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Old 12-11-2015, 09:52 AM   #1
Helirich
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Default Crazy idea?

If I understand a controller right, I limits the power going from the battery to the motor. Not sure if it is limiting voltage or amps or both. When you buy a bigger controller (higher amp), the max amps that can get to the motor is what the controller will allow when the pedal is on the floor. I assume that is with full pack voltage.

Now, if you wanted to bypass the controller altogether, I would think you could just link the batteries to the motor with a selinoid. The problem would be the cart would jump so hard that it might break something. (Your neck?)

So what if you ran a stock controller, but at the bottom of pedal, you have trigger for this bypass selinoid. That way, you excelerate normally until you hit the button. Then you have all the power your motor can draw.

There would be some issues to work out so your not in reverse and happen to hit the bottom of the pedal and give a direct short. (Because the selinoid is wired for forward). But I think you could rig some relays in there so it could only fire when in forward.

Crazy?
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Old 12-11-2015, 10:23 AM   #2
Yamahaman
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Default Re: Crazy idea?

Crazy ?? no as it has been discussed before.The problem always seems to be the same scenerio at the end,A WILD RIDE. The problem is when all those volts and amps melt those switches together and dump all those volts,amps directly to the motor then your in deep doo doo. You have no way to stop it but relax,you still have a steering wheel to guide your rocket ship
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Old 12-11-2015, 11:23 AM   #3
JohnnieB
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Default Re: Crazy idea?

It is crazy only because it is a solution to a problem that barely exists.

The output of a controller is chopped DC. An array of a dozen or so MOSFETs (Metal Oxide Field Effect Transistor) connected in parallel is located between the battery pack and the motor and the MOSFETs are switched from completely OFF to completely ON about 18,000 times per second. The ratio of ON time vs Off time determines how much power is forwarded to the motor. The technical name for the process is called PWM (Pulse Width Modulation) and the duty cycle varies from 0% with throttle up to 100% with throttle wide open.

Although full battery pack voltage is applied to the motor each time the MOSFETs are turned on, when we measure the output voltage to the motor with a voltmeter, we read the average ON time and it appears that the output varies from zero volts to full pack voltage as the PWM varies from 0% duty cycle to 100% duty cycle.

As for the problem that barely exists: When turned ON, the MOSFETs are not perfect conductors, so there is a slight voltage drop across the controller when its output is at 100% duty cycle. Typically, no more than about 0.1V per 100A of current flow.

By using a solenoid to bypass the controller, you could eliminate that voltage drop, but is a tenth of a volt, or so, worth the effort?

How many amps a motor draws is determined by the voltage applied and motor's RPM. The faster it spins, the fewer amps it is capable of drawing and a motor doesn't have to be spinning more than about 1000 RPM before it is incapable of drawing all the amps a stock controller will pass.

Granted, bypassing the controller while the motor's RPMs are low may increase the amp flow through the motor by a fraction of 1% and up the torque produced by a similar factor, but it may also allow the motor to self-destruct by allowing it to produce more heat than it can dissipate.

The top speed will also be increased by a fraction of 1%, so if a cart's top speed is 14MPH, it will increase to about 14.14MPH.

In a nutshell, the time and money would probably be better spent improving the existing amp delivery system. The high current cables, contacts and connections typically drop more voltage per 100A of current flow than the controller does, so upgrading the cables, solenoid and F/R switch (on series carts), is likely to yield a grater bang for the buck.

----------
On the other hand, there are a few members of this loony bin that have used solenoids to bypass a stock controller and add an addition battery or two to the pack when the pedal is on the metal.
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Old 12-11-2015, 11:30 AM   #4
mardad
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Default Re: Crazy idea?

Quote:
Originally Posted by johnnieb View Post
it is crazy only because it is a solution to a problem that barely exists.

The output of a controller is chopped dc. An array of a dozen or so mosfets (metal oxide field effect transistor) connected in parallel is located between the battery pack and the motor and the mosfets are switched from completely off to completely on about 18,000 times per second. The ratio of on time vs off time determines how much power is forwarded to the motor. The technical name for the process is called pwm (pulse width modulation) and the duty cycle varies from 0% with throttle up to 100% with throttle wide open.

Although full battery pack voltage is applied to the motor each time the mosfets are turned on, when we measure the output voltage to the motor with a voltmeter, we read the average on time and it appears that the output varies from zero volts to full pack voltage as the pwm varies from 0% duty cycle to 100% duty cycle.

As for the problem that barely exists: When turned on, the mosfets are not perfect conductors, so there is a slight voltage drop across the controller when its output is at 100% duty cycle. Typically, no more than about 0.1v per 100a of current flow.

