Anyone done this before?

CaptBobO

CaptBobO

Member
Aug 31, 2020
49
Boat Info
2000 410 Sundancer
Engines
8.1L Mercruiser Horizon
I noticed that the alternator is connected to the starter with a 90 amp fuse, then the starter has a cable to the battery bank for that engine. Has anyone bypassed the starter and just got straight to the positive on the battery bank? Why is it set up this way originally?
Anytime you have connections or breaks in a cable, you have the opp to lose amps/power.

The reason I want to do this, is to see if my alternators will have a better job at keeping the batteries charged at idle speed. These little 70amp alternators just are not keeping up with the electrical demand from my stereo and electronics while idling around the bay.
Im already looking at upgrading to a 105amp alt for this reason.
 
If you upgrade the alternator you should increase the wire size from the alternator to the battery (or starter terminal). If you have a serpentine belt that drives the alternator it "should" be sufficient to drive the 105 amp alternator without slipping. BTW do you run your generator while cruising around should supply plenty of power for your DC loads.
 
I do have a serpentine belt, which is why I feel like it can handle to 105 amp alt.
I would def increase the wire gauge, and prob just bypass the starter route. I cant see any real reason why I would need "another" connection in the power route.
The thing that is drawing the most power for me that I can see, is the radio. If i have the radio at half volume, my amp gauge at the panel jumps from 5 to 20 amps at loud parts of the music.
All new group 27 batteries as well.
My battery issue is when idling around the bay for an hour or so listening to music. My engines will eventually cut off due to low volts. I have to start my generator to recharge and I am all good.
 
Not sur
CaptBobO said:
I do have a serpentine belt, which is why I feel like it can handle to 105 amp alt.
I would def increase the wire gauge, and prob just bypass the starter route. I cant see any real reason why I would need "another" connection in the power route.
The thing that is drawing the most power for me that I can see, is the radio. If i have the radio at half volume, my amp gauge at the panel jumps from 5 to 20 amps at loud parts of the music.
All new group 27 batteries as well.
My battery issue is when idling around the bay for an hour or so listening to music. My engines will eventually cut off due to low volts. I have to start my generator to recharge and I am all good.
Click to expand...
How many amps and watts are you pushing?

I have about 750 watts and can run all day with the engine off.....

I have 2 group 31’s for each bank, stereo only runs of one of the banks Along with 2 refrigerators
 
An alternator spinning at idle speed is not going to provide much power. You need some RPMs in order for the alternator to do any work. I wouldn't mess with the wiring, its not going to help. The electrical loss your talking about is minimal at best.

Even with a great charging system - the type of battery you have will dictate the rate of charge it will take, and how long before its fully topped off. Kicking the throttle up a tad may help generate enough alternator power to run the stereo, and not drain power from the battery. Not sure if your in a no wake zone - or just idling around for kicks.
 
Chris-380 said:
Not sur

How many amps and watts are you pushing?

I have about 750 watts and can run all day with the engine off.....

I have 2 group 31’s for each bank, stereo only runs of one of the banks Along with 2 refrigerators
Click to expand...

Right now I have a small amp on a fusion head unit, but i will be adding two 400 watt amps next week.
Speaking with my installer, and he recommends that we just have a dedicated bank for my stereo and not mess with the engine/house banks. I think I will be running new cables and going that route, this way the engine voltage isnt effected while at idle/ 5mph zones.
 
something isn't right... like I said, i have 2-group31 batteries that run my stereo and 2 fridges (one is apartment size like you have probably) and i can run hours with no issues... there is a main ground on my block, that can be a pita.... maybe thats loose.... but if your less than 750 watts now, there is something else to it....
 
Chris-380 said:
something isn't right... like I said, i have 2-group31 batteries that run my stereo and 2 fridges (one is apartment size like you have probably) and i can run hours with no issues... there is a main ground on my block, that can be a pita.... maybe thats loose.... but if your less than 750 watts now, there is something else to it....
Click to expand...

You are correct. I agree that something isn't right.
I will check the main ground on the block and see if its loose or I need to clean it.
Thank you for the advice.
 
CaptBobO said:
You are correct. I agree that something isn't right.
I will check the main ground on the block and see if its loose or I need to clean it.
Thank you for the advice.
Click to expand...
On mine, I got a 1/4 turn (maybe), so I pulled it apart, cleaned up the 7 terminations, added no-ox and then re-tightened. I did add star lock washers between each connection to try to improve my connections....
 
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