Alternator

[RiverLance2012]

I have 3.0 Mercruiser with I believe is a 65 amp alternator. Problem is I have a high powered stereo that is eventually gonna eat my batteries up. I have a 600 CCA starting battery and then I have a marine deep cycle 225 ah tied in parallel with all my stereo equipment hooked to it. I have not had any issues with the batteries being low. My boat is now dry docked at a marina and I won't be able to charge my batteries like I could when I trailered it. Do you think I should put a bigger alternator on it and if so what are the recommendations???

 

[mark1905]

Re: Alternator

DB Electrical sells a good 105A unit for under $70. One wire: http://www.dbelectrical.com/p-3609-...ine-alternator-mercruiser-1-wire-adr0334.aspx or the three wire: http://www.dbelectrical.com/p-3610-...ercruiser-3-wire-110-amp-10si-ho-adr0106.aspx

Upgrade the ground and charging wire to 6AWG and use high quality ring terminals.

Prepare yourself for an onslaught of debate on this one from many old timers that will try and tell you that you that you'll fry your battery, that the stock one is good enough, yadda yadda yadda. You won't fry your batteries, the stock one is NOT good enough once you start sucking serious juice out of the system, your stereo amps will sound better when the alternator is running due to supplying a constant source of 14.5V and you'll charge your batteries quicker. It's an all around good thing to do.

 

[RiverLance2012]

Re: Alternator

Okay Im just gonna go ahead and swap alternators then, just curious anything special I should know before doing this??? Ive done it on a car before but never a boat.

 

[mark1905]

Re: Alternator

Just make sure to use 6AWG marine grade power cable along with high quality set screw type ring terminals such as these: http://www.sonicelectronix.com/item_20686_Raptor-PHDRT4.html?from=94-332

You may have to go to Ace Hardware or something and get a longer ground screw than comes with the alternator along with a couple of washers.

 

[Jlawsen]

Re: Alternator

Good Advice from Mark1905. The only thing I might suggest is that you check with the manufacturer and find out what the output on the 105 is at different RPM's. If your load is more than it can output at your normal cruise RPM then it will still be using the batteries. Some of the higher output alternators have really low output until about 2500 rpm. Just double check before you pull the trigger and your problem will be solved.

 

[mark1905]

Re: Alternator

Good Advice from Mark1905. The only thing I might suggest is that you check with the manufacturer and find out what the output on the 105 is at different RPM's. If your load is more than it can output at your normal cruise RPM then it will still be using the batteries. Some of the higher output alternators have really low output until about 2500 rpm. Just double check before you pull the trigger and your problem will be solved.

I ran one of those 105s up until a few months ago, and it seemed to kick in around 1200 RPM. They're nice units.. and it's so important to upgrade the wiring along with the swap in order to really get the max potential out of it.

I'm of the philosophy that when it comes to wiring, over-doing it by a little is always a good rule of thumb. I would much rather have a little too much capacity than not enough.. and you'll kick yourself when you have to do it all over again. A smooth running, strong charging electrical system makes everything that much happier including the owner!

FWIW, here's a picture that I snapped of my 200A just now. Note the 1AWG cable on the ground connection and the charging wire along with set screw type ring terminals.



A word of advice: Make sure to re-check those set screws every once in a while to make sure that they're good and snug. The last thing you want is one vibrating loose and a cable flying while WOT..

 

[bruceb58]

Re: Alternator

I have a 600 CCA starting battery and then I have a marine deep cycle 225 ah tied in parallel with all my stereo equipment hooked to it.

Curious why you are running these in parallel. They should be separated and only connected together while the engine is running. Use a battery switch where you can put them in parallel with a switch or even better to use an ACR. Generally, its not a good idea to run different battery types and capacities in parallel. Personally, I prefer not to run identical batteries in parallel either.

Don't use set screw ring terminals in a marine environment. Worst thing you can do. Go here and order cables that are crimped and have shrink sleave on the connector.
http://stores.ebay.com/Genuinedealz

I am probably one of the old timers Mark is referring to. I am also an EE. Don't get a high output alternator unless you actually have to have it.

