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Old 01-27-2009, 12:01 AM   #1
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wire size for solar generator?


i have a 750 watt inverter, hooked to a marine battery, hooked to a solar charge, hooked to a 50 watt solar panel. the battery, inverter, and charger is in my room. its ran to my panel through wires out the window. what i want is to have the battery under my floor and the inverter in my room. i already have a hole in my floor for my internet wire to go through and i have enough space for a pen to go through, i really want to get by with the least amount or no drilling through my floor. i have thought of jumper cables to hook from the battery up through the floor to the inverter, and someone also told me that house wire would work. what do you guys suggest? and please make it safe too.

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Old 01-27-2009, 12:32 AM   #2
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wire size for solar generator?


You need to get this thing set up properly. Dedicated, accessible equipment space, and wires properly routed and connected. I would not rely on jumper cables for the connection, as these are meant for a temporary connection. You size the wire to the load and fuse size. "House wire" will work if properly installed.

Remember, just because this is 12 V doesn't mean you can just rig it up any ol' way. A 12 V house fire costs just as much as a 120 V house fire.

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Old 01-27-2009, 04:59 PM   #3
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wire size for solar generator?


Doesn't the battery need to be vented to the exterior?
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Old 01-27-2009, 05:58 PM   #4
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wire size for solar generator?


Quote:
Originally Posted by krisman View Post
750 watt inverter,
hooked to a marine battery,
hooked to a solar charge,
hooked to a 50 watt solar panel.
Since the solar panel already has a high internal impedance (if Vopencircuit = 15v and Ishortcircuit = 3A, Rinternal = 5Ω which means the max power is at Vload = 7v and is Pload = 10W) the voltage drop on this wire probably doesn't matter much.
You have a link to the panel?

Charge out of a battery = ~1/2 of charge into a battery, so 8 hours of charge with bright sunlight at 50w gives you 750w for 1/4 hr.
No arc welding for you. Several cups of heated coffee, maybe.

Last edited by Yoyizit; 01-27-2009 at 06:45 PM.
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Old 01-27-2009, 06:25 PM   #5
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wire size for solar generator?


Quote:
Originally Posted by Yoyizit View Post
Since the solar panel already has a high internal impedance (if Vopencircuit = 15v and Ishortcircuit = 3A, Rinternal = 5Ω which means the max power is at Vload = 7v and is Pload = 10W) the voltage drop on this wire probably doesn't matter much.
You have a link to the panel?
(Head slap) of course I should of thought of that!
I always like your thoughtful responses.

By the way what did you say? Please put it in laymens terms since I didn't do so well in Physics,Chemistry or Trig and algerbra.


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Old 01-27-2009, 06:41 PM   #6
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wire size for solar generator?


Quote:
Originally Posted by Gary_602z View Post
(Head slap) of course I should of thought of that!
I always like your thoughtful responses.

By the way what did you say? Please put it in laymens terms since I didn't do so well in Physics,Chemistry or Trig and algerbra.


Gary
I said you could do much better with a parabolic mirror heating a copper pipe with a flat black finish to provide hot water: nowadays this is a high school project.
You can do better with almost anything with a conversion efficiency of more than the 10% these panels give you. Waterwheels, tidal movement, wind, a stationary bike, and flywheels-in-a-vacuum for energy storage.
If you live under power lines make a large coil on the ground and steal power from PoCo (until they accuse you of http://en.wikipedia.org/wiki/Theft_of_services
)
Just kidding, PoCo!

Last edited by Yoyizit; 01-27-2009 at 06:46 PM.
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Old 01-27-2009, 08:24 PM   #7
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wire size for solar generator?


Does aluminum foil under my hat help any?

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Old 01-27-2009, 08:45 PM   #8
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wire size for solar generator?


Quote:
Originally Posted by Gary_602z View Post
Does aluminum foil under my hat help any?

Gary
It worked for a USPTO examiner in the late 90s. If she didn't wear the foil under her clothes she had evil thoughts.
http://en.wikipedia.org/wiki/Thought_insertion

Another had red velvet ropes around his desk; kept away evil spirits.

