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Hotbed question

Posted by davedavedave 
Hotbed question
May 20, 2015 05:03PM
Hi I have a question regarding installation of hotbeds. so ive seen they vary in sizes and my printbed is about 16 by 16 inches in both the x and y direction. so I was wondering if I could get 4, 4 inch hotbeds and solder them together to make a 16 inch hot bed? since they will probably be drawing the same amount as if it were a 16 inch hotbed. the thermistors could all be soldered together or something like that. I understand that this might be one of the dumbest questions out there but if I am right I might win the nobel prize or a trip to the hospital. thanks for your time
Re: Hotbed question
May 20, 2015 05:50PM
Solder them in series and you will need higher voltage same amps, solder them in parallel and will use same voltage but higher amps. You can't connect the thermistors together, you will use only one unless you use thermocouples.

Do not connect this setting to the board directly use an SSR.
Re: Hotbed question
May 20, 2015 08:30PM
How would I solder them in parallel? I also have no clue what an ssr is but am searching up the term. so this is the bed I want to use. the 3rd wattage chart titled "Square/Rectangular SRMU Heat Blankets (4" to 8" Width)" shows the wattage. I will be using the first option (4 inch width 4 inch length) if it is possible. Link to heatbed chart
Re: Hotbed question
May 20, 2015 08:44PM
SSR solid state relay.

Parallel: all red wires solder together, all blacks solder together.

Serie: black-red-black-red.
Re: Hotbed question
May 20, 2015 08:50PM
My advise:

Go to Aliexpress and get a custom made silicone heater to the total size you want and get it for 110 volts AC, and use the SSR to turn it on and off. I get one for a total of 50 dollars.
Re: Hotbed question
May 20, 2015 08:54PM
I ordered with this vendor: Shenzhen Ali Brother Technology Co., Ltd. They are really nice people that will answer all your questions and will do whatever you ask them to do.
Re: Hotbed question
May 20, 2015 10:56PM
Those heaters are pricey... 4"x4" 10W/in2 = $26 each.

8"x8" (200x200mm) is a common size, so you should be able to get those cheap off e.g. AliExpress, and use 4 of them.

I think if it was me, I'd have a switch on all except the 'home' heated pad so that they could be enabled/disabled individually, so that if you're only doing an 8x8 print you can turn 3 of them off and save some electricity.

Maybe only use the thermistor on the 'home' pad as the sole temperature sensor, and assume that the other 3 were close enough in temperature?

But, given you don't appear to be up to speed with electrical wiring, I agree with @ggherbaz and suggest you get a custom 16x16 pad made for you.
Re: Hotbed question
May 21, 2015 01:42AM
Another dumb question from me:

On all Pictures I´ve seen, the Prusa MK3 heatbed ( black) was mounted with the solderpads on top and the aluminum side was bottom.
How would you solder 4pcs. together? Where would you put the cables?

Or is it save to turn these heatbeds upside down?
Re: Hotbed question
May 21, 2015 03:13PM
The aluminum plate on the Mk3 is for support because older Mk2 will bow in the middle. You can't flip them because you will be heating air, they are intended to be use with a glass sheet.

As to how you will manage the wiring, pretty simple, all connectors should face outwards the built plate like 2 facing the front and 2 facing the back or side to side. And the using appropriate gauged wires you connect them from under the built plate or at the SSR output.

Edited 1 time(s). Last edit at 05/21/2015 03:13PM by ggherbaz.
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