Battery storage idea

[Winston Ellis]

So my charging idea seems to be working well. Batteries are in the cart and disconnected from the cart itself, split into two 24v banks, then ran in parallel to a distribution block. Each bank is protected by a 30 amp fuse, the charger is located in the basement. The charging cable runs through a conduit I have going to our patio with 8 gauge wire, about 20 feet to the distribution system. The charger connects to the distribution system and is fused @ 40 amps. There is also an inline fuse at the charger itself.


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[Winston Ellis]

By the way, it’s 28 degrees out and snowing.


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[ThreeCW]

Winston,

The recommended float charge for Trojan lead acid batteries at 25 deg C / 77 deg F is 2.25 volts per cell at = 27.00 volts for your 24 volt winter charging system.

For lead acid US Batteries, the recommended float charge at 80 deg F is 2.17 volts per cell = 26.04 volts for your 24 volt winter charging system.

It appears you are float charging at 28.15 volts which is higher than optimum for either Trojan or USB. More on that below.

You might also want to check the actual voltage across each battery bank with your meter, as you may be losing some voltage with your cable extension.

What make of batteries do you have?

I also notice you have your charger on the Cold / AGM setting, which is a higher voltage setting than the normal mode (possibly about 0.6 v higher). It being colder out, you may be able to run a higher maintenance voltage but you might want to check into that a little more to ensure you are still within the recommended voltage for your batteries.

Your Noco charger manuals says the following:
"Step 8: Maintenance
Continuously monitors the battery to determine when
a maintenance charge should be initiated. If the battery
voltage falls below its target threshold, the charger will
restart the Maintenance cycle until voltage reaches its
optimal state and then discontinues the charge cycle.
The cycle between Optimization and Maintenance is
repeated indefinitely to keep the battery at full charge.
The battery charger can be safely left connected
indefinitely without the risk of overcharging."

It will be interesting to see if that 28.15 volts that you are seeing is the result of a surface charge that continues to decrease until the voltage drops below the target threshold (what ever that voltage is ?) and the charger kicks in again to repeat the charge, hold/monitor, recharge cycle.

I suggest that you monitor and understand your voltages and if they stay above the recommended float voltage, you might want to go back to the normal mode.

I will try dig up some information on temperature compensation for float charging at colder temperatures, but my gut feel is that you are likely at a higher than recommended float voltage even if temperature compensation is included.

[Winston Ellis]

Thanks ThreeCW for the very informative reply. I have Interstate GC8-UTL batteries. I disconnected from the charger earlier this morning. Later tonight I will measure the pack voltage and put the charger back on, but not on the Cold/AGM mode. Battery pack voltage was 27.8 when i measured it while it was still on float mode this morning.

[Winston Ellis]

So when I put it on normal 24v mode, it floats at 27.2v at the charger.


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[ThreeCW]

Were you able to measure the pack voltages before you put it back on the maintenance charge?

[Winston Ellis]

yeah, it was 25.2ish

[Winston Ellis]

25.92****


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[ThreeCW]

Trojan's recommended charging temperature compensation is as follows:

Add 0.0028 volt per cell for every 1°F below 77°F.

Subtract 0.0028 volt per cell for every 1°F above 77°F.

For example, at 32°F, with your 24 volt charging system (12 cells) float charge can be temperature compensated by increasing the float voltage by:
12 cells x (77°F - 32°F) x 0.0028 volts per cell = 1.5 volts

24V System Float Charge at 77°F = 27.0 volts
24V System Float Charge at 32°F = 27.0 + 1.5 = 28.5 volts (temperature compensated)

It appears that the temperature corrected float voltage is a bit higher than I expected. If the weather stays cool, using your COLD maintenance mode of 28.15V should be OK (it is within the temperature corrected specification). At higher temperatures (above 45°F), you would want to ensure you were on the NORMAL mode.

Floating your batteries at higher than recommended voltages can lead to shorter battery life.

[Winston Ellis]

Thanks, luckily for me it usually does not get over 50f I till spring. I sent an email to Noco asking if it’s possible to adjust float voltage.


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