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Author Topic:   Dual Battery Charging without AC
blackfoot posted 03-01-2007 05:32 PM ET (US)   Profile for blackfoot   Send Email to blackfoot  
Need some advise to setup my 1998 Montauk for fishing. I have a 90-HP [Yamaha] two-stroke that has a 10-Ampere [battery charing output]. I have a Scotty electric downrigger and a Lowrance Chartplotter and SONAR. The boat currently has a starting battery. I am thinking about adding a deep cycle for the downrigger and electronics.

What's the best design approach: battery switch? Or isolator?

Is there a way to charge both batteries from the truck's alternator while towing the boat? I fish in isolated areas with no AC power. I can't pull into a garage and plug in a charger.

Thanks for your help!

jimh posted 03-01-2007 08:22 PM ET (US)     Profile for jimh  Send Email to jimh     
Install two batteries, one a cranking battery and one a deep-cycle battery. Use the appropriate primary battery distribution wiring and switching. There are several articles on this in the archives.

Isolate the loads, engine on the cranking battery, electronics and other loads on the deep-cycle.

Use an automatic combiner relay (ACR) to permit the engine to recharge all batteries, giving priority to the starting battery. Read the several articles in the archives of prior discussions about these devices, how they work, and what is available. The choices are basically BEP or Blue Seas.

Charging from the vehicle's 12-volt system is possible. There is a device called a Stealth Charger that does this. Consult the manufacturer's website for details.

where2 posted 03-01-2007 09:23 PM ET (US)     Profile for where2  Send Email to where2     
Actually, if you had a hookup with an additional ACR you could charge from the tow vehicle without the stealth charger. The stealth charger is best used for charging a 24v setup from the tow vehicle (or boat engine) while the engine is running.

I am envisioning one ACR with a feed from the tow vehicle, charging the starting battery. The second ACR will engage the "house" battery and charge it once the boat starting battery is full.

The ACR is a better choice than the isolator because the isolator works using a diode that typically draws 0.7v off the top of your charging voltage. The ACR uses a relay system so it applies all the charging voltage to the battery.

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