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Max Amps?

Posted: Mon Jun 18, 2018 9:04 am
by abasel
I have the following power supply https://www.aliexpress.com/item/60W-Dua ... 35968.html

The 5V option is rated for 4A with a range of 0.3A-6A.

Will this cook my Raspberry Pi 3 B+ or should it be fine?

Re: Max Amps?

Posted: Mon Jun 18, 2018 9:37 am
by Z80 Refugee
The current rating of a power supply tells you the maximum it can supply, not the amount it will supply. If the current rating is not sufficient for the load, all that will happen is things won't work properly. As long as the current rating is at least as much as you need, that's fine.

It is the voltage rating you need to be sure about, which must not exceed the maximum voltage specification of the load.

Re: Max Amps?

Posted: Mon Jun 18, 2018 10:25 am
by abasel
Thanks for that. It looks like the voltage of this power supply can peak at 5.5V while the Raspberry can only take 5.25. Is there some sort of circuit/filter that I could put between the two so that the voltage does not go above 5.25V?

Re: Max Amps?

Posted: Mon Jun 18, 2018 10:30 am
by mahjongg
Not really, if your power supply peaks above 5.25V, it may damage any USB devices connected to it.

IMHO this supply is not suitable, because of this.

the official PSU is cheap enough not to risk this.

Re: Max Amps?

Posted: Mon Jun 18, 2018 10:35 am
by abasel
Thanks. The reason that I was wanting this PSU is that the entire project needs a 12V feed as well and so I was hoping to kill two birds with one stone. Oh well, so be it :)

Re: Max Amps?

Posted: Mon Jun 18, 2018 12:27 pm
by achrn
abasel wrote:
Mon Jun 18, 2018 10:25 am
Thanks for that. It looks like the voltage of this power supply can peak at 5.5V while the Raspberry can only take 5.25.
How do you conclude that? It can be adjusted to deliver 5.5V, but the spec says total combined voltage tolerance is 2%. If you don't want voltage above 5.25V, don't adjust it to above about 5.15V

Re: Max Amps?

Posted: Mon Jun 18, 2018 12:31 pm
by klricks
abasel wrote:
Mon Jun 18, 2018 10:25 am
Thanks for that. It looks like the voltage of this power supply can peak at 5.5V while the Raspberry can only take 5.25. Is there some sort of circuit/filter that I could put between the two so that the voltage does not go above 5.25V?
You misunderstand the specification. The 5V is adjustable (Voltage Adj Range) from 4.75V to 5.5V by turning a potentiometer with a screwdriver. See the orange part on the front panel marked +V ADJ.
The 12V is not adjustable.
So the power supply is suitable for use with the RPi. Start with the power supply adjusted to 5.00V then connect the RPi. Measure the voltage again on the RPi and adjust if needed.

Re: Max Amps?

Posted: Mon Jun 18, 2018 12:37 pm
by mosespi
Abasel,

It has a voltage adjustment and the datasheet lists the adjustment range as 4.75v to 5.5v. The combined line, load and 'set up tolerance', which I assume means the adjustment tolerance, is listed at 2% which is pretty good. I would set the output voltage to 5.1v and give it a try, if it meets the specs as listed I see no reason why it would not work. If you are concerned about the regulation or just want to test it before use on the Pi, use another load and watch the voltage with a multimeter.

Alternatively if you need 12v, you can always start with 12v and use a suitable DC-DC converter module to lower it to 5v for the Pi. They make pretty small, cheap and efficient ones these days which are not expensive.

Regards,
-Moses

Re: Max Amps?

Posted: Mon Jun 18, 2018 12:39 pm
by piglet
I never know how you're supposed to make supplies like that safe. You'd have thought it was easy but took a lot of looking for an enclosure when I got one, and it was was fugly and cost more than the actual transformer....

Re: Max Amps?

Posted: Mon Jun 18, 2018 2:54 pm
by mosespi
It is industrial type stuff intended to be used in controlled environments or enclosed.. not really intended for the average home user. I wouldn't put one where non-trained fingers could get to it.

Regards,
-Moses

Re: Max Amps?

Posted: Mon Jun 18, 2018 2:57 pm
by Heater
If you are going to use a supply that can deliver many amps and 60 watts I suggest putting a fuse in the line to the Pi. Otherwise short circuits in whatever you are doing with the Pi can be rather damaging and even a fire risk.