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Author Topic:   Moving Batteries to Console from Transom
jwestwood posted 12-11-2013 02:14 PM ET (US)   Profile for jwestwood   Send Email to jwestwood  
I plan to relocate twin batteries to the console and add switches. Looking for documented/illustrated procedures similar to many others on this sight for various repairs. Wiring diagrams Jim has put are very helpful. Thought there might be some battery installation instructions or does and don'ts of the project. As always, thanks in advance for the help. Boat is a 1974 Outrage 21, twin 1988 90 Yamahas and twin batteries.
PeteB88 posted 12-12-2013 01:26 AM ET (US)     Profile for PeteB88  Send Email to PeteB88     
My plan too.
jimh posted 12-12-2013 10:06 AM ET (US)     Profile for jimh  Send Email to jimh     
When you move the battery farther away from its principal load, the electric starter motor of the outboard engine, you should consider:

--the significant increase in voltage drop that will occur in the longer conductors

--the location of any splices or joins in the conductors with regard to exposure to water

--the risk of running unfused conductors of such high current capacity over a long distance

There are many prior discussions regarding the need to properly compensate for the voltage drop due to longer conductors. See

Many installations seem to use inadequate conductors that have more voltage drop than the conductors provided and recommended by the engine manufacturers. This results in a situation where there is much less margin or tolerance for low battery voltage due to the battery being in a discharged state. The engine may start with a battery with a very high charge and good voltage, but if too much voltage drop exists in the conductors, the engine will not be able to start with lower battery voltage and charge states.

It is best to avoid making any sort of joint or splice or connection in the power conductors between the source and load, and this is particularly true for primary power distribution conductors. Even more critical is the need to avoid making a joint or splice or connection in power conductors which will be located in an inaccessible area, such as in a tunnel between the helm and transom. And most critical is to avoid making any sort of joint or splice or connection in the power conductors which will be in an area exposed to water on a chronic basis.

There is a general practice in small boats that the battery is located only a few feet from the outboard, and the power conductors are not fused. If you relocate the battery to be ten feet or more away from the outboard, it may be prudent to provide over-current protection for the conductors. At the least, the electrical disconnect for the primary power should be very close to the batteries. Regarding fusing, I don't know what the regulations say or what the recommended practices are. It would be prudent to check with a good source like the American Boat and Yacht Council (ABYC) to see what that body recommends regarding fusing of long primary power conductors. In a cursory reading of an older ABYC recommendation (from 1990) it appears to me that they give conductors "for engine cranking motors" an exemption from over-current protection.

russellbailey posted 12-12-2013 11:33 AM ET (US)     Profile for russellbailey  Send Email to russellbailey     
Get ready to spend some dollars to do this. I did it in my 1984 Outrage 25 this summer to less weight on the transom (which has twin Optimax 150s). It is not cheap between the wire and connectors. For me, it was worthwhile for getting 3 batteries (2 start and 1 house) forward and weight distribution. I understand the Classic 21's can handle a lot of weight in the stern, so I presume you have another reason for wanting to move them forward? I'd not have done it but for the weight.

This is great for how to make your cables. I followed it and it worked very well. For the main cables I used 2/0 wire with 200 amp fuses for my power hungry Opti's and the long run on the 25' hull, and that has worked great. For me, I'd not do it without a fuse on the power conductor - it is not hard or costly to add. I then used smaller 2 gauge wire for the very short runs between the fuse block, BEP switch, and batteries. I'm sure you could go a lot smaller on your engines.

Use a BlueSea or BEP switch. The BEP may be smaller and fit in a tighter space - I chose it for its more compact size. Both are good.

jwestwood posted 12-16-2013 09:17 AM ET (US)     Profile for jwestwood  Send Email to jwestwood     
Thanks for your replies and all the good input. The primary reason for moving the batteries was to get them out of sight. They are currently on the starboard side where the storage bin or well would be. It seems that the distance creates some [concerns]. That in mind, I am thinking that perhaps the narrow configured batteries might fit between the hull and the well or bin. That would give me equal weight distribution and not add the distance. Any thoughts?

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