# Ghetto HBP

## by bryanandaimee, published Oct 20, 2011

Ghetto HBP Oct 20, 2011

## Description

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.

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Ive tried another approach using a high density PCB with lots and lots of parellel traces... and managed to get it up to 30 Ohm resistance (oh boy): that works out at 0.4 amps or 0.8 amps depending how its wired up (which in turn works out at 4.8W or 9.6W depending on how the PCB is wired)

Reckon that's too low to do the heating?
Aww the PLA's great - prints without heating at all xD (in fact, some say it prints bettwer without heating xD)

Anyways - I'll look into it. I've got a ready supply of stripboard - so doubling up again won't be too heard (though I've not got a lot of space inside.)

I've also got a couple of grip heaters (which I gracefully rejected upon realising they have horrific design and will put a live current through my aluminium bed (I have insulation measures but I'm not putting these anywhere near it: they're from some yung hung low unbranded workshop and have all the engineering precautions of a rock on a stick)

Ganging up additional boards is probably the best option: I'll look into it xD
100x100 is about 1/4 the area of a regular prusa bed. You need about 120 W to heat that so 30W might be adequate. Less than that and you'll likely have trouble with ABS. You would still likely be OK for PLA. You could try making the heated bed double sided if you still want less wattage. Just tape another stripboard to the back and make it twice the resistance. Or a 2.5 ohm 25 W resistor. Or get a bigger supply. :)

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## Instructions

1. 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.

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.

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.)

#### Size

Im having problems with getting the resistance high enoug to avoid overloading the psu - any suggestions? The longest possible trace is currently being used but im 3 ohms away from the target current.

Take it shoving a resistor at one end will cause uneven heating?
bryanandaimee - in reply to cprobertson1
Adding a resistor in series won't cause uneven heating but it would likely need to be a very high power resistor. For instance if you are running the heater at 5 amps then a 3 ohm resistor would need to dissipate 75 watts. What is your target current and resistance? What voltage? I'm just guessing, but either you are using a very small board, or your psu is underpowered.
cprobertson1 - in reply to bryanandaimee
Both! Small AND underpowered! Muahahaha!

Its for the Printrbot Simple (sorry, was on my phone when I sent the first text and missed out a lot of the info to save time xD) and thus is only to heat a small area (the printbed is about 120 x 200mm and the actual print area is 100x100mm so i've not a lot of space to work with)

The power supply is from a laptop and is going via the PrintrBoard: 12V 6A

Stripboard (2 strips - single trace: covering most (about 80%) of the underside of the printbed) is sitting at 2.4 Ohms giving a current draw of 5 Amps which doesn't leave a lot for the hot end to play with (though I don't have an accurate read on the printers current draw)

To summarise:
Stripboard resistance = 2.4 Ohms
Supply Voltage = 12 V
Stripboard current draw = 5 Amps
Stripboard target current draw = 2 Amps (Rating of the thermal fuses though I can cheat if required)
Current Stripboard Power Draw = 60W
Available current = 6 Amps*

*I can alternativelyt set up an arduino based control circuit: but the printrboard already has all that in it which is why I was trying to use it's built in capabilities xD**

** I've just discovered that the pritnrbot without a heatbed draws 5-6 Amps so I'll need to upgrade the power supply anyway by the looks of things - or - work out a separate circuit (which shouldn't be too hard: I have a box of around 20 arduino nanos so I can use one of them without bother xD)
cprobertson1 - in reply to cprobertson1
Ive tried another approach using a high density PCB with lots and lots of parellel traces... and managed to get it up to 30 Ohm resistance (oh boy): that works out at 0.4 amps or 0.8 amps depending how its wired up (which in turn works out at 4.8W or 9.6W depending on how the PCB is wired)

Reckon that's too low to do the heating?
bryanandaimee - in reply to cprobertson1
100x100 is about 1/4 the area of a regular prusa bed. You need about 120 W to heat that so 30W might be adequate. Less than that and you'll likely have trouble with ABS. You would still likely be OK for PLA. You could try making the heated bed double sided if you still want less wattage. Just tape another stripboard to the back and make it twice the resistance. Or a 2.5 ohm 25 W resistor. Or get a bigger supply. :)
cprobertson1 - in reply to bryanandaimee
Aww the PLA's great - prints without heating at all xD (in fact, some say it prints bettwer without heating xD)

Anyways - I'll look into it. I've got a ready supply of stripboard - so doubling up again won't be too heard (though I've not got a lot of space inside.)

I've also got a couple of grip heaters (which I gracefully rejected upon realising they have horrific design and will put a live current through my aluminium bed (I have insulation measures but I'm not putting these anywhere near it: they're from some yung hung low unbranded workshop and have all the engineering precautions of a rock on a stick)

Ganging up additional boards is probably the best option: I'll look into it xD
Thanks for this! I made a video showing how I made a version to heat a 300mm x 300mm bed. You can check out my make of this to see it. Total cost: ~\$15
Thanks. That's just the kind of thing I'm looking for. Made a small one as the base heater for a yoghurt-maker.
One question though: Plugging mine directly into a power supply, tends to trip or blow them. Is there something I can do to prevent that from happening?
bryanandaimee - in reply to Dylanvdb
What size board did you use? Did you use a single long track or gang the strips? If you ganged the strips, you could try it as a single long strip. If you use a lower voltage power supply that will lower the current. Or just use a higher current supply.
Dylanvdb - in reply to bryanandaimee
The board is about a half a full strip-board (a square half). Yeah I 3-way ganged the strips - well actually more like divided the surface into three areas each with a single track, so basically like three separate resistors in parallel. Heated surprisingly well though. Suppose it's behaving more like three short circuits in parallel. Anyways, when the Yoghurt maker is finally cranking; I'm totally calling it a remix of this! On to do some math...
bryanandaimee - in reply to Dylanvdb
That's probably way lower resistance than you want, and probably drawing a grundle of amps. You could try wiring the ganged strips in series. Even then it might be a bit overkill for a little 4x4 heater. It would heat very fast though if the power supply can handle it. Another reason to rewire might be safety. A single ganged serial heater might hit equilibrium at a more reasonable temperature and that would add a safety factor if your temperature control system malfunctions. You don't want to end up with a fire just because your thermistor wires get loose.
I haven't ordered anything from veroboard.com/ but it looks useful!

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
Ã‚Â°C measured on the copper, between 70Ã‚Â°C and 80Ã‚Â°C when kapton is placed.

My cross shaped warping test when well. I can now print ABS, thanks !
Anonymous - in reply to DeuxVis
Awesome! I'm glad it worked for you.
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.
That sounds like quite the project. Good luck:)
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