Relocating Batteries

[Regulate It]

I am possibly going overboard but had several questions. I am thinking of relocating the batteries from the stern compartments in a 21SE to the console. While doing this I am adding a second switch panel to the new electronics box I just added. Long story short, while I am in there, I think it would be a good time to clean up/redo the wiring in the console since I am adding 2 HDS systems, a structure scan and misc. other stuff. First question - I know the battery cables to the motor need to be lengthened and at that guage its costly. How can I determine, or does anyone know the amp draw for a 150 HPDI so I can size the wiring? More questions to follow

 

[windknotnc]

Step 1.
Determine maximum amp draw and round up to nearest 10.

Step 2.
Measure distance from the battery to the power outlet or motor connection.

Step 3.
Take the determined length (Step 2) and multiply by two.

Step 4.
Select a gauge of wire you think may be applicable.

Step 5.
Consult the Voltage Loss Chart to determine voltage loss per foot so you may match the wire gauge to be used.

Step 6.
Take the Determined Length (Step 3) x 2 = Doubled Length. Take the Doubled Length x Voltage Loss = Total Voltage Loss.

Step 7.
Work through equation to determine best gauge wire to be used. The best gauge selection will be matched with the lowest voltage loss.

For optimum performance, voltage loss should be between zero and one, but no greater than one.

Voltage Loss Chart

AWG 5 AMPS 10 AMPS 20 AMPS 30 AMPS 40 AMPS 50 AMPS
4 .0012V .0025V .0005V .0075V .01V .0125V
6 .002V .004V .008V .012V .016V .02V
8 .0032V .0064V .0128V .0192V .0256V .032V
10 .0051V .0102V .0204V .0306V .0408V .051V
12 .0081V .0162V .0324V .0486V .0648V .081V

Voltage Loss / Ft

Example:
You want to run 20 ft of wire in your boat, and the maximum amp draw is 37Amps.

Step 1.
Round up the amp draw from 37 to 40 amps.

Step 2.
20 ft of wire which is needed.

Step 3.
Take 20 ft x 2 = 40 ft.

Step 4.
Starting with 10AWG. Check the chart above for 40 amps and 10AWG.

Step 5.
.0408V is charted for the voltage loss.

Step 6.
Take 40 x .0408 = 1.632V – Not acceptable over 1V.

Try 6AWG. In working through the equation it equals .064 – which is under 1 volt, which is acceptable.

 

[Regulate It]

Thanks WindKnotNC - If I am reloacting the batterys 10 feet forward, I am trying to figure the guage wire to run back to the motor for starting. I am by far no expert, but I understand the sizing charts and the information you provided, just don't know the draw on the motor I have tallied up the total amount already +/- 55 amps for all devices, lights etc, with everthing on and even tallied 3 samp alotment for led whichin reality really draw nothing. I am good on sizing for the device runs, but my concern is guage wire to run back to a block that will tie to the motor to start the engine.

 

[windknotnc]

You are going to need a dedicated pair to the engine. I am guessing a #4 fine strand should work. How far from the batteries is the engine?

 

[Regulate It]

Thanks - total length back should be around 9-10 feet. Can I damage the alternator running a #1?

 

[windknotnc]

I wouldn't think so as the wire size isn't the limiting factor on the output from the alternator. I am not sure how many volts the F150 puts out but I am guessing around 13.5v /35amps. There would not be any negligible voltage drop in that short of a distance with that size wire. In fact I am not sure you need that big of a wire.

 

[Mike S]

I have two AGM batts in the console for my trolling motor. I have two in the rear compartment for starting. I am going to do the same as you - move a SINGLE starting battery to the console, ditch the second starting battery, and use the TM batt bank for emergency starts. I will move the battery switch as well. I plan on using #2 cable for the run, which is about 9' each way.

 

[Regulate It]

Mike, I have the same set up. The boat had Lenco trolling tabs and 2 batteries under the console, which prompted the idea in the first place. What about using 2 deep cycle batteries. I am also moving the switch. Let me know how your relo goes

 

[DaleH]

Your OB cables need to sized to carry the PEAK amps that the starter has while cranking, which is typically about 225 amps peak and 175 amps continuous on a V6 motor, but not I'm not sure what the ratings on the F150 are, but most V4s usually use the same starter as V6 motors.

Sizing your main DC power run for all accessory items is a different matter.

 

[Regulate It]

Dale - I understand that - I guess it goes back to my initial question - is a #1 or #2 wire sufficient to run from the console back to the motor,and could oversizing the wire harm anything? I can figure the guage sizes for the various lights and pumps, but I have yet to get any info on the amperage required for the 150 HPDI

 

[Mike S]

Dale - I understand that - I guess it goes back to my initial question - is a #1 or #2 wire sufficient to run from the console back to the motor,and could oversizing the wire harm anything? I can figure the guage sizes for the various lights and pumps, but I have yet to get any info on the amperage required for the 150 HPDI

Using larger cable is not going to do any harm, except dent the wallet a bit. The bigger the wire, the less voltage drop you'll get. Be sure that it is flexible enough to make all the bends. Most marine power cable is fairly easy to work with. Remember to include the return as well in your calculation for wire size.

I plan on doing the relocation in the next couple of weeks. The main reason for this change is that I added a 30 gal bait tank in place of the pilot seat, and the stern sits a bit lower, with the rear batteries causing a slight list. The relocation will loose about 60 lbs overall and center the weight forward of the bait tank.