# Need help

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I am trying power a heating element with dc power and not sure of the power requirements. I have a 24 v dc 200 watt element. How many amps do I need to achieve 160-180 degrees f?

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I need to take a trip in my car. How many gallons of gas do I need to get to Seattle?

Without knowing the thermal characteristics of the thing you're putting the heating element _into_, we have no more chance of answering your question than you do of answering mine.

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Tim Wescott
Wescott Design Services ```
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Less chance in fact, since we could safely make the assumption that you're somewhere on the earth (I've seen you, so you're clearly not a disembodied brain) so the required amount of gasoline is finite.

temperature rise at all.

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do

True, but it can't take more than 8.3A, so there's an upper bound.

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the power requirements. I have a 24 v dc 200 watt element. How many amps do I need to achieve 160-180 degrees f?

None if you start out at "160-180 degrees f".

assuming your power supply is 24v the element will want a little over

4A when turned on. you'll probably want a thermostat but it's impossible to tell from what you wrote.
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umop apisdn

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Jason what info do you need from me to calculate the amperage

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200W / 24V = 8.333333333333333333333333333333333333333333333333A

Next question, how long does it take to heat up 1 degree!

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What's the ambient temperature (i.e., what's outside the box or whatever it is you're trying to heat), and what is the equilibrium temperature if you just slap 24V onto it and leave it there until the temperature isn't changing?

```--
Tim Wescott
Wescott Design Services ```
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Before or after the fire?

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There's no way to tell with only the information you've posted.

What is it you're trying to do?```
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Mate you might be in a bit over your head :-) but a 200watt 24vdc element should draw about 8amps (200/24 is about 8amps). So you either need a thermostat for the load you are heating and control it that way or get a motor controller and control the power to get the temp you want by observation, but that would have variations due to voltage changes in the supply if any.

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I think a calorie raises a pound of water a degree centigrade or something like that. Really, I do not deal with that type of thing except once in a w hile when it deal with heat sinks in electronic equipment and even that I h aven't done lately.

The biggest question is exactly WHAT is to be heated. Air is fairly easy if you keep it boxed up. Heating a whole room from normal ambient temperature , say 70 degres, up to 160 is way beyond the capability of a 200 watt elema nt unless it is totally insulated and you have ALOT of time. Not likely.

If you are heating water, which is not uncommon for scientific experiments, it can take alot of energy, but art least it doesn't lose as much to the s urroundings.

If you are heating metal, there is a big difference between heating pig iro n, high steel, aluminum, copper, stainless.

So you need to start at a certain temperatire, figure out the thermal mass of what is to be heated and just how fast that heat is lost by convection, and in fact by conduction and radiation as well.

Now if you just want to heat the ELEMENT itself to 160 degrees, that is qui te a bit easier, but that doesn't guarantee that anythong else will be at t hat temperature. If it is immersed in a liquid, your heat will dissipate qu ickly into the liquid. Actually if that's the case you can probably push it beyond 200 watts, as long as the whole thing is immersed all the time.

This is why knowing the application is crucial. What's more, alot of the fo lks around here will refuse to "do your homework" so to speak, and give you some formulae to work out on your own. My problem with that is I am stuck on old math. I can figure things out but the old fashioned way.

So the biggest question is WHAT is to be heated and how big is it. Even wha t does it weigh ?

Most of the time, you are better off controlling anything like this thermos tatically bcause you never know what the ambient temperature, humidity and barometric pressure will be. They will all affect the actual power needed t o achieve the desired temperature, listed from the most significant effect to the least.

In a way it's like asking which is heavier, a pound of lead or a pound of f eathers.

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elemant ?

I really do not understand some of thesse typos. I do know how to spell the word, this is wierd and it is happening more lately.

Am I senile ?

I have typoed "you are now crazy" insted of "you are not crazy". One of these days I am going to get in trouble...

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Presto, You have to say what you are heating - lets assume its a quart of water. Then to get a steady state of 170 F, you will need X amps. X depends on the heat loss from the container or oven you are heating. In general, ee designers will ESTIMATE the power requirement, but put the system under FEEDBACK CONTROL using a thermostat device which senses temperature.

If you don't need that fine control, you can vary the power until a thermometer reads what you want. It will be a rough system, but for some apps, that's OK. (Drying food, etc.) From the "seat of my pants," a container of water, uninsulated, might need

150 watts guesstimate. So that would be 5-7 amps. A well insulated bottle might need 1-2 amps.
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I am trying to heat air in small container and I will be blowing air across the element to create a stream of warm air. I am being very vague because I am trying to invent something and without having a signed NDA I don't wan t to give it away. I was able to achieve 130 degrees surface heat on my ele ment with 24 v. At 2 amps but when a fan blows it will cool it. I need a s teady stream if 140 degrees air at the output vent.

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How very audacious of you. You ask for help from professional engineers and successful men who are directing their own companies, but you need an NDA? Are you willing to pay their prices? I'm sure that some individuals will give you a quote for their services, if you ask nicely.

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ss the element to create a stream of warm air. I am being very vague becaus e I am trying to invent something and without having a signed NDA I don't w ant to give it away. I was able to achieve 130 degrees surface heat on my e lement with 24 v. At 2 amps but when a fan blows it will cool it. I need a steady stream if 140 degrees air at the output vent.

The heating effect will depend on a lot of things with air flowrate being t he most important, there are factors like air density, moisture content and the temperature of the incoming air. You have a 200W heater, so get a 200W power supply for experimentation purposes. You need to figure out a way to either throttle the power supply or turn its output full on and full off t o regulate the temperature, Then you also need to figure out how to measure the outflow air temperature and convert it into something that can be used to control the power supply. Just measure maximum power usage under simula ted worst case conditions before you settle on a production power source.

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Play with that.

I guess you can down load an app to use locally..

Jamie

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sounds like you need a bigger powersupply, (2A at 24V is only 48W) a weaker fan better thermal insulation a stronger heating element other factors that are not obvious or some combination of the above.

you will almost certainly also need a thermostat.

```--
umop apisdn

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You will need many more WATTS.

Jamie

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