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Old 10-14-2010, 03:48 PM   #57
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Its still about power. Your example on charging is invalid.

Batteries act as a load to a constant current power supply that has an upper voltage limit (This is what a charger is). The power supply will match its output voltage to the battery voltage and supply its maximum current until the upper voltage limit is reached. Once that voltage is reached, the current will begin to drop.

A 30V limited constant current supply at 5 amps will immediately drop to 12V on a battery that is discharged to that level. It will deliver 60W of power at that voltage. It will continue to deliver 5 amps of current to the battery until it reaches 30V. At 30V it will be delivering 150W of power. Of course, the battery will be damaged if the charger actually reaches that voltage.

15V @ 10 amps will be subject to the same conditions as above, it will initially limit to 10 amps at 12V, so 120 W. It will eventually get to the 15V and provide the same 150W. This time however, you won't damage the battery as badly. You'll likely boil off some of the electrolyte and equalize it some.

So, within the bounds of battery charging, my statement is correct. We are interested in power.

To get more in depth.

The area under the curve is what we are interested in. If we make a -power- plot that shows the power delivered over time for the 14.4V battery charger and then again for the 14.8V battery charger, the total delivered -power- will be greater for the 14.8V charger...It will remain in constant current mode for a longer period of time.

The reason I say power is what we are interested in, is because that's what the chemistry demands. You must put in Coulombs of energy to make the chemistry work. Coulombs translate back to watts, ultimately.

When I've looked at the information that SolarBob has put out there, I had to try to understand -why-. At first, I thought, well, its the cabling, but when I did the math, it didn't work. I started to look at the other things that he does. The only thing that he does differently, from the standard, is related to the termination voltage of the charge cycle. I had to satisfy myself that this really was the thing that made the magic happen.

Its a hard concept to grasp. We have to make assumptions to arrive at why there is a difference. The biggest factor is that we are limited in time to arrive at a full charge state. Given that we have to charge the battery fully in a limited amount of time, the more power we can put into the battery in that time, the closer we'll be to a full charge state. If we set the bulk charge termination voltage to 14.8V, that allows us to remain at the full current of the charger for a while longer, thereby, delivering more power to the battery in the same amount of time. It doesn't seem like much, but I'm convinced that's where the magic is.

I can show it using spread sheets and assumed values, I want to be able to show it works in real life too. I'll put together an experiment, monitor things and see what happens.
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Old 10-17-2010, 01:12 AM   #58
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Rocketdork... I think we are arriving at the same conclusions, just by a different path. I too agree that it is the 14.8 volt constant current increase that is responsible for the total increased watt-hours going into the battery.

The point I was making was, it is the CURRENT- the amps- that is responsible for the "filling" of the battery. In water terms, the increased voltage threshold is keeping the "valve" open longer so more flow can go into the tank (the battery). This results in increased amps being stored before the charge controller cuts in and begins limiting the amp flow to protect the battery.

My point of emphasizing amps over voltage in a solar setup is that I see alot of people choosing higher voltage panels over higher amp panels thinking that watts are all that matter. For example, a 22 volt, 10amp panel will not give as much battery charging as a 17.5 volt, 12.5 amp panel, even though both are rated at 220 watts. If the controller could convert the excess voltage into amps, as in an AC transformer, then fine. But in a DC solar setup, any excess voltage beyond that needed to overcome wiring losses and controller inefficiencies is just lost.

In practical use, I have relatively low voltage (17volt) panels putting out more amps into my batteries daily. I don't even use a controller yet since my total system voltage rarely goes over 14.4 while recharging. If I added more panels then I would definitely need a controller. But in the real world, my large pack never really gets that filled.

Most people who boondock will never get to that point either, and that is why I recommend investing any money in more panels first. Once you have an EXCESS of production from those panels, THEN it's time to invest in a controller to protect your batteries. And that's really what the charge controller is there to do. Many people I meet however, think that the controller will GIVE them more energy into their batteries than the solar panels are putting out daily. And as I'm sure you know, that's just not possible.

