Heated Bed 220VAC USA 2phase hot wires wiring question
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@jens55 Yes, I am in the USA. I will draw an updated sketch, as I will need 2 SSR or one double pole single throw for each hot wire. OK I understand what you are saying, so I only need the one hot and the neutral and ground to go to the power supply for 120VAC. I don't need the full 220VAC for the power supply. I sent an e-mail to Keenovo just to make sure that the heated bed is not missing a neutral connection, because there is no return for the current. The bed then just uses everything up, no need for the neutral return path. OK thankyou for clarifying, Yes I will have a power switch as I have one now that I am only using the 120VAC outlet for the powersupply, so that the bed heater also has a switch. I didn't think about adding a fuse, but you are correct that needs to be in there.
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@jsinicro, The easiest way to think of the 220V line is that the current goes from hot to hot. It doesn't need neutral. Any 120V device you hook up goes from one hot to neutral.
You only need one SSR to interrupt the current. Two is nice if one happens to fail in the closed position (safety factor) but it gives you a false sense of security as you would never know if one SSR is shorted.
Yes, you would use a double pole single throw (on/off) switch to disconnect both hot wires.
You do not need (but of course you can) have a separate power switch for the power supply and the heater.
You should be using two fuses, one for each hot leg.Better yet, you could have the two fuses for the two hot legs matched to the heater plus the expected other power use and use a separate fuse for the power supply which is rated based on the power demands of the printer minus the heater.
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@jens55 OK, I only have one SSR, and you're saying that the current will be interrupted with the one SSR and the bed will not be energized with the other hot going directly to it. Hopefully I can go to Lowes and pick up some fuses. OK so in AC power the current travels between the two hot wires no need to have a return path to the main panel?
Thx, -
@jsinicro Quick question, so the power supply is am Mean Well RSP-750-24 it says the input is 100-240VAC and 10Amps. The Output is 24V DC and 31.1Amps This is a higher end supply as it reverse polarity and it's fused, but you saying I should connect a fuse there as well?
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@jsinicro said in Heated Bed 220VAC USA 2phase hot wires wiring question:
@jens55 OK, I only have one SSR, and you're saying that the current will be interrupted with the one SSR and the bed will not be energized with the other hot going directly to it. Hopefully I can go to Lowes and pick up some fuses. OK so in AC power the current travels between the two hot wires no need to have a return path to the main panel?
Thx,The current will be interrupted yes but the bed will be 'energized'. If ou were to measure the voltage at the bed towards ground, you would read 120V AC but because the current can only flow from hot1 to hot2 and since that path is interrupted by the SSR, the heater will not be heating. You just have to remember that there is still AC on it even though it is off .... keep your fingers off
Let me try to explain the current flow in a bit of a different way using two batteries, let's say 9V each. Each battery represents the 120V you get in your normal house outlet.
You wire the two batteries in series, minus terminal on one battery going to the plus terminal on the second battery. If you were to measure the voltage across both batteries wired in series, you would measure 18V. That is sort of how you get 220V AC in your house. If you measure across each battery individually you would of course get 9V for each. That represents the 120V in your house.
You have the wire connecting the two batteries - if you were to connect a white wire to that wire and called it 'neutral', and two black wires connected to the negative on one battery and positive on the other battery and called them both 'hot', you'd have what represents your house system.Measure one hot to neutral it's 9V measure the other hot to neutral it's 9V, measure from hot to hot you get 18V.
You have three potential current paths - hot to hot, hot1 to neutral and hot2 to neutral. Current can flow in any or all of these paths. Depending which wires have a load determines how much current travels in the various wires. Just because you don't connect the neutral wire does not mean you have no return path to the panel.Man, that turned into a long ramble ... it's real easy to explain in person but not so much in writing ... sorry
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@jens55 maybe it is better to draw a picture?
I would suggest one 2-pole fuse for the heater, it could be handy if you want to cut the power and be sure that none of the hot wire will be energized.
I usually also connect the negative of the secondary side of the PSU to ground. -
@jsinicro said in Heated Bed 220VAC USA 2phase hot wires wiring question:
@jsinicro Quick question, so the power supply is am Mean Well RSP-750-24 it says the input is 100-240VAC and 10Amps. The Output is 24V DC and 31.1Amps This is a higher end supply as it reverse polarity and it's fused, but you saying I should connect a fuse there as well?
Maybe I am being a bit over cautious here but I'd rather replace an easy to access external fuse then an internal fuse that I would have to take the power supply apart for. Yeah, maybe that is getting carried away.
Usually fuses are connected right after the power switch and protect the wiring in the device being powered. The idea being that if more than the rated power is being drawn, something is amiss. Would the little bit of wiring to the power supply need to be protected if things go pear shaped? I can't say. I do not know what the electrical code says.As always, you make up your own mind, consult an electrical engineer, get his stamp of approval, go through your local electrical inspector and get his signature etc etc etc.
My advise is worth exactly what you paid for it (nothing) ....
Hopefully this all covers my buttBTW, The only reason I suggest seperate fuse for the power supply is because there is a huge difference in current draw between the heater and the power supply. The fuses for the heater are rated way above the point the power supply goes up in flames
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@falkia said in Heated Bed 220VAC USA 2phase hot wires wiring question:
@jens55 maybe it is better to draw a picture?
I would suggest one 2-pole fuse for the heater, it could be handy if you want to cut the power and be sure that none of the hot wire will be energized.
I usually also connect the negative of the secondary side of the PSU to ground.Agreed on connecting the negative on the PSU to ground. I have not seen a 'two pole fuse' other than a circuit breaker in the house panel which is why I suggested two separate fuses. If there is such an animal as a two pole fuse then yes, that would be the way to go.
Just as a way of explanation, on a two pole fuse/breaker, when one side fails the other side is also interrupted which is an important safety factor but pulling the fuse should be advised against for working on the device. You should disconnect the power cord instead.Re drawing a picture ..... not used to drawing stuff and am too lazy
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@jens55 That was pretty awesome explanation. I never connected AC and DC like the battery example. I am a software engineer, so all the electronic stuff I been doing has been from online references. Now I need to find out how to solder the fuse inline and make it look nice.
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@falkia what do you mean secondary side of the PSU?
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@jens55 no, you're not being to cautious, that's a very good idea. I rather buy a fuse than trying to fix a PSU.
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@jsinicro -V (negative) on the load side.
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@falkia So you connect the negative on the DC output side to the same ground that the AC ground uses?
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This is the kind of fuse I ment. It's like two fuses that have the same lever.
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@jsinicro said in Heated Bed 220VAC USA 2phase hot wires wiring question:
@falkia So you connect the negative on the DC output side to the same ground that the AC ground uses?
Yes, correct.
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@jsinicro I suggest you add a thermal cut out (TCO) in series with the power to the heater, and mount the TCO on the heater. Don't get a heater with adhesive. Mount the heater using silicone.
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@mrehorstdmd OK, I got the heater bed custom made 700x700mm from Keenovo and includes a 3M self adhesive.
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@jsinicro The manual says you should seal the edges with silicone- I think it prevents the adhesive from drying out/oxydizing/letting go. Without sealing the edges the adhesive is good for about 2 years of heat cycling before it starts to let go. As it lets go, there will be air between the heater and the plate. The heater will scorch in those areas.
When I replaced that heater I got one without the adhesive and used silicone to mount it. It's been about 2 years since then and it appears to be holding fine.
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@mrehorstdmd Wow, OK Thx
