Turning a 12v heater into a 24v heater - Mod

[Plastifier]

For those wishing to upgrade to 24v, you can turn your 12v heater into a 24v by a quite simple hack, using a cutter and a solder iron.

The principle of this mod is based on keeping a constant power (producing same heating), and by reconfiguring the resistive heater tracks.

Here is the math:

- Power using 12v is noted P[12v], power using 24v is noted P and we keep it constant P[12v] = P[24v]

- Ohm law gives: U=RI, P=UI and P=U2/R (U2 is U squared, sorry for the notation)

- Constant P gives: U2 [12v] / R [12v] = U2 [24v] / R [24v] 

- We double the tension: U[24v] = 2 x U[12v] , we can substitute U2 [24v] by 4 x U2 [12v]

                      U2 [12v] / R [12v] = 4 x U2 [12v] / R [24v]

- Suprressing U2 [12v] on both side: 1 / R [12v] = 4 / R [24v] we finally got R [24v] = 4 x R [12v]

So, we must multiply the heater resistance by 4

Removing the cork layer protecting the adhesive resistive heater, we find 4 copper tracks conducting the current in //.

So this is equivalent to 4 resistors in // and R[heater] = R[onetrack] / 4

We must turn this R[heater] in resistor value by 4, that is the R[onetrack] value.

If we use 2 tracks in // we get half resistance value, and we combine 2 sets in serie, we get the R[onetrack] value.

In the 12v scheme, the 2 wires are soldered to each black bars. the mod is the following:

- Unsolder the wire connected to the left black strip

- Cut the right strip in the middle

- Solder the wire we unsoldered to the half right strip

You can use an ohm meter in the 12v configuration, before cutting the track, and after modding to check the resistance increase by 4.

It works great for me, and save me a valuable heater!

Jenn.

[Bryan Boettcher]

Which heater is this for, and do you have pictures?  That sounds like a great mod, good work.

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[Tony Shulthise]

Do you have any photographs of the mod?

[Plastifier]

 This is for M2 heater in 12v.

I modded mine some months ago, having an early model (Stainless steel & blue)

Sure. I'll plan to add some pics here very soon.

 

[Tony Shulthise]

Thanks.  I'm specifically interested in seeing exactly what you peal back and where you cut.  The right photo(s) would give enough detail to approach it with confidence.

[Erik Akia]

Since one of the big reasons to upgrade to the new 24 volt power supply is to be able to use a bigger bed heater that will heat up to ABS temperatures faster I thought I would point out that doing this modification does not raise the power of the heater but allows you to use the old heater on the new power supply. So you will have the same heat up times as before. Though I would imagine that the rambo would be happier with you.

Some one please correct me if I am wrong but I think the other reason to upgrade the power supply was to reduce the amperage to run the motors?

Was there any other reasons to upgrade?

Thanks
Erik

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[Dale Reed]

Erik,

Reducing the bed heater current is a major plus, judging from the number of people who have fried the Phoenix power connector on the back of the RAMBo board.  Pulling less current also reduces voltage drop in the wiring to the heater and (slightly) across the power semis on the board.  So I suspect there would be "more" (maybe not "noticeably more") power to the heater.

I've not been using ABS, so I don't need "more" power.  But just the "less current" aspect is enough for me.  So I've received my upgrade kit, just waiting for a couple free hours to put it in.

I too would like to see how the mod to the 12V silicone heater is done.  Never hurts to have a spare!

Dale

[Plastifier]

Using a higher voltage not only reduces the current value related to the resistive heater, it also enhances steppers actuation.

High current helps connector pins oxydation buildup, adding a resistive path, provoking the well-known Molex burning.

Here is a pic of the mod, showing the simple cut, splitting the upper orange pad.

I did not have to unsolder and solder, just using 2 wires, and unconnected the midpoint wires.

Jenn.

[Tony Shulthise]

So, you cut the trace under your "24V" label but it looks like you didn't cut it all the way across.  How did you get to the trace under the wire that is shown bridging under the 24V label?

Also, my heater has the full sheet of rubber UNDER the smaller rectangular rubber pads that go over the wires.  It looks like yours had the full sheet OVER those.  Or, did you just do a really neat job of cutting around them?  I'll attach a picture of mine here for reference.

Did the rubber peal off without pulling the circuit traces off or did you do something special to protect them?

Thanks again for this info!

[Plastifier]

Your full rubber heater is different from mine.

