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5v pocket projector x 2a = 10 watts an hour
5v hdd palyer x 1a = 5 watts an hour
10w + 5w = 15 watts an hour
5 hour a day proposed use time for both so 15 watts x 5 hours = 75 watts
75 watts x 1.5 (system losses) = 112.5 watts a day
112.5 watts / 5 hours sun a day (winter solar insulation) = 22.5 watt solar panel
22.5 watts x 5 hours sun a day = 112.5 / 12 volts = 9.375 Amp Hour battery at 12v
9.375 amp hours x 2 (charging losses) = 18.75ah
18.75ah x 5 (allowing 20% discharge of batteries) = 93.75 amp hour battery bank @ 12v
is my math ok???
5v hdd palyer x 1a = 5 watts an hour
10w + 5w = 15 watts an hour
5 hour a day proposed use time for both so 15 watts x 5 hours = 75 watts
75 watts x 1.5 (system losses) = 112.5 watts a day
112.5 watts / 5 hours sun a day (winter solar insulation) = 22.5 watt solar panel
22.5 watts x 5 hours sun a day = 112.5 / 12 volts = 9.375 Amp Hour battery at 12v
9.375 amp hours x 2 (charging losses) = 18.75ah
18.75ah x 5 (allowing 20% discharge of batteries) = 93.75 amp hour battery bank @ 12v
is my math ok???
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Re: solar math gurus please read
Thu, August 13, 2009 - 3:06 AMWell, it's not watts an hour, it's just watts. watts an hour is a rate of change in power consumption. Your 75 watts, then, would be 75 watt-hours (Wh), and you 112.5 would also be in watt-hours.
No math errors, though, only a semantic one. -
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Re: solar math gurus please read
Fri, August 14, 2009 - 5:44 PMi agree with glen, you should be good here.
you have taken a very conservative approach with your inefficiency variables which means you will probably do fine. however if you hedge it a bit more you might be able to carry around a lighter battery pack that is less certain to perform. choice is yours.
how do you plan to go from 12v battery pack to your 5v devices?
let us know how things worked out after bm if you can.
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Re: solar math gurus please read
Fri, August 14, 2009 - 5:48 PMwait,
the last multiplying times 5 would be for if you want to have 5 days of storage in your battery pack. you would in that case not have toe power in solar to regenerate that entire pack, but if you only use your load like you said, you should be able to restore that much every day. -
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Re: solar math gurus please read
Fri, August 14, 2009 - 5:51 PMi would go for 9.375ah x 1.2 (80%discharge)= 11.25 ah battery at 12 v
that would recharge fine with your solar and run your laod for 5 hours a night.
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Re: solar math gurus please read
Sat, August 15, 2009 - 3:52 AMYou sure about that? If these are lead-acid batteries, I wouldn't discharge them below the 80% mark (okay, maybe 75%) on any kind of regular basis.
On going from 12V to 5V: I do NOT recommend using a 7805 for this -- it just creates a resistance and effectively "burns off" the difference, which will also introduce heat dissipation issues. You can, however, use a 78HC05 -- they cost more initially, but are, at worst, 85% efficient. -
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Re: solar math gurus please read
Sat, August 15, 2009 - 5:54 AMIF you can afford to ignore cost the voltage translations are always more efficient using dc -dc converters. Many dc-dc converters are 95% efficient or better. Regulators as Glenn says are not power efficient. -
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Re: solar math gurus please read
Sun, August 16, 2009 - 7:54 AMFurther to B's point, the 78HC05 is a DC-DC converter with the same pinout as the 7805. That's why it earns my recommendation. As I say, 85% is its *absolute worst possible* performance; it only goes up from there.
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Re: solar math gurus please read
Sat, August 15, 2009 - 5:54 PMi was trying to maintain his variables cuas they were the ones he likes,
but he also multiplied by 2 right before that so the battery wont be discharging even to 50 percent. -
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Re: solar math gurus please read
Sun, August 16, 2009 - 7:55 AMTrue. There is a very large margin of error in there, as there should be. -
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Re: solar math gurus please read
Sun, August 16, 2009 - 12:07 PMthank you all for your insight and help, to clarify where i am going with this i thought i would show you some of the components i have bought so far:
i got 2 of these:
cgi.ebay.com/ws/eBayISAPI.dll
specs:
High efficiency module---17.25% Mono-crystalline Silicon
Low iron tempered glass
Suitable for prolonged outdoor use, water proof
EVA laminate and TPT backsheet
Anodize aluminum frame
Bypass diode minimizes power drop by shade
10 years limited warranty of 90% power output and 25 year limited warranty of 80% power output.
Maximum Power: 10.3W watt
Maximum-power Voltage: 17.8 volt
Maximum-power current: 0.58 Ampere
Open-circuit voltage: 22.1 volt
Short-circuit current: 0.69 Ampere
Size: 350 x 285 x 18 mm ( 13.8" x 11.2" x 0.7" )
Weight: 1.25 KG (2.8 pounds )
Surface of the cell: 125 x 125 mm
Temperature: -40 ° C / +80 ° C
Temperature coefficient of Pm (%): -0.47 / ° C
Temperature coefficient of Im (%): +0.1 / ° C
Temperature coefficient of Vm (%): -0.38 / ° C
Tolerance: + / -5%
one of these but will upgrade to mppt version soon:
cgi.ebay.com/ws/eBayISAPI.dll
specs:
12V, 5A Solar Charge Controller/Regulater
Handles up to 5 amps of array (solar panel) current
Three LED indicator: Over Discharge, Over Charge, Charging.
