Wednesday, Jul 19, 2017 at 12:37
A couple of comments and observations.
Prior the the battery nearing the end of it's bulk charging phase and beginning to "gas freely" ..yes sealed batteries gas but we don't want them to gas freely or excessivly. ... because excessive gassing causes damage to the plates and outpaces the recombination process ..... causing excessive pressure resulting in the battery venting. .... ( if the vents don't work the battery blows up like a balloon or the joints split, yeh seen it, changed it cleaned up the mess)
Anyway prior to that point .... voltage matters little, the limiting factors are current and temperature.
Most battery chargers are current limited by some means or another.
Calling it a constant current source realy is not correct ....... it is a current limited, voltage regulated source ... there are significant differences.
15 to 16 volts is nothing new for charging batteries ......
many old school tranny and rectifier chargers had open circuit terminal voltages in that range
One of my multistage chargers has a manually activated 16 volt cycle ... it is time limited and used for breaking down charge resistance and boost charging.
Now back to current limited chargers ........ this is something that is all to often overlooked.
Pretty much ALL of our
well engineered charging systems have some sort of current limiting factor. ... it is just that the advertising department does not go round blowing a trumpet about it.
It is very important that the charging system and the battery are sized with their limits in mind.
you may not think that current limiting is a factor in many systems but it is there
Even if you have a 100 amp alternator, there will be some sort of current limiting to prevent excessive current in the battery.
If you have a 100 amp alternator and a standard N70 battery ...... the ability of the charging system to deliver is limited by design to be within what the battery will tolerate.
Some vehicles with larger alternators and perhaps smaller batteries are effectivly current limited by use of small wiring in the charging path providing a series resistance ....... that wire might look reasonably beefy .... but do the maths and that fraction of an ohm is your current limiting factor.
My eyes where opened to this when I hooked up a 7Ah SLA to the charging system of my old Corrona which charged at 13.8 volts.
That reasonably healthy battery got quite hot quite quickly and greatly exceeded its maximum charge rate. ... like a matter of seconds as I held it.
I connected an older less healthy battery of the same size, the charge acceptance had suffered with age and the charge current was far less excessive.
I keep coming back to the issue, that within reason voltage matters very little, it is current and heat that are the parameters to be controlled.
It is current that will charge your battery
It is current that will break down sulphation
It is current that will cause excessive heat and it is current that will cause gassing and excessive gassing
It is current that will overload the sometimes inadequate internal connections in the battery.
Voltage only serves to cause the required amount of current to flow.
NOW many of the smaller and cheaper multistage chargers, change stages based on voltage alone, they have no current sensing capacity.
All but the upper end of the market multistage chargers lack on battery temperature sensors.
So much of the time charge voltages and stage changes are voltage based ..... because there is no means to do otherwise.
As long as the charger is not very large in comparison to the battery ( by that I mean will not produce more than the battery will safely accept) the maximum charge voltage of that initial stage is not particularly important ..... PARTICULARLY if the change from the first bulk charge stage to the second is current bassed. ... even more particularly if there is an on battery temperature sensor.
BECAUSE most of that charging step will be spent sitting on the current limit and the terminal voltage will be lower than its regulated point.
Now to the float charge stage. ...or in truth the "non boost charge stage"
Pretty much every lead acid family battery I have seen to date calls a long term stand by voltage of around 13.5 to 13.8 volts.
YES you can fully charge pretty much any healthy lead acid family battery from anything a little over 13.2 ish volts.
that voltage has be chosen as I have mentioned because it does not cause excessive gassing and heating.
exactly what voltage is selected is a compromise, the lower the voltage the less gassing, heating and lost energy, the higher the voltage the more electrolite loss and so
forth ......... designers will argue about this all day, many times i will come down to voltage steps and component values available.
13.8 volts is convienient because it is 23 (0.6V)silicon semiconductor junctions in series 14.4 is 24, 15 is 25 ..... they may seem to be wisely contrived voltages ... but it realy is near enough is good enough
These battery charger manufacturers try and baffle us with science, but much of what they offer simply is not borne out by battery manufacturer recommendations.
as for recommending a string of different voltages for different generic classes of batteries ........ here we are back at unreliable generalizations.
That maximum voltage limit on the initial charge stage is a compromise no matter the battery.
You could pretty much effectivly charge any lead acid family battery long term at an initial charge voltage limit of 14.4Volts ...... or push it at 15 volts or higher if you are in a hurry ....... as long as the stage is current or time limited and the charger is not too big for the battery.
Anybody who thinks this is a finely divided science is dreaming.
Cheers
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