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Hotbed for $18.25

Posted by Waiata 
Hotbed for $18.25
August 20, 2013 07:03PM
Hotbed for $18.25

I recently made a Hotbed for my printer, total cost $18.25
Naturally the concern was how good will it be and now having printed more than 30 components on it both in ABS and PLA “Well actually pretty Good”. Whilst this is not a new idea it is quite a lot cheaper than using the large wire wound metal frame resistors but it requires a little more work. Initially I thought that standard glass would break but because the heating is reasonably even this has proven not to be a problem.

Here’s the lowdown –

210mm x 210mm of 3mm standard window type glass $5.00

104 Metal Film 10 Ohm resistors from Jaycar $6.50

100 K thermistor from Element14 $6.75

All the10 Ohm resistors were evenly spaced out in a 8x13 format (see photo) and fastened to the glass using JB Weld. The thermistor was placed in reasonably close proximity to one of the resistors near the centre of the bed.

The resistors are connected 4 in series giving a resistance of 40 Ohms.
There are 26 rows of the 40 Ohm series.
Supply voltage is 13.5 Volts total resistance is 1.538 Ohms with a current of 8.77 Amps and a total wattage of 118.4 watts.
That’s 1.14 watts per resistor

With an insulated backing it can reach a temperature of 140 degrees C (Not bad for $18.25)
open | download - Hot_Bed.jpg (533.5 KB)
Re: Hotbed for $18.25
August 22, 2013 01:33AM
Nice work, looks very professionally done. The bonus of this home-made method is you can make any size bed you like and not be stuck to the std 214x214mm size.
Re: Hotbed for $18.25
August 27, 2013 01:36AM
Yeah, that does look kinda neat (I was about to say it looked cool, but I then realised the irony).
I agree with your calculations, but there's one that I think might end up causing some issues in future.
The resistors you've specified are 1/2 W resistors, and yet you've clearly (and correctly) stated you're pushing 1.14W from each one at max power! I suspect they might 'let out the magic smoke' in due course! In order to stay within the 0.5W rating, you'd have to limit your heater PWM duty cycle to about 30-40% which would limit the max avg power accordingly.

Personally, I'd have used a slightly different method...
Jaycar wire is marginally cheaper than your 104 * resistors. I'd also suspect it would heat up more 'evenly' along its length as opposed to just heating each individual resistor body. There would also be a lot less joints to make (104 resistors = 208 solder joints).
In order to attain about the same maximum wattage, you could cut it into 6 equal lengths of about 660mm (10.3275 ohms each) and parallel all 6 lengths across your 13.5V supply to give you a max of 120W heat.
The nichrome wire could possibly be directly attached to the bottom of the glass with some Kapton tape? (Unsure!)
The only 'difficult' part would be laying out the wire carefully (avoid shorting to itself) and laying it out to make connection of the supply as straightforward as possible (maybe positive on one side and negative on the other?)
Re: Hotbed for $18.25
August 29, 2013 02:43AM
Great way to build a custom size hot bed. Thanks for posting this smiling smiley


Richmond, New Zealand
Thingiverse ~ YouTube
Re: Hotbed for $18.25
September 03, 2013 12:51AM
A very simple solution Mr Waiata and sounds like it's working well. Very glad to hear you're printing up a storm with that printer.

For others who may not be as keen to DIY at that level My heatpads have been used directly stuck to glass sheets.
They cost another $20 but they have the thermistor embedded in them and all wired up.

Makershop - Reprap parts, adding new stock almost daily.
Re: Hotbed for $18.25
January 22, 2014 07:31AM
Nice work the only problem i see is the glass if its normal glass it will be very prone to temperature changes ie if its hot and you happen to put something cold on it it could shatter
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