Heated bed causing wires from PSU to get really warm

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Heated bed causing wires from PSU to get really warm

Postby tlum » 2016-Nov-Sun-17-Nov

I have the Simple Metal with the extended bed and heated bed upgrade. I noticed today when I was moving my power supply (the PC PSU stock from PB) that the wires coming from the PSU were really warm. What should I be looking for to remedy this situation?
Thanks,
Tom
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Heated bed causing wires from PSU to get really warm

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Re: Heated bed causing wires from PSU to get really warm

Postby RetireeJay » 2016-Nov-Sun-20-Nov

More copper. Are you using six wires from the PSU to the Printrboard? Whether your Printrboard is Rev D or Rev F, if you are using a heated bed then you need to be using six wires from an ATX supply. In the case of Rev D, you do this with a Y jumper that connects the 4 pins on the board to a total of 6 wires coming from the PSU.
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Printrbot Plus operational January 2013
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E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
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Re: Heated bed causing wires from PSU to get really warm

Postby tlum » 2016-Nov-Sun-20-Nov

Yes, I have the huge PSU brick with 40 wires and I am using the 6 wire connector. It is definitely something with the heated bed. If I turn off the bed, the connector returns to a normal temp. I actually can't hold the connector where the PSU connects to the printer 6 pin connector, it's that hot. I can hold the wires running from the board out to the heated bed though, they aren't really even that warm. Could it be my power supply?
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Re: Heated bed causing wires from PSU to get really warm

Postby RetireeJay » 2016-Nov-Sun-22-Nov

No, it's not the power supply; it's fine.

When electricity is flowing, it will cause heat to be created wherever the resistance to the flow is relatively high. In some cases, that's what you want, e.g. the heated bed and the heater for the hot end (extruder). In other cases, you want the resistance to be as close to zero as you can get it, so that little to no heat is generated. Since the excess heat is right at the connector where the wires plug into the board, that is where your problem is. For some reason, there is excess resistance there. The more current, the more heat - so when you turn on the heated bed you are pulling much more current from the power supply and therefore making the small but significant excess resistance at the connector generate more heat.

There are several possible causes:
(1) The connector is not fully seated, so the metal parts are not making good contact.
- Try unplugging and re-seating the connector, making sure it's pushed all the way down.
(2) There is corrosion or contamination preventing good clean metal-to-metal contact inside the connector.
- This is unlikely unless the connectors have been exposed to excessively moist conditions or there's lots of dust or dirt around.
(3) One or more of the wires going to the connector is not properly crimped to the metal part that's supposed to make contact with the pin on the board.
- You can test for this by pulling fairly firmly on individually on each wire. If any wire pulls out of the connector, then you know it was not crimped properly. In that case, there are different avenues for repair, but I won't go into all of them because that's also fairly unlikely.
(4) One or more of the mating parts of one of the connector halves is bent and not engaging properly with its mate.
- This could be either on the board or in the power supply connector.

You are wise to be concerned. There's a whole long thread in the forum about "Printrbot on fire" where a heated bed connector was overheating.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
User avatar
RetireeJay
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Re: Heated bed causing wires from PSU to get really warm

Postby tlum » 2016-Nov-Mon-15-Nov

We have a few Printrbots at school so I decided to check my heated bed resistance against one I know works well and doesn't melt the wires. My bed had a resistance of 1.2 ohms while the school printer had 2.0 ohms
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Re: Heated bed causing wires from PSU to get really warm

Postby RetireeJay » 2016-Nov-Mon-16-Nov

Maybe your heated bed is larger than the ones at school, or maybe it's a different make. Some heated beds are specified to have a resistance of 1.0 to 1.2 ohms, so yours is not out of line. At 1.2 ohms, that would be drawing 10 amps - which should not be a problem for a Rev F board. Something is funny about your power connector going in to the board.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
User avatar
RetireeJay
My next printer is...
 
Posts: 4587
Joined: 2013-Jan-Wed-13-Jan
Location: Greenville, SC
Reputation: 474


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