Random thoughts on deep cycle battery chargers:
Quite a few years back, I "inherited" a string of mostly mountaintop land
mobile communications sites. Mostly strung together from bailing wire and
old mobiles, all had battery backup. The charging sources ran the gamut
from 1 amp solar panels to unregulated car chargers stuffed into a hole
with the radio.
I guess the last requires explaining. The, er, regime that installed the
sites was notoriously cheap. They used old mobiles to kludge together
repeaters. To save having to buy equipment shelters, they actually buried
septic tanks on the top of mountains and 'installed' repeater, duplexer,
and charger (where there was AC power) in them. Unfortunately they weren't
always watertight. Ever have to repair a repeater with a waterline? I have.
And them there was the hiker that had an urgent call, broke the lock off of
the tank lid, and used it for its original intended purpose. Fortunately,
that was before my time. I took over the position of the individual who
had to clean up after the hiker. For some reason he left seeking other
employment.
But I digress...
Trying to clean up the mess (the radio installations, not what you were
thinking), we investigated charging sources for our AC powered sites. The
car chargers were notorious for causing early battery failure (and we
suspected, frequent radio failures). Our research turned up the
interesting fact that the best communications site battery chargers are
pure DC chargers, similar to a good bench supply. Unfortunately, we simply
could not afford to buy enough of them to equip all our AC sites along with
the new radios we were purchasing.
Instead, we used Newmar ABC15 marine deep cycle chargers. Initially we had
some concern that these would cause problems. They occasionally pulse the
battery in order to maintain full charge. This kick put a spike on the DC
line. However, it didn't seem to bother the new GE Mastr II equipment we
installed them with.
I point this out to emphasize that battery chargers are seldom as clean as
a good bench supply. They all rely to some extent on the batteries
themselves for filtering. Some provide nothing else.
Any site running on a non pure DC output charger runs the risk that an
internal battery failure (open) or bad terminal connection will subject the
radios to unfiltered power.
Also, there are at least four different kinds of deep cycle battery
chargers: ferroresonant, SCR, switching, and transformer/FET. The
ferroresonant variety are notorious for undercharging batteries that have a
load, and overcharging those that don't. The SCR variety pulse the DC line
(at least those I have used do), the switching variety seem to have a high
failure rate in my experience (they also seem to be built to a price). The
transformer/FET types are usually combined with an inverter, and are the
most expensive.
If I add battery power to my shack (which I should do because I live in the
boonies in the hurricane belt, and we have very unreliable power), there is
no question in my mind that I will simply add an isolation diode and use my
30 amp Alinco supply with Trojan T105s, since it can be adjusted high
enough to compensate for the diode drop.
I did buy an automotive charger from WalMart. Its transformer developed an
open the first time I used it after the warranty expired. Retail battery
charger salesman made the pizza that the battery salesman was selling
yesterday, with exceptions of course.
West Marine and Boat/US are two marine stores with locations throughout
much of the US. They carry deep cycle chargers and batteries. Their
salesmen were NOT making or selling pizza yesterday. They were scraping
barnacles off of boat bottoms somewhere, which pays less than pizza making,
with exceptions of course.
All of the above in my experience. Contrary opinions welcomed, no
exceptions of course.
73, Malcolm WX4YZ
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