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Old 04-10-2007, 09:41 PM   #1
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Solar system question

I'm gathering parts for my solar system, and have a few questions. I've got 6 15 watt panels that are going on a platform on the roof to give me 90 watts of charging power. I'd like to have either 6 or 8 deep cycle batteries getting the charge. I've already got the power isolator so my alternator can charge them also when the bus is runnin'. I'm looking at getting a controller that has the added feature of a menu that will allow me to set the charge cutoff voltage, the low voltage dropout, and the voltage at which the load will reenable. The problem is, I don't know any of those settings. Has anyone here set anything similar up that can help a newbie out? The last thing I wanna do is burn something out while setting it up.
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Old 04-10-2007, 10:02 PM   #2
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Usually the cut-in voltage is 13V and cut-out at 14.2V. I have never seen mine cut out from too much voltage but it is interesting at how little light is needed for the panels to still be above the cut-in limit. Sure it is very small current but I was surprised that they were still working while the sun is going past the horizon.
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Old 04-10-2007, 10:08 PM   #3
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also, do ya'll know if I put a piece of plexi glass over top of them, will I be cutting down on the sunlight input to much? also would eight deep cycle batteries be overkill with just 90 watts worth of panels?
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Old 04-10-2007, 11:01 PM   #4
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I think putting plexiglass over them would greatly reduce the way they work, it would also be a pain to keep the plexiglass and the panels clean. I have more batteries on my bus than you are using but I do not use a generator.

I dont know what you mean by overkill, you will mostly be running off of battery power and while your are off the grid you will be slowly depleating the power in your bank, I think it all depends on the period of time you would like to be able to run on electric power before having to find another source of energy.
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Old 04-11-2007, 12:14 AM   #5
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8 batteries at 225 amp hours (assuming you get high capacity GC2's) will net you 900 amp hours of capacity since you have to series-parallel those guys up to 12 volts. With 900 amp hours you really shouldn't discharge more than 50% for the sake of your batteries giving you 450 amp hours of actual usable capacity. With your charger putting out 90 watts at ~14.2 volts you should be getting a current of roughly 6.5 amps to the batteries under ideal conditions. 450 amp hours divided by 6.5 amps equals 69 hours!

So what was a I getting at? Your battery bank really can't be too large for the most part, but without a large solar array don't expect miracles in the way of charging. 69 hours is a long time to be charging. Of course you're going to have a lot of run time too and obviously you can be charging while you're draining the batteries. 6.5 amps over say 12 hours is 78 amp hours you can theoretically use before draining on the batteries.
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Old 04-13-2007, 09:10 PM   #6
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Well, I think I found my battery bank. they decommisioned a power sub station and there's twelve 12 volt 150 amp hour batteries for sale. Looks like I'll have approx 1800 amp hours. So far I have 90 watts of solar panels, and two 2000 watt power inverters. I have a 20 amp (up to 300 watt) controller on the way, and a power isolator. Does anyone know what kind of fuse box I need to setup for this kind of system?
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Old 04-14-2007, 03:06 PM   #7
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Hi,
There is a general rule that the ideal solar/battery system is based on 1 amp of battery to 1 watt of solar panels. And the size of the system is based on your daily power needs plus how many days you want to go without sun.
To start out with a giant battery with no way to charge it is putting the cart before the horse. In this case most people end up having to run a generator most of the time and pissing everyone off around them. If you have any money at all, buy solar panels. You can find batteries anywhere. the problem is charging them. Of course none of this may matter to you because of your lifestyle. It all depends on how you live with your system and whether or not you have a power pole to plug into.
There's a lot more than just a fuse box involved. With 1800 amps of batteries you could melt your bus. The best way to figure out how to hook all the stuff up and what other stuff you might need is to refer to the manuals that came with the inverters and charge controllers. They will tell you where the fuses and shunts and circuit breakers go. It freaked me out too but they covered everything. Also with 1800 amps of batteries, all the wires, fuses, breakers and anything else involved has got to be BIG, and I mean REAL BIG meaning REAL EXPENSIVE. I found out by going thru the process and trying to fake it and buy stuff at the junk stores and wrecking yards. You go from a 20 amp fuse for $2 to a 500 amp low voltage fuse for $200.Big amps means big bucks.
I have lived with solar panels for more than 20 years and seen many people who live with them also. Almost ALL of us had enough batteries. ALL of us did not have enough solar panels. Two days with no sun and we were in the dark. We were always trying to get the batteries back up to 100% after days of cloudiness. I say again, The ability to charge is the weak link. Solar panels first, batteries second. Just my humble opinion.

The main reason we have so much power now is because we have a 10.5 cf 110 volt refridgerator. We bake our own bread. Soon we will be making our own beer and growing our own veggies Aeroponically (growing in the air) Electricity comes in handy when you have to make everything yourself and are just trying to survive with little or no money.

In my bus I have 1580 watts of solar panels
1580 amps in 8 Trojan L-16HC Batteries.
2 MX60 70 amp MPPT Charge controllers
3000 watt sine wave inverter
Backup is a 2000 watt sine wave inverter generator with 100 amp 110 volt charger and a 400 watt air-x wind turbine.

Good Luck
Jerry
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Old 04-14-2007, 06:00 PM   #8
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realistically, I'll only be taking this out maybe once or twice a month, for a couple of 3 or 5 day weekends. So, at this time, I won't be needing continuous power, and I'll have long periods of charge coming in between uses. Right now I guess I'll have to work with what I have. I will go ahead and start shopping for more panels though. Anyone know where I can score some good used ones?
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Old 04-14-2007, 09:05 PM   #9
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You said 1800 amp hours, right? That would mean the run time and not the current carried by the wires. You could have a 1 amp fuse and 18 gauge wire coming off an 1800 AH battery bank. The key to the size of stuff is the actual draw at any given time.

BTW, Jerry....I'm WAY jealous of that setup. Very cool! I only wish I could justify a system like that. Of course justification is only part of the equation...I'd have to be able to afford it too.
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Old 04-14-2007, 10:21 PM   #10
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here's a draft pic of what I have drawn up so far...

http://afriendlyface.com/solar-system.jpg

Thanks for the input so far, lookin' for all the help and wisdom I can get from others. This is the first solar system I've built.
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