Defroster grid replacement

[Mikes Z car]

I am replacing the defroster grid on my 240Z with the vertical lines using the Frostfighter 2616 kit by turning the kit 90 degrees so it is vertical. Could someone please measure the current draw to a working rear defroster grid for a 240Z with vertical lines so I can verify the new installation won't overload the 240Z wiring?

I plan on epoxying the brass bus bars to the glass instead of using the double sided tape provided and I plan on soldering all of the grid lines to the bus bars if that is practical. Also, the factory instructions call for 4 runs with 4 lines in each run with a minimum run length of 40" (and a max of 61.5") which is too big for a Z. To get around this I plan on six runs with 3 lines in each run to keep above the minimum run length total of 160" (4X40")- see drawing. On my car six runs will give 6X27" or 162". This will give 18 grid lines which are two less than stock however if I follow the kit plan for grid spacing between lines the width covered will wind up within 1/4" of the original defroster grid area. Turning this install idea 90 degrees so the lines are horizontal should make it fit a 280Z grid area as the total run length will then be 216" (6X36" the width of the back glass) which is within the maximum total run length of 246" (4X61.5"). Installing with six runs will require cutting the brass bus bars that come in the kit. My defroster grid is dead including the painted on bus bars. I figure solid metal conductors may last longer than the original grid.

They make craft type narrow copper tape but I didn't want to try that.

Thanks in advance for any assistance or ideas!

Mike

[SteveJ]

What is the minimum number of gridlines that Frostfighters will support? Three seems kind of low at first blush. If you lose one gridline, the current through the other 2 will go up significantly.

[Zed Head]

You could put a small rheostat in line somewhere and adjust it up until you get desired performance. Or get a few resistors and do trial and error to see what you need. That way you can just go for it and make it work, but still be safe on the wiring. Plus, the heater circuit might already have a fuse in-line, or you could/should add one.

[Mikes Z car]

SteveJ, The Frostfighter can use one gridline but as Zed Head said you would have to use resistors to limit current. If you make that one gridline long enough (160"-246") by zigzagging you don't need resistors. Soldering the gridlines to the bus bars should eliminate grid line failures.

Zed Head you are right resistors could make almost any configuration work including doing the install as intended by Frostfighter. The 2616 kit comes with a 20A fuse though I already have a 20A fuse in the defroster circuit. It looked like that that is what it is for as the PO changed the wiring. I am amazed that it seems smaller gauge wires are allowed to handle more current in a car than what you would find in a house. 14 or 16 gauge gauge wires with a 20 A fuse? I don't understand that philosphy.

Mike

[Mikes Z car]

I finished replacing the back hatch vertical defrost lines on my 240Z using the Frostfighter 2616 kit. I am not affiliated with Frostfighter in any way.

http://www.frostfighter.com/prt2600.htm

The 240Z hatch glass is too narrow for the 2616 kit as sold because the kit requires a minimum glass width of 40 inches. This is easily overcome by increasing the number of runs used in the kit from 4 to 6. For a 240Z with vertical lines the kit can be installed with lines running up and down instead of sideways like the kit was designed for. I installed the new lines on top of the old ones since I could not remove the old ones. I used 4 lines for 6 runs giving 24 defroster grid lines, 4 more than stock for the vertical grid back hatch. If you use 3 lines per run for 6 runs this gives 18 total lines, two less than the original number of lines on a vertical grid 240Z. If you go the 18 line route the kit will provide enough bus bars and other material as is however I wanted to increase the total number of lines to 24 which required two additional bus bars which I made from the flat metal bar that came from the paper part of a hanging file folder. Be certain when cutting bus bars from the kit that you cut them so that the two connectors on the short bus bars are at the top outside for the car wiring to access. The hanging file bars solder well, cut easily with tin snips and are the same thickness as the bus bars that come with the kit though a bit narrower. I attached those with double sided carpet tape (must be better tape somewhere) though I used a tiny drop of epoxy at both ends of all bus bars for further mechanical security. I drew 4 lines on the outside of the hatch glass where the 4 new grid lines were going to go as a guide; two were on each side of the existing grid. I put the other new grid lines on top of the old ones. The high resistance of the failed existing grid lines guaranteed they would not interfere with the new lines and they don't interfere as indicated by consistent voltage measurements between adjacent bus bars at the top of the hatch while the grid is in operation. The installation process described here will also work on horizontal line 240Zs and 280Zs by installing the defrost lines horizontally, see drawings.

I scraped off the existing grid lines and bus bars with a razor blade so that they looked shiny to make the adhesive stick better as I put new grid lines on top of the old lines and used double sided tape on top of the existing bus bars. I unrolled the four paper rolls with the conductors and re-rolled them the opposite way to take the curl out. I hung them by one end from the side of the fridge for further flattening. I taped popsicle sticks flat against the rubber where the bus bars were going to go to space the bars out from the rubber. This differs with the instructions which call for 1/4" spacing but I though the bus bars would look closer to stock if they were closer to the rubber. I taped colored post it paper to the hatch metal next to where the bus bars were going to go including gaps in the paper to correspond with gaps between the new bus bars to keep the location and length of the bus bars straight. I used four bars at the top and 3 at the bottom of the hatch. The 3 at the bottom and the 2 inside bars at the top were all the same size; just longer than the spacing of 8 existing grid lines. The 2 outside bus bars at the top were just longer than spanning 4 grid lines. I used the kit bus bars and finisher cover at the bottom of the hatch as the driver would see those in case the hanging file bus bars used at the top would not look as nice. The kit calls for installing the grid lines so they go under the bus bars but I did not do that to prevent the possibility of a short between the new grid lines and the existing bus bars. I could have put the grid lines under the new bus conductor bars as the instructions call for if I had moved the bars further from the edge of the glass to avoid possible contact with the old bus bars though this might not have looked as nice. I soldered all connections between the grid lines and the bus bars for a solid connection though the instructions do not call for this. I feel soldering these connections is a significant improvement in the installation process.

I tested the installation by connecting the grid to a 12 volt power supply rated for 19 amps. The glass got hot enough all over the grid after 20 minutes that I did not want to leave my hands on it. I also verified proper current flow by measuring the voltage between adjacent bus bars at the top of the window to ensure consistent voltage reading; all 3 readings were about 4.1 volts. I have enough defroster grid line material left over to replace more than 5 entire grid lines should that be needed. Any repairs can be soldered as the grid lines are largely copper.

07 Tech info.txt

[SteveJ]

Hot to the touch? Maybe 4 runs of 6 would reduce the current through each line.

Thanks for the detailed write-up.

[Mikes Z car]

SteveJ, you are welcome for the write up. The attached drawing shows the minimum kit grid line length next to the modified layout I did to achieve that with the runs straightened out to make them easier to see. The bars at the end of each run represent the bus bars. Since the 240Z window vertical grid lines are approximately 26.5" each run you need 6 of them. If you use 4 runs the total grid line length is too short and you will have more current flow than the kit was designed for as shorter total length lowers resistance with resulting increase in current. The easiest way to reduce current if that is desired is to use 6 runs of 3 grid lines each run instead of the 4 grid lines that I used. Using three lines instead of 4 calculates to give 11.8 A. Note that the 15.7A with my setup is what you would get using the kit as designed on a 40" width hatch window so it should not be a problem.

The total grid length has to be in the range of 160" to 246" whether you use 4 or 3 grid lines in parallel for all of the runs. Shorter than 160" and the grid will be hotter than the manufacturer designed, longer than 246" and the grid will be cooler than the manufacturer intended. Hope this helps.

Mike