Heated Bed 220VAC USA 2phase hot wires wiring question
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Hi
I just received the custom heated bed, and I thought I understood the wiring however not sure what to do with the neutral and not sure what to do with the power supply since it only has a GND, Neutral, and one Live connections but it is rated from 100-240VAC. This picture shows an example of the wiring but also here where's the neutral, and also this is probably only 1 phase 120VAC the 220VAC has 4 wires black, red -are the hot each at 120VAC at different phases, I did see some comments that this is not a true 2 phase, but that's another discussion. Ok, so then the 3rd wire is the neutral and the 4th wire is the ground AC ground which is actually just the appliance ground. The second picture below are the connections that I am thinking.
I've come up with this drawing but still not 100% convinced:
![IEWZ3622[1].JPG](/assets/uploads/files/1621975586344-iewz3622-1-resized.jpg)
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Just to make sure, you are in the USA and the bed is rated at 220V AC?
The wiring from the 6H to the SSR is correct.The SSR has only two terminals so that will be one hot from the wall outlet going to the SSR, one wire going from SSR to heater, the second wire from the heater goes to the other hot leg. Neutral is not used.
I am not following the remainder of the sketch.
The USA house wiring is a single phase system but it is split in the middle with neutral. If the bed is run at 220V it must connect the two hot wires only.If your wall plug has 4 connections it will be hot,hot, neutral and ground. The ground is used to ground the printer bed, the printer frame and the printer power supply. If the printer power supply is to be run at 120V, you need one hot leg and neutral (and ground). If the power supply is to run at 220V input then you would be using hot, hot and ground. Neutral would not be used.
Neutral is only used if you want 120V AC anywhere.
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To clarify, when I say one hot wire from the wall goes to the SSR ... in actual fact you have the power connector, the power switch and a fuse in the circuit as well. Those were assumed to be there and were not separately mentioned in my reply
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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.
