Robert Harsell

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since Nov 16, 2012
have worked construction, commercial fishing in the Florida Keys, and have traveled most of the USA...still do...on a regular basis.

founded and directed a watershed association for a decade, the Arthur Kill Watershed Association

born in 1946
Greenville, Augusta County, Virginia
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Recent posts by Robert Harsell

Why not tie a block to the critter's neck and then toss him in the pond?

Why does he have to be ground up?

He'll rot and get eaten whether he's ground up or not, won't he?
5 years ago

Rob Sigg wrote:Yeah I was confused as to why my voltage was so high but my amps werent. I forgot that since they are in series the amps dont add up just the voltage. That was why I started the whole post, but in the process I learned alot of new things thanks to you guys. So thanks!




I was right. I did have some studying to do.

I was not aware that the MPPT controller involves the use of a DC to DC converter.

Your panels put out about 72 volts and 8 amps, but the MPPT controller can turn that into lower voltage and higher current.

Then I take it the current you measured was between the panels and the controller. If you were getting 8 amps at that point, then the current between the controller and the batteries was much higher.

7 years ago

Long ago (I almost forgot about it), I figured out a more efficient vehicle. It was electric.

It had a small battery to carry it at low speed. It would arrive at a main artery which had an overhead rail. The car would hook onto the overhead rail and from then on would be carried by power in the rail, which was supplied by solar panels mounted over the rail. The car's battery would charge on the rail.

The car had a computer which could be programmed to dispatch it back onto it's wheels at a predetermined location. The destination could be programmed before departing and once on the rail passengers could sleep, read, or otherwise occupy themselves.

I asked myself the question: Would people really buy something like this? In the interest of not trying to kid myself, I try to be honest with myself, so I answered myself honestly.

nah

So I forgot about it... almost.



Electric cars are definitely cleaner for big cities with smog problems. Los Angeles, Mexico, and Kathmandu would be well served by electric cars.

I don't have much faith in our technological future. I think all of the peripheral factors of building and using electric cars will prove them to be a bad move. I see it as a mental mistake as much as anything else. I don't believe we need to be thinking about cleaner cars. I think we need to be thinking of thinking... hard thinking... like learning to stay put. That'd save a lot of electricity.

7 years ago

Mike Dayton wrote:We have options, but there has to be a push from the top to make the country more efficent and make us all use less Fuel. By the way, it WILL be painful for us as a Nation to Change.



I'm a trucker. I used to haul produce out of the central valley before California outdated my rig. (CARB)

I play mental games to entertain myself while rolling. On one trip I mentally calculated how much fuel for each cantaloupe in my reefer. An eight ounce glass of diesel came with every cantaloupe. That really put things into perspective for me.

I could rant for hours on the subject, and I'm a trucker, but simply stated, why haul things across country that can be grown, baked, built, or caught, locally?
7 years ago

Rob Sigg wrote:You are correct mostly, I get a bit over 8 amps. IM getting it right now actually. I think a good test would be to rewire them to compare. My panels are about 35 to 50 feet away from the charge controller, but batteries are 2 feet.




When you rewire them, run the wires from the three panels down to the charge controller and make the parallel connections at that point. The more wire you have carrying the current, the less loss you'll have.

Another way to do it would be to parallel the panels where they are, then go to Lowes or Home Depot, etc., and buy heavy duty wire for the trip from the panels to the controller. The heavier the wire, the lower the loss.

If the wires haven't been cut in order to facilitate the series connections, I'd go with the former.

7 years ago

Rob Sigg wrote:OK I got the skinny. My MPPT controller can handle up to 150 volts and it will take any combination to put the max amount of power into the batteries etc. He tells me that its always better to have the higher voltage rather than amps since there is no line loss with voltage. If we went parallel our amps would be much higher, but the net gain would be less due to loss. Now I understand why my volts are so high but my amps arent



Okay that's a new one on me. I don't do large commercial installations and am not familiar with the technicalities involved. Obviously your friend knows more about this. The controller can handle the high voltages but I don't think that is at the core of the problem.

I have a small set up, which I used for years although since the last time the batteries went bad on me I haven't replaced them. I'm not home much (over the road trucker) so I haven't gotten around to getting my panels useful again.

I'm not qualified to rebut your friend on the advantages of series configuration of panels, other than to remind you that you have a small system, and the issues which may add up to large losses or gains in a large system may not be the same ones with which you must deal.

If your panels are not far distant from your charge controller, and the parallel connections are made near the controller, taking advantage of the extra conductivity in 6 wires versus 2 wires (were the panels paralleled where they are located), then the resistive losses should be comparatively small for your system.

