Pins melt with 12v fans

[onlypalmero]

Hi people,

I'm trying to control 4 fans depending of some conditions.

My components are 4 power supplies (12v 5a) and 4 fans connected to 4 relays on a protoboard ( and sensors, extensions of wires etc.)

The positive wires of fans and power supplies stay connect to each relay. The negative of fans and negative of power supplies stay connect on a protoboard beside GND of PI (inline). Once started, the GND pins get heat and melt quickly.

Some idea about what happening or what i need check?¿ Thank's

[dustnbone]

How much current are you pulling through the pins?

https://en.wikipedia.org/wiki/Ampacity

[rpiMike]

Post a photo of your wiring.

[onlypalmero]

A quickly diagram => https://drive.google.com/file/d/1FFnU2h ... 3J7Fp/view

[jamesh]

So....no Raspberry Pi in that at all, just an Arduino?

If so why are you asking on the Raspberry PI forums?

[rpiMike]

I suspect feeding 4x 5Amps through a breadboard causes massive heat build up due to resistance.

A quick google suggests max 0.3 amps at 15 volts.

Breadboard is commonly rated for five volts at one amp or fifteen volts at one-third of an amp

https://www.circuitspecialists.com/blog ... fications/

[pcmanbob]

If your fans are really drawing 5A each then the cable size you require to connect
fan / relay contact / PSU will not fit in a bread board.

I would suggest you need to be using 0.5mm sq or 16/0.2 sized cable

I suggest you post links to your fans ,power supplies , relays else can see the actual specifications.

[onlypalmero]

So....no Raspberry Pi in that at all, just an Arduino?

If so why are you asking on the Raspberry PI forums?

I trying develop this for both.

I suspect feeding 4x 5Amps through a breadboard causes massive heat build up due to resistance.

A quick google suggests max 0.3 amps at 15 volts.

Breadboard is commonly rated for five volts at one amp or fifteen volts at one-third of an amp

https://www.circuitspecialists.com/blog ... fications/

Mmmm i understand, the problem is the protoboard, what you suggest? Maybe apply some little resistors?

[klricks]

....
...
Mmmm i understand, the problem is the protoboard, what you suggest? Maybe apply some little resistors?

No it is not a problem with the protoboard.........
The black (-) wire of each power supply should be directly connected to to the black (-) wire on each fan and nowhere else.... Not to the protoboard and NOT to the RPi.
Use terminal blocks if needed: viewtopic.php?f=91&t=276316#p1674314

[onlypalmero]

....
...
Mmmm i understand, the problem is the protoboard, what you suggest? Maybe apply some little resistors?

No it is not a problem with the protoboard.........
The black (-) wire of each power supply should be directly connected to to the black (-) wire on each fan and nowhere else.... Not to the protoboard and NOT to the RPi.
Use terminal blocks if needed: viewtopic.php?f=91&t=276316#p1674314

Ok, i think that it works. I'll run this a long time for test how works. Very thank's!

[pidd]

The black (-) wire of each power supply should be directly connected to to the black (-) wire on each fan and nowhere else.... Not to the protoboard and NOT to the RPi.

Why? Fairly normal practice to have a common negative rail. The power supplies should either have isolated outputs (most likely) or negative earths, neither of which would do any harm.

I agree it could be done either way and is therefore optional.

The biggest melting problem is caused by having twenty amps flowing through one wire (and its contacts) - the wire that links the two negative strips on the breadboard, this happens in more than one place. however as stated the contacts are only rated at 1A not 5A therefore there are other problems

I agree that terminal blocks should be used because of the current but care is still needed to make sure 20A isn't flowing through one wire and isolating the power supplies would automatically achieve this.

[davidcoton]

Certainly not resistors. That will end in tears.

As already stated, you do not need to make the 12V negatives common. Just make sure all the 12V wiring (+ve and -ve) is in at least 0.5 sq mm cable, and any connectors are also rated for 5A (some terminal strip is only 3A -- smaller, but it will get hot at 5A).

If you must have a common negative for some reason, then the common parts must be wired with 2.5 mm sq wire (rated 20A under most conditions). That will need 20A connectors, but properly crimped or soldered connections are preferred.

If your total conductor run for any PSU/fan is more than a metre or so, you may want to use thicker cables to reduce the voltage drop. (Voltage drop means reduced fan power and increased conductor temperature, which is a Bad Thing™.)

[klricks]

The black (-) wire of each power supply should be directly connected to to the black (-) wire on each fan and nowhere else.... Not to the protoboard and NOT to the RPi.

Why? Fairly normal practice to have a common negative rail. The power supplies should either have isolated outputs (most likely) or negative earths, neither of which would do any harm.

I agree it could be done either way and is therefore optional.

The biggest melting problem is caused by having twenty amps flowing through one wire (and its contacts) - the wire that links the two negative strips on the breadboard, this happens in more than one place. however as stated the contacts are only rated at 1A not 5A therefore there are other problems

I agree that terminal blocks should be used because of the current but care is still needed to make sure 20A isn't flowing through one wire and isolating the power supplies would automatically achieve this.

One big reason is to prevent back EMF from entering the sensitive electronics when the fans are turned off. Isolation of high current loads is half the reason a relay is used.

[pidd]

One big reason is to prevent back EMF from entering the sensitive electronics when the fans are turned off. Isolation of high current loads is half the reason a relay is used.

They aren't sharing supplies, it is just a common negative rail. There is no circuit for the back EMF to get back to the board. Not only would I have the common negative rail, I would also earth it so that the power supplies are included in RCD mains protection (UK standards).

As always I would recommend putting protection diodes across the fans, this will save a lot of wear an tear on the relay contacts and eliminate the back EMF.

[davidcoton]

Not only would I have the common negative rail, I would also earth it so that the power supplies are included in RCD mains protection (UK standards).

Earthing the negatives will only make mains-side RCD protection effective in the event of failure of the PSU isolation, which is a fairly unusual fault. The degree of accessibility of the 12V wiring is also a factor. In some circumstances earthing an isolated output introduces additional problems -- in particular bypassing the RF suppression.

[offtopic]
More worrying is the number of IT PSUs that are not marked as double insulation (two concentric squares symbol) and do not have an earthed output. These will always fail Portable Appliance Tests, because they cannot be considered as Class II without the correct symbol, and there is no earth continuity as required for Class I.
[/offtopic]