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Author Topic:   Designating a Battery as "BATTERY 1"
David Jenkins posted 03-30-2009 08:25 PM ET (US)   Profile for David Jenkins   Send Email to David Jenkins  
One of my boats has two batteries: an old deep-cycle battery and a brand new starting battery. I have a switch to choose between using battery 1, battery 2, or both batteries. One battery (I'm not sure if this is battery 1 or 2 but it is on the port side), has one positive cable and one negative cable coming to it. This battery also has smaller positive and negative wires going from it to a bar where radios etc get their 12 volt power. The other battery (starbord side) has one positive cable and two negative cables coming to it, but no small wires.

Does it matter whether I put the new starting battery on starboard or port?

Landlocked posted 03-30-2009 09:18 PM ET (US)     Profile for Landlocked  Send Email to Landlocked     
I'm far from an expert but I did just finish wiring a second battery and isolator switch on the Montauk. I also stayed at a Holiday Inn Express Last Week.

First, assuming you are using the same classic large dial selector switch I am, Battery "1" should be all the way to the right of the dial. The connection stud and nut inside the switch is also on the right side if it's assembled and you are looking at the front of the dial. Thus the cable coming out the bottom right is probably #1.(unless they are twisted and there is little room for that inside) But - to be sure just try disconnecting the positive cable of each battery with the setting on 1. When you lose power, you found #1.

As far as which one's #1 and Which is #2 shouldn't make any difference as long as you know which is which. You should know so you can isolate your starting battery when anchored and runniong accessories or trolling. I mounted the switch inside the console on the back facing the stern and I elected to make #1 which is on the right side of the switch go to the starboard or right battery which is the location of my deep cycle. #2 on the left is my starting battery.

Re: the secondary set of cables powering your accessories. Personally, Id remove the positive from the battery post and relocate it to the common on the selector switch. You can leave the negative on the battery or you can wire up a negative bus bar - your choice. I like the idea of the accessories being hooked to the switch because now I can kill the whole system when I store the boat.

The only accessory I have wired directly to the battery is the NMEA network and Lowrance GPS/Depthfinder. This accessory has it's own dedicated bus that I wired per manufacturers instructions.

Landlocked posted 03-30-2009 09:54 PM ET (US)     Profile for Landlocked  Send Email to Landlocked     
Re-read your post and I'm a bit confused as to your setup.

Here is what you should have...

The Red Cable from your motor should go to Common on the switch.

The black from your motor should go to the negative on your starter battery.

There should be a black battery cable connecting the negatives of each battery together.

There should be a red wire going from each battery positive to the switch. One to the #1 pole and one to the #2 pole.

Your accessory red should probably go to the common while the accessory black should either go to a negative bus bar or to one of the negatives on the batteries. Doesn't really matter.

If you have the need to leave the accessory bus powered when the batteries are off then you would need to run red and black accessory wires to your deep cycle (not your starting battery). Only reason I can see to do this would be if you wanted your bilge pump to remain powered when the battery selector was off.

The battery you describe as having only one positive and two negatives coming to it should be your starter battery. The positive should be going to the switch. One negative is going to the motor. The other is the jumper over to the negative on the other battery.

David Jenkins posted 03-31-2009 10:39 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Thank you!
jimh posted 04-01-2009 06:45 PM ET (US)     Profile for jimh  Send Email to jimh     
The designation of a battery as the "1" or "2" battery in accordance with the legend on a switch is not significant electrically, nor is the location of the battery with respect to the vessel centerline.
SC Joe posted 04-01-2009 09:28 PM ET (US)     Profile for SC Joe  Send Email to SC Joe     
>>>>The designation of a battery as the "1" or "2" battery in accordance with the legend on a switch is not significant electrically, nor is the location of the battery with respect to the vessel centerline. <<<<

On the much smaller whalers, does the boat not list to the side with more weight?

How muh does a trolling motor battery weigh (group 27-31)? 70 or so pounds?

