My project is basically a tank robot that drives over a charging plate. Its 2 stainless steal strips on a arc that makes contact with a strip underneath. The strip underneath is held on with a screw and a wire wrapped around it going to the charger.
When I connected to a charger directly its fine. But when powered via the charging plates I get a hissing sounds. I am using the Sparkfun 6Ah battery.
I can't really tell where the sound if coming from. Maybe the battery? Doesn't seem like it is from the charger though.
I am working with ideas to get better contact but not sure if that is the problem. I tested with a multimeter and the highest was 600-700ma which is 1/2 of what it should be. The charger is set to 1.2A so seems like it can't draw enough power. Adafruit said the charger will pull what power is available.
I also have a dc-dc step-up in my project between the battery and the arduino.
I suspect the added resistance from the track charging plate is at the root, as you state a direct connection of the battery to the charger seems to function ok.
What would hiss though? Could it be the electrons "jumping" from plate to plate? Just a wild guess. Moving it while on there seems to affect the sound, as well as moving any of the contact points. Sometimes its loader than other tests. Sometimes if it can't pull over 300ma the charger stops and try's again.
you say that the charger will stop if it can't pull over 300ma it stops. just a shot in the dark but it isn't starting and stopping so often that it's producing a sound in the audio range?
Its high pitched and moving the robot affects the sound so it seems.
Seems louder the lower the current it is able to draw.
It stops if it can't get above 300-400ma consistently. Using the multimeter I have a hard time getting a stable reading. I did once and it was just under 700ma. The charge LED turns off and then on again when it try's again. I have only left it connected long enough to test. It doesn't turn off and on that fast, it tires for a bit.
I should add though that the sound doesn't start till the charger starts to try to pull current. At first power on its at 120ma and then the charge light turns on and like 2 seconds later the sounds starts and the current rises well tries to.
Long story short I used a power supply with higher voltage (12v) and it is much better. The resistance of the plates was dropping the voltage below 5v which is the min for the charger. 12v is the max. I need to find a PS that about 8v 1.2A+. The one I have is only 750ma.
Last night I got everything set permanently and redid the bottom plates on the robot. Its much better now but still can't draw more current. It
would be okay but its can't draw enough to overcome the robot's draw and charge the battery.