lossless 24v, 3 battery bank charging system.

[monkfish24]

Hello guys, my first post so hello all.

I've just moved from aeronautical to marine engineering. I have joined my first vessel as the sole engineer and was after some thoughts on charging a triple battery bank.

I have a 24v charger wired to a diode splitter, this has a 0.6v drop and then splits off to 3 banks of 24v batteries. These battery banks are made up of two 12v batteries. These batteries are used to start the two generators and main engine and nothing else.

I am currently seeing just over 27 volts on the charged batteries when sat on the charger, the skipper has complained that the batteries only last a year to fourteen months before requiring replacement. How previous engineers have tested these batteries to prove this, i don't know.

I am also getting warm batteries on only one set whilst they are being charged, by it's respective engine. Normally no more than 50°c.

So a couple of questions,

1) Am i seeing anything abnormal?
2) is the skipper expecting too much from the battery life considering each engine starts at least once a day
3) I have the task of upgrading the charging system if required, what would be my best set up?

I am an electrician by trade but due to mostly being on aircraft i have a lot to learn about DC and batteries.

 

[Compositepro]

Are these vented lead-acid batteries? Each battery chemistry has its own unique characteristics. And what do you mean by lossless? It doesn't seem to have anything to do with your question. Using one charger to charge batteries while they are in series and in parallel, and powering loads, never works well for numerous reasons. You probably need to be able to periodically switch-out individual batteries from service so you can give them a complete charge off-line. Individual cells never have exactly identical capacity so some must be overcharged slightly to completely charge others (this causes a little electrolysis of water). Voltage of individual cells will vary slightly. I suggest doing a Google search to find instructions about how to properly maintain your batteries. The manufacturer of your batteries is a good place to start.
The answer to your question is somewhat complicated and you have not provided enough information for one.

 

[IRstuff]

The typical car battery starts twice a day, and is charged in-situ by the car's alternator.

While the "charged" batteries are showing ~13.5V for each 12V battery, which is more or less normal, what's the actual voltage during charging. A typical car alternator hits around 14-14.5V, so anything more than that could be overcharging the batteries.

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[Compositepro]

Sorry, you did say that these are used only for starting. That does make it easier. You just need the correct type of charger which has the necessary controls to keep your batteries healthy. You also have to monitor the health of the batteries and the charger. One bad cell will keep the charger from working correctly and result in damage to the other batteries. And the batteries will go bad in 3-7 years. Occasionally sooner.
When the batteries are charging you should see over 28 volts, so this may indicate a problem. It is also possible that the charger switches to a lower voltage after it senses the batteries are fully charged.

 

[monkfish24]

Compositepro, Thank you, sorry i may have digressed from the title. They are sealed lead acid.

I was curious as to wether i should be seeing more than 27v, wether just one battery bank should be so warm whilst being charged from it's engine and what would be a more modern set up than a diode splitter.

I'm afraid your post comes off rather prickly for a reply to a first post on a forum.

 

[Compositepro]

Now that you mention the diode splitter again, it could be a major problem. Dropping the the actual charging voltage to the batteries by 0.6v completely upsets how the charger works. You will not get the voltage high enough for the equalizing charge part of the cycle which completes the charge of a low cell after the other cells in the series are already charged. This will result in one cell going bad eventually. Why do you have a diode splitter if these batteries are only used for starting. I guess this may be why I thought you were running other loads.

 

[monkfish24]

Compositepro,

Thankyou, i was making the assumption that the diode wasn't helping. I'm not sure why it is there, i have only been on the vessel for two weeks and it was fitted previously.

What could i fit to ensure that all the batteries get the charge they require?

 

[Compositepro]

You may just need to take the diodes out. Make sure the wires connecting the batteries to the charger will not burn-up due to cranking one generator and drawing current from the other battery banks. This may be why the diodes are there. An adequate wattage resistor or long enough wires will work better because they will not change the final, full-charge voltage applied to the batteries. Or better is to provide separate chargers. Chargers are designed for the battery capacity and may very well not work correctly if applied to too many batteries at once.

 

[GregLocock]

I'd say your post comes off as rather clueless even for a first post, for an engineer. What capacity are the batteries? What is the current draw when starting? How long does it continue for? what do the battery specs say about that? How hot is warm?





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[waross]

I am also getting warm batteries on only one set whilst they are being charged, by it's respective engine. Normally no more than 50°c.

If the engines charge their own batteries, why do we have a charger?

I am currently seeing just over 27 volts on the charged batteries when sat on the charger

That is a normal, charging voltage for 24 Volt lead Acid batteries.

I am also getting warm batteries on only one set whilst they are being charged,

May be a shorted cell

I have a 24v charger wired to a diode splitter

These splitters work without problems in millions of RVs.
Your batteries are possibly failing from excessive vibration.

Bill
--------------------
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Jimmy Carter