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Author Topic:   House Battery and Starting Battery Designations
rtk posted 12-17-2006 07:38 PM ET (US)   Profile for rtk   Send Email to rtk  
I have been reading recommendations regarding designating a house battery and starting battery in a switched dual battery system.

The way my switched dual battery system is wired on my boat, and the way I have always installed a switched dual battery system is the 12 volt accessory (house) and engine starting system positive leads are connected to the common pole on the battery switch. The only positive lead that is connected directly to a battery source is the bilge pump float switch. That way all 12 volt power can be shut off except for the feed to the automatic bilge pump, and that is limited to one battery.

The individual positive leads from the battery are connected to the battery switch at seperate poles, and they feed the common either individually or in parallel in position both.

Switch to position 1, 2 or both provides current to both the 12 volt accessories and the engine starting system from a single battery, or paralled at the both position. There is no way to direct power to one single system individually, or isolate one battery feeding one side and another battery feeding the other side if you wire the dual battery switch conventionally.

Perhaps a better way to describe the house battery/starting battery designation is battery management when utilizing a dual battery switch? Or do you actually designate a particular isolated battery as a start/house battery? One battery for one purpose, the other for another.

For example, if you have been running a while on battery 1, and you know the battery is well charged, switch to battery 2 at anchor if you will be operating 12 volt accessories for a while when the engine is not running. That way, if you run battery 2 down, you can switch to battery 1 to start the engine.

The "house/starting" nomenclature is confusing to me, it infers separate, dedicated batteries for separate purposes.

I have AGM batteries that serve as dual purpose batteries, good for starting and deep cycle use to facilitate my battery management method.


jimh posted 12-17-2006 08:56 PM ET (US)     Profile for jimh  Send Email to jimh     
The "house/starting" nomenclature is confusing to me, it infers seperate, dedicated batteries for seperate purposes.

The house battery and the starting battery are separate batteries, and they are wired and intended for different purposes. On a small boat it is very typical that one battery serve both purposes, or that a bank of two batteries be wired to select either one or the other to server both purposes. This probably came about because of the nature of the electrical switching gear that was available. However, there are now available several very nice specialized switches which permit maintaining a dual battery installation in which one battery is used exclusively for engine starting and another is used exclusively to power non-engine loads.

andygere posted 12-18-2006 01:21 AM ET (US)     Profile for andygere  Send Email to andygere     
To truly isolate 2 batteries, that is have one for starting only, and the other for house loads, you need to replace the simple 1-2-both switch with a system that has a voltage sensing relay. With these devices, the start battery is truly separate from house loads, and only the primary outboard is wired to it. Here's a link on a discussion thread on this method of managing dual batteries:

Here is a somewhat fuzzy diagram of how I've wired my system: BEPwiring.jpg

jimh posted 12-18-2006 08:44 AM ET (US)     Profile for jimh  Send Email to jimh     
The advantages to using separate batteries for the HOUSE and STARTING functions are:

--sensitive electronic device loads running off the HOUSE battery will not experience voltage transients during engine starting.

--the STARTING battery will not be drained by non-engine loads, thus it cannot be run down by accidently leaving the lights on too long.

Most arrangements provide for a temporary parallel switch to combine HOUSE and STARTING for emergency engine starting or other needs. The use of a voltage sensitive relay (VSR), also called an automatic charging relay (ACR), to combined the batteries in parallel for charging when the voltage on the STARTING battery exceeds 13.6-Volts is an effective way to sustain the charge on both batteries from a single charging source like an outboard motor.

jimh posted 12-18-2006 08:50 AM ET (US)     Profile for jimh  Send Email to jimh     
The BEP Electronics installation that Andy used is a very nice solution to the problem. Another approach which was just recently introduced by BLUE SEAS is a single switch with specialized arrangement of the contacts. It keeps the HOUSE and STARTING separate. They also have a VSR for automatic charging.

For Blue Seas, see:

Blue Seas products are in wide distribution in the United States.

For BEP, see:

In the United States, BEP is available at Boater's World stores.

rtk posted 12-18-2006 08:44 PM ET (US)     Profile for rtk  Send Email to rtk     
Thank you Andy and Jim for clearing that up for me. The part I was getting stuck on was how to easily charge the house battery that is isolated from the engine start and charge system.

I do like the BEP cluster, and the price is not bad.

It does make alot of sense to me now. A system like the BEP and the Blue Seas will eliminate my need to make sure I run the boat on different batteries either on alternating trips or switching during the day to charge both batteries.

It does the thinking for you.


Chuck Tribolet posted 12-18-2006 08:48 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Not only does it do the thinking for you, it lets you use the
right sort of battery for each side: starting battery for
starting battery, deep cycle for house battery.


pglein posted 12-19-2006 06:29 PM ET (US)     Profile for pglein  Send Email to pglein     
It is actually quite easy and inexpensive to have truly independent house and engine battery systems that can be connected for charging or manually isolated without the use of expensive charging relays or battery isolators. The catch is that you have to remember to set your switches properly both while underway and while at anchor.

The trick is to use TWO 1,2,All switches, not just one. On each switch, run from the "1" terminal to the battery. Then, run a cross link between the "2" terminals on each switch. Then, from each switch, run your leads to the house panel and engine respectively.

This is a very simple system that was used by by the manufacturer on our 36' Albin Express Trawler. For a sophisticated boat like that, it was a little to simplistic. But for a Boston Whaler in which switches and connections need to be kept to a minimum, and the operator can be trusted to remember to set the switches correctly, it is very effective.

To leave the two banks combined, have both switches set to "ALL". To run them both simultaneously but isolated, set both switches to "1". To turn them off, set them to "OFF".

Technically speaking only one of the switches need be of the "1,2,ALL" variety. One can be "ON,OF", but it's a little easier to remember how to set the switches if they match.

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