A HBP made from stripboard. The only trick is finding a supplier of large enough stripboard. I had to try it out before I sent boards out as prizes for the contest. http://www.thingiverse.com/thing:11497. Wouldn't be much of a prize if it didn't work. :) The PDF below is just my pathetic attempt to draw the solder connections I used to wire up the board.
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 + 20.04 = .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 .13/57 = .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.
Get some big stripboard. The only place I've found so far is electronics express. Here's the link. www.elexp.com/pro_pb16.htm. You want pb17. It's the biggest (9 inch x 4 inch). And it's cheap! ($2.65) You will need two side by side to cover a Mendel platform.
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.
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.
Calculate the current required.
compare to your power supply subtracting the load already in use.
If step 4 is less than step 5 cross your fingers and plug it in.
- 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.)