Voltage sag, battery advice

Revolution · 05-19-2015, 10:17 PM

So my Club Car XRT 72 volt series cart with a Plum Quick Rattle snake 2 is experiencing severe voltage sag.

It has six 12 volt continental 2gc-12v batteries, they were a lot less than the trojans, what can I say.

Correct me if I am wrong but 1.5 volts per cell is the lowest you should let your batteries drop under load. So I should not drop the pack to less than 54 volts under load to avoid damage to the batteries.

I treat these batteries pretty well, the normal everyday load on them is 200-250 amps max and 1-3 miles at 5-18 mph, then back to the charger. They work quite well like this, I suspect they would live lots of years this way.

BUT, every now and then I like to do doughnuts, sling mud and gravel, leave a 30 foot black streak in reverse, pull the front wheels an inch or two in forward, make small children cry, and get speeding tickets in a 40 mph zone.

That fun stuff takes amps and lots of them, my motor can take them, the new Alltrax SPM 72650 I just installed can dish them out. My poor 12 volt batteries can't keep up. At 500 amps they drop down to 52-56 volts, danger territory. My new controller is capable of 740 amps max and 650 for two minutes, so I can't come close to using its full power.

I have been over everything in the cart today, cables, contactors, batteries fully charged and in good condition. I just can't get more than 500 amps with out damage to the pack.

Lithium pack is out of the budget for now, the batteries themselves are not so bad but BMS and another charger gets out of my budget for fun.

I need some batteries that can handle 700 plus amps with a lot less sag. I am open to any suggestions.

cgtech · 05-21-2015, 02:42 AM

Odyssey batteries? Huge amp abilitys. High price (less than lithium). I dont have much data on their deep-cycle capabilities. They are top-notch for lead based batteries. But, I can say from experience, lithiums dont "sag" in any golf cart use i have seen.

Revolution · 05-21-2015, 12:54 PM

The Odyssey batteries look pretty good. From their web site

"Some batteries offer enormous cranking power. Others, deep cycle reserve power. Unbeatable ODYSSEY® Extreme Series™ batteries do both. Even at very low temperatures, ODYSSEY Extreme Series batteries have the power to provide engine-cranking pulses in excess of 2250 amps for 5 seconds – double to triple that of equally sized conventional batteries. And they can handle 400 charge-discharge cycles to 80% depth of discharge."

That would meet and exceed my needs for now. I am going to call the closest dealer.

Revolution · 05-21-2015, 01:28 PM

Ok I emailed Odyssey directly, we will se what they say.

Any other suggestions?

Nate · 05-21-2015, 10:44 PM

Something does not make sense, at first I thought maybe the 2GC was a deep discharge over long period of time type of battery but I looked up the specs. The Continental 2GC-1275 is an 82 lb battery. That should push 500A fairly easy without too much sag.

What are you using to charge the pack with?

What is the finish voltage of the pack?

What is the voltage of the pack a few hours after the charger has shut off?

What is the voltage of each battery a few hours after the charger has shut off?

Do all the batteries sag? Are we sure there is not one bad battery in the pack?

Personally I don't take my batteries below 1.8vpc for driving and not below 1.7vpc for hard starts.

Revolution · 05-22-2015, 02:29 AM

Charger is a DPI.

Right after unplugging the DPI in the float stage its 79.7V. The max charge finishing voltage is between 88.5 volts and 90 volts, depending on which of my meters you would trust. The Axe72450 that was in it before showed 90 volt max while charging.

I just unplugged the charger for the above voltage and will measure the pack when I get home tomorrow afternoon.

About a month ago I did attempt to measure each battery voltage under acceleration. Its difficult to make six consistent runs but no battery dropped below 9.2 to 9.5 volts. Ill re try tomorrow afternoon.

Revolution · 05-22-2015, 09:09 PM

So here is what I got.

Pack voltage after 16 hours or so off the charger. 75.7 volts.

I forgot to check each battery voltage before testing under load.

