I have a 12v 45w panel that I had connected to a deep cycle battery which in turn was connected to an inverter.
It worked great but I am wondering, if I had another battery in the loop would the panel be producing enough power to charge both batteries or is it a pointless exercise?
I was hoping to boost the amount of evening hours I got from the batteries without adding a 2nd panel.
Any ideas?
Thanks.
Phil
It worked great but I am wondering, if I had another battery in the loop would the panel be producing enough power to charge both batteries or is it a pointless exercise?
I was hoping to boost the amount of evening hours I got from the batteries without adding a 2nd panel.
Any ideas?
Thanks.
Phil
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SF Bay Area
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Re: 2nd Battery for my solar setup?
Thu, July 26, 2007 - 7:33 PMWell, it depends on the size of the batteries. You want the current that flows from the panel to be between the 10 and 20 hour rate (typically written as C/10 or C/20).
So, for instance, if you have a 45W, 12V panel, that is going to put forth about 3.75A of current (45W divided by 12V). This is a quick and dirty, so don't take that as gospel.
Now, that said, if your current battery is around 37Ah, then it is currently running at the 10 hour rate (C is the 37Ah rating, so C/10 = 3.7A). Adding a second identical battery would then put you at the 20 hour rate, by raising C to 74Ah (37Ah X 2 batteries).
So really, the starting point is to know what size your current battery is. -
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Re: 2nd Battery for my solar setup?
Thu, July 26, 2007 - 9:10 PMdischarge cycles are limited in individual cells
discharge cycles include all of the charging and discharging that happens in the life of the cell. For example, the Ah rating of the battery may only be discharged to 50% of capacity and then recharged. Even though the battery is not comppletely discharged, it counts as cycles on the battery life. Two 50% discharge-recharge cycles count as 1 complete charge cycle.
Even Ipods can only be used so long, their batteries are not replaceable.
Glenn is absolutely correct that you will go from a 10 to 20 hour capacity.
As important might be that you are adding to the total discharge-recharge cycle capacity of your supply.
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Re: 2nd Battery for my solar setup?
Thu, July 26, 2007 - 9:52 PM50 amp hours x 12v= 600 wh (watt hours). you wont cycle all the way so with 2 batteries call it 1,000 wh or 1kwh.
45w x 6 hours = 270 wh
you can adjust the calculations for your specs and see if it will work, same math different numbers.
Make sure your charge controller can handle the current of 2 batteries. -
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Re: 2nd Battery for my solar setup?
Fri, July 27, 2007 - 9:10 AMThanks, my panel has a built in charge controller and it doesn't say anytrhing about to batteries, do this mean I can't add a 2nd one?
Would it be of any advantage if I simpy added the 2nd battery in parallel with the first or is that a bad idea?
The batteries I was gonna use are one of these:
www.partsamerica.com/ProductList.aspx
A basic deep cycle from Kragen.
Thanks,
Phil -
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Re: 2nd Battery for my solar setup?
Fri, July 27, 2007 - 4:41 PMthats not a link to anything useful. get the specs and say them here, like amp hours and volts. you are definitely gonna want to make them parallel for the voltage to be correct. 12v nominal charge controller will put out 14 volts. 2 batteries in parallel will be 12v nominal. 2 batteries in series will be 24v nominal. 12v is probably what you need for your panel and inverter. -
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Re: 2nd Battery for my solar setup?
Fri, July 27, 2007 - 4:51 PMThanks Vida, as I haven't got the batteries yet, what would be a decent amount of Amp Hours to look for in a battery?
Also, how can I tell if panel (with built in charge controller) would charge 2 batteries?
Sorry for being so ignorant and asking basic questions but I'm pretty knew to this game.
Cheers.
Phil
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Re: 2nd Battery for my solar setup?
Sun, July 29, 2007 - 5:32 AM"what would be a decent amount of Amp Hours to look for in a battery? "
Take your panel's power output. Downgrade it to 80%. Divide by the nominal voltage. Multiply by 10 to get the smallest battery size, 20 to get the largest.
Example for a 50W, 12V panel:
50W X .8 = 40W This is the thermally derated output.
40W / 12V = 3.33A. This is the current you can expect to come out of the controller.
3.33A * 10h = 33Ah. This is the smallest battery you should use
3.33A * 20h = 67Ah. This is the largest battery you should use.
IMPORTANT: The Ah figures you get out of this is the total for ALL OF THE BATTERIES that are in parallel.
ALSO IMPORTANT: All of your batteries should be the same type and size. If what you are proposing to get isn't the same as what you have, you will have issues. -
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Re: 2nd Battery for my solar setup?
Sun, July 29, 2007 - 5:56 PMThis perfect, thanks Glenn.
If the maximum is say 67AH, would there be a downside of using a 100AH battery? Would it never reach full charge?
Is that a bad thing?
Also, is there any benifit of having 2 33AH batteries or 1 67AH?
Thanks again.
Phil
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Re: 2nd Battery for my solar setup?
Mon, July 30, 2007 - 3:50 AMWe had a similar question here a few months ago. Using an oversized battery would potentially result in it not getting up to a full charge (hence shortening its life) by burning off the energy you feed it just overcoming its internal resistance.
I don't think there is any special benefit to having 2X33 over 1X67.
There are two benefits to having 1X67 over 2X33:
1. Simpler system wiring
2. No charge balancing issues -
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Re: 2nd Battery for my solar setup?
