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Old 08-04-2009, 20:24   #1
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Connecting Alternator to House Bank

Currently, my alternator charges the starting battery, which seems to be the standard setup. I have often heard that it is better to connect the alternator to the house battery bank and then use something like the Xantrex echo charge to connect the house and starting batteries. My question is about making the change.

Based on the wiring diagram, it seems very simple. Currently, the + line out of the alternator goes to the ammeter and from there to the starting solenoid and to the starting battery. It appears that all that is necessary is to disconnect the wire between the ammeter and the starting solenoid and connect it between the ammeter and the house battery. Is that all there is?

I wish I had a dime for every time I thought something was simple only to discover that I was wrong. Are there any problems or disadvantages of making such a change?

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Old 09-04-2009, 01:18   #2
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No news is good news...

I installed an Xantrex Echo charger a few months ago.
Installation went as you describe, save I isolated everything from the steel hull.
Batteries seem to be charging OK...

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Old 09-04-2009, 03:45   #3
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The current "wisdom" on the topic is to have a large house bank and a smaller start bank which can be combined in a pinch for starting purposes.

The alternator is a high output one which charges the HOUSE bank and the house bank is then used to charge the START Batt with something like an Echo Charger.

Make sure your wire size is appropriate for the current the alternator puts out and then connect it to the POS on the HOUSE bank and then install the Echo Charger between the HOUSE POS and the START POS. It's a few hundred dollars. Your start bank doesn't need much charging typically as your HOUSE does. So it can take a larger output alternator and then send the excess to the Start via the Echo.

I have had this system for several years and the Start bank is always 100% topped up. So even when my House is low I can turn the engine over and begin recharging the House at a high rate.
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Old 09-04-2009, 03:48   #4
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Disconnect the positive wire from the alternator away from the ammeter. Then take this wire and hook it up to the positive on the house battery. Standard practices require you to fuse the wire at the house battery. Look up and see what wire size you have coming off of the alternator and use the amp rating of that wire at engine room temp BoatUS BoatTECH Guides: Choosing Cables & Terminals for Marine Service. For instance, #8 wire can only handle 68 amps inside engine room. So you would like to fuse this wire at the battery at 68 amps. If you cannot find a 68 amp fuse, most likely, fuse it at the closest value that is under 68. If your alternator puts out more than 68 amps then you will need increase the wire size. I know, this is cumbersome but this is the safest approach and will prevent headaches in the futre.
As far as the echo goes, it is a good system. Just remember to mount the echo in a cool and dry location. I have seen many of them destroyed within a year because of excess heat and moisture. Make sure you hook up the echo with the house wire going to the house battery and the start wire going to the engine battery. If you hook it in reverse your echo will pull amps out of the start battery and try and charge your house battery. NOT GOOD. You also want to properly fuse both red wires at each battery. Trust me, this is recomended and it is the safest approach.
About the ammeter, it really is not a good idea to run your alternator through an ammeter because if that ammeter goes then your alternator goes. This is a good chance.
If you ask about why fuse the wires. This is prevent a catastrophic fire. Yes, if the fuse for the alternator blows out then you will loose charging abilities but you will prevent a damaging fire caused by excessive amperage through an underated wire.
RECAP: Look at your alterantors amperage. Make sure the wire you have on there can support it at engine room temp (link provided). Fuse the wire correctly at battery. Hook up echo correctly in good location.
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