Simple heater question SOLVED

wilriker

@surgikill I cannot disclose any details but he needs to find an appropriate amount of heating power that suffices his project.

But you are right. PWM of the heater connectors could really work in this case easiest. Since this is purely about evaluation and not something trying to use a 12V heater on a 24V VIN this will probably work without any additional hardware.

Surgikill

@wilriker Well, I have the equations here if he's interested. It's cheaper than going out and buying power resistors too.

deckingman

@surgikill said in Simple heater question SOLVED:

Why do you care what power it is? It's all PID controlled anyway, by using a lower power heater it's just going to take longer to heat up and have a harder time holding temperature.

How do you know that when I haven't given any details about the application? You know nothing about the thermal masses involved because I haven't given any details. You know nothing about the desired temperatures and desired rise times because again, I haven't given any details. You know nothing about the flow rate and temperature differential of any incoming fluids because I haven't given any details. You know nothing about how many heaters are involved and what their configurations and orientations are, with respect to each other and with respect to the design as a whole.

So how do you know that lower powered heaters are going to have a hard time time holding temperature? Or I just use a high powered heaters and rely on PID? And what happens when a FET fails and the PID gets stuck on full power and burns someone's house down?

And I'm not going to provide that information because this is a prototype design of something that may end up as a marketable product and I don't want to give out any details at this time. The only thing that is relevant to this thread is my first sentence, quote " I have a need to evaluate some heater power requirements." And my question was answered in the first reply.

End of.....

Surgikill

@deckingman Hope you have a good day. Please remove the stick out of your ass before you sit down somewhere.

@surgikill said in Simple heater question SOLVED:

@deckingman Hope you have a good day. Please remove the stick out of your ass before you sit down somewhere.

Trap 2

Surgikill

@calvinx I mean he's arguing with an engineer.The whole point of a FET failing and burning somebodies house down is bullshit. If you wanted to get a heater cartridge that topped out at a certain temp (say 300C), short of using a resistive wire that increases resistance with temp, it's going to be a shit design with not enough power, unless you are only trying to hold 50-80C, which I'm assuming he isn't because he's talking about high temp heater cartridges.

Furthermore, he talks about a lower power cartridge being able to perform the same as a higher power cartridge. This just isn't true. A higher power cartridge will have decresaed rise times and be more responsive to environment variables such as moving air. There's no arguing that, it's just physics. The only reason you would want to use a lower power cartridge is for either size or power requirements.

IDK if he had a bad day or what, but if he's as smart as he is posturing then there was no need to create this post in the first place.

@surgikill said in Simple heater question SOLVED:

@calvinx I mean he's arguing with an engineer.The whole point of a FET failing and burning somebodies house down is bullshit. If you wanted to get a heater cartridge that topped out at a certain temp (say 300C), short of using a resistive wire that increases resistance with temp, it's going to be a shit design with not enough power, unless you are only trying to hold 50-80C, which I'm assuming he isn't because he's talking about high temp heater cartridges.

Furthermore, he talks about a lower power cartridge being able to perform the same as a higher power cartridge. This just isn't true. A higher power cartridge will have decresaed rise times and be more responsive to environment variables such as moving air. There's no arguing that, it's just physics. The only reason you would want to use a lower power cartridge is for either size or power requirements.

IDK if he had a bad day or what, but if he's as smart as he is posturing then there was no need to create this post in the first place.

As an engineer, have you never heard of a Sanity check ? I'm a Mechanical Engineer, but I would never profess to think I know any more than the next man, we can all learn something from others, and to tout the "I'm an engineer" line smacks very much of arrogance im afraid.

deckingman

@surgikill
I don't think I'm the one having a bad day here - in fact I'm pretty chilled.

I don't really want to get into a discussion with someone who has to resort to personal insults, nor someone who seems to have some sort of paranoia syndrome, but I think you need to re-read my posts before you go off on a rant.

I never said that a low power cartridge would work as well as high power one. Read what I wrote again. You rightly say that a high power cartridge will have decreased rise time. However, because you don't know anything about the application, you don't know that a rapid rise time is in fact undesirable in this case.

