Association Forum - Battery isolators

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Battery isolators

New Topic

Topic Locked

Printer Friendly

Author

Topic

sweetcraft
Admiral

Member Avatar

USA
816 Posts

Initially Posted - 03/03/2005 : 00:08:21

Who uses battery isolators to charge two batteries? Have you had problems using them or know of boats that have had problems?

Edited by - on

Frank Hopper
Past Commodore

Members Avatar

Pitcairn Island
6776 Posts

Response Posted - 03/03/2005 : 07:11:32

Why do you think you need one? Doesn't a quality charger provide all the isolation needed during charging? Why does my battery switch have a both position if it is not ok to have them in parallel? My battery switch is NEVER moved from "both" and my two battery charger is wired to the back of the switch. This is a subject I have never grasp.

Edited by - on

Dave Laux
Captain

Members Avatar

318 Posts

Response Posted - 03/03/2005 : 07:40:28

Almost no one uses battery isolators at all any more except those that already have them. The reason is that they have about a 1/2 volt forward bias (reducing the charge voltage by that amount) This leaves systems with good voltage control ( not true of outboard motors) in a continuous undercharged situation. This voltage drop and the associated current reduction is why they are built as a massive heat sink. Those vessels that need a dedicated starting battery mostly use an automatic relay to connect the start battery for charging and disconnect it for house loads on engine shutdown.
The last big boat that I designed and built had 335 total amperes of charging capacity (thats about 6 horsepower) for a 1200 ampere hour (equivilent of 24 grp. 24 batteries). Dave

Edited by - on

sweetcraft
Admiral

Members Avatar

USA
816 Posts

Response Posted - 03/03/2005 : 09:52:29

Does the reduced voltage using isolators reduce the life of the btrys? I also want to know if the reason for the heat sink is for the excess heat which could be a fire source, how many systems have caused a fire? I use a 10 amp charger from the outboard so is this enough to overload the isolator? On our small boats keeping the system simple was the reason for chosing the isolator and the cost too and not using the relay. Having a choice of btrys if one goes bad was also a reason for the isolator and the btry switch. Doesn't in a 2 btry system with parallel wiring and no switch the btry with the higher charge control the charging rate?
I am kind of at a cross road wondering if I should keep the isolator in the system. Since the units are available in our marine catalogs makes me wonder what system is safer? What's the better system?

Edited by - on

Dave Laux
Captain

Members Avatar

318 Posts

Response Posted - 03/04/2005 : 16:59:38

In your case the answer is maybe. Helpfull right? Overload is not likeley to be a problem for you because your charging system and load demand are low. The voltage drop is always there but your outboard has no voltage regulator so your system volts are probably higher than the 13.8 to 14.2 for maintinence or charging after your engine has run for a while. Many of them get up into the 15 volt range after a while.
While the battery charging system behavior is fairly complicated you can imagine that it is a constant voltage system. If your alt. is producing 6 amps at 14.5 volts, and one battery is at 12 volts and the other is at 13 then most of the 6 amps will go through the 12 volt one because its internal resistance is lower. However if they are permenently paralleled there will not be any volt difference to start with and charging current will be even.
A straight on/off battery swich has something to be said for it for disconnecting the batteries in an emergency. I've never had one (emergency) where that would be an appropriate response. But switching from one bat to another on a daily or whatever basis does not seem to me to make any sense. Whatever percentage of the capacity you use between chargings will be twice as much with one bat instead of two. Its easy to envision circumstances where use of the alternating switch leaves you with one much discharged battery and one fully charged one. Any time you reduce the state of charge of the battery below 50 % you are really reducing battery cycle life.
I guess that if you use appropriate LED indicators to indicate circuits that are left on and are not supposed to be and pay attention to the system you are not likely to get suprised with a dead battery. Dave

Edited by - Dave Laux on 03/04/2005 17:15:19

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.