Batteries individually under close to full load.

1- 8.87
2- 8.45
3- 8.63
4- 8.45
5- 8.50
6- 8.50

After a hour rest, the pack is at 76.1 ( I don't really know why it went up )

1- 12.74
2- 12.72
3- 12.75
4- 12.74
5- 12.71
6- 12.68

Revolution · 05-22-2015, 09:39 PM

I think the batteries are fine for normal cart use. They just can't push high amps. With the Axe 72450 the voltage sag was not as much of a problem. With the SPM 72650 the batteries are not keeping up.

Nate · 05-23-2015, 11:18 AM

All your charger numbers look good, I wanted to make sure the charger was fully charging the batteries.
Resting voltage after surface charge is gone is a little lower than I would like to see.
Loaded voltage is definitely in the danger level, the batteries probably took some damage which explains the resting voltage being a little low now.

All your numbers point to your original thought, these Continental 2GC-1275 cannot handle high amp surges, they can't keep up with the load chemically. Probably a decent replacement battery for a stock cart.

In my opinion batteries have to handle some current, I too enjoy occasionally doing doughnuts or spinning tires. Thanks for giving the additional battery information.

Just curious how old these batteries are and how far you typically drive?

Revolution · 05-23-2015, 01:03 PM

The batteries are a year and a half old, I drive it 1-10 miles a day.

05-19-2015, 10:17 PM	#1
Revolution Voltaholic Join Date: Dec 2013 Location: Close to Navasota Texas Posts: 934	Voltage sag, battery advice So my Club Car XRT 72 volt series cart with a Plum Quick Rattle snake 2 is experiencing severe voltage sag. It has six 12 volt continental 2gc-12v batteries, they were a lot less than the trojans, what can I say. Correct me if I am wrong but 1.5 volts per cell is the lowest you should let your batteries drop under load. So I should not drop the pack to less than 54 volts under load to avoid damage to the batteries. I treat these batteries pretty well, the normal everyday load on them is 200-250 amps max and 1-3 miles at 5-18 mph, then back to the charger. They work quite well like this, I suspect they would live lots of years this way. BUT, every now and then I like to do doughnuts, sling mud and gravel, leave a 30 foot black streak in reverse, pull the front wheels an inch or two in forward, make small children cry, and get speeding tickets in a 40 mph zone. That fun stuff takes amps and lots of them, my motor can take them, the new Alltrax SPM 72650 I just installed can dish them out. My poor 12 volt batteries can't keep up. At 500 amps they drop down to 52-56 volts, danger territory. My new controller is capable of 740 amps max and 650 for two minutes, so I can't come close to using its full power. I have been over everything in the cart today, cables, contactors, batteries fully charged and in good condition. I just can't get more than 500 amps with out damage to the pack. Lithium pack is out of the budget for now, the batteries themselves are not so bad but BMS and another charger gets out of my budget for fun. I need some batteries that can handle 700 plus amps with a lot less sag. I am open to any suggestions.

05-21-2015, 02:42 AM	#2
cgtech Over This Interview Is... Join Date: Jun 2012 Location: AZ Posts: 17,449	Re: Voltage sag, battery advice Odyssey batteries? Huge amp abilitys. High price (less than lithium). I dont have much data on their deep-cycle capabilities. They are top-notch for lead based batteries. But, I can say from experience, lithiums dont "sag" in any golf cart use i have seen.

05-21-2015, 12:54 PM	#3
Revolution Voltaholic Join Date: Dec 2013 Location: Close to Navasota Texas Posts: 934	Re: Voltage sag, battery advice The Odyssey batteries look pretty good. From their web site "Some batteries offer enormous cranking power. Others, deep cycle reserve power. Unbeatable ODYSSEY® Extreme Series™ batteries do both. Even at very low temperatures, ODYSSEY Extreme Series batteries have the power to provide engine-cranking pulses in excess of 2250 amps for 5 seconds – double to triple that of equally sized conventional batteries. And they can handle 400 charge-discharge cycles to 80% depth of discharge." That would meet and exceed my needs for now. I am going to call the closest dealer.