Sat, August 4, 2007 - 5:29 AMGlenn I have a question about the formula you offered. I currently have a 12v array that I have been building up with matched modules going to 12v *busses*, I then have these busses in parallel leading to a trunk feed to the controller. I am using a Xantrex G-35 and overall the system is producing 180 watts nominal and often a constant 200 watts at midday.
My dilemma is this; the Xantrex is both a 12 and a 24 volt system and I have been thinking of rewiring the busses to operate in 24 volt series circuit but when I applied the formula the result I got for balancing battery capacity was somewhat incongruous because the battery capacity appears to drop by a four fold factor rather than by half as I would expect since the total wattage output is reduced in half when I raise the system voltage. For example, when I wire two 20 Ahr batteries in series I get one 24v 20Ahr battery bank but this result is a little incongruous when I use the formula you offer because the overall amount of energy being produced is unchanged.
Could you please help understand what is happening?
Here are the actual numbers:
180w, 12v producing 12 amps, with a battery capacity of 120 to 240 Ahrs.
The same array could produce 90 watts at 24 volts but this results in a 3 amp output ( a four fold reduction) that can only power a 30 to 60 Ahr battery bank. I would normally expect the Ahr capacity of the battery bank to only drop in half but in fact it appears to be much more.
Why? and is the result of a misapplication of the formula or a missing element? -
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This is the maximum depth. Additional responses will not be threaded.
Re: 2nd Battery for my solar setup?
Sun, August 5, 2007 - 5:57 AMI don't see why your array would only produce 90W at 12V.... it should still produce 180W. The current should cut in half, the voltage double, and the power remain the same.
In other words, at 12V, you see 180W, which is 15A. At 24V, you should still see 180W, but it would now be only 7.5A.
...so I think it just a misapplication of formula.
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Re: 2nd Battery for my solar setup?
Sun, August 5, 2007 - 10:08 AM("I don't see why your array would only produce 90W at 12V..."it should still produce 180W. The current should cut in half, the voltage double, and the power remain the same.")
Did you mean 90W at 24V?
It is producing 180 watts at 12V now but I would be putting two banks of the arrays in series to get 24V so it should be only getting half the wattage at 24V at least that is how we treat batteries in series. However if you mean 24V... then:
"it should still produce 180W. The current should cut in half, the voltage double, and the power remain the same."
When we stack batteries 2 X 12v at 20 amps does not equal 24V at 40 amps, it equals 24V at 20 amps. So I have been treating the wattage as 2 X12V, 15 watt panels in series as being 24V at 15 watts because the power is not cumulative like when they are wired in parallel.
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Re: 2nd Battery for my solar setup?
Sun, August 5, 2007 - 6:04 PM"Did you mean 90W at 24V? "
Um. Yeah. Let me try that whole sentence again.
What I meant to say is: I don't see why your array would only produce 90W at 24V... it should still produce 180W.
So, yes, that was what I meant. Sorry.
"It is producing 180 watts at 12V now but I would be putting two banks of the arrays in series to get 24V so it should be only getting half the wattage at 24V"
No, that's the part that's wrong. Double the voltage, halve the *Amperage*. The wattage remains constant.
When considering the batteries, we, for reasons I cannot fathom, measure amp-hours, not watt-hours. Since it's based on amps, then, yes, series doubles voltage, parallel doubles amperage, and thereby, amp-hours. The watts, and thereby, watt-hours, however, always remain constant for a given set of components. -
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Re: 2nd Battery for my solar setup?
Mon, July 14, 2008 - 5:54 PMhi, I want to buy a 50w panel solar, a charge controller, a 67ah deep cycle battery and a 500w inverter. I would like to know if the panel solar will always keep the battery charge while im taking out power of the inverter. Or would i have to disconnect the inverter from the battery to let it charge and also how long would it take for the 50w panel solar to charge the 67ah battery. help please, im a new guy!
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Re: 2nd Battery for my solar setup?
Mon, July 14, 2008 - 6:34 PMOne thing that helps (this is not for you Glenn you know this) but don't work in watts. That is really not helpfuil. Always work in amps (and volts of course). But if your panels and charege contoller and battery all match in voltage then you can just work in amps to know if your are charging at the correct rate (between C/10 and C/20). Amps are so much easier to deal with. -
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Re: 2nd Battery for my solar setup?
Sun, July 20, 2008 - 12:08 AMthe battery im getting are two 6volts battery both together is 12volts and 105Ah each, so what type of panel solar and charge controller should i look for meaning how many amps. thank you and sorry cuz i got back at u late. -
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Re: 2nd Battery for my solar setup?
Sun, July 20, 2008 - 5:08 AMA 105Ah battery should be charged at between 5.25 and 10.5 amps.
The lower figure (5.25) is 1/20 of the ampacity; the 10.5 is 1/10, i.e. 105/20=5.25; 105/10=10.5 Get it?
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Unsu...
Re: 2nd Battery for my solar setup?
Sun, July 20, 2008 - 8:58 AMsure, slow is better. buttttt...... most chargers, and the better controllers have three stages. bulk. taper and float. while the battery is depleated, it is ok to put up to 20% of the capacity , ie 20 amps as the charge, this reduces the time it takes.
this is a somewhat odd size battery. i am sure there is a reason you are getting that size. the best bang for the buck, are t-105 . golf cart batteries. if this is what you are referring to. they are a nominal 220 ah. each.
maybe someone can explain where the 105 name came from??
sooooooo, 220 amp. , if you were to use say 100 amp....... and live in a zone where you get 5 hours of full sun. you need at least 20 amps of solar panels. ie. three , 120 watt panels. and that is being optimistic.
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