alternator and battery question?

[1553]

Just bought a 1997 Maxum 23SC with a 5.7 merc. There are three batteries on the boat with a 55amp alternator. Two of the batteries are in parallel for an inverter and stereo amp. and one for starting. It is wired with one orange wire coming from the alternator to the starter and then from the starter to the starting battery to charge it and another red wire coming from the same post on the alternator to a isolator and from the isolator to one of the batteries in parallel to charge them. The batteries in parallel are connected by there positive and negative post and one negative running to the starting battery to ground the ones in parallel . The starting battery has a ground to the engine block. <br />The question is are the batteries in parallel isolated from the starting battery I need to keep two batteries in parallel to give me 210amp from two 105amp batteries because I need the extra amps to run a microwave and tv between charges. Please help

 

[Ralph 123]

Re: alternator and battery question?

From what you say, it sounds like it is isolated. Here is a schematic for the setup you have.<br /><br />

<br /><br /> http://www.boatfix.com/how/Ele2.html

 

[Zeusdafreak1]

Re: alternator and battery question?

In the above diagram can the 2nd battery added be grounded to the negative on the starting battery? I would like to just be able to run my ground on my new deep cycle battery to the ground of my original starting battery since it is already grounded to the Mercruiser motor.

 

[bruceb58]

Re: alternator and battery question?

The batteries are isolated but because of the voltage drop through the isolator, your second set of batteries will never get fully charged. If you do run an isolator, the isolator should be set up for both sets of baterries...not just the one like it is now.

Look into getting a combiner. It is a way better way to charge all of your batteries. Isolators are the old way of doing it and not nearly as good.

 

[bruceb58]

Re: alternator and battery question?

In the above diagram can the 2nd battery added be grounded to the negative on the starting battery? I would like to just be able to run my ground on my new deep cycle battery to the ground of my original starting battery since it is already grounded to the Mercruiser motor.

You can do that. I don't think it is as a good a way as bringing it down to the block. Reason is that you now have two attach points for that second battery ground.

 

[Zeusdafreak1]

Re: alternator and battery question?

The only thing the second battery will power is the audio for the boat.

Also, I have two 10 gauge wires coming from my alternator, one orange and one black, with a couple other smaller wires. I assume I am to just cut this orange wire, terminate it from going to the starter, and reroute this to go to the isolator center post. I hope I am doing this right. Then each of the other two posts on the isolator will go to positive on battery one and positive on battery two. Battery one is already in operation so it should be good, battery two will need to be grounded, which I would like to ground to the ground of battery one and I am done.

 

[bruceb58]

Re: alternator and battery question?

Sounds fine...I would actually remove the wire going all the way down to the starter...not cut it.

 

[Zeusdafreak1]

Re: alternator and battery question?

Thanks. Ive got it wired up now and the batteries are finished. I am working on the amp and running the speaker wires now. Is there any way to test the 2 battery system without putting it in the water? I sure would like to know before the family is loaded up.

 

[bruceb58]

Re: alternator and battery question?

Start it up and measure voltage at the alternator output and the voltage at the two batteries. The voltage at the battery will be about 0.7v lower than the alternator output.

 

[Boatist]

Re: alternator and battery question?

Sure test it in the driveway but make sure you have water going to your water pump. Check your voltage before starting then start her up and check again. Voltage should be 12.6 volts before starting and 13.8 to 14.8 volts after starting and running at a fast idle.

Also if your alternator has a external regulator connect the input of the regulator to the battery side or the isolator for your starting battery.

I would just run all the grounds back to the engine block.

 

[Zeusdafreak1]

Re: alternator and battery question?

Also if your alternator has a external regulator connect the input of the regulator to the battery side or the isolator for your starting battery.

I am not sure about this one. I used the orange 10 gauge wire coming straight from the alternator to the isolator block center post. I hope this was correct.

I would just run all the grounds back to the engine block.

I did go the easy way out and attached the fround from the second battery to the ground on the first battery. I hope this too was OK.

 

[Boatist]

Re: alternator and battery question?

As far as the grounds go it will work if you ground back to the ground on the first battery. The only reason I like to go back to the engine block is if the ground to the block on the first battery comes loose or corrodes then you loose both batteries. Going to the block with both batteries then if one ground fails you still have the other battery working.

You alternator output to the common post on the battery isolator is correct. Then wire post one to battery one and post 2 to battery 2. If 10 guaged is what was already comming from your alternator then that will work. Normally I use 10 guage for 30 amps and anything more I use 8 guage. Since you have 55 amp alternator 10 might be a little light. First time both battery are low I would start her up and run at 1000 rpms then go back and check your 10 guage wire. If it cool then you are ok but if it warm or hot then change to a higher guage. Most batteries will only charge at max for a few minutes right after starting then the amperage drops down as the batteries charge.

If you have a external regulator for your alternator then I would move the voltage sensing wire to the battery side of your isolator. I would put it on the starting battery. With a internal regulator then what you have set up will work just fine.

 

[Zeusdafreak1]

Re: alternator and battery question?

It may be 8 gauge from the alternator instead of 10. Its a 70amp alternator.

How would I tell if I have an internal or external regulator?

 

[Boatist]

Re: alternator and battery question?

Most alternator that have a external regulator will have 3 wires. The big heavy output wire that is on all alternators. Then a F and R wire. The F or field input to the alternator comes back from the voltage regulator and engerizes the field winding in the alternator to produce more current output and voltage until the voltage. When the voltage reaches voltage the regulator is set for the regular will reduce the current to the field winding and keep the voltage constant. As the battery charges up the current output will drop way down but the voltage will remain very steady.

I guess the short answer is look for a field winding input to your alternator. If the regulator is internal then you will not see a field winding input. In general older alternators had external regulators and most newer alternators are internal.

 

[Zeusdafreak1]

Re: alternator and battery question?

Ok. I have two larger wire connected to each "post" of the alternator, both of which are 10 or 8 gauge heavy wire. There are a couple of tiny black wires also connected to the back of the alternator. I do not know where they go.

I have a 2006 4.3 Mercruiser. Since this is new I will assume it is internal.

Thanks. I would have never known to check for that.