Heat Distribution on Heated Bed

[ex-egll]

What started off a week ago as as "simple" change to my Z offset (as noted in my Senior Moments thread) has taken me down the path of upgrading to Marlin RC-8, a short bout with repetier and back to Marlin.

Now the firmware is all in place, and most of the tuning is completed, I took a look at some of the hardware. My heated bed was slow to heat anywhere warmer than about 85 degrees. A little measuring showed it was only getting 10.8v at the bed. I was losing 1.2v (only had a 12v Supply, which did pump out 12 v even with the bed on) going through the Solid State relay, which dropped about 1v and another .2v was lost in about 4ft of 12ga wire. I had a 25 Amp 13.6 v power supply gathering dust, so that was pressed into use for the bed heater. In supplies 12.4 v at the heater. Heating was noticeably quicker now.

The problem I now have is uneven heating, not 3 or 4 degrees difference across the bed but more like 30 degrees from back to front! (back is where the power is connected) I looked at the back of the bed (the original Makerfarm 12x12 bed) and it looks to be in pristine condition. From what I can see the power "rails" run across the top in each direction from the input and down each side with "elements" joining them going across the board. I suspect there is a significant voltage drop along these power rails so the elements at the bottom pf the bed are getting way less the those at the top.

My thinking is to run a wire (12-14ga), from the input to the board, to a p(o)int at the end of the rails by scraping off a little of the red covering and soldering it. This should bring the voltage up a bit.

Good, Bad or Stupid idea?

Thoughts please