Using 2 seperate power supplies

Just finished building a Prusa. Electronics are Sanguiolou. I've copied Adrian's Prusa Notes including his heat bed set-up with remote mosfet, power supply, wiring etc.
The problem is that whenever the heat bed switches on or off, the stepper motors skip steps. I've tried totally seperating the heat bed wiring from the stepper wires but no change.
I figure running a seperate power supply just for the bed might help but have no idea how to wire it so that the temp is still controlled by the Sanguinololu on the original power supply. Help!
Dave

You probably want a solid state relay between the bed and the Sanguinololu. As an example, look at the Heated Wolfbed.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

Have you wired the bed circuit to its own power connector? There should be no ground connection between that circuit and the rest, other than at the PSU.

If you have wired it like Adrian's diagram and it does not work it may be because the PSU cannot provide enough current and the 12V rail dips. More dummy load on the 5V and 3.3V rails may help.

I have used a very similar circuit with two PSUs so I can have the bed at a higher voltage. I left the grounds unconnected to avoid the bed current flowing through the controller's ground. I rely on the fact that both PSU have grounded outputs, so the MOSFET sees about the right gate voltage and it has to be a protected MOSFET. If one or both PSUs have floating grounds then you need to link them.

---

[www.hydraraptor.blogspot.com]

Traumflug Wrote:
-------------------------------------------------------
> You probably want a solid state relay between the
> bed and the Sanguinololu. As an example, look at
> the Heated Wolfbed.


And be able to read it!

---

Andrew

Based in Slough, United Kingdom

translated

Update.
Couldn't get mosfets to work - probably due more to me being an electronics basket case than anything else.
Ended up using one of these mosfet based solid state relays SSR. Bit of an overkill and normally expensive but I found one at a flea market.
Works fine.