Gen7 request replace HD connector for bed/heater with 4 pin atx12V connector

Here's the issue this is the second time I burned the molex wire (last time I burned the whole connector) drawing 12A+ on a single atx power supply wire is just unsafe, the solution is replacing that hard disk header with with an atx+4 12V connector it is rated for 12A (the tin ones with nickel) 13A the gold ones per pin hence a total of 26 A since the wire can only sustain about 10A usually that would be 20A but it would be in reality a 6A 6A split which would be a safe solution the hd connector and the 12V wire on it is rated for a max of 10A and drawing 12A during heating of the bed is heating the wire quite a bit. A work around for now is soldering an additional 12V wire to that connector but the only real safe alternative is replacing this connector with the 12V cpu connector.
Traumflug please alter the github pcb schmatic and the board to ensure safe reprapping in future.
thank you
terramir

I don't think even those 4 pin 12V connectors are safe with 10A. I have one that is starting to go brown.

5A per pin seems to be too much as both the wire and connector get hot. I think the only way to go is screw terminals and remove the PSU connectors and connect all the yellow, red and black wires together. Event then I doubt one can get the rated current.

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[www.hydraraptor.blogspot.com]

well accroding to the spec it's at least rated far greater than a single molex drive connector if a little browning was my problem I'd just replace the connector the insilation off my wire burned I fixed it but cutting off the plus four connector and now soldering two leads to the hd 12V but that is really a stop gap measure yes screw terms or the 12V atx connector might be a solution if you have the square one nophead are you talking about sangiunololu? because that draws all power from that source it would be bed hotends and motors for a total of about 16 to 20A ( depending on your motors) I'm just talking about hotend and bed which would be 12 to 13 A and should be manageble. I also replaced the bed kk156 connector with a molex 2 pin rated for 12A just for the bed that should be enough it's a hack but it will do. however for 1.4.1 a atx4 connector might be the solution for the bed and hbp power supply
terramir

I'm pretty sure I've compared specifications before deciding for the disk power connector in favour of the ATX12V connector. The result was, the single pin on the disk power connector is specified for (almost?) the same current as both in the ATX12V together, so there was no point in giving up compatibility with older PSUs.

If you have these specifications handy, terramir, please provide them here. Apparently I either didn't document my findings or misplaced them since then. The second disk power connector was introduced in June 2011.

In general the specified current typically depends on the crimp pin inside the connector. Like always: a chain is as strong as the weakest link. At least for the Molex KK100 and KK156 several crimp pins exist for the same header/pin housing, with different maximum current specifications.

I'd also be interested in wether you soldered the wire onto the crimp pin. Either with or without crimping. I'm aware crimp-only pins are considered to be slightly more reliable due to better mechanical stress distribution (less prone to wire break under movements/vibrations), but solder undoubtly increases electrical contact rigidity.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

The problem with the disk connector is there is only one wire, so that is the weakest link. I think it needs at least 24/0.2 for 5A but the wires on my PC PSU are only 24/0.15 IIRC so even two wires are not enough for 10A.

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[www.hydraraptor.blogspot.com]

well here is the page for the 4pin (atx +4 cpu) connector Molex's direct page for this type here the rated current is 13A per circuit and there are two circuits in contrast to the one circuit on the hard drive connector at 12V
Just thought you might want to take a look of course with the wiring on most psu power supplies the current should be limited to 20A max so still keep the hard drive connector for the motors or it would exceed spec again.
Edit: also here is the matching header for the board traumflug I really think this would be a safer solution at least for most of us, Some people might have to buy a connector to refuninsh some older power supplies as long as the power supply have three accessory lines that is doable as well.
Just some food for thought

terramir

Edited 2 time(s). Last edit at 05/28/2012 02:10AM by terramir.

I was just looking up the link you gave to the Molex MiniFit connectors. There's some strange inconsistency on their web page. In the common case of having 20AWG wire, the max current is only 7A for brass and only 6A for bronze.
Although the maxmum current is specified as 13A per contact on both the web page and the "Datasheet", the "Product specification" mentions only maximally 9A per contact, and only for the brass version, and only when connected to 16AWG wire:

[www.molex.com]

The hard drive connector can have up to 7A per contact for the common PC power supply with 20AWG. Only in the best case with 16AWG wire, it can stand up to 10A per contact:

[www.molex.com] (wire-to-wire connector)
[www.molex.com] (wire-to-PCB connector)

*Note that the wire-to-pcb connector probably needs the copper on the PCB as heat-sink.

So that explains why a 2.5Ohm heat bed at 12V, that takes almost 5A plus another nearly 2A from a 6.8Ohm extruder resistor are at the limit of what the single pin on the disk drive connector can handle. If someone uses a more powerful heat bed or extruder resistor, or If the connector is a bit old and the contact is not perfect anymore it will overheat easily.

I would pledge for a 4-pin Mini-Fit connector, which should be able to handle 12A on 20AWG.
And maybe it's a good idea to use also two disk drive connectors for the motors, which can all together also consume 4x2A=8A with all pololus on full power. Of course it should be mentioned not to use daisy-chained disk drive connectors.

For now I'll use StepSticks, which are limited to 1A each so one disk drive connector will be okay for me, but for the heater+extruder I soldered two wires to the board and I hooked them up with a MiniFit.

I would also suggest to add two 10A slow-blow fuses somewhere on the board, one for the MiniFit and one for the two disk drive connectors. I guess, that people often leave their printers running unattended for some hours, so some extra protection could be a good idea.

I have some more ideas for the design, which I will post in a separate thread.
Cheers,
z)