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Old 07-31-2015, 08:41 AM   #21
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Charger, alternators etc are not constant current devices. A 40 amp charger has a max current of 40 amps but will deliver much less except under certain conditions and briefly.The cut back current as the voltage increases on the batteries. Battery voltage increases as the charge increases depending on ability to take charge, called acceptance rate. As batteries age or wear out the ability to accept charge decreases meaning the voltage increases sooner.


Are your batteries getting long in the tooth?? Are all connections clean?
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Old 08-01-2015, 09:11 AM   #22
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Do you have a diode isolator between the house and start batt?

Does your alternator output go to your hot lug on the batt switch?
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Old 08-09-2015, 10:21 AM   #23
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I don't have a diode, I use a Echo charger for the start battery and yes the alternator wire goes to the lug on the main switch. Can that make a difference?
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Old 08-09-2015, 03:48 PM   #24
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Can that make a difference?

IF the rotary switch just selects engine start batt 1 or start batt 2 No

But if on one terminal is the start batt , and the house is on the other, charging will frequently be poor.

This is because the alt V reg sees the voltage of both the almost full starts and the 1/2 dead house.

Slow charging is the result , esp with a stock vehicle V regulator.

IF you select house alone , the charging will get better as the alt regulator now sees the discharged house.

Sadly the stock V regulator does a lousy job on 1/2 dead batts,

The 3 or 4 stage marine regulators are worth the expense.

Any rotary switch must be the field disconnect style (two little terminals on the back) to keep from frying the alt should someone switch to OFF , with the engine operating,

"Stuff happens"
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Old 08-09-2015, 07:28 PM   #25
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Quote:
Originally Posted by Fotoman View Post
I don't have a diode, I use a Echo charger for the start battery and yes the alternator wire goes to the lug on the main switch. Can that make a difference?

Wire the alt. direct to the house batt. use large wire to minimize voltage drop. Let the Echo charge take care of the start batts. independent of the house. Someday change to a high output alt. with a smart charge direct to house as well.

Only have starter batts. hooked to starter and everything else to the house bank. Have the switch only to the starter and use ut only to cross feed the house to starter if needed. This way the system is foolproof you never need to touch the switch and you can't run down the start battery bank with any house loads.

Solar to house bank as this will also maintaine start when making current via the Echo charge
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Old 08-10-2015, 09:11 AM   #26
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Thanks Scott. Except for the alt being wired directly to the house batt, that is pretty much the setup that I have. When I got the boat one of the first things I did was to change the alt wire to a bigger size (#10) to make sure I got the maximum juice. I did wire it to the switch lug but my switch is actually never used. I have 2 house banks but only use the first one. The other one is there as a backup (kept the original batts and bought new ones for bank 1). I have a dedicated starting battery that is charged with the echo charger from house bank #1. So apart from sending the alt wire directly to the main house bank, that's it.

The only other thing that I see as being a potential problem is the wires that connect my 2 4D batteries together (house #1). There is a bit of green stuff on the terminals and they are old wires. Just ordered new ones so I'll be able to replace them and see if that makes a difference.
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Old 08-10-2015, 10:28 AM   #27
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Some good info. for you.

Musings Regarding External Regulation - SailboatOwners.com

1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

Wiring & Installing A Battery Monitor - SailboatOwners.com

Compass Marine How To Articles Photo Gallery by Compass Marine How To at pbase.com


If you have read this then my apologizes, I learned a lot from the above.
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Old 08-11-2015, 01:31 AM   #28
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Sounds like the 2 units are sensing each other and cutting the amperage right back to tick over.
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