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Relocating Cranking Battery

D

Dforbert

New member
Hi all,

First of all, I’m new to the forum (as a new boat owner) and look forward to interacting with and, hopefully, contributing to the forum in the future.

I’ve been restoring my grandfather’s 1997 Alumacraft Classic Deluxe which has a 1997 Mercury 40 HP ELPTO (4 cylinder) and am making good progress.

At this point, I’m looking to replace the trolling motor battery, the cranking/starter battery, as well as the onboard charging system. Both of the new batteries are AGM, deep cycle batteries, with the cranking battery being a dual pupose Optima Blue Top.

The problem that Im facing is that the cranking battery (and wiring) is currently located at the rear of the boat and the charging unit that I’m interested in (here) has leads that are only 6’ long which will not make it to the back of the boat.

So my perceived options are to either extend the leads from the charging unit and keep the trolling motor battery up front and the starter battery in the rear (which I’m afraid if the voltage gets thrown off by the new length, it could damage the battery) OR store both batteries up front (where the charging unit can reach them) but then extend the engine battery cables 15’ to reach the front of the boat.

Which is the lesser of two compromises? Alternatively, if there is an alternate approach that I haven’t considered, please let me know.

Thanks in advance!
 
Some of your decision will be about balance in the boat and how you will load and use it. Will it cause a balance issue with both batteries up front?

Simply from an electrical perspective it would probably be the lesser of two evils to extend the leads from the charger. Those wires will carry less max/peak amps in normal use than the amp draw from either the trolling motor or the starter on the main motor - so you can get away with smaller gauge wire (in comparison) and would be less worried about voltage drop on the wires from the charger.

Both of your options are viable so it's mostly deciding what will work best "for you" and using the appropriate gauge wire for the distance you will be running it.
 
Thanks for the advice (and the quick response), Galamb. Given the size and weight of the boat, I don't believe that a weight issue would be presented by relocating the battery. I agree that extending the length of the motor battery cable could present challenges far greater than not getting the ultimate longevity out of a battery. With that in mind, I agree that extending the charging unit leads is the safest route to proceed towards.

The only bummer is that the manufacturer of the on board charging unit, Noco, doesn't provide lead extensions, so any modification would be a retrofit. That said, Pro Mariner makes a cable lead extension that allegedly (based on an answer in the Q&A section of the Amazon listing) would work for the Noco Genius unit that I am looking at.

I've read that when extending the leads, you will want to go larger in size (gauge) in order to compensate for a longer distance, so I guess the question now is, is the difference between the Pro Mariner wire gauge and the Noco Genius lead sufficient? Getting info on both wires has proven to be difficult to confirm, but I'll keep digging.


Alternatively, would you recommend an alternative extension to the Pro Mariner product?
 
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It is widely understood that AC is more controllable than DC because of transformers. Only recently have engineers developed transformers capable of adjusting DC. For your boat we are stuck with DC, of course, so we have to use heavier conductors. You have a 16 foot boat so you want to go one gauge larger if you use copper, or 2 gauges larger if you want aluminum. Your leads will only have to be extended maybe 12 feet, I would go copper as it is likely more flexible too. I would make my own extensions so they are perfect length. I recommend using a copper coupling and terminals, soldering it, then a double coating of heat shrink insulation where needed. Don't forget to slide the heat shrink on first. I sometimes forget when I'm in a hurry.
 
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You can google dc wire sizes for marine applications.

Once you figure out the (load) - say 10 amps from the charger and measure the distance you can look up what wire size for either a 3% or 10% "drop" - the 3% would be recommended and will always result in a heavier gauge wire (in comparison).

I ran a 3 bank Pro Mariner on my 26 footer. It didn't come with leads at all so I just made them up myself with some marine (tinned) wire that I picked up from the local marine supply.

If you can buy a ready made harness/extension that will work AND the wire gauge checks out on the chart for the length you will need to run, then why not go that route.
 
galamb said:
You can google dc wire sizes for marine applications.

Once you figure out the (load) - say 10 amps from the charger and measure the distance you can look up what wire size for either a 3% or 10% "drop" - the 3% would be recommended and will always result in a heavier gauge wire (in comparison).

I ran a 3 bank Pro Mariner on my 26 footer. It didn't come with leads at all so I just made them up myself with some marine (tinned) wire that I picked up from the local marine supply.

If you can buy a ready made harness/extension that will work AND the wire gauge checks out on the chart for the length you will need to run, then why not go that route.
Click to expand...

Agreed. Considering all variables, I am going to go with a different charging unit. I found a Minn Kota charging unit that has factory-made extensions available, which seems like the safest bet.

Really appreciate all of the info!
 
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