To power my telescope, mount along with the rest of the prehipherals, I created this power distribution box.
I had the following requirements:
- Wide voltage input range
- Load balancing and input failover
- High efficiency (so as not to waste precious battery power)
- High power capability
- Easy to plug/unplug in the dark.
Buck/Boost Regulator
I used a buck/boost regulator based around the LTC3780 chip to allow for a wide input range of 5v - 32v. This would allow me to use many types of batteries or DC power bricks of various voltages. It also boasts a rating of 12A on it's output when operating at around 12V and a maximum efficiency of 98%.
Speakon Connectors
I used 4-pin speakon connectors for all of the 6x connectors. Each connector is wired such that inputs are on pins "2+ /2-" and outputs are on pins "1+/1-". This allows any connector to be used as both an input or an output, perfect when fumbling around in the dark!
Load Distribution & Failover
I wanted to be able to automatically combine all of the available inputs without problems. Simply wiring all of the inputs together would cause problems if, for example, a 20V power brick was connected at the same time as a 12V battery and would almost definitely cause damage to the battery (and probably everything else).
Diodes can be used to combine inputs together. This would allow multiple batteries and power sources to be plugged in without backfeeding any current into any of the batteries.
However, diodes have a ~0.7v drop which would waste precious energy when running solely on battery power.
The Perfect Diode!
The LM5050 chip can actively switch on a MOSFET if the input voltage is higher than the output and switch it off again when the input voltage falls below the output.
There are 6x LM5050 chips and MOSFET pairs (one for each input) that can simulate a perfect diode. This provides me with the lossless failover that I required.
You may notice that in the diagram, the MOSFETs seem to be connected in reverse. This is because MOSFETs can conduct in both directions when on, but the reverse body diode would allow current to flow backwards when off if installed in the conventional way.
Power Monitoring
I used a simple power monitor that can display votlage and current along with the total energy used in the session. This allows me to see at a glance, the voltage remaining in the batteries as well as how much energy an imaging session has used.
Finishing Touches
A dymo label printer and clear heatshrink makes for a great way to label cables. Don't forget to fuse any battery connections too!
Finished Pictures
