External PSU for an Arduino Nano.

Apologies if this seems to be a repeat of a question that others have asked many times. I have tried searching the forum, but the answers don't seem to fit my needs...so here goes:-

I have connected a 5vdc 2A phone charger power supply to the Vin and Gnd terminals of a Nano, and taken a tapping off to power a 4 relay driver board. Each relay draws about 10mA when energised.
I want to use the 5v output from the Nano to drive a voltage divider (with a current load of about 500uA), but find that, even with no relays being energised, the '5v' Arduino pin is only at about 4.2vdc. I can only assume that the on-board voltage regulator has robbed me of the missing 0.8v.

Would it be sensible therefore, to replace the 5v PSU with, say, a 7 to 9vdc PSU, and would this stabilise the Arduino's 5v pin to its nominal value of 5vdc?

A second apology may be due too, as I haven't managed to grasp the technique to show my circuit graphically yet, and it seems that you helpful folks love a schematic or two.

GM

It would be more sensible to get a actual 5v power supply that would be regulated, not a cheap phone charger.

Who makes a 10ma 4 relay board? Likely the op-isolator needs 10ma to trigger the relay circuit that would use 70-100ma per relay coil at a minimum.

Glorymill:
I have connected a 5vdc 2A phone charger power supply to the Vin and Gnd terminals of a Nano, and taken a tapping off to power a 4 relay driver board. Each relay draws about 10mA when energised.

Unusual relay board, or incorrect advertising (happens a lot).
Most relay boards with blue 5volt sugarcube relays need ~75mA relay coil power (when energized).
And 2mA signal current from the Arduino I/O pin.
Post a link to the relay module.

Glorymill:
I want to use the 5v output from the Nano to drive a voltage divider (with a current load of about 500uA), but find that, even with no relays being energised, the '5v' Arduino pin is only at about 4.2vdc. I can only assume that the on-board voltage regulator has robbed me of the missing 0.8v.

No 5volt on the 5volt pin because of a USB reverse protection diode between USB socket and 5volt pin, that drops about 0.4volt. So you usually have ~4.6volt on the 5volt pin on USB supply.
4.6volt is not a problem for the board though, but it could be for certain sensors.
Also note the 500mA limit of that diode (and USB from the laptop), so four 75mA relays 'on' at the same time is quite a load.

The onboard 5volt regulator is only used if you power the Nano on V-in.
Problem there is that you can't draw much from the 5volt pin through that regulator before it overheats.
With 9volt on V-in, you can only just power ONE relay coil.
Leo..

Glorymill:
Apologies if this seems to be a repeat of a question that others have asked many times. I have tried searching the forum, but the answers don't seem to fit my needs...so here goes

Surely if you have studied the forum, you will realise that you must not attempt to supply power to a Arduino (UNO, Nano, Pro Min, Leonardo, Pro Micro) via "Vin" or "RAW" or the "Barrel jack" on a UNO?

The microprocessor requires regulated 5 V (or at least a stable voltage near that). It has a "5V" pin to which to power it. You need a 5 V regulated power supply for the Nano and anything else requiring 5 V.

Thanks for your replies.

Each relay coil measures about 70 ohm, so at 5v operating potential each should consume about 70mA, however the Arduino output will only power each opto-isolator directly, the coil current being supplied directly from the external power supply....

I think I need to go away and find out how to post one of those pretty schematics, or I risk misleading you guys and wasting your time, time that I am very appreciative of.

Thanks again.

GM

We don’t need a schematic to understand your putting 5v into the “vin” pin and that doesn’t work right because “vin” will drop the voltage 2v to regulate it for the processor.

Maybe attach a usb connector to your power charger and send that power through the USB port on the nano.