By using a solenoid to bypass the controller, you could eliminate that voltage drop, but is a tenth of a volt, or so, worth the effort?

How many amps a motor draws is determined by the voltage applied and motor's rpm. The faster it spins, the fewer amps it is capable of drawing and a motor doesn't have to be spinning more than about 1000 rpm before it is incapable of drawing all the amps a stock controller will pass.

Granted, bypassing the controller while the motor's rpms are low may increase the amp flow through the motor by a fraction of 1% and up the torque produced by a similar factor, but it may also allow the motor to self-destruct by allowing it to produce more heat than it can dissipate.

The top speed will also be increased by a fraction of 1%, so if a cart's top speed is 14mph, it will increase to about 14.14mph.

In a nutshell, the time and money would probably be better spent improving the existing amp delivery system. The high current cables, contacts and connections typically drop more voltage per 100a of current flow than the controller does, so upgrading the cables, solenoid and f/r switch (on series carts), is likely to yield a grater bang for the buck.

----------
on the other hand, there are a few members of this loony bin that have used solenoids to bypass a stock controller and add an addition battery or two to the pack when the pedal is on the metal.
dang!!!!!!
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Old 12-11-2015, 01:47 PM   #5
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Default Re: Crazy idea?

so jonnieB-if i did the extra battery(s) bypass,the rear end-axels/motor will be the only weak links?
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Old 12-11-2015, 01:57 PM   #6
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Default Re: Crazy idea?

No.....I think what JohnnieB is saying is the bypass is not really getting you what your looking for.....if what your looking for is neck snapping off the line torque. So, for all of the work you put in to bypass the controller, you get very little.....less than 1% more torque in output of "neck snap". Why bother? Beef up your high amp wiring to 2-ga. welding wires that have the lugs crimped and soldered, and make sure you have the best connectors that you can buy and keep them clean plus use the right contact "gack" so they constantly keep the current flowing.

But, if I'm wrong someone will chime in.
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Old 12-11-2015, 03:05 PM   #7
Helirich
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Default Re: Crazy idea?

So why do people buy a 500 amp controller if there is no benefit over a 275?
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Old 12-11-2015, 07:38 PM   #8
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Default Re: Crazy idea?

Quote:
Originally Posted by Helirich View Post
So why do people buy a 500 amp controller if there is no benefit over a 275?
Tangible benefits are received from controllers over 275A.
With a 500A controller, a series wound DC traction motor will produce 82% more low end torque than it will with a 275A controller and with a 600A controller is will produce about 120% more low end torque. However, top speed does not increase with a higher ampacity controller.

The net result is that you can haul/tow a heavier load and that you can accelerate from a standstill faster and that the cart can climb a steeper hill without stalling the motor.

However, once the motor is spinning above the RPM at which it cannot draw more than 275A, there is little performance difference between a 275A, 500A, 600A or 2,000A controller, other than the higher ampacity controllers are less likely to overheat when worked hard.

I don't have a Torque vs RPM curve for a stock series motor, but I do have one for an aftermarket motor and the principle is the same even though the specific RPM and torque numbers are not the same.

Connected to a 48V battery pack, the unnamed motor can draw 526A and produce about 80ft/lb of torque at about 1,000RPM
Same motor connected to same battery pack can only draw 408A and produce 60ft/lb of torque at about 1,250RPM.
Same motor connected to same battery pack can only draw 291A and produce 40ft/lb of torque at about 1,575RPM.
Same motor connected to same battery pack can only draw 231A and produce 30ft/lb of torque at about 1,800RPM.

At some RPM between 1,575 and 1,800, this motor cannot draw more than 275A, so below that RPM there is a significant performance difference with a higher amp controller and above that RPM, there isn't.

FWIW: The motor in the example has over 15HP (About 11.5 @36V) while a stock series motor is only about 2.5HP.

Since this motor can draw over 500A at low RPM, a 600A or larger controller is needed to obtain maximum performance from it. A 500A controller is about all a stock series motor can handle and about 450A is max for a PDS motor.
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Old 12-11-2015, 09:48 PM   #9
ticklechicken
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Default Re: Crazy idea?

JohnnieB - I love all the technical explanations. Very informative. Thanks.
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Old 12-11-2015, 10:17 PM   #10
Helirich
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Default Re: Crazy idea?

Yea, I knew there was not any real speed to gain unless you were going slow due to weight. But there is no speed to gain from a higher amp controller either. (Unless you change the motor too.)

I was just thinking for someone who wanted more power, it would be a lot cheaper than a higher amp controller.
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