Solar That Really Works

[SpursMVP]

Originally Posted by ralper

#6 wire is too small for 400 watts. Use a #4 wire. Even better use a #2 wire. Too small of a wire will not transmit the power to the controler and batteries.

Reread Solar Bob's web site.

DO NOT SKIMP ON THE WIRE SIZE !

My bad...I actually had ordered 25 ft of 4 gauge jumper cable. Must have had too much Dr. Pepper when posting this. Since each panel puts out 18.1 v I figure the calculator presented above is probably accurate. It shows that 4 gauge at 25 feet at 24 volts with 22 amps would have a drop of 1.6%. I may be figuring this wrong.

[wildbill100]

My six, six volt batteries are wired with .0004 welding cable to a marine battery cut off switch.....which is wired with the same cable to the inverter....the solar controller is also connected to the cut off switch with #4 welding cable......

[Wetboy5776]

Originally Posted by ralper

#6 wire is too small for 400 watts. Use a #4 wire. Even better use a #2 wire. Too small of a wire will not transmit the power to the controler and batteries.

Reread Solar Bob's web site.

DO NOT SKIMP ON THE WIRE SIZE !

It is true that you don't want to skimp on wire size, but based on his panels' combined amperage at full out put, he will have less than a 3% voltage drop at that length. That is definitely acceptable for a solar installation.

[Wetboy5776]

Originally Posted by SpursMVP

Handy Bob provide a great photo of how to make a combiner box. After looking at it for a while I went to Home Depot and bought a 4 X 4 X 2 waterproof junction box and 2 grounding bars. In addition I picked up two ground lugs which fit into the bars.

This will allow me to split the incoming panel wires into positive and negative and drop them through the bottom of the junction box. The cool thing is I used JB Weld (works on thermoplastic) to attach the grounding bars to the junction box so there are no additional holes.

Also ordered a 25 ft #6 set of jumper cables for the primary wiring. Since this wire is primarily within the coach I don't need to worry about the UV impact. Also odered 15ft MC-4 extension wires from the panel because the Evergreen warranty indicates that if the cables coming from the panel are altered the warranty will be void. These wires are #10 (UV resistant too) and will run to the combiner box. We're going to drop the jumper cable wire down through the back of the coach (it's a diesel pusher) since that section is easy to access and is close to the compartment where the controller will be mounted.

Question for the experts....the wires coming out of the controller go where? I know they go to the batteries; however with 4--6 volt batteries I am curious where the wires are attached on the 4 batteries.

It's slowly coming together and as the sytem is put together I'll be sure to take some photos.

Two 6 volt batteries should obviously be wired in series to 12 volts. Then those two are connected in parallel to the other two 6 volts, also wired in series. You are probably already set up this way. At the point one pair is connected to the other pair, that's where you want to connect the output from the controller. You can verify the lines you want to connect to is 12 V by using a multimeter.

Oh, saw where you got the 4 gauge cables. You should have NO problem with voltage drop now! Just make sure you use only as much wire as you need.

[SpursMVP]

Hi everyone....well the Morningstar 45 charge controller and trimetric 2020 battery meter have arrived. I've also completed the creation of the combiner box that will go on the roof of our coach. The two--200 watt Evergreen panels should arrive in the next day or two. With shipping to a local shipping terminal (about 5 miles from me) the total cost was $117 for shipping. Pretty reasonable considering each panel is 42 lbs before any crate material is attached.

The 25 ft #4 jumper cables have also arrived so it looks like I will begin the internal assembly this weekend. Slowly but surely the system is coming together. I'll take photos with my EVO phone and hopefully be able to post them here as the work begins.

Thanks to everyone for the great ideas. One question....I've been searching for the appropriate charge rate for the Interstate 6 v golf cart 2200 batteries. These are the wet cell type and I can't seem to find the manufacturer suggested charge rate. Can I run with the 14.8v like the Trojans?

[ralper]

Yes

[Kodydog]

Hi SpursMVP

Which model of Evergreen Solar pannels did you get. Also I would be interested to see how you get the #4 cable from the pannels down to the charge controller. So photos would be great!

