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General: Charge controller ratings...
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Author:  techanic [ Sun Sep 18, 2005 10:20 pm GMT EthGMT ]
Post subject:  General: Charge controller ratings...
I'm new here.

I've been studying solar for a while now. I think I have an understanding of how a system is put together and the options involved - but some things still leave me puzzled.

For example, the "largest" charge controller I have run across is the Xantrex C60. But 60 amps isn't really that big a system is it? (It's bigger than I can afford, but just in general I see systems with 20 panels all the time, that is more than 60 amps).

So what is the deal, can you run more than one charge controller on the same battery bank or what? What am I missing here?
Author:  robert_winfield [ Mon Sep 19, 2005 2:22 am GMT EthGMT ]
Post subject: 
Quote:
but just in general I see systems with 20 panels all the time, that is more than 60 amps). .


in a string of PV panels, to make the math easy, say they are 5amp and 25volt each

4 panels in SERIES would be about 100 volts but only 5 amps.
volts add, amps stay same

4 panels in PARALLEL would be about 25 volts and 20 amps.
amps add, volts stay same

these groups of 4 would then be carefully brought to a central junction point and combined

as a thought experiment you can probably see that combining the 5 SERIES groups of 4 for 100volts for a total 25 amps looks easier/less complex

there are consideration also. you gotta look at Voc and Isc
a 24v panel will have a higher voltage, somewhere in mid 30's open circuit Voc
if you put too much voltage into a controller it may smoke and there goes $500 or so
there is a 1.25 multiplier for voltages
voltages vary depending on temps of panels cooler temps, higher outputs

panels are putting out voltages WHENEVER the sun is shining on them.
miswired electronics make intresting flashes ,puffs of smoke, noises etc.
(never put 110 v on a 5v sense wire, it vaporizes)

this is naturally very basic as there are other factors that make these numbers vary a bit

hope this helps
(henry, is all this correct? i am but a beginner)
(My MX60 is ok, i didnt smoke that)
(My Omnion 2200 inverter tests my repair skill occasionally, thankfully only with $40 diodesand a digital multimeter)
(darn ASi panels, does anyone buy used ones and a used 2200?)


http://www.solarenergy.org/resources/store.php a basic book on sizing, math etc
Author:  techanic [ Mon Sep 19, 2005 8:23 am GMT EthGMT ]
Post subject: 
So if I read you correctly - folks keep the amperage below "60" (an arbitrary number) by wiring some in series to increase the voltage instead or the current?

Also, yes, I'm keenly aware of what 400 amps of DC current (a battery bank) can do if the + ever touches the - :)
Author:  halfcrazy [ Wed Sep 21, 2005 8:55 pm GMT EstGMT ]
Post subject: 
well on a c-60 you will have to wire the panels at the same voltage as the battereys and add a second c-60 if the amperage is going to exceed 60
Author:  Solar Guppy [ Sat Oct 22, 2005 10:31 pm GMT EndGMT ]
Post subject: 
It's not an arbitrary number.

Losses in the electronics is the current square rule, that being the losses in the FET's, wires , inductors and other gizzards goes up with the square of the current.

for example 30*30 = 900 * resistance = loss
for example 60*60 = 3600 * resistance = loss

an inductor might have a 5 milliohm resistance , so

30 amps = 4.5 watts heat
60 amps = 18 watts heat

4X the losses for a 2X of the current

Its an exponential increase and 60 amps is about as much as one can push thru connectors,relays, board etchs without burning things up.

Keep in mind each piece in the Charger Control has resistance, connector, FETS, Inductor, shunt back out connector (the flow thru the charger).

This is why the world wants to run at high voltages, you get the same POWER running at a high voltage but use lower currents which means for the same V*I=P , higher Voltage means lower losses due to the current being lower
Author:  techanic [ Tue Jan 24, 2006 9:24 pm GMT EthGMT ]
Post subject:  I assume..
....then I have to assume that a typical setup includes multiple charge controllers charging the same bank of batteries. Is that correct?
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