Newbie with some questions

KLA

Hi,

This is my first post here.
I got a free 92 EZGO electric which had some problems. The first was some of the batteries were dead. Easy fix.

The second was that the motor cut out as soon as I gave it more than about 2/3 throttle. In this forum I found that the controller will go into fault mode as soon as it reads more than about 5 kOhm on the potentiometer. I measured it, and the pot resistance reads smoothly across the entire range, but measures 8.1 kOhm at full throttle. Seems like the resistance trace was worn down a bit.
This was easily fixed by wiring a 15 kOhm, 1/4 W resistor parallel to the potentiometer terminals on the controller. A fix that cost a few cents compared to replacing the pot box.

The third problem was that the rear end produces a loud and annoying whine when driving forward, but not in reverse.

I pulled the rear end apart and the input shaft gear teeth are worn. In fact they are worn such that I cut my fingers on the teeth crowns when I lifted the shaft.

The wear is such that only the center parts of the input shaft teeth, where they engage with the intermediate gear, are badly worn. The outer 1-2 mm of the teeth on either side are not worn.
I assume that during forward drive axial play of the input shaft causes these outer parts to contact the intermediate gear and cause the whine. Axial play would go into the opposite direction during reverse and is probably more stable there.

I'm still waiting for my new input shaft to arrive to find out if that fixed the whine.

While waiting I was contemplating what to do with the cart in the future. I like electric drive for its convenience, but I would like a little more power.
So a 48V conversion might be in order.

Question 1: Does the stock motor and controller handle 48V?
If yes, would the solenoid need to be changed or can it be done by just wiring a small resistor in series with it so it only sees 36V?

Question 2:
I as also contemplating a gas conversion. However, that seems to be complicated, requiring centrifugal clutch, gearing, and the problem of reverse.
Therefore I want to know if somebody has done a serial hybrid conversion of a golf cart. In that case a small gas motor would drive two 150 A/24V heavy duty truck alternators. The alternators would be isolated from each other so they can charge two 24V battery sets wired in series to produce 48V.
The gas engine would autamically started as soon as the battery voltage drops below a set point to keep battery charge up. Because the batteries in that case would only supply drive power when going up steep hills and during acceleration, normal 12V car starter batteries could be used. The system could therefore be lighter than the very heavy 8-6V batteries. Any thoughts from the forum members on that?

BGW

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yurtle

Q1: The 36 volt solenoid can be wired to just use 36 volts of your 48 volt battery pack, but you'll need a new controller, and if you go to 48 volts, you'll likely upgrade the controller, so you'll need a heavy duty solenoid. 48 volts means a new controller, solenoid, HD FNR, thicker cables, BUT, you can use the motor.

Q2: The alternator probably can't output nearly enough current to drive a buggy.

KLA

Thanks for the information


Well, the GE motor is rated for 2.75hp continuous duty output power. If I conservatively assume that the motor and controller total efficiency is about 70%, that would mean 2.9 kW needs to be supplied by the alternators when the motor runs at its rated power. And at 48V that would mean 59 Amp draw.
The heavy duty truck alternators can supply 150A. So there would be ample excess current to keep the batteries charged during more or less level cruising.

Of course, the peak current draw is much higher, but only when starting from a standstill and possibly during hill climbs. That's where the batteries would act as buffer to supply that.
Automotive starter batteries can supply more than 400A peak current. Especially the ones designed for high compression engines. So for a short time they can supply the peak current needed.

JohnnieB

FWIW: Here is the EZGO hybrid:
http://www.ezgo.com/Exceed.html

kab69440

How are you going to fit all those batteries, a gas motor and those giant alternators under the seat?

KLA

The truck alternators are not much bigger than a normal car alternator, so they are not that big. A run-of-the-mill 12V car alternator can deliver typically 100A. 150 and 200A+ alternators are available also. They also output much higher than 12V if the battery is disconnected. In a 12V alternator the diodes break down at about 36V, and a car alternator will output that, but destroy its diodes in the process. A 24V truck alternator is basically the same, but with the diodes rated for a higher voltage and possibly a few more windings in the rotor.

