Battery starting and alternator issues

[jeepwx03]

I have a 1989 3.0L Mercruiser with two batteries on a switch with 1,2, or both options. The problem started last weekend when I was running all day and wasn't paying attention to the volt gauge. After about 6 hours of boating I wasn't able to get the boat to start, the batteries were dead. The volt gauge was reading below 10 volts. I got a tow back to the dock and charged the batteries that night. I also tightened up the alternator since the bottom bolt had vibrated out and caused slack in the belt. I thought this was the problem of why the alternator wasn't charging the batteries. I sent out the next day and had the same problem.

I've have since had the batteries tested at Advanced Auto, they're good. I also replaced the alternator with a new sierra one. I took the boat out on the water again to test. I only used one battery at a time and the with the switch on 1 or 2 the starter would click like there wasn't enough amps, but if I held it there long enough it would slowly crank over and start. If i put the switch on both batteries it would start fine. The new alternator would keep the volt gauge at around 12 volts.

I would also have issues when trying to trim while underway, the engine would die and back fire.

The guy at the auto store suggested checking the cables and ground for corrosion. the ground was tight on the plate and there was some corrosion on one of the grounds but only on the wire, not on the brass connector and it was very little.

could it be the switch degridating <sp?> the amps to the starter?

Any suggestions would be great, we are planning another trip this weekend and I only have a couple days to figure this out.

 

[Gary H NC]

Re: Battery starting and alternator issues

If you had corrosion on the ground or hot battery cables its time to cut the ends off and have new ones crimped on.Or better would be to just replace them. It does sound like a grounding issue..Those cables corrode inside and its easy to over look that..
Also i would run the boat and start testing voltage at different connections. See what voltage you get at the alt. then the battery..

 

[Haut Medoc]

Re: Battery starting and alternator issues

If you had corrosion on the ground or hot battery cables its time to cut the ends off and have new ones crimped on.Or better would be to just replace them. It does sound like a grounding issue..Those cables corrode inside and its easy to over look that..
Also i would run the boat and start testing voltage at different connections. See what voltage you get at the alt. then the battery..

Good advice^......
And....
Try connecting just one battery, with out the switch & see what that does.....
With the engine running you should read about 13.7 volts.....

 

[wire2]

Re: Battery starting and alternator issues

It sounds like a poor connection somewhere to me. After cranking, feel the various connections for heat.
Don't just look for surface corrosion at a connection, undo it, separate the lugs and look at all the surfaces. Clean them with abrasive, then coat with clear synthetic grease, and do it up again tight! The grease will allow an electrical connection while keeping moisture and oxygen off the metal. That includes your battery posts. You'll never see corrosion there again.
In a pinch, regular, non metallic grease will do also.

 

[jeepwx03]

Re: Battery starting and alternator issues

Very good advise, thank you. I have some dialetric grease to put on the connections. I noticed the connections are mostly brass, assuming so there is no spark. I have some gold ring connecters for my car stereo projects. Would those be safe to use coated with the grease?

 

[Haut Medoc]

Re: Battery starting and alternator issues

Yep, but like was said before, if those wires get hot from cranking the sterter, that means there is resistance & they should be replaced.....​

 

[bruceb58]

Re: Battery starting and alternator issues

Instead of cranking and feeling for heat, do it the right way and use a voltmeter and measure voltage drops across the various cables.

 

[TBarCYa]

Re: Battery starting and alternator issues

I had a very similar problem that I just fixed the other day. Check to see if both batteries are grounded to the engine block or if one battery is connected to the other. You want both grounded to the block. Next check how long your battery cables are from your starting battery to the switch and then to the starter. If you can use shorter cables by moving the starter battery to the other side of the boat, you should do it. My problem was that my starting battery was on the opposite side of the boat from the switch and starter so current had to flow across the boat thru the switch and then to the starter. The ground from the house battery went acros the boat to the starting battery and then to ground. That's about 8' that the current had to travel to make the starter work. Once I moved the starting battery to the same side as the switch and starter and shortened the cables, everything is now working as it should and the current path is only about 3'.

 

[jeepwx03]

Re: Battery starting and alternator issues

i have two starter batteries next to each other, right next to the starter, both grounded to the block with aprox. a 2 ft. cable. positive wires are similar lengths.

 

[wire2]

Re: Battery starting and alternator issues

Instead of cranking and feeling for heat, do it the right way and use a voltmeter and measure voltage drops across the various cables.

In theory that's a better way, Bruce, but you get only a second or so of cranking and the engine starts, especially if it's already warm. Then there's no appreciable voltage drop across a resistance connection of .1 or .2Ω

You could pull the coil lead and just keep cranking while measuring, I suppose.

Once current through a resistive joint heats it, it will stay warm for a while.

Bottom line solution;
open every connection, clean it, apply silicone grease or dielectric compound, tighten securely.

Jeep, your car stereo connectors, are they as large as the original connectors in the boat? If they're smaller, don't use them. Current transfer from 1 metal part to another is VERY dependent on surface area, and to a lesser extent, the actual metal. Silver is the best conductor, followed by copper, gold, aluminum, brass, iron, lead.

I'm not trying to teach physics here, just showing that a lead battery clamp needs to be much larger than a copper lug for the same ampacity.

 

[bruceb58]

Re: Battery starting and alternator issues

In theory that's a better way, Bruce, but you get only a second or so of cranking and the engine starts, especially if it's already warm. Then there's no appreciable voltage drop across a resistance connection of .1 or .2Ω.

If you have a .1Ω resistance, that would be way too much. You probably wouldn't even turn the starter with that much resistance. A starter is going to be drawing over 100 Amps. A .1Ω would be dropping 10V across that connection!

I stand by my suggestion to measure the voltage across all cables...including grounds.

 

[jeepwx03]

Re: Battery starting and alternator issues

Thanks for all the help guys! I figured out what the problem is. I took the battery switch apart and it was rusty and corroded. My left over connectors from the car stereo stuff is actually bigger then what was currently being used. I rewired the switch after cleaning it and was getting great starts and 14.55 volts at the batteries when the boat is running. i was able to run all weekend on only one of the batteries with no problems. I attached a picture of how bad it actually was. I'm not even sure how it was able to run for as long as it did.

 

[Haut Medoc]

Re: Battery starting and alternator issues

Yep, that would do it.....​

 

[SuzukiChopper]

Re: Battery starting and alternator issues

If you have a .1Ω resistance, that would be way too much. You probably wouldn't even turn the starter with that much resistance. A starter is going to be drawing over 100 Amps. A .1Ω would be dropping 10V across that connection!

I stand by my suggestion to measure the voltage across all cables...including grounds.

Actually, because the windings in the starter would be somewhere around 2ohms in series with the .1 or .2 ohm resistance of the wire, the starter is going to have the largest voltage drop across it, not the wire