Hi folks,
Sorry, could not think of a better title...
My circuit:
MOSFET is IRL540N
I have a Pb battery with a smart charger connected to it.
When there is a load on the battery I want to disconnect the charger. Both switching of load and charger are arduino-controlled.
Charger is a 25A charger, the battery is 3 390Ah batteries in parallel.
In testing I substitute the smart charger for a PSU and the battery-to-be-charged with a dummy load. Everything works as it should. The MOSFET turns off, the load (and load LED) turns off and vice versa.
All happy so far.
Now I test with the battery charger(s) (I tried more than one) and the battery and this is where I get confused. The charger sees the battery even though the MOSFET is turned off. The voltage drop across the fet is 200mV so it is conducting even though the gate is held low. This happens with the fet disconnected from the arduino (but still with the pull-down resistor in place)
I'm confused. Why does this work when it is a normal power source and load but swap the power source for a charger and the load for a discharged battery and it misbehaves?
Grounds are all common, Arduino is powered from USB or separate battery.
Any help on where I have gone wrong / misunderstood?
TIA
Crispin
Sorry, could not think of a better title...
My circuit:
MOSFET is IRL540N
I have a Pb battery with a smart charger connected to it.
When there is a load on the battery I want to disconnect the charger. Both switching of load and charger are arduino-controlled.
Charger is a 25A charger, the battery is 3 390Ah batteries in parallel.
In testing I substitute the smart charger for a PSU and the battery-to-be-charged with a dummy load. Everything works as it should. The MOSFET turns off, the load (and load LED) turns off and vice versa.
All happy so far.
Now I test with the battery charger(s) (I tried more than one) and the battery and this is where I get confused. The charger sees the battery even though the MOSFET is turned off. The voltage drop across the fet is 200mV so it is conducting even though the gate is held low. This happens with the fet disconnected from the arduino (but still with the pull-down resistor in place)
I'm confused. Why does this work when it is a normal power source and load but swap the power source for a charger and the load for a discharged battery and it misbehaves?
Grounds are all common, Arduino is powered from USB or separate battery.
Any help on where I have gone wrong / misunderstood?
TIA
Crispin