I'm confused, you said halving the duty cycle doesn't halve the power, then said that when the PWM halves (from 100% to 50%) the power halves (4xPrated to 2xPrated)… I'm definitely not trying to be difficult I just think the math says otherwise.

Let's establish some rated conditions. At Vr=12v, the heater draws Ir=Vr/R where R is the (more or less) fixed resistance of the heater. The power Pr=Ir*Vr=(Vr^2)/R.

If I have a switch driven by Vin and pulse the switch with a 50% Duty Cycle, the average output voltage is 12v. Because we only care about the long term effects (relative to the PWM frequency) we can use the average value in our calculations.

So at 50% DC (duty cycle) with Vin=24v, Vpwm is DCVin=12v and because the heater resistance is broadly fixed, the heater Power is (VpwmVpwm)/R, which is also (DC^2*Vin^2)/R.

So doubling Vin means DC^2 needs to reduce by a factor of 4, which means the duty cycle is only reduced by a factor of 2.

Let me know if I got something wrong, but that's why I think you'd limit the PWM to 50%. The non-intuitive part comes from squaring both voltage and duty cycle in the power equation.

Just to reiterate, don't risk the hotend turning into a puddle of molten plastic metal and flames..

But if I'm not mistaken, a PWM output is pretty well molded as a duty cycle controlled voltage source, so halfing the duty cycle, which halves the average voltage, actually reduces the average power by the factor of 4 required. Power has a quadratic relation with PWM duty cycle.

For what it's worth I've used some name brand high current industrial power supplies that have the same issue when you really tighten the screws.

What sort of connectors are you looking for? Wurth makes some 20A pluggable terminal blocks (Model 313 it looks like) that go for about $1 for the block/plug pair (2 pole). I've never used wurth (phoenix contact for me) but they don't seem like a bad deal.

A complete guess, but the lattepanda board probably underwent its own certification process, since the wifi transmitter is integrated into the board itself. Since the ESP is self contained and you never have to route the RF signal or create an antenna for it, the certification it has covers a product using it, as long as it remains in the same configuration as it was certified,

http://www.emcfastpass.com/rf-modules/

Thanks for the info!

I noticed that the RTD boards are using SPI, is the two board limit just because of the available CS lines on the main board? It looks like there are a few more CS lines available on the expansion header I could use as well.

I'm definitely going to put a hold on the current sensing for now. I have enough to do just trying to get a functional delta built and calibrated. Can come back to the fancy stuff later…

Howdy!

I'm starting to design my first homebrew delta (built a kit, don't like it, used lots of Cartesian machines, got bored) and I really like the Duet board. I'm having some trouble figuring out if I can do a few things though…

I'd like to add some spare temperature sensors (Ideally RTDs) around the printer, say on a power supply, the hot end heat sink, motors, etc. I'd also like to have the possibility to add some current sensing for things like hot ends, bed heaters, power supplies. It seems like the Duet has the spare I/O I'd need to make it work, but I'm wondering what's supported in the firmware or what I might have to hack together to make it work.

I don't mind modifying the firmware if I have to, but for compatibility, I'd love to avoid it.

Also I'd just like to say I saw the work y'all are doing with the Delta and the PCB effectors and I'm quite jealous. Looks great.