wanting to convert that into a fabed PCB with the same theory behind it ... though I don't really know if there is a way to determine the resistance of the PCB from the design software.

OK, GOOD!
Now we are getting somewhere.

I know this might not be the final design and I understand the resistance spec above could change... but let's assume this will be the spec so we can walk through the rest of the design process. Once you see how it's done, you can hopefully then use it for other future projects.

I understand you want to make something like a hot plate for your lizard... though not something that too hot. More like a warm plate, I presume - at least that's what 45-50C is. Either way, to avoid lengthy math calculations and somewhat complicated formulas about power, surface area, and temperature, it may just be easier to determine this experimentally. How? Experiment by running power sources of various voltage outputs connected directly through your "heating element" and see how hot it gets. Do that until you get one somewhere in the ballpark of your target temperature or maybe a little higher.

The only formulas you really should learn are Ohm's law and power. These in particular:

V = I * R
P = (V^2) / R
P = (I^2) * R

In this case we have R and we can choose V to get a certain P level. If the P level doesn't work for us (too low), we increase V. If P level is too high, then we use lower V.

Let's say you try it with a 5V source first and the heating element connected directly across it. If it really has 1.5 Ohms of resistance, then it should draw...
I = V / R = 5 / 1.5 = 3.3333 Amps of current.

And the power it uses will be....
P = V^2 / R = 5^2 / 1.5 = 25 / 1.5 = 16.7 Watts

Now 16.7 Watts may be too much or may be too little. It will all depend on how large that etched PCB is - particularly its surface area. But we are not changing that (yes?), so we can only adjust the power levels to get to a temperature we can use.

Let's imagine that after a few minutes of heating, the surface area of the PCB has reached more than 50C... like 70-90C. Higher is better in our case, because we can now use a switching/controlling device (be it BJT, MOSFET, or whatever) to regulate the power of the heating element. In turn, this will regulate the heat given off of the plate and get you to your target temperature.

- Notice above that I said to regulate power and not current. Doing so make it easier to drive the "heating element", regardless if you picked BJT or MOSFET. This is where it's helpful to understand Duty Cycle.

If you only partially turn on the MOSFET or BJT to control current through the load (the heating element), then you will be wasting a lot of power (and produce a lot of heat) on your MOSFET / BJT - possibly even more than what the "hot plate" / heating element is producing. This is inefficient and also harder to design for, because now you will need a really big heatsink for the BJT / MOSFET. You will also need to make sure it's coupled well to it. But most importantly, you will now have to look at ton of datasheet parameters and curves (SOA, temperature vs. power dissipation, and etc.) when it's time to pick a part from your inventory, because you would need to determine if the part is even suitable for your design.

In short, trying to control the current through the heating element in a continuous (linear) fashion is not recommended. It's harder and more wasteful. There are exceptions to this, like with linear regulators (where low electrical noise output is more important or really needed.) But here, we don't need any of that. We just need a temperature between 45-50C and that's it.

So the best way to drive a heating element, at least for your project here, is with duty cycle - i.e. cycle power to the heating element On and Off to keep it, on average, between 45C and 50C.

There are many different ways you can do this. Since this appears to be a relatively small plate with not much thermal mass, then using large-period duty cycle may not be ideal. For example, if you keep the plate On for 5 minutes, then Off for 5 minutes, the power output will be 16.7 Watts for the first 5 minutes and then 0 Watts for the other 5 minutes. This will give an average of 16.6/2 = 8.3 Watts of power for the entire 10 minute period. But again, because the PCB that you are using as a heating element is rather thin and with not much thermal mass, you might find this to yield unsatisfactory results, where in the first 5 minutes, the temperature gets too hot (too much over 50C) and then too cold (too much below 45C) in the other 5 minutes.

To get around this, you can change the period. Instead of 5 minutes on and 5 minutes off, you could do 30 seconds On and 30 seconds Off... or even 5 seconds On and 5 seconds off. This will give a more controlled and stable temperature of the PCB. If that's not enough, you can go into even smaller increments: 500 ms On and 500 ms Off... or even 50 ms On and 50 ms Off. This way, essentially you are now supplying the heating element / PCB with only half of the power that it would normally use at full 5V.

