batteries 4

Vulcan Rider wrote:

sushidog wrote:
150 watts of solar eliminates AGM type batteries as you won't have a high enough charge rate,

That depends on the average load and how much of the sunlight day there will be little or no load.

A solar array capable of delivering 10 amps would be more than adequate to maintain or recover the charge with AGMs......if they are not drained dead and enough time ensues.

The effective charging rate and necessary charging voltage is not THAT much different with AGMs. If it was, they would not be an appropriate choice for such a wide range of applications......and they ARE.

At 10 amps max. (assuming 5+ hrs of sunlight/day with flat mounted panels) a 150 watt panel can replace 50 amp/hrs/day. So if you had a 400 ah battery bank and discharged it to 50% in a single day, it would take at least 4 days of charging in perfect conditions, with no cloud or shade to recharge them. In the winter, or with partial cloud cover of real world conditions, we are looking at at least a 5-6 days recovery time when the batteries cannot be used. If a 600 ah bank is needed then it would extend the recharge time 50% more to 7-9 days. I don't think over a week of charging to replace the energy used in a single day would be acceptable performance to most folk, how about you?

According to the Concord Sun Extender AGM battery manual on page 19 it states: "For repetitive deep cycling applications (deeper than 50% DOD), chargers should have an output current of at least .2C (20 amps on a 100 AH battery). If the output current is less than this value, the cycle life of the battery can be negatively affected."
http://www.sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Trojan also uses the same .2C minimum. This means that the recommended charge rate for a 400 ah bank that is deep cycled (according to both Trojan and Concord) is 80 amps.

I don't remember where, but I seem to remember a .15C figure being bragged about from one AGM manufacturer. Still, that means that to deep cycle a 400 ah bank one would require at least a 60 amp charge rate for max battery life. Of course if your battery bank is shallow cycled (less than 30%) then much lower charging rates can be used. But why buy a deep cycle battery if you don't plan to deep cycle it?

I know AGMs can be charged 3 times faster than a typical FLA, but it seems that charging them too slowly can hurt their life too.

Chip