New heated bed with more power - cable cross section

Hi,

I upgraded to a new heated bed with a silicone heater with 300 Watts at 12V. Before I had about 200 Watts at 15V.

The cables have a cable cross section of 2,5 mm². Doing the math the new one will draw 25 Amps (old one 13,3 A).

The bed is well insulated and at 50°C its not on very often, so the cables don't heat up.

When the bed is set to 100°C the cables get a little bit wormer after a few minutes (about 30°C, room temp 24°C).

So my question is, is it still save to use 2,5mm² cables?

Yeah, you probably want to upgrade that. I recommend at least 10AWG (5.26 mm²). What's the length of wires? (from the heat bed to the power supply)

It won't be easy to replace cables in a silicon heater pad. They are crimped, i guess. Don't try to solder the cable.
I'd leave it as is. A 2.5mm² cable is good for up to 50A peak.

I'm a little confused now, because I got different recommendations.

I attached a sketch of my setup. The silicone heatbed cable is 2,5mm², length about 40cm.

The cable from the XT60 connector to the power supply is a 2,5mm² speaker cable. The length is approximately 120cm.

So the total length is about 1,6m.

Wouldn't it be useless to use bigger cables at one section, while leaving it at 2,5mm² at the silicone heated bed?

Also the manufactor chose an 2,5mm² cable for the heated silcone pad. Shouldn't this tell me that is is save to go with the 2,5mm²?

Edited 1 time(s). Last edit at 06/02/2017 04:39AM by h4nc.

First off- Get rid of the speaker wire.

2.5 (14AWG) is the bare minimum for a 2% voltage drop at ~25A. I may have been a little enthusiastic with my 5.26 (10AWG) estimate, but I like to add in a 20-50% buffer. Since you're replacing the speaker wire anyway, I suggest getting 3.31 (12AWG).

Some areas you don't want to skimp on wire size: constant-on, high-temp, and high current, such as bright lights, heating elements, and drive motors.

Thank you, could you explain what is wrong about speaker wires? I have a 4mm² here, so I could use this one. Again only the right side on my sketch.

Which cables should I get and what is the difference?

As a consence, I'd keep the 2.5mm² cable as short as possible and use bigger silicon-isolated wire to extend it to the controller ( same silicon wire for controller-PSU cable )
Solder the new wire to the heatbed wire in a save distance. Remember the heat from the bed heater is creeping up the cable, too.