Power Supply for i3v 12 Kit

[Cameron]

Hi guys,

First post here but somewhat long time lurker.
Just ordered my i3v12 kit after way too many hours of study and deliberation and am super excited! Actually I guess it is a good thing that my research took so long as the 12" kit just came out.

It just occurred to me that I have a really nice Astron 35 Amp power supply that I use for all of my Amateur Radio gear (I actually have a spare). The radio gear runs off 12V, and this supply puts out a very stable 13.6V DC. It can handle 27 amps continuous and 35 at 50% duty.

That seems like a really good fit for a 12" kit. Now most circuits that I know of that can handle 12V can handle 13.6V, but do you guys know if there would be any problems using this to power my i3v12?

Thanks!

Cameron

[old man emu]

If 13.6V DC doesn't fry your 12V DC radio gear, then the printer should handle it. BUT!!! Ask Colin first. He's only an email away.

I might be wrong, but I seem to remember that the 12V supply is used mostly for the heated bed, and that supply now runs through a relay, so it doesn't actually touch the board. I don't know the construction of the board, but most have a little circuit that drops 12V to 5V, which is the usual operating voltage for things electronic. That circuit should handle 13.6V. But again, Ask Colin.

Read what Printbus said about power supply here: http://3dprintboard.com/showthread.p...ooby-questions

Old Man Emu

[ex-egll]

Hi Cameron, I can't answer your question, bur I will be following your progress as I will be putting in an order for the same kit in a couple of weeks. What electronics kit did you get?

By the way, you've given me a good idea on the PS, I too have a spare one lying around from an HF Transceiver I sold, 1-15v DC at 30 amps, you just saved me a few dollars!

[Cameron]

Colin didn't know.....

Hmmm.. Wish my PSU could change voltage to make sure. So far in my limited research, it looks like the extra volts might be nice for the heated bed.
As for the electronics, I went with the default.

Now to figure out if the default electronics was the smart thing to do??????? argh

[printbus]

Well, let's talk through this point by point. A 12V (or thereabouts) source is used in the printer to power the electronics, the motors, the fans, the hot end heater, and the heated bed.

By default electronics I assume you mean RAMPS. Arduino specifies the MEGA2560 board as good to 20V, and that spec likely applies to the clones being used here. The driving limit is really the power dissipation in the 5V regulator on the MEGA2560 board and not the voltage input, and there's not a lot of margin to begin with. Would it work? Maybe? For RAMPS, you can bypass any issue with power dissipation in the regulator by always having the printer USB port connected to a computer or USB charger; when 5V is applied to the USB the MEGA2560 board will use that as a 5V source instead of the 5V regulator. If you add any 5V load like a servo for bed leveling/compensation, you have this problem anyway. As I understand them, both RAMBO and RUMBA support a higher voltage input.

The motors are essentially managed through the adjustable stepper drivers on the electronics, so they likely aren't an issue. Power dissipation in the stepper drivers might be, however. You might watch for that and add a fan to the RAMPS area if the stepper driver heatsinks get very warm.

The fans are intended for use at 12V. Will they work at 13.6V? Probably, but maybe not as long? Depending on the fan, some are spec'd as good to 13.8V. I don't have a spec for the HXS fans included in my April-2014 era i3v-8.

The hot end heater is intended for 12V, but a slightly higher voltage will likely just get compensated for in the temperature control loop.

Then there's the heated bed. They're also intended for 12V. The temperature control loop will be able to adjust for the difference, but I'd be concerned on what your total current draw on the power supply turns out to be. I don't recall anyone measuring just the heated bed, but the total printer has been reported as drawing 27+ amps at 12V. Running 13.6V could put you over 30 amps. You may want to keep the wiring to the heated bed lighter gauge than you'd normally want in order to pick up some resistance/voltage drop in the wiring. You could always consider adding a high-current diode or two in the heater circuit in order to drop the voltage down some.

[old man emu]

Printbus,
Methinks we need a nice clear schematic on how to wire the PS, board, bed and extruder heater and extra fans. An Electronics 101 grade diagram would suffice.

Would you expand on this: " You may want to keep the wiring to the heated bed lighter gauge than you'd normally want in order to pick up some resistance/voltage drop in the wiring. You could always consider adding a high-current diode or two in the heater circuit in order to drop the voltage down some," please. I know where you are coming from, but others may not have got experience in using resistors to set voltages.

OME

[Cameron]

Thanks for talking through the points.
Yeah the electronics are RAMPS.

OK I wil probably play it safe and send USB 5V to the controller.

My PSU has a voltage and amp meter so I can monitor it pretty well as the machine runs so if it is looking like it is drawing too much for too long, I will know and can take measures.
This PSU is pretty heavy-duty. It weighs about 20 lbs and can handle a big load.

So my real worry could be the poe dissipation in the stpper drivers. I will monitor them with my infrared thermometer.

If the fans run a little bit faster with the extra 1.5ish volts, that will be OK. Fans are easy and cheap to source and replace.

I'll give it a try and see....

Here is the PSU:
http://www.aesham.com/transformer/astron-rs-35m/


Hmmm I just read that internally I can change the voltage!.
I guess I will take a look and see if I can dial that in before I hook anything up.
Awesome!!!!

[printbus]

Printbus,
Methinks we need a nice clear schematic on how to wire the PS, board, bed and extruder heater and extra fans. An Electronics 101 grade diagram would suffice.

You might remember this thread getting thrown together in a rush a while back - Clarifying i3/i3v heat bed and heat bed relay wiring. It covers a lot of it. After that initial panic, I'd meant to go back and clean up the drawings and the thread in general, but then MakerFarm complicated things by also offering printers using RAMBO and RUMBA electronics in addition to RAMPS.

Would you expand on this: " You may want to keep the wiring to the heated bed lighter gauge than you'd normally want in order to pick up some resistance/voltage drop in the wiring. You could always consider adding a high-current diode or two in the heater circuit in order to drop the voltage down some," please.

For anyone that wants it -

By rearranging ohm's law, we know that I=V/R, or current in amps equals voltage divided by resistance. The resistance of the heat bed may go up a bit as the circuit traces on the bed heat up, but it can generally be viewed as a fixed resistance. So, if we increase the voltage applied to the heat bed, the current will up proportionally. R is actually the total resistance in the circuit, including the heat bed itself, resistance in the wiring, and the contact resistance of the heat bed relay. In running heat beds on true 12V supplies, people have been using large gauge wire (AWG #12) in order to supply as much power as possible to the heat bed so that they will heat quickly. As I recall, threads have mentioned one 30A supply croaking and the terminals on a 35A supply melting with that load.

Looking at the I=V/R equation again, if we're using a 13.6 or 13.8V supply we can keep the current the same by increasing the resistance of the heater circuit. Since the resistance of the bed is somewhat fixed, you could do this by using a lighter gauge wire. Experimentation or research would have to determine what gauge would cancel out the effect of the higher voltage. The diode(s) essentially game the V term in the equation.

[Cameron]

OK mini victory. I pulled up a schematic for the PSU and found the pot that adjusts the voltage. Now I am at a steady 12.2V. I can live with that!