A blog about SCAMP (Small Craft Advisor Magazine Project) boats. Covering the build, sailing the boat and the scamp community that has formed around this little portly boat.

Sunday, October 12, 2014

Big electrical purchase today

I spent the afternoon in West Marine; I made some decisions about the electrical and needed to execute my plan.

First, I ordered the well recommended Casey book on Sailboat Electrics. That won't be here until Tuesday, but not actually having knowledge hasn't stopped me before.

First, I gathered what I knew:
  1. I needed to physically fit the battery through a hatch opening 20" x 9". It could be no taller than about 8 1/2".
  2. The 12V trolling motor that I ordered uses 50 amps when full open. I'd like to have around 2 hours at full open. That means 100AmpHour battery.
  3. I have no idea how to mount the battery so it doesn't move.
  4. I want a 12v system to run a GPS chart plotter and maybe a VHF radio. These have to be removable so that I can stow them safely.
  5. I want LED navigation lights on a switch.
  6. I want cabin lights (this is easy, LED strip lights).
I can't believe that it took me over an hour, but I had a lot of decisions to make. In the store, I could design all the details in my head.

I had a simple wiring diagram drawn in pencil. Once I had everything purchased, I enhanced it (thanks to Digikey):
Wiring diagram

For inside the well, I bought:
  1. 79AH AGM battery (group 24) and a housing for it. This has a little less capacity than I wanted, but should still have plenty of juice. And it will definitely fit in the well and I know I can mount the  housing inside the well.
  2. a 350 amp battery main switch. They didn't have anything smaller that I could mount easily. 
  3. some 6 AWG red & black wire from the battery terminals to a 100A dual bus. This can carry 50A to the trolling motor without burning up.
  4. A 10AWG lead with connectors from the trolling motor section. Half will be connected  directly to the battery. (The version I bought had round lugs on it, the one on the link doesn't.)
  5. A 15A offboard charger. I'll cut off the clamps and add the other 1/2 of the connector from #4. Then I can just drop the charger in the boat, connect it and 6 hours later have a fully charged battery.
  6. A fuse holder and a 30A fuse. This will go from the bus bar up front to the switch panel. I used a 30A fuse so that I could use 10AWG wire to the switch panel.
  7. All the crimp connectors I needed.
To mount on B3:
  1. A 4 circuit breaker/switch panel with 2x 12v cigarette adapters. Unfortunately, one of the switches controls the two 12v adapters, so that leaves me with only 3 switches. Which is just enough, but I may regret no more space later. The panel has 15A circuit breaker switches. I think this means it could handle up to 60A, but that would have been #6 wire all the way to the panel and that seemed ridiculous, so I fused it at 30A so I could use 10AWG.
I even bought some accessories, like cable clips, screws and velcro.
I don't know where the nav lights will live, so I didn't buy any.
And I don't want to invest in a GPS or VHF quite yet.

It was an expensive trip, but I know what I can do this week.

What's really weird: I wanted to ground everything to the chassis. Duh, you can't do that on a wooden boat. And when I work with the FIRST robotics program, they won't let you do it for the robot either. At least FIRST supplies you with a ground bus.

I have an idea on how to mount the GPS and radio on B4 so that it is easily visible, although I may do like Noddy and put it inside on B3.

Now, I need to start laying out components and crimping connectors onto wires. I'll mount the battery box down, but I'll probably have to cut it up a bit to get it to fit correctly. Then I can finish priming and painting behind B3 so that I can get everything permanently mounted.
I do still need some strain relief and preferably a waterproof (yeah right) grommet for when I run though the bulkheads. I know bcbimmer is using PEX as a conduit. That seems like a good idea. 

I'll also need to figure out how the motor will be wired. Hopefully that will arrive this week.

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