Powerwise 2

[Mridgley100]

Hello Folks, I have questions related to the charging process and what I am experiencing.

Cart: 1988? Marathon - Manuf. code 88M10. << yes... resistor... and I know.. replace it..
Charger: Powerwise 602718 36V / 21A charger.
Batteries: NEW Duracell 6V 230AH - Model # SLIGC115 (6 in series)

Charger history: Charger came with the cart.. condition unknown. Discovered it was bad (would not turn on). Replaced controller and was able to get charger to power up.

Connected the charger to the pack and the ampmeter drove up to 11A. Left it overnight and checked batteries. Individually, batteries read 6.80v, 6.73v, 6.57v, 6.37v, 6.52v, 6.37v. Pack reads 39.36V. This is after about 10 hours of charging...

Took hydro readings of each battery - not individual cells just each batt. 3 of the batteries (batteries above in the 6.57+ v) are in the white reading about 1220. The other three are showing good voltage (6.37) but are in the red with 1150(ish) readings.

I isolated 2 batteries in a 12v pack and put on my 8A car charger to see if I can get them up to 1270 sg. FFW about 14-15 hours and here are my findings. Charger completed its charge cycle and was in maintain mode at the end of that 14 hours.

Battery 1 - 6.61v - Cell 1: 1.200 Cell 2: 1.200 Cell 3: 1.200
Battery 2 - 6.58v - Cell 1: 1.250 Cell 2: 1.250 Cell 3: 1.200 <bad cell?


Question 1: Why are these batteries not able to get SG readings consistent with what is expected after a full charge - 1.277?

Question 2: I have not timed the 36v charger but after approximately 10 hours of charging, I should expect 100% full charge on the pack correct? Voltages are there but SG's are all low...

Question 3: Why does my 21A charger max out in the 11A range during the charge cycle?

Thanks in advance!

[JohnnieB]

1. Getting accurate SG measurements is as much an art as it is a science.

a. Most accurate is a refractometer, a glass float type hydrometer with built-in thermometer is next and then the dial types with pivoted float.

b. What hydrometer was used and was temperature compensation applied?

c. Is 1.277 the correct fully charged SG for Duracell SLIGC115 batteries?



2. The PW-II charger shuts off when the On-Charge voltage reaches 45V +/-1V.

a. How long it take to reach the cutoff voltage normally depends on what the SoC (State of Charge) when the charge cycle was initiated, but the initial charge on a new set of batteries can take up to 20 or so hours.

b. The At-Rest voltage (about 12 hours after the charger shuts off without any use) is tied to the SG, so something is amiss with either the voltage or SG measurements.



3. The PW-II is a ferroresonant transformer type charger and only puts out its max amps when the On-Charge voltage is below about 40V.

a. The attached charge profile is the basis for the PW-II design.

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No two 2V cells are exactly the same, but they should be fairly close in the same battery since they were most likely built from the same batch of materials. If the separate batteries in the set have different date codes, they may not be as closely matched.

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Also attached is the type hydrometer I use, but I mostly use voltages rather than SG.

[Mridgley100]

Originally Posted by JohnnieB

1. Getting accurate SG measurements is as much an art as it is a science.

a. Most accurate is a refractometer, a glass float type hydrometer with built-in thermometer is next and then the dial types with pivoted float.

b. What hydrometer was used and was temperature compensation applied?

I use a glass float type but does not have thermometer for temp compensation. We're in the mid 90's here in Texas.

Originally Posted by JohnnieB

c. Is 1.277 the correct fully charged SG for Duracell SLIGC115 batteries?

I have searched and cannot find any specs on this battery short of what is listed on Battery Plus's website. Will the value really be that much different?

Originally Posted by JohnnieB

2. The PW-II charger shuts off when the On-Charge voltage reaches 45V +/-1V.

a. How long it take to reach the cutoff voltage normally depends on what the SoC (State of Charge) when the charge cycle was initiated, but the initial charge on a new set of batteries can take up to 20 or so hours.

b. The At-Rest voltage (about 12 hours after the charger shuts off without any use) is tied to the SG, so something is amiss with either the voltage or SG measurements.

