Txt shuttle gearing upgrade

Stretch

I have a 2002 txt electric shuttle, 26" tires, # 2 welding lead, HD solenoid & F/R, 700 a controller, high torque PQ motor, 48 v with new Trojan 8 v batts. This limo has a stock ratio of 15:1..... Lots of torque but only 16-17 mph with either stock motor or the new PQ motor....not happy! I have cut no corners here. I have a set of 12.44:1 gears I want to try, but don't want to waste my time installing them if someone can assure me that a higher gear ratio would suit me better. Most of the time I haul 2-4 people, occasionally, up to 6. It's not a race cart but would love to see it move at 22-25 mph or better on occassion. Please enlighten me.

BGW

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JohnnieB

The specs on a 2002 Shuttle 6 indicate the differential gear ratio is 14.7:1 and it has a series wound motor running at 48V.

That gives it 12-15MPH on stock height (18") tires, which is a pretty wide range, so let's stick with the 3800RPM rating on the stock motor, which is roughly 14MPH.

Mathematically, just going to the 26" tires should give it a 31% increase in speed, or about 20MPH, but you are only getting 17MPH, so some power is being lost someplace.
The 700A controller. 2Ga cables, HD solenoid and F/R switch should be able spin the motor at 3800RPM with the tall tires on it, but I noticed you mentioned you have new Trojan 8V batteries, so the problem may be that the battery pack cannot provide the needed Amps.

The stock 48V battery pack consists of eight T-105's (6V - 225AH)
If your 48V battery pack is made up of T-890's (8V - 190AH), it is 15.6% smaller than stock.
If your 48V battery pack is made up of T-875's (8V - 170AH), it is 24.4% smaller than stock.
If your 48V battery pack is made up of T-860's (8V - 150AH), it is 33.3% smaller than stock.

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Theoretically, with 26" tires and 12.44:1 gears, the cart should do about 24MPH with the motor spinning at 3800RPM.
However, at the 17MPH the cart is now reaching, the motor is only spinning at 3200RPM and upping the gear ratio by 15% will decrease torque by 15%, so I doubt it will go more than 18MPH or 19MPH. In fact, it might even go slower than it does now because the taller gears will increase amp draw on the battery pack.

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What does the battery pack voltage drop to at max speed?

Stretch

Thanks johnnieb for your time...I do have the T875s. With the stock motor it dropped to 42.7 before climbing back up. I don't know the draw down with the plum quick motor but I'll let you know late this afternoon. I understand what you're saying about about the lack of amps now that I went to 6- 8 v. I didn't realize that difference until you informed me. It made room for my amp rack and stereo battery, guess that's the only benefit here. Thanks again, I'll be back in touch tonight.

Stretch

Johnnyb, with the high torque plum quick motor and 4 passengers, the voltage will drop to 42v for about 2-3 seconds then it climbs straight to 45-46v. Once at full speed it holds 46.8-47.7 depending on slight changes in street elevation. Flat ground was about 47-47.2v. Today's speed was 14 with a slight uphill grade and then 17 coming back down the same slight grade. The steepest hill in the neighborhood only allowed 18mph. I appreciate anymore help with this issue.:

JohnnieB

There may be more than one issue. The battery pack voltage is dropping a couple volts at speed on level ground, which is reducing speed, but only doing 17 or 18 downhill shines some new light on issue.

Check for something dragging. Brakes, bearings, under-inflated tires.

Stretch

Johnnieb, based on the voltage drop and recovery that I have, do you think my voltage drop/ recovery is average, below average, or above average?

JohnnieB

Your voltage drop is very high, bordering on destructive.

Check the footnotes in the published battery specs from the various battery manufacturers. While closely monitoring their batteries under controlled conditions, they'll load them down to 1.75VPC (Volts per Cell) to compile data for Amp-Hour ratings and Run-Time minutes and the like, but you are hitting that VPC level during take-off and most likely going below 1.75VPC when the batteries are less than fully charged.

A fully charged 48V pack is 50.9V and 42V is 1.75VPC.

It takes a huge number of Amps to turn those 26" tires and a 700A controller will deliver a huge number of Amps, but can a 170AH battery pack deliver it and not self destruct?