In a bar, probably in Crystal City, one examiner was overheard making a threat against a female examiner, so for a while our tax dollars paid for her bodyguard.
They finally fired her. Apparently she was extremely provocative.

These people did good work in the tedious but well paid work of examining patents, as long as you didn't step on their delusions. With 3000 examiners you're bound to get some on the fringe. Plus they had quotas, and at least one supervisor was of almost legendary obnoxiousness.

So, can I sell you any tinfoil, parabolic mirrors or perpetual motion machines? There is actually a patent on this last item.

Last edited by Yoyizit; 01-27-2009 at 08:48 PM.
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Old 01-27-2009, 10:22 PM   #9
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wire size for solar generator?


Quote:
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So, can I sell you any tinfoil, parabolic mirrors or perpetual motion machines? There is actually a patent on this last item.
I actually have been working on a perpetual motion machine I just have to figure out how to fuel it!

Gary
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Old 01-27-2009, 11:43 PM   #10
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wire size for solar generator?


do i have a link to the solar panel itself? yes, http://www.cdtsolar.com/50_watt
the solar generator no
i want that battery outside even if it is sealed. what size wire would you recommend i get? i know nothing about wire sizes. i built it to run my computer for an hour every couple of nights. have even thought of leaving everything outside, plugging in an extension cord and running it up, but that would require leaving the inverter on all the time, which would drain the battery. the last thing i want to do is cause a house fire, so i need step by step directions. also, i have been kind of interested in building a wind turbine too, and you say they put out a lot more power, maybe you guys could help me with that too.
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Old 01-28-2009, 09:44 AM   #11
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wire size for solar generator?


What is the maximum current? For starters use the same rules as for 120 volt wiring; take the maximum current, add 25% because this is a continuous load or flow as opposed to plug-it-in-use-a-little-while-turn-off aka intermittent load.

15 amperes or less, 14 gauge wire. Up to 20 amps, 12 gauge wire.

For a long run, over 50 feet for "low voltage" applications, you will need more calculations to see if heavier wire is needed. This is because voltage drop is the same number of volts (not a percentage) regardless of the original voltage, all other things like wire size and kind, and number of amperes, being equal. Losing 3 out of 12 volts in the wires is a much bigger percentage energy loss compared with losing 3 out of 120 volts.

For short distances the 12 gauge for 20 amps etc. rule still applies because the heat generated in the wire depends on the voltage drop per foot and the number of amperes, not the original number of volts.
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Old 01-28-2009, 10:22 AM   #12
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wire size for solar generator?


Quote:
Originally Posted by krisman View Post
http://www.cdtsolar.com/50_watt
the solar generator no
With Peak voltage(Vmp):17.0Volt and Peak current (Imp): 2.95 Amp the internal panel resistance is 17/3=~5.7Ω and max power with a 5.7Ω load is 5.7(1.48) = 12w at 8.4v.

You should ask them what value of load resistor can pull 50w from this panel. They might have used voodoo to figure their rating method.

3A with a 10% drop (let's say 2v) gives a wire resistance of 2/3 rds Ω loop resistance. 35' or less of two conductor #20 with 60℃ insulation should work.

Get some numbers from the solar people before you put any more labor into this project.

A computer for one hour = 500 w∙h. Once/week would be 500/168 = 3 w∙h on average.
The battery needs to supply 500/12 = 42 amps for 1 hour, so a 42 A∙h deep cycle battery is needed as a minimum.

This duty cycle is extremely low; it might actually work.

Last edited by Yoyizit; 01-28-2009 at 10:25 PM.
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Old 01-28-2009, 11:34 PM   #13
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wire size for solar generator?


the wire will just be going about 10-15 feet through the floor to the inverter from the battery if that helps. ive been using it a month so far with no problem. so a 12 gauge, 60 degree size should be good? that will mean more drilling through the floor then?

i also have another question, the battery max is about 12.5 volts when charged. the charger is made for 12v, but says it kicks in at 13.2v and stops charging at 14.2v. does this mean i have too small a battery for the controller?

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