One engine starts fine the other doesnt but with a twist

[StormSplurge]

Hey all,
So, I have a sundancer 300 with twin 350 mag mpi motors. four batteries with two battery switches. The starboard motor cranks fine. The port motor always struggle with starting like the batteries are dead. After starting the starboard side, I can use the the button thats between the start buttons (I dont know what that button is called), to start the port motor and it cranks fine. I checked the batteries, disconnected of course, and all four are between 12.6 and 12.7, which is fine i believe. The terminals are clean and tight. Im gonna follow the cables to see if there is come corrosion somewhere else, but I thought I would ask here to see if anyone else might know or have any ideas. Thanks all.

 

[markrsimon]

How old are the batteries? Have you load tested them? Do you have two for port, and two for starboard - or three and one? (or is one for the gwnerator) Are they all dual purpose, deep cycle, or starting batteries? Guessing regular lead acid batteries.

Throwing out a guess without any info - you have a single battery on the port side, and its a deep cycle thats 3+ years old?

Pictures of the batteries so we can see how they are wired would also help.

 

[ttmott]

Swap the batteries and see if the issue follows that.
More than not the negative cables and their terminations end up being the issue.

 

[StormSplurge]

Swap the batteries and see if the issue follows that.
More than not the negative cables and their terminations end up being the issue.

Pulled all the cables, cleaned and ohmed and they are all good. It seems to be a bad connection somewhere between where the button on the dash is and the battery connection. And there lies the problem. The negative cables go right to a ground bar right on the bulkhead in the engine compartment. The positive? Uh, through the bulkhead and who knows where. I would think they would go to the battery switches, then a main power board to go around the boat for misc power. From there a relay or something to the engine start switch and back to relay to power the starters. Anyone else have any experience with this?

 

[techmitch]

Thoroughly check the large ground connections on the engine block.
Remove, clean, reinstall tight and protect whether it looks like they need it or not.

 

[StormSplurge]

How old are the batteries?

probably a few years old. I bought the boat 2 years ago and they were in it.

Have you load tested them?

No, but on my list to do. They do have 12.6 or 7 volts each so I think they are ok, but...

Do you have two for port, and two for starboard - or three and one? (or is one for the gwnerator)

two starboar two port. Gen runs on one set, but I dont know which one at the moment. Port motor starts with starboard set of batteries, starboard motor from port. I have no idea why they did that.

Are they all dual purpose, deep cycle, or starting batteries?

Dual

Guessing regular lead acid batteries.

Yes

Throwing out a guess without any info - you have a single battery on the port side, and its a deep cycle thats 3+ years old?

Pictures of the batteries so we can see how they are wired would also help.

I will get a pic, but the batteries are set up two port in parallel and two starboard in parallel.

A quick drawing.

 

[Golfman25]

Check that the batteries have water. I had a similar situation. Battery exploded when I hit that crossover switch.

 

[Lazy Daze]

It doesn't sound like a dash switch issue to me.

As noted above, it's still a good idea to load test. Battery voltage is different than amperage. Swapping batteries is a good quick test to check if the batteries or the wiring is the issue.

In addition to the other things mentioned to check, pull your battery switch and check those connections. Even swap switches if you want.

 

[ttmott]

Pulled all the cables, cleaned and ohmed and they are all good. It seems to be a bad connection somewhere between where the button on the dash is and the battery connection. And there lies the problem. The negative cables go right to a ground bar right on the bulkhead in the engine compartment. The positive? Uh, through the bulkhead and who knows where. I would think they would go to the battery switches, then a main power board to go around the boat for misc power. From there a relay or something to the engine start switch and back to relay to power the starters. Anyone else have any experience with this?

continuity (ohmed) doesn't validate cable/connections will carry the current needed.

 

[markrsimon]

That switch between the two starting switches is your 'emergency start' switch. Its a solenoid that connects both +POS cables of each battery bank together. Allows you to use all batteries at once -- or get the additional power from the alternator of the running engine.

Given that it just ties your Positives together, your issue would seem to be (a) the ground cables on the [bad] port engine side, or (b) the port engine batteries themselves.

Swapping batteries is a good/easy test. Getting them load tested -- a bit more work, but worth the effort.

Would also be a good time to make sure your battery charger is working as expected (eg: charging both banks).

 

[Jimmy Buoy]

My suspicion is that you have a battery issue. Even a bad battery can produce a 12vt or more reading on your multimeter. That doesn't mean that the battery won't fall flat on its face when called upon to provide amperage (like when you hit the starter switch).

Testing the battery without the positive post attached with a LOAD TESTER will quickly determine if the battery is capable of providing the cranking amps required. Load testers are relatively inexpensive and easy to obtain. My old one uses a heat element (like a toaster) that when the test button is pressed and the battery is connected, will begin to glow red hot. I count to 10 holding the test switch down and watch the meter to see if it stays in the "green zone". If not - its a fail.

A friend was going to buy a used battery and borrowed my tester. The battery was fully charged according to the seller and was at 12.8vts however it failed the load test miserably (went as low as 3vts when the button was pressed. He obviously passed on the used battery! The seller pretended not to know but he made sure to shine the battery up to look like new - it was purdy after all!

 

[waterman]

You probably have a bad starter or solenoid on the starter. It is not leting enough amperage thru to turn the starter, or the starter brushes are dragging. Thats why when you give it more amps from all 4 batteries thru thr emergency start switch it will start