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Old 23-04-2017, 06:17   #1
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Second Alternator vs larger primary

I intend upgrading my charging capacity on a Yanmar 4JH3HTE. On my previous boat I mounted a second 160amp alternator running along side the factory fitted 65amp but Genmaax have suggested going to a single 215amp replacement that will fit where the existing Hitachi is mounted along with anEmaax Pro and a serpentine kit.
Has anybody had experience with this set up - positive or negative?
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Old 23-04-2017, 08:57   #2
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Re: Second Alternator vs larger primary

Have you got large loads run with the engine that would make productive use of the increased ampage?

And/or do you regularly need to run the engine just to recharge your battery bank?

If so, then go big, you could go to a larger AH capacity. If you don't already have a bank with a high charge acceptance rate, when the time comes to replace it, make that CAR a key factor in your choice and you'll be able to reduce engine runtimes, especially if you run in the AM, and also have a little solar for completing the long tail.

Ideally get the Balmar MC-614 to give maximum flexibility in matching charge output to what is ideal for future upgrades.

The other alternative is a little suitcase genny with a good matching shore charger.
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Old 23-04-2017, 11:20   #3
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Re: Second Alternator vs larger primary

Thanks John,
I need to charge 3 x 140ah AGM house batteries, 1 x start battery and a bowthruster battery (ah's unknown).

Running a 35amp watermaker off the start battery when motoring only, two electric fridges off house bank along with normal lighting, instruments etc and Raymarine ST6001 autopilot when sailing.
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Old 23-04-2017, 11:46   #4
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Re: Second Alternator vs larger primary

In my peculiar rig, one big alternator and fancy Balmar controller charges the house bank, just as does the fancy charger when on shore power. But, redundance is wonderful. Ordinary Delco single wire chargers recharge the starter batteries to the engine and to the genset, and as John suggests, the shore power charger is matched to the house bank as is the Balmar, and the suitcase genset can be plugged into the shore power cable. But, then it's possible with a few switches and a jumper to start either the engine or the main genset from either the house bank, the '''other" starter battery, or even parallel the starter batteries for extra kick on a cold morning. Ultimately, you could start with a completely dead system, pull the hand cord on the little genset, and within an hour have the entire system up and running.
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Old 23-04-2017, 12:03   #5
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Re: Second Alternator vs larger primary

How are these three different battery banks currently charged by the alternator? For example does the alternator charge the house bank and are the other two banks connected by voltage sensitive relays?

If you run two alternators how would you connect them to the batteries?


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Thanks John,
I need to charge 3 x 140ah AGM house batteries, 1 x start battery and a bowthruster battery (ah's unknown).

Running a 35amp watermaker off the start battery when motoring only, two electric fridges off house bank along with normal lighting, instruments etc and Raymarine ST6001 autopilot when sailing.
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Old 23-04-2017, 12:33   #6
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Re: Second Alternator vs larger primary

OK The big alternator with the fancy regulator runs off a double belt on the front of the engine. It nominally just brings the large house bank up and maintains it while running without itself overheating. The second super simple Delco single wire also runs off the main engine, but nominally only charges the separate starting battery for the main engine. Hooking it to the house bank would burn it out. Another single wire runs off the front of the main genset and charges just the genset starter battery. Delco single wires run abou $35 with a returned core; I keep a spare on board. They have crude voltage regulaors included, and if they were big enough, I still wouldn't trust my expensive house bank to one. The real point, though, is thinking through how you can use the batteries so charged to help you out when one is low or dead. Being able to cross connect otherwise isolated batteries gives you a bunch of layers of redundancy. What I would never do is store all my reserve of energy in one battery bank. That would mean that if it were dead, you'd be dead in water.
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Old 23-04-2017, 12:47   #7
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Re: Second Alternator vs larger primary

Hi John, short answer is the alternator doesn't charge all three at present. There is a factory standard Hitachi on the Yanmar charging 3 x 140 flooded batteries and the start battery through the standard simple Beneteau system. There is only one fridge currently.
I am adding a second fridge unit to an ice box and a bowthruster and trying to establish the best charging system.
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Old 23-04-2017, 15:40   #8
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Re: Second Alternator vs larger primary

So the big fancy alt+VR rig + any other significant charge sources direct and matched to the big House bank.

Regular alt to the propulsion electrics and Starter battery.

Ability to combine in a pinch via 1/2/B switch.
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Old 23-04-2017, 15:53   #9
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Re: Second Alternator vs larger primary

I personally would simplify to two banks total, get rid of the third battery for the bowthruster.

Consensus among those I respect seems to be put it onto House, so ignore my unorthodox position in this informative thread

Electrical Systems - Starting or House?
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Old 23-04-2017, 16:12   #10
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Re: Second Alternator vs larger primary

How many hp and volts is you thruster and how far is it from the house battery bank?

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Hi John, short answer is the alternator doesn't charge all three at present. There is a factory standard Hitachi on the Yanmar charging 3 x 140 flooded batteries and the start battery through the standard simple Beneteau system. There is only one fridge currently.
I am adding a second fridge unit to an ice box and a bowthruster and trying to establish the best charging system.
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Old 23-04-2017, 16:32   #11
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Re: Second Alternator vs larger primary

Use the original for the start bank. Add the big one for house bank.
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