Battery Isolation Question

[sjhantzis]

On a 2005 25' cruiser . . .

If I select Battery #1 (the starboard side battery) with the battery selector switch, does that physically isolate Battery #1 so that I can directly connect a trolling motor to Battery #1 and not risk running down both units?

Thanks,

SJH

[Byrdman]

Well, definitely maybe I guess would be my answer. You have to actually look at the wires on each battery, figuring you have two on board, and see where the wires run in relation to your selector switch. Some items may even be straight wired to your battery as to "always be on". Also, take a look at exactly what type of batteries are in your boat. Could be a crank battery, a deep cycle battery or a multi-purpose battery.

Let's just say Battery # 1 is a crank battery. Good for sudden, sharp spiked demands like cranking the motor. (shorter demand spikes now that we have sweet starting 4 stroke motores)
Then, Battery # 2 is a deep cycle, house battery for things when on the hook. Radios, reading lights, an inverter for the coffee pot or microwave without starting a gen set....

Or, both batteries "could be" a multi-purpose battery.

Each individual boat has the possibility of being something different and/or a mix of it all. That said, some would, or could, run two multi purpose batteries wired in parallel as to give two individual 100 Amp-Hour batteries the same 12 volt system, but, double the Amp-hours to 200....as to make each individual "hit" from any source needing power, a smaller percentage hit thus allowing the batteries as a "team" to last longer, ....but,....both be discharged, not leaving you a for sure crank battery.

There is no "for sure" answer without looking in detail at YOUR boat and YOUR switches and how they are ran.

Take a peak at TRAILER BOAT Magazine, May 2010 issue. Great article on batteries.... and a good read.

Sorry, no for sure answer here.

The way Charlie wants his boat wired could be different from how Bob wants his boat set up which could be different to how any of the Rogers wants their boats set up....and, same could be true for folks that ran the stuff in your boat.

Byrdman

[journey on]

I can only speak for Journey On. Since das boot is also a 2005, it could be similar.

A positive cable goes from each battery to the selector switch. When battery 1 is selected (BAT 1), that battery, and only that battery is connected to the switch output. If one selects BOTH, then both batteries are connected in parallel. The output of the battery switch powers the DC system AND connects to the main outboard.

Please note that many other wires are connected directly to each battery: bilge pump, battery charger, etc

Boris

[BrentB]

Here is an example
4 position switch position (sp) #1, # 2, #3 Both, #4 Off

Switch position #1: One battery is connected to the engine and second battery is not (isolated). Check the wiring to the selector switch then label each battery as #1 or #2

sp #2: second battery is connected to the the engine and first battery #1 is not (isolated)

sp ALL: Batteries #1 and #2 (ALL) connected to the engine

sp OFF: Both batteries are disconnected (OFF) from engine

Product manual for a Perko
http://www.perko.com/
_________________



I use sp #1 for engine start battery
and sp #2 for the second battert

[sjhantzis]

Okay, forget about the AGM verses Starter battery issue. Not important. Both of the switched batteries are Group 27 starter types. Still, not important.

All I'm trying to determine prior to actual sea trail is: If I directly connect a trolling motor to the posts of Battery #1 and select Battery #1 on the battery selector switch, will I also draw current from Battery #2?

[BrentB]

[thataway]

My question is what will you be doing with a 12 volt trolling motor on a C Dory 25? 12 volt trolling motors are limited to about 50 lbs thrust. Not a not of power--yes it will move the boat at a couple of knots. But you don't have a long time of reserve.

I would put in at least one dedicated battery for the trolling motor. You are going to "Sea trial" a trolling motor? What do you want to use the trolling motor for?

I have a 80 lb thrust trolling motor in my 18 foot Caracal--and that runs off two group 31 12 volts, wired in series. That might be OK for a C Dory 25--but when you get to the bigger trolling motors, then you want to consider the weight and battery weight. I believe that there is a boat for sale currently with Lenco trim tab trolling motors--and those are 24 volts. You should contact that person to see how the boat performs.

There is never any guarantee how any one of the C Dories are hooked up. They mostly have #1 battery wired directly to the engine--and that is the starting battery. Some have the engine wired to the common of the switch directly. There is a danger there if you turn the switch to "off" that it will damage the charging circuit diodes. You don't want to run an auxially motor on the main engine starting battery. You can look at the wiring when you are one the boat and determine how it is wired. Be sure and take your voltmeter along--to check for any decrease in voltage along the circuit--due to corrosion or bad wiring. Also take a hand held GPS for speed determinations.

Have fun.

[wilbe asea]

You will only draw from both batteries if your battery selector switch is set to "both".