Cut-in Voltage: 11V. Cut-out Voltage: 14.2V
Prevents over-charging the 12 volt storage battery being charged by your solar panel. It also prevents the discharging of your battery during hours of darkness.
Provides three sets of connection: Input, battery, output
Max input power: 60W
Dimension: 3'' X 3'' X 2''
Condition: Brand New. Bulk package
and this lot of four 12ah agm batteries:
cgi.ebay.com/ws/eBayISAPI.dll
specs:
FOUR (4) 12V 12Ah SLA Sealed Lead Acid Battery
ZEUS PC12-12F2 *No wires or cables are included*
PC12-12F2 Battery Specifications
Weight (lbs) 9.69
Volts 12
Ah 12
Length (in.) 5.94
Width (in.) 3.86
Height (in.) 3.74
Terminal F2 (1/4”)
SLA batteries may be used in a wide range of applications, such as UPS Systems, Emergency Lighting, Underwater Fish Finders/Cameras, Fire & Security Alarm, Game Feeder’s, Game Decoy’s, Radio Control, Robotic, Invisible Pet Fences, Communications, Telemeters, Camera’s & Photographic Equipment, Hobby Equipment, Small Toys, Street Lighting, Pumps, Solar Power
Not sure if our batteries will work in your application? Feel free to contact us for varification.
Power-Cell Battery is a leader in competitively priced sealed lead acid batteries. Our ZEUS line is comparable to many well known manufacturers, including Universal, Power-Sonic and Yuasa batteries. While are batteries ship out with 80-90% charge in them, it is strongly recommended to top charge prior to first use to prolong the life of your battery.
REASONS TO CHOOSE ZEUS:
· Maintenance Free
o Valve regulated
o Safe to discharge in any position
o Electrolyte is absorbed into the positive and negative plates and separator
o No need to add electrolyte
· Ease of Shipping
o Requires no special handling
o Completely sealed construction
· Life Expecancy
o Will last up to 5 years in stand-by applications
o 200 – 1000 cycles in cyclic applications depending on depth of discharge
· Ease of Design
o Wide variety of sizes and amp ratings
o Maximum flexibility in the design
o Pack assembly, stand alone, standy-by and cyclic applications
· Shelf Life & Storage
o Stored in fully charged conditions
o Top charge every six (6) months in ambient temperatures to prevent permanent loss of capacity
o Store at temeratures less than 50 degrees F & 10 degrees C or lower to extend shelf life
hows it sound? -
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Re: solar math gurus please read
Sun, August 16, 2009 - 12:10 PMobtw dc to dc converter:
cgi.ebay.com/ws/eBayISAPI.dll
specs:
This is a professional Step Down DC / DC Converter circuit.
Dimension: 44 mm*22mm*7.2mm (L*W*H)
Input Voltage: 4 - 25 VDC;
Output Voltage: 1 - 10 VDC ( Default ) or 1.22 - 6.7 V ( more high-precision )
( Adjustable ) (To work normally, the input voltage must be at least 1.55V higher than the output voltage)
Maximum Current: 3 A
The efficiency can reach 90% -93% with a quite low heat power!
If the output side is short-circuited, the circuit will be automatically protected!
The quiescent current of the circuit is 5 mA.
The input side is connected with a red LED, while the output side a green LED
The total consumption of the circuit is about 10 mA.
The value of adjustable resistance on the circuit board is 50K
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This is the maximum depth. Additional responses will not be threaded.
Re: solar math gurus please read
Sun, August 16, 2009 - 12:12 PMhow do i decide what size fuses to use? what needs to be fused? -
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Re: solar math gurus please read
Sun, August 16, 2009 - 12:18 PMi overestimated a tun on watts needed as well so i scaled it down a tad as you can see above i am now running:
2 x 10w solar panels to 4 x 12v 12ah agm batteries so
20 watts solar panels to 48ah @12v -
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Re: solar math gurus please read
Tue, October 13, 2009 - 7:48 PMhow did it work out? -
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Re: solar math gurus please read
Mon, October 26, 2009 - 3:43 AMhi vida got your message, i wasted the agm batteries after a month of use but truthfully they were ok until it got cloudy for a few days and i discharged my batteries too much, i picked up a deep cycle marine battery with 120ah and its fiune now i use it every night at least 4 hours if not 8. -
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Re: solar math gurus please read
Mon, November 2, 2009 - 8:39 PMwow. so i was way off hey?
i gotto go back through my math and find the error.
are you sure about the current draw and the rest? -
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Re: solar math gurus please read
Tue, November 3, 2009 - 7:49 PMyes BUT i watch it late at night and leave it on sometimes all night long thus the over discharging.
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