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Discussion Starter · #1 ·
If I took a series dc motor and advance it how much would I be able to increase the voltage without doing damage? Since the higher voltage decreases needed amp would that cause less heat production?
 

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If I took a series dc motor and advance it how much would I be able to increase the voltage without doing damage? Since the higher voltage decreases needed amp would that cause less heat production?
It does not work like that!

Your controller gives the motor the voltage that it needs for the demanded current

So when stationary it may need 10 v to get the desired 600 amps
As soon as the motor is spinning it develops a back EMF - so it needs MORE voltage for the same current
Example
Stationary 600 amps - 10 v -
1000 rpm - 600 amps - 40 v
2000 rpm - 600 amps - 70 v
3000 rpm - 600 amps - 100 v
4000 rpm - 600 amps - 130 v

The Three terms - current/voltage and rpm are linked

Advancing the motor enables you to use more RPM - but it also drops the torque from a given current at low speeds

My motor is advanced by 8 degrees - that means that I lose nearly 20% of my torque
Or that I need to run about 20% more current to get the same torque - the opposite of the effect you wanted

Increased battery voltage does reduce battery current
Example - 150 volt battery
Stationary 600 amps - 10 v - - 150v - 40 amps
1000 rpm - 600 amps - 40 v-- 150v - 160 amps
2000 rpm - 600 amps - 70 v- - 150v - - 280 amps
3000 rpm - 600 amps - 100 v- 150v - 400 amps
4000 rpm - 600 amps - 130 v- 150v - 520 amps

Example - 300 volt battery
Stationary 600 amps - 10 v - - 300v - 20 amps
1000 rpm - 600 amps - 40 v-- 300v - 80 amps
2000 rpm - 600 amps - 70 v- - 300v - - 140 amps
3000 rpm - 600 amps - 100 v- 300v - 200 amps
4000 rpm - 600 amps - 130 v- 300v - 260 amps
 

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Discussion Starter · #4 ·
So why do people advanced them if there losing power by doing so? So i need to give it alot more voltage and it would help with the amperage and production of heat in the wires.. I just ran amp test on it, stationary it's pulling 150-165 max and setting down to 97-110 @12v at 24v+36v 135-144 start, settling at 80-90. When I hooked it up to 48v it had a much better startup time and sounded like more torque behind it I haven't tested 48v's amperage yet. So do I need to do something to it to be able to give more v without damaging it? It's a 12-24v Clark forklift drive motor
 

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So why do people advanced them if there losing power by doing so?
They advance brush timing to increase the power available at higher motor speed, at the expense of lower power and efficiency at low motor speed. Like everything else in life, and especially in technology, it's a tradeoff.
 

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Discussion Starter · #6 ·
Ok I get that,but at higher speeds less torque is needed to keep a constant speed all power needed would really be for takeoffs I mean unless you are not worried about taking longer to takeoff from like from a light.. its like turning the motor from diesel to gasoline (diesel only has power at low rpm whereas gasoline at higher rpm) I don't get why we would want to do that unless there motor much stronger than necessary
 

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Discussion Starter · #7 ·
So As I understand it if I give a higher voltage it'll pull less amperage to reach the same wattage does that change the output torque? And as I understand it would extend the battery life because the more amps you pull the faster the batteries drain right? and make the rpm higher?
 

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So As I understand it if I give a higher voltage it'll pull less amperage to reach the same wattage does that change the output torque? And as I understand it would extend the battery life because the more amps you pull the faster the batteries drain right? and make the rpm higher?
Nope
If you use a higher BATTERY voltage it reduces BATTERY current
But motor current remains the same!

