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Ni-Fe Batteries

Q22: Battery Hydrometer tests

Begin with all caps off, H2 pipes removed, voltmeter ready to go and your battery hydrometer, with pen and recording card.

We start on the postive end, at cell 20, and test specific gravity of solution.

It reads 1.225 . Hmm?

Voltage cell ( for both posts) 1.43 Volts.

And some cells tested slightly better:

It reads 1.250 . Wow? Voltage was 1.44V

A summary for all the cells, on FLOAT:

1.43

1.230

1.44

1.225

1.43

1.230

1.43

1.225

1.43

1.230

1.43

1.235

1.43

1.225

1.43

1.225

1.44

1.230

1.41

1.235

1.44

1.225

1.43

1.250

1.44

1.230

1.43

1.250

1.44

1.250

1.43

1.225

1.43

1.225

1.43

1.225

1.43

1.225

1.43

1.225

Notice the gray -ve end, Cell No:1 is charged least at 1.41 Volts, at FLOAT. The pump was on so the system was drawing 22 amps but 22 amps was coming into the battery bank also.

At the pink +ve end, Cell No:20 the voltage is 1.43, more or less the same for every cell.

Cell 15 scored the highest reading at 1.250.

Some companies say replaced the electrolyte if the gravity is less than 1.19

Well we are well better than 1.190, in fact at FLOAT according to Lead Acid, we are 60% fully charged.

The EMF of a fully charged cell is 1.4 V which decreases to 1.3 V rapidly. The average EMF of a cell is 1.2 V and reduces to 1.0 V when fully discharged. SOURCE

I read somewhere that once a month Ni-Fe has to be exercised, whatever that means, otherwise it forms a memory and forgets to go back to it's manufactured storage capacity?

Such things are difficult to research and verify, so I may require some help as to how to get my 400 amp/hr battery bank back again?

Battery temperature is not a fact, as the temperature ranges from 31 degrees C to 39 degrees C on hot days in Queensland.

The proper equalization voltage is 1.65 volts per cell. If 10 cells were used, the proper equalization voltage would be 16.5 volts. This equalization charge is applied for 8 hours using at least C/10 current. According to Edison's original manual from 1914, it is best to completely discharge the batteries from time to time before applying the equalization charge. SOURCE

Seems to be saying to apply 33V with 50 Amps for 8 hours, after completely discharging the battery?

This equalization charge is no different to my solar panel charging?

Seems to be saying I should have charged 31V for my bank, instead of 33V?

In contrast to lead acid, the NiFe battery can be overcharged for decades at a time without damage. SOURCE

Doesn't seem to hold up for me? but I hopeful, something can be done?

Today the batteries are at 19V again, after using 220 amps over night, seems like water pump coming on early before sun hits the panels is a problem. Actually its more likely my storage capacity is empty. I probably only have, 160 amp/hr.

I find this funny because my hydrometer shows 60% charged for lead acid, and that would be 300 amp/hr of storage, but I have no where near that. However if I used 220 amps, I have 80 amps left, so a load of 20 amps might pull down the voltage to 19V? Hmm? Might be OK?

Now my batteries are on 19 V under load, what is my hydrometer readings?

I tested 4 of them, and they are the same, 1.225, no change when charged or discharged as the sources say.

I will clear history again, and assume my battery bank 400 amp/hr is doing as it should? Maybe a exercise deep discharge to zero volts might do it good? But has anybody tried this?

Of course having a bigger tank would make my problems go away, ie 48 V system, another $9,000; I am trying to do things cheaply.

But I can make do with what I have, learn to live with my storage capacity.

Late last night at midnight the fan went off. Below 19V. Battery flat. The fan was moved to mains supply and our fridge also, the only two things connected on the batteries at the time. We consumed 3300 W according to the BMV 712 monitor, and 6300 W went into the battery. Overnight we consumed 151 Amp/hr and at no load the Voltage is 23V.

Summary is:-

  • Amps out = 137 amps
  • Amps in = 262 amps

  • In theory, we still have 125 amps left, but the load (around 6 amps) was not able to cope, so the voltage went from 23V to 19V.

    I find this rather a poor performance?

    I was watering late, and the bore pump switched on , until I turned it off, so this consumed some amps from our night supply.

    So watching your night time load is a worry.

    Cell voltages at this depleted level are 1.33 at +ve end and 1.32 at -ve end .

    This is no where near 1.00V, which indicates a dead flat battery.

    Need cell voltage verses SOC for Ni-Fe?

    On the positive, I am learning lots from battery technology.

  • 24V water pump uses 5Amps
  • 240V water pump uses 20Amps
  • 240V fridge uses 5Amps
  • 24V LED lights uses 1Amp
  • 240V Fan uses 2Amps

  • From sunset to 8:00pm, we use 100 amps every day.

    This comes from the fridge and fan, and showers at night.

    If we come into night on 25 V I know we will not make it to next morning, on say fridge and fan loads.

    So I need to add more solar panels to the WEST, to remove the power draining from 3pm until 8pm, when we finally sleep, with fridge and fan only running.

    Last night we ran out of power, and it's cloudy today.

  • Amps IN 225 A
  • Amps OUT 62 A

  • Voltage tonight is 27V, so should make it through the night, with fridge and fan (7 amps) draining the batteries all night.

    Maybe the Victron solar chargers are going to BULK and FLOAT too early?

  • Maybe I need solar panels at say 34 V and
  • 60 - 80 amps coming into the batteries
  • with manually control, no MPPT control;
  • force battery to charge up;
  • charging for 5 hours, giving 300 amps.
  • This might work, increasing my storage.

    Ni-Fe can handle this robust charging easily, worst case, I get is a little water loss.

    Need to do something, got nothing to lose?

    I notice the MPPT can do a manual equalization ? What does this do?

    I found these comments on the Internet:-

    ...www....... ... "The average time of charging of a battery is 7 hours and discharging time is 5 hours. Another characteristic of Edison battery is that continuous operation at higher temperature decreases the life of the battery, the same thing happens if the battery is charged for more than the average time of charging"

    So charging longer than 7 hours spoils the batteries? So does this mean absorb and float times as well as bulk times all be done under 7 hours? Or does this refer to bulk time charging?

    "The proper equalization voltage is 1.65 volts per cell. If 10 cells were used, the proper equalization voltage would be 16.5 volts. This equalization charge is applied for 8 hours using at least C/10 current. According to Edison's original manual from 1914, it is best to completely discharge the batteries from time to time before applying the equalization charge. Edison also recommends a 1.7 volt equalization charge and he recommends changing the electrolyte every 5-10 years"

    So that's 34V at a minimum of 60 amps for no more than 8 hours, seems to be my manual charge?

    "In contrast to lead acid, the NiFe battery can be overcharged for decades at a time without damage".

    Hmm?

    Edison manual

  • shorten life of batteries if greater than 46 degrees C

    My batteries range from 31 to 39 degrees Celcius, during summer.

    "Edison says batteries, which have become sluggish through lack of work, may be restored to normal by overcharging."

    OK, hope here?

    " Edison says if the battery lacks capacity, the battery should be given one cycle of overcharge".

    OK, hope here?

    "Edison says a normal charge for 20 cells is 37.0 Volts. "

    Is this too high?

    So it seems one cycle of overcharge might work, increase my capacity.

    Next we look at adding a fourth MPPT controller facing due EAST.

    Ni-Fe battery technology

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