Voltage - Battery or Alternator Issue?
 

Hey everyone,

My last time on the boat, it had been sitting for a week. After starting like normal, I noticed the voltage gauge showed 10.5 volts. I revved it up a little, and it went up to the normal ~14 volts. But after letting it come back to idle it showed 10.5 again. I then took it out for a 5 minute run to see if that would cure it. During that time, it showed 14 again. Went to the cove to hang out, looked at it about an hour later, and it was back at 10.5. My whole drive back to the slip (at idle, as it was dark) it stayed at 10.5.

My question is this... Do I have an issue with the battery/batteries, or the alternator? The batteries are only 1.5 years old, and I've never had an issue before. I installed the new amp/stereo and have had numerous nights out lately that could have just drained them and never let them fully charge again. I'm hoping that's all it is - I'll be skiing/tubing later today, which should charge them back up. So this question may just be wasting everyone's time. I'll provide an update tomorrow, but was hoping to get an idea of the problem before going out this afternoon.

Oh yeah, here's a picture of my last time out (trying to charge the batteries on that 5 minute run ;) had nothing to do with a speed fix :yes_grin:)

Thanks!

What type of batteries do you have installed in Ryan? If they are just starting batteries rather than deep cycles then discharging them below 9 - 10 volts can damage the battery beyond repair and they usually will not hold a charge again. Deep cycles are designed for repeated charge and discharge but starting batteries are designed to remain around 12 - 13 volts.

If it were me, i would go pickup a brand new battery and see if that solves the problem. Double check on the return policy though in case the problem persists even with the new batteries. Then you'll know its the alternator.

If a new battery still doesn't solve the problem then you can pull the alternator and take it to an auto parts store that does testing. They can hook it up to a machine and put an artificial load on it and see if the alternator is still good.

Let us know what you find out!

They're both deep cycle. I'm heading out right now and will report back tomorrow (if I'm able to move - I'm going to slalom for the first time in about 12 years).

Thanks for the help.

I slalomed for the the first time in several years. It wasn't too bad the next day, although I could not/did not go very far before letting go.
Good luck with that.

Also doublecheck all your connections, sometimes all the wires don't get hooked back up when installing things. I'm guilty of forgetting a wire when connecting everything, but usually catch it 10 minutes later. duh!

All is good! I drove around the lake, then did my skiing, and it's now back to normal. I must have been out too many nights and not giving them a chance to charge back up. Even at the end of the night, without the engine running, it indicated just under 12 volts.

BTW - I got up on the first try!!! Made a few cuts, fell, got up again on the first try, made one cut and bit it hard. After that, I was done! It was a LOT harder than I remembered - I guess 12 years and 20+ pounds will add a little more difficulty!

Ryan, mine does that too. At low idle speeds, the voltmeter will show low even though at times I had topped off my engine battery with a trickle charger overnight. I don't lose much sleep over it! As long as your running voltage stays up in the green.

Doug, glad to hear yours runs likewise. Mine acts the same, as long as it jumped up to normal at higher speeds, I did not worry too much about it.

Yeah, mine always showed just under 12 at idle, then about 14 while cruising. What worried me was when it showed 10.5 at idle. Looking back on it, I realize there were probably 3 nights out on the boat, stereo rockin', and idle speed back to the slip that didn't allow them to charge back up. I'm confident they are good now. Thanks for the responses!

Mine is the same way. Occasionally when I feel the urge, I'll start the boat up and run the throttle up in neutral, until the lights brighten up and the voltage goes back up to around normal. i'll run it for about 3 minutes or so, and then turn it back off. I see lots of people doing this for concerts and raft-ups and such. I'm planning on putting a dual battery monitor onboard just for that peace of mind, as I plan to actually overnight on mine next year quite a bit, somehow I managed to indirectly convince the GF, and she WANTS to stay onboard! :wink_thumbup:

Howd you manage that one? Care to share your methods, haha?

Back to the battery voltage issue. The only time i've ever seen a voltage drop in the batteries is when our battery combiner joins the batteries during charging and the house battery is low.

This is how our voltage pattern goes. Go to start the boat and voltage usually around 11.5 - 12.5. Boat starts the combiner joins the batteries. If the house battery is low then voltage stays around 12.5. Once both batteries or the house battery is charged the voltage jumps up to 13.5 and stays there regardless of engine speed or electrical load (stereo, lights, etc.).

The pattern i'm seeing above with everyones alternator "problem" is that it seems to be happening on MerCruiser motors. Maybe MerCruiser undersized the alternator or their wiring is different and the alternator doesn't put out quite enough at idle? 13-14 volts is indicative of a "healthy" alternator.

Just my $.02 on the subject. Anyone with volvo motors experience the issue described above?

It's all about the plush cuddy interior and mood lights. :yes_grin:

Voltage wise, get this.