On the brightest day of the year, at high noon, the most you will probably see from a 240 watt panel is 8 amps. I'm taking for granted that the wires supplied by the manufacturer are capable of transmitting 8 amps without significant loss. I believe this to be true because it would not be in their interest to manufacture powerful panels only to have the loss in the output wire so high that the buyer and user would experience poor performance.

If your panels are configured in series, the highest current you can expect is 8 amps. If the panels are in series, the voltages will add but the current will not. One panel produces 8 amps. Three panels in series produce 8 amps. The voltage may have gone to 72 volts because of the series configuration, but the current will still be 8 amps.

Now, if your batteries are in a configuration supplying you with 24 volts, then no matter how many volts you have coming out of your panels, you won't go much higher than 24 volts at the battery end. Actually, fully charged, you'll get about 28 volts, as 12 volt lead/acid batteries are about 14 volts at full charge. The batteries will not climb to the 72 volts of your panels. Again, the batteries will stay at about 28 maximum. To simplify the discussion and for the sake of understanding, let's stick with nominal whole numbers. At noon on a bright day, with your present configuration, you can charge 24 volt batteries at 8 amps, 72 volts or not at the panel end of the circuit. Three solar panels will not provide the current of an automotive alternator, so your 12 volt batteries will probably not climb much beyond 14 volts even while charging. For power, let's say you'll have 8 amps X 28 volts = 224 watts. If the panels were configured in parallel, you'd be charging with 24 amps at 28 volts, and your power would be 24 amps X 28 volts = 672 watts. I know the panels are rated at 240 watts maximum, but the rating is taken from test conditions rather than the actual operating environment, so these numbers from a 240 watt rated panel are actually pretty much okay.

Losses in power lines are a major factor in the transmission of electricity. It is because of this that the high tension wires one sees strapped all over creation are run at such extremely high voltages. In your case, the losses in the relatively short lines from the panels to the charge controller, resulting from the relatively low current of 8 amps, are relatively small, perhaps a few percent. However, the loss of 16 amps of charging current resulting from the series configuration versus parallel configuration is a huge loss. You're losing 2/3 of the capability of your panels.

If you had 6 batteries configured in series to equal 72 volts, then yes by all means the series configuration of your panels would result in less resistive loss. There is no doubt about that and all the calculations would back it up. But again, your batteries are at 24 volts. Lead/acid batteries do not climb to triple their nominal voltage ratings.

You need to get all of the current you can into your batteries. I know this from experience. Solar power is great, but it has its disadvantages. Perhaps the greatest disadvantage is the lack of sunlight. When the sun is shining, you need to have everything right so that your batteries will not sit in an uncharged state for long. If they do, they'll die. Desulfators are not all they're made out to be.

If you tell me you're getting much more than 8 amps with your present configuration then I have a lot of studying to do and I'll have to rethink everything I've stated above.

7 years ago
Remember that by putting the 3 panels in parallel, you are getting 3 times the current. Parallel configuration means that no matter how many panels you parallel, you still have only 24 volts. However, for each panel you add in parallel, you get an additional approximately 8 amps.

The power output of your panel array increases by 240 watts with every panel you add. The increase in power comes from the increase in current (amps), not from any increase in voltage. A 24 volt system is a 24 volt system. All your additions of panels should be in parallel.


7 years ago

Rob Sigg wrote:My panels are in series, so you are correct. A solar installer friend of mine set them up that way. And yes I have a 24 volt system. Not sure why he would have set it up wrong are we missing something?




Your batteries are configured to 24 volts, which means you have a 24 volt system.

The panels are 24 volt panels. If you configure three 24 volt panels in parallel you have 24 volts. If you configure three 24 volt panels in series you have 72 volts. You don't want to charge a 24 volt system with 72 volt panels. The open circuit voltage of each of your panels is almost 35 volts. Under full load, the panels should be a little over 24 volts.

Try reconfiguring the panels to parallel and see how things work out.




7 years ago
I don't know if you are familiar with equations for current, voltage, resistance, and power. If not, this might help:

"I" stands for current (in amps).

"V" stands for voltage (in volts).

"R" stands for resistance (in ohms).

"P" stands for power (in watts).

I = V / R

Consequently, using simple algebra:

V = I X R, or more simply expressed, V = IR

Likewise, R = V / I



Now for power. The power in a circuit equals the product of the voltage and the current.

P = VI



If you have a 24 volt system running at 1 amp, you have a system delivering 24 watts. 24 volts X 1 amp = 24 watts.

If your 24 volt system is running at about 31 amps, it'll be delivering about 746 watts, which approximately equals 1 horsepower. Watts and horsepower are both expressions of power, in different units of measurement.



These things should help you understand what is going on with your panels, batteries, and charge controller. Volts, amps, resistance, and power are all related through the above equations. One factor does not change without a corresponding change in one or more of the other factors. The changes are dictated by the relationships described by the algebraic equations.

7 years ago