Adding a second battery

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jhnmdahl
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Adding a second battery

Post by jhnmdahl » Thu Apr 02, 2015 8:39 am

Adding a second battery can be as easy as bolting one in and installing a switch to switch between positive battery terminals (negative terminals are tied together to establish a common ground), or can be more complex.

One problem faced with a simple switch is that if the switch is turned to an "off" position while the engine is running, the alternator will no longer be charging a battery and the output voltage will spike up, potentially damaging diodes in the alternator's output rectifier. More complex switches therefore include an alternator field disconnect (AFD) feature which can be configured to cut power to the alternator's field windings when a switch is turned "off," thereby disabling the alternator and saving the diodes from damage.

One such switch from Blue Sea is configured as follows, using the F1 and F2 terminals coupled to the regulator of the alternator to perform the AFD function:
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Some installations make use of an automatic charging relay (ACR), which couples the batteries together during charging, but leaves the batteries separate when discharging or when starting engines. "Add-a-battery" kits including ACR and a switch may not include AFD functionality in the switch, resulting in potential damage to the alternator diodes if the switch is inadvertently turned off while the engine is running. See, for example, the Bluesea 7650 add-a-battery kit.
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wdcfrog
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Re: Adding a second battery

Post by wdcfrog » Fri Apr 17, 2015 5:27 pm

I did this with the ACR kit, the advantage being that you don't have to remember to switch back and forth between batteries when using the boat - just use "off" or "on" as normal. There is a "combine" setting with a warning logo next to it that can be used for starting if the engine battery is too low to start.

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Re: Adding a second battery

Post by kettcb » Tue May 19, 2015 7:57 pm

I think having an ACR that automatically switches between batteries so you're not fussing while using the boat is a lot more useful than an alternator field disconnect, unless the batter switch is unusually accessible. In my Cobalt, it's under a seat (that always has stuff in it and someone on it).

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liquid
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Re: Adding a second battery

Post by liquid » Tue Apr 19, 2016 6:45 pm

What is the cost typically associated with this? - just dropped off my boat at dealer to get summerized. They only install Cobalt parts. I brought a battery which i had...

Quoted around $500, less the battery ($140ish) so around $350. They also make sure the boat is balanced and it's done correctly. I've done plenty of wiring myself and am sure I could do it cheaper - but most likely not better.

I'm thinking aside from the parts the time/0 headache and factory made Cobalt parts makes this reasonable.

Thoughts?
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jhnmdahl
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Re: Adding a second battery

Post by jhnmdahl » Tue Apr 19, 2016 7:53 pm

I think Cobalt uses off-the-shelf switches (Blue Sea?), and even my 210 has a flat location for a battery on either side of the engine. I imagine the hassle of cutting and crimping the wires, and having all the right tie-downs and experience, might make it worth paying the dealer if I were in your shoes.

I started pricing it out and the switch alone (a Blue Sea 9002e) was $40 or more, and heavy-gauge wiring's not cheap. I figured I'd have over $100-$150 in parts plus another $100 or more for the battery before even starting to think of labor.

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liquid
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Re: Adding a second battery

Post by liquid » Thu Apr 21, 2016 11:48 am

My dealer uses the Perko Switch. Here's a vid:

http://www.perko.com/sstv_video/sstv_ba ... or_switch/

Obviously the wiring is the expensive part of it. They've put the new battery on the other side so we're nice and balanced. Frankly, this is the one issue that has always nagged at me - starting the boat after 30 minutes or so with music playing simply because of past experience getting stuck - and it's worth it to me to never think about it again.

Aside from sitting on a lake with everyone staring at you while the engine won't turnover i've had the privilege of waiting for Seatow a few miles off the Florida Keys because of a battery.
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Re: Adding a second battery

Post by kettcb » Thu Apr 21, 2016 7:26 pm

That sounds like reason enough alone to spend the $500. Or be the first boat that carries jumper cables!

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liquid
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Re: Adding a second battery

Post by liquid » Tue May 03, 2016 11:42 am

Sorry for the blurriness but here's a pic... and of course i din't take a pic of the switch. I can tell you it has 1, 2, ALL & Off.
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