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Old 12-29-2015, 01:20 PM   #6 (permalink)
oil pan 4
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This is a fraction of the size of a rear window defroster.
If it draws 10 amps it will eventually burn up the grids.

This is what happened this morning:
I called the Planned Products LLC (the frost fighter company) to order more little parts to I can use the left over grid to put a defroster on the passenger side rear glass of my suburban.

I told them I chopped up their system and put it in a passenger vehicle.
Their response was because I was calling to order parts.
Apparently these grids will burn up if you run them for extended time with no current limiting. They always get calls when this happens.
So don't do that.
Apparently there is a fine line between disaster and success. These grids hooked up to straight vehicle power with no current limiting, a 1.3 ohm grid on 14 volts would draw around 10.8 amps. According to their specifications I should limit my grid to 8.8 amps (0.44 watts per absolute inch of grid line).
Adding the 0.3ohm resistor to the grid with battery voltage at 12 volts will limit amps to 7.5, running it at 14 volts, engine on will limit it to 8.8 amps.
So according to the frost fighter parts/tech support people the extra 2 amps you get form no current limiting is enough to fry it.

Then when I told them I used their technical specifications to calculate the amount of wattage needed per inch of grid then scaled it down to my application they were pretty surprised, they have never seen any one do that.

$15 for parts plus shipping got me enough bits and pieces to use up the rest of the grid on my suburban side glass.


Here is where I believe most people go wrong when they go off book. They look at the rear defroster and see the grids go straight across and copy that. These grid lines are too thick to do that.
Just wiring these grids straight across is a recipe for disaster.
You want to double the distance the current has to travel.



I am thinking I would like to retain use of the incorrect configuration, where power is wired straight to the grids.
Put it on a ToF relay, a time to off relay and set it so it can only draw full power for maybe 20 or 30 seconds then the relay times out and switches power through the resistor.
The High setting would likely be used for snow and blizzard conditions like what we had here last weekend.
(so much for man made globul warming soon making snowy winters a thing of the past)
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Last edited by oil pan 4; 12-29-2015 at 01:26 PM..
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