RAMPS 1.3 and Heat Bed Connection?

Hi, so I have a heat bed coming soon and I want to nail down a couple of things first so I don't fry myself or the electronic. I want to replace the old setup(single 12V 5A PS) with a PC power supply that has 18A to power the whole thing including the new heat bed(Max 11A). Do I just use these 2 yellow pc plug and have them go to 5A+ and 11A+ plug and the black one to negative?

That should work as long as your computer power supply is rated for enough amps. Depending on the gauge of wire on your power supply, I would hook both grounds up, though this is unnecessary if the wire gauge is large enough.

With a computer power supply you will also need to signal it to turn on. This is done by taking the (usually) green wire from the motherboard connector, and hooking it up to a ground wire (black).

You can also hook the green wire to your RAMPS board, and turn the power supply on/off via M80 and M81. The connector for this is located right next to the reset button, you can see in the diagram here.

Simply hook the "PS On" pin to the green wire of your power supply and it should work. Note you'll have to power the arduino via USB to be able to issue the M80 command to turn the power supply on.

I was a bit worry that 18A yellow plug would be too much amperage for the 5A positive slot without some resistor in place. I will be connecting my mother board pin14 green to pin16 blk like you mention. As for the heat bed I am going to use some excess nema 17 motor wire (1.4mm thick) to connect to the D8 slot of my ramps and use the same wire to extend to and from the PSU if it is too short. Not sure if that wire is rated high enough but if there is smoke then we would know the answer. If that is the case would connecting both ground to 11A negative slot first and then a single out to 5a negative slot do the trick? Or do I need to separate them and run two individual set of black wire to both 5/11A negative?

sypher Wrote:
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> I was a bit worry that 18A yellow plug would be
> too much amperage for the 5A positive slot

It does not work like that. The voltage is set by the PSU. The resistance is set by the circuit. The amperage is determined by ohms law. The amperage listed on the PSU is a capacity, not a statement that 18A will flow come what may.

I wouldn't use the excess motor wire to connect the heated bed. Your putting over 10A through that wire, the motor its originally connected to is rated for under 2A. Its not going to stand up to the heat.

The wiring on your typical ATX PSU is rated at, IIRC, a bit over 5A. I use three 12V and GND conductors for the 11A side and two for the 5A side. This is overkill, but the wires are free so why not?

Amperage cant be too much in the direction you are talking.

Amperage is a measure of what the device uses - if you hook a 10a thing up to a 1a source, you will damage the source.
If you hook a 1a device up to a 1000a source, you paid too much for your source and your device will use a fraction of what the source can produce. The device will be very happy.

If the analogy helps, think of a car battery and car stereo. The car battery can produce up to 400 amps. The car stereo needs maximum 3A. The wires that connect the car battery to the radio are rated for 15A, so they put a 15A fuse in the line near the battery.

The car stereo happily sucks 3a from the battery during normal operation, even though it could try and use 400A. If a short circuit happens, that is also known as infinte current. This would create a lot of heat, and without the fuse, the wire would heat up as the full current flows through the tiny wire, melting through its casing and then (possibly) cause a fire. This is also what breakers do, if too much current goes through it for the wire between the panel and the plug, the breaker will trip. Want to use the microwave, kettle, and hairdryer on the same circuit? Increase the size of the wire (so it won't overheat) and increase the size of the breaker, and now you can suck more watts through the same connection even though each device uses only what it needs.

I did a quick search and found this page
[wiki.xtronics.com]

according to that resource, make sure your wires are at least (and because the gauge goes backwards, at "most") 18 gauge between the power supply and RAMPS board (the wire should have the gauge written on it in tiny letters). For the bed, I would personally use the same wire but you could get away with smaller wire.

Thanks for all the information but I can't get it working for some reason. I connected 2 Yellow / 2 Black to 11A and 1 yellow/black to 5A all 22 AWG and have a wire connected from GREEN to BLACK. When I turn it on it just power the system for a second then it power off. Tried connecting pin 1 to pin 11 but that didn't help. I checked Green connection multiple times and tried connecting to another black but still no go. Any idea what is missing?

Some ATX PSU's won't run without a load on the 5V rail, which reprap doesn't use.The usual solution is to put a 10 ohm power resistor, or a small lightbulb, on the 5V rail to serve as a dummy load.

Hi, this is what happen when I used a load such as a small bulb. Connected it to a red/black wire and the system stayed on until I manually power it off (5-10sec). I turn it back on to test it again and the system and bulb power on for a sec then shuts off. Only time it would turn on again for over a sec is when I relocate to a different red/blk wire and the process repeat it self. Pretty bizarre if you ask me. What is the work around for this problem?

Maybe the inrush current, before the filament heats and increases its resistance, is damaging the PSU? A power resistor wouldn't have that effect. Or it might be time to buy a new PSU which isn't as fragile.

Ok so it look like the problem was in fact the PSU. I replaced it with a brand name one with max amperage of 28A and the unit is working fine so far beside a small mishap that invole spark when I tried measuring. There is no problem trying to power my heatbed and hotend seperately but the PSU would give and die out if I tried powering both so that earlier spark did a number on something and the only way to get it back up is to reinsert the green/blk wire. Is there a way to salvage this PSU or do I need to order a third one?

Can you be more specific with:
>> here is no problem trying to power my heatbed and hotend seperately but the PSU would give and die out if I tried powering both so that earlier spark did a number on something and the only way to get it back up is to reinsert the green/blk wire. Is there a way to salvage this PSU or do I need to order a third one?

First, what exactly sparked? It sounds like your PS is fine if it is still giving enough juice for your heated bed.

Your power supply might have different sections within the +12v - that is overall the power supply can give 28A, however on any single section it can only give 10A. If you try and power everything on a single wire the overcurrent protection kicks in. Try one of the +12v wires from another area (use the hard drive hookup for the hotend/motors, use that 4 pin 2black2yellow connector for the bed)

What do you mean when you say "the only way to get it back up is to reinsert the green/blk wire" - these need to remain connected for the power supply to stay "on". My guess is turning it off and on will reset the overcurrent protection too, but that's just a guess.

I had it hook up to some 6 pin connector and everything went well but when I try to measure the 5A power slot it cause some sparks and as soon as that happen the whole system shut down (Ramps and PSU). I couldn't power it on afterward and had to reset it by pulling out the green/blk pin. I tried moving and powering the 5A side by connecting the 6 pin cable and it didn't change anything. Still couldn't power the unit on. It could be that that cable is limited so I will try all the other yellow wire some time tomorrow.

Just a update that it appear that something fail during the spark as I can not get a constant flow to power both the hotend and heatbed from the same PSU. I tried PCI-E to heatbed and sata/8pin to hotend so it does not look possible. Would just die as soon as I try. The weird thing is that it work once..when I power the heatbed first then the rest but...I can not recreate the same result again..

Had some time to test some more and giving this PSU a third attempt to power the whole system and is working somewhat. The max temp it can do before failing is 30C to the heatbed. I attached the 5A to the yellow 24pin cable. I can set 185C to hotend and 30C MAX to heatbed in my test. Not sure if that is the optimal temperature for PLA and if running this for entire print at peak is dangerous. Any thing I can do to really test this PSU to make sure it is working right? My PSU I am currently using is Corsair CX430.

[www.corsair.com]