The Importance Of Heavy Wire and Controller and Voltage

adamj12b

So I have been reading this forum for a few months now and keep noticing everyone suggesting that all the wiring in the electric golf carts be increased inorder to improve speed and torque of the vehicle. Also, I keep seeing some posts with questions about sizing controllers, I hope to make it easier to understand those as well.

Before I start, I will give a little about my background.

I am an Electronic Engineering Student, and have been dealing with power circuits in-depth for the past few years. I have successfully built my own 144V 500A DC motor controller and have tested it for over 100 hours.

So the first thing that starts to bother me is the controller sizing. This will all apply to SERIES wound motors, NOT REGEN!!


Now for how an electronic controller operates.

The controller is responsible of modulating the motors current, voltage, or both. Most controller modulate current as torque is what makes the vehicle move. Torque is directly related to the current it receives. A controller works by switching the power to the motor on and off very fast. Usually around 16K times per second. In doing this, it allows the controller to vary the amount of voltage or current it is outputting. The controller uses a system called Pulse Width Modulation. This is simply the amount of time the controller spends in the on and off positions.

I will not go into depth on this because is a topic on its own. Please refer to the Wikipedia article for more information on how it works. http://en.wikipedia.org/wiki/Pulse-width_modulation

When the controller is operating, the pulse width is varied to allow the output to do what the input (throttle) is commanding.

So, A few other little things that will be important. Battery Amps and Motor Amps.

These are not the same!! When you buy a controller and it says its good for 400A, this is motor amps. Motor amps is greater then battery amps as long as your not at 100% duty cycle. Motor amps is the amount of current the motor wants to use. This is dependent on load. If the motor wants 200A, but the controller only wants to give 100A, then 100A is all the motor gets.

Now, Battery Amps is the amount of current flowing from the batteries to the controller. This is the actual amount of power being consumed.

So for the math, Duty is a number 0 to 1. Battery Amps is calculated from motor amps as: Motor Amps * Duty = Battery Amps. ex. 400 * 0.5 = 200 Battery Amps.

Motor Amps is calculated from battery amps as: Battery Amps / Duty = Motor Amps. ex. 200 / 0.5 = 400 Motor Amps.

Both of these are figuring on a 0.5 (50%) duty of the controller, basically 1/2 throttle.

True:

• A electronic controller will increase motor torque over a solenoid drive system.
• A electronic controller will increase overall range.
• A electronic controller will not usually make the cart go faster.

False:

• A 400 Amp controller requires the batteries to put out 400 Amps.
• Battery Amps and Motor Amps are the same thing.
• Motor torque is dependent on the number of batteries.

So I will explane each of these now.

Trues:
[*]A electronic controller will increase motor torque over a solenoid drive (resistor coils) system.

The controller will increase the motors output torque at low RPM because it will be able to provide higher current at low voltage. Since torque is proportional to current in series motors, you will have more torque with this drive system. The resistor coils limit the available current to the motor to limit torque, and thus speed.
[*]A electronic controller will increase overall range.

The electronic controller will increase the range of the vehicle when upgraded from the solenoid drive system because of the increase of efficiency of the drive system. When speed is limited with resistor coils, the extra current is burned off in the coils, wasting power as heat. The electronic controller only wastes a few watts of heat, instead of a few thousand. This will increase your range.
[*]A electronic controller will not usually make the vehicle go faster.

This is true because there is no extra voltage being induced into the system to increase the top RPM of the motor. However, If there happend to be excessive resistance in the solenoids, or some wiring, this would limit the current to the motor. When you replaced this faulty equipment, and added the new controller with less in circuit resistance, it might increase the speed slightly.

False's:
[*]A 400 Amp controller requires the batteries to put out 400 Amps.

This is not true. The 400A rating on a controller is the motor amps output rating. In order to pull 400A from the batteries with an electronic controller, you will have to be either low duty (low throttle position) with heavy load on the motor, or very heavy load on the motor at full throttle. As the throttle position changes, or the vehicle starts moving, the motor current will drop.
[*]Motor torque is dependent on the number of batteries.

This is not true. Torque at mainly dependent on the amount of current the motor is receiving. At 0 RPM of the motor, torque will be directly proportional to current. As motor voltage rises, if the current is kept the same, torque will be the same, but the RPM and HP of the motor will be increasing.



Power Cables.

It is not always necessary to change out all the power cables in a golf cart inorder to get maximum power. When and electronic controller is used, you should use heavy power cabled from the controller to the motor. This is because of the Motor Amps.