Advancing reduces the available torque - but it enables me to run more rpm
Which is what I need
https://www.youtube.com/watch?v=LUpyAY2sFWw
 

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Discussion Starter · #9 ·
I guess I miss read the article on this topic so I would need more batterys to extend my range, I appreciate the help to properly understand the situation
 

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Discussion Starter · #11 ·
So you're saying diesel don't loose power the higher the rpm? So why tf the they put so many more gears in the semis ? Diesel is not ignited it combust from compression so how does that make power from higher rpm really work. And gasoline don't get much power behind it until you get to a higher rpm
 

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Discussion Starter · #13 ·
Thanks for clearing up the original questions I appreciate your assistance and given knowledge. I'm still kinda young and trying to learn what I can since school doesn't teach you stuff like this unless you go to college. And the internet can be deceptive, misleading, and/or unclear sometimes
 

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So you're saying diesel don't loose power the higher the rpm?
...
Diesel is not ignited it combust from compression so how does that make power from higher rpm really work.
Of course diesel fuel is ignited; "ignition" just means the initiation of combustion. The more generic name for diesel engines is compression-ignition engines, while gasoline engines are normally spark-ignition.

While high-speed ability of diesels is limited by the duration of combustion (since the fuel is burned as the fuel is injected, rather than rapidly as in a spark-ignition engine), this isn't an issue at normal automotive engine speeds. Many diesel engines are designed for low speeds; that doesn't mean that you cannot have a high-speed diesel engine, and the Audi R10 racing engine produced peak power at 5,000 rpm... more than twice the maximum speed of a big truck engine.

This illustrates the importance of understanding why things work as they do, not just observing a trend and thinking it is a fundamental limitation.

So why tf the they put so many more gears in the semis ?
A heavy truck (such as a highway tractor with semi-trailer) weighs 20 to 60 tons loaded, and is driven by an engine only capable of a few hundred horsepower, and even that only at one specific peak engine speed. To make the most of the engine, many gear ratios are provided to keep the engine close to the optimal point.

And gasoline don't get much power behind it until you get to a higher rpm
That's not true. The speed of the peak torque of an engine depends on the specific engine design, including intake and exhaust tuning and camshaft profile. The big difference between common diesel and gasoline engines in low-speed torque production is that all of the diesels are turbocharged, and few gasoline engines are. If you compare a modern turbodiesel and modern turbocharged direct-injection gasoline engine of the same displacement at the same speed and boost, the gasoline engine will produce comparable or higher torque... but most people compare turbodiesels to non-turbo gas engines, or huge (6.7 L) diesels in pickup trucks to much smaller turbocharged gasoline engines.

Power is just the product of torque and speed, so if two engines produce similar torque at low speeds but one of them can continue to work well at higher speeds, the higher-speed engine will produce more power... and yes, the extra power will be at the highest speed, even though the higher-speed engine may produce superior power at all speeds, even the low end.

This illustrates the importance of considering the application context of any technology, instead of jumping to conclusions about the fundamental technology.



While this may look like it is all about gasoline and diesel engines, it is really about understanding the characteristics of technical designs, such as DC and AC electric motors, rather than jumping to invalid conclusions based on incomplete knowledge of some specific applications.
 

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Thank anyway I thouggt when they started electric motors was full torque and was all the way to top speed
Regardless of type, electric motors are typically limited in torque by current, and limited to a fixed maximum current from zero speed to a significant part of the way up their speed range - that's the constant-torque region. At the other end of the scale, the current through the motor is limited by the available voltage at high speeds, as an increasing amount of voltage is required to overcome back-EMF at higher speeds. In-between, while the motor itself could be limited by current or voltage, in practice in EVs they are limited by the power that the battery or controller or cooling system can handle, so they are effectively constant-power (so decreasing torque with speed) over much of their speed range.

So
  1. constant-torque (limited by current) from zero to some transition point,
  2. constant-power (limited by battery, electronics, and cooling) from the transition point to nearly the maximum speed, and
  3. decreasing power approaching top speed.

In a DIY system with a brushed DC motor, it may go straight from constant-torque to decreasing power, since it is so voltage-limited and control is so basic.

If the design of the system is messed up badly enough, it might be current-limited over the entire usable speed range - that would give you constant torque from a standstill to top speed, and indicates poor use of the capabilities of the battery and/or the motor.
 

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Discussion Starter · #16 ·
I think I understand what you're saying , so back emf is the resistance created by the motors generated magnetic field? Thank you for explaining that so well that a layman can understand.. that's why I joined was to learn. Sorry to everyone about my response to a response that to me felt like was disrespectful and demeaning whether or not it was meant to be. Either way I should have been more civil when responding. Thanks again Brian
 
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