When I "re-alternatored" my boat with a smart charger etc. I sized the alternator so as to not put too much drag on the engine. I sized my at 80 amp for a 33 hp diesel. I estimate I lose 3hp when full on charging. Any more, and you start losing, in my opinion, too much HP.
David F. Risch 1981 40-2 (401) 419-4650 (cell) From: dwight...@gmail.com To: cnc-list@cnc-list.com Date: Wed, 18 Dec 2013 10:38:57 -0400 Subject: Re: Stus-List Battery charger recommendations? 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 _______________________________________________ This List is provided by the C&C Photo Album http://www.cncphotoalbum.com CnC-List@cnc-list.com
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