glider battery duration problems

Dave Springford wrote, On 10/2/2013 5:57 PM:
I guess it depends on how one defines capacity. If you take it as
voltage drop from 12V then it is probably the 3% value that you use.
If you take it as the battery's ability to do work and the SLA stops
doing useful work at 10 V, then you have a 2V range from which the
percentage is calculated resulting in the larger drop I quote.

Of course, the thing about statistics is that they will tell you
whatever you want if you torture them long enough.

Capacity is defined as amp hours (sometimes energy is used). It is
definitely not defined as voltage or voltage lost, though measuring
"standing" voltage is one way to estimate the state of charge. Fully
charge an SLA battery, let it sit for a month at 68 deg F, measure the
amp hours, and they will be about 3% less than if you had measured them
right after charging. That means an 8 amp hour battery loses about 0.24
amp hours a month. The voltage will also fall during the month,
approximately 3% of that two volt working range, or about 0.05 volts.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

The original post was evidently about old batteries that just need replacing with anything new. Replace with the less expensive SLA if you don't intend to fly long days or multiple days without charging, and don't mind replacing again soon. There are no "made in USA" SLA batteries. Hawker Cyclon (used to be Gates X Cell) are the only holdout.
All the "SLA replacement" LiFePO4 batteries have overcharge and over discharge protection. You can use any good multi-stage charger for 12V batteries. Personally prefer the Xenotronics.
Here's a controller (from a much earlier thread) you can use in the trailer to charge two onboard batteries. Works for LiFePO4, but misses the top few millivolts. You can still do a 750k or so on one 10AH LiFePO4 charged with them if you have a full modern panel (VGA display, transponder, com, flarm, etc)
Jim

http://www.futurlec.com/Dual_Charge_Controller.shtml

snipIf you can't find it on the charger, connect the charger to a battery
and measure the voltage across the terminals with a Voltmeter.

That won't work too well due to the internal resistance unless the battery
is already practically fully charged. I've looked at some of these
batteries on Amazon and some have a bundled charger which is probably the
best of both worlds.

My 14v charger brings my 14v battery up to about 15.6v. That might be too
much to safely charge the LiFePO4 batteries. My 12v charger may be too
little...

Call me an energy whore, but I'm looking at this one:
http://www.amazon.com/Bioenno-Power-...ifepo4+battery


"Papa3" wrote in message
...
Further to Dave's comments, I've done some simple discharge testing on my K2
12V/10AH LiFePo4, and it's pretty impressive. At a discharge rate of over
1C, I'm seeing the nearly the full rated capacity (1.2A bulb simulating the
load). It never drops below 11V until it starts to fall off rapidly and
shuts itself off. I'm seeing 7 hours at that rate (the capacity is
theoretically derived at a discharge rate of 1 Amp, so it "should" be a
little less than 10AH at the higher discharge rate as I understand it. I
use the same smart charger that I used to use for 12V SLA batteries, and it
seems to be working just fine. I would love to see an even higher capacity
version, even with the larger foot print. The energy density is such that
it would still be significantly lighter than an equivalent SLA battery.

P3



On Wednesday, October 2, 2013 7:15:29 PM UTC-4, Dave Springford wrote:
Don't confuse the Li-Ion batteries with the LiFePo4 batteries that are
mentioned above. While the Li-Ion batteries have the instability problems
associated with thermal runaway during rapid discharge, the
Lithium-Iron-Phosphate (LiFePo4) chemistry is stable and do not have these
problems.