[SpursMVP]

Originally Posted by Kodydog

Hi SpursMVP

Which model of Evergreen Solar pannels did you get. Also I would be interested to see how you get the #4 cable from the pannels down to the charge controller. So photos would be great!

We picked up the ES-200-FA3b panels. The b panels are about $100 cheaper due to cosmetic issues; however there is no impact on the power output, etc. Sun electronics had these.

The plan is to run the #4 through the engine compartment. After my RV guys pointed this out it makes complete sense. The rear of our HR diesel pusher is pretty much hollow (as are most MH's) and it's really easy to access the wire, run it down the side of the compartment and into the basement where the charge controller will be located.

I plan to start this weekend and will take pictures as we go along.

[Wetboy5776]

Originally Posted by SpursMVP

We picked up the ES-200-FA3b panels. The b panels are about $100 cheaper due to cosmetic issues; however there is no impact on the power output, etc. Sun electronics had these.

The plan is to run the #4 through the engine compartment. After my RV guys pointed this out it makes complete sense. The rear of our HR diesel pusher is pretty much hollow (as are most MH's) and it's really easy to access the wire, run it down the side of the compartment and into the basement where the charge controller will be located.

I plan to start this weekend and will take pictures as we go along.

Welcome to the wonderful world of solar! I'm writing now listening to the waves lap up on the shore as the sun sets....using juice produced by my solar panel all day. There's just something so organic about not being connected to an AC outlet, but letting the sun provide your power.

Perfect weather all this week down here in Florida doesn't hurt either!

Looking forward to seeing those pics. I think tomorrow I'll snap a pic of my setup here at the beach and post it. Let is know of you have any install ???'s

[Kodydog]

What kind of tilt mounts are best for the pannels?

[RocketDork]

I've been reading this stuff and HandyBob's page. I'm scratching my head a little bit here.

When we charge a battery, we are putting in power. Power is measured in Watts. We don't care about volts, or amps. Power is what we use to make all the electrical stuff function in our coaches.

When I start doing the math behind changing wire size in a hypothetical situation of a 25 amp panel setup, I can't make it all work out the way that Bob says it should...

When using 10 AWG I get a loss of ~40 watts, 6 AWG has a loss of ~15 watts and 1/0 has a loss of ~4 watts.

Total system power at a 17.5V Max power point would be 437.5 watts

So, when I make an assumption of using a perfect charger (energy in equals energy out), the total number of watts delivered in a typical day (4.5 hours full power equivalent) where I live would be;

10 gauge - 1788 watt/hours
6 gauge - 1901 watt/hours
1/0 gauge - 1951 watt/hours
Superconductor, no losses - 1968.75 watt/hours

So, the dramatic difference that Bob notes is likely not ONLY due to wire size changes. The math doesn't add up. Delivered energy isn't different enough to explain it.

So, what else does he do?

1. Controller close to batteries
2. Adjust controller to deliver 14.8 V to the batteries
3. Maintain 14.8V for an hour prior to switching to 13.5V float.

So, taking a look at those changes to standard, I think this is where the magic is.

1. Charger closer to batteries will make the voltage delivered to the batteries closer to what the controller believes it should be. The voltage drop between the charger and battery will definitely have an effect on the state of charge of the battery at the conclusion of charging. This can be partially compensated for by having a voltage sense connection on the controller.

2. Adjust the controller to 14.8 V at the batteries. The standard line is 14.4V...14.8V is going to allow for more charging at a constant current mode than 14.4V. During the bulk charging stage of a three stage charger, this is where the real power is delivered. So terminating the bulk stage at a higher voltage is going to deliver more power to the battery prior to moving to acceptance charging. Power is what we are after...not volts, not amps, but the combination of those...power.

3. Maintain 14.8V for an hour prior to switching to a 13.5V float charge. I'm not sure why he's doing it this way, an hour isn't long enough for an acceptance charge to complete. However, 13.5V will continue to charge the battery at a lower rate and get it to a full state of charge, if there are enough hours to do it.

