Another battery problem?

[MapisM]

Is this what you guys describe as a 'smart' charger?

Indeed.
And according to its specifications (half of 4th page), charge voltage is:
28.5 when either in bulk or absorption mode
26.5 when in float mode (Q.E.D. )

Consequently, the 28.4 you mentioned in your OP is fine, if the charge mode was NOT float, when you spotted it.
And yes, I would think that a repeated use of several toilets could well have trigged, if not bulk, at least absorption mode.

I don't think it's easy to answer your "how long off charge" question, though.
Pretty sure it depends on the batteries state, their type, construction quality...
Fwiw, I did leave my FLA Trojan domestic batteries disconnected for more than a couple of months (probably three) several times, with no apparent deterioration.
YMMV, though.

 

[skipmac]

Mmm getting some mixed messages here chaps The last comment by skipmac may be correct in that prior to leaving the boat I had been flushing each of the toilets several times with disinfectant so its possible that could have kicked the charger into bulk charge mode

FWIW the charger is a Mastervolt Mass 24/75 charger which I assume is the original on the boat which makes it 10yrs old. Is this what you guys describe as a 'smart' charger?

Not specifically familiar with older Mastervolts but they are top end kit and ten years old was definitely NOT pre-smart chargers. I am 99% certain that is a three stage, smart charger.

In case you aren't familiar, they are typically three stage charging with an occasional fourth call equalization which is a method of short time, high voltage charging that keeps FLA and some other types/brands healthier for long term.

The three stages are:

Bulk - for when batteries are down and can safely take a high charge. Pumps a lot of amps in as fast as the battery can accept.

Absorption - batteries are +/- 80% charged and the charge acceptance is lower (internal resistance has increased) so rate of charge should be reduced to prevent overheating and battery damage.

Float - batteries are fully charged and the charger puts out just enough to maintain the battery fully charged without overcharging.

Bulk and absorption charge at the same voltage, for 24V system +/- 29V but the charger limits the amps during absorption. Float should be around the 26.5V you report you normally see.

Equalization would be as high at 30-31 volts but for a short period, maybe a couple of hours or so. This is usually done once every month or three depending on your batteries and how you use them.

Based on your information about multiple flushes just prior to checking the battery voltage I will hold to my original opinion.

 

[skipmac]

Back to the question about how long you can safely keep the batteries off the charger, as previously mentioned, there isn't an exact, down to the number of days answer.

My rule of thumb.

A week, certainly. A month, OK. Two months, probably OK. Three months I think is pushing the limits for maximum battery health and long life. You can go to the higher end of this range if the temps aren't tropical, there is no draw on the battery and the batteries are still in reasonably good shape.

Longer than 2-3 months I would prefer someone charging them up occasionally although leaving them 4-5 months would not bring absolute, certain death but not the best practice.

The specific factor that limits how long you can store a FLA battery is the rate of self discharge. For a new battery with no defects or any current draw that is about 5% per month. This rate increases with temperature, battery age and condition.

You say you normally see about 26.5 V when you leave the boat. That is consistent with the float voltage of a smart charger. If you turn off the charger and let the batteries sit for a few hours you should reach the true battery voltage called resting voltage which should be around 25.2V.

Assuming this to be the case a month off charge the resting voltage would be around 24V; two months 22.75V. Maybe check this if you're away for a while with the charger off.

 

[Portofino]

As I said its madness to turn the shorepower off and "smart" modern charger off --- on a big boat
Over and above "equalisation " of static batts see the Q+A at the foot re loosing 4% per week
http://www.progressivedyn.com/battery_basics.html

 

[A_8]

As I said its madness to turn the shorepower off and "smart" modern charger off --- on a big boat
Over and above "equalisation " of static batts see the Q+A at the foot re loosing 4% per week
http://www.progressivedyn.com/battery_basics.html

Each to their own I suppose and I read your comment on all the fuses etc that would keep the boat safe but consider a scenario where one of the individual batteries fails and start eating charge currents from the other batteries as well as the charger. Any intelligent charger will supply the current needed and the only way the charger would know anything is wrong is through the temp sensor...however the temp sensor can only measure at one place and in a big boat with lot of batteries one battery can be faulty (and getting hot producing flammable gases) and unless the temp sensor sits close by the faulty battery the system will keep eating currents and produce heat with higly fammable gases.
Eventually the faulty battery will have heated up the rest and the charger would notice something is wrong but that will take days or weeks with a few hundred kilo's of batteries.

