Losing power going up hill

NotSoSmart

Good afternoon. I have an EZ-GO Express S4. It is electric and it will run about 19MPH on flat ground and up to 23-24MPH down hill. However when I go uphill it slows to a crawl at about 7-9MPH. The batteries are less than 6 months old and are fully charged. It does it when I am on it by myself or have all 4 seats occupied. Any thoughts on what could be causing this or is this normal?

BGW

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onabeachsomewheresoon

What type of controller, motor type, and wheel size?


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NotSoSmart

Its all stock. 48V DC Drivetrain, 250 amp solid state controller, 20in trail tires.

scottyb

There are upgraded after market speed controllers available which increase power and speed. Please ID your cart's drive system using the chart attached

Attached Images

Ezgo TXT drive system ID.jpg (205.7 KB, 0 views)

JohnnieB

A stock Express S4 has a Sepex motor and 250A controller with a 48V battery pack, 20" tall tires and 14.76:1 differential gears. Published speed on level ground is 17.5MPH +/- 0.5MPH.

I'm not sure if the controller is the same one used in a TXT-48 (Curtis 1206HB) or not.

The top speed is in the ballpark for stock, but slowing to 7-9 MPH going uphill seems excessive.

What are the make/model of the batteries?
What is the battery pack voltage at-rest (neither charged or discharged for 12 hours after charging)?
What does battery pack voltage drop to going uphill?
Do any of the high current cables get hot?

nickybobby16

Scottyb and JohnnieB, The OP of this thread is my neighbor and I am going to help him out with this issue.

Specifics to the questions you asked in January are below but I wanted to give a little more background on the situation.
The cart was purchased from EZGO as certified rebuilt cart in 2016. The low speed going uphill has been an issue since he first purchased it. I checked the specific gravity and individual battery voltages in late summer/early fall of 2016 and everything checked out fine. I do not have the pad that I recorded that information on so I can't give any more specific information from that time.

He then contacted EZGO because the cart was under warranty and they sent a service tech to his home. They replaced the battery pack(complete pack swap) in 2017. The new pack did not fix the problem so he contacted the EZGO again. They picked his cart up and took it to Augusta for further testing and he was told that it was operating as intended.

Somewhere along the way, a service tech mentioned to him that a batch of the certified rebuilt S4 models were equipped with a controller that was undersized. However, his controller was never replaced.

Two weeks ago, he took the cart to a local EZGO sales and service shop and was told that it may be a controller issue and/or possibly a motor issue. He was told this before he unloaded the cart off the trailer. He had only described the issue to the tech. The rough estimate was $1300 for the controller and $2200 for the controller and motor. He called me when he was given that estimate and I recommended holding off on that until we got some other opinions from this forum.

I personally think it is a controller issue but I would like to get some advice from the subject matter experts on here.

As far as performance expectations go. He is only looking to not slow to the speed of smell going up hill! Not looking for any increase in top speed. Any suggestions on what can be done will be greatly appreciated.

Motor and Controller:
Sepex motor w/ 250A controller.

Tire Size:
23x10.50 Backlash on 14" wheels

What are the make/model of the batteries?
- 6 x 8V Trojan - T875
- These were replaced by EZ-GO last year while the cart was still under warranty. I can check later today but I am pretty sure these are 2017 packs.

What is the battery pack voltage at-rest (neither charged or discharged for 12 hours after charging)?
~ 50.9 when I checked it after the installation of the new pack.

What does battery pack voltage drop to going uphill?
- Have not checked the voltage drop going uphill yet but I can this evening.

Do any of the high current cables get hot?
- They do not get hot.

nickybobby16

Follow up to my earlier post with more details.
Speed on flat surface:19mph
Speed on mild hill: 11mph
Voltage @ rest: 50.52V
Full throttle run on flat surface: 45.5V
Full throttle run on hill: 44.45V

Checked cables again and no excessive heat. However, they are 6 gauge
Confirmed tire size is 23x10.00, not 10.50.

JohnnieB

Tire height is the main problem, but there may be others.

Stock height is 20" tall and 23" tall tires are installed.

I'm pretty sure the Express S4 uses the same controller and motor as the TXT-48 does, but need to confirm the controller is a Curtis 1206HB.

A stock TXT-48 has 18" tall tires and 12.44:1 gears for a final drive ratio of 16.59:1
A stock Express S4 has 20" tall tires ans 14.76:1 gears for a final drive ratio of 17.71:1
That means the S4 has 6.8% more torque available where rubber meets road and should not slow as much on the same hill as a TXT-48 does. (Percent of speed loss from top speed, rather than actual MPH.)

With the 23" tall tires and a 14.76: gear ratio, the final dive ratio is now 15.40:1.
This means the your friend's S4 ought to have a top speed 15% faster than a stock S4, but have 13% less torque, so it will slow more on hills than a stock S4.

The theoretical top speed ought to be roughly 20.5 MPH, so tire width and inflation pressure might be holding it back a little, which also increases speed loss on hills.

I don't suppose your friend wants to go back to 20" tires, so more torque is needed from the motor.

A good set of high current cables (all ten of them 4Ga or thicker) will help a bit and going to an Alltrax XCT48400 controller and at least a 200A solenoid might do the trick without changing the motor. I'd communicate with Scotty and/or Alltrax to find out if there is a field map for a stock S4 motor that has better mid-range torque. (Sepex motors can be transformed from high torque to high speed or something in between by field mapping. )

If that doesn't do the trick, put in a Admiral MOT-B2. It has more speed as well as more torque than the stock S4 motor, but with the XCT controller you can RPM limit the motor to whatever your friend is comfortable with. (4100 RPM will be about 19 mph.)

nickybobby16

JohnnieB, Thanks for the response. The wheel/tire combo that is on the cart came installed by EZGO so the owner is not wanting to replace them.

I completely understand the issue that he faces with less torque and the issue it causes uphill but I really appreciate the detailed response you gave and the math involved. I may use that as a word problem for our kids! Seriously, awesome information and very much appreciated.

While riding and getting the numbers for you guys yesterday, he and I spoke about going with the Alltrax controller. I used Scottyb's pricing on Carts Unlimited to explain his options.

Option 1: XCT48300 w/ 4 gauge cables and keep factory motor

Option 2: XCT48400 - 200A Solenoid w/ 2 gauge cables and keep factory motor.

The pricing difference between the two setups is not bad. The main concern I had for him was using the 400A on the factory motor. I would hate to install the controller and then end up having motor issues. I have explained that motor failure could possibly happen. I understand that we can limit the RPMs so hopefully that will protect against destroying the motor.

My reasoning behind worrying about the factory motor is because I had a motor failure on my Yamaha YDRE after installing an XCT48300 and 4 gauge cables. The difference in my situation and his is, my cart came off a golf course and that motor was beat to heck so it was probably on the last leg anyway. The armature was in bad shape and just could not withstand the extra juice. I am not sure what EZGO does for the motor when they are "certified factory rebuilt" carts. However, I think it is pretty safe bet that his cart was not used on a course daily by golfers so his motor should not be in as bad of shape as mine was. Do you happen to know how the EZGO certified program works?

If Scottyb doesn't respond this thread, I will reach out to him via PM or email and get a better idea of the direction we should take.

Thanks,
nickybobby

Raystar57

Go with option #2. Good upgrade option for future motor upgrade.
You can limit the current to the stock motor so it wont go out as quickly.
When you get a motor upgrade just turn it back up.
RPM limit is good for safety either way.