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hallamore
Member
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# Posted: 19 Nov 2010 16:29
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Hello All,
I have a Xantrex C35 Charge controller with an array mounted on my roof that right now is producing anywhere from 5 Amps per hour to 10 Amps per hour. I am not using the array and have set the C35 to equalize the batteries. I am NOT using the array until the batteries are equalized. My bulk is set to 14.4 (8 6v golf cart batteries wired for 12v). I see my batteries during the day raise as high as 13.7 v but never gets above the 14.4. How will my batteries ever equalize without ever reaching above 13.7????
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Rob_O
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# Posted: 19 Nov 2010 17:07
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What is the voltage on the battery array when it is not charging?
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hallamore
Member
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# Posted: 19 Nov 2010 17:41
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do you mean the battery bank? if so its 12.9 to 13.5
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MtnDon
Member
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# Posted: 19 Nov 2010 17:50 - Edited by: MtnDon
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Take the reading on the input to the C35 (panel output in other words). What is the reading there? That should be higher, maybe as much as 17 to 18 volts. That needs to be above battery voltage.
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Rob_O
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# Posted: 19 Nov 2010 18:25
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Bank, array, call it what you want. I believe yours is about 900 a/h
If your solar system is putting out 9 amps, you are charging at a 1% rate. That's barely enough to overcome the internal resistance of the batteries. Cut the battery array in half and you might be able to generate enough power to equalize that subset, repeat for the second subset
There is a great post on another forum that discussed this, I wish I could find it right now. Maybe Don was smart enough to bookmark it, I did not. From what I remember you need at least 5% of the battery capacity for proper charging
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hallamore
Member
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# Posted: 19 Nov 2010 18:35
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great idea. Thanks for the advice
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MtnDon
Member
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# Posted: 19 Nov 2010 18:52
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Me, think to bookmark? I have too many as it is... should really edit them someday.
But that is right, at too low an input it can take "forever" to recharge fully. It's a bit of a balance act between battery capacity, power output of the PV modules and ones wallet.
How many panels and of what size, voltage, watts... model number would be good to have.
I get people/systems they have confused and mixed up.... You have 8 golf cart batteries IIRC? So yes you might be deficient on the input current/modules.
The maximum charge rate is C/8 or C/10 depending on where your info comes from.
One other factor can be in play. If you have panels that are rated for a 12 volt system, it is possible for their output to fall low enough (voltage) under fading sunlight conditions, that the voltage from the PV modules is too low to provide an charge. If you have 2 panels or other multiples of 2, connecting in a series or series/parallel configuration provides a higher voltage (double) and may work better on dull days. You have to be careful though to be absolutely certain that the Voc of the series connection does not go over the C35 maximum of 55 volts.
Marginal conditions is a place where an MPPT charge controller excels. More $$ though.
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hallamore
Member
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# Posted: 19 Nov 2010 19:04
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i think i would be better off purchasing an inverter/charger that will equalize?????
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hallamore
Member
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# Posted: 19 Nov 2010 19:09
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one more point....i only use this cabin on the weekends. I thought that a small array would charge the whole week to recharge the batteries
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MtnDon
Member
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# Posted: 19 Nov 2010 20:06
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Lots of variables. Over a five day period of non use you would expect the batteries to regain full charge.
Do you / have you taken hydrometer readings on the batteries? It is a good idea to keep a record of each cell with readings taken periodically. That can help find a cell/battery that is going bad if that happens sometime. Not to mention that the hydrometer is the best indication of charge, period. Reading have to be corrected for temperature of the electrolyte too. A good hydrometer will have a thermometer built in. Checking the reading when you return after an absence will provide a true story of the batteries state of charge,
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hallamore
Member
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# Posted: 30 Nov 2010 14:30
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Don,
Quoting: MtnDon Take the reading on the input to the C35 (panel output in other words). What is the reading there? That should be higher, maybe as much as 17 to 18 volts. That needs to be above battery voltage.
How do I take this reading? I just look at the charge controller to tell me how many watts I am putting out.
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MtnDon
Member
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# Posted: 30 Nov 2010 14:55
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A multimeter is a handy tool to have. With it one can measure both AC and DC voltages, resistances and current. One that is autoranging is handy as there is no need to select the proper voltage range, the meter sorts it out. A digital readout is much better than an analog (needle movement).
typical meter
With one of these you would hold one probe on the positive wire or connection from the modules to the charge controller and the other probe on the negative. In bright sun a panel rated as a 12 volt panel should be putting out 17 to 18 volts, maybe more. That would tell you if the panel is performing well. There should be a label on the back of each panel.
Vmp is the maximum power voltage, the number that the panels should achieve in bright light and connected to the charge controller.
Voc is the voltage that should be reached in bright sun and disconnected from everything.
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