The cabling that goes from the batteries to the controller, can most of the time be left at 6 AWG. The 6 AWG power cables are good for 101A in open air conditions, such as a golf cart. For the 400A controller I have been talking about, this would result in 400 Motor amps from standing still, when you peg the throttle. Quickly after this, the motor is up to speed and the current is quickly dropping off.

Heres a graph of this situation.

As you can see, Current spikes, at the full ability of the motor to to pull current. It starts quickly tapering off as it starts to spin. Within 1 second, current has gone from 0 to 360 amps and down to 270 amps. After that, current keeps tapering as load decreases and the vehicles speed increases.

So back to wire size. The only real way that wire size can decrease the performance of the vehicle is if it has been heavily overloaded in the past. When copper is heated, it will cause an annealing process to take place. This will raise the resistance of the wire and cause a voltage drop as well as limit current. So unless you will be pulling hundreds of battery amps continuously, super heavy wire might not be needed.... I still run #6 with no problem with a 500A controller.

I want to hear what you guys have to say.

-Adam

BGW

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wilster734

HUH , your mom has no potential?

adamj12b

HAHA, I didnt realize that was in that picture. That was my friend being a loser when we were programing the interface software for the controller. I will get it edited and reposted.

Thanks for pointing that out

-Adam

wilster734

nice artical though hows that controller workin out now and do you have any upgrades on the solenoids?

redriderno22

good info adam!

wilster734

so most important cables to upgrade are the ones from the controller to the
motor.

gornoman

Adam, I take exception with one part of your logic. If the motor is calling for 350 amps, and the controller is allowing 350 amps, then those same amps are coming through the solenoid AND the battery pack. You can call them whatever you want to, but amps are amps. Also, even perfectly good brand new cable has resistance, and larger high-strand count cable has less resistance than stock low-strand count cable. The upgrade is warranted if you want to ensure highest efficiency. Your stock cables will work. They COULD work better.

BTW, nice post.

bigk

Hey adam thank's for showing up . Keep the forum alive ! Later Big K..

adamj12b

The controller works great!! In testing, it was sitting on the passenger side floor, heat-sink side down. I was not able to get the heat-sink above 85 Degrees F, in the fall weather.

No, I have not upgraded the solenoids at all yet. I am current using one of the original resistor solenoids for the main on/off solenoid. These are them: http://www.evparts.com/prod-SL1935.htm

I have not hooked reverse back up yet, because the only way to do this is to switch the motor output side. The original solenoids: http://www.evparts.com/prod-SL1936.htm , can only handle 100A continuously on one set of the contacts. I am worried about welding these shut, so I just didn't put them back in yet.

Well, it is possible for the motor to see 400A at low duty cycles. With the low duty, the batteries will only have a few amps being pulled from them, but the motor could have the full ability of the controller with only a few volts on it. Its still 400A though!!

Hello Gornoman,

I really appreciate hearing from somebody with a large presence on the forums, such as yourself.

I am going to have to disagree with you on the first part of your reply. I will explane. When the controller is regulating current, It is looking at the output of the controller and not the input. This is different from the input because of the switching function of the controller. Another name for this is a Buck Converter. http://en.wikipedia.org/wiki/Buck_converter Basically what this is doing is is varying output voltage of the controller as a side effect of controlling the current. At low voltages, the motor will get HUGE amounts of current and hence, loads of torque. The motor wont go very far, or fast, without voltage. As the voltage rises, the motor starts to spin faster, even if its only a few RPM. This is the condition of low duty cycle. The duty cycle will usually be proportional to throttle position. So if you push the throttle 1/5th of the full travel, you will have a 0.2 or 20% duty cycle. (Duty Cycle is 0-1) with a 20% duty cycle, power is applied to the motor 20% of the time, or 0.2 seconds of 1 second. This doesn't all happen at once, but is divided over 16 thousand times in 1 second. So using the formula: Motor Amps * Duty Cycle = Battery Amps. So the 350 motor amps times 0.2 for duty cycle would equal 70 Battery Amps (350 * 0.2 = 70). The only time that motor current and battery current will be equal, is when duty cycle is at 100%.

I do agree with you about the cable. All electrical conductor has some amount of resistance. The finer the stands, the less resistance. This is how welding cable carries such high currents over long distances without burning up. I do not know where to find resistance information for stock or common low quality cables, but I would love to find that information so that I could compare the differences between that and a high quality welding cable.

-Adam

EZGOmywallet

wow, way over my head, but I think G-man is gonna like you Like bigk said, I am glad you are here and I think you could be a big asset to this forum !