Battery charging problem

[xavpil]

Hi all
My starter, windlass and bow thruster batteries (regular 12 V) are not getting charged properly.
I have
2x 400w solar
2 Victron mppt
2x 200Ah Dakota lithium
Multiplus inverter charger
DC to DC charger

What’s happening:
When engine running my ENGINE BATTERY ( name shown on my dashboard) goes from 11v to 14.1v. as we drive.
When the engine stops and I am only solar power or shore power the battery level keeps going down to 11.9…
And now I noticed my windlass and bow thruster batteries are also under 12v.
I can’t remotely monitor the charge level of these two batteries so I don’t know if they are getting charged while the engine is running but I doubt it because after 14 h of engine working the bow thruster died on me….

NOTE: the victron DC to DC charger is missing the remote HL switch and on the Victron app it says it is Off….. I am trying to find a replacement switch of course but regardless, the DC to DC has nothing to do with charging the windlass, starter and bow thruster batteries, right?

Any ideas of what to look for?

 

[JBP-PA]

Hmm, unless the DC-DC charger has a fault and is draining the batteries it is meant to charge. Seems like something is drawing them down.

Can you put an ammeter on the starter/windlass/thruster batteries when they are supposed to be idle?

Then again, it could just be that your batteries are worn out. Did you check the water?

 

[xavpil]

when they are supposed to be idle?

English is my second language: what does this mean:

 

[JBP-PA]

"Not being used". When the battery is not being used, the current at the battery should be zero. If you find a current draining them you can start trying to figure what is causing it.

 

[dlochner]

When battery voltage drops below 12.5v when it is not being used, it is an indication the battery is at its end of life. When the voltage goes up to 14.1 while running the engine it shows the battery is being charged, however, when it drops back to 11v, it is not accepting a charge.

How old are the batteries?

he DC to DC has nothing to do with charging the windlass, starter and bow thruster batteries, right?

Depends on how the charger is wired. A common practice is to use a DC-DC charger to charge thruster and windlass batteries because a smaller wire can be run to the batteries typically in the bow. This saves money (less expensive wire), weight, and is easier to run smaller wires.

If you have a wiring diagram you can share, it would be most helpful, otherwise we are just guessing.

 

[JoeWhite]

My guess as mentioned above, one battery may be bad and draining the other batteries.

 

[xavpil]

My guess as mentioned above, one battery may be bad and draining the other batteries.

I learned from the previous owner that they are 6 years old so yes, I should change them.
But there is still the mystery of knowing how/if they were getting any charge, especially with a DC to DC being Off ....

 

[BarryL]

Hello,

On my Jeanneau 409 when the engine is running the alternator charges ALL batteries. I have 4 batteries for the 'house' which run electronics, refrigerator, lights, pumps, etc. I have battery dedicated to start the engine. In the bow area I have 2 batteries for bow thruster and windlass.

Again, when the engine is running all 7 batteries are being changed. On shore power, the battery charger will charge all 7 batteries. I have a small solar panel, that will ONLY charge the 4 house batteries.

My batteries are all standard deep cycle flooded lead acid, except for the engine start battery with an AGM.

The ONLY way I know how to tell if a battery is being charged is to use a multimeter to measure the voltage of the battery. Measure the voltage with the engine off. Start the engine, measure again. If the voltage goes up then the battery is being charged by the alternator.

DLochner - can you explain how a DC DC charger allows you to use a thinner gauge wire? Are we talking 12V or or something else like 48V being changed to 12 or 24V at the thruster? I don't understand.

Barry

 

[xavpil]

On my Jeanneau 409 when the engine is running the alternator charges ALL batteries. I have 4 batteries for the 'house' which run electronics, refrigerator, lights, pumps, etc. I have battery dedicated to start the engine. In the bow area I have 2 batteries for bow thruster and windlass.
Barry

We had the exact same setup, Barry, until I upgraded to a solar system with house lithium, but kept the original acid batteries for starter/bow/windlass.. However my electrician is lost in the set up and doesn't really know what is doing what... yes... I can't believe it either.
The DC to DC had been in the Off position since the beginning in fact. (a part is missing).

Thanks for the great tip about the alternator

 

[dlochner]

DLochner - can you explain how a DC DC charger allows you to use a thinner gauge wire? Are we talking 12V or or something else like 48V being changed to 12 or 24V at the thruster? I don't understand.

Thrusters and windlasses use short durations of high currents which ends up being not very much total power when measured in watt hours or amp hours. Because the amperage draw is high 100+ amps they need heavy gauge 1/0 or fatter cables to safely carry the power. The batteries need to be connected to a charging source, either a dedicated charger or to the charging bus. In operation if the windlass/thruster battery is connected to the main charging buss, the buss where all charging occurs the cables connecting the battery to the buss must be capable of carrying the 100+amp load over a long distance. In a 40 foot boat the round trip distance could easily be 60 feet.

