Battery problem??

[jb2c]

I'm only getting 51.0 volts from my pack. This is after an overnight charge and no use. My digital handheld voltmeter and the digital display I just installed match exactly. I just hooked it up and charged it again for 4 hours and checked the voltage with the charger still hooked up. 51.3 volts. These are Trojan T1275 12 volt batteries that came with the cart, but were new March 2018 (according to the seller and the date code on the batteries). I have a hydrometer and will check specific gravity next time I'm down. But it sounds like I have a battery problem. I believe I should be seeing 59-61 volts when the batteries are fully charged. I'm not even close.

How much voltage is required for the cart to run? It has been fine so far. But I have only taken it on short runs of 10-15 minutes round trip.

[orangeman6]

Here’s a soc chart from johnnieb.

[jb2c]

If I'm rading that chart correctly, then 50.3 volts would be between 80 and 90% state of charge. Which would tend to indicate to me that everything is OK. But I'm sure I've read somewhere that 48 volt systems should charge up fully to 59 to 61 volts??

[JohnnieB]

Originally Posted by jb2c

1. I'm only getting 51.0 volts from my pack. This is after an overnight charge and no use. My digital handheld voltmeter and the digital display I just installed match exactly.

2. I just hooked it up and charged it again for 4 hours and checked the voltage with the charger still hooked up. 51.3 volts. These are Trojan T1275 12 volt batteries that came with the cart, but were new March 2018 (according to the seller and the date code on the batteries). I have a hydrometer and will check specific gravity next time I'm down.

3. But it sounds like I have a battery problem. I believe I should be seeing 59-61 volts when the batteries are fully charged. I'm not even close.

4. How much voltage is required for the cart to run? It has been fine so far. But I have only taken it on short runs of 10-15 minutes round trip.

1. The At-Rest (12 hours after charger is disconnected from cart and cart not moved) voltage for Trojan batteries is 2.122VPC (Volts per Cell) and a 48V battery pack has 24 x 2V cells, so 100% SoC is 50.928V, but newer batteries will be higher and older batteries will be lower.

2. Sounds like the charger had turned off and the pack had rested for a few hours. The On-Charge voltage will peak about 60V. (Max On-Charge voltage depends on make/model of battery charger used.)

3. Your batteries appear to be okay. 59-61V is the charger cut-off range for the On-Charge voltage, not the At-Rest voltage.

4. Has to be above whatever the low voltage cutoff is set to in the controller. which will vary with drive type series, sepex or AC. What drive type do you have?

On the other hand, it is generally recommended that the battery pack never be discharged below 50% SoC, which is 48.4V for a 48V pack. However, you will see the battery pack voltage drop below that while under load. Try not to drop the pack below 42V during operation and never take it below 36V. that is where irreversible physical damage to the batteries begins to occur.

[cgtech]

There is a difference between "at rest voltages" and "on charge voltages".

[JohnnieB]

Originally Posted by jb2c

If I'm rading that chart correctly, then 50.3 volts would be between 80 and 90% state of charge. Which would tend to indicate to me that everything is OK. But I'm sure I've read somewhere that 48 volt systems should charge up fully to 59 to 61 volts??

50.3V is 86% SoC.

The ~60V is the On-Charge voltage needed to fully charge a 48V battery pack and a 48V battery pack will read about 60V the at or about the instant in time the charger shuts off. Over the next 12 hours or so, the voltage will decrease at an inverse exponential rate until it reaches a plateau at about 50.9V. After reaching that plateau, the voltage will continue to decrease, but at a much lower rate, about 1% SoC per day or about 0.05V per day.

[JohnnieB]

Originally Posted by cgtech

There is a difference between "at rest voltages" and "on charge voltages".

There are also "under load voltages" and all three are measured at different times under different conditions and have different significance in troubleshooting.

At-Rest: Measured about 12 hours after the charger shuts off automatically and without the batteries being discharged during that time period. Good yardstick for battery health.

On-Charge: Measured while the charger is actively charging batteries. On-Charge voltage will start at whatever the battery pack voltage was when charge cycle began and will climb to whatever voltage the battery pack voltage climbs to at end of charging cycle. Peak voltage will vary by make/model of charger.

Under-Load: Measured while the batteries are being discharged. In and of themselves, the 24 x 2V cells in a 48V battery pack will drop about 1.5V per 100A of current being drawn from them. The high current cables, connections and contacts have resistance, so they will also drop voltage. The Under-Load voltage can be used to determine battery health and quality of amp delivery circuit.

[cgtech]

I understamd this, and thanks for putting this info up once again for all to see! Thank you for typing what I "didn't want to" type.

[JohnnieB]

Originally Posted by cgtech

I understamd this, and thanks for putting this info up once again for all to see! Thank you for typing what I "didn't want to" type.

I knew you knew, I just added to your post.