As for the FET failure, as an engineer you will know that they can fail in a way that means they are fully on. So, if you are using a PID to control a heater using PWM, and that heater is too highly rated for the application then you will know that in the event of a FET failing fully on, the heater could reach a dangerously high temperature and cause a fire. This is why when you tune a heater, the predicted maximum temperature is reported and flagged as a potential fire hazard. You think this is bullshit? Then I am singularly unimpressed by your claim to be an engineer.

Suggest you take a chill pill and re-read what has actually been posted before you launch into your next rant.

Oh and BTW, I don't have a Donkey but if I did, why would it have a stick in it and why would I need to remove it before sitting down?

wilriker

@deckingman said in Simple heater question SOLVED:

Oh and BTW, I don't have a Donkey but if I did, why would it have a stick in it and why would I need to remove it before sitting down?

Maybe, because once you sat down it will be harder to find the motivation to get up again to finally take that stick out of the donkey - the poor animal should not suffer longer than necessary. (Sorry, couldn't resist )

Surgikill

@calvinx Yes I have. I'm sorry but if you read the exchange I had with wilriker I simply threw ideas out there and then had a rant thrown at me. The only reason I question his capabilities is because he became extremely defensive of his decision without even providing anything to back it up. That usually reeks of somebody that has no clue what they are talking about. I'm sorry that I responded with the same level of arrogance I received in his post. Maybe I should just lay down and let him have his way with me?

@deckingman You seemed to want the cheapest way out of it from what I read in the previous posts. You also said that you are going to have your own cartridges made. You could still use PWM for testing purposes then get your own cartridges made, be my guest. All I'm trying to do is help YOU not run around wasting money like I have done before, but apparently you knew what you wanted to do from the start, which was use power resistors. Be my guest. Don't understand why you come here for advice and then get pissed about it though.

I'm also not going to get into the FET failure. If you really want a detailed answer then I'll provide it assuming you aren't an ass about it, but simply put you will have extremely poor performance if you are looking for a heater cartridge to work at 200-300C but not exceed 400C

deckingman

@surgikill said in Simple heater question SOLVED:
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I'm also not going to get into the FET failure. If you really want a detailed answer then I'll provide it assuming you aren't an ass about it, but simply put you will have extremely poor performance if you are looking for a heater cartridge to work at 200-300C but not exceed 400C

Who said anything about a working temperature of 200-300C? I certainly didn't.

There you go again with your assumptions. I'm not arguing with anything you say, just pointing out that the "facts" as you state them are based on false assumptions which in turn are based on some pre-conceived notion of what it is I'm working on.

You have no idea of the application or configuration because I haven't given any details. Yet for some reason you know better than I what it is I need. You go off on a rant that I'll get extremely poor performance for a heater cartridge that will work at 200 -300 deg C and not exceed 400C. That may be factually correct but it's irrelevant because I'm not looking at those temperatures. I never said I was. For all you know I could be working on something that'll re-heat my coffee to 60 deg C when it gets cold.

As for PWM vs a series resistor - you might be right. I have never disputed that if you calm down a bit and actually read what I have written. As it happens, I do have reservations that simply limiting the max PWM value would give an accurate simulation of a higher resistance heater. I don't know enough about the PID algorithm that Duet uses to have an opinion. I wonder about things like the dead time for instance and how that might be different between a fixed value resistor and a lower value resistor being fed at half PWM . Maybe it wouldn't matter - I don't really know. But I'd rather use a series resistor as I believe (rightly or wrongly) it will give me a more accurate simulation. The reason for starting this thread was that I just needed a quick confirmation on the application of Ohms law because it was some 50 years ago when I was taught that and I haven't used it much since.

So if you just calm down a bit and read what I've actually written, the only thing I have an issue with is that you are basing your recommendations on some pre-conceived notion of what it is I am working on, which in actual fact is quite a way off the mark.

deckingman

Oh and yes, you are absolutely right when you say that I had made up my mind to use series resistors from the outset. That's why I asked a simple question about Ohms law.
I never asked the question "what is the best way to evaluate heaters". Yet that is the question that you and others decided to answer.