There are many knock-off Chinese battery packs on the market that are
called LiFePo, but be careful what you buy. I am a re-seller for K2
Energy batteries, and these are made in the USA, true LiFePo4 chemistry.
I have spent hours on the phone with Mark Stoker at K2 comparing their
batteries to some of the cheaper competition and some of the competitors
numbers don't add up. The LiFePo4 chemistry is patented and K2 pays
patent fees to the patent holder to use it, while many of the others
don't. Visit the K2 website for more information at:
http://www.k2battery.com/battery-packs-12v.html



Some of the advantages of the LiFePo4 chemistry over the SLA's (sealed
Lead Acid) is that it holds peak voltage for much longer during discharge.
The SLA's discharge curve is a continually declining slope that quickly
reaches the 10 V level where things start to shut-off, while the LiFePo4
discharge curve is almost a straight line from the initial charge of 13 V.
See the discharge curve he

http://www.foxonecorp.com/images/sto...0discharge.png



Advantages of the LiFePo4 batteries



provide much longer battery use during flight.



can be used for at least 2000 discharge-recharge cycles, compared to
300 for SLA's



hold their charge during the off-season loosing only 1% per month
(unlike the SLA batteries that loose 25-30% per month)



don't have the special charge/discharge requirements of the early
Li-ion types and can be charged with most normal SLA chargers as long as
they can provide a 14.6 V peak charge voltage



The K2 batteries have the highest capacity available at ANY discharge
rate available on the market.





Contact me if you would like more info



Dave Springford

www.foxonecorp.com

On Thursday, October 3, 2013 10:06:36 AM UTC-4, Dan Marotta wrote:
Call me an energy whore, but I'm looking at this one:

http://www.amazon.com/Bioenno-Power-...ifepo4+battery



P-l-e-a-s-e use batteries in rugged (e.g. ABS) cases, not poly shrink wrap.

I've had good luck so far with the Bioenno 12 AH LFP battery + charger.

-Evan Ludeman / T8

"P-l-e-a-s-e use batteries in rugged (e.g. ABS) cases, not poly shrink wrap."

How about bamboo!?
http://www.electric-bike-kit.com/lit...placement.aspx

GO SOLAR ! I have not charged my batteries since spring! Why spend money on a new Lithium with specialized charger when we fly only on sunny days? Paper thin solar panels are only around $100 each and the regulator can be bought on Amazon for $11. Your battery is charging the instant you roll out of the trailer. Here is just one of many places to buy the panels:
https://www.jameco.com/webapp/wcs/st...0001_228208_-1

On Wednesday, October 2, 2013 10:05:09 PM UTC-4, Dave Springford wrote:
I will confirm with K2, but it is likely too high.

K2 tells me that as long as the battery has the BMS, your 14 V charger with 15.7 V output will be OK to charge their LiFePo4 battery.

The battery I linked to is by the same manufacturer you're espousing. I've
read the technical details and can't find anything about the case, much less
"poly shrink wrap". Where did you come up with that description?

If it is, indeed, a flimsy wrapper, I could always make a fiberglass box to
house it and bond it into the fuselage very near the CG.

"Evan Ludeman" wrote in message
...
On Thursday, October 3, 2013 10:06:36 AM UTC-4, Dan Marotta wrote:
Call me an energy whore, but I'm looking at this one:

http://www.amazon.com/Bioenno-Power-...ifepo4+battery



P-l-e-a-s-e use batteries in rugged (e.g. ABS) cases, not poly shrink
wrap.

I've had good luck so far with the Bioenno 12 AH LFP battery + charger.

-Evan Ludeman / T8

Please describe your layout with a parts list.

Just a quick look at the products in your link would lead me to believe I'd
need 7 or 8 (or more) of those, at about $90 EACH plus a controller. The
LiFEPO4 battery at $200 can be charged 2000 times at 100% charge. At my age
I don't think I have another 2,000 flights left!

Or... Is it your suggestion simply to supplement your SLA batteries with
the solar cells rather than power your ship with them?

"Soartech" wrote in message
...
GO SOLAR ! I have not charged my batteries since spring! Why spend money on
a new Lithium with specialized charger when we fly only on sunny days? Paper
thin solar panels are only around $100 each and the regulator can be bought
on Amazon for $11. Your battery is charging the instant you roll out of the
trailer. Here is just one of many places to buy the panels:
https://www.jameco.com/webapp/wcs/st...0001_228208_-1