SG rising up on ROLLS

Re: SG rising up on ROLLS

Roughly, we "recommend" 5%-13% of the battery's C/20 (~40 Hour rating) for charging current... For yours:

24 amps / 530 AH = 0.045 = 4.5% rate of charge.

This is a relatively low charging current so it can take awhile to recharge your bank. Basically, you are at C/20 rate of charge (5%), so for every 5% change in State of Charge, it will take 1 hour of 24 amps to recover.

Roughly, from the Battery FAQ, you are looking at ~0.015 Specific Gravity [fixed--was 0.15--missing a "0"] for every 10% change in State of Charge (~2 hours on your 24 amp charge rate).

If you are pumping in 24 amps, and you see no change in specific gravity after ~2 hours (at 5% charge rate/24 amps)--then your battery cells have pretty much reached 100% capacity (from the Rolls Charging FAQ, they say full charge is ~1.265-1.275).

In theory, ~25C batteries, charging at ~24 AH and 14.2-14.7 volts. Once the batteries are mostly charged, you should hold the 14.x volts for ~2-3 hours, Then stop charging or reduce to float voltage of 13.2-13.4 volts.

5 Hours of charging at 24 amps should move the SG by ~0.025 [fixed] points (assuming your battery was at ~75% state of charge or less). If your battery SG started out near 1.250 and hardly moved (and you see bubling in the battery, and you know that ~24 amps where flowing)--Then you pretty much have done an Equalization and the SG reading you saw will be the maximum for your battery set.

By the way, what was the voltage at the battery bank over the last 5 hours while you where running 24 amps into the bank (14.x or 15.5-16.0 volts)?

At 15.5+ volts, that would hve been equalization. If 14.x volts, I would guess that the charging current should have reduced automatically to well below 24 amps (bulk/absorb charging).

-Bill

Re: SG rising up on ROLLS

Note: I made a mistake in typing the SG change per 10%... Should be 0.015 not 0.150 (and 0.025 not 0.250) like I originally typed.

Do you have a remote battery temperature sensor for your charge controller? It was found that the smaller MPPT charge controller (15 amp) really needed the RBTS. The controller tends to run hotter than the battery bank which suppresses the output voltage otherwise.

I don't know anything on the Tristar MPPT controller--How do you know it is on PWM (light?) vs just normal reduction due to less sunlight.

Also, what is the voltage on the controller output terminals vs battery bank. Although, it sounds like everything is OK now that you are seeing 14.7 volts on the battery bank during charging (and the controller would be reducing charging current at that time).

What is the load like? From the SG and resting battery voltage, it sounds like you are discharging down to ~60% State of Charge (using 40% of the battery bank capacity).

530 AH * 40% = 212 Amp*Hours consumed (approximate guess)

At a 20 amp average charge--that would take 10+ hours of recharging...

Really need to know what your nightly loads are... It sounds like you are pulling 2-3 times more energy from your battery bank than your existing solar panels are able to output during the day (especially in winter).

Do you have any measurements of your nightly load? (I could be all wrong here--just guessing).

-Bill

Re: SG rising up on ROLLS

14.7 volts is fine... And you will see the battery/charge controller accepting less current as it gets fully charged. As long as you reach at least 90% state of charge every few days, and don't stay below ~75% state of charge for more than a day--you should be fine in normal operation.

Regarding charging, if you use 65 Amp*Hours in a night, you should be replacing ~110% at most during the charging (~73 AH).

Don't try to get to 100% state of charge every day... That is probably approaching an overcharging issue.

By the way, how is the water usage? You should be replacing some every month... Zero water usage or nearly exposed plates every month is not right.

I have to go now...

-Bill

Re: SG rising up on ROLLS

In general, any charge rate between 5% and 13% is fine... However, when running a genset, you probably want to output load on the genset to be near 50% of the generator's rated capacity (if not a bit higher). Should end up being more fuel efficient for you (generators are typically pretty fuel efficient from 50%-100% rated load. Below 50%, the fuel flow remains at ~50% fuel flow even if it is outputting 5% rated power).

You can run into issues where it would be difficult to get more than 50% rated capacity out of the generator with many battery chargers. The older battery charger designs have poor Power Factor (the AC current wave form is not in phase with the AC voltage and/or the current wave form does not look like a sine wave). Poor power factor will make the battery charger "look larger electrially" than it actually is.

Power Factor for AC battery chargers is not usually stated--So without actually measuring it is a bit of a gamble to figure out what any charger's power factor may be. If you find one listed as "Power Factor Corrected" -- that should be a good sign.

I am sorry--Power Factor is a bit technical and if English is your second language you may want to look it up in some local references (you are doing better in English than I do at times--and English is my only language :cool: ).

-Bill