Being a M2 early adopter, I got an heater version having a cork layer pasted on top of the adhesive resistive heater.

I did this a long time ago, and I must bring some corrective explanation:

I removed some rubber on one of the bad just to check that the copper track was not continuous.

From here, I understood that the 4 wires revealed two independent resistive tracks.

So, you can connect them in serie or in //

The early M2 (until recently) has 12v PS, and the 2 tracks are connected in //, in order to get a low resistance.

The mod to have the heater fed with 24v is just to connect the 2 tracks in serie.

I chosed the solution to link the "unconnected" wires together.

So, your heater with full rubber protection having 4 wires should follow the same scheme.

Here is what you can do:

-Have the 4 wires unconnected

-Get an ohmmeter to identify the 2 independent circuits.

-Now just connect one wire of each circuit to have them in serie.

- And connect the 2 remaining wires to 24v.

You can have a resistance check by measuring the resistance of each circuit, let's say R value.

When you connect in serie you will get 2R (good for 24v), in // you will get R/2 (good for 12v).

I hope my explanations are now clearer!

Good modding.

[Tony Shulthise]

Gotcha.  Checking resistance and switching wiring to series should be easy enough.  Great tip!

[Plastifier]

Try it just for fun, perhaps. Which resistance values did you get? unconnected/parallel/serie.

[Tony Shulthise]

I haven't done it yet since I have the 24V bed already.  I'll make a note to try it tonight.  In the meantime, here's a pick of the 24V heater...

I made some mods to the bed to make it and the glass build plate attach magnetically.  After seeing the conductor pattern in your post I started second guessing where I drilled the holes.  I'm glad I checked because I probably would have shorted something out if I would have not checked.  Your post saved me some headaches ;-)

[Bryan Boettcher]

Wish I'd saved my 12V heater now.

[Tony Shulthise]

Below is a pic of my 12VDC bed heater with the trace cut to convert it to work with 24VDC power.  

I measured and recorded the resistance before and after trimming part of the trace away using an exacto knife.  

I hooked it up to a power supply to test.  My power supply doesn't have enough power to do the full 24 volts but at 18.6V and 4.9A the heater was getting up to around 120C and temps were very even everywhere I measured using a thermocouple.  

There's a small discrepancy between the power supply implied resistance (3.8 ohms) and the multimeter measurement (4.0 ohms) but the are close enough I suppose.  Also note that the resistance of the new M2 24VDC bed heater is 3.4 ohms which is significantly less.  That may mean that the modified 12VDC bed heater may take longer to heat up than the new one.

I don't know what gauge the wires are on the 12V system but now only two wires are being used.  They should be fine since the current should be less than before the mod since the resistance is more than twice as much.

Using the modified 12V heater may require a different calibration table.  I haven't actually tried it plugged into my M2.  If I get some time to try that I'll post results.

On Tuesday, March 25, 2014 6:36:49 PM UTC-4, Plastifier wrote:

Try it just for fun, perhaps. Which resistance values did you get? unconnected/parallel/series

[Dale Reed]

Tony,

As shown in your photo, tie off wires 1 and 2 so they are not connected to anything.  Connect wires 3 and 4 to the red connector for the M2 wiring harness.

Current will go from wire 3, around the traces to wire 2, which goes straight over to wire 1, back around the traces to wire 4.   Effective circuit is this:

 3  ------/\/\/\/\/\/-------- 2 ---1 -------/\/\/\/\/\/----  4

              12 volts                      12 volts

Hope that made sense.   Two heaters in series splitting the 24 volts evenly gives 12 volts per heater.

Before you cut the trace, the effective circuit was

3 ----+------/\/\/\/\/\/-------+---- 2

       |                         |

1--- -+------/\/\/\/\/\/------+-----4
                 12 volts

Two 12 volt heaters, in parallel.

Works for me.

Dale

[Plastifier]

Dale,

You put it very clearly in your graph,  the cut is to configure the 2 resistive path in serie.

@Tony

The resistance between 1 and 2 is actually in the 0 ohm vicinity, wires being soldered so close.

This is because resistance cannot be measured with an ohm meter in an accurate way, speaking of less than 1 ohm.

Even the digital meter wires resistance is taken in account! :-)

You would need to use a wheastone bridge method to get something a meaningful value. This is a accurate way to conduct this kind of measurement.

The 4 ohm is a ballpark figure for 24v, when 1 ohm was for 12v.

[Plastifier]