Losing Power With Decent Voltage

[Phil0411]

I have a 2003 TXT PDS recently rebuilt but mostly cosmetic although the mechanics were checked over. I did put in brand new GC2 batteries manufactured 7/21 so they’re new. They charge up fine and hold 38.5v or better after days of sitting. Driving the cart fully charged is awesome. With the Freedom chip in I can get 20-21 mph no problem. With the steep hill chip, 14 mph (I made that switchable with toggles). It was in the steep hill mode today because we would be moving slow most of the time. Today was its first day outing at a huge event here in Florida. Everything was great for the first couple hours, but then it seemed to run down very quickly. Checking the voltage after sitting a minute was still over 37 and it recovered a bit more while sitting. I have my meter set for 38.3 as 100% and 36.4 as the low. The meter never showed under 67% but it just wouldn’t go. The solenoid clicked and it tried to move but wouldn’t. If I let it sit for 5 minutes, the voltage came up some and off we’d go. I decided not to chance it so we made it back the mile or so to the trailer and loaded up. I unloaded when I got home and parked it. I just went and checked without charging at all and voltage is back up to 38.2v and 96% on the meter. All cables are new 4ga. All cable connections at the batteries are clean and tight. Running 20” wheels with street tires and the brakes aren’t dragging. The only thing I didn’t do was replace the controller or the motor because it was running excellent until today when it was ran on and off for a couple hours. What gives? Connections? Controller? Motor? Suggestions?

[ojo]

Sounds like batteries, check each individually with your meter, probably one is bad. If they're close together, check the voltage while driving ( under load ).

[Mooncarter]

How did your batteries go from run down, then you drove it 2 miles and without charging go up to 38.2 which is optimal?

[Phil0411]

Originally Posted by ojo

Sounds like batteries, check each individually with your meter, probably one is bad. If they're close together, check the voltage while driving ( under load ).

All batteries checked at the exact same voltage after I got home at 6.4 volts without charging. That’s what’s so strange.

[Phil0411]

Originally Posted by Mooncarter

How did your batteries go from run down, then you drove it 2 miles and without charging go up to 38.2 which is optimal?

That’s why I’m asking. It makes no sense at all. I know about battery recovery so it makes sense they really only lost very little voltage when said and done, so my question remains, what other components could cause the cart to loose power even with good batteries that had power remaining.

[JohnnieB]

Might be the controller overheating.
1. The steep hill mode (as well as the mild hill mode) has regen braking which adds to motor and controller heat.
2. Taller than stock tires (Stock = 18") increase controller and motor heat.
3. Driving slow causes motor to draw more amps and more amps means more heat.
4. Taller than stock tires reduce motor RPM for any given speed and the slower the motor turns, the motor amps it can draw and the more amps the more heat.

Put the controller into diagnostic mode and listen for error codes as you dive cart slowly in steep hill mode. If the failure repeats itself, there ought to be a code telling you why.

How to get into diagnostic mode is explained by text at bottom of attached PDS label.

[Phil0411]

Originally Posted by JohnnieB

Might be the controller overheating.
1. The steep hill mode (as well as the mild hill mode) has regen braking which adds to motor and controller heat.
2. Taller than stock tires (Stock = 18") increase controller and motor heat.
3. Driving slow causes motor to draw more amps and more amps means more heat.
4. Taller than stock tires reduce motor RPM for any given speed and the slower the motor turns, the motor amps it can draw and the more amps the more heat.

Put the controller into diagnostic mode and listen for error codes as you dive cart slowly in steep hill mode. If the failure repeats itself, there ought to be a code telling you why.

How to get into diagnostic mode is explained by text at bottom of attached PDS label.

Thank you. Today I went out and ran it again for over a mile on pavement with no problem. I haven’t charged it yet either. Voltage was running 35.5 under load at full speed. After I finished this little drive, the voltage after a couple minutes was back up to 37.5. I’ve also read that the batteries really need to be cycled 15-20 times before they reach peak performance. I will keep on trying to figure this out because I built this into a very nice cart and want to be able to run it a lot longer between charges that it went yesterday.

[Mooncarter]

Put it on the charger and let it charge.

[JohnnieB]

Originally Posted by Phil0411

Thank you. Today I went out and ran it again for over a mile on pavement with no problem. I haven’t charged it yet either. Voltage was running 35.5 under load at full speed. After I finished this little drive, the voltage after a couple minutes was back up to 37.5. I’ve also read that the batteries really need to be cycled 15-20 times before they reach peak performance. I will keep on trying to figure this out because I built this into a very nice cart and want to be able to run it a lot longer between charges that it went yesterday.

The average SoC maintained plays a very significant role in how long the batteries last, so charge after each use. Never discharge below 50% SoC and never let batteries sit overnight in a partially discharged state. Also, too late for this set but for future reference, new batteries need to be fully charged prior to first use and that first charge may take 20 hours or more, so you may have to restart charger.

With little exception, my batteries have been either been in use or being recharged or on float charge since new (13-Nov-12) and just turn nine years old. Of course, the range is less than a third of what it was when they were in their prime, but still enough to get me to the store and back or a drive through the nearby park.

New batteries only have about 75% of their rated storage capacity when new and it take a couple dozen charge cycles to get them up to their rated AH capacity. Also, storage capacity is temperature dependent. Batteries are rated at 80°F and lose about 10% of their storage capacity for each 15°F below 80°F.