Taz extended bed heater options

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gghouck
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Location: Seward, Alaska

Taz extended bed heater options

Post by gghouck » Sat May 27, 2017 6:55 pm

I'm considering extending the bed of my Taz 4 to 450mm in the Y axis. My holdup at the time is with the bed heater. I priced one of the size I need and it came out to over $300. I've come up with a few options and need some advice on them:

1) Use a stock silicone heater and center it on the new glass bed, knowing the glass that extends past the heater will likely not be up to temp

2) Same as #1 but put a sheet of copper between the glass and the heater, hoping to spread the heat better at the risk of some issues with the copper and the glass expanding differently.

3) Use a copper plate for a bed and attaching a thin pei sheet to it, knowing this will add some weight over a glass bed.

4) Find a different type of heater that will work but is reasonably priced.

5) Any other suggestion....

gghouck
Posts: 197
Joined: Fri Oct 03, 2014 11:35 pm
Location: Seward, Alaska

Re: Taz extended bed heater options

Post by gghouck » Sun Jun 25, 2017 9:39 pm

Any help will be appreciated

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piercet
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Re: Taz extended bed heater options

Post by piercet » Mon Jun 26, 2017 11:07 am

Extending the heated bed to 450mm is a challenge due to the Rambo board. The Taz 12" bed is already very close to the limit of the Rambo power and the fuse in it. to go much bigger than that you need something like a solid state relay to turn the higher draw bed on and off as needed. You could take 4 mini style bed heaters for example, wire them in series and put one thermistor on the center of your bed, attach them to a separate power supply and use the relay to trigger the heater from the stock heated bed wires.

Glass is an insulator. It will not spread heat effectivly beyond the edges of the heater mat. If you are going bigger, go with an aluminum tooling plate (or a copper plate either is fine here) Eliminate the glass entirely and adhere the heater to the metal itself. PEI or buildtak goes on top of that. If you do it right, the metal bed should be lighter than the glass equievelent

gghouck
Posts: 197
Joined: Fri Oct 03, 2014 11:35 pm
Location: Seward, Alaska

Re: Taz extended bed heater options

Post by gghouck » Tue Jun 27, 2017 10:20 pm

OK, so my next question is does the Rambo limit the current when it gets near temp, or is it a pulse-width scenario? I'm guessing because it is controlled by a mosfet it pulse-width of sorts, and that is why only an SSR is needed.

Also, is silicone rubber designed for mold making appropriate for the bed? I am deciding between using two sheets of silicone rubber and bonding my element between them and pouring a mat with the element embedded in it.

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piercet
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Re: Taz extended bed heater options

Post by piercet » Wed Jun 28, 2017 9:28 am

I think it's Pulse width, but i'm not 100% sure. But a relay will usually work fine. There are more than a few people using large 120v car engine block heaters on separate power supplies and relays on RAMPS and Rambo boards out there.

Silicone rubber is usually going to be fine with the temperature range. There are specific "high temperature" silicons but you shouldn't need them in this case. If you are building your own composite element, you may consider putting a layer of insulating material on the bottom of the heater as well to increase efficiency.

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