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Old 09-22-2011, 02:58 PM   #1
simple man
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Default Controllers and load.

I've been noticing a lot of posts about hunting carts and needing more torque. My question is why is it hard on the controller to make the cart go slowly? I use mine this way a lot and had no idea this is bad for it. I always thought " balls to the wall " is what is bad! Please bear with me and if there are " simple " things to do, let me know! I know an improved heatsink for the controller will help and any little tips you guys have will too!
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Old 09-22-2011, 03:18 PM   #2
rib33024
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Default Re: Controllers and load.

This all depends on what drive system you have, this applys to PDS and DCS systems, what year cart, and drive system is yours
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Old 09-22-2011, 03:51 PM   #3
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Default Re: Controllers and load.

Quote:
Originally Posted by rib33024 View Post
This all depends on what drive system you have, this applys to PDS and DCS systems, what year cart, and drive system is yours
I'm not sure of the year, ID tag gone, but it is an industrial cart with series system. Right now I am using a 1206 controller at 36V. The motor is an Advanced DC Inc. 48V motor. It has 11-11-97 on it so I'll guess that is a date of manufacture. I'm not having any problem, I just am curious about what I can do to keep from having a problem. This controller and the ITS throttle came from a junk cart I picked up. I'm just using these temporarily until I can get another controller that's 48V. My original controller is a Curtis 1205 with a pot throddle. It succumbed to a few years of total abuse! It is a 24-36V that was run on 48V for over a year! It also was driven until it wouldn't go forward and then reversed to get home. I intend never to treat it this way! This cart was obtained from where I used to work and this is how it was used, so not being a electronics whiz, I'd just like a heads up on how to use the cart properly! Thanks guys!
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Old 09-22-2011, 04:37 PM   #4
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Default Re: Controllers and load.

oooh, thats a good one!

so in a nutshell, when voltage is applied to a motor it naturally wants to spin at its top speed for the given voltage and load. (this is due to counter-electromotive force, CEMF.) any difference in this speed and the actual speed results in current. (for more on this look up Lenz's Law.)

alright, so the motor is saying "top speed, top speed, gotta get to top speed!" BUT, we aren't letting it get there. the slower the motor goes, the bigger the difference between actual speed and the top speed its shooting for. the bigger this difference, the higher the current.

for most controllers, the speed is regulated by pulse width modulation. (PWM aka duty cycle) for 25% throttle, the controller pulses the motor 25% on, 75% off. for half throttle its 50% on, 50% off. for 100% throttle, its full on, no off. its only when we reach 100% throttle that the motor is given the chance to fully balance the back EMF. this is the point at which current is the lowest. soooo, the lower the throttle input, the higher the current through the motor and controller.

make any sense?
-sj

image source 1: https://rdl.train.army.mil/soldierPo...m0703/lsn4.htm
image source 2: http://www.netrino.com/Embedded-Syst...dth-Modulation
Attached Images
File Type: gif fig4-20.gif (7.9 KB, 5 views)
File Type: gif PWMFigure1.gif (5.4 KB, 4 views)
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Old 09-22-2011, 05:52 PM   #5
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Default Re: Controllers and load.

Quote:
Originally Posted by sonicj View Post
oooh, thats a good one!

so in a nutshell, when voltage is applied to a motor it naturally wants to spin at its top speed for the given voltage and load. (this is due to counter-electromotive force, CEMF.) any difference in this speed and the actual speed results in current. (for more on this look up Lenz's Law.)

alright, so the motor is saying "top speed, top speed, gotta get to top speed!" BUT, we aren't letting it get there. the slower the motor goes, the bigger the difference between actual speed and the top speed its shooting for. the bigger this difference, the higher the current.

for most controllers, the speed is regulated by pulse width modulation. (PWM aka duty cycle) for 25% throttle, the controller pulses the motor 25% on, 75% off. for half throttle its 50% on, 50% off. for 100% throttle, its full on, no off. its only when we reach 100% throttle that the motor is given the chance to fully balance the back EMF. this is the point at which current is the lowest. soooo, the lower the throttle input, the higher the current through the motor and controller.
make any sense?
-sj

image source 1: https://rdl.train.army.mil/soldierPo...m0703/lsn4.htm
image source 2: http://www.netrino.com/Embedded-Syst...dth-Modulation
Actually, yes it does! I do a lot of slow driving, mostly on firm, but sometimes soft ground. My motor gets just warm, but the controller is what I'm most concerned with. How hot is too hot? It gets hotter than the motor. Will a bigger heatsink help? Thanks!
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Old 09-22-2011, 06:26 PM   #6
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Default Re: Controllers and load.

werd!

for a quick and dirty temp test.... if you can't hold you hand on the controller for more than a few seconds, its too hot!

a better heatsink will work but might take a lot of effort to retrofit. using a thermal coupling pad or thermal grease will help the heat transfer to the heatsink. a fan helps tremendously!
-sj
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Old 09-22-2011, 06:50 PM   #7
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Default Re: Controllers and load.

Quote:
Originally Posted by sonicj View Post
werd!

for a quick and dirty temp test.... if you can't hold you hand on the controller for more than a few seconds, its too hot!

a better heatsink will work but might take a lot of effort to retrofit. using a thermal coupling pad or thermal grease will help the heat transfer to the heatsink. a fan helps tremendously!
-sj
There we go! a simple, but effective temp test It doesn't get that hot! I can keep my hand on it. Thanks for the info. A fan sounds like a cool idea!
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Old 09-22-2011, 08:24 PM   #8
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Default Re: Controllers and load.

Quote:
Originally Posted by sonicj View Post
oooh, thats a good one!

so in a nutshell, when voltage is applied to a motor it naturally wants to spin at its top speed for the given voltage and load. (this is due to counter-electromotive force, CEMF.) any difference in this speed and the actual speed results in current. (for more on this look up Lenz's Law.)

alright, so the motor is saying "top speed, top speed, gotta get to top speed!" BUT, we aren't letting it get there. the slower the motor goes, the bigger the difference between actual speed and the top speed its shooting for. the bigger this difference, the higher the current.

for most controllers, the speed is regulated by pulse width modulation. (PWM aka duty cycle) for 25% throttle, the controller pulses the motor 25% on, 75% off. for half throttle its 50% on, 50% off. for 100% throttle, its full on, no off. its only when we reach 100% throttle that the motor is given the chance to fully balance the back EMF. this is the point at which current is the lowest. soooo, the lower the throttle input, the higher the current through the motor and controller.

make any sense?
-sj

image source 1: https://rdl.train.army.mil/soldierPo...m0703/lsn4.htm
image source 2: http://www.netrino.com/Embedded-Syst...dth-Modulation
Lost me right after: "oooh, thats a good one!"
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Old 09-22-2011, 08:43 PM   #9
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Default Re: Controllers and load.

Great explanations sonicj and pretty concise given the variables explained.
Some of the EV cars are even using liquid cooled controllers (Soliton and Zilla) for the overheat situations.
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Old 09-22-2011, 10:10 PM   #10
scottyb
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Default Re: Controllers and load.

You can hold your hand on 105 degrees for a few moments before the impulse to withdraw it can't be ignored but 105 is still relatively cool to the motor. The fans don't even come on on the new SPM control at that temp..... anybody know what temp the fan comes on in the new Alltrax controls?
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