What is your trimetric measured battery AH vs manufacturer AH specs ?

jeffkruse wrote:

I also show from 60 (on the very low end) to 110 (on the high end) AH of use every night, but due to cloudy weather my batteries might not be fully charged. The deepest I have gone is 180AH (as shown on the Trimetric) I forget what the SG was but I think it was about 60% on the worst cell.

“Sundown to sunup the pentametric measured 85AH discharge @ 48.4V leaving a 77% state of charge indicated on the Pentametric.”
I would think 48.4V is 50% SOC but Voltage readings are not good to use because they probably are not at rest. Your Pentametric is dividing 85AH/370AH=77%SOC. The 48.4 could have been you turning on the microwave or the defrost of the fridge going on. It’s a low voltage but if your drawing 3+KW it could dip that low.

“However the voltage dropped from 56.4V (my float charge setting - bulk/absorb is 49.2V) to 48.4V”
What do you mean?
Bulk V should be the same as absorb V but doesn’t really mean anything because it should be set as % of Max current. What is your Absorb V and Time?

My Absorb Voltage I adjust as needed. I under charged my first set of batteries for several months because I was told to use default settings. Based on time of year, usage, weather, and water usage I may adjust my absorb voltage. I think I now have it set at 59.8ish which gives me 59V at 20ish charging Amps at the batteries. That’s just above the max absorb spec of 58.8V. I also have my absorb time set to Max (480min)

You definitely need a good Hydrometer.

jeffkruse wrote:

What do you mean?
Bulk V should be the same as absorb V but doesn’t really mean anything because it should be set as % of Max current. What is your Absorb V and Time?

jeffkruse wrote:

You definitely need a good Hydrometer.

Determining the 50% state of charge Voltage Reading

Most three steps chargers or inverters monitor the voltage and have an adjustable set point that determines when the batteries are low (50% discharged) and should be charged. Once this set-point is reached the inverter will either sound an alarm or start a generator or tie the battery bank back into to grid power. The voltage set-point maybe factory set but could require verification. Consult your inverter manual for the section on “Cut-off voltage” or “Over discharge protection”. Since the voltage will change depending on whether or not the bank is on load the set point can be determined by a specific gravity reading. A gravity reading of 1.200 is equal to 50% discharged.

Battery cable lengths, system set-up and other variables can affect the voltage readings as well. Below is a procedure to verify the 50% mark and table 2 gives approximate cut-off voltages at various state of charge. Notice 100% is given as an open cell voltage and all other as under load.

When using a generator with a low voltage cut-off, set the generator to start at the 50% mark given by table 2 and put the bank into service (11.6 V for a 12V system) (46.32V for 48V system). When the generator starts-up measure the specific gravity of one cell in the bank. Compare this to the table 1, Specific gravity versus state of charge. If the measured specific gravity indicates the state of charge is more than 50%, decrease the low voltage cut-off setting. Similarly if the specific gravity indicates the state of charge is lower than 50%, increase the low voltage cut-off setting. Note: 50% is the desired depth of discharge but it does not have to be exactly 50%. For practical purposes a range of 45-55% is acceptable. The actual battery voltage corresponding to 50% will change with a change in load. In general, the higher the discharge amperage, the lower the corresponding voltage.

To determine or verify the 50% voltage set point:

1. Put all or as many loads as possible on the battery. Disconnect any in coming current inputs such as panels / windmills and grid power. Contact your dealer for specifics.
2. Take the specific gravity of one cell.
3. Take another reading 15 minutes and ½ hr later this should give you an indication of how fast the batteries are dropping.
4. Continue to take readings until 50-55% state of charge is reached according to the specific gravity readings.
5. Take and record voltage readings (when on load) of any meters to be used for monitoring the state of charge and take a voltage reading across the terminals of one battery.
6. Compare to table 2.
7. These readings will then give you a very accurate voltage reading which can be used in the future either as a set point for the inverter or as a day to day monitoring parameter.

Extending absorb beyond this point is just going to stress batteries and reduce their lifetime.

BB wrote:

And, my two cents... If your batteries are using a bit of distilled water per month--you are probably OK. If you are using none, or a lot per month--then you are probably under or over charging.

* Undercharging and operating for long periods (below ~75%) is damaging to lead acid batteries.
* Overcharging is less damaging to flooded cell batteries (at the cost of distilled water and wasted energy).
* Overcharging sealed batteries (AGM, Gel, VRLA, etc.) can be fatal to those types (venting electrolyte).

How would that increase the absorb time? Wouldn't it do the opposite?

One question - I noticed my weakest battery per SG readings is the one tied to the positive inverter cable. It is consistently 0.010-0.020 less than the rest. I have tried two different batteries in this location and it is the location not the battery. The battery moved away from +INV goes up in SG, and the one moved to +INV becomes the lowest SG in the string. Is this normal ?