I took the boat out last night after probably not using it for a week & a half, and she started up like a champ. (Using Battery 1) Got out on the river, went to raise the trim up, and the radio kicked off. Let go of the trim up button, radio came back on. So I drove around for a bit, tried again. same deal. I knew it was something electrical, for some reason my radio is the tell-tale for electrical issues. I ended up driving around all night on battery 1 with my trim all the way down.

So I get back to the harbor, and I have to get my outdrive up. I hit the trim up, same deal. So I try the "Trailer" button. click click click, like the battery is dead. I switch over to the 2nd battery, the lights dim, and it won't even start. Apparently my trim power supply is sourced to the 2nd battery only. Can someone verify this is how the setup is supposed to be? It doesn't seem right to me.

I was able to get the drive up by running the motor on bat 1, and then switching to bat2 and throttling up to about 2k to put a small charge on it. But, I'd like to figure out what's going on here. Either the charger isn't charging both batteries, or I need to tap the trim pump into the main system and not just bat 2.

Any ideas?

I"m sure there are people on here that likely know more than I do, but I'll yap a bit anyway.

First, the voltmeter reflects system voltage while running and that is determined by the alternator. You could have a battery that needed jumpstarted and within a few minutes, it would be reading high on the voltmeter. Don't consider a 13-14 volt reading on the dash voltmeter as a charged battery or a reason not to throw a charger/maintainer on them.

Second, I would invest in a battery charger and use it with regularity. Consider how cheap shore power is and how expensive it is to charge a boat battery by running the engine. One of two things will happen. You'll either burn a bunch of gas, or put a constant load on your alternator; or both.

Thirdly, and this is no answer just a general comment about boats, I think a great deal of our charging/lighting/ and just plain ol mysterious electrical problems can be traced back to poor grounding. Unlike a car where you have almost every metal piece of it usable as a ground, on boats that wire has to go back to the battery to close the circuit. Not only that, but it has to go back to the battery you're getting power from!

I charge my stereo batteries every evening, they're not even connected to my boat's charging system. They are 2 31 series deep cycles. I'd have to run the boat for 10 hours to charge them fully after a day's worth of amp draw. And I top off my cranking battery every few weeks just to make sure its charged. Especially if I've been out at night running slow with lights on....

And thats all I've got to say about that....(Forrest Gump voice)

Yeah.. you do have that cuddy cabin going for ya. No overnighting in the bowrider:(

I'm guessing your batteries did not get charged which is why the stereo was turning off when you hit the trim. A few weeks ago i was using the stereo in our boat and every time the bass hit the setero would turn off then come back on again. Turns out the 5 year old battery we were using for the house circuit that originally came with the boat finally crapped out. Even after charging it wouldn't hold a charge for more than 12 hours. A new deep cycle house battery solved the problem right away.

How old are the batteries you are using in your boat Chris? Just curious if maybe its about time to replace or if they just need a good charging.

Definetely a good point to mention. The voltmeter is thus very misleading in determining whether your batteries have been fully charged. As far as charging our batteries besides when on the water running the alternator, is during the off season. I have a 4 bank battery maintainer that charges then maintains the batteries during the off season. Once boating season starts up again the batteries go back in the boat. Since doing the dual battery install and re vamping the electrical system, we've never once had an issue with low batteries or had a problem starting the boat no matter how long we run the stereo!

Voltage issue
 

What you all are describing sounds like my 97 Z210 powered by a 5.7LX. When I first start her the alternator does not seem to charge the battery until I run the RPMs up to about 2,000 at least once. Before reving the voltage meter reads about 10-11 volts. after reving once it goes to about 13.8 and stays there as long as the motor is running, even at idle. If I shut her down, same thing. I have to rev her to about 2,000 to get the volts up again. This, it seems to me, is some kind of Mercruiser issue.

Captain Steve

My electrical systems behaves exactly as Captain Steve describes below. It has since I bought my Z202 Shabah 5 years ago... and I have the same battery as when I purchased the boat.

I replaced battery 2 with a same size deep cycle earlier this year, because it was dead. And now after thinking about it, maybe it wasn't, it just wasn't getting a charge. I'm going to do some serious investigating this week and trace my electrical system down.

I have a built in charger/maintainer for the boat, with a standard 110 3-prong outlet on the transom. No shorepower, and really no place to charge it either. So I'll most likely bring down my powerpack thing and let it charge for a while.

Correct me if I'm wrong, but if battery 1 is on, and the engine is running, shouldn't it be charging all the batteries, or does it only charge one battery at a time? And why would something as important as the trim pump be hooked into only one battery? That should be wired into the main battery selector to use whichever battery is "live" shouldn't it?

Chris - I believe if you're on "battery 1" at the selector, the alternator is charging only battery 1. Battery 2 is completely isolated from the system.

Trim pump??? I'm with you on this, but I'm going to do some investigating now. I've always left it on "both" and never had anything to worry about. Your scenario is making me curious. I'll see how mine is wired sometime this week.