Power to heat big Mic-6 bed

papilio

I picked up a great deal for a Mic-6 cast aluminum tooling plate on eBay, but it's a bit larger and thicker than I was planning on – 14 3/8" diameter, 3/8" thick. My delta's still under construction but I've already gotten a 300mm 24v 270-watt silicone heater from Shenzhen Ali Brother Technology Co.

What sort of heat-up times might I expect with this combination, will I be woefully underpowered? The heaters are cheap, if necessary I don't mind ordering a more suitable pad from them. What sort of specs would be recommended?

Phaedrux

I have a similar sized plate (13" square, 1/4 inch, with 600w heater). It gets up to 60c in a couple minutes. The top surface measures a few degrees behind but evens out after about 5 minutes.

So your plate is a little thicker and a little less than half the power. So say 10-15 minutes to reach equilibrium?

Your heater is probably safer from a thermal runaway standpoint. I went overkill.

papilio

Thank you Phaedrux, that's just what I was hoping to find out and gives me a good idea. I should have mentioned that I prefer waiting a bit longer if I must in order to mitigate fire hazard as much as is reasonable, though I'm also installing thermal cutoffs on the bed and hotend for a bit more peace of mind. I'm thinking that I'll get a new heater to span the entire bed, the diameter mis-match would amount to something like a 40% difference, but I'll likely keep the wattage about where it is.

Mike

As for the thermal safety… https://www.amazon.com/Electronics-Salon-Normally-Thermostat-Assortment-Temperature/dp/B017ATCUQK/ or something similar for the peace of mind. I've also opted for more expensive brand name SSR just to be sure. Thickness of the plate really doesn't matter much, just means it'll take 1 or 2 minutes more to reach temperature equilibrium.

If you're still looking for the heater, you could also get one with a thermal cutoff built in. I've got my 600W AC 200x300 heater mat from Keenovo, they've put in a 150 degrees bimetallic switch in there upon my request. This way you get real nice heating performance and can get away with relatively low power PSU for the printer.

papilio

Hi Mike, thanks for the Amazon link. Those like great, certainly nicer than the one-time thermal fuses which I picked up. And yes, definitely, I've got the Crydom SSR here ready to go.

I also very much appreciate the tip on the heater, looks like that's a great way to go!

papilio

Since I'm on the topic of silicone bed heaters …

Shenzhen for some reason sent me two of them by mistake (arriving separately a week apart), and while telling me that it was fine for me to keep both they differ in appearance and I wish to be certain that, if they're not actually of the same specs, I'm able to determine which is the 24v unit which I ordered. I sent them photos of each but they were unable to tell me whether both were 24v 270w just from appearance.

So, is there an electronics test which I can apply to them in order to sort what's what?

Thanks!

Mike

papilio, it's fairly simple since those are resistive heaters. Do you have a multimeter? You would need to measure the resistance between the 2 heater wires. You can then use that to approximate the power using Ohm's law. For 24v 270W it'd be 11.25 A of current, so the heater resistance should be around 2.13 Ohms.

I also messed a bit with the thermal fuses at first. This solution seems a lot more robust as you won't need to tear off layers of RTV silicon if you happen to trip the fuse.

DADIY

There's a good online converter which you can give 2 values for either watts,volts,amps or resistance and it fills in the blanks.

https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html

papilio

Yes Mike I have a multimeter here, thanks. And fine, that sounds pretty straightforward – a good thing as electronics remains the area of printer construction with which I struggle the most, though I guess I knew at least enough to suspect that the method for checking would be something like that.

And that will be a valuable link for me to bookmark DADIY, thank you too!

papilio

Thanks again guys, both heaters do indeed check out as 24v 270W.