Need Help To Figure Out A Solution To Charge Two 12v Batteries...

[rs14smith]

Hi all,

For a project I'm doing, I have two 12v batteries connected in series to give me a total of 24v, and those batteries are connected to a motor controller.

Now, the two batteries are inside a battery enclosure that's mounted inside my projects frame, so I can't open the enclosure to access the terminals...at least not that easily.

What I want to be able to do is, I want to find a way to charge both batteries without having to remove the wires from the motor controller (unscrew the terminals on the motor controller and take the wires out), as well as not having to physically un-connect my two batteries from being in series.

Instead of physically doing that, I'd prefer to use a mechanical disconnect "switch", but then I still need a professional way to connect a charger (battery charger) to the batteries without having access to the battery terminals; just the wires.

Attached is an image what I currently have setup.

Hope that's enough info

 

[MikeMl]

During charging, the voltage will need to be 29.4V. How much current does the motor controller draw at that voltage if it is left powered, but the motor is not running?

 

[rs14smith]

During charging, the voltage will need to be 29.4V. How much current does the motor controller draw at that voltage if it is left powered, but the motor is not running?

That I am not sure of. It does have a LED that indicates if it is receiving power or not enough power, but I would assume it doesn't consume much power while nothing is going on. I'm using the Sabertooth 2x25 motor controller: Sabertooth 2X25 regenerative dual motor driver

Why do you ask?

 

[MikeMl]

...Why do you ask?

My original thought was just to parallel an external charger with the controller/batteries. The standby current of the controller is not listed on the data sheet you linked. Since you do not want the standby current from depleting the batteries when the robot is not in use, you could use a high-current toggle switch to break the connection to the controller and then wire in a connector from the battey-side of the switch which will let you plug-in the charger.

Ideally, your charger would be current-limited, voltage-limited, and time-limited, in that order of priority. Suppose your batteries are almost discharged at 22V. When you first connect the charger, it should be current-limited to what is specified by the battery maker as "Initial Charge Current", likely a few Amps. As the battery accumulates charge, its terminal voltage will rise. The charger should voltage-limit at 29.4V, and hold the battery voltage at that level for several hours. That is where the time-limit comes in. If you want to "float" the batteries indefinetely, then the charger should be switched to voltage-limit at 27.00V.