I've spend a significant amount of time studying battery charging techniques. I've talked to the experts in batteries at my job...I've arrived at what I think is making the difference in Solar Bob's system...

To charge a battery fast, our experts say...

1. Set the bulk charge voltage at as high a voltage as you can. The limiting factor is the out gassing of the electrolyte. The battery MFG's will usually tell you where this is. Flooded cell Lead/Acid only. AGM and SLA's are a totally different game.

2. Once you hit a predetermined voltage in bulk charge mode, maintain that voltage until the charge current drops to a small value...typically around 3% of the 20hour Ah rating.

3. Once you've hit the small current value, drop to a float charge voltage.

This is the typical 3 stage charger "algorithm". Step 2 is the hard one and is where virtually all of the chargers that I'm aware of make compromises. The issue is this, the chargers aren't aware of what current is going to charging the battery and what current is going to other loads (lights, water pumps, etc). The chargers are also unaware of what the 20 hour Ah rating of the battery bank they are charging.

If they aren't aware of these two things, they can't accurately determine when the acceptance phase of charging is complete. They MUST make a decision of when to stop this phase of charging or the charger will damage the battery. Most chargers make the decision to terminate acceptance charging after a specified time.

The acceptance charging part of the cycle is really only responsible for about 10% of the state of charge, so if you make compromises here, you aren't likely to really effect things significantly.

So, I think the magic in HandyBob's techniques come down to this.

1. Try to eliminate power losses in wiring. No reason to throw the extra away as heat. Depending on how things are wired, you could get 10% more power in a typical day.

2. Change the bulk charge termination voltage at the battery terminals from 14.4V to 14.8V. -THIS- is the magic. It allows the constant current mode of charging to continue for a longer time. More power is delivered, therefore, more power is available.

I need to devise an experiment to see if my idea is even close to reality.

So, after I made this post too long, what do you think?

[John Hilley]

RocketDork, I agree completely with your statements.

[SpursMVP]

I think you're right on target here. When reading my installation manual for the Tri-star 45 charge controller it lets you set up the voltage going out. Although it's not installed yet I plan to set it at 14.8 v and have it within 30" of the batteries. Will be running 4 gauge wire from the junction box to the controller and using the MC-4 10 gauge wires from the 2 panels to the junction.

I've got everything in my office and garage and now just need the time to get it installed. I think the extra time spent reading all of the manuals has actually been a good thing to fully understand the workings of the parts before installing them.

Pictures will be sent once the installation is finished.

[Wetboy5776]

I agree with most of your conclusions, RocketMan...except this...

"Power is what we are after...not volts, not amps, but the combination of those...power."

In rocketry, total power, or thrust, may be what we are after, but charging is a different animal. For example, we could safely start charging a near-dead 12V battery at at 30 volts and 5 amps. Or we could start with 15 V @ 10 amps. Both would equal 150 watts of POWER, but the 10 amps would charge twice as fast.

This is because what we are really trying to accomplish is moving a certain amount of Amperes into the battery. The voltage is merely the "pressure" by which we are moving it. If we were fueling a rocket with a 1000lb of fuel, we could do it at 1000lb per hour, or 100 lbs over 10 hours. Either way the rocket would end up with the same total amount of fuel...

But if we only had a limited amount of time to fuel, as is the case when charging with solar, putting the most amount of fuel (amps) in as quickly as possible is the key. Therefore, we want to increase the amp flow into the battery, not the voltage. As long as the voltage is sufficient to move the charge, of course. After that, it's all about the amount of charge you can get into the battery bank.

Therefore, using total watts into a battery is NOT the primary measure we should be using, but rather total amp/hours. Particularly, as this is the way we will be measuring the OUTFLOW of energy.

All of this is for the bulk charge, of course. Once we get to ~90%, it's all about the QUALITY of the final charge, not so much the quantity. That's where the 3 stage charger comes in, as you said... It's alot like filling your gas tank. You can go all out on the pump till your tank is nearly full. But to "squeeze" that last few gallons in, you have to back of the pump and fill the remaining space slowly.