I am building a robot platform (radio controlled for now) and I would like to have the ability to plug the charger for the batteries in without a manual switch separating the charge and run circuits . I essentially would like to plug it in and charge anytime without feeding the charge voltage to the electronics. I have searched every where for a solution but come up empty handed every time. I enjoy electronics and learning but this has me stumped and my project has been on hold for nearly a month thinking of a solution. I should know how and as soon as I see it I will be embarrassed I had to ask. Thanks for any suggestions or criticism on my included set up for now. If you need pictures or clarification please let me know. Thanks again.
Hey Weatherjack
You want a way to alternate between charging and discharging through some kind of automatic switch, is that correct? I’m not quite sure I understand what you mean, could you elaborate?
Ok I want to to add a battery charger to the circuit I have designed for my robot but do not want to use a switch (think on/off/charge) to isolate the components from the charge power. Maybe a better way to say it is I want it to be like a cell phone or mp3 player where you can plug it in at any time without turning it off first. My concern is plugging in the charger with damage the motor controller unless it is isolated some how from the charger.
Hi,
First, as an advice, it’s better to use a DPDT switch as a power cut-off switch to completely isolate your power supply (batteries or power adapter) from the rest of your circuit so that when you power off the motor controller, both + and - are isolated.
As for your question about charging the batteries without isolating the controller circuit from the supply, this can be done by simply connecting the charger in parallel with your batteries (connected in series). However, some points are to be considered :
- Make sure not to operate the motors when the charger is ON and batteries are fully charged. When the batteries are fully charged and the charger is still ON, regenerative CEMF (counter-electromotive force) from the motors can become dangerous for the charger if the regenerative voltage bursts exceed the charger’s maximum output ratings.
- Depending on the charger being used, a charger that will work for your application is one that has large output electrolytic capacitors. Therefore, even when the charger is not connected to AC main and batteries are fully charged, the output capacitors will be able to take the regenerative voltage bursts when braking the motors.
- In case batteries are not fully charged, there shouldn’t be any danger on the charger as regenerative voltage bursts from braking will recharge the batteries.
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That makes sense. I never took into consideration on the regenerative aspect either. Thanks. I will use a switch.