Battery charging while under way

W

willronco

New member
My fellow C-Brats, I'd like to share some GREAT news. We bought a boat! And had a DELIGHTFUL shakedown cruise last weekend, about which more in another thread.

In this thread I'm trying to puzzle through a battery charging strategy and I request your help. We have 2 batteries on board - house and start. Each has a battery switch, and they can be combined with an "emergency combine" switch.

In normal operation, I have both battery switches set to ON, and the combiner set to OFF. While underway, the engine alternator charges the start battery only.

My goal is for the engine alternator to charge both batteries while the engine is running. What is the best/safest way to do this? My ideas so far are:

* Combine the batteries by turning the battery combine switch to "combine" BEFORE starting the engine. Possible advantage: no sudden voltage change while engine is running. Possible disadvantage: lower house battery impedes engine's ability to start?

* Combine the batteries by turning the battery combine switch to "combine" AFTER starting the engine. Possible advantage: more fully charged engine battery better for engine start. Possible disadvantage: flipping switch while engine is running not good for engine/alternator/something else I am not thinking of?

In the future, I'd like to install some kind of automatic switch that will do all this automatically in a smart way. This will also minimize the risk that I forget to un-combine the batteries and accidentally drain the start battery while at anchor. My guess is that device will be something like this: http://www.bluesea.com/products/7601/m-Series__Automatic_Charging_Relay_-_12_24V_DC_65A But that is probably a winter project.

For now, I really want to minimize the risk of engine damage while also charging both of my batteries while under way. Can anyone point me in the right direction on this?
 
Combine batteries after starting to charge both. And uncombine after shutting down the motor. Otherwise, you effectively have one big single battery and lose the safety benefit of having dual batteries.
 
I've always been told not to turn the switch while the battery is running. I think you are correct that it will send a surge through your system and possibly damage the motor electronics, or on board electronics. I cant remember which one. I have never tried it so I don't have any experience! thankfully :smile

What we do is turn the switch so we are running both batteries most of the time while we are cruising or fishing. When we are ready to anchor/dock for the night, I switch to the house battery only. Switch it back to both batteries in the morning before we start up the motors.
 
The automatic combiner switches work very well. You do not haave to do anything or worry about forgetting to uncombine.
I have one on my boat and love it.
Jerry C Nile
 
PaulNBriannaLynn":3tscblzq said:
I've always been told not to turn the switch while the battery is running.
Click to expand...

There used to be a time when the conventional wisdom was to pump the gas pedal in your car before starting it on a cold day, or even holding it down while cranking the motor. This is no longer the case with modern fuel injected engines. Systems improve over time. Convention must change with it.

Although there remains risk of damage if a master battery disconnect switch is turned OFF while the engine is running, in today's world, the danger of wrecking an outboard's charging system by changing the position of the battery switch has mostly gone the way of the carburetor. Modern charging systems are more robust than they previously were. And modern marine battery multi-switches are overwhelmingly of the make-before-break type. So there is very little risk of causing problems due to switching between batteries while underway. (The Bluesea ACR actually performs this switching automatically, and that device is generally accepted as a welcome addition to any dual battery system.)

Furthermore (although it would be nice to have some details about the age and configuration of willronco's system), the three switch setup described in the OP is even less prone to such issues when combining, as it doesn't have a multi-switch that could possibly disconnect the charging circuit before combining batteries. Effectively, what the dedicated combine switch does is add an additional load to system if the house battery is low (like operating a downrigger or windlass would) or reduce the load on the system if the start battery is low and the house is full (as happens regularly when turning off a downrigger or windlass).
 
Although many combine switch or the 1 2 on off switches have a make before break (field disconnect does not work with our outboards), there are some which do not. There are also older switches which do not.

The simple way is the combiner. This allows good charging of both batteries--not something to worry about (and forget), Your concerns are valid. The other concern is that it is better for electronics to not be subjected to low voltage or voltage spikes during startup. Many outboards do not have the modern regulators which we have in car alternators.

The combiners are not expensive in comparison, and can be hooked up in a very short time.
 
Bob, I noticed when you were getting "Thisaway" ship shape you installed a BEP VSR to you battery switch
DSC00891.jpg

I want to do the same for Far C'r but I am unsure of how it is wired into the switch. Does the BEP come with a wiring diagram? Is it in series with just one battery?

Hoping you can shed some light on the subject and it might help willronco as well
 
Basically the VSR is wired between the two input terminals of the Start and House battery. The BEP diagram often uses their on/off switch rather than the 1,2 all off switch. The Motor lead goes to the terminal in from the start battery, and "load" lead goes to the house battery battery terminal on the Perko switch.

The diagram which comes with the BEP unit is at:
http://www.bepmarine.com/media/product/pro4c27c846d96d1.pdf
 
Thank you very much for all the feedback, folks!

My battery combining switch is a fairly new Blue Sea systems switch, so I will not worry too much about using that switch while underway in the short term.

In addition, I will make sure to get my hands on an ACR type relay as soon as possible to minimize the risk of my own forgetfulness.
 
One thing I didn't see anybody mention, do NOT turn the battery switch through or too the OFF position while the motor is running.

Bill Kelleher
 
I vote for the ACR setup. The only thing I do recommend with the ACR is put it in a place where you can see the LED. That let's you know it is working at a glance unless you have a voltage readout on your chart plotter or other engine instrument. On my current boat with a Blue Sea ACR, I didn't rewire anything to install it. I simply ran a heavy gauge cable from the positive side of the start bank and the house bank to each terminal on the ACR and connected the ground lead. When the voltage on either bank reaches 13.6 VDC the ACR then combines the banks. This works pretty well both underway and when tied to shore power. The 110VAC battery charger is tied to the house bank and the alternator is connected to the start bank. If the ACR ever fails (I have had that happen once with a BEP setup), you can combine the banks with the battery switch and share the charge until you get the ACR repaired.

Tom
 
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