SLA batteries opinions?

A few things about SLA batteries.

The capacity is usually defined when discharged at the C/20 rate - so for a
7Ah battery 350 mA for 20 hours. The capacity at higher rates is reduced.
If you try to take 1.4A out of a 7Ah battery it won't last 5 hours.

I have found that if you treat them well they last well. Treating them
well means not to over discharge them, or overcharge them, and to recharge
them as soon as possible.

I have had good results with a simple constant voltage charger, charging to
13.6V. This seems to be enough to recharge them overnight. I've had
batteries last for 5 years or more.

The trick is to look at your energy budget, how much current do you need?
For a fairly simple system, a LX7007 (260 mA), a radio (200 mA) and a nav
device (200 mA), that's about 7 Ah in 10 hours. That lot should run off 2
7Ah batteries with no trouble. If you have higher demands then install
enough capacity that you only use 50% on the average day's flying.

The reservation about Lithium based batteries I have is their tendency to
catch fire. I realise that this depends on the chemistry and manufacture
but there have been enough instances of this that I'd be inclined to be
cautious unless the reduced mass and increased energy density is
essential.

And regardless of what chemistry your batteries use and what other things
are in place put a fuse in the battery lead close to the battery. All
batteries have enough capacity to produce an entertaining amount of acrid
smoke in the cockpit if you get a short.

Chris


At 14:40 04 April 2018, Dan Marotta wrote:
I have to ask, then:Â* Why keep putting SLA batteries in your glider?Â* Do

you need them for weight and balance?Â* Why not just two LiFePO4?

My experience with the lithium batteries was nothing short of terrific.Â*

Prior to the switch, I couldn't power everything with two SLA batteries
for 5 hours (15 AH combined).Â* After switching (10 AH LFP), I never had
a shortage of power.

On 4/3/2018 9:05 PM, wrote:
I have flown with both an LFP and SLA battery in my ship for 5 years.
I
alternate which one is primary and which one is secondary on each flight.

A PowerSonic 12V14Ah SLA vs Powerizer 12V15Ah LFP. With all my
instruments
running the SLA voltage drops below the minimum requirements of my radio
by
5 hours. My LFP has never failed to power everything up to a 7 hour
flight. The SLA gets replaced after 3 years. My LFP is six years old
and
still working perfectly.

When I fly in very cold conditions (0C) the SLA is usually not driving
my
radio by three hours. Again, the LFP has run up to six hours without any
significant voltage drop.




--
Dan, 5J