Trojan batteries

[lw395]

Just found some actual data from August in the algarve, 300W solar, 2 x t105 batteries so 225Ah when new. Flat and absorption both set to 14.8v from memory. If float was set lower then little chance of getting to full charge. As it is it looks doubtful if 100% SOC would be reached these days.

I assume that the periodic stepping is caused by the fridge cycling?
It's actually asking a great deal of the Victron controller to work out when a battery is fully charged with a load cycling like that.
Rather than hold the battery volts at 14.7 or whatever absorption, what's actually happening is almost 100% of the time, the controller is chucking out as much power as it can.
If this sort of thing is happening, fretting about having the latest edition of the firmware is at best, a distraction.

 

[noelex]

What's the equalization charge I have seen mentioned please.

An equalisation charge is a special very high voltage charge that is done periodically, primarily to reduce electrolyte stratification and sulfation.

It is recommended for some battery types, especially flooded lead acid batteries.

You should check your battery manufacturer’s details to see if this is suggested for your battery and exactly how this should be done.

An example would be to do an equalisation charge once a month consisting of keeping the battery at 16v for two hours.

 

[noelex]

Rather than hold the battery volts at 14.7 or whatever absorption, what's actually happening is almost 100% of the time, the controller is chucking out as much power as it can.
If this sort of thing is happening, fretting about having the latest edition of the firmware is at best, a distraction.

Yes, if the controller is never reaching regulation then the charging algorithm is irrelevant.

The new software has some cool features such as graphs and a measure of the total power output if you have multiple controllers, but the much improved charging algorithm is only of benefit in helping to prevent over or undercharging the battery when the output of the solar array, or other charge sources is enough that the battery is reaching a reasonably high state of charge.

 

[vas]

I assume that the periodic stepping is caused by the fridge cycling?
It's actually asking a great deal of the Victron controller to work out when a battery is fully charged with a load cycling like that.
Rather than hold the battery volts at 14.7 or whatever absorption, what's actually happening is almost 100% of the time, the controller is chucking out as much power as it can.
If this sort of thing is happening, fretting about having the latest edition of the firmware is at best, a distraction.

you are right, but how can one deal with that?
following this thread and having spent the last 3-4 mornings on the boat, next to the BMV700 and monitoring the Victron MPPT 100/30 via bluetooth, I'm about to give up!
OK, starts in the morning with as much as the panels can dump, MPPT reporting bulk, voltage circa 27, amps 12-15
by 11am it manages to switch to absorption which I guess means that MPPT managed at last to up the voltage to 29.6V, amps around 10-15again
sometime in the afternoon it goes to float and drops to 27whateverV and around 1A

Now the Amp values is a deduction from what the MPPT reports as pumping and what the BMV reports as going to the batteries. Well, it's more or less what the BMV reports as one or two fridges (at 2A each) kick in and out (ambient in galley/salon at 30C...)

OK, I can make some sense out of that, but I wonder how does the MPPT know when it's OK to go to float since it does get requests for an extra 5-6A from devices???
BMV is installed correctly btw, E V E R Y T H I N G goes through it (spent ages doing it!)

V.

 

[lw395]

An equalisation charge is a special very high voltage charge that is done periodically, primarily to reduce electrolyte stratification and sulfation.

It is recommended for some battery types, especially flooded lead acid batteries.

You should check your battery manufacturer’s details to see if this is suggested for your battery and exactly how this should be done.

An example would be to do an equalisation charge once a month consisting of keeping the battery at 16v for two hours.

Equalisation is making sure the cells in a battery are all equally fully charged.
To do that, any cells which are more charged than the others will be over charged and will gas a lot.
In healthy batteries it is mostly about acid stratification, which can make some cells gas before they are fully charged. The gassing stirs the acid as well as forcing the whole cell to charge.

Sulphation and desulphation is a whole other minefield. Much snake oil and mumbo-jumbo.

Ideally you should avoid the need for equalisation by charging the batteries with enough current to stir the acid in the first place.
Equalisation is not kind to batteries, it's better not to do it if the cells are already equal. If the cells all need the same amount of water, you probably don't have an equalisation problem.

You can also equalise your 6V batteries by charging each one alone, not as a 12V pair.

The other 'equality' point is to be sure two parallel strings of batteries are equally charged. Some people would charge each string separately now and then.
Or even every time in some non-boaty applications.

 

[noelex]

OK, I can make some sense out of that, but I wonder how does the MPPT know when it's OK to go to float since it does get requests for an extra 5-6A from devices???
BMV is installed correctly btw, E V E R Y T H I N G goes through it (spent ages doing it!)

If the charge algorithm is set up well, it will respond to these challenges fairly well in most circumstances.

If there is a reasonable load then the controller will drop out of float and return to the bulk state of charging. This is controlled primarily with the bulk return voltage.

The Victron controllers label this slightly differently as the “Re-bulk voltage offset”. This is adjustable by entering the expert mode, although the default setting works well for most systems. Only alter the default value if you are sure the controller is not returning to the bulk phase appropriately.

 

[lw395]

you are right, but how can one deal with that?
following this thread and having spent the last 3-4 mornings on the boat, next to the BMV700 and monitoring the Victron MPPT 100/30 via bluetooth, I'm about to give up!
OK, starts in the morning with as much as the panels can dump, MPPT reporting bulk, voltage circa 27, amps 12-15
by 11am it manages to switch to absorption which I guess means that MPPT managed at last to up the voltage to 29.6V, amps around 10-15again
sometime in the afternoon it goes to float and drops to 27whateverV and around 1A

Now the Amp values is a deduction from what the MPPT reports as pumping and what the BMV reports as going to the batteries. Well, it's more or less what the BMV reports as one or two fridges (at 2A each) kick in and out (ambient in galley/salon at 30C...)

OK, I can make some sense out of that, but I wonder how does the MPPT know when it's OK to go to float since it does get requests for an extra 5-6A from devices???
BMV is installed correctly btw, E V E R Y T H I N G goes through it (spent ages doing it!)

V.

I don't get involved with Victron kit on boats.
But a modern car for example controls the battery voltage according to what the battery monitor measures, not just what the alternator 'sees'. So the charge controller is not confused by turning loads on and off. Cars of course have different priorities and there is a lot of software calculating the state of charge, optimising the charging and reducing fuel consumption. There are many ways of deciding when a battery should go to float, from simple timers through to measuring the battery's response to pulses of current and lots of proprietary stuff.
There seem to be a lot of different configurations of Victron kit, a lot of settings to fiddle with and a variety of firmware.

 

[sailaboutvic]

You can also equalise your 6V batteries by charging each one alone, not as a 12V pair.

The other 'equality' point is to be sure two parallel strings of batteries are equally charged. Some people would charge each string separately now and then.
Or even every time in some non-boaty applications.

Surly if you try and equalise a 6v batteries with a MPPT that set for 12v you damage the batteries .
Wouldn't you need a charge for 6v charging that will equalise?

 

[lw395]

Surly if you try and equalise a 6v batteries with a MPPT that set for 12v you damage the batteries .
Wouldn't you need a charge for 6v charging that will equalise?

Yes you'd need a 6V smart charger, or you'd need to know a little about electronics.