Hi Rich

 

I am not sure what my alternator output rating is but my ammeter never shows
more than 60 and even that is not for long as it settles out to between 15
and 30 fairly quickly, like after a a minute of steaming.  If I switch from
one battery bank to the other during steaming I can sometimes notice a
slight drag on the engine (it seems to slow down a bit) but even that is
momentary (a second or 2).  My house bank is two, 6 volt deep cycle
batteries connected in series and my start bank is one Group 24 deep
cycle.they have been on the boat for 7 years continuous and have never let
me down.  I run an old 1720 Furuno radar when I need it (fog or dark) and I
run an Adler Barber in icebox refrigerator freezer.  I try to remember to
manually cycle the fridge on and off since I disconnected the thermostat and
now can't remember which wires go where to reconnect it.Last season I left
the boat unattended on the mooring for about 5 days but I forgot to turn off
the fridge.  Much to my surprise after those 5 days there was still power
left in the battery and the fridge was still cold and I have no added
insulation around the ice box yet!!  I was able to start the engine from my
start battery and recharge my house bank from the engine. Probably some
sailors use more power on a regular basis than I do but 100 amps seems like
a pretty high charge rate.  Would a 100 amp charge rate not be hard on the
cells?

 

 

  _____  

From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Rich
Knowles
Sent: December 18, 2013 8:38 AM
To: cnc-list@cnc-list.com
Subject: Re: Stus-List Battery charger recommendations?

 

And to increase the presumptuous factor:

 

The alternators that were supplied as original equipment with most small
boat engines until recently were from 35 - 55 A with internal, single
voltage output regulators. A good percentage of the engines were destined
for use in small motor vessels and these alternators were adequate for that
application. For our use, which sees greatly increased loads from, as Rick
notes, radar and refrigeration, and lengthy battery discharge periods
between charges, those alternators are bordering on inadequate, and
certainly not as efficient and appropriate as higher power units with multi
stage regulators. 

 

For sailing vessels, a central component of optimizing the electrical system
should be upgrading the generating capacity of the charging system. This
will involve replacing the alternator with the largest unit that can be
fitted, taking physical restrictions, drive belt capacity and depth of
pocket book into account. For most 20-35 HP engines, around 100A works well.
There are a number of external regulators available that should be
considered for installation as part of the new system. A new alternator with
a multi-step regulator will considerably reduce the engine run time needed
to replenish the batteries. Other devices such as wind generators and solar
panels are important for long range travels as well to further reduce the
dependency on the engine. 

 

For calculation purposes, I generally consider the usable capacity of
batteries to be 30% rather than 50% of rated capacity. This stems from the
fact that a 50% discharged battery will charge to around 80% at a fairly
linear rate which will drop significantly as the state of charge nears 100%.
Trying to achieve the last 20% can take a long time compared to the first
30%. This will vary depending on battery type and condition, so my 30%
figure is somewhat arbitrary, but fairly realistic.

 

A shore power fed battery charger from 20-40A will generally suffice to
sustain loads from refrigeration, lighting and entertainment devices
operating while the boat is alongside, and also provide enough power to
replenish the batteries. Again, a multi-step unit designed for marine use
should be chosen. There are lots of good marine chargers on the market. 

 

I note that non-marine AC chargers may not completely isolate the input from
the output, a potentially dangerous situation on the water, and should be
avoided. 

 

As Rick notes, designing an efficient, reliable electrical system is
complex. 

 

It's snowing again. Grrrr!

 

Rich Knowles

INDIGO - LF38

Halifax, NS

 





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