1. What mosfet shall we use? Can you recommend the exact part no.? We will use 15v dc to "activate" this mosfet by the way.
2. Will the switching of mosfet be fast enough that the arduino will not reset?
3. What diode shall we use? Is the common 1n4001 appropriate?
4. We want the charger to be connected to the AC mains only when the robot is docking on the home base, can we use a relay to do this task?
One that handles the voltage and current, and can turn fully ON with the gate drive you have. Cant recommend one without knowing all your sources and loads. The MOSFET is activated by the presence of external power, are you supplying +15 V DC to the interface between docking base and robot?
With the usual filtering and bypass capacitors on voltage regulators and Arduino it should not be a problem. Add more capacitance if you have trouble.
Common rectifier is OK if you dont exceed the ratings. That one is good for up to 1 amp. An even better choice would be Shottkey diode which has lower forward voltage drop.
Yes. Or a mechanical switch.
What parameters of fet shall we watch out for?
Before the IC, we will put 100uF/25v, after we will have 330uF/16v.
So we will use 1n5820 (20v 3A).
Do you reckon microswitch is better than relay for connecting AC?
One that handles the voltage and current, and can turn fully ON with the gate drive you have.
cant say, as I dont know the purpose of this. to turn off +15V when the dock is empty? what will activate the microswitch or relay? can it be falsely activated? is +15v easily accessible? current limited? why does it matter?
sorry it just makes more sense to me drawn this way.
Since your VEXT is so much above your battery voltage, the body diode of the FET might conduct, so I added a diode after the FET, too. But since you have plenty of overhead voltage you no longer really need the FET, just a pair of diodes will be fine.
This version also shows advice from the various gods, such as the heavy loads need to be wired with their own "home run" to the single point ground. The BRAIN is Arduino plus sensors, no heavy loads. If your other servos are substantial loads they can have their own ground too. This "star" ground ensures the charger and brain dont get confused by IR drop from common ground current.
For switching heavy loads use FET and include a few K of gate resistance. That way any "ground bounce" can get dissipated harmlessly. This might cause some ugly switching but you'd rather have it there than mixed in with your low level IO.
As the gods pointed out the Arduino battery monitor voltage will depend on loads. Best to monitor voltage when heavy loads are idle. You can test the battery under load, but you need to know the current and use different criteria for voltage vs charge.
What FET do you think will handle this?
I hope the image below will clarify what I am trying to say before. ^^
I don't understand.
So you are saying I need to connect the grounds of heavy loads direct to the negative of the battery?
Do you think 2k ohms will do? If I am controlling the FET's gate directly via Arduino, then sending a HIGH will switch the FET? 5v 40mA to a 2k resistor will still switch the FET?
If the vacuum pump + servo are running, will the voltage from battery decrease?
By how much?
Do you recommend other means of detecting charge of battery other than the voltage divider?