So are you suggesting that my readings might be off because I am measuring just at the end of the charge cycle?

Originally Posted by JohnnieB

3. The PW-II is a ferroresonant transformer type charger and only puts out its max amps when the On-Charge voltage is below about 40V.

a. The attached charge profile is the basis for the PW-II design.

--------
No two 2V cells are exactly the same, but they should be fairly close in the same battery since they were most likely built from the same batch of materials. If the separate batteries in the set have different date codes, they may not be as closely matched.

--------
Also attached is the type hydrometer I use, but I mostly use voltages rather than SG.

Thanks for your responses.

What are your thoughts on the smaller 12v pack being at full charge (voltage wise) but having a SG reading of 1.200. I would love to just use voltage but I keep reading that you have to use SG to determine the real health of the battery...

If the SG is low now... and charging doesn't seem to bring them to 1.270-7 level as seems to be the standard... does this mean the battery is bad?

[JohnnieB]

Originally Posted by Mridgley100

1. I use a glass float type but does not have thermometer for temp compensation. We're in the mid 90's here in Texas.



2. I have searched and cannot find any specs on this battery short of what is listed on Battery Plus's website. Will the value really be that much different?



3. So are you suggesting that my readings might be off because I am measuring just at the end of the charge cycle?



Thanks for your responses.

4. What are your thoughts on the smaller 12v pack being at full charge (voltage wise) but having a SG reading of 1.200. I would love to just use voltage but I keep reading that you have to use SG to determine the real health of the battery...

5. If the SG is low now... and charging doesn't seem to bring them to 1.270-7 level as seems to be the standard... does this mean the battery is bad?

1. Need to add 0.004 for every 10°F above 80°F, so if the electrolyte temperature is 95°F, you need to add 0.006 to whatever the float says. Batteries have a huge thermal mass, so electrolyte temperature will lead (or lag) air temperature by several hours. Best to measure electrolyte temperature directly. The hydrometer I use has a thermometer that measures the temperature of the liquid aspirated into the tube and has a scale marked in the number to add or subtract from the float reading.

2. Duracell golf cart batteries are relabeled Deka/East Penn batteries. Attached are some things I've found. From what I can tell, they have a slightly lower voltage and SG than Trojan batteries.

3. That is a possibility. Lead acid batteries acquire a "surface charge" while charging. The electrolyte in intimate contact with the lead of the plates has more sulfate ions (stronger acid) than the electrolyte further away from the plates and the lead on the surface of the plates has fewer sulfate ions the the lead deeper inside the plates, so until the electrolyte and plates have the time needed to equalize, terminal voltage will read artificially high while the SG will read artificially low. A similar, but opposite effect occurs when amps are drawn from the battery, but the equalization is quicker, about 1hr vs 12hr.

Also, as a battery sit, the electrolyte stratifies with the heavier acid migrating towards the bottom as the lower SG solution migrates upwards. Aspirate and discharge the hydrometer several times before taking a measurement. Be careful not to splash the 30% acid solution.

4. A lead acid battery is not "fully" charged until the SG ceases to increase while a charging current is passing through the cells. Since terminal voltage is tied to the SG, it can be inferred that the battery isn't fully charge until the ON-Charge voltage ceases to rise while a charging current is passing through the cells. State-of-the-art chargers use dV/dT (change in Voltage over change in Time) technology to determine when to terminal a charge cycle. Some battery manufacturers publish their recommended dV/dT rates. IE: US Battery recommends 4mv per cell per hour for their products. Legacy chargers such as the PW-II shut off at a predetermined voltage (45V +/-1V) which a compromise voltage picked that ought to "adequately" charge new batteries while not overcharging old batteries.

5. Too early to tell. Need some At-Rest SG readings.

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Also, you might try contacting East Penn. They might provide some better SG and voltage values.