Supporting > Additive Machining
3D Printer problems - Monoprice/Wanhao D6
Muzzer:
Take the relay out (you'll have to do that anyway) and either trace the NC track by eye to see if it is routed anywhere - or if you can't manage that, check the resistance to ground with a DVM. With the board unpowered and using a modern DVM, you should see something under 100k if there is any form of connection to that pad. I can't imagine there is but you seem uncertain.
Modern equipment is supposed to be ESD resistant, as it's such a common event - we would expect it to be tested to IEC61000-4-2. But the guys who "designed" this equipment presumably didn't see the need for it - or more likely had never even heard of ESD. Hopefully the same level of amateurs didn't "design" the mains power supply.
It should work without the heated bed, depending what filament you are using. It's usually stuff like ABS that needs heated beds, whereas the default PLA is happy with a cold bed. Why not just do without the heater altogether for now?
ddmckee54:
I've still got my Prusa clone that I built from a kit 5 years ago, so it's not like I'm unable to print. I plan on working on the Wanhao motherboard when I get the replacement parts from Aliexpress. They verified my order, and told me that my order had shipped yesterday.
I've had a relay that's a drop in replacement for the original Songle relay recommended to me by a supplier in Texas. It's identical to the original relay except it's got 20A contacts instead of 10A contacts. I'm still waiting to hear back from the supplier about minimum order quantities and whether I'll need to sign away my first-born to get some of them.
Admiral_dk:
I would be surprised if a 20A AC rated relay isn't good enough for at least 20A DC, as most are able to withstand more DC than AC - but there might be a contact material where the opposite is true - I just haven't got a clue witch one that would be ....
You could also find a good number off CMOS 'transistors' that are rated for much more that 20A for $2 a piece - this might demand that you also find an OPTO-Coupler to go between the "relay coil" and the "24V. Power" circuit .... if you by the DVM decide that the NC part of the relay isn't used - though I will say that I would feel more safe if the reading is infinity (as in absolutely no connection) ....
ddmckee54:
According to the DC rule of thumb that I found on the Carling Technology website, any contact with an AC amp rating but no DC amp rating should be good for use at up to the maximum AC amp rating, when used at 30VDC or less.
It's the other way around with contact ratings, usually a contact has a higher AC rating than DC. It's harder to extinguish the DC arc when opening the contacts since there's no zero crossing like there is with AC. There are contact materials the are used to help extinguish the arc, but these materials take the relay out of the 2 buck per unit range that the original Songle relay was definitely well within.
If you think about it, that's actually that's not a bad racket for Wanhao to be in, as long as they can get away with it. Selling a motherboard at $200-ish because a $1.36 relay went bad. If it works maybe I should go into the Wanhao D6 relay replacement business? I might make a fortune, but I don't think I'll quit my day job just yet.
Don
Muzzer:
Yes, DC ratings are generally less than AC ratings for the same relay but low voltage DC relays are far from rocket science.
There are loads of 12V relays out there, on account of the automotive market, so 20 - 30A contacts are commonplace. I've no idea what footprint you need but there's a wide selection available for peanuts at places like CPC:
https://cpc.farnell.com/w/c/electronic-electrical-components/switches-relays-solenoids/relays/prl/results?range=inc-in-stock&st=relay%2012v
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