OK, so you determine that perhaps the above (5 "something" periods On and 5 "something" periods Off) yields too low of a temperature. Then just bump up the duty cycle. Maybe try something like 7.5 "something periods On and 2.5 "something periods off... i.e. perhaps 750 ms On and 250 ms Off... and repeat this every second. If this yields a temperature in the range of 45C to 50C, then you just program your MCU to toggle the MOSFET or BJT On and Off with the following periods above.

Now let's say the room temperature changes a little... or more than a little. It could make it that this 750 ms On and 250 ms Off scheme is no longer outputting temperature in the range of 45 to 50C. This is where you use the temperature sensor of your MCU and program the MCU to change the duty cycle as needed to adjust the temperature. For example, if the room is hotter and 750 ms On / 250 ms Off is too hot, then the MCU switches to something like 600 ms On / 400 ms Off scheme. Still too hot? Let it switch schemes again in the code. Maybe 500 ms On and 500 ms Off? If that all of a sudden is too low and the temperature is below 45C, then have the MCU bump back the scheme to 600 / 400 ms. If that's not enough, go back up to 750/250, and etc. Just make sure to program it so that when the MCU switches "schemes" as stated above, it stays with a certain scheme for at least 10-100 such full periods of the scheme. This will avoid a situation where the MCU is over-reacting to its own constant re-adjustment of schemes.

Essentially what I describe above is quite similar in many ways to what PID does. But the above is in much more simplified form and one you can easily modify to suit your design with some trial and error.

With that said and going back to driving the heating element, which was the main question at hand in this thread...

OK, so you found that a 5V source can produce enough heat to drive your heating element more than hot enough for your needs. Next, we're tasked with picking a part than can drive the heating element. In a circuit similar to the one shown above in your first post, when the transistor (be it BJT or MOSFET) is fully On, we determined that the current the heating element will draw is 5V / 1.5 Ohms = 3.333 Amps. I see you listed IRF510N as one of your available parts. Let's look at its datasheet. It says it can handle up to 100V between Drain-Source and up to 4 Amps of continuous Drain current at T_case = 100C (or 5.6 Amps with T_case = 25C... but let's assume the worse rating, just in case - i.e. 4 Amps.) In theory, this MOSFET should be able to handle this heating element as a load if you drive it / toggle it fully between On and Off states (hence the whole explanation above of duty cycle.)

So now all you really need to do is connect this MOSFET in your design, like you showed in the first post (but with correct symbol, please, now that you're aware of what device you will be using ). And then have the MCU sent full 5V to the MOSFET's Gate to turn it On or shunt the Gate to 0V to fully turn if Off. Just add something like a 1-10 KOhm pull-down resistor to ground (in place of R1), in case the MCU output floats for some reason (otherwise you could be stuck with a fully turned On MOSFET all the time.)

And that should be pretty much it.

The rest will be all code and you experimenting with it to determine a "base" duty cycle, where the temperature of the heating element is in the range of 45-50C, along with how the duty cycle "schemes" can vary so that the surface temperature of the heating element will stay between 45-50C regardless of the room/surrounding temperature.

I'm ok with that... but I'm also wondering what that diode is protecting since this circuit is intended to always be on and current will always be flowing in one direction.

Well, in the case where you drive a real heating element with a high inductance, once the MOSFET or BJT turns Off abruptly (assuming you are doing duty-cycle / PWM driving) the heating element will have some electrical energy stored in it due to its inductance. Now remember this: inductors do not "like" "sudden" changes in the current flowing through them. Any time a sudden change tries to happen, the inductor will try to push / sustain the same current that was there before, until it runs out of energy. This is called inductive kickback. If you don't deal with it properly, the voltage at the MOSFET/BJT end of the heating element can overshoot greatly and break down / damage your MOSFET/BJT. You don't want that! Having a diode in reverse bias in parallel with the heating element provides a path for the inductor to sustain / maintain its current until the energy stored in it is depleted. Otherwise with no such path, your MOSFET / BJT will be force to provide one... and when that happens, it will go

So for future projects, particularly if you ever have to drive relays, motors, or any such similar inductive device, then read up on inductive kickback and how to curb it. A simple reverse-bias diode is the most simple way to do it..., but it may not always be enough. As the inductance (and stored energy) gets larger and larger, more complex circuits will be needed to handle this energy. Read up Snubber circuits if you'd like to understand this better. I think even Electroboom had a good video on that matter a while back that had good visuals in it so you can see what's happening.

