I try to use the D24V6AHV step down converter to charge a camera battery from a solar cell.
The camera battery is a Lipoly battery 2 cells = 7.4V and has a protection circuit. I opened the orginal wall charger and saw that it just supplies ~8.4V constant voltage.
I bought a cheap 15V 1.5Watt solar panel
amazon.com/PowerFilm-Peel-St … B003VKM87E
and the Pololu step down converter:
(which is based on the LM2841)
The problem is the following: When I connect the input power to the converter first, and than put the load (battery) to the output, than everything seems to work fine. But if I have the load=battery connected to the output of the regulator and put in the solar module = input later, than the regulator is shut off and does not charge the battery.
The same behaviour happens if I use a power-supply instead of the solar cell. I thought about adding a diode between regulator and battery but than the regulation cannot be exact anymore as the voltage, lost on the diode, depends on the current.
Finally, I it looks like I destroyed the regulator. By accident, I shortened the output, and while I hoped that the regulator would survive this, it now only shows around 2.3V at the output, regardless of the load or the turning of the potentiometer .
Therefore, I would like to know, before I buy the next one, if the regulator is suited for this purpose and if anybody has an idea why the regulator keeps to be shutoff when the load is connected before the power supply.
I don’t know why you got the behavior you did, but I suspect it has to do with the various protections (e.g. short circuit protection) getting tripped in one case and not in the other. It’s difficult to comment specifically without knowing more about the battery and charger, but I would be very wary of just connecting power straight to the battery, even if it has some kind of protection circuit.
I’m directly connecting the battery to the step-down converter.
The original charger is not more than a constant voltage source. Therefore, replacing this by a constant voltage source using the step-down converter shouldn’t be a problem for the battery (especially, as the solar cell can provide less much current than the original charger).
Getting away from my application:
How does the overcurrent protection work?
1.) Let’s say I connect a load to the output of the converter which causes a higher current than the converter can provide (>600ma). Does it completely shut down, or does it just provide the maximum allowed current?
2.) Let’s conenct a load which causes a current which is inside the converter specs, but stronger than the power source can supply. Than the power source voltage drops below the minimum value required to keep the voltage at the output constant.
Will the regulator shut off, or start to oscillate like shown in the specs?
Finally, could it be that the problem is not any overcurrent, but just that the converter doesn’t like it if a battery is connected first to the output and there is a current flowing backwards?
Could it help to modify the circuit by putting a diode at the output (but before the feedback input of the step-down converter)
There are many variables that affect the overall behavior, and we do not really have these characterized beyond what we have on the web page. Here are more question-specific replies:
1.) There’s some window where the output current is not thermally limited, so in such a case, you could see the output voltage drop without completely shutting off. However, with the various tolerances that are in play, I don’t think you can count on consistently being in that window.
2.) I’m not sure what specs you are talking about showing an oscillation. It seems almost certain that you can get some mix of power source and load characteristics to get oscillation going.
3.) The battery could be the problem. Again, we don’t have it characterized, and I have no idea what you’re connecting to. I’ve only done simple battery charging (no Li-based stuff), and some diode was always present.