a battery question of efficiency

[bob g]

of the two technologies, flooded lead acid and absorbed glass matt

which has a higher charge efficiency when used to 80% state of charge?
(basically the top 20%)

i am working on a very specific application where picking the battery with the highest charge efficiency
within this range is going to be the one i likely end up going with.

if i were to go down to 50% i would pick the flooded lead acid battery such as the rolls/surrette 5000 series
however the rolls/surrette like all flooded lead acid batteries are not particularly efficient in charging when it comes to
the top 20% of charge.

anybody got some info on AGM batteries under this regime?

thanks
bob g

[joestue]

I think this is going to depend on how fast you charge them, basically the ones with lower internal resistance towards end of charge is the answer, and if one  reaches full charge a half volt lower, that's the one i'd go for.
If you want efficiency and have a specific task for them to perform I should think lithium batteries will be more cost effective.

[B529]

I have a set of Unigy II batteries, AGM's. I installed a few sets of IBE flooded lead acid for a couple neighbors.

I went with the AGM's because of the price, got them used for a steal, they were only 6 months old. A local forum member, Chuck Morrison, gave me the lead on them several years ago.

If I were buying new, would get a quality FLA battery. Witnessing how each battery will take a charge toward the top, the FLA are more efficient. You can "stick it" to the FLA batteries more so on the top. The AGM's are much less efficient towards the top.

My batteries as well as the IBE's I've installed, have almost the same charge current to AH capacity ratio, 20-25 to 1.

The obvious disadvantage to the FLA is they take more work, watering.

[bob g]

i was hoping for something a bit more technical, like perhaps a link?

the flooded cells need to have the current and voltage tapered back as the battery starts to gas
and that is something around 75-80% state of charge

i am seeing some reference to AGM's ability to go up to about 90% before tapering back

anybody got any links, or white papers on the subject?

thanks
bob g

[B529]

i was hoping for something a bit more technical, like perhaps a link?

the flooded cells need to have the current and voltage tapered back as the battery starts to gas
and that is something around 75-80% state of charge

i am seeing some reference to AGM's ability to go up to about 90% before tapering back

anybody got any links, or white papers on the subject?

thanks
bob g

You can simply do a an experiment and buy two cheap batteries of each type, same AH's, charge/drain charge/drain them.

[ghurd]

I am guessing weight is an issue?

Time to recharge is not?

No white papers, but I have run a lot of stuff perfectly fine when the math said the solar was not even close to keeping up with.
Big FLA battery, small solar.

No white papers, but a half dead 7AH SLA and 250ma PV can get to control voltage in a very short time.
Not efficient if the power stored is compared to the power available.

I believe it may all come down to the charging rate.
Slower seems better, if only efficiency is looked at.

Gut feeling-  might be more efficient if the SoC was used between 60 and 80%?
G-

[wpowokal]

http://www.vonwentzel.net/Battery/01.Type/index.html

[taylorp035]

What is the application?

  If you don't mind, A123 cells are good for 99%+ efficient, which I have tested my self.