I used think like you and keep my modern and intelligent chargers on at all times until this specific scenario happened, I don't anymore and would not advice anyone else to keep their charger on at all times. Put them on a timer if you can't get to the boat every 1-2 months or so.

 

[BartW]

Mike,

I'm not sure about the 28,4V when the charger is in float,
tbh I think it is too high, unless there was a reason for the charger to be in "bulk" or "absorbtion" mode
I have a small remote panel that shows with led's the workmode of the charger,
I don't remember the voltage that shows during each stage,
but I do know ao, that if I re-connect shore power that the charger will go for a short while in Bulk mode even if the batterys are full. in that situation, the bulk charge time is very short, but voltage should read something like 28,5V.

I'll check the voltages of each working mode, next time when I'm on the boat,
and then call Victron if I see unexpected values


apparently I am one of the few who alway's leave shore power on when away from the boat,
I found that It is almost impossible to get a zero consumption on the 24V DC systems, ao there is the alarm, and a wifi router for the camera, and a few other things that consume a small amount of electric,
so If I would witch off shore power, the battery's would be drained below 12V, which will cause damage.

moreover,
in a bank of several battery's, the internal resistance of each battery will not be the same, especially not when the battery's get older, the result is that battery's connected in a bank will discharge each other,
so much quicker than a standalone battery,
It is impossible to predict how long this will take, as it is depending on the quality and number of your battery's in one bank.
so that's anothe reason for me to leave shore power on.

in reality on my boat, it is impossible to leave the shore power off longer than 4...5 day's
(I have had a few accidental shore power disconnections during my absence)

It is easy to install a alarm, that send a message to your Phone when there is a problem with your 24V supply.

when I leave the boat, I arrange that as many as possible electric cirquits are switched off,
and the charger is in a stable float mode,
the statistical risc of something going wrong with electric is than VERY small

 

[Deleted User YDKXO]

Thanks guys for your additional comments. All very interesting. It sounds like my charger had kicked into bulk mode for some reason. Actually what I didnt mention is that I have 2 chargers on the boat and next time I'm on the boat I'll select the other one and see if the voltage behaves in the same way.

One final silly question. The charger obviously charges both engine and domestic battery banks. If the domestic batteries demand bulk charging, is the same bulk charging going into the engine batteries even though they may be fully charged?

 

[Portofino]

Each to their own I suppose and I read your comment on all the fuses etc that would keep the boat safe but consider a scenario where one of the individual batteries fails and start eating charge currents from the other batteries as well as the charger. Any intelligent charger will supply the current needed and the only way the charger would know anything is wrong is through the temp sensor...however the temp sensor can only measure at one place and in a big boat with lot of batteries one battery can be faulty (and getting hot producing flammable gases) and unless the temp sensor sits close by the faulty battery the system will keep eating currents and produce heat with higly fammable gases.
Eventually the faulty battery will have heated up the rest and the charger would notice something is wrong but that will take days or weeks with a few hundred kilo's of batteries.

I used think like you and keep my modern and intelligent chargers on at all times until this specific scenario happened, I don't anymore and would not advice anyone else to keep their charger on at all times. Put them on a timer if you can't get to the boat every 1-2 months or so.

