Variable resistor in line with heated bed

I'm building a heated bed, it will draw more current than ramps will allow, so I was wondering about the effect of putting either a pot or just a single resistor in series to raise the resistance so I can drive it off ramps. I'm looking at a seven switch, but it would be nice to use the bed now.

The question is;I'm using resistance to make heat, so will the pot or resistor get astoundingly hot? I could work a single series resistor into the heating loop, thereby using its heat, but I sort of prefer the pot idea so I can tune.

Thanks
Ian

Ps, also, how would I choose a suitable pot with a range of 0 to 2 ohms?

Yes, the resistor will get very hot. As it's not got anywhere to radiate that heat like a heat bed (eg: an Alu or glass plate), it will most likely get hotter than the bed.

What do you expect the resistance of the bed to be? Can't you adjust the parameters of the bed design to increase its resistance?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Just get an SSR and be done with it.....

It needs to be about 1.4ohm if used with RAMPS and half that if with the seven switch. I have a cunning plan though. As I need to halve it, I'm going to have two heating loops in series and just disable one as necessary. I think that will do the trick

Quote
UkIan
I'm going to have two heating loops in series and just disable one as necessary.

Putting two loops in series would double the resistance. For halfing it, you'd use them in parallel.

That said, when you make a bed yourself there's no reason to do such tricks. Simply calculate wires/tracks properly and you're done. See [reprap.org] and [reprap.org]

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Yes, I currently have half the resistance I need, so was going to add a second loop in series

I think the trick *is* calculating the values correctly in the first place. I made a mistake somewhere, so I'm actually between where I want to be for direct replacement and where I want to be for more ampage :/