Anyways, hopefully this "essay" is specific enough to answer some of the questions in regards to your project here, yet also broad enough to use for other projects you may have.

[eccerr0r]

Re: The best way to drive a heating element?

Don't forget about Rds(On,IRF510)=0.54Ω which limits power dissipation to around 12W, ~4W of which will be in the switch and only 8W goes to the heat pad...
And if you draw your pcb heatpad correctly, you will get negligible inductance...

[momaka]

Re: The best way to drive a heating element?

Don't forget about Rds(On,IRF510)=0.54Ω which limits power dissipation to around 12W, ~4W of which will be in the switch and only 8W goes to the heat pad...

Good call!

Totally forgot to mention that bit.

With R_ds = 0.54 Ohms, the total circuit resistance of heating element with MOSFET fully On will be about 2 Ohms... and the current through will only be 5V / (1.5 Ohms + 0.54 Ohms ) = ~2.5 Amps instead of 3.33 Amps. (Again, if continuing with the above example.)

So with I = 2.5 Amps, the MOSFET's power dissipation will be:
P_d = (2.5^2) * 0.54 = ~3.4 Watts

That's -not- insignificant. At 3.4 Watts, the IRF510 will run very very hot without a heatsink, possibly increasing it's R_ds to even higher levels.

With that said, if using source with less than 12V, perhaps it would be a good idea to get PC motherboard MOSFETs instead. I have a stash of 60N02 and 85N02 from dead Xbox 360 motherboards. As a comparison, those (the 60N03) have only 8.5 mOhms resistance (i.e. R_ds = 0.008.5 Ohms) which is a few magnitudes lower than the IRF510. With the same current, the 60N03 will run cool as a cucumber.

And if you draw your pcb heatpad correctly, you will get negligible inductance...

Parallel paths in opposite directions?

[eccerr0r]

Re: The best way to drive a heating element?

Thumbs up on 60N02. IRF510 is a flaming heap. or will be one if one tries to use it as is.

BTW of that list

IRF510N - will become a flaming heap
IRF520N - will become a flaming heap
IRF530N - will become a flaming heap
IRF540N - may become a flaming heap
IRFZ44N - will become a flaming heap
IRF640N - may become a flaming heap
IRF740 - will become a flaming heap
IRF840 - will become a flaming heap
IRF3205 - may not even work
IRF9540N - at least it will match the schematic he drew... May even get fried lizard without frying the FET.

But...

60N02 - will work well
85N02 - will work well
IRL540 - will also work

[EasyGoing1]

Re: The best way to drive a heating element?

First off, I'd like to say THANK YOU for this response. I know this took a long time to write and I very much appreciate that.

I understood that part.

However, to drive even such "heating element", you still need some technical specs. Can't do without them.

I did go into the drawing yesterday and take some measurements.

Size: 100mm x 50mm

Trace: 1 continuous on both sides of the board for a total length of 5100mm at 1.2mm wide

Using a value of 35µm for trace thickness, the resistance calcs out to 2.19 ohms based on this link

Essentially what I describe above is quite similar in many ways to what PID does.

What you described above was excellent! I had been thinking about this problem from the wrong perspective this whole time, under the assumption that a continuous current would be the best way to heat the element, but it makes a lot of sense to do it as you describe.

I'm thinking a solid-state relay might be the best option instead of trying to control a MOSFET. However, looking at the available options that can mount to a PCB, they seem to be rated for only 2 amps ... but, if I limit the source voltage to 3 volts for the element, it will take more time to heat the element, and ill have to make sure that I can even get it to temp with 3 volts but if so, then that's the way I'll do it.

I could also use a small mechanical relay that can handle more current I'll just have to check the noise level to make sure it wont be disturbing ... I tend to work without much ambient noise and hearing a clicking noise all the time would be distracting.

Using the relay to switch the source for the element would also make the code a lot simpler. At that point it's just a matter of creating the methods to determine and then implement the duty cycle that the relay will execute.