Landlocked posted 04-01-2009 10:04 PM ET (US)     Profile for Landlocked  Send Email to Landlocked     
Don't know the weight difference but my reasoning in placing the larger trolling motor battery on the starboard side was that it was heavier. Since I stand at the port side when piloting the boat and I've got a hundred pounds or so on my first mate - thought it might help balance things out a bit.


jimh posted 04-01-2009 11:48 PM ET (US)     Profile for jimh  Send Email to jimh     
In any small boat the distribution of weight affects the trim of the hull, both fore and aft and side to side. Since this is an electrical discussion, the distribution of weight in the boat is not an electrical consideration. The battery can't tell where it is in the boat in terms of its electrical operation
David Jenkins posted 04-02-2009 06:21 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
With one battery having two negative cables coming to it and the other battery having just one cable, I perceived that they were somehow "daisy chained" and that one battery's negative charge might have to run through another battery to get to the engine. I did not know if the location in the daisy chain (one negative cable versus two) might make the starting capacity of one battery a bit stronger or weaker than the other.

Following the advice here, I have put the starting battery on the starboard side with the two negative cables coming to it. I now understand from jimh that the position in the daisy chain has no significance.

jimh posted 04-02-2009 08:21 AM ET (US)     Profile for jimh  Send Email to jimh     
The voltage drop between the battery and the engine starter motor will be lower in the circuit which has the least amount of wire resistance.

Unless a battery negative bus connector is used, on smaller boats the engine battery cable is typically connected directly to the negative terminal of a battery. If there are two batteries, a heavy cable connects the two negative terminals of the batteries.

When the battery selector switch is moved to the battery to which the engine's negative lead is directly connected, there will be slightly less resistance in the circuit than when the other battery is selected. The difference will only be the resistance of the heavy cable connecting the two batteries. For this reason the size of the cable connecting the two batteries should be as large as or larger than the size of the cable used to connect the engine.

Typically in a small boat the batteries are located no farther apart than the width of the boat, or no farther apart than about 7-feet. The resistance of a piece of 4-AWG wire that is 7-feet long is

.0002533-ohm/foot x 7 = 0.0017731-ohms

If the starter current is 100-amperes, the voltage drop in the extra wire will be

100 x 0.0017731 = 0.17731 volts.

If you use 2-AWG, the resistance lowers to 0.001593, or 0.1115-volt

It is unlikely that the slighly greater voltage drop in the circuit when the other battery is used for starting will be significant.

jimh posted 04-02-2009 08:34 AM ET (US)     Profile for jimh  Send Email to jimh     
If two different types of batteries are used, and one battery will normally always be used as the engine starting battery, then the engine battery negative cable should be connected directly to the negative of that battery, unless a battery negative wiring bus accessory is used. This will remove a slight amount of resistance from the wiring.
Landlocked posted 04-02-2009 09:00 AM ET (US)     Profile for Landlocked  Send Email to Landlocked     
David Jenkins posted 04-02-2009 09:20 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Wow, Jim. Thank you.

One last question: Is there any advantage or disadvantage to starting the engine with the battery selector switch in the ALL position? I was once told that I should start the engine in the BATTERY 1 position and then (while the engine is running) move the selector switch to ALL in order to keep both batteries fully charged.

Landlocked posted 04-02-2009 09:32 AM ET (US)     Profile for Landlocked  Send Email to Landlocked     
The advantage as I understand it would be to keep the two batteries usage completely seperately. If you are only starting from #1 and only trolling from #2 then you'll never run down #1 trolling.

Personally, since I troll very little I leave the switch at both. That way, under normal starting/running conditions in daylight hours, I never really have to think about it. If I'm trolling or anchored at night fishing running lights and radio, I'll switch to the deep cycle.


jimh posted 04-02-2009 12:09 PM ET (US)     Profile for jimh  Send Email to jimh     
The advantage to be gained during engine cranking by placing the battery selector switch in the BOTH position (which has the effect of connecting the two batteries in parallel) is an increase in the cranking current available. It is typical that the batteries be placed in parallel to start an engine when neither of them alone has sufficient current capacity to crank over the engine. The more cranking current delivered and the higher the voltage it is delivered at, the faster the electric starting motor will crank the engine. Faster cranking usually leads to faster starting.

