Welcome to the SeeMeCNC Community

I have my Rambo running on the workbench now. I have most things running. The 400 something watt atx powers supply I got from seemecnc doesn't seem to be up to the task. I can have either the extruded or the bed running but not both at the same time. The ps trips after only a short time. Is this normal? My solution is to add a second ps just for the bed. Do I have a bad ps?

The good news is the bed heats up to 100 degrees in just slightly more than five minutes. The bed is just sitting on a glass table top in free air, no glass or metal plate.

I guess this is the first post in this section....

X

Do any of the wires feel hot?

What trips? The mains power supply? The power supply unit (PSU)? The fuse on the Rambo board?

Myself I'm using the PSU that was supplied by SeeMECNC, pretty sure it was 430W

On the workbench I assume you have everything connected via the Rambo. How many wires are connected from the PSU to the Rambo for the Hotbed? And what colours?

It is the seemecnc 430 watt power supply. The power supply just quits after about a minute of running both the extruded and heated bed. Either the extruder or bed will run forever but not both at the same time. In a few minutes I can turn it off and then back on and all is good. The wiring seems to be correct no shorts or anything. There are no shorts to the workbench or wires laying around. I connected a 100watt old computer power supply just for the heated bed and it is running just fine. No wires are getting too hot. The resistance for the bed is 3 ohms and the extruder is 5.5 ohms. I believe that is close enough to not be a problem. No smoke, no sparks, no loud noises, nothing seems unusual on the Rambo. I have not tried leaving the ps on to see if it auto resets. I'm not that brave or perhaps stupid. Four steppers connected but not engaged. They are current limited in configuration.h with "135" each. That is something about one amp or so. Shouldn't be a problem. I can run it with two power supplies i guess. I thought the 430 watt power supply would run the whole show tho...

X

September wrote:What trips? The mains power supply? The power supply unit (PSU)? The fuse on the Rambo board?

Myself I'm using the PSU that was supplied by SeeMECNC, pretty sure it was 430W

On the workbench I assume you have everything connected via the Rambo. How many wires are connected from the PSU to the Rambo for the Hotbed? And what colours?

Just to clarify things more, everything connected via the Rambo. The fusee on the Rambo board are ok. The mains to the psu are normal. Yellow and black wires to the Rambo. 12.24 volts to the Rambo. Correct polarity. Three yellow and black pairs of wires from the power supply to the Rambo. The wires are not getting hot. The pus just shuts itself off.

Thanks,

X

you should have a total of 5 pairs of wire ..from psu to rambo .
Three for the heat bed .
one for the heater
and another one for motor and stuff .

*FOUR* for the heated bed. Start reading at page 97.

g.

Xavier,

I am having the exact same problem with my Rostock. I re-verified that I have 4 power wires to the bed. Here is a picture of the power supply box that housed the ps that came with my Rostock from seemecnc. I think I will try to add another set of power conductors to the bed heater by using the ones I dedicated for powering the fan and add a second power supply for the fan.

My second power supply (in 4 months) bit the dust last night. I'm shopping for a different, better one today.

What I'm learning is that the 480 watt rating of these supplies isn't all available to the +12v output. At 12vdc, the OEM Logisys only provides 16A of current. This equals only 192 watts of the 480 that the supply is capable of producing. Keep in mind that the wattage rating on the box for something like this is usually the max max max that it can possibly produce. In common practice, you can only reasonably expect a device to perform at RMS (.707) of its specified max wattage, and that's if they're being honest with the rating on the box. That's also not usually recommended to run anything 'turned to 11' for an extended period of time. Anyway, that was the long drawn out way of expressing that you're probably only capable of sustaining 50% of the specified current draw on something like this, so I wouldn't expect to get more than 8 *real* amps out of the OEM power supply.

So... With a 3ohm bed and 5.5ohm hot-end that both run on 12v, you're drawing a full 6 amps before taking all 4 stepper motors and the Rambo board itself into account (plus any fans, LEDs, powered end-stops, and whatever else you're using)... I bet that's at least 10 or 12 amps when everything is moving, and there's just no headroom for the power supply to operate happily under the load.

If I was building a machine like this from scratch, and had done the above math in the design stage, I would not recommend a power supply that was rated for less than 25A @ 12Vdc. That's what I intend to buy at a minimum, I'll let you know what deals I find.

The 16 Amp OEM unit can be had on Newegg for about $17. For a cheap upgrade ($22) to a 25 Amp unit, check out this one: http://www.newegg.com/Product/Product.a ... 6817170028

I would strongly recommend, if you are going to use a computer power supply, looking at the ones that multiple 12v rails. Jimustanguitar is right the 12V rail of these el'cheapos does not have enough umph to supply the Rambo. Using a dual 12v rail model allows for separating the load produced by the hot bed from the motors and electronics.

Typically multiple rail ATX power supplies have one rail that is able to higher currents (the bed) and one or more that are designed for less (everything else). It is also worth noting that most ATX power supplies will struggle to produce amperage on the 12v rail without at least a little load on the 5v line.

foshon wrote:It is also worth noting that most ATX power supplies will struggle to produce amperage on the 12v rail without at least a little load on the 5v line.

What sort of a 5v load would you recommend? Do you have your LEDs or Peek fan running on this rail?

Jimustanguitar wrote:

foshon wrote:It is also worth noting that most ATX power supplies will struggle to produce amperage on the 12v rail without at least a little load on the 5v line.

What sort of a 5v load would you recommend? Do you have your LEDs or Peek fan running on this rail?

10ohm 10watt (from radioshack) resistor on the 5v line will work, for this purpose to simulate a load. however you could also attach a 5v fan, or device. That' could also work if it drops enough load.

Jimustanguitar wrote:The 16 Amp OEM unit can be had on Newegg for about $17. For a cheap upgrade ($22) to a 25 Amp unit, check out this one: http://www.newegg.com/Product/Product.a ... 6817170028

Keep in mind that I'm biased -- my Logisys caught fire before I ever powered it on. That said, there's no way I'd buy another Logisys with just marginally more amperage on the +12V rail. There are lots of good power supply vendors out there. The thing is, the good supplies cost more than $25.