Anyways, hopefully this "essay" is specific enough to answer some of the questions in regards to your project here, yet also broad enough to use for other projects you may have.

This was amazing. up and beyond the call... as it were and I very much appreciate it.

Thank you!

[eccerr0r]

Re: The best way to drive a heating element?

SSRs will result in design failure too unless you're using higher voltage - if you're switching 5v, most SSRs will drop a volt and you'll lose one heck of a lot power through it. a mechanical relay is so much better if you can deal with the clicking and slow operation.
if you have a mosfet SSR, then you basically still using a mosfet...and did away with all the complexities with driving the mosfet.

[EasyGoing1]

Re: The best way to drive a heating element?

Good call!
As a comparison, those (the 60N03) have only 8.5 mOhms resistance (i.e. R_ds = 0.008.5 Ohms) which is a few magnitudes lower than the IRF510. With the same current, the 60N03 will run cool as a cucumber.

Looks like I can get the IRL7833 on amazon and it has a logic level on voltage and an Rds of 3.8mΩ

Perhaps this would work?

[eccerr0r]

Re: The best way to drive a heating element?

you'll get a flaming Q2 once you try to turn it on and the mosfet off...
you need to current limit base and current limit collector.

btw the whole point of using 60n02 85n02 irl540 irl7833 is that I thought you didn't want that Q2 to begin with - drive the gate directly with your microcontroller output. If you had the flexibility to add the driver here like Q2 and perhaps a 12V supply somewhere, then you can use those old mosfets you had in your kit you bought from amazon.

[EasyGoing1]

Re: The best way to drive a heating element?

you'll get a flaming Q2 once you try to turn it on and the mosfet off...
you need to current limit base and current limit collector.

btw the whole point of using 60n02 85n02 irl540 irl7833 is that I thought you didn't want that Q2 to begin with - drive the gate directly with your microcontroller output. If you had the flexibility to add the driver here like Q2 and perhaps a 12V supply somewhere, then you can use those old mosfets you had in your kit you bought from amazon.

The original thought as to driving the MOSET directly from the MC was when I thought it was a good idea to vary the current going to the heating element. But now that the element will be either always ON or always OFF based on a duty cycle to keep the temperature steady, adding the transistor after the MC was just to switch the MOSFET on and off thinking it would be better to do that through a transistor.

But perhaps my thinking on that was incorrect... where this might be a better option?

[eccerr0r]

Re: The best way to drive a heating element?

The problem is you got to remember the whole system. The MC is CMOS and likewise has MOSFETs there to turn that output on and off. Except 'on' is probably 3.3v and 'off' is near 0v. While that resistor there is helpful in turning the FET off, the main driver is the MC output pulling that output down to 0V.

As STJ and I have said, and same as what we said when we were helping you with your PWM LED dimmer, is that it's best to turn a mosfet fully on and fully off to reduce power consumption. In the LED case you had to turn it on fast else you would see flicker.
And to reiterate what we said in the past, a not-fully-on signal to the MOSFET would induce it to get hot.

However in this case you have an additional degree of flexibility: since the heater is SLOW to respond unlike your eyes that can detect flicker, you can run the heater PWM *much* slower than LEDs. The heat capacity of the board and environment will tend to even out the pulses - you have the heater on for 1 second, the heater won't heat the environment up to full temperature in 1 second whereas LEDs you will get to full brightness to your eyes in fractions of a millisecond.

I don't know if you cook with an electric cooktop with resistive heating elements, I don't know if you realize that when you have the elements on 'low' the heating elements aren't really low... it actually turns the element on full blast for a short period of time, then turns it off for many seconds, and repeats itself. You want to emulate this behavior with your MC.

Again you have to go much, much faster with LEDs else you see flickering. But with the cooktop you won't even notice the heat being full blast for those short bursts.

[EasyGoing1]

Re: The best way to drive a heating element?

The problem is you got to remember the whole system. The MC is CMOS and likewise has MOSFETs there to turn that output on and off. Except 'on' is probably 3.3v and 'off' is near 0v.

