Question on power supply (Circuit Boards)

[circuit]

I am getting ready to order a mini circuit board for a mini portable amp I am building. I would like to be able to power the amp in 2 ways.. with a 9V battery.... and a wall plug. I have attached a picture of the miniature amplifier. In the wiring diagram it shows that it is a 2 interface input, which leads me to believe that this would work for a 2 option power supply configuration (9v battery and 9-12v wall charger). Am I correct in assuming this? If this is the case, does it matter where I wire the 9v battery and where I wire the wall plug? When it is plugged into the wall I would like it to override the 9v battery.


Any help would be GREATLY appreciated!!!!

[52 Bill]

In the wiring diagram it shows that it is a 2 interface input, which leads me to believe that this would work for a 2 option power supply configuration (9v battery and 9-12v wall charger). Am I correct in assuming this?

There may be two places to power the circuit, but that does not mean that it will work as you want it to.

This board appears to be a stereo power amp probably originally designed for use in a car stereo application. If you power it from a standard 9 volt battery, I would expect that battery life will be disappointing.

Unless you plan to use some sort of rechargeable battery pack, you will need to have a way to unhook the battery from the circuit when the wall power supply is connected. This is usually done with a switching power supply jack, like the ones on most guitar FX pedals.

Oh, and welcome to the place.

[greekie]

Welcome to the place!

What is the max voltage of the circuit? I bet it's more than 12V if that amp was made for a car system. And if so, you can use a rechargeable car or motorcycle battery. Or one for a scooter for that matter. And you can build in a charger circuit as well very easily!

Get a good 13-14V power pack able to deliver 5A or something like that. It should be plenty to charge a battery. Now, from the input power jack you should connect the minus/ground to a common ground-post. Connect the + from the power jack to the anode of the diode. Connect the cathode (the one with the stripe) to a large capacitor of 25V or higher rated voltage. Now, connect the battery + to that +, and the battery - to the common ground post. You now have a simple battery charger. An ampere-meter in series would be good to monitor current and check when the battery is charged, so it doesn't overcharge. And a on-off switch would also be good.

[circuit]

Bill52 and Greekie thank you for your answers, it is very helpful information.

I did a search on ebay and found this

NEW Portable 12V 1800mAh Li-ion Rechargeable Battery Pack | eBay

It is a rechargeable battery pack. My question is would it run the board sufficiently when in portable mode. Also is it ok to have it plugged in all the time and run it off the wall outlet, or would it ruin the battery pack?

Thanks again in advance.

here is a link to the amp, if you would like to look at specs

DC 9V

[g1]

They recommend a 12V 2 amp power supply. The battery you linked is 1800mAH or 1.8 ampere hours. So it would run that amp for about an hour, depending on how loud you are using it. You need to figure out how many hours you want the battery to last. A 20AH battery would give you 2 amps for about 10 hours.

[greekie]

Most starter-batteries found in scooters here in Denmark, are around 12V / 4Ah. That'll give you about 2 hours of play time at max volume. As they weigh 1,6 kg (around 3,5 pounds) each, you can just add as many as you want in parallel, to get the desired power storage you feel you need.

You must remember though, that the larger the battery, the higher rating your power supply and charging circuit must be. A 12V car battery can draw as much as 25-40 amps when being charged from total depletion. This will normally not be the case for you, but be wary. That sets a certain demand for the power supply and the diode. Let me be the first to recommend you a SMPS power supply. They are very inexpensive! Get a good 50A diode and you should be all set.

DC 12V 20A Double Output SMPS Switched Power Supply | eBay

[J M Fahey]

It looks like a 15+15W RMS car amp.
Nice but too loud , forget about 9V batteries and even Li Ion ones; 12V lead Gel cells minimum which is *heavy*.
And you will still need a preamp, you can't plug your guitar straight into it.
Unless you want to play at a beach or public square with a couple dozen people , I guess your best bet will be to start with an LM386 amp which is happy both with a 9V battery and any wall wart.
Plus being simple and light.
Did I mention cheap too?

[circuit]

Thanks for all of the replies. I like the idea of the of the larger 12V battery. I found this one on ebay

SEC1055 12V 5AH Replaces Zeus PC5-12XBALT1-12 Volt 5 Ah Security Alarm Battery | eBay

So my next question is I would like to use this power supply to charge the battery and run the amp when it is plugged into the wall.

CCTV Security Camera Power Supply Adapter 12VDC 500ma | eBay

I found this circuit wiring diagram online and was wondering if this is a acceptable way of accomplishing charging the battery while plugged in, and running the amp when plugged in. There is a 12v car charger in this circuit, which i will not be installing. Will this work?




Thanks

[g1]

500mA is half an amp of current. The recommended supply is 2 amps. Plus you also want to be able to charge the battery. So you will need a large 12V supply. I don't know of any "wall wart" style adaptors that will put out that kind of current. Some kind of car battery charger might be a better solution. You also need to consider how long you want to wait for the battery to charge.

[circuit]

Okay, I think I found the right power supply.

New AC 100-240V To DC 12V 2A Power Supply Adapter US | eBay

My main concern now is wiring it up so that it charges the battery while it is plugged in.

Could someone please take a look at this schematic and tell me if it will work properly.



Thanks

[Steve Conner]

A lead-acid battery needs 14.4V to charge fully. So no, your circuit won't work as you have only 11.3V left after the diode. However, you can buy wall-wart battery chargers that will.

1500mA charger for 6V & 12V sealed lead-acid batteries | eBay

I would just get one like that and connect it directly to the battery. If you're lucky, it will run your amp too, though it would take a lot longer to charge the battery if you were playing loud all the time.