Stabilized symmetric power supply from battery

batteries

I'm making ECG device and for that I need a dual power supply.

I decided to use 3 x 9V batteries and below there is my scheme:

enter image description here

unfortunately I encountered a problem. I created that power supply using that scheme but after connecting to the output small computer fan, the RPM (and voltage) gradually decreased and finally stopped rotating. construction was hot but after a couple of sec it started to work again but with the same result. where is the problem ? virtual ground ? maybe I should make scheme with 4x 9V batteries ? like this :

enter image description here

greetings

Best Answer

Did you happen to use the "heavy duty" 9 volt battery? They have an amazing capacity of only around 50 mAh! So if you put any real load on them, their voltage will drop quickly and they will likely heat up as well due to high internal resistance which is tripled when put 3 in series. Take away the load and the voltage will go back up some.

The same will happen to a lesser extent with alkaline 9 volt which have a capacity of around 300-400 mAh.

You would be better off with lithium batteries, but if you want to keep it simple, consider AA, or C, or D alkaline in series.

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