I ve only got two pairs of 185 ah 12 v in series to give 24 V and up to 370 ah cap for each set -- house /engine .
With a "pararell " x-over on the dash ,so I can rob the house if neccassary when starting up .
For a 14.5 M boat -but you can scale up those numbers to 20M etc --principles the same -for bat management -as follows -----
Only one temp sensor per pair with AGM ,s I understand primary is to regulate the "bulk " --so,s not to ram too much of the 100ah available into the 370 capacity too fast .
So the charger needs a sample temp -of a batt it's pushing charge -ones enough .

I take your point re multiple bank of say 3 or 4 pairs and a temp sensor fitted on one of the middle pairs .
Middle due to "interconnect "issues more likely to be the one that fails 1st
Assume it's not fitted on the duffer as in your scenario .
Remember i f correctly installed there should be a fuse on the +ve out of the bank .
The duff /dead batt /middle /none temp sensored - as it fails ,heats up cos of inc resistance --then this fuse will blow and cut the charge supply to this chain of bats .
If that fuse does not blow (rember the temp sensor s on good bat ) then the other fuse on the unit will detect inc resistance
ER --- hopefully , and shut it down with appropriate alarm LED,s showing ?
Obviously I not tested this , nor my airbags on my car .

Also being having spent a life time on charge @ the mooring I would expect minimal Sulphating ,ie decrease chance of knackered -ness .....the very reason for the scenario in the 1st place ,if understand your illustration example correctly .

Got a guardian who cleans it ,check it every two weeks .One of the tasks is infact checking the shore power and charger is on indeed with the previous boat a Sunseeker it had trad wet lead acid batts ,he supposed to top up the water in them .
So with trad wet lead acid bats if they dry up and not so "smart "charger set up-- then sure you can cook a bat .

But for those folks ,with charger off they are looking at 4 % drop per week = increased Sulphating ='more knackered -ness .

Each to there own I guess

 

[Portofino]

Thanks guys for your additional comments. All very interesting. It sounds like my charger had kicked into bulk mode for some reason. Actually what I didnt mention is that I have 2 chargers on the boat and next time I'm on the boat I'll select the other one and see if the voltage behaves in the same way.

One final silly question. The charger obviously charges both engine and domestic battery banks. If the domestic batteries demand bulk charging, is the same bulk charging going into the engine batteries even though they may be fully charged?

No -mines a 2015 modal --so smart it has 3 outlets managed indipendantly
See the other thread from Medmillo .explaining how I know that !

If it did that ram "bulk " into a 98% ish charged engine bat it would blow it up.

 

[Deleted User YDKXO]

No -mines a 2015 modal --so smart it has 3 outlets managed indipendantly
See the other thread from Medmillo .explaining how I know that !

If it did that ram "bulk " into a 98% ish charged engine bat it would blow it up.

OK understood!

 

[skipmac]

Thanks guys for your additional comments. All very interesting. It sounds like my charger had kicked into bulk mode for some reason. Actually what I didnt mention is that I have 2 chargers on the boat and next time I'm on the boat I'll select the other one and see if the voltage behaves in the same way.

One final silly question. The charger obviously charges both engine and domestic battery banks. If the domestic batteries demand bulk charging, is the same bulk charging going into the engine batteries even though they may be fully charged?

Hi Mike,

I am 90% certain this is not a concern but let me do a bit of research to confirm.

I am 100% certain that as a battery reaches a higher state of charge the internal resistance of the battery increases so it will accept less charge. So connecting a 98% charged start battery in parallel with a bank of 50% charged house batteries, the house batteries will show a much lower resistance to the charger so will accept almost all of the charging amps while the higher resistance of the start battery will allow very little charge. True the starting battery will be seeing the higher bulk charge voltage but don't think it will immediately explode.

As a reference, there are many products used very commonly in boat charging systems that do this. With these devices all charging sources are connected directly to the house batteries: charger, alternator, solar, etc and the starting battery is isolated from the system. Then when any of the charging sources are active the device automatically connects the start battery to the system. This protects the start battery from accidental discharge as it is isolated from the house batteries but still allows it to be charged anytime charging takes place. I have not heard of any battery explosions happening with the use of these auto combiners so again, don't think this is a concern.