good except when your dockside DC devices can consume more than 20A, lighting DC refrigeration, computer,
TV stereo etc. etc.. In this case you could have a 20A charger sized at 10% of "bank capacity" but still be
drawing your bank down, and not charging it, anytime the DC loads exceed what the charger can deliver. As I
said, "with some caveats".. Size carefully and don't forget to consider the dockside DC consumption.
The Sterling PCU chargers have no problem charging a large bank and can run at full output for hours & hours
on end. The cooling fan on these chargers is a variable output design to let these chargers run quieter.
Chargers with single speed fans are most often louder as the fan is either on or off. I have yet to have the fans
kick on very often with the Sterling PCU chargers.
Some chargers, usually fan-less units, can not charge large banks without suffering from internal heat build up.
This can result is a shortened life for the charger if it is not sized correctly. The more efficient the charger is the
less heat it will produce. The Power Factor Corrected Sterling PCU is near 90% efficient which is a boost over
non Power Factor Corrected chargers of as much as 40%!
What the heck does that mean? What it means is you'll have a cooler running charger, less noise/fan, a smaller
foot print because leas heat needs to be dissipated and you'll use less AC power to charge at the same DC
output than a non Power Factor Corrected charger. Even the Sterling PCU 60A model will easily run off a Honda
EU2000i generator and leave you with LOTS of left over wattage, about 700W left over, to run other devices
while charging your bank at 60A. NOTE: The Honda EU2000i, a popular gas suitcase generator used on small
boats, has a constant load rating of just 1600 watts and is not really a "2000 watt" generator for constant
loads.
Sizing to the 10% rule, or better yet, the manufacturers suggestion, is a better choice with non Power Factor
Corrected chargers as they develop more heat. The Sterling Chargers are highly efficient so being in the 10% of
capacity range is not as crucial with these units or other Power Factor Corrected chargers. The "time" you need
to charge can be simply based on just that, "time".
If you had a 400Ah bank and wanted it charged from 50% state of charge, to full, over one day, you can get
away with a 20A charger. Even if the charger is sized at just 5% of total bank capacity your really only drawing
your 400Ah bank down to 50% state of charge. By following the 50% max depth of discharge rule for house
banks you would only need to replace 200 amp hours, plus charge inefficiencies. If however you need it
charged back to full in 10 hours, well that's just not going to happen with a 20A charger.
Conversely if you power your charger off a generator, when away from the dock as many boaters do, you will
want as much charger as your batteries will accept to keep generator run times as short as possible. My one
and only real gripe with the Sterling chargers is the largest single charger is 60A. On vessels with large banks
or AGM or other types of batteries that have high acceptance rates as 60A charger can limit your recharge
times when using a gen set to charge while away from the dock. For larger chargers Victron & Mastervolt make
good ones, or simply double up on the Sterling. Using two separate chargers will give you the added benefit of
a back up if the other charger fails. In bulk mode, what you'd be doing mostly with genset charging, both
chargers will be pumping out to max acceptance of the bank or their limit. Need more, you can go to three..