It's a 5 volt MC so output on that pin is most likely somewhere between 4.5 and 5. The MOSFET is rated to be fully on at 4.5V.

and repeats itself. You want to emulate this behavior with your MC.

Yeah, that's what I got from momaka's reply when he explained how PID generally works.

Your initial statements where you pointed out that the MC is CMOS and likewise has its own MOSFETS ... was that meant to be relevant to my last schematic in terms of turning the heating element MOSFET on and off using the configuration in that schematic? Or were you just pointing that out to be thorough?

[EasyGoing1]

Re: The best way to drive a heating element?

As STJ and I have said, and same as what we said when we were helping you with your PWM LED dimmer ... And to reiterate what we said in the past ...

What is your goal when you constantly remind me of what was said in past posts? What is the value-add in such statements to THIS thread? Because it comes off as condescending and I don't like being talked to like a child. Perhaps you should just avoid my posts altogether because other than feeding your ego, I see no relevance to such statements in the context of this thread or any thread I might start in the future.

[eccerr0r]

Re: The best way to drive a heating element?

Do realize you need to check the actual output. A 5V circuit is likely TTL and designed for TTL loads and TTL does not go to the high rail.

And the goal for reminding you of the past is because the two designs are so similar, almost exactly the same, I would have hoped you use information you learned in the past and apply it to this situation.

[EasyGoing1]

Re: The best way to drive a heating element?

And the goal for reminding you of the past is because the two designs are so similar, almost exactly the same, I would have hoped you use information you learned in the past and apply it to this situation.

I have no circuits like this one that I have built in the past.

And since this thread is ongoing, your hopes in that regard are obviously without fulfillment, so I don't see the point.

I don't make posts here for entertainment value, if I have a question that I don't know the answer to I prefer posting it here because I find the feedback and answers to be valuable. Your constant criticism is of no help at all.

I am kindly asking that you stop doing this.

From now on, I'll use hand-drawn schematics with generalized components when I'm not trying to reference specific components and when I need to discuss specific components, I'll post a more accurate schematic. And if you think there was a past post that would address a new post, feel free to reference it and point out why the current post is the same as the one in the past.

Part of getting to a solution to a problem is having a discussion where questions are asked for clarity then knowledge can be applied based on that clarification.

This post started because I wanted to find out the best way to heat the heating element without having a MOSFET that sits there and burns too hot to touch. The process in the discussion has helped me realize that my approach to accomplishing my goal was all wrong. Nothing from my past posts would have helped me realize this since I've never designed nor built a circuit like this one before.

But PLEASE, stop criticizing me and don't condescend me anymore. I'm 52 years old and I haven't earned that kind of treatment in here. I don't treat people that way and so no one should treat me that way.

[eccerr0r]

Re: The best way to drive a heating element?

Every single mosfet circuit you came up with is basically the same: a PWM or software controlled on/off switch. It's always a microcontroller driving it. Did you not have to deal with MOSFETS burning up when you were experimenting with your previous projects? I'd be surprised if you didn't. What did you learn from those experiments from lots of LEDs to solenoids? What worked, what didn't work? On your last paper schematic, replace "ELEMENT" with a solenoid, heater, LED, relay, and perhaps change the voltage, but now don't they look the same as what you did in the past?

BTW your tone of voice with me is likewise offensive, so I respond in kind. Nobody ever deserves any special treatment on a forum or any other communication, you should have learned over the years. Heck I didn't even get credit from you for covering a calculation hole that could have saved a "why does this not work' and get downplayed on all my effort trying to show you potential pitfalls.

To be brutally honest I am quite jealous you can afford getting so many PCBs printed, maybe it's just that. I can't afford mistakes. I can't afford making the same mistake over and over again.

[sam_sam_sam]

Re: The best way to drive a heating element?