When I had a new E-TEC 250-HP motor on my boat last season, I noticed that it would crank over noticeably faster when I had the battery switch in the BOTH position. I normally never use the BOTH position for starting of my older V6 outboard, but, with the new E-TEC, the starting cranking speed was much better with the batteries in parallel. The batteries are both engine starting, 1,100-MCA batteries in good condition. Frankly, this surprised me because I thought my primary battery distribution and wiring was in good shape. When we rigged the E-TEC we used my engine's battery cables, so everything in the starting circuit was the same as before. My conclusion is that some of these new motors really need more starting current to crank them than older motors did.

The reason you might want to parallel the batteries to get a high cranking speed is to exceed the minimum cranking speed necessary for starting. Many modern engines suppress the ignition spark until the engine rotation speed reaches a minimum speed. If a single battery can't crank your engine faster than this minimum, it will never start, but, if by paralleling the batteries you can increase the speed, the engine will fire.

David Jenkins posted 04-02-2009 12:27 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Thanks, Jim.
swist posted 04-03-2009 09:10 AM ET (US)     Profile for swist  Send Email to swist     
Jim H wrote; "Many modern engines suppress the ignition spark until the engine rotation speed reaches a minimum speed."

Any idea why they do this? They are just making the engine harder to start under marginal battery conditions. I would think you would want to maximize the chances of the engine starting under most conditions, except those that might damage the engine.

jimh posted 04-04-2009 03:22 PM ET (US)     Profile for jimh  Send Email to jimh     
To discover the thinking of engine designers who have created engine control systems in which the generation of spark is suppressed until a minimum crankcase rotation speed is reached during engine start, you will have to ask those designers; I can only speculate, which I do as follows:

The voltage output from the permanent magnet alternator that generates the primary voltage for the ignition spark coils varies as a function of engine speed. (For a thorough discussion of the basic principles of a permanent magnet alternator, see the reference section article.) If the engine cranking speed is too low, the voltage being generated by the alternator may also be too low to provide the necessary spark needed for proper ignition. By delaying the onset of spark firing until the engine rotation reaches a minimum speed, the engine control system ensure that when ignition spark is provided it will be a strong spark and occur at the proper time.

It is typical that the spark primary coil voltage generated by the alternator is accumulated on a storage capacitor. The spark coil primary voltage is provided from this capacitor. The designers may have intended that the engine be allowed to rotate without firing a spark plug in order to build up a voltage charge on the spark discharge capacitor so that when the first spark coil is fired, there is plenty of voltage available and a very strong spark is generated.

If the engine were allowed to fire no mater what speed of rotation was reached, the capacitor might never accumulate enough charge to provide a good spark. One good spark can provide a substantial boost to the rotational speed as the cylinder fires and contributes to the engine operation with a power stroke.

By the way, withholding spark until a minimum cranking rotation is reached is not limited to 2009-model year engines. My 1992 engine has that feature, and I think many other engines from that same era do, too.

swist posted 04-07-2009 12:03 PM ET (US)     Profile for swist  Send Email to swist     
To comment on the original topic, my last boat had dual identical batteries (combo starting/deep cycle) and I just alternated between 1 and 2 every time I went out. To tell you the truth, when I installed this system, I knew it didn't really matter which battery was 1 and which was 2, so I wired them to maximize the neatness of the wiring.

But at my age you forget things and I have to admit in the 11 years I owned that boat, I never really remembered which battery was #1 and which was #2. Don't laugh you young guys - your time will come too.

David Jenkins posted 04-07-2009 10:31 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Somehow I don't think Jim will forget.
jimh posted 04-08-2009 08:28 AM ET (US)     Profile for jimh  Send Email to jimh     
Both these comments gave me a laugh. The first one got me thinking, "Which battery is number one in my boat?" I couldn't say for certain. I think the starboard side battery is number one, but I wouldn't bet on it.

The second one also gave me a laugh--my in-person image does not live up to my on-line image!

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