Disconnect battery from load while charging

Thread Starter

shmrpk2911

Joined Sep 5, 2017
4
I am designing a switching circuit that disconnects the load from the battery when it is charging and connects battery back to load after charging is removed. Any suggestions on how to design the circuit?
 

Thread Starter

shmrpk2911

Joined Sep 5, 2017
4
What is the application?
We are trying to build a mobile robot platform. During docking, it will get connected to wall adapter and I'm concerned since wall adapter supplies more power it may damage the micro controllers used, so I want to disconnect the load while charging the battery.
 

dendad

Joined Feb 20, 2016
3,008
It is good design practice to add transient protection to your power supplies, along with reverse supply protection. The regs you use should have a decent head room for input volts. In a hostile environment, like driving motors, transients abound.
There should be no real need to disconnect the regs while charging if you have built them correctly.
 

dendad

Joined Feb 20, 2016
3,008
If you are controlling the motor anyway, just do not turn it on. It will be disconnected from the battery.
If you still must disconnect all from the battery, have a relay driven from the charger directly, and then feed the charger to the battery via a diode. This diode will stop the relay operating on the battery volts.
The relay contacts normally closed feed the battery volts to the rest of the circuit, but when it operates, it breaks the circuit.
But you really do not need to isolate the circuit when charging anyway.
Having the circuit disconnected means it relies on you manually putting it in the charger and removing it, so why not have a plug in battery that you unplug from the circuit and plug it into the charger. Disconnected!

Edit...
How about a barrel jack and use the built in switch contact to disconnect the circuitry -Ve line.
I still think you don't need to disconnect anything though.
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
3,584
Years ago I took a battery charger out of an emergency lighting system (small wall unit) and put it and a battery in a speaker box. In a second speaker box I put a car radio. Hinged the two together and put a strap across the top to carry it. Saw no need to disconnect the load during charging. Even if the charger didn't have enough output to power the radio, it would charge when the radio was off.

OK, your application is a little different. Still, if you disconnect the load when the robot docks then how do you reconnect the load without having to do something manually?

As for power consumption, the battery is going to take as much or as little current as it wants / needs. Based on the charger, if it can deliver the current the battery wants then it will. If not then the battery will take what the charger can give. Your microcircuitry is more at risk from transients caused by the motors and a relay clicking in and out than from a power supply. As long as the supply doesn't have a higher voltage than what the electronics can tolerate then you're golden. Either that or the electronics powered from the battery must be regulated. Say your electronics operates at 5 volts and you have a 12 volt battery. If your regulator can handle 25 volt peak then anything the charger is going to do isn't likely going to cause any problems with the electronics. And if you're still concerned then you can pre-regulate the voltage so you don't exceed the capacity of the regulator.

But asking someone to design a circuit - I have this question: How much are you willing to pay for engineering services?
 
Last edited:

crutschow

Joined Mar 14, 2008
23,352
Assume that the load is a simple motor, can you please design a circuit with the use of a relay which disconnects the motor from the battery while being charged.
You want us to answer your question, but you ignore ours.
That's not how this works.
So I'll ask again, what is the charging circuit and where is it located?
 
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