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Merc 150 4s alternator/battery combo

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Merc 150 4s alternator/battery combo

Old 11-24-2019, 02:00 PM
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Default Merc 150 4s alternator/battery combo

Hey I wanted to know if you guys agree with this setup because I’ve burned up two alternators in 5 years and two sets of batteries.

I have twin Mercury 150 4 strokes rigged up to three Duracell Group 34 AGm (Sam’s club). Supporting a normal load associated with a center console, 2 Simrad’s, stereo, pumps etc.

I’m wondering if the high 60 amp alternators are causing an issue or is this just a fluke thing??

Thanks!

RA

Old 11-24-2019, 02:15 PM
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Need to know how all three batteries are wired up. 60 amp alternator output has nothing to do with you potential trouble.
Old 11-24-2019, 02:27 PM
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one dedicated to each motor and one isolated house
Old 11-24-2019, 02:44 PM
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Is the house getting fed via ACR or aux charging lead off of both motors, or just one?

Any idea how the alternators failed? I actually in the alternator business, and can give you a bit better incite if I know how they died. Also, (3) group 34's are a lot of battery to support with a pair of 60 amp alternators. A pair of 24 or 27 cranking batteries tied to a single larger house AGM would be more appropriate IMO.
Old 11-24-2019, 04:05 PM
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Thanks Autobahn70. The house is fed from the ACR.

I’m not really sure how the alternators died. One went bad (a diode maybe) and repaired it but it didn’t take. The other side was charging but at a lower output and died after another year or so.
Old 11-24-2019, 04:12 PM
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Diode failure almost always is an indication of too much load/battery bank size, or batteries in poor condition. In either case the running voltage drops, which the regulator sees as a call for current, and they ramp up output until set point voltage is achieved. If this does not occur for a long time, the rectifier (contains the diodes) overheats and diodes fall. Can also frequently take out the stator (outer windings).

personally I would drop down in size for the 2 cranking batteries, and connect both to the house via 2 ACRís so that they are sharing the workload.
Old 11-24-2019, 04:24 PM
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Ok thanks. Maybe I’ll move two of them to the TM.

The manual says I need 1000 MCA / 800 CCA or 180 ah. Would 27s work? The ones I looked at were lower
Old 11-24-2019, 04:46 PM
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Originally Posted by Reelassets2 View Post
Ok thanks. Maybe Iíll move two of them to the TM. Does it matter between 27 or 24s?
not really. I would lean towards 24ís though given the size of your house, assuming you can parallel it to either side in an emergency. May also consider a cranking to cranking parallel circuit just in case.
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Old 11-24-2019, 06:02 PM
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I’m on my 3rd alternator on same motor. Also using blue seas acr system. Top Merc mechanics - first choice marine in st Pete - said about one of the only things they see go wrong with these motors so far. I also had an iac valve go bad under warranty.

Old 11-24-2019, 06:16 PM
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Not sure if this helps but I alternate between two group 27 AGM’s on my boat with a single Merc 150fs. Plenty of cranking amps. I lost the alternator 2.5yrs ago, I think it’s a weak link (Chinese?). I just replaced my AGM’s, 8yrs on the last set.
Old 11-24-2019, 06:21 PM
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Alternator is Delco on most Mercuryís, but itís a valeo based design. Solid unit honestly, but Iím not a fan of the regulation set points. IMO they are set too high, and donít always play nice when combined with AGM batteries. AGMís are really good, but have a tendency to absorb charge such that they show lower voltage than does wet cell.
Old 11-24-2019, 06:38 PM
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I’m using wet cell. Single Merc 150 4s two group 27s house and crank. almost 300hrs on the dot per alternator
Old 11-24-2019, 07:19 PM
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Originally Posted by Icatcher22 View Post
Iím using wet cell. Single Merc 150 4s two group 27s house and crank. almost 300hrs on the dot per alternator
Interesting. Would love to see a dissection of the failed units to know more. If/when your warranty goes out, I would figure out if there is a local shop that can repair the failed unit vs replacing.

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