Dual power supply (relay?)

Hello,

I am running a prusa I3, ramps 1.4 arduino package with a relay to power heated bed.

I cant seem to find any spot on discussion about this topic, hence this post.The printer has been working fine up to the point where I need to crank up to 110c for ABS

I have attached specs on power supply.

Relay attaches to D8, and the firmware is set to run in bang bang mode.

I have used cardboard as an insulator from the aluminum y plate below, and seems to work fine. I can hit around 100, but upon removing heated bed cover (cardboard) the temperature drops about 10c and never returns (full output). The bed is a large 8.4 x 12.6 PCB link below

[www.makerfarm.com]

I have a spare ATX PSU that I can use. How can I go about either:
1) Squeezing more power to heated bed
2) Hooking up two power supplies to ramps / relay?

Thanks

Have you measured the voltage across the terminals of the heated bed when it is on? The first thing to check is that you really are getting close to 12V there.

A simple way of getting more power to the heated bed is to use a 12V LED power supply turned up to 14 to 15V. 14V will hive you 36% more power. If you use the same power supply to power the Ramps and you have an LCD or anything else with a significant current draw connected to the 5V rail, then you will need to use an external 5V supply or regulator to avoid overheating the regulator on the Arduino.

ATX psus normally have the 0V outputs connected to mains ground, so they can't be connected in series without modifications.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Mean Well power supplies like the one you linked have trimpots next to the output terminals to adjust the voltage. The spec sheet says that the SE-350-12 can be cranked up to 13.5V, which may make a difference. The big question is how your RAMPS board will handle the higher voltages. I don't use one, but have heard that there's concerns if your voltage exceeds +12.00001 volts. If you can get a stable +12V out of your ATX power supply, you could run the +12V to your RAMPS from that but feed power to the heatbed from the Mean Well SE-350-12 through your relay with the voltage cranked up. (Be careful with the trimpot, they are fragile.)

My SeeMeCNC Onyx 300mm diameter heatbed has about the same power draw/curve as the MakerFarm one you linked above. When I was running it from 12V, I had to throw a magazine over the glass and wait 30-40 minutes while it struggled to reach 110C. I bought a Mean Well SE-600-24 (24V, 600W) power supply, and turned it down to 19.5V on the trimpot. I was already using an external SSR and heat sink, so this power supply drives the bed at 19.5V. To power my 32-bit controller board, I picked up a 24V->12V buck converter from Amazon:

http://www.amazon.com/gp/product/B00BWKXTUU/

The net result is that my heated bed is running from 19.5V, the controller is being fed a regulated 12V with enough overhead to run triple extruders if I wanted to, and I only need one power plug to a wall outlet. Granted, my wallet is $120 lighter, but you can't put a price on a heatbed that goes from 20C->110C in 6 minutes without insulation and has no problem holding (or even overshooting) 110C.....

Edited 2 time(s). Last edit at 02/14/2015 10:01AM by vreihen.

The cheap 12V Chinese LED PSUs generally go up to at least 14V. You can safely feed up to 15V to the Ardiuno/RAMPS combo if you are not running an LCD or anything else from the 5V rail. But you said you were using a relay, and if the relay coil is powered from 5V then you may already be overloading the Arduino voltage regulator with 12V input.

You should preferably put three IN4001 or similar diodes in series with the fan(s) to drop the fan voltage back to 12V.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hey guys thanks for the quick response:

Results are:

11.92v @ PSU terminals going to relay
11.94v @ PSU terminals going to ramps

11.70v at relay and 11.30 at bed running max
11.92 at D8

I'm reading a 11.89amp draw from bed at terminals, and only 4 amp draw from ramps when extruder kicks on. I don't really trust these readings as it is only a 10amp max multi meter.

.4 amp draw from d8 to relay

Upon inspection of wiring there is by default 16ga from bed to relay. Then 14 GA from relay to PSU on V- wire. I put 16 GA on V+ by accident. (This project has been months of moving this, rewire that so something like this was bound to happen)

Could this be the voltage drop? I'm going to store to pick up thicker wire possibly 10-12 gauge.

But it seems if there is only a 12 amp draw at max power on bed and a 4 amp draw from ramps with extruder on, I should have sufficient power, or am I being current limited by my gauge of wire to bed & ramps.

Wire to bed is warm but by no means hot.

I am really liking the idea if stepping Up the psu to a 450w 37-40amp. Or larger.

Sorry if I can't provide enough accurate information, I'm not an electrician.

Thanks again for the help

According to the spec sheet link you posted above, the heatbed should be drawing 17A when cold. You can measure the actual resistance across the terminals of the cold heatbed, and use Ohm's law to see how many amps your exact heatbed should be drawing at your measured input voltage. It may be that your heatbed has too high of a resistance. There are several posts for how to do this and interpret the results.....