What current draw do you currently measure when your stereo is operating? What size battery is your deep discharge battery. Without knowing these, its pretty pointless suggesting alternator sizes. If you have a 70 amp hour battery for your deep discharge, you are way better off charging it slower with your current alternator. By the way, you should never discharge your battery more than 50% so you really shouldn't be discharging it more than 35 amp/hr. Can you see why it doesn't really make sense to get an alternator that is more than you already have? Now, if you have a set of Trojan 6V 200Amp/hour batteries in your boat at $200/each I would be saying something completely different.

Many suggest never charging a battery more than C/8 where C is = to the capacity of the battery. This is if you want your battery to last a long time. If you don't mind changing batteries out more often, then you can go with the higher output charger and charge quicker. Your choice on the "cost" of that convenience factor.

 

[fishrdan]

Re: Alternator

I agree with Bruce, especially....

Don't use set screw ring terminals in a marine environment. Worst thing you can do. Go here and order cables that are crimped and have shrink sleave on the connector. http://stores.ebay.com/Genuinedealz

Those set screw ring terminals are a bad case of corroded connections, just waiting to happen. Get the crimped cables Bruce suggested or solder (torch) on some tinned cable lugs.

That DB 105 amp alternator's cut-in RPM is about 1200RPM, but it throws out 50-60 amps at idle (I use one for charging 2 trolling motor batteries while trolling off the main). At cruise RPM I bet it' kicking out close to 100 amps. 100 amps going into a SINGLE severely discharged battery is not a good thing.......

 

[mark1905]

Re: Alternator

Quick, run!



I've used set screw terminals for years with zero corrosion or problems. On the flip side, trying to successfully crimp a 4-6AWG for most people is a daunting task and will usually end in tears. If you're using marine cable, then heat shrink isn't such a necessity. Everyone has their way of doing things and obviously everyone thinks they're right, or they wouldn't be doing it.. right?

I warned you about this crew..

 

[bruceb58]

Re: Alternator

On the flip side, trying to successfully crimp a 4-6AWG for most people is a daunting task and will usually end in tears.

Always a daunting task if you don't have the correct tools and which is why I suggested the link above.

 

[Jlawsen]

Re: Alternator

That's a hard point to argue. Not sure what size battery's he running but I can tell you that on a high end shop charger, it takes 2 hours to charge a Interstate Pro Group 29 that was down to 90%. You do have to condsider that my charger is high end and will not risk harming the battery so in the last 1% is goes through a complex finishing cycle. That probably lasts 30 minutes. So yes, if you let them get down to 40% and then try to bring them back up on the alternator you'll probably run out of gas first.

However, I think the OP's problem is that the alternator can't keep up with the load so it's pulling off the batteries when the engine is running. If he can meet the load requirement via the alternator then his batteries will be fresh for when he's not running the engine.

 

[bruceb58]

Re: Alternator

I have a marine deep cycle 225 ah tied in parallel with all my stereo equipment hooked to it.

You sure about that? Do you realize how massive a battery that would be even if they make one that is 12V?

Here is an example of a 6V one that is 225 AH and since it is only 6V, 2 in series are needed.
http://www.altestore.com/store/Deep...ttery/p1771/?gclid=CKzuhMvN368CFWYJRQodzFZB_A
If you do have this setup, then a 100A alternator may be ok but I still believe it is not needed.

Here is Trojan's advice:
http://www.trojanbattery.com/BatteryMaintenance/ChargerSelection.aspx
The reality is that the charge current of the alternator will taper so even a 100A alternator will drop its charge current fairly fast. So unless you have a huge load that the alternator needs to supply other than charging the battery, like refrigerator or heater, not likely to need a higher output than what you have.

 

[MH Hawker]

Re: Alternator

Yea actual people who have electric experience. Not people who are guessing or making it up as they go along.