What to consider in a design

PID loop

Duty Cycle

Define your Parameters

Know what your Voltage is

Known what your Current is

Using Ohm Law

And your explanation and examples that you gave in your presentation

I like your presentation this is very helpful when considering a project

EasyGoning1


This was very informative and what needed to be considered even before you chose the the part that are needed

In some cases an ( off the shelf device ) ( a 3D printer heater bed mosfet controller board very good design works very good with a micro controller ) might be the solution but not always but you would not know it if you do not know what your parameters are and what you want to accomplish and how you will achieve it

It is not easy to do try to design a solution to an issue that you do not have all the correct information about whether or the heater element is the right choice or how you can power the heating element or weather or it will be battery powered or from an electrical outlet or some other type power source

I am giving these examples because I have gone down some rabbit holes not having all the correct information and getting distracted by some part of the solution but not the hole solution picture and getting very frustrated because not finding a solution to the problem and ( if you have followed some of my posts about the issue with my battery testing machine ) I can tell you that I have been very frustrated many times but I either find a work around to overcome the limitations of the device or find a circuit design that might work better than what I have now or is the device malfunctioning in some way or is algorithm is the issue which you can not change or just not understanding exactly how the device actually works

What I can tell you about testing 18650/21700 batteries on the battery testing machine is that the machine and the software has its limitations can I work around them yes but I know what the limitations are so finding batteries with the same exact specifications for amp hours are limited to the accuracy of the battery testing machine and the software that controls and the way you interpret the data results that are given for each battery tested but if you are wanting to have balance battery pack cells it is a lot better with the battery testing machine than putting a bunch of new battery cells and hoping for the best outcome

With that said what are you willing to accept for what limitation that might exist

[EasyGoing1]

Re: The best way to drive a heating element?

Every single mosfet circuit you came up with is basically the same:

I might have asked questions in the past about using a mosfet in a PWM situation, but as I sit here and think about the circuits that I've actually created into something that I've used, I can think of a couple where I used MOSFETs to drive small motors several years ago and I don't remember heat being an issue with any of those. All of the LED circuits I've created had ZERO mosfets driving them. My last LED circuit was the ring LED replacement for my magnifying lamp and I ended up using an off the shelf PWM dimmer for that circuit. I later had a question about that same circuit because I wasn't happy with the dimmer and I was considering using a 555 timer to replace it and I built one on a breadboard but that never went any further than that. Still using the dimmer that Im not to fond of.

Then there was the circuit where I wanted to create an electro-magnetically driven stirrer for vape juice, and I ended up using off the shelf stepper motor drivers for that circuit, but I could never get the magnetic strength that I needed to spin the juice fast enough so I changed that design to a motor spinning some neodymium magnets underneath a platform that spins the magnetic pill inside the liquid and that motor is controlled by an off the shelf motor driver that has variable speed control and it works amazingly well.

Nobody ever deserves any special treatment on a forum or any other communication

I'm not asking for special treatment. I'm asking for treatment that is at least consummate with the way I treat others and I'm asking that if you're at least going to bring up the past, then you should reference specific posts that I've made because your memory on these things is not accurate and so you should at least hold yourself accountable for your criticism and make sure you're accurate in what you say.

To be brutally honest I am quite jealous you can afford getting so many PCBs printed, maybe it's just that. I can't afford mistakes. I can't afford making the same mistake over and over again.

I have never ordered a PCB that didn't work. I always test my circuits on a breadboard or a home-etched board before I order a PCB. I know it works before I even order it.

My first ever PCB order was in April of 2019, I've ordered PCBs a total of 8 times since April 2019 for an average cost of $48. That's less than $100 a year on PCBs and almost half of that is shipping costs. It costs me $85 to fill my tank with gas and I do that a lot more often than once a year. And if you're curious or you think I'm fibbing, I only order PCBs from JLCPCB, and after reading your post, I logged into my account and looked my history so everything I just said is completely accurate.

I think your impression of my activities in electronics is far grander than it actually is.

[EasyGoing1]

Re: The best way to drive a heating element?

This was very informative and what needed to be considered even before you chose the the part that are needed

I agree, momaka's response was amazing and it was the post that turned me in the right direction with this circuit.

It is not easy to do try to design a solution to an issue that you do not have all the correct information about

This is why I ask questions in here. All of you regular posters on this site are far more advanced in your knowledge of electronics than I will ever be.

