Solid state relays can be real problem solvers. Learn how and how not to use them!
http://www.youtube.com/watch?v=TiEwNf1H_Tc
great video, it really helped me and i book marked the links for near future use.
I’ve been hoping you’d cover this.
As you say, there are also DC-DC solid state relays that really suits 12v or 24v powered hotbeds (not the huge kind of 220VAC bed you need on this huge printer, agreed - but uncommon and riskier indeed). Many people want to use regular DC-AC ones for their low voltage DC beds, and it does not work. The load must be AC (as you mention). For DC loads, you tell about mosfets, that are the ubiquitous component to switch beds on and off indeed. But when making it yourself, DC SSR may still be easier to use than mosfets, mostly because the real internal resistor of the latter must be double checked. Precisely because of this, never trust the too cheap… and fake ones on ebay! They will get way too hot and they may even burn something – even though the (fake) label says you bought the “proper” MOSFET. Now, sure, SSR are sexier than relays, and they work with PWM as you mentioned (high frequency on-off command to achieve intermediate temperatures). Still, good old relays are easier and cheaper to work with for heating a bed in my opinion. They still require the firmware to be re-configured in “bang-bang” (slow switching) mode, but they work as well as any other component, with the added benefit of hearing it click. I think PWM for a heated bed is overkill anyway, as a variation of a few degrees on the bed has no real impact, contrary to the head.
Btw, the regular AC SSRs you speak about are also very well suited to implement a “suicide mode” on a 3D printer. The deal is to shut the printer automatically off when the job is done for more safety and less power waste when it is left unattended on a long print (full howto in this old post http://www.tridimake.com/2012/11/auto-shutoff-at-end-of-print.html ). It is strange to me that so few printers have suicide modes, given the small cost, simplicity and benefit. The existing firmware even supported it for years.
BTW, +1 for such videos, short and informative without getting too technical as a howto.
Fotek SSR-40 DD is a DC-DC solid-state relay that has worked well for me for a while, even with PID/PWM.
I use it to run a MK2B heatbed with a separate 24VDC PSU (ramped up to 30VDC).
@Oystein_Krog What about this one as a US source?http://www.phidgets.com/products.php?category=9&product_id=3957_0
@Richard_Turnock I think it should be OK, but if you can find one with a higher amp rating it would be even better.