05-21-2015, 01:28 PM	#4
Revolution Voltaholic Join Date: Dec 2013 Location: Close to Navasota Texas Posts: 934	Re: Voltage sag, battery advice Ok I emailed Odyssey directly, we will se what they say. Any other suggestions?

05-21-2015, 10:44 PM	#5
Nate Gone Wild Join Date: Dec 2006 Posts: 679	Re: Voltage sag, battery advice Something does not make sense, at first I thought maybe the 2GC was a deep discharge over long period of time type of battery but I looked up the specs. The Continental 2GC-1275 is an 82 lb battery. That should push 500A fairly easy without too much sag. What are you using to charge the pack with? What is the finish voltage of the pack? What is the voltage of the pack a few hours after the charger has shut off? What is the voltage of each battery a few hours after the charger has shut off? Do all the batteries sag? Are we sure there is not one bad battery in the pack? Personally I don't take my batteries below 1.8vpc for driving and not below 1.7vpc for hard starts.
Nate Gone Wild Join Date: Dec 2006 Posts: 679

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05-22-2015, 02:29 AM	#6
Revolution Voltaholic Join Date: Dec 2013 Location: Close to Navasota Texas Posts: 934	Re: Voltage sag, battery advice Charger is a DPI. Right after unplugging the DPI in the float stage its 79.7V. The max charge finishing voltage is between 88.5 volts and 90 volts, depending on which of my meters you would trust. The Axe72450 that was in it before showed 90 volt max while charging. I just unplugged the charger for the above voltage and will measure the pack when I get home tomorrow afternoon. About a month ago I did attempt to measure each battery voltage under acceleration. Its difficult to make six consistent runs but no battery dropped below 9.2 to 9.5 volts. Ill re try tomorrow afternoon.

05-22-2015, 09:09 PM	#7
Revolution Voltaholic Join Date: Dec 2013 Location: Close to Navasota Texas Posts: 934	Re: Voltage sag, battery advice So here is what I got. Pack voltage after 16 hours or so off the charger. 75.7 volts. I forgot to check each battery voltage before testing under load. Batteries individually under close to full load. 1- 8.87 2- 8.45 3- 8.63 4- 8.45 5- 8.50 6- 8.50 After a hour rest, the pack is at 76.1 ( I don't really know why it went up ) 1- 12.74 2- 12.72 3- 12.75 4- 12.74 5- 12.71 6- 12.68

05-22-2015, 09:39 PM	#8
Revolution Voltaholic Join Date: Dec 2013 Location: Close to Navasota Texas Posts: 934	Re: Voltage sag, battery advice I think the batteries are fine for normal cart use. They just can't push high amps. With the Axe 72450 the voltage sag was not as much of a problem. With the SPM 72650 the batteries are not keeping up.

05-23-2015, 11:18 AM	#9
Nate Gone Wild Join Date: Dec 2006 Posts: 679	Re: Voltage sag, battery advice All your charger numbers look good, I wanted to make sure the charger was fully charging the batteries. Resting voltage after surface charge is gone is a little lower than I would like to see. Loaded voltage is definitely in the danger level, the batteries probably took some damage which explains the resting voltage being a little low now. All your numbers point to your original thought, these Continental 2GC-1275 cannot handle high amp surges, they can't keep up with the load chemically. Probably a decent replacement battery for a stock cart. In my opinion batteries have to handle some current, I too enjoy occasionally doing doughnuts or spinning tires. Thanks for giving the additional battery information. Just curious how old these batteries are and how far you typically drive?
Nate Gone Wild Join Date: Dec 2006 Posts: 679

05-23-2015, 01:03 PM	#10
Revolution Voltaholic Join Date: Dec 2013 Location: Close to Navasota Texas Posts: 934	Re: Voltage sag, battery advice The batteries are a year and a half old, I drive it 1-10 miles a day.

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