[aprssig] Battery & Charger for APRS Station

Richard Amirault ramirault at verizon.net
Mon Apr 21 08:15:16 EDT 2008

Your eMail program seems to capitalize the first letter of each "new" line. 
It might be better not to hit RETURN until a new paragraph.

Richard Amirault
Boston, MA, USA
----- Original Message ----- 
From: "Ray McKnight"

> SLA (and non-sealed lead acid, they're basically the same thing)
> realize their longest life when kept at or near 100% charge.  Caveat,
> As long as they are NOT overcharged.  The best way to determine charge
> State is specific gravity, but that isn't possible with an SLA, so
> Chargers generally rely simply on voltage.  A healthy battery will
> Be very close to the known, full charge voltage, after it's allowed
> To rest, usually about 1 hr.  It's even better to have a temp sensor
> To monitor battery temp to avoid excessive heating during charge, but
> Usually this is only done with larger batteries being charged at or near
> Maximum rate (30-50 amps).  Excessive heating may cause the batt to
> Vent, a bad thing and a precursor to premature failure or at least
> reduced
> Life.
> Since you do have a fairly constant drain on your battery, the charger
> needs
> To overcome that PLUS the constant loss of voltage which occurs even
> without
> Any load, I believe usually around 10%/month.  Keep in mind, the hardest
> part of any lead-acid battery charge is the last 10%, it requires far
> more
> Time and more energy to get it from 90 to 100%.  Thus, most folks
> usually
> See that it's "close enough" and quit before 100% is achieved, which
> adds
> To premature failure.  (since few ever bother to measure specific
> gravity).
> Another trick you can use to get maximum life out of a lead-acid is to
> perform an equalization charge about once per month.  Over the routine
> Use, your cells will become slightly unbalanced in their charge and
> voltage.
> "Zapping" the battery with 18+ volts while monitoring temperature will
> help
> equalize cells thus prolonging overall life, avoiding or slowing the
> inevitable "dead cell" syndrome where one cell fails because it stops
> accepting charge.  But few chargers have this mode and most users don't
> have
> any way to do it manually themselves.
> If your battery is installed in a remote location this might be
> impractical.
> Many sailors (particularly sailboats) use this as they rely heavily on
> battery power underway and charging is very challenging.
> One thing I'd be weary of is that you likely have no isolation of the
> charger from the TNC/transmitter.  Be sure it's providing a clean DC
> Voltage and not introducing any unwanted things like hum into the TX
> Audio.  It might be fine during receive but TX could get into the
> charger
> And give you problems.  Look at signals on a scope to see any unwanted
> audio
> Or ripples.
> It sounds like you're okay, just a few concerns to look at for 100%
> peace
> of mind, the batt should be fine with that charger and last as long as
> possible.
> One last thing - those el'cheapo "float chargers" so popular and sold
> By the zillions at Home Depot and Costco etc for $20 or less are sure
> fire
> Death your battery, as they are completely stupid, they don't measure
> ANYTHING even voltage, and simply continually spit voltage at your
> battery
> Even when it finally reaches 100%.  BIG PROBLEM especially on RV's as
> they
> Seldom have any type of smart charging, it's simply brute force or
> "constant
> trickle" which will cook your batteries, that's why you replace them
> every
> 2-3 years (also because you buy those $39 Costco "deep cycles" which
> really and VERY cheap disposable crap batt's).
> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of John Habbinga
> Sent: Sunday, April 20, 2008 10:42 PM
> To: TAPR APRS Mailing List
> Subject: [aprssig] Battery & Charger for APRS Station
> I am installing a digipeater in a location that I want to have
> reliable battery backup power.  For the last month or so I've been
> testing out a setup where the radio and TNC run off of a 12 volt, 35
> Ah sealed lead acid battery.
> The battery is connected to the radio/TNC and it is connected to the
> battery charger.
> The charger is a CTEK Multi US 7000.  It is a multiple stage charger.
> When it finishes charging it STOPS charging completely.  Every ten
> minutes or so the charger tests the battery and if it needs to be
> charged, then it adds current.  So it is not a 'trickle' charger.
> My observation is that about once an hour the charger kicks in and
> tops off the battery.  I don't get any interference from the charger
> at all, even on HF frequencies.  You can find out more on the charger
> I'm using at http://www.ctek.com/EN-US/Default.aspx
> At 20+ charging cycles per day, am I prolonging the battery life by
> frequently recharging when the battery is at such a shallow state of
> discharge, or shortening it?
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