Help me design a 12v electrical system

[The Jeff]

I'm planning to modify a 12 volt trolling motor and run it from a control panel, basically copying the idea here: https://archeryrob.wordpress.com/201...r-stern-mount/

I'd like the control panel to incorporate a voltmeter to measure the battery, an ammeter to help calculate range in various conditions, a USB charger, and the speed control knob from the trolling motor itself. I'm not that great with electronics so I'm not entirely sure if this schematic is set up correctly, but this is my best guess after a lot of Googling. What do you think?



1. The trolling motor comes with a 40 amp circuit breaker. I assume it should go right up by the positive battery terminal so the whole system is protected?

2. I imagine some switches would be nice. Maybe one that turns the USB charger off and another that turns everything off?

3. Are the voltmeter and ammeter in the right locations in the circuit? Or should they go elsewhere to better measure what's going on?

4. I figure 15' maximum run from battery to motor and back, so 8 AWG wire according to BoatUS?

5. If I suddenly go from 0 to 5 on the speed controller will the inrush current damage the ammeter?

My long term plan is to make a solar bimini to charge a LiFePo4, much like rgthom's setup. But that's probably a year or more away so I'm currently just going to focus on modifying the motor and getting a basic electrical system going.

[Arlc]

check out newwiremarine.com

[rgthom]

It looks fine to me. Definitely have the main breaker or fuse at the battery. The motor should not have much inrush if it is run from a controller, the ammeter should not be at risk. Are you going to use digital meters? Just curious.
I did not put in a main switch, as it was not something I expected to use much. The power stays on most of the time, disconnecting the battery at the terminal is easy enough. A switch means more wiring, terminals that can corrode, and it is a possible point of failure.

- Rick

[rgthom]

Oh, and the ammeter is measuring motor plus USB current but USB should be very little so it hardly matters.

[Breakaway]

The usb charger will not be drawing unless a cord is plugged in. No need to switch it, IMO. Probably want circuit protection to protect your phone/ device however.

K

[The Jeff]

Rick, I stole your idea of some big analog meters. Perhaps not entirely necessary but I thought it'd look cool, give me a way to improve my electronics skills, and might be easier to see in the sun.

I put the ammeter before the usb since I thought it might be interesting to see the affect of charging different things. But thinking about it harder, the charger can draw 3 amps so worst case scenario I could have 33 amps of current which would peg the meter. Maybe I should put it after.

Kevin, the usb has a digital volt meter in the middle so my thought was it will be drawing some (probably insignificant) amount of current. I think I'll hold off on switches and see if they'd actually be useful. The charger I bought comes with a 10 amp fuse holder, but it's only supposed to draw 3 amps when charging two devices. Perhaps I should put in a 5 amp fuse or something?

[rgthom]

I do like big steampunk analog current meters, definitely more visible and accurate enough for what we are doing. For the voltmeter, you may need a digital meter if you are monitoring the battery charge state. An analog voltmeter does not have enough resolution.

[The Jeff]

You're right, the analog volt meter is a bit useless. Maybe I should leave it out and just use the digital one on the usb charger. I tried searching for one that was 10-15 volts, but couldn't find anything in a style I liked. I did come across a guy who made a 0-5 volt scale work, but the extra circuitry is beyond me. http://english.cxem.net/izmer/measured44.php

[timo4352]