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2 Battery Starting/Lighting Circuit


chunkytrout

Question

Wondering whos considered running two batts in your Starting/Instrument/Lighting circuit. Can a stock alternator handle the load of charging 2 batteries?

chunky

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If the alternater can handle one battery then it should handle two with know problem as long as there is not to much draw on either battery. It really depends on the kotor you are using. If you let me know what motor and size i will get you the info. Make sure you give me the year too. good luck.

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JIM PAYNE

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78 Johnson 60. Thanks Jim.

Chunky

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still looking for your answer on two batteries. the dealers tell me you should not but they told me three years ago i could not charge trolling batteries from your tow vehicle. got them didn't I. i will be with a guy this weekend with a motor simular to yours and I will do some testing for you. thanks

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JIM PAYNE

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My suspicion is that it will "work" but will it work to you're satisfaction? Marine alternators typically don't put out a lot of current, and dividing it between two batteries may yield a result that they charge, but not quite as fast as they drain. Therefore, you might be able to go longer than you would without charging, but then then have to put the batteries on a trickle charger to catch up. Also, there might be interference on the electronics when under charge. As long as you understand these two consequences and monitor what's happening, I say, give it a try. My '91 Northwood was wired with such a system and had a switch to direct the current to one battery or the other. You could do that if you're electrical skills are up to it. But I've never used it as the salesman tolm me they just weren't that practical, at least on that model.

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Found a guy with same motor as yours that has been charging two batteries four three years. Hw said he makes sure not to drain battery to far but has never had any troubles. I agree if you don't drain either battery to far you will be ok. Good luck and keep us informed.

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JIM PAYNE

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You need an isolating diode between the two batteries. The isolating diode prevents the starting battery from being discharged at the same rate as the acessory/trolling motor battery. The device is around $70.

Or, have a manual switch, as you motor around the lake, switch it to starting battery for 2 minutes or so, it should be fully charged by then, then switch it to the accessory/trolling motor battery to charge this battery. A real hassel, but workable.

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Good Luck!

[This message has been edited by MT Net (edited 05-08-2003).]

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He is not talking about charging his trolling battery. He is talking about using a battery for his acc,. and if his starting battery is hooked in parallel he should not need any isolater. he is just going to get 12 volts off two batteries and not just one.

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JIM PAYNE

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That's what I was talking about. If the 2 batteries were run in parllel and connected to the alternator, both would charge at the same rate and get 12V. When running the lights, GPS, Locator, livewells, radio, etc. both batteries would also be discharged at the same rate.

In parallel, there is enough amperage to start the motor, between both batteries. If the alternator can handle charging both batteries at the same time, which is the original question. I have been told the alternator wouldn't put out enough amps to charge 2 starting batteries.

As a solution, I was advised by a couple of people, (in my previous post) the starting battery is completely isolated from an acessory deep cycle battery. Where the accessory battery could be used for the lights, locator, radio, etc, and recieving somewhat of a charge back to the battery while under motion.

I'm just working through the scenario, I'm thinking about doing the same thing, too much drain off the starting battery. Just a different approach, now I'm not sure if I got good advice or not.

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you really should not have any problem if like i said do not drain them both completely. If you are really worried about it just put a 20amp circuit breaker on the positive post of the starting battery and the acc battery. if you have a great problem call me and i will help you out. 612-590-5833.

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JIM PAYNE

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One word and why I didn't think of it cause i already suggested it to some one else. ISOLATOR.

chunky

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The only thing a isolater will do for you is to only charge a battery when the motor is running. That is not what you said you wanted to do. You can put a switch in there so to only charge one battey at a time but that is not what you wanted. Here is what you should do. Hook both batteries up together positive to positive and neg to neg and take a amp meter on the water with you and check the amps draw on each battery while motor is running. If the amps is more then 20amps then you should not charge them togehter. use the boat accesseries for a few hours and then check it again. let me know what happens, good luck.

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