# Slightly OT - basic electrical class

Solar Expert Posts: 99 ✭✭✭
I've been asked to put together a training session for basic battery electrical systems.

The audience is RV techs, so they're familiar with the basics of batteries and such, but we're seeing a lot of confusion about electronics basics and a huge amount of mis-information so we're going back to elementary electrical training.

I figure someone out there has done this, or knows of resources I can use to start the lesson plans.

Basically I need to cover:

Solar power, alternators, inverters, batteries
Wire sizing, wire connectors, fusing, thermal breakers, and fusible links
Current, voltage, resistance (Ohm's law)
Power, current, and voltage P= V x I
Resistance in wires, both as a function of size and temperature
Effects of corrosion on conductivity

And anything else that might pertain to an off-grid system.

I would appreciate any ideas or links.

• Solar Expert Posts: 1,386 ✭✭✭✭
edited September 2016 #2
measurement (eg why you might want a peak reading DC clamp ammeter)
surge currents
parallel balance and why it's so sensitive
AC vs DC (eg why a breaker might arc with DC)

I am available for custom hardware/firmware development

I think you got the basics... The big difference for "us" is we tend to design systems in Watts and Watt*Hours because we may work with 120/240 VAC loads and 12/24/48 volt battery banks--The typical RV/automotive/marine folks stay in Amp and Amp*Hours -- Which confuses them with 120v*10a AC load side =120watts=1 2v*100a on the battery side... (10amp at 120 VAC is not 10 amp at 12 VDC).

Have also seen even electricians not understand that a 14 AWG wire which can carry 12 amps at 120 volts (1,440 Watts) needs to be 1/0 AWG wire to carry the same 1,440 watt load power at 12 VDC.

Here are some book suggestions:

http://forum.solar-electric.com/discussion/comment/99323#Comment_99323

There are a lot of Marine type electrical courses out there that do a good job--And you really only need to "bolt on" the solar panel+chargers education.

I always try for "balanced designs"--Which means that we are always asking first about power needs and loads (and suggesting conservation). The "cook book" with rules of thumbs is a bit simplistic--But it lets folks design their system quickly, and get a reasonably balanced system quickly (that will usually meet their needs)--And then they can tweak the system, if needed, to meet their specialized needs (running a business during the day, dedicated water pumping, etc.).

To keep things simple--I suggest understand loads to design battery bank first (and 2 days storage, 50% maximum discharge makes battery bank, nominally, 4x the daily DC loads).

Then design the charging system to properly charge the battery bank (5% to 13% rate of charge).

Then finally to double check the loads vs amount (hours) of sun per day (i.e., larger solar panel array for those folks up north, heavy winter loads and smaller arrays can work well in the desert south west).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset