2800 scr battery isolator installation? - Maxum Boat Owners Club

Baby Blue · 03-16-2014, 01:55 PM

1998 Maxum 2800 scr
7.4L Mercruiser
Bravo 3 outdrive

I'm looking to install a battery isolator in this boat so the alternator will charge both batteries regardless of what the battery switch is set to? anyone on this board install one. Looks pretty straight foward for 1 alternator 2 battery set up.
alternator charging wire to center post of isolator (alternator post). then from isolator battery 1 and battery 2 to each positive on the battery.
sound about right?
what approx size and color is the charging wire coming off the alternator?
they also sell different size isolators to accept higher amp alternators. any idea on the factory alternator size for the 7.4L. Boat is in storage an hour from our hour and like to order asap.
thanks, BB

mmwjr · 03-16-2014, 04:30 PM

BB the isolator should come with a wiring diagram but what you described sounds correct. I beleive the alternator is a 55 amp.

I can try to look it up but latter as i am busy working on my truck before the snow starts tonight, oh joy.

Baby Blue · 03-16-2014, 04:39 PM

oh... I hear ya.. Cold and snow is getting way old here in Cleveland! especially when you buy a new boat in February.
BB

shrew · 03-17-2014, 02:14 PM

This is not a good idea. The alternator should only charge one battery. What you are considering would be the equivalent of setting the battery switch to both. Incidentally, you should have a battery switch on that model from the factory.

Baby Blue · 03-17-2014, 04:28 PM

Quote:

Originally Posted by shrew

This is not a good idea. The alternator should only charge one battery. What you are considering would be the equivalent of setting the battery switch to both. Incidentally, you should have a battery switch on that model from the factory.

it only charges one battery at a time and which ever needs charge. from my understanding it's a diode and only allows current to go one way, in. also prevents overcharging. the mechanic that did the survey recommended it. 36 year marine mechanic and seems to really know his stuff.

mmwjr · 03-17-2014, 05:04 PM

After thinking about it I agree with shrew. The alternator is not designed to have 2 loads (batteries). The isolator is used to prevent 1 battery from drawing down the other (blocking diode) it will not prevent overcharging.

If you have a dual select battery switch you will be fine. I just switch between batteries every other trip and never use the both position.

Do you plan to be on the hook for long times while drawing a fair amount of power? If so you should install a house battery.

biggerseagar · 03-17-2014, 05:45 PM

I believe the red comes off the starter and black find a bolt that is screwed to the block. You are putting the isolator in between the starter and battery/is for all this to work.

Roger

Baby Blue · 03-18-2014, 03:08 AM

The mechanic that suggested it is very knowledgable.I'm going to take his word on it and give it a try. from what ive researched they are very safe for the batteries.
thanks for all the replies and info.
BB.

Prevent Over-Charging Your Batteries
All Charles Battery Isolators are ignition protected and prevent over-charging. They feature a heat chamber design, protective boots on heavy-duty 5/16” battery and alternator studs, corrosion-resistant casings, are compact and easy to install. Either leg of the Charles Battery Isolator handles the entire alternator output amperage rather than a portion of the rated load.
1-year warranty, made in the USA.

mmwjr · 03-18-2014, 04:16 AM

Let us know how it turns out

Jerryh3 · 03-18-2014, 10:35 AM

I used this for my boat. Seems to work great. I believe I used 4 AWG for all of my connections.

http://charlesindustries.com/main/battcom.html

ss3964spd · 03-19-2014, 04:22 PM

I'm trying to get my head around why the Alt would care how may batteries it's charging. Enlighten/educate me.

Scenario 1: Two 12V, 200 Ah batteries, fully charged. Battery switch set too "both". If the battery and switch wiring is correct the alt "sees" only one 12V, 400 Ah battery, as does all the loads (electronics, starter, etc). The alt should have no problem maintaining the charge of the "single" battery, as long as the draw does not exceed the alt's output. However, the same can be said if there is only one physical battery installed.

Scenario 2: Same as above but one battery has been drawn down to 10V. When the switch is set too "both" current from the fully charged battery floods to the depleted battery until they both equalize, resulting in one 11V battery. Now, and dismissing the obvious havoc 11V may play with certain loads, the alt still sees only one 11V battery and will charge "it" at a rate up to it's rated output. Again, as long as the draw on the battery is less than the alt output it will charge them both but it will certainly take longer.

I'm likely missing something. The only thing I can think of is that the load on the alt - running at it's rated output for a longer period to charge a large battery, may ultimately piss it off. The same thing would happen if there was just one physical battery drawn down to 11V. If you can get the engine started on 11V the alt is going to do the same thing - max it's outout until the battery is charged - it just won't take as long to charge it.

WutamImissin?

mmwjr · 03-19-2014, 04:58 PM

Dan you are not really missing anything. My comment was for worst case scenario, 2 deep cycle batteries being rather low and trying to charge both at the same time will cause the voltage regulator to run hard until they recharge. If this happens on a regular basis the life of the regulator will be shortened.

Just seemed to me the OP was making changes while he wasn't sure he really needed to for how he will be using the boat.

ss3964spd · 03-20-2014, 02:43 PM

Thanks for the sanity check, Mike. I do understand the potential issue of cooking the alt/reg from running at it's rated output for a long period of time.

I've run mine on "both" many times and have suffered no ill effect - yet, but only when the batteries are already pretty well charged. If I know one is down after hours on the hook I start on the good one then switch over to the discharged one once under way.

Baby Blue · 03-20-2014, 05:45 PM

Quote:

Originally Posted by ss3964spd

Thanks for the sanity check, Mike. I do understand the potential issue of cooking the alt/reg from running at it's rated output for a long period of time.

I've run mine on "both" many times and have suffered no ill effect - yet, but only when the batteries are already pretty well charged. If I know one is down after hours on the hook I start on the good one then switch over to the discharged one once under way.

that's kind of the idea behind the isolator. You don't have to change the battery switch in order to charge either off the alternator. The alt wire goes to the isolator then a wore comes off the isolator directly to each battery. this way it will charge whatever battery is in need regardless of what the battery switch is set to.
BB

mmwjr · 03-20-2014, 05:57 PM

Quote:

Originally Posted by Baby Blue

that's kind of the idea behind the isolator. You don't have to change the battery switch in order to charge either off the alternator. The alt wire goes to the isolator then a wore comes off the isolator directly to each battery. this way it will charge whatever battery is in need regardless of what the battery switch is set to.
BB

Yep fully understand that. The bigger concern is to prevent running down both batteries when on the hook for a long time while having electronics on.

I manage both by alternating which battery i user every other trip. batt 1, then batt2, back to batt1 ,....