30 to 12v or 60 to 24v which is better?

[unyalli]

Which system will produce more heat. Taking 30v in from array to charge a 12v battery system or taking 60v in to charge a 24v battery bank? Assume a 1kw array in both systems charging a 440ah battery bank.

-Jeff

[ClassicCrazy]

I believe the closer the input voltage is to the charging voltage the more efficient the controller is so less heat. But the bigger consideration is the voltage drop of your wiring. Usually you would want a higher voltage on the input so you can use a smaller wire gauge.

Also if you go with 24v battery you can reduce the size of the cables and breaker size needed for any inverter you might put on there.

Larry 

[wrt]

I would take a little from both sides. Run 30v in to charge a 24v battery. The classic will generate heat from converting the voltage down, even when on float. So the bigger the difference the more heat.

Running the higher volt panels you can still save on cable size by running single 24v panels rather than the traditional multiple parallel 12v ones.

[b4solar]

I would certainly use the 60V input on a 24V system in all cases UNLESS...... If it was a really small system with only 2 or 4 golf cart batteries and if the 24V equipment cost significantly more.

A 60V input to a 24V battery bank is close to the 2 to 1 efficiency/performance rule.

On the 12V option, the wire loss would be greater than the small amount lost in the step-down conversion.

If we were talking 120+ input volts, or smaller than 500 watts of solar then the 12V option might make sense

[unyalli]

I guess I was thinking with higher voltages the circuitry in the charge controller would work more efficiently even if the amperage was the same.

[dgd]

A 60V input to a 24V battery bank is close to the 2 to 1 efficiency/performance rule.

Thats the first time I have heard of that rule.
Where did it come from?
If true then it sort of makes nonsense of using higher voltage Classics to charge a 12 to 48v battery bank.

dgd
(charging 24v bank with 90v mpv input to Classic 150 that stays cool)

[vtmaps]

Thats the first time I have heard of that rule.
Where did it come from?

It's not a rule.  I think it comes from (and applies to) the popular 30 volt Vmp panels. 

With those panels, for a 12/24/48 volt system the optimal string length is 1/2/3 or 30/60/90 volts, which works out to approx a 2:1 ratio. 

A 2:1 ratio is not necessarily the optimal input:output ratio, but with 30 volt panels it works out that way.

--vtMaps

[dgd]

Thanks for the info, I never used the 30v MPs panels so didn't understand the logic.

Dgd

[BlackwaterPark]

So, speaking of voltages and what not...i have a pair of 30v panels (the Canadian solar 250w) in series,  feeding 4 t-105re wired for 24v.  The incoming voltage is ~ 68v and on the right side of the screen under battery is about 27v.  Are these on par with where I should be, or could I be adjusting to gain more efficiency? A good day will see a harvest of around 1.6-1.8 kwh (that's in maine... winter, obviously.

[Westbranch]

well according to this  sheet you are a bit low Should be ~ 29.4 if they are Trojans,  ...http://www.trojanbattery.com/pdf/datasheets/T105RE_TrojanRE_Data_Sheets.pdf