UM17 - Battery Manager

This small units purpose is to supply an uninterrupted power supply on the output from the two connected batteries on the inputs.

So the decision to make the UM17 battery switcher was made as a way to avoid one large battery unit. A large battery is difficult to transport and takes longer to recharge. By having several smaller units I could create a unit that would monitor the state of these batteries and change from a depleted one to fully charged one automatically.

My description of the UM11 or UM19vB battery units show that I've been through a change to the configuration of these power units. This change was front a +/-12vdc system to a single 24vdc system. The decision to make the UM17 was before I had changed to the single 24vdc system. So I initially had a design where this unit would detect the voltage of the batteries and change over based on it's own evaluation of a depleted battery. When I changed to the single 24vdc system it made sense to take advantage of the UM19 battery units own shutdown circuit and report this state to the battery switcher hence removing a double up on circuitry and code within the battery switcher. This data is transmitted on the now spare pin of the 3 pin power connector.

I have three 24vdc battery units called the UM19vA, B and C. They are all identical in that they are made up of two 12v 18Ah sealed lead acid batteries though one does have 20Ah batteries. These are used to power my UM12 motion control timelapse rig. From my tests I can run the whole rig with all motors running for about 11 hours from one of these battery units but I often do shots which take longer eg. over night with stars, where I would be taking shots for up to 14 hours plus. So I needed something that would switch to a second battery unit once the first became depleted.

The UM17 Battery Switcher doesn't monitor the voltage of the connected batteries. The UM19 battery units do that themselves. But the recently added Data pin on these battery units allows the battery units to set this data pin high and low to reflect the state of the battery. The UM19 batteries are configured so that they signify that the battery is depleted by setting the data pin to low and then turning off after 10 seconds. The UM17 monitors the data pins on both the input battery units and will switch from the battery that goes low to the other battery, if it is high, to output a continuously uninterrupted power source. The depleted battery can be replaced with a charged battery and the UM17 will take note of this and change to this battery once the other battery is depleted. You could potentially have a non-stop supply of power if you had a non-stop supply of fully charged batteries but as we well know the time it takes to charge these batteries is longer than they take to deplete so at the moment I can potentially supply about 30 hours of fully loaded motion control rig.

UM17 Battery Switcher

The front panel has two leds which are linked to the two input battery connections. There is a large button on the front panel also. If you press this button it will light the leds. The leds will display which battery input is active by being permanently lit whereas a battery in waiting will flash. If the connected battery is depleted then the led will not light or if there is no battery connected. If you hold the push button down for 2 seconds then the unit will change the battery over to the other battery if it is charged and ready to go. This could be useful should you chose to remove a battery when it is the current battery but you need it for something else. One example might be that you have run the battery for 8 hours and wish to put it on charge so that it is ready for another shot down the line and you can leave the other fully charged battery to continue for the remaining time. The main reason for having this function is for flexibility.

The unit is controlled by an Arduino Nano for the logic processing, a small buck converter to supply power to the Arduino and relays. It is a very simple unit from a hardware perspective. The unit has two outputs which are simply paralleled together for multiple outputs so you can have lights as well as the timelapse rig attached in the same area.