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Author Topic:   Battery Switch with OFF-1-BOTH-2
bhawes posted 01-27-2009 07:02 PM ET (US)   Profile for bhawes   Send Email to bhawes  
I recently installed a battery switch on my single engine, dual battery configuration. My reason was purely to save the starting battery from becoming drained in prolonged periods of instrument use in periods of shut down. I now see that there are other reasons and concerns. Some concerns that I have are as follows:

With the selector on battery 1 (or battery 2); are both batteries being charged? Or only the one selected? Could and should the Blue Sea 7610 be installed in conjunction with my battery switch, or would it be redundant?

I generally start my boat with "both" and then switch to battery 2 during shutdown. If I start with "both", do I run the risk of causing the voltage drop mentioned, and the subsequent loss of data from my 2007 model GPS and Chartplotter 2007?

Thank you for any information and advice forthcoming.

jimh posted 01-27-2009 08:49 PM ET (US)     Profile for jimh  Send Email to jimh     
In the usual wiring associated with a primary battery distribution switch with OFF-1-BOTH-2 selections, when the switch is in the I or 2 position, only one battery is connected to the load distribution, and the other battery is not connected to any loads or charging sources via the switch. Of course, if there are direct connections of loads to a battery, those loads remain connected no matter where the OFF-1-BOTH-2 switch is positioned.

Could you describe a Blues Seas 7610 and what function it performs? I do not think most are sufficiently familiar with the Blue Seas product line to recognize their products only by the model number.

Using the BOTH position for engine starting puts the two batteries in parallel and increases the amount of cranking current available to run the engine's starter motor. In normal operation it should not be necessary to parallel the two batteries to get the engine started. There should be a single battery with enough capacity to start the engine without assistance.

During engine starting the voltage at the battery terminals may sag due to the very heavy load. One of the purposes of having an isolated battery to which the vessel electronic loads are connected is to prevent the electronic loads from experiencing this voltage sag at start up. The concern with some electronic devices is that they may re-boot their internal computer controllers if the supply rail voltage sags. This is typically a concern with more sophisticated devices like a navigation system. Simple electrical loads that do not contain microprocessors which require a few moments to start up are generally not affected by slightly lower voltage excursions.

towboater posted 01-27-2009 09:09 PM ET (US)     Profile for towboater  Send Email to towboater     
I asked the same question to my marine tech years ago regarding a Cole Hersey 3 way switch.

Yes, you can move to/from any battery combo without losing 12v power to your buss or cause the diodes in the charging system to blow.

Never turn to off position while the engine is running.


jimh posted 01-27-2009 09:57 PM ET (US)     Profile for jimh  Send Email to jimh     
I just about never move the primary battery selector switch when the engine is running. I might in an emergency, but not in normal operation.

You cannot make blanket statements about all switches. You have to check the individual switch to see if the contact arrangement is make-before-break.

Moving the switch through the OFF position disconnects everything. It is a good way to damage the charging system if there is a motor running.

swist posted 01-28-2009 08:10 AM ET (US)     Profile for swist  Send Email to swist     
If you have a two battery system to separate continuous usage from engine starting (a pretty common configuration), then why would you defeat it by starting in "both"? A single healthy battery should start any outboard. Starting with both batteries should be reserved for an emergency situation where you can't get enough juice out of either battery.
pglein posted 01-28-2009 01:17 PM ET (US)     Profile for pglein  Send Email to pglein     
I concur that you should start in "1" or "2". Once the engine is started, you can switch to "Both" to ensure that both batteries are charged, but if the engine shuts off for any reason, you should immediately swith to "1" or "2" to preserve the charge in at least one of the batteries in case you have trouble re-starting.

In most installations, charging will occur only on the battery is selected. In some cases, the charging voltage bypasses the switch and goes directly to the batteries, usually through a charging regulator that ensures both batteries are charged at the optimal rate. These installations are exensive and quite rare in small boats. I would be surprised if your boat was set up this way.

Assuming a typical installation, selecting one battery or the other, or "both" while starting will not protect your electronics from a voltage drop. Not that you need to; most electronics are designed to deal with this kind of voltage drop by shutting off and restarting when the voltage comes back up. This is more of an inconvenience than a danger to the device. The recommended solution is simply to wait until after the engine is started to power on your electronics.