Modern car batteries have also gotten very small. Their capacity in Ah ist not that great compared to a normal golf cart 6V battery, but their peak current rating is very high because of the high plate surface area. That's what they are designed for. A modern high peak current battery for a race car for example is 12V and about 1/2 the size of a 6V golf cart battery.

An alternative to the alternators (no pun intended :-) ) would be a 48V SEPEX motor used as generator. That would need a custom controller for the field current, so it outputs the correct voltage.

JohnnyB:
The Exceed hybrid kit is very close to what I mean by a serial hybrid. However, as I understand, with that the golf cart is normally running with the generator off and the generator is manually engaged if needed to recharge the batteries. What I envision is that the generator is always on and ramps up its generation power (rpm) depending on load, while the batteries only supply short term peak current if needed.
Basically the alternators and electric motor form a continuously variable and reversible transmission in any but peak load operation.

JohnnieB

The way I understand the Exceed system is that there is the option of running the generator while cart is in motion, charging the battery pack while the motor is draining it.
The motor draws more amps than the generator produces, therefore the net result is extended range.

Sounds like you are aspiring to shrink the Diesel-electric locomotive concept down to golf cart dimensions and add some buffer storage to compensate for the diminutive ampacity of a gasoline powered generator small enough to be hauled around in, or on, a cart.

KLA

Not quite :-).
The primary reason hybrid cars have been invented is that a normal midsize car requires only about 15-20 hp to drive at 65mph on the freeway. An internal combustion engine runs most efficiently (in fuel used per hp-hr) when running near peak torque at full throttle. The much higher rated power of the engine is only used for acceleration and hill climbs. With an electric motor and battery, charged by the motor as generator when power demand is low, the internal combustion engine can be smaller and runs for longer periods in operation in its most efficient power band. Most hybrids are parallel though, like the Prius, where the electric motor augments the smaller gas engine during high power demand.
But an example for a serial hybrid is the Chevy Volt, where you can drive shorter distances on pure electric, but for long distance the on-board generator provides enough power to keep the batteries charged, essentially producing enough to supply the AVERAGE power demand for the vehicle.
The batteries provide the averaging.
Because the generator has to supply only the average demand, it can be sized quite a bit smaller.
In the Exceed the generator uses a 6 hp engine. As I said earlier, the max sustained hp of the GE electric motor is 2.75 hp. Even with a generator efficiency of only 70%, it could supply 4.2 hp in electric power continuous. I think a golf cart would need far less on average. Therefore the Exceed range is the sum of battery charge + tank capacity of the generator.

In a diesel-electric locomotive the diesel generator has to provide enough power also for the peak demand. That's the major difference.

JohnnieB

There are a lot of variables, but when cruising, 36V Golf cart motors draw about 50A or 1.8kW and at 745.7kW per Hp that equates to about 2.4Hp.
Cruising Amps will be lower with a 48V system, but kW and Hp will be the same.

With my stock PDS controller (300A), peak energy to the motor is about 10.8kW, which develops about 14.5Hp.
With a 500A controller, the same motor will have about 18kW available and will develop about 24.1Hp until the smoke leaks out.

With a 48V battery pack a 500A controller peaks at about 24kW to the motor, or about 32.2Hp.

If I understand what you are thinking about doing correctly, the on-board gasoline powered generator will produce about 2kW for the cart to cruise on, plus a few more Watts to recover the peak demands ex post facto.

Interesting project, but I believe I'll continue to charge my batteries with electrical energy produced more efficiently by coal fired power plants.

KLA

Yes, you got it. I will be using the cart to drive around the neighborhood, but, because it has a utility bed, I also want to use it as "riding wheel barrow" around the property.

For a 48V system with 8 typical golf cart 6V batteries, the total battery weight is around 560 pounds (~70 lbs per battery). These 560 pounds have to be lugged around, accelerated and so on.

A 6.5 hp honda clone engine, coupled to two 24V-150A large frame alternators, weights about 110 pounds for engine and alternators together, incl. mounting. A typical car starter battery weighs about 30lbs and 4 are needed for 48V. So the "power source" weight will go down from 560 lbs to around 250 lbs, the equivalent of 2 adults in weight reduction and therefore also some significant reduction in peak power demand (or better acceleration/climbing ability).