power question

Hello I'm new to the reprap 3d printing and getting close to installing the ramps board. My question is on the power is 12v hook to both terminals on the board? If not what are they. Also I have been reading about people using relays with the ramp and the heat bed. I did do a resistance test and I'm getting 1.1-1.2 on the bed. Any and all comments would be helpful..

You need 12v on the outer ramps socket for motors and hotend - the inner 12v is for the heat bed only. So you can test your machine for operations with just the outer plug connected. I would think your heatbed will be fine.

---

_______________________________________
Waitaki 3D Printer

The RAMPS board allows you to power the printer from two different supplies. They don't have to be the same voltage. One supply, typically 12V, drives the board, electronics, and motors. The other is just for the printbed heater. The printbed heater side has a MOSFET switch and a thermal cutout (a varistor?) that will shut down power to the printbed if you try to drive too much current for the MOSFET switch (and/or PCB traces) to handle. When the thermal cutoff trips, you'll have to kill printbed power to reset it.

There is an LED on the RAMPS board that lights when power is being applied to the printbed heater. If the LED isn't lighting up the MOSFET isn't switching power to the printbed. If the light isn't working, try disconnecting the printbed and its power supply and check it again. If the LED starts working, you probably tripped the varistor. The printbed heater won't work if you don't have the printbed's thermistor connected to the RAMPS board (you'll get a MINTEMP error on the LCD display if you have one).

I believe the PWM frequency of the printbed heater driver is about 7 Hz. I am using that output to directly drive an SSR (probably not intended to be switched so fast) that switches 117VAC into the primary of a 24V transformer that drives my printbed heater (24V @ 23A). The SSR has a zero crossing detector built in so it only switches when line voltage is low. It works well and doesn't cause the room lights to flicker. The SSR seems to be holding up just fine and doesn't even get warm.

Ok Thanks for the reply's. When you say the outer connection that's the one that marked 5v? and the 11v is just for heat bed. bbut i can connect two 12v 30 amp to them? Also im using a atx psu for the power. I had it laying around from my last pc build so what the hack. It is a good psu rated at 1000v and with six 12v rails two of witch are rated at 30amp. there really should be a problem with connecting these the the ramps board. Alo i have been reading that some people are using a relay on the heat bed to keep from messing up the ramps board. I bought one to day it not an ssd but someone else said that they where using an maniacal one and it was working ok with bang bang. I think it was cnc rick, i think. I'm just trying to cover all my bases so i don't burn anything up. Wife is always over the shoulder.. lol.

Although the mechanical one should work it wasn't me who recommended a mechanical one I would recommend an SSR quieter operation longer-lasting

A mechanical relay on the printbed heater circuit will drive you nuts with all the clicking, and probably won't last long because of the large current being switched. You don't need to use a relay at all if you have a 12V heater, as long as the current is less than about 10A. The MOSFET on the RAMPS board will switch the full 10A for you without complaint.

I have moved away from switching power supplies due to reliability problems. I now run the printbed from AC via a transformer and use a linear regulated supply for the 12V power to the controller board (not sure regulation is necessary). When you use a power supply that is grossly overrated you run the risk of doing severe damage when something goes wrong. Your power supply should be rated for about the maximum power needed and not too much extra. Computer power supplies, especially high power types, usually have a noisy cooling fan that runs all the time. That will get tiresome.

O sorry I just remembered seeing someone that i think you were talking to and got a little confused. Sorry about that. i am just trying to make sure that i am going to be safe and not burn up the ramps board.

the fan is not very loud at all. I think it run at like 10 to 15 dbl. Also as far as the 10a rage, i think i have tested this right but i needed to test resistance and then multiply that by the voltage, which is the right when i an getting 14.4. The resistance is at or between 1.1 and 1.2.

Quote
demongimp
When you say the outer connection that's the one that marked 5v? and the 11v is just for heat bed.

These are not marked 5v and 11v, they are 5 amps and 11 amps. Amps - not volts. I am using an industrial 12v 30A power supply. This power supply actually has 3 pairs of terminals each supplying 12 volts, the sum of which cannot exceed 30 amps. I have 1 connected to the 5A rail, one to the 11A rail, and one to power other accessories like lights and a small cooling fan aimed at my j-head thermal break