Share a power supply between two devices

[TechTree]

Hello, I have recently converted an old bluetooth speaker into a Aux input device for a guitar amplifier. You can see how I converted it here. So now I'm trying to power both the bluetooth device and the guitar amplifier using the original amplifier's power supply.

Here is the power that each device requires:
Bluetooth device = 5v DC 500mA
Guitar amplifier = 12v DC 1A

Would it be possible to use the original amplifier's power supply to power the bluetooth device as well? If I connected the bluetooth device to a 5v 500mA car charger taking an input of 12v. Then just connected the car charger to the output of the amplifier's power supply? Would I also need to upgrade the guitar amplifier's power supply to 1.5A?

Many thanks.

 

[anorlunda]

A car mobile charger sounds like the right way to go.

Will you run both the guitar and the charger in parallel? If so (and if the charger is only 50% efficient) you need 12*1+5*1=17 watts rather than 12 watts from the power supply.

It is impossible for us to say if that will fry your power supply. Do you have any nameplate info on the power supply separate from the guitar's needs?

 

[Rive]

You can either properly measure the overall power consumption to determine the actual power requirement (and it can be within the original 12V 1A limit) or you can just get a 12V PSU with 1.5A rating (what is a very safe and conservative approach).

Usually the PSU ratings has a decent reserve to the requirements so there is a chance that the original PSU will still suffice, but blindly assuming something like this is not engineering

 

[TechTree]

Thanks for the replies! I have replaced the bluetooth device I'd like to power in parallel with the guitar amplifier with a device that consumes much less power, just 80mA now rather than 500mA. I'm guessing a device which uses that little power should suffice being powered by the amplifier's original power supply.

I'm just slightly unsure where to find a PSU that takes an input of 12V (from the amplifier's PSU) and outputs 3.7V 80mA? It just seems too specific.

Thanks!

 

[russ_watters]

Would it be possible to use the original amplifier's power supply to power the bluetooth device as well? If I connected the bluetooth device to a 5v 500mA car charger taking an input of 12v.

Yes, that should work. I have a similar setup powering my 12V telescope, several 12V accessories and a 5V USB hub.

Then just connected the car charger to the output of the amplifier's power supply? Would I also need to upgrade the guitar amplifier's power supply to 1.5A?

Is that an external power supply? Does it have a nameplate that says 1.5A output and the amplifier has its own nameplate that says 1.5A input? It *might* work...worst case you overheat and burn out the power supply. But you can buy 3rd party 12V power supplies pretty cheap:
https://www.amazon.com/dp/B01GD4ZQRS/?tag=pfamazon01-20

https://www.amazon.com/dp/B01461MOGQ/?tag=pfamazon01-20

Heck, I probably have half a dozen from discarded electrical devices in a box somewhere...

 

[russ_watters]

I'm just slightly unsure where to find a PSU that takes an input of 12V (from the amplifier's PSU) and outputs 3.7V 80mA? It just seems too specific.

Wait, where did the 3.7V come from - you said 5V before?

But no, that's not an uncommon voltage. Even it was, you could use an adjustable voltage converter:
https://www.amazon.com/dp/B06X3S76J9/?tag=pfamazon01-20

https://www.amazon.com/dp/B07JZ2GQJF/?tag=pfamazon01-20

 

[TechTree]

Wait, where did the 3.7V come from - you said 5V before?

Sorry if I made it unclear, but I replaced the device I was wanting to power with a much lower power device instead, hence 3.7v 80mA rather than the 5v 500mA device.

The 3.7V device used to be battery powered and used a 80mAh battery and lasted for about an hour. If I use a power supply with the same voltage will it only take what it needs? Even if the power supply can offer 3A and I'm using just 80mA?

 

[davenn]

Sorry if I made it unclear, but I replaced the device I was wanting to power with a much lower power device instead, hence 3.7v 80mA rather than the 5v 500mA device.

The 3.7V device used to be battery powered and used a 80mAh battery and lasted for about an hour. If I use a power supply with the same voltage will it only take what it needs? Even if the power supply can offer 3A and I'm using just 80mA?

You just need a linear / or switching regulator off the 12V line to step it down to 3.7V

DC-DC switching buck converter, one just like this and dirt cheap, you couldn't build it for that price

https://www.ebay.com.au/itm/Waterproof-DC-to-DC-buck-Converter-12V-to-3-3-3-3-7-5-6-9V-Power-Module-Supp-IL/173574617102?hash=item2869da780e:m:mpIvE4dqDG0KizqVMAqe8xw
Dave

 

[rbelli1]

Even if the power supply can offer 3A and I'm using just 80mA?

Yes. The load determines the amount of current. As long as the power supply can supply at least enough current then everything should be fine.

Please note that for unregulated supplies you may get a larger voltage than expected at very light loads.

BoB