Ghetto HBP
Description
Update: Made some measurements to help the designers out there. With three strips ganged together as in the PDF soldered in a long series trace across two stripboards the current at 12V is 10 amps cold and 8.2 amps hot. That gives you 120 Watts cold and 98 watts hot. So that means that the total resistance cold is 1.2 ohms, and individual strips have a resistance of 0.13 ohms. To calc. that I had to assume that the two wide buss strips were equivalent to 3 ganged central strips. So 0.13 per strip and about .04 ohms for each of the two wide strips on the outside.
So 4 ganged together should give about 0.13/4 * 9 = .3 ohms + 2*0.04 = .38 ohms per board or .38*2 = .76 ohms for a prusa bed giving 16 amps cold and 189 watts at 12V.
5 ganged together would be .13/5*7 = .182 ohms +2*.04 = .262 per board and .52 ohms total for the heated bed. Giving 23 amps at 12 V and 275 watts.
6 ganged might be "OK" for 5V at about .3 ohm and 17 amps (5V) but it might not get that hot at only 85 watts. (I'm thinking at 5 or 6 you will probably want to think about pairing the bus strips on the sides with a couple normal strips to keep the heat even across the board.
7 ganged would probably work pretty well at 5V at about .22 ohms 23 amps and 115 watts. (same here use 2 or 3 strips ganged with the wide bus on the side. )
Well, that was quite an extrapolation so don't trust the numbers too much way up in the 5,6,7 gang calculations.
Instructions
2. Solder the stripboard into a long series-parallel trace. For me it worked well to wire it up in groups of 3. Each trace is about 0.13 Ohm. There are 35 traces and two thick buss traces on each board. So if you wired it up as a single long trace one trace thick it would have about 9 ohms resistance and only generate about 16 watts. So I ganged 3 traces together and wired those in a long trace. Seems to heat up pretty well at 12V. Haven't printed on it yet as I'm still finalizing the Prusa.
3. Measure the resistance. As pictured in the PDF below the total resistance across two boards is 1.2 ohms. Giving 10 amps cold and 120 watts.
4. Calculate the current required.
5. compare to your power supply subtracting the load already in use.
6. If step 4 is less than step 5 cross your fingers and plug it in.
7. Enjoy
8. Still here? Want a 5V HBP? Try 7 strips ganged together or possibly 8. (at your own risk) A 24 V HBP? Maybe 2 ganged together or even single strip all the way through. None of these configurations is tested except the one described. (And even that I don't know exactly what temp you'll get. About 100 is my guess.)
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Made one for my Huxley.
Size 10x15cm. Single lane (no gangs), draw 2.8A when cold.
Using a very old PC Power supply that can do 3A on the 12V line.
Heats up to 95
°C measured on the copper, between 70°C and 80°C when kapton is placed.
My cross shaped warping test when well. I can now print ABS, thanks !
This concept could work nicely for experimenting with an addressable tiled bed. One that only heats the tiles under the actual print area and quickly cycles power to the tiles one at a time. The idea with cycling the power is that maybe the thermal mass is high enough to exchange longer heatup time for lower overall watt usage.
This is an interesting idea and a great example of using what you have lying around.
Note that for a given bed size, you want a specific number of watts. If you're using a lower voltage, you'll need proportionately more amps. for a 5V bed you'd want to put units in parallel to lower the resistance.
I find that for a Prusa printer (200x200mm) I want at least 200 watts. The "sta
ndard" Prusa HPB at 1.2 ohms running on 12v doesn't do it. At 12 volts it takes forever to get to sufficient temps for ABS printing and I find it impossible to maintain those temps with a fan blowing on the work piece.
I run mine at 18v, 15 amps for a total of 270 watts. This is perfect for my us
e. FWIW I have a 5mm piece of pyroceram glass over the HPB that I print on. It takes a while to heat that up even with 270 watts.
At 5 volts you'd want to be able to deliver at LEAST 25 amps, so you'd want to shoot for a 0.2 ohm load. And have a VERY hefty power supply, probably in excess of wh
at would be readily available.
At 12V a prusa sized platform using this concept with traces wired in gangs of four would probably give you between 20 and 30 amps for a 200-300 Watt heater. Problem will be finding a supply that will handle that much in addition to the motors and hot end. For instance the 500W PC power supply in my basement only does 22 amps total on the 12 volt lines. 5V line can handle up to 30 amps though, so that might work. Gangs of 5 or 6 would likely give the desired wattage. I don't have real good data yet on other configurations and the 0.1 ohm per strip is not a very precise measurement.
This is awesome. I just tried making one of these out of a piece of small stripboard (about 2"x3.5"), for a resistance of just under 1 ohm (hard to measure accurately that low, but the math matches pretty closely). You could wire several of these in series/parallel and attach them to the bottom of an aluminum sheet to make a decent heated platform. I got 30 pieces of this a while ago for 20 bucks (about 25% more per square inch, but it's cheaper to use what you've got), and this method may make it easier to make other sizes/shapes. I'm working on a machine that will need one just under 200x200mm, and this might be the way to do it.
License
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I haven't ordered anything from http://www.veroboard.com/ but it looks useful!