PCB Heat Bed Resitance

If some one has a PCB heat bed that was manufactured with too high of a resistance, what do you guys think about shorting some traces to reduce the resistance? If feasible, I guess it would have to be done in such a way as to minimize interruption of heat distribution.

The shorted tracks won't heat.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Sure, anybody know how bad that would effect things?

It might be ok if you put a heat spreader (aluminum foil) between your PCB and glass. Just dont short anything to the aluminum foil...

Which bed do you have? What is your resistance? Lets do some math first.

If you made an adjustable grid arrangement, you could adjust the bed arrangement to compensate. Say you have 20 elements. Arranged 5x4, you have 5 parallel elements in 4 series, for a lower total resistance. Reconfigure with cuts/jumpers to 4x5, and you have 4 parallel in 5 series, for a higher total resistance.
With enough elements and an easy arrangement for adjustment, you could fine tune the configuration across a broad range and still get complete heating.
But it's really marginal to bother doing this vs just get the resistance nominally correct and adjust in the power supply for fine tuning.

Depends on the resistor; what are you using? If you are are using a standard MK2 bed then you have 4 resistor going in parallel.

It was another guy who had an out of spec bed, so I'm not quite sure what his actual resistance was. If I remember correctly, it was a MK2. Aren't the resistors on the bed just for the LEDs, not actually in the current flow path for the bed it's self?

Wait what? You add some resistors if you want to use the LEDs, yes. But the board is a giant resistor. The resistor dissipates heat; if you change the resistor's value you change the amount of heat dissipation.

If I were desperate and didn't want to buy a new board because the resistance was too high I would use sand paper.
The resistance is a function on how the "wire size" width and length are set; the height is supposed to be 35µm. So technically if you use a fine grade sand paper you could reduce the resistance back to 1.0 Ohm.

That solution would remove the protective layer of the PCB; kind of dangerous as most people wouldn't bother recoating it. So don't do it.

I don't follow the logic, taking away material would normally cause increased resistance.

You are correct, I was trying to go the other way; Forgot the original problem.

There is a tolerance on all things. That includes the amount of copper on a pcb layer. Most processes are optimized to deliver some minimum amount of copper to meet a spec. In the case of "low cost" processes that's a pretty low spec. The real answer is to have multiple layouts and match them up to what the supplier is doing.

Yes, I know, that's not easy at all. Yes I lay out pc boards as part of my real job....

So wider or narrower traces of the same pattern based on the thickness of the copper coming from the manufacture?

uncle_bob Wrote:
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> There is a tolerance on all things. That includes
> the amount of copper on a pcb layer. Most
> processes are optimized to deliver some minimum
> amount of copper to meet a spec. In the case of
> "low cost" processes that's a pretty low spec. The
> real answer is to have multiple layouts and match
> them up to what the supplier is doing.
>
> Yes, I know, that's not easy at all. Yes I lay out
> pc boards as part of my real job....

Actually the solution is to use a board with rolled copper for the surfaces. That way you can contorl the thickness much better than with a plating process. If you go into the doc's on the heated bed layout it's pretty specific about this.

About the only real solution for a high resistance bed is to feed it a higher voltage. What ever gets you into the 120 to 150W range the "right" voltage for your bed. The rest of your electroincs may or may not like what ever voltage that happens to be....