What I can tell you about testing 18650/21700 batteries on the battery testing machine is that the machine and the software has its limitations can I work around them yes but I know what the limitations are so finding batteries with the same exact specifications for amp hours are limited to the accuracy of the battery testing machine and the software that controls and the way you interpret the data results that are given for each battery tested but if you are wanting to have balance battery pack cells it is a lot better with the battery testing machine than putting a bunch of new battery cells and hoping for the best outcome

I actually attempted to make a batter tester myself. I looked up the algorithms and understood them in concept, but when it came time to implement them in a microcontroller, the numbers just didn't turn out right and I lost interest fairly quickly after that. The issue came down to getting accurate current readings while the battery discharged into a load, then couple that with the fact that not all Arduinos are exactly the same where it comes to their computation of millis() and that adds unknowns.

If I were to attempt it again, I would probably use an RTC for timing and make sure I take current readings at consistent intervals then figure out how to convert all that into MAH ... which is where the magic is in that setup ... if you can get the mah calculated correctly, then you're in business.

I wrote and published an Arduino library that lets you create non-blocking timers very easily. It's called BlockNot and I've used it to drive stepper motors down in the hundredths of microsecond precision and it works very well. You can access it directly from within the Arduino IDE if you search for the name with the library installer.

With that said what are you willing to accept for what limitation that might exist

I'm not exactly sure what you mean by that statement. This circuit is fairly simple conceptually. No where near as complicated as your battery tester.

[eccerr0r]

Re: The best way to drive a heating element?

See they are exactly the same, you admit it now, it's a mosfet driving some load. I was correct. The load may be different but it's still a mosfet switching some load and they all suffer from the same problems.

And yes you *are* asking for special treatment. You state your age and believe you're entitled to a certain type of treatment not only in this thread but you request it again here.

When you read posts, you should take the post as they are. You are the one who is forgetting things, drawing things wrong over and over again. Stop making these pointless mistakes and making us point out errors that we can't make assumptions you know what you're doing - you even claim you're not an expert that could make these mistakes. Who ... or actually WHAT should we believe?

And look at that, you once again decide to take an olive branch and beat the person handing it to you, Now do you understand why you deserve a beating stick instead of an olive branch? I shall no longer hand you olive branches.

Gosh why do I even bother helping anyone when people like you decide to beat back when we point out mistakes you yourself make. Obviously you are making them over and over again. Now act your age, you know this is the internet and people will be pointing them out your mistakes - don't be such a snowflake. You'll melt as fast as that 2n3904TF crowbarring your 5v line when you try to shut off the mosfet in your circuit in 27.

The beating continues until morale improves. Or at least take your beatings, learn from them and get back on topic. I merely try to point at examples from your past that you should have learned from, think back to those times and apply knowledge. If you didn't learn anything from back then, that's on you, is it not?

[EasyGoing1]

Re: The best way to drive a heating element?

See they are exactly the same, you admit it now, it's a mosfet driving some load. I was correct. The load may be different but it's still a mosfet switching some load and they all suffer from the same problems.

And yes you *are* asking for special treatment. You state your age and believe you're entitled to a certain type of treatment not only in this thread but you request it again here.

When you read posts, you should take the post as they are. You are the one who is forgetting things, drawing things wrong over and over again. Stop making these pointless mistakes and making us point out errors that we can't make assumptions you know what you're doing - you even claim you're not an expert that could make these mistakes. Who ... or actually WHAT should we believe?

And look at that, you once again decide to take an olive branch and beat the person handing it to you, Now do you understand why you deserve a beating stick instead of an olive branch? I shall no longer hand you olive branches.

Gosh why do I even bother helping anyone when people like you decide to beat back when we point out mistakes you yourself make. Obviously you are making them over and over again. Now act your age, you know this is the internet and people will be pointing them out your mistakes - don't be such a snowflake. You'll melt as fast as that 2n3904TF crowbarring your 5v line when you try to shut off the mosfet in your circuit in 27.

The beating continues until morale improves. Or at least take your beatings, learn from them and get back on topic. I merely try to point at examples from your past that you should have learned from, think back to those times and apply knowledge. If you didn't learn anything from back then, that's on you, is it not?

There was nothing hostile in my last response to you so I don't know where all this aggression is coming from. And concerning that UPnP comment from that other person, he was splitting hairs... type case doesn't make any difference unless you have OCD.

You can point out my mistakes all you want, I'll just ignore you from now on. Your criticism doesn't help me at all.