To sum up...for the same wattage panel, always invest the higher amp panel unless yoo are anticipating large voltage drop through undersized or long wiring runs. In most RV environments, this will not be the case. As long as your voltage from the solar panels at the batteries exceeds 14.8 volts (if that's what it is set for), the controller is going to let all that amperage pass anyway. The key is getting all the amp-hours you can into the batteries while the sun is shining. Any excess voltage, hence excess wattage, will be wasted as it will not be converted to amps in a DC system.
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Old 10-17-2010, 01:19 PM   #59
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My point of emphasizing amps over voltage in a solar setup is that I see alot of people choosing higher voltage panels over higher amp panels thinking that watts are all that matter. For example, a 22 volt, 10amp panel will not give as much battery charging as a 17.5 volt, 12.5 amp panel, even though both are rated at 220 watts. If the controller could convert the excess voltage into amps, as in an AC transformer, then fine.
Except on any partially occluded day when your 17V panels simply cannot make the required power, my 21V panels still have enough headroom to continue on without issue. It still takes voltage to deliver current..
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Old 10-17-2010, 01:25 PM   #60
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I agree in a round about way.

The caveat that I'd mention is related to MPPT controllers. They can and do convert the wasted energy of the difference in the cell and the battery.

That allows for some fun things...you can wire your cells in series (assuming that you have multiples of the same cell) and use smaller wire. Easier to buy, easier to route and easier to hide.

I struggle with the stuff I hear about solar. There seems to be little science and a great deal of "I did this and it worked"...Teasing the science out of the noise and trying to apply it is time consuming.

MPPT controllers are a case in point. If you have low voltage cells like I do, a MPPT controller will do almost nothing for you. The real benefit comes in the form of the higher voltage cells. They tend to be cheaper per watt than the low voltage stuff that people seem to want.

I have to admit that its fun to examine this stuff though.
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Old 10-17-2010, 06:59 PM   #61
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now you guys have the solar down, how do we get water???

what ideas and systems work for collecting rain water , as the situation arises

and filters !

thanks in advance
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Old 10-17-2010, 06:59 PM   #62
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wildbill 100 i just emailed you

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Old 10-17-2010, 10:28 PM   #63
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I am glad my original post made all of you folks sit up and take notice of a good solar system. That was my intention.
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Old 10-18-2010, 02:01 AM   #64
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I am glad my original post made all of you folks sit up and take notice of a good solar system. That was my intention.
And every time someone replies to the thread it dings my email to remind me that I still want to replace the controller to battery cable (besides it's fun to read smart guys spar over theory).

Has anyone developed a cal procedure for the AM Solar HPV-30? 1st they said one was being written, now they say one doesn't exist. Obviously BS because someone sets these up on the bench. Probably not a deal to figure out but I'd like to know how the factory did it.
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Old 10-18-2010, 05:10 PM   #65
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dunderbill - get the dehydrated water. It has a long shelf-life, and takes very little storage space.
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Old 10-18-2010, 07:11 PM   #66
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dunderbill - get the dehydrated water. It has a long shelf-life, and takes very little storage space.
And for all you "Doubting-Thomas's" out there: Dehydrated Water

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Old 10-18-2010, 10:39 PM   #67
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And for all you "Doubting-Thomas's" out there: Dehydrated Water

Okay I spent about 45 seconds too long on that website...good for a chuckle.

Now a serious solar question. When 2 panels are hooked in parallel do the volts or amps double.

My evergreen panels are about 17v each and have an 11 amp output each. I'm trying to ensure that I have the proper fuse size on the switch box as I prepare for installation.
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Old 10-18-2010, 10:41 PM   #68
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Amperage sums in Paralleled configurations...voltage remains the same.
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Old 10-19-2010, 08:43 PM   #69
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Okay I spent about 45 seconds too long on that website...good for a chuckle.

Now a serious solar question. When 2 panels are hooked in parallel do the volts or amps double.

My evergreen panels are about 17v each and have an 11 amp output each. I'm trying to ensure that I have the proper fuse size on the switch box as I prepare for installation.

yep...just like batteries, your voltage stays the same but amperage adds on to the circuit.

Oh, and for those of you seeking Dehydrated water, I have some left in stock. The cost per can is pretty high, but due the light weight, the shipping is dirt cheap.
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Old 10-19-2010, 09:04 PM   #70
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I'll take 2 five gallon jugs of dehydrated water. How much does it make when re-hydrated? ;-)

Thanks for the info on the amps and volts. My house batteries must be wired in series than since they are 6 volt golf cart batteries.
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