Domestic battery bank shows 11.8v, charger on «*float*»...

Minn said:
Which has gone pear shaped - the batteries or the charger?

Starter batteries happy as Larry... is it possible that the charger is sensing them ? But it is designed to handle up to three banks.
Click to expand...

Depends on charger design, some have one output which split via three diode to give you three outputs, one diode may have blown feeding domestic battery output.
Brian
 
Is 11.8V across the batts, or at the charger o/p? Bad connection?

If batts: test to see if one is duff, then recharge ASAP and cross your fingers.

Depending on above: can you individually test the voltage across each of the three charger outputs?
 
Isolate and measure each battery individually. Are they sealed or can you measure the specific gravity of each cell?

Next step is to get charger on ASAP. Check that it's charging, but don't worry too much if voltage is a bit low as it may be current maxed out. If all batteries have similar initial resting voltage, you can charge all together, but check that one batt doesn't start to overheat. If one batt is dud, chuck it.

After a few hours, disconnect and run a few power systems - doesn't matter which - off each batt to see if one collapses early. Then see if you can fully charge them overnight.
 
Last edited:
Oh no, top quality AGMs ...well worth a bit of blue light :distress:

Forget about specific gravity then, and see what you find. Also check the warning lights on that charger, not to forget the fuse. And check that it's set to AGM.
 
Last edited:
Charger is behaving normally - shows
- it is sensing AGMs
- if turned off then on, goes to timed constant charge, then quickly to float charge.

I had to leave the boat but before doing so I took the gas detector - a very thirsty beast - off line, having of course turned the gas off at the bottle.
 
Minn said:
Charger is behaving normally - shows
- it is sensing AGMs
- if turned off then on, goes to timed constant charge, then quickly to float charge.
Click to expand...

How many amps were the batts taking during the constant current phase?

All constant charge generally means is that the charger is whacking out all it can, unless some fancy limiting algorithm has been programmed in. It should then go to absorption for a while, and then float.

However: depending on current flow, good chargers are set-up not to keep going into absorption following a short power outage: AGMs can easily be overcharged like this. That's why we need to check the current delivery during the constant current phase.

Also, as this is getting a bit blue-lighty, do double check all connections and test for any excessive resistance in the cables.

Edit: do remember that AGMs can mostly be discharged a lot deeper than standard lead acid. 11.8V is probably discharged to 25-30% of capacity, which is hopefully within the operational parameters. Just!

Edit 2: Naturally well ventilate batt locker + boat. Also listen carefully for any hissing sound as well as keeping an eye on temp. If any hissing is detected, stop charging and remove suspect batt.
 
Last edited:
The batteries will have their lives shortened by leaving them down at 11.8, assuming they are not already dead.
It does not sound like the charger is doing its job.
I'd suggest disconnecting the engine start battery, maybe try connecting that output to the house bank.

It hey were my batteries, I would separate the house bank into individual units if the bank as a whole cannot be got up to a sensible voltage.

I would suggest not leaving this unattended, if it starts putting lots of current into a duff battery, there is fire potential.

I do not like 'multi bank' chargers, people who have them never seem to be terribly clear about how they are deciding each bank needs boosting or floating.
 
Sounds plausible: in which case I'd just disconnect the starter batt and jury-rig that charger o/p to the house bank in order to get the recuperative charge under way. Then sort it out properly later.
 
It's important to make sure one battery hasn't failed (as mentioned above) before trying to charge them back up. If a cell has shorted in one battery, charging the bank has the potential for a fire or exploding battery.

If you're sure there isn't a failed battery, disconnect the negatives from the engine batteries and turn the emergency parallel switch on. That will allow the engine battery output of the charger to charge the domestic bank, should help identify if the charger has failed.
 
PaulRainbow said:
It's important to make sure one battery hasn't failed (as mentioned above) before trying to charge them back up. If a cell has shorted in one battery, charging the bank has the potential for a fire or exploding battery.

If you're sure there isn't a failed battery, disconnect the negatives from the engine batteries and turn the emergency parallel switch on. That will allow the engine battery output of the charger to charge the domestic bank, should help identify if the charger has failed.
Click to expand...

Paul - if a battery has failed, surely the charger would be working overtime rather than announcing that it was at “float”?

Or am I missing something?
 
Minn said:
Thanks very much. One possible explanation is that the charger is only connected to the starter batteries...ie there is a loose connection somewhere.
Click to expand...

Minn said:
Paul - if a battery has failed, surely the charger would be working overtime rather than announcing that it was at “float”?

Or am I missing something?
Click to expand...

It should be working as you think, but i'd still want to check the batteries before leaving the boat unattended.

Check the voltage at the charger outputs, on each of the three outputs. All should be similar. If the domestic output is 11.8v ish and the un-used one is float voltage, move the domestic cable to that output. If the only output that is charging correctly is the engine bank, then use that one as a short fix, or try charging with the emergency combine switch turned on.

But, if any of the charger outputs has failed, it's time for a new charger.
 
Minn said:
Paul - if a battery has failed, surely the charger would be working overtime rather than announcing that it was at “float”?

Or am I missing something?
Click to expand...

only if connected to charge circuit. also depending on sensed voltage many chargers will lock-out around 10.5V assuming that the batt is dud. some are programmed to similarly lock-out based upon other characteristics.
 
Minn said:
Paul - if a battery has failed, surely the charger would be working overtime rather than announcing that it was at “float”?

Or am I missing something?
Click to expand...

What happens to the voltage if you turn the charger off ? have you tried swapping domestic charger output with a engine output ? a shorted cell would have a very hot battery, basically a 10 volt battery in circuit with a 12 volt battery.

Brian
 
You must log in or register to reply here.

Other threads that may be of interest

W
Battery suicide
Replies
17
Views
655
Refueler
Refueler

Share this page

Top