Alternator upgrade
 

Hi gang. Last year I upgraded my electrical system from one battery to two deep cycle batteries. Since I did this, I have had problems with the batteries staying charged. My stock alternator only pushes 55 amps. Would an upgrade to a high output alternator cure this problem? If so, how big should I go? I've seen them from 90, 100, 130 and even 140 amps.


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Re: Alternator upgrade
 

That is odd. I have not had any problems with that battery iso system. My alternator is the factory 65 amp. The group 27 handles most all of the electric as the group 29 runs the sound system - two amps totaling 1000RMS. No problems charging and we sit with the stereo going for periods at a time. The batteries seldom read below 70% on the charger when they are first hooked up after going out.

Re: Alternator upgrade
 

Thanks, Moto.

Maybe my alternator is just old and worn out. I've had the boat for three years, so I'm not sure when it was replaced last. There's a good chance it is the original since it is black and the previous owner never did any work to the boat at all. (i.e. the shifter boot was cracked and letting water in the boat. Instead of fixing it, he just left the bilge pump run all the time, lol).
I have noticed the voltage guage bounching around from 10-12 volts when it is idling and would never get over 12 when cruising. I was thinking of going with a larger alternator since I have added a lot of extra stuff on the boat like extra lights, stereo and amp, etc. but not sure how big would be too big

Re: Alternator upgrade
 

You might be able to find that info somewhere out there on the internet. As for your volts while underway I am pretty sure Im running around 14 on the Faria and my Lowrance is reading high 13's. That could be your issue. A buddy turned me onto these DB Electrical alternators. He likes his and it was 1/3 the cost of a Mercruiser part.

Re: Alternator upgrade
 

Thanks Moto,
I'll look into the DB alternators. Mercruiser is mighty proud of their parts!

Re: Alternator upgrade
 

so I ordered a new alternator yesterday. It is a 130 amp, plenty big enough to keep my two batteries charged up and run my lights, stereo, etc. Now do I need to install a larger charge wire? The existing wire (orange, I'm sure is stock factory) looks to be a 8 or 10 gauge

Re: Alternator upgrade
 

You are going to need to at least double the size of the original or parallel it with the same size. Does your boat have a battery isolator? If so, is it rated for 130A?

Re: Alternator upgrade
 

I do have an isolator. I think it is a blueseas unit. I'll have to find out the rating


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Re: Alternator upgrade
 

Blue Seas make nice products. I believe their ML series is capable of 500A , all other series are rated well below 130A.

Re: Alternator upgrade
 

Thanks, Steve for the great info. I will check to see which series I have. Do you think 130 amps is overkill?

Re: Alternator upgrade
 

I have the same isolator you have Paul and I think they might be rated for 120 but it's been a long time since I put mine in and I can't say for certain that's correct.

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Re: Alternator upgrade
 

ok, thanks, Moto. Dummy me... I didn't even think about the isolator having an amp rating. I'm at my office now (yea, I'm getting lots of work done playing on the computer,lol) and will check it when I get home and look at it. I probably shouldn't have gotten that big of an alternator, especially if I'll have to change the isolator and other things for it to work

Re: Alternator upgrade
 

I found the add a battery kit we have HERE showing 120. The ACR is part number 7610 and the whole kit number is 7650 of you are looking them up.

Re: Alternator upgrade
 

I found mine on some old pics I had on my phone. It's the one rated for 120 amps. dangit!

Re: Alternator upgrade
 

Paul,
130A is a lot of alternator but bigger is always better, right? 130A alt will just charge the batteries faster or allow you to run a lot of electrical accessories and still charge the batteries. I have the standard 65A in my Z280 and it has no issue running my boat and charging 3 batteries, a group 24, a group 27 and a monster 4D. Do you have a monster stereo on your boat? A 65A alt should support up to almost 1000W without draining the batteries. Or do you do a lot of idle cruising? The alternator only puts out its max amperage at a specific RPM (>3000RPM). Your present alternator may have one or more of the rectifier diodes out which would only give you 1/3 to 2/3 of its rated output.

If your ACR is rated at 120A you are probably OK. I doubt your 130A alternator actually puts out 130A unless you have some ideal conditions...but i cannot guarantee it.

Re: Alternator upgrade
 

Good info Steve! I was unaware of the RPM at which the alternator put out it's rated amps. Similar to your experience I have not had any charging issues with the stock alternator and 2 batteries.

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Re: Alternator upgrade
 

Steve, I have a 400 watt stereo. A lot of our time on the water is spend either anchored in a cove with stereo going and engine off, or idling around the coves but we do pull a tube at higher speeds. I will cruise at full throttle some, too, but not all the time. I have thought about the "actual" output of an alternator. Like a lot of things, the advertised rating is somewhat higher than the actual, but not sure. I can't remember the group size of my two batteries. I think they may be 27's. I do remember they have something like 850 cold cranking amps

Re: Alternator upgrade
 

Finally got the new alternator on. Left the original hot wire on the alt and ran an 8 gauge wire to the starter solenoid, too. Ran it at the lake all day and no problems!


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Re: Alternator upgrade
 

Good deal. What voltage was it running at? Where did you get the alternator?

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Re: Alternator upgrade
 

It ran almost 14 volts. Was big enough to keep both batteries charged all day. I got it on eBay. Can't remember the name of the seller


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Re: Alternator upgrade
 

I just looked it up. The name of the seller is powermaxusa. He has tons of alternators


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Re: Alternator upgrade
 

Do you have any pics of how you setup both ur batteries?

I am trying to find a clean way of getting both batteries organized on my 18ft baby mariah!

Re: Alternator upgrade
 

http://uploads.tapatalk-cdn.com/2016...c4e8318e10.jpg

Here is a pic of my dual battery setup. Not a very good pic, but it should give a general idea of how I did it. This is in the rear compartment on the right side of the motor


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Re: Alternator upgrade
 

What brand alternator was it that you bought? I'm thinking of replacing mine also

Re: Alternator upgrade
 

Back to the subject topic on hand, topcop, it's an off brand alternator. Wasn't going to pay the high dollar price for a mercruiser brand. I've had my boat out a few times with the new alternator and it works just fine!


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Re: Alternator upgrade
 

Great thanks. I have the same year boat and engine as you was the alternator hard to get to for replacement?

Re: Alternator upgrade
 

Great job...clean install!

Re: Alternator upgrade
 

Topcop- it was an easy replace. I contacted to guy on eBay and sent him a picture of the back of my alternator. He knew exactly what I needed. Changing it out wasn't too bad. I removed one coolant line that goes from the top of the engine to give me some more room to work and loosened the power steering pump. I've been running the 65amp alt for several weeks now and no problems at all!


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