I am using axuillary relays to supply voltage to my 12Vdc power relays. The spec for the auxillary relay is 5Vdc, 170mW 130ohm. If I am not mistaken, this means the relay current is just under 40mA. As the relays are non-latching they will be on for long periods of time. I am thinlking of using 2 output pins to share the "continuous load". The current required to operate the auxillary relay relays is just below the 40mA absolute maximum (excluding in-rush peaks). As the outputs will switch on with a small delay, the first output will have to supply the full current before the second pin is switch on. Once both pins are on, I assume they will share the load roughtly 50/50.
I am not sure of the duration/magnitude of the in-rush current - will this also be shared by both output pins? Also what if there is a reduction of the 5V voltage?
I am using a 12vDC 4500mA power supply connected to Vin. and will be using 3 auxillary relays plus a couple if LEDs
Hope someone can advise me. Thanks
Not a good idea. Use direct port writes to set the pin states at the same time.
It would be much safer to use a transistor to switch the relay coils, and to use a separate power supply for them. Or, just buy a relay board designed for Arduino.
The Arduino on board voltage regulator is NOT designed to handle significant loads and may overheat in your scheme. Avoid using a 12V supply on Vin, as that makes the problem worse. 7V is much better.
That is unlikely to be a valid assumption.
Thanks for your swift reply. I did originally think of using an Arduino relay shield, but as I´m using a screw shield plus a Wifi shield, the addition relay sield seemed a bit too much.
I´m using din rail relay sockets for the auxillary relays. I think I have ust found a suitable solid state relay that might solve all my "problems". The SSL pulls only 10mA so maybe the problems solved (just need to make certain).
the addition relay sield seemed a bit too much
You don't need to use shields.
The SSR is a much better choice than attempting to use pins to drive relay coils. Keep in mind that relay coils require diodes to suppress inductive voltage spikes.
I think I am going to use SSR´s. Thamnks for your input.
…or logic level MOSFETs.
Would be a good idea to actually cite the datasheet itself.
Relays are inductors. There is no such thing as an "in-rush current". You need to study up on inductors. 
Very bad idea!
Sounds perfectly reasonable to me! The effective internal resistance of about 30 Ohms is likely to be very similar per pin as they should have identical geometry.
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