Can i use a resistor to reduce amperage draw within a curciut

[c0mputerking]

I have an electrical inline heater used to heat fuel in my truck, it is designed for a 12V system, and is described as inherently self-limiting.

I am not exactly sure how this device limits itself, but it must just be some sort of fancy resistor?

Its specifications at max operating capacity are

12V @ 32A producing 384 Watts which should only temporarily be required

However my truck runs at 24V (NATO specification) with a 35A alternator. Each time i turn this device on my lights get dim and i can see my voltage drop considerably on the Volt gauge.

Already you might see my problem 24V through the same fancy resistor requires twice the amps to make the same amount of heat right?

I think i am asking my 35A alternator to produce 64A, guessing the batteries take up most of the slack but still!!! 64A

Is there a way to lower the amperage draw of this device by placing a resistor in series with this heater? if so what size of resister do i need?

 

[WGJ]

You'd need a 0.375 ohm resistor rated at something more than 384 watts, I think.

Bill

 

[patprimmer]

Or a second resistor in series.

Regards
Pat
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[patprimmer]

UUUMMMMM Dumb me

That is of course second heater in series

Regards
Pat
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[WGJ]

Yes, I should have said "in series".


Bill

 

[dgallup]

With what you have you are quadrupling the power dissipation. So instead of 384 watts it is pulling 1536 watts. I think it's going to burn up soon and maybe you with it. Is your battery a 24 volt battery or two 12 volt batteries in series? If you have two 12 volt batteries you could wire the heater to just run off one of them.

 

[c0mputerking]

Thanks everyone for all your infos this far

So from what i can see posted it should work with about 0.375 ohm resistor rated at 384 watts connected in series. That should effectively reduce the current load on my alternator by half? I will go to my elec supply shop and get one for testing.

What if i were to purchase another of the same device and connect it in series with this one?
Or i was thinking some electical heat tape of about 300 watts in series that way i would not be just wasting the heat but could wrap my fuel lines in it.

PS dgallup where are you getting 1536 watts seems a bit off to me. Yes it is 2 12V batteries in series just in case anyone else reads this drawing from one battery is always a bad idea causes a voltage differential and ruins both batteries if i am not mistaken

 

[DRWeig]

computerking,

dgallup is right. Power is V^2/R. You're doubling the voltage across your heater, which quadruples the power.

With the fix you're proposing, you'll have a second heater in series with the first, both putting out 384 watts of heat. Not very efficient, eh?

If you have somewhere else to use the heat, do it (heat trace cable is a thought, but that's a LOT of cable).

Best if you re-invest in a heater rated 24V for the power you need.

Goober Dave

 

[c0mputerking]

hmmm i do not think they make a 24V version of this heater however they do make a 12V @ 20A version. What if i were to get a couple of them, and hook them in series?

I have lots of volts (24V) and 2 huge 1000A batteries to work with, and for this system more heat is a good thing.

My only concern is reducing the current draw on the alternator.

 

[dgallup]

They make dual voltage alternators that put out both 12 & 24 volts, not sure how easy they are to come by & if you could install one.

Running off just one battery will discharge just that one. You could alternate which one you use. It would be a PITA but better than burning up.

You are currently creating a serious electrical overload.

 

[DRWeig]

12V x 20A = 240W

If you put two in series, they'll total 480W with 24V end to end.

If you put just 24V across one, it'll draw 40A and dissipate 960W.

Good luck!

Goober Dave

 

[c0mputerking]

Here is a bit of a description of the heater this is the standard version i of course went with the mega which is 32A as discussed in previous posts

Uses solid state, advanced heating technology with inherent self-limiting function.

approx. 20A max. amperage draw, 240W@12V,

 

[c0mputerking]

Looks like 2 of the standard versions in series would work quite well! but still a bit confused.

Would be 12v@20A twice, but in series that would double the Volts 24V which i want!

Also in series the Amps stay the same right 20A? which alternator should handle fine.

Extra watts are also a good thing as this would make more heat for me 480W right?

Then when the self limiter kicks in the amps should drop even more right?

 

[c0mputerking]

The heating device in question is a PTC type limiting device just for some more background infos, and thanks again for everyones help so far.

PTC ceramic: This material is named for its Positive Thermal Coefficient of resistivity. Most ceramics have a negative coefficient; most metals, a positive one. While metals do become slightly more resistive at higher temperatures, this class of ceramics (often barium titanate and lead titanate composites) has a highly nonlinear thermal response, so that it becomes extremely resistive above a composition-dependent threshold temperature. This behavior causes the material to act as its own thermostat, since current passes when it is cool, and does not when it is hot.

 

[patprimmer]

Well then why does it draw to much current on 24 volts.

Regards
Pat
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[c0mputerking]

Not sure but wouldn't 24V generate half the resistance through the same substance thus increasing the current flow????

 

[patprimmer]

The resistance wont change directly because of volts. The more volts pushes more amps through the same resistance.

This is starting to get real repetitive and real boring.

Are you actually any sort of engineer.

Did you even pass high school physics

Regards
Pat
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[c0mputerking]

Thanks.

 

[WGJ]

PTC materials have what is called a Curie Temperature.

At this temperature, the material undergoes a structural change which results in a massive change to its electrical resistance.
So, if the PTC can't dissipate the heat generated by the flow of current, the Curie temp will be reached fairly quickly, at which point there is a massive rise in electrical resistance and the temperature of the PTC stabilises, along with the current flowing.

Bill

 

[waross]

Heat loss by both radiation and flowing fuel may be keeping the heater below the limiting temperature. Note that this is temperature limiting, not power limiting or current limiting.
Go with two 20 Amp models in series.

Bill
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