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Electric EZGO Electric EZ GO Marathon, Medalist, TXT and RXV.



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Old 07-11-2013, 09:48 PM   #1
gotmud10
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Default 94 medalist SLOW!

I am rebuilding a 94 medalist and put a high speed motor in that was on another cart I owned. My other cart went 18mph with this motor and stock tires. The medalist goes 14-15mph with 22s, new t605s (were only at 37.7 when testing), 4g welding wiring, new solenoid, and heavy duty cam on f&r. I also pulled the rear and replaced a few bearings that looked ify. I can push cart around easily so the brakes aren't dragging either. Is there something that I'm missing here? I should be seeing 20-22 I figured. Any help or suggestions would be appreciated. My stock solenoid isn't limiting me with my other upgrades is it? Still stock controller as well.
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Old 07-11-2013, 10:55 PM   #2
JohnnieB
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Default Re: 94 medalist SLOW!

The 22" tires are costing you 21% in torque, high speed motors have lower torque than standard speed motors, the AH capacity of the new batteries is 7% less than the standard size batteries and they are only 85% charged, plus you are using a 275A controller.

To turn the oversize tires with a low torque motor (High Speed motor = Low Torque motor) is going to take a lot of amps and you have three things limiting the amps: Controller, Solenoid and Batteries.

With a high speed motor and tall tires, the cart has the potential of the low to mid 20's, but you've got to feed it more amps to get there.

Since they are new, I suspect you are locked into the batteries for a while, but when you replace them, go with a higher Amp-hour and/or higher voltage battery pack.

Upgrade the controller to at least 400A and the solenoid to at least 200A and you should see some better speed.
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Old 07-12-2013, 08:07 AM   #3
gotmud10
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Default Re: 94 medalist SLOW!

Thanks for the response Johnny...great info as always. Ill just go back to stock. It is what it is I rekon. Should've posted about it before I bought everything.
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Old 07-12-2013, 04:28 PM   #4
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Default Re: 94 medalist SLOW!

Getting your batteries fully charged and keeping them that way as much as possible, will help.

And you probably can run oversize tires (maybe not 22") OR a high speed motor, just not both until you up the amperage of the controller and solenoiod.
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Old 07-12-2013, 07:07 PM   #5
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Default Re: 94 medalist SLOW!

I helped gotmud a little today. I had a spare series 36v motor from a 97 txt and we swapped it in place of the high speed motor. Results? A very sad 11 mph with 22" tires. Needless to say we put the high speed motor back in and got 14 mph again.

We tested reverse and it was same speed as forward.

Can a controller fail to output full throttle yet still function? We checked the ITS and it seemed adjusted properly.

What are we missing? Seems it's very common to put a lift and up tire size for more speed but not with this cart for some reason....
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Old 07-13-2013, 06:36 AM   #6
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Default Re: 94 medalist SLOW!

The fact that Volts = Speed is coming into play.

Connect a DVM between A1 and S2 and monitor the voltage.
(Or whatever terminals are the most positive and most negative the way the motor is wired.)

Connect a second DVM between the main positive and main negative terminals on the battery pack.

If the two DVMs read the same when cart is at max speed, the battery pack is the problem.

If the voltage applied to motor is lower than the pack voltage under load, the high current loop is the problem.

-------------
It takes torque to turn tall tires and it takes amps to generate torque.
The more amps drawn from a battery, the lower the voltage drops.
The more resistance in a cable, connection or component, the more voltage is lost for every amp that passes through it.

Mix those facts together and repair/replace (or eliminate) what is holding the speed down.

-----------
There are hundreds of series carts turning tall tires out there, some with standard speed motors, some with high torque motors and others with high speed motors, so it can be done. That means something is wrong with the setup and the trick is to find the culprit.

-------------
I'm seeing the battery voltage drop problem with my old batteries that are currently installed.
When I accelerate hard, the voltage drops way down and the cart won't reach max speed until the pack voltage recovers.
If I take off more sedately, the voltage doesn't drop as far and I reach top speed sooner.

Nothing is getting more than slightly warm (except the motor, which is where the energy is concerted to motion or heat), so the old batteries cannot supply the amps needed. More correctly, the amps needed drop the pack voltage too far, so the present AH storage capacity of the old batteries is less than what is needed for the new application.
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Old 07-13-2013, 06:48 AM   #7
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Default Re: 94 medalist SLOW!

Quote:
Originally Posted by sportcoupe View Post
.................Can a controller fail to output full throttle yet still function? We checked the ITS and it seemed adjusted properly................
Yes. A controller can have internal problems (failures) that will limit the number of amps it will pass.

Connect a DVM between B- and M- and monitor voltage while at WOT.
Voltage should be zero or very close to it.

The control element (a dozen or so MOSFETs in parallel) is located between B- and M- and the voltage drop across it, is what limits the voltage being applied to the motor, thereby controlling the cart's speed.

It varies with the amp rating of the controller, but with a stock controller, you will see about 0.5V per 100A of current flow when control element is fully turned on (100% duty cycle)
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Old 07-13-2013, 01:21 PM   #8
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Default Re: 94 medalist SLOW!

Fully charged battery pack. Got a +1 increase to almost 16mph. Nothing big.

Put two DVM's on battery pack and motor (A1-S2). Battery pack was 38.2v static, 36.5v under load (full throttle, flat road). Motor was 0.01v static, 23.7v under same load.

Measured individual batteries (static/loaded)
1) 6.44/6.12
2) 6.36/6.10
3) 6.35/6.11
4) 6.35/6.12
5) 6.34/6.12
6) 6.38/6.11

Swapped in a rebuilt controller. No change.
All high current wires are newly homemade. Rebuilt f&r with heavy duty bars.

Seems he has a problem in the high current loop but we can't find it.
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Old 07-13-2013, 11:03 PM   #9
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Default Re: 94 medalist SLOW!

The pack dropping 1.7V under load sounds about right, or at least in the ballpark. However, losing about 1/3 of the pack voltage isn't.

If nothing is getting hot or mighty warm, the controller isn't passing the amps like it should be, or it isn't being told to go to a 100% duty cycle on the PWM.

Check the voltage between B- and M- at top speed and WOT.
I suspect it will be about 12.8V (36.5V - 23.7V = 12.8V)
It shouldn't be much more than a volt when at 100% duty cycle.

You've tried a different controller, so that leaves the ITS sensor and wiring.

According to the 94 Medalist service manual, when the solenoid first clicks, the voltage on Pin-2 (Black wire) should be slightly above 14V, but less than 15V.
Pin-1 (White wire) should be 0.45V - 0.53V when the solenoid first clicks and rise to at least 1.5V when pedal is on floor.

There is an in-line connector between the controller and ITS box, make sure those connections are clean.

(I'd post the manual, but the pdf file is too big to attach.)

Good luck find the missing voltage.
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Old 07-14-2013, 10:29 AM   #10
gotmud10
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Default Re: 94 medalist SLOW!

Got 12.14v between m- and b- at rebuilt controller. Next ill swap the its and clean connections
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