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Solar Power: Making Connections

By Edited Oct 18, 2015 0 0
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My background is pretty solid in electronics, but my work experience was with small wires and low currents. When I started working with solar power equipment I had to learn a few things about using huge wire. Instead if 12 gauge wire and smaller, I was using 4/0 wire that requires different connectors, tools, and techniques to easily complete a safe, and secure installation.

Solar Panel Wiring
I'm using MidniteSolar external junction boxes for my solar panels, mounted to the pole that the panels are mounted on. I then like to run 2 guage wire run into my building that houses my system. I use red colored tape to identify each end of the positive cable so there's no chance of error when the cable is wired in. The PV combiner allows you to optionally use DC breakers appropriate for your system to protect each panel. I have found that using cable one size smaller then the maximum specified size of the connector is easier. A 1/0 cable in a 1/0 connector is a very tight fit.

The Correct Inverter Cable
The first thing that will help you is to buy your wire from a welding supply store. They stock the big wire (used for arc welding) and they have the connectors, crimping tools, and expertise on how to make a good connection. Welding cable is very flexible due to its large number of conductors, has rugged insulation, and is really nice to work with. Be sure that the connector is a snug fit on your cable before crimping the wire. I use a propane torch and rosin core solder after the connector has been crimped to help create a low resistance connection.

Electrical supply houses sell 4/0 cable that is far more rigid, and while it is good quality cable it's difficult to bend, and more difficult to connect. It'll work but I don't recommend it. Life is tough enough.

For cutting this large cable I've had a lot of good luck using a large bolt cutter. You end up with a neat and clean cut, and it's quick and easy to use. A hack saw works, but side cutters will have you hating life in no time.

When you buy connectors for your cables, get them with a properly sized mounting hole. If the hole diameter is large, you lose contact area when you bolt your connections together. The larger the contact area the better. This reduces connection resistance, heating effects and makes for a more reliable connection. Use brass washers to spread the contact area.

Corrosion Prevention
Battery connectors are exposed to acid spray and tend to corrode. Corrosion reduces the quality and reliability of the connection.

After cable and connector have been fastened together, you need to protect the connector. Yes, there are spray can products at your automotive supply store that do a good job, but I've had good luck using Vaseline. Make sure you wipe over the exterior of the connector and any exposed copper wire as it enters the connector. Do this after soldering, not before.

I forgot to give some cables the treatment, and you can sure see the difference! Petroleum jelly works for me, but whatever corrosion control product you choose, make sure you apply the treatment to the connectors. It saves you money and the hassle of redoing connections down the road.

In case you do need to change a cable connector later, leave yourself a little slack in the cables. An extra few inches could save you money and irritation later.

Remember that loose connections are a hazard. The currents that the batteries supply to your inverters, and the charging current supplied by your inverters to the batteries are large! This means that if the resistance is high the connector can get extremely hot. So be sure that all connections are tight and low loss. Connectors should be checked and tightened annually. I had a loose connection that almost caused a fire, so I can tell you from my own personal experience that this is important.

Never attempt to splice this big cable. Use a terminal block inside a junction box if you have to extend a cable. A better idea is to put in a new cable the right length and forget splices and junction boxes entirely. It'll probably be cheaper anyway.

High Current DC Fuses/Switches
Special fuses and fuse blocks are readily available for the high currents you're dealing with. Be sure to use switches and fuses rated correctly for your installation.

Most inverter manufacturers offer switches, breakers, and fuses designed for DC applications. Start looking for the components there, and shop around. There are a lot of really good sources for these parts. Which wasn't the case in the recent past. Some companies like OutBack offer completely pre-wired panels you can mount on the wall, so all you have to do is wire in the batteries and bring in power from the solar panels or wind turbine.

In my system here I use class T fusing, which has worked out well. Breakers are an excellent

option because it also acts as a switch allowing easy disconnecting of the batteries. Also breakers are resettable, while a fuse requires replacement. My fuse has never blown even with a catastrophic inverter failure due to lightning.

Give Yourself Room
Install your equipment so that you have easy access and enough room to expand in the future if you need to. A tight fitting installation can be trouble and make things harder to get at for maintenance or a repair. Be sure to label equipment so that anyone who has to work on your system will know exactly what he's looking at. Mount everything securely, using wire-ties to group cabls together. Do it right in the first place, and you'll be glad you did.

Knowledge And Budget
Whether or not you decide to use a professional installer is matter of budget and the level of confidence you have to tackle it yourself.  If you can afford it, professional installers will usually do a great job, but you're always better off if you have a good understanding of the issues involved. You know what to ask the installer, you know more how to maintain your system, and you can make changes properly.

If you're on a tight or incremental budget, you can do all or some of the installation yourself. I like this path because my income has been a bit variable and I've been able to incrementally make improvements over the years. This has given me time to learn a lot without making expensive mistakes. When I get a windfall I upgrade. A step at a time. In hindsight I think I would have wasted a lot of money building a system all at once. I was not aware of what I didn't know. A bit too self confident! So budget contraints probably saved me.

However you build your system, take time to research things out and try to use high quality equipment designed to last. Haste makes waste is an old proverb well suited to the problems of assembling a high quality solar power system.

Photovoltaic Design and Installation For Dummies
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(price as of Oct 18, 2015)


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