drawing 12v from 24v

Re: drawing 12v from 24v

Also, when you discharge the batteries (upper/lower 12 volt string) they will discharge unevenly. And when you charge with a 24 volt charger, some of the batteries will over charge and others will under charge.

There are ways of getting 12 volts from a 24 volt battery bank "safely" (this is frequently done on RV Bus and Truck chassis conversions where the vehicle runs at 24 volts and the house runs at 12 volts)--But the costs/efforts to do that are generally more costly (and less efficient) than just getting a 24 volt AC inverter instead. And if you have some 12 VDC loads, use a 24 to 12 volt or even a 120 volt to 12 volt converter.

-Bill

Re: drawing 12v from 24v

You will have to look at the solar panel Vmp/Imp closely...

You can put panels in parallel if they have the same Vmp (within 10% or better--I.e., two 17.5 volt Vmp panels in series for Vmp~35 volts; in parallel with your 38 Volt Vmp panels). And similar with Imp's.

If the panel Vmps/Imps are too far apart, you may have to put them on two different arrays on two different charge controllers.

Otherwise, you may look at the value of your existing smaller panels. The 80 Watt panels can be replaced by a single 250+ watt panel--Fewer panels, fewer connections, and the new panels are frequently not too expensive on a $$$/Watt basis (many folks sell their old/smaller panels and get pretty good prices for them).

Regarding batteries--If you have good experience with batteries in general (first time off grid folks can kill their first set or two of batteries), sealed AGM batteries are pretty nice--But about 2x as expensive and usually not quite as long as service life vs good quality flooded cell batteries.

If you go with flooded cell batteries, I would highly suggest a Battery Monitor (Victron is a very good European brand). If programmed correctly, much easier to see what the state of your battery banks are (and sealed batteries, you cannot measure specific gravity).

Lastly, make sure you check the charging current supported by the sealed batteries. In the US, our GEL batteries are frequently limited to C/20 (5%) maximum charge rate--Higher charge rates cause permanent bubbles in the the GEL--And kill battery performance. AGM types are better here.

Although, there are some European GEL batteries that seem to support higher charging rates--Be careful and check the specifications/manuals.

-Bill