can I use hook 2 power supplies in parallel?

First, I'm a noob, I bought a reprap mendel prusa off craiglist a couple days ago. Did sprinter, pronterface and using slic3r.

So far, I've got everything running and calibrated all the axis, but i'm having trouble getting the print to adhere to the glass plate. I have ABS judging by the sooty flame when I light it. (great test btw to tell ABS from PLA).

I've looked and most people suggest kapton tape for ABS. so I ordered some, it will be here tomorrow. I'll be using hairspray on the glass for tonight's attempt.

The issue I'm having is with my heated bed (MK1). The temperature is only going up to 70C. From what I read it should be 110C. I added some cardboard insulation to the bottom of the heated board to help, but I think my main problem is my power supply. Its at 350 Watt converted computer supply. It puts out 12Volts, but when I have the extruder heater on and the bed heater on it drops to 10.6Volts. I'm thinking my power supply doesn't have the juice.

I have another AC/DC converter that outputs 12Volts, 4Amps. My question is can I hook them both up at the same time to the same terminals on my Sanguinololu to supply more amps? Let me know what you think. I know if it was batteries it would be OK, but with power supplies I'm not sure.

... you can try with wiring a small resistor (e.g. 0.1 Ohm / 5 Watts) from +12V of the smaller PS to the 'bigger one' driving the heated bed - check if the resistor gets too hot when drawing big currents ...

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Viktor
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Why do I need the resistor?

The simple answer is no, you can't parallel them.

The more detailed answer is that they are not adjustable for output. Which ever one is running the slightly higher voltage will put out all the current. You can't tweak them to be the same output voltage. If you could then a pair of low value resistors might help you share the current. More likely you still would have one hog all the current.

Better solution, use one for the 11A supply, use the other for the 5A input.

Best solution - spend $44 or so on a proper industrial 12V 30A supply.

... the idea behind coupling with the 0.1Ohm-resistor is that, when the voltage of the 'big' PS drops below 12V, then the 'small' PS could add some current.

Without drawing current the 0.1 Ohms between them should reduce weird things like overregulating or 'wobbling' because of wrong input-currents ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

If your machine requires 13 amps and you connect two perfectly matched (highly unlikely) power supplies in parallel, then each one would deliver half the load (6.5A), so you've already over-loaded your 4 Amp power supply.

It's a lot more likely that you need a 20A supply than that you need a 10A. The heated bed can easily pull 12A all by it's self. The hot end can add another 3 or 4A. Your motors probably use current as well (5 motors, two windings, some amount of power per winding ....)

To get the correct 12V from your original PSU you need to add a dummy load to the 5V rail. It then won't drop as much when you load the 12V rail.

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[www.hydraraptor.blogspot.com]

Let's set aside the workarounds for a moment.

Look at the OP's description. He's using a 350W power supply. Almost everything I've read says you need 400W or better. Most folks user 450W or better. So he's already at a deficit. Trying to force a 350 to generate 400+ watts of power is a fire waiting to happen.

However, I've seen several solutions, that are all very safe.
1. Get the correct sized power supply. Uncle_Bob, FTW.
2. Use a second power supply. - yes, this can be done. If you move the heatbed off the controller board, and run it independently, then the 350 has enough power for the printhead and motors. Just configure your software to run like there is no heatbed. If you need some measure of temperature control, you could install a rheostat on the heatbed. It's fuggly, but it would work.

My recommendation, to keep the control and eliminate the fire hazard, get the new power supply. You'll be glad you did.

Oh, and make sure that you are plugging into an outlet rated for that power. (you won't get 30A of power from a 15A house circuit)

Black Dragon, amperage at you household outlet is measured at 120 volts (in the US, varies in other countries) If therefore you have a 12 volt load, you can run 10 such loads of the amperage of your outlet safely, the actual draw in watts will be the same. Simply apply ohm's law. Nothing wrong with multiple PSUs. I'm using 2 and running a 120VAC heat bed.

30A at 120V = 3600W, so I don't think you're going to need that much power! P=I*V (Power = Current x Voltage) so at 12V you do need 30A to acheive 360W, but you only need 3A from the 120V side (well a bit more to account for inefficiency in the PSU).

Whoops. You both be right. My math was way off.
That will teach me to try to reply while doing four other things at once.