AlbertHall
- Joined Jun 4, 2014
- 12,345
But to work as described it must be an N-channel FET.As it is a P-Channel FET
But to work as described it must be an N-channel FET.As it is a P-Channel FET
It should be an N-channel FET and then the problem is that the FET cannot be turned on.I have difficulty seeing how T2 can disconnect again?
Yes your right, I think the key is to use the uC to measure voltage drop over Q2. It would need a soft control, as once the charger has finished and terminated Q2 Vf would drop to 0 and the uC would turn off Q1 and in turn Q2 would close. The charger would then see the cell had disconnected and increase it's output voltage to sense the next battery for charging. This increase in voltage would be seen across Q2 and in turn make the uC believe the charger had just been plugged in - not a great scenario for a battery.Regarding the circuit in post #16.
I have difficulty seeing how T2 can disconnect again?
When the charging circuit is connected then both T1 and T2 is on.
When the charging circuit is disconnected after the charging, then T2 still provide battery voltage back into the "+ Ve Charge" terminal.
Thanks for your feedback.Have you considered inductive charging? Making reliable electrical contacts in salt water will be problematic.
That is correct, which is why it has to be P-channel, otherwise I would have to include a charge pump / FET driver.It should be an N-channel FET and then the problem is that the FET cannot be turned on.
As I said to Kjeldgaard, I now plan to measure Vf across Q2As I noted previously, your circuit suffers from the problem that it is difficult to detect when the charger is removed since he battery voltage will appear at the charge port through the ON MOSFET when you remove the charger.
Given that, how do you plan on detecting when the charger is removed?
That's the question, Vref is 2.5V and I'm using a 10bit ADC, so that should give me a resolution of 2.4mV. I would expect the V drop to be around 30mV dropping to 0 at the end of the charge. I could always include an Opp Amp if it was a significant problem.But how will you measure this small voltage difference?
Can the uC measure that voltage difference when it is riding on the battery voltage?
It might be easier to use an N-MOSFET in the negative (ground) side of the connection to disconnect the charger (unless the battery negative is connected to the chassis).
You just have reverse the control voltage polarity.
That way you would be measuring the small voltage drop at ground level, which generally is easier to do.
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