In the mean time …
Easter sunrise service on Castle Island in South Boston …Wow!
The view to the east is amazing. I am not going to try to describe it, but it is worth getting up early for … At least once!
I had been providing the sound system for the event for a couple of years and had really enjoyed setting up the sound gear in the dark and watching the new day arrive.
The airplanes are not landing at Logan airport across the harbor at 4:00 in the morning and you can actually hear the harbor, the sound of the waves hitting the shore, some large ships going by … Add the flash of light from Boston Light and the slightest hint of change out on the horizon … It is very nice!
This year I had asked my contact with the Castle Island Association if I could try powering the event with one of my solar powered battery rigs and he said yes!
Normally … By the time most of the people arrive for the Church service the generator is already running with its constant drone covering up everything but the “red eye” flights coming in and the occasional overhead sea gull.
This year the first sound breaking the harbor “soundtrack” was the “Good Morning” from the priest celebrating the Mass … I’m sorry if it startled anyone!
The system ran for 2.5 hours and used .35 kWh of power … a tiny amount by any standard. Basically the “idling” current draw from having the four wireless microphones, mix rack and amplifier on … With no background noise to compete with, the overall sound level did not need much power to cover the audience standing an an area almost the size of a football field.
The small “solar system” I brought to power the event was about the same size and weight as the generator that I helped off load from the park rangers utility tractor in previous years. Something else to think about … Eventually!
But back to rewiring …
The battery systems had worked wonderfully at powering the events so far. But I had unknowingly been getting a little help from good old fashioned “dumb luck”.
If this project was to get out of the tinkering stage I wanted to do it without needing that help.
Adding the battery meters was going to provide some very useful information, adding fuses was going to keep everything and everyone safe … and spending a little “quality time” with my coffee pot and calculator was going to get the systems performing as well as they could … For a long long time!
To find out how long you will have to check back later … Hopefully much later!
In working with 12 volt DC power it is very important to size everything for what you are trying to do … In my case … Powering all the equipment needed for an outdoor concert.
Sizing the wire used and laying out the equipment so that as little power as possible is lost to resistance in the wiring of the system … Ideally keeping the loss between the batteries and the inverter to less than 1%
To do that I needed to use the largest, shortest wires possible.
Using a voltage drop calculator like the one found in “rapidtables.com” you can see what size wire you will need to use. For this part of the project I used short (18″) #2 cables to go from each of the batteries to a pair of insulated buss bars, and total of about 8′ of #2/0 cable to get from the buss bars, through a circuit breaker, fuse and shunt to the inverter and back again.
If I’m doing my math correctly I am only losing .1463 volts (1.17%) to voltage drop with a 200 amp, 12.5 volt DC load … A little more power than what you could get from a standard household 20 amp circuit.
It sounds like an awfully small amount of loss to get excited about, until you realize almost everything in a 12 volt system will shut down when the voltage drops below 10.5 volts. Losing .1463 volts from 12 volts does not seem like much … But if you only get to “play” with the 2.4 volts between 12.9 volts (a full battery “at rest”) and the 10.5 volt “shut off point” … Losing that .1463 volts means I would lose between 5 and 8% of my total power at full current … And if I wanted to keep the batteries alive as long as possible I do not want to discharge them fully … I could be losing over 10% of my power … to wire!
I am hoping to give you a little “photo” tour of how I wired one of the systems in my next post.