Starting voltage

[David W]

Hi everyone, looking for some perspective on something I noticed last weekend.

Engine: 2QM15, circa, not this decade

Starts in just a few cranks when the shorepower is connected and Xantrex 20 is on.

Shorepower disconnected and starting takes more cranking and use of the preheater to get her to fire. Even when the shorepower has only been disconnected 15 mins or so.

Exactly the same throttle position and air temperature in both situations.

Battery setup is two group 27s house bank, one group 24 for starting. When I start the boat, I combine all batteries.

On the hook, I see a resting battery voltage of 12.5 to 12.65 volts. On the charger, voltage is 13.2 volts.

She's clearly capable of firing off quickly. I have to assume the higher voltage is spinning the starter faster leading to a quicker start.

Any opinions on how I can achieve a "plugged in" starting experience when unplugged?

 

[Paul Mermelstein]

It's hard to tell but you may have one (or two) battery(ies) starting to fail that draws off some current from the others when you combine them for starting. Isolate each battery (disconnect them entirely) and test for voltage. If one is low, then voila. If not, then hook up each battery one at a time and try starting the engine. Any one of those batteries, if healthy, should start the engine. If you observe a slower or non-start situation with any one battery, that is the weak one.

 

[David W]

It's hard to tell but you may have one (or two) battery(ies) starting to fail that draws off some current from the others when you combine them for starting. Isolate each battery (disconnect them entirely) and test for voltage. If one is low, then voila. If not, then hook up each battery one at a time and try starting the engine. Any one of those batteries, if healthy, should start the engine. If you observe a slower or non-start situation with any one battery, that is the weak one.

Thanks Paul, that makes sense. The batteries are not all the same vintage: the starting battery came with the boat when we bought it so it is the oldest at at least 8 years old. The two house batteries are newer but are about a year apart in age.

I'm thinking it is time for trio of new batteries.

 

[Paul Mermelstein]

Yeah, when your batteries are all connected together you will see the composite voltage, and that masks weakness in any one. Plus, eight years is very old for a battery. It is advisable to replace all batteries at the same time.

 

[Bill Roosa]

If all you are seeing is 13.2 volts when the charger is on then something is wrong. Those batts would be suffering from chronic undercharging. Should be something like 13.7-14.4 volts while the charger is on.
Turn on the charger then measure the voltage "on the terminal" and on the wires. since 99.44% of all electrical problems are corrosion you may just need to clean and then give them a good charge to fix the problem

 

[Maine Sail]

If all you are seeing is 13.2 volts when the charger is on then something is wrong. Those batts would be suffering from chronic undercharging. Should be something like 13.7-14.4 volts while the charger is on.
Turn on the charger then measure the voltage "on the terminal" and on the wires. since 99.44% of all electrical problems are corrosion you may just need to clean and then give them a good charge to fix the problem

Depending upon which float setting is chosen, and temp compensation setting, 13.2v is entirely plausible for that charger, if he's in float.

Sounds like some old tired batteries to me...

 

[DougMc]

You need to test with a a hydrometer.(cheap) Fill it and then empty 4 or 5 times before taking a reading. It is one of the best battery monitors. I learned this after having the same problem. Turned out my new 40 amp Xantrex charger had defective software. Charger killed one battery and took a of life out of two more. Charging should be 14.2 and float above 13.4. Checking battery by voltage can only be done after battery has all load or charging totally disconnected for 24-48hours.

 

[David W]

Depending upon which float setting is chosen, and temp compensation setting, 13.2v is entirely plausible for that charger, if he's in float.

Sounds like some old tired batteries to me...

The charger is set to bulk/absorption/float on the flooded battery, with the temp setting adjusted according to season. The 13.2v is the float voltage. The resting voltage is what I typically see in the morning after a night at anchor. We use minimal power: no fridge, Oil lamps or LEDs on disposable batteries, no stereo. Really basic setup.

 

[David W]

If all you are seeing is 13.2 volts when the charger is on then something is wrong. Those batts would be suffering from chronic undercharging. Should be something like 13.7-14.4 volts while the charger is on.
Turn on the charger then measure the voltage "on the terminal" and on the wires. since 99.44% of all electrical problems are corrosion you may just need to clean and then give them a good charge to fix the problem

Whoops should have said 13.2v was on float. On bulk mode it shoots up into the mid-14's.

 

[Stu Jackson]

In addition to the earlier responses, 99% of electrical issues are in the CONNECTIONS. Inspects, remove and CLEAN, all of your electrical connections" batteries, 1-2-B switch, starter, batteries, you name it.

Or your banks are dead or going there. Check at resting voltage with a hydrometer.

NOT a good idea to combine banks UNLESS charging is present, 'cuz the bad bank will draw down the good one.

 

[Benny17441]

I indeed sounds like tired batteries. Charged to 100% but not holding adequate storage capacity.

 

[NYSail]

8 year battery probably is failing and killing your newer ones. A single battery should be plenty. Go to SAMs club and get some new duracells and start fresh.

 

[David W]

8 year battery probably is failing and killing your newer ones. A single battery should be plenty. Go to SAMs club and get some new duracells and start fresh.

Thanks all, looks like I'll be shopping for some new batts. I can squeeze in a pair of T105's. Seems like a lot more capacity in the same footprint. Comments?