Looking at an ampacity table it is necessary to use a 4/0 cable to have a 3% voltage drop or a 4 ga cable for a 10% loss. Those are pretty big cables which spend a lot of time just sitting there doin nothing.

By using a DC-DC charger, the windlass/thruster battery is disconnected from the main charging bus because it has its own dedicated charger. A Victron 12v 30a charger has a continuous output of 30 a with a 10% efficiency loss charger will draw about 35-40a to provide the 30a charging current. The charger should be located near the batteries. Going back to the ampacity tables, we only need a 1 gauge wire for a 3% voltage drop or an 8 ga wire for a 10% voltage drop. In practice, the max wire size this particular charger can accept is 6 ga, so that would the size I would use.

This works because the thruster/windlass battery is not directly connected to the alternator or charge bus and because only a small amount of energy is actually used, a 30a charger will easily maintain a battery bank up to about 200ah, or 2 group 31 batteries when used to charge windlass and thruster batteries.

Doubling the voltage to 24v reduces the amperage by half, instead of needing 40a for the charger, it drops to 20a, for a 3% voltage drop only a 6ga wire is needed.

 

[Davidasailor26]

The ONLY way I know how to tell if a battery is being charged is to use a multimeter to measure the voltage of the battery. Measure the voltage with the engine off. Start the engine, measure again. If the voltage goes up then the battery is being charged by the alternator.

Check the voltage at each battery’s posts with all of the chargers off. Then start the engine and check them all again. Any batteries whose voltage goes up (usually by at least a volt) are charging somehow (either directly or through the alternator). You can repeat with the solar and shore chargers (independently to not get any measurements confused). Beyond that you’ll probably need to start tracing wires to see what goes where, but the voltage tests are a really good starting point compared to guessing just based on effects.

 

[xavpil]

Thrusters and windlasses use short durations of high currents which ends up being not very much total power when measured in watt hours or amp hours. Because the amperage draw is high 100+ amps they need heavy gauge 1/0 or fatter cables to safely carry the power. The batteries need to be connected to a charging source, either a dedicated charger or to the charging bus. In operation if the windlass/thruster battery is connected to the main charging buss, the buss where all charging occurs the cables connecting the battery to the buss must be capable of carrying the 100+amp load over a long distance. In a 40 foot boat the round trip distance could easily be 60 feet.

Looking at an ampacity table it is necessary to use a 4/0 cable to have a 3% voltage drop or a 4 ga cable for a 10% loss. Those are pretty big cables which spend a lot of time just sitting there doin nothing.

By using a DC-DC charger, the windlass/thruster battery is disconnected from the main charging bus because it has its own dedicated charger. A Victron 12v 30a charger has a continuous output of 30 a with a 10% efficiency loss charger will draw about 35-40a to provide the 30a charging current. The charger should be located near the batteries. Going back to the ampacity tables, we only need a 1 gauge wire for a 3% voltage drop or an 8 ga wire for a 10% voltage drop. In practice, the max wire size this particular charger can accept is 6 ga, so that would the size I would use.

This works because the thruster/windlass battery is not directly connected to the alternator or charge bus and because only a small amount of energy is actually used, a 30a charger will easily maintain a battery bank up to about 200ah, or 2 group 31 batteries when used to charge windlass and thruster batteries.

Doubling the voltage to 24v reduces the amperage by half, instead of needing 40a for the charger, it drops to 20a, for a 3% voltage drop only a 6ga wire is needed.

WOW!!
i ll have to read this a few times to understand but thanks a lot for the education.
so a dc to dc dedicated to the windlass/bow thruster batteries is a good idea

 

[dlochner]

WOW!!
i ll have to read this a few times to understand but thanks a lot for the education.
so a dc to dc dedicated to the windlass/bow thruster batteries is a good idea

The part many people have trouble getting their minds around is how a high current draw, like a windlass, thruster, or starter, can use very little energy. It's all in the math.

Stored energy in the battery is measured in amp hours. An amp hour is 1 amp of energy used in 1 hour, so a 100 ah battery could support a 1 amp draw for 100 hours, a 2 amp draw for 50, and so on.

Assume the thruster is used for 6 seconds and it draws 100 amps. To calculate the energy consumed multiply the draw (load) by the time, 100 amps * 6 seconds. There are 3600 seconds in an hour (60 seconds * 60 minutes), thus 6 seconds is equal to 0.0017 hours. Doing the math, 100a * 0.0017 hours = 0.17 amp hours.

It is necessary to have a large enough cable to allow the 100 amps to pass through easily even though it is only used for a short time. Think of 100 cars going down a road, In a multi-lane highway 100 cars can pass quickly while in a single lane road it will take a long time even if the cars are traveling at the same speed in both situations. It's more or less the same with electrons in wire, bigger wires have less resistance than smaller wires and can allow more amps to pass easily.