If you feel the need to protect your electronics, you could install a system with dedicated "Start" and "House" batteries. In this kind of system, a four-position rotary switch is not necessary (though is sometimes installed to allow bypassing the system). Instead, the engine is wired directly to the "Start" battery, and draws only on it for starting. The "House" battery supplies power to the electronics and other non-starting loads, and is linked to the "Start" battery via an isolator or Automatic Charging Relay. If you think of electricity like water, this is essentially a one-way valve that only opens when the voltage coming from the "Start" battery indicates that the engine is running and the alternator is producing power (about 13.5 volts). When it drops below this voltage, the valve closes, preventing the house battery from being drawn down by the engine. Also by not "opening" until the higher charging voltage is reached, it prevents you from drawing down your start battery when the engine is not running by leaving on the electronics, lights or other loads. Using an ACR is a very cost effective way of making your battery management "idiot proof".

westcoastwhaler posted 01-28-2009 02:30 PM ET (US)     Profile for westcoastwhaler  Send Email to westcoastwhaler     

If electronics is a concern when you are starting up, you can isolate all of the electronics on one distribution panel with a master on/off switch and have this turned off before starting.
bhawes posted 01-28-2009 10:44 PM ET (US)     Profile for bhawes  Send Email to bhawes     
Thanks everyone.
The reason that I start on "both" is that my starter is on 1, and my electronics on 2. I have to navigate out through a very shallow channel, and depth knowledge is critical, so I like to fire up my Sonar as soon as I'm started.

There were some excellent ideas put forth and once it warms up (it's -20C now), I'll go over the configuration that I now have and implement some suggested improvements.

Thanks again.

Liteamorn posted 01-30-2009 08:15 AM ET (US)     Profile for Liteamorn  Send Email to Liteamorn     
You might want to do some rewiring of your electronics. It is not recommended that you run your switch in both. I want my electronics running all the time. The only thing that shouldn't go through your switch is your bilge pump if you slip your boat. I alternate batteries every trip. The only time I have battery problems is if I don't use my boat enough and then I just throw a charger on them (one at a time).
Andrewdavis34 posted 02-07-2009 10:39 AM ET (US)     Profile for Andrewdavis34  Send Email to Andrewdavis34     
Hi. Just last winter I went through [adding a OFF-1-BOTH-2 primary battery distribution switch] with my 170 Montauk. I installed dual batteries and ran all my electronics thru a Blue Sea Systems 6 fuse panel. With this set up the electronics can be powered by battery 1, 2, or BOTH.

Here is the link to the installation, if anybody is interested.


newt posted 02-07-2009 01:16 PM ET (US)     Profile for newt  Send Email to newt     
Andrew, what is the make and model of the circuit breaker box you have next to the selector switch? I may need something similar.
jimh posted 02-07-2009 01:58 PM ET (US)     Profile for jimh  Send Email to jimh     
Generally when a primary battery distribution switch is added, such as the usual OFF-1-BOTH-2 style switch, it controls all the battery distribution, for both the main engine and auxiliary loads.

I don't understand Andrew's installation with reference to the switch controlling only the electronics or house loads. Perhaps if we could see a schematic diagram, it would facilitate understanding. Electronic circuitry is best shown with a schematic diagram, and it can be confusing to describe it in narrative form.

Andrewdavis34 posted 02-07-2009 03:25 PM ET (US)     Profile for Andrewdavis34  Send Email to Andrewdavis34     
Here is the link to the Blue Sea System Fuse Panel that I have.

As far as the wiring is concerned I followed Jim H's installation wiring diagram for dual batteries. Basically the Pos(+) lead from the Fuse panel goes to the common power post. And the Neg(-) lead from the panel goes to the Buss Bar that was installed from the factory.

If anyone is interested here is the wiring


Andrewdavis34 posted 02-07-2009 03:39 PM ET (US)     Profile for Andrewdavis34  Send Email to Andrewdavis34     

IF anyone is interested in installing the fuse panel. BSS make labels that go on the cover of the fuse panel. There is no need to order a label kit. I called Blue Sea Systems and the receptionist mailed the labels that I needed for free!


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