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I am going to build a small system in my cabin to run a few things so I don't have to run my generator as much. It will be like an RV system. It will be 12V with 2X100Ah lithium batteries. I will only have two panels, my question is about two panels, I can get Renology 450W panels, 34.67V, 12.98A, or Silab 490W 54V, 9.06A. I will have a Victron Smart Solar charge controller, Are amps or voltage more critical to the charge controller as far as charging the batteries? I know not to exceed the max voltage, but should I go for more volts or amps? The distance from the PV array to the controller is very short, maybe 25-30 feet.
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[FONT=Comic Sans MS]Craig
Loveland, CO[/FONT] -
Think of volts and amperes like peas and carrots. If you are hungry looking for a meal, which do you think will fill your stomach faster, the peas? or the carrots?
In reality either way, what you want is a bowl of food. If that bowl is half peas and half carrots, or if the bowl is 3/4 peas and 1/4 carrots, it is still a bowl of food.
In this scenario the bowl is wattage.4400w, Midnite Classic 150 charge-controller. -
The higher wattage will in theory deliver more power in all situations. In
this case the Silab 490W has the advantage. It also operates at a higher
voltage/lower current. This will give higher efficiency over the loop, which
could easily be 70 feet of wire total. You need a true MPPT controller
for this to work. Bruce RoeComment
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I understand what you’re saying, just not sure how the MPPT charge control handles the volts versus amps as far as charging the battery.[FONT=Comic Sans MS]Craig
Loveland, CO[/FONT]Comment
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An MPPT controller has a broad range of inputs. My Victron 100/50 can take up to l00 volts in and output 50 amps. If I push this at 50 amps to charge a battery at 12 volts that’s 600 watts. The MPPT doesn’t care whether the input is 17 to 100 volts. If it’s 30 volts and 20 amps, this is 600 watts, it will output 600 watts at 12 volts and 50 amps. If its 60 volts in and 10 amps, still 6000 watts, the output will be 12 volts and 50 amps.
My PWM controller can only handle an input of 14 volts to 24 volts, and there is more loss int he conversion.Comment
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It is easy to get lost in the weeds.
Designing a solar power system, you must pay close attention to the volts, and to the amps. But as a user you need watts.
4400w, Midnite Classic 150 charge-controller.Comment
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I did not intend to be insulting. I do apologize.4400w, Midnite Classic 150 charge-controller.Comment
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4400w, Midnite Classic 150 charge-controller.Comment
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Power loss is proportional to the square of the amps so its best to run as high of a voltage as you can. This is why transmission lines run at 100's of thousands of volts. Of course NEC code comes into play when ever a system is over 50 volts.BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installedComment
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But it looks like you don't yet know that the nomenclature convention is that S.I. units named after individuals have their abbreviations capitalized (but when spelled out, the word is not capitalized).
Thus: kWh, not kwh.
Also, and also just for the record, you know wrong. It's kilowatt-hour with a hyphen, not kilowatt/hour with a slash.
Seems like a small thing to the uninformed but not getting this stuff right can cause big problems as a lot of working technical folks and engineers have seen.
If you're going to attempt communication about technical stuff, start by getting the basics and communication rules right.
See: "NIST Guide to the S.I., Chapter 9: Rules and Style Conventions for Spelling Unit Names"Comment
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So true, I am working on my capitalization out of respect, but getting theOriginally posted by J.P.M.
units right is critical to communication and calculations. Bruce RoeComment
Love the analogy and learned about volts and amps thanks to this thread. 
(just for the record, I know kwh=kilowatt/hour 
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