and thanks in advance for not blasting me for this question.
I am trying to find a way to power a 20V 1A Ac circuit. using 12vdc Li-on or LI-po cells. The device has a 120vac to 20v 1 amp transformer, So I was thinking I could use a dc-ac converter and just tie into the primary circuit of the transformer, but I am assuming that using a dc-ac inverter will have a lot of wasted energy in the conversion, so I think that the dc-low voltage ac would be an easier and longer running circuit.
Any thoughts? any Ideas?
thanks all
So i ordered a replacement 20v AC 1 A transformer, didnt realize but it has 2 primary leads and 3 secondary, so i powerd the primarys and check the leads to see which two had 20V AC. Soldered them into the board and fliped the switch and pop went the fuse. Tried the 11V circuit of the other leads and no fuse pop, but the amp does not produce any sound and it appears one of the transistors is getting very very hot. Any ideas?
Additionally i took the old transformer apart and found the parimary lead wires to the coil burnt but rhe secondary seems intack can i check the se ondary windjngs in anyway to make sure we specked the transformer properly?
Thanks for all the help everyone!
Best Answer
Figure 1. AC input circuit showing DC connection points.
simulate this circuit – Schematic created using CircuitLab
Figure 2. Battery power circuit.
How it works:
Run time
Let's look for some clues on the mains side.
And let's look for clues on the audio side.
The two calculations are crude but agree. 0.4 h = 24 minutes. If you're playing heavy metal with the volume at '11' then that's about it. If you're playing occasional jazz fills at civilised volume levels your power demand will be much reduced.
Output power
You may be interested in the output power of the amplifier. We saw that the peak voltage was 10 V. The RMS (root-mean-square) voltage is given by
$$ V_{RMS} = \frac {V_{PEAK}}{\sqrt {2}} = \frac {10}{\sqrt {2}} = 7~V_{RMS} $$
The maximum speaker power for an undistorted sinewave is given by
$$ P = \frac {V^2}{R} = \frac {7^2}{4} = 12~W $$