Bulk voltage is a bit of a misnomer as during bulk charging, voltage can start as low as 10.5v if the battery was drained that low. During bulk it climbs to the max regular voltage and they are saying that, and calling it bulk, is 14.85v.
Bulk charging also is also kind of misnamed when one is using solar, as many manufacturer recommedendations are not for solar, but for a plug in charging source. Say this plug in charging source is capable of 20 amps, in 'Bulk, it will apply 20 amps until battery voltage rises to the max, however long this takes. But with solar, the amperage slowly climbs to solar noon. Once absorption voltage is reached then less and less amperage is required to maintain that voltage in this constant voltage phase.
After 14.85v is reached with a max amperage of 30 per 100 Ah of battery capacity, then they have absorption voltage at 14.55v, then once absorption complete, float at 13.5v
Interesting recommendation, thanks for posting their reply, dated in '09.
Absorption being lower than Bulk will slow charging somewhat, and likely use less water, offgass slightly less.
14.85v as a termination point of the bulk/constant current phase is 0.03 higher than trojan's recommendation, but trojan wants battery to be held there, not dropped to 14.55v once it has been attained.
The thing to remember is that any voltage above the natural resting voltage of a fully charged battery~12.8v, is going to charge the battery. The higher the absorption voltage at the battery terminals, the more electrical pressure and the faster the charging will be.
But 1 amp is going to take a LOT longer than 10 amps in getting a depleted battery to absorption voltage.
With solar the amperage is limited by the sun and its angle in relation to the panels and amount of atmosphere it has to travel through. basically when the sun can make the most, at solar noon, the batteries should really be about to or already at absorption voltage, or in this case, 'bulk' voltage.
The higher the amperage, the faster the voltage will climb to bulk/absorption voltage
The lesser the depth of discharge the faster the voltage will climb to B/A voltage
The Older and more sulfated the battery is the faster the voltage will climb to B/A voltage, but then it must remina up at that voltage for longer to fully charge.
All of the voltage recomendations are for a battery temperature of 77F. Automatic temperature compensation is not a feature on many systems that achieve good to very good, perhaps excellent battery life, so the ideal charge voltage recommendations are just guidelines. The length at which absorption voltage is held is more important than the exact absorption voltage held. If there is not enough time for the solar to do the job, then consider boosting absorption voltage, as it is more important to at least get the batteries full, than is is to overvoltage them slightly.
One thing not to do is blow past the 14.85 volts. Get them there and hold them there until they are 'full' If a hydrometer reveals they are not full after several hours at ABSV, or the cells vary more than 0.015, then an Equalization charge is called for.
EP says here 15.75v for EQ voltages, Trojan and Rolls surrette recommend 16.2v.
On my previous flooded battery, the hydrometer and many tests revealed it took 45 minutes at 16v what took nearly 4 hours at 15.5v.
The hydrometer reveals all, if One cares to use it, adjust settings and test specific gravity again.
But No one HAS to do this.
How many cycles the battery lasts, whether that number is acceptable to the owner, is subjective.
Manufacturer recommendations are good starting points, but ultimately the depth of discharge, the amount of solar available, along with other charging sources, really determine how high and how long to hold absorption voltage, so any blanket recommendation by a manufacturer, is just an attempt to get the dart somewhere in the middle of the dartboard, as they do not know the Depth of discharge nor the amount of charging current available to the end user.
But if they said this outright, that perfection requires the User to suit up and do hydrometer readings each subsequent recharge with all the variables accounted for, reconrded, and compared to arrive at perfect voltaeg and duration at that specific depth of discharge and temperature, then the masses would then decide to buy the competitor's product which did not say this was a requirement.
Getting to 100% is truly important, but doing it each and every single recharge is asking a lot. Those with light usage patterns and or a lot of solar wattage to their capacity ration can do so easily. Those who planned on just enough will only be able to get there on a good sunny day, perhaps with a lesser overnight usage the night before.
Use the hydrometer, or Simply get a huge solar wattage to capacity ratio and program the manufacturer recommendations.
