Overheating

[soninja8]

So I just got a ton of car bodies with a ton of gold (servos) and motors from my friend who knows nothing about electronics....shame....well anyways, i made a car out of it with a servo for steering (in pic) and a servo for throttle (also in pic) and im using the motor that came on the car (pic)....my problem is that im using this old type of throttle control where the servo turns, and it touches these panels that send a current to the motor. There is 2 panels for forward, making it 2 speed, and 1 panel for backwards, meaning it goes full throttle (very fast) backwards. The thing is that after about 5 minutes of use, my battery (8.4v 1600mah in pic) gets to the point where it burns me on touch....There are no shorts....is this because of my wiring, im not using a big gauge wire, or is it because the battery is just to high on amps? Can the motor not take the amps? Or is it just the old throttle? whenever i move the throttle back and forth, sparks fly for a second, and then the car moves as normal, but the battery gets very very hot....

Thanks,
Soninja8

[TrickyNekro]

I've got the impression that discharging a NiMh battery the reaction in the battery is exothermic...
That means that yes it actually heats up no wonder...

Batteries have a self resistance so it's not that hard to imagine that even more energy is converted to heat there...


You are probably in need of big currents when running the car. Take a multimeter measure the current and reply :p

But yes heating up is not abnormal. In fact there are some RC manufactures that label the battery compartment as
"Warning hot after use"

So it's not that of a big deal really... For now measure that current (also try breaking the motor a little to see how much the current will increase)

Finally, the sparks you see are also normal. They occur because the coils in the motor try to maintain the voltage across their terminals.
And that spark is widely know as back EMF. (or ElectroMotive Force)

[soninja8]

By current do you mean voltage? If so, the ln my battery Is usually at 9.4 volts when fully charged with my smart charger. And what do you mean when u say break the motor?

[TrickyNekro]

By current I mean current.... It's as simple as this...

It's specified as the flux of charged carriers through a surface  over time

[Fr0stAngel]

The DC motor you are using has probably high current demands ( i once used something similar, that took upto 3 amps at no load) so yes, no wonder the battery overheats. its supplying excess current in a short amount of time. if you can ,try getting a battery having greater mAh matching the current requirements of your motors. aside from lasting longer, they would stay cooler too (a battery's output is a function of temperature too)
The sparks are normal too, as sir TrickyNekro said , its because of back emf. but try not to reverse the change motor's direction suddenly at higher speeds ( back emf is a function of speed)..

[TrickyNekro]

The sparks are normal too, as sir TrickyNekro said , its because of back emf. but try not to reverse the change motor's direction suddenly at higher speeds ( back emf is a function of speed)..

Sir?? haha, I'm at my 20ies not that old :-p


The truth is that back EMF is a function of current mainly, but can be of speed also.

EMF = -DΦ/dt and Φ = LI. Where Φ is the magnetic flux through a surface, L is the inductance of the motor coil. I is current and t is time.... ;-)
There are many things you want to consider before building a very good and efficient motor controller ;-)

So yes actually it is a function of speed as DΦ/dt is higher at greater speeds but people miss most of the time is that EMF is not voltage.
It's measured in volts but actually it's current delivering capability... ;-)

[soninja8]

The DC motor you are using has probably high current demands ( i once used something similar, that took upto 3 amps at no load) so yes, no wonder the battery overheats. its supplying excess current in a short amount of time. if you can ,try getting a battery having greater mAh matching the current requirements of your motors. aside from lasting longer, they would stay cooler too (a battery's output is a function of temperature too)
The sparks are normal too, as sir TrickyNekro said , its because of back emf. but try not to reverse the change motor's direction suddenly at higher speeds ( back emf is a function of speed)..

This is exactly right, that motor is demanding to high on amps, I found this out earlier, because i used a smaller motor, and my battery stays fine. But my problem is I dont know what this motor demands....I accidently threw away the labeling...any suggestions? 3000mah is probably a good start right?

[waltr]

Measure the motor characteristics. Here is an article on some motor basics:
http://www.micromo.com/motor-calculations.aspx

A voltmeter and a resistor along with Ohm's law will get you the info needed.

[soninja8]

http://cgi.ebay.com/TENERGY-8-4V-5000mAh-Flat-NiMH-Battery-Pack-RC-TRAXXAS-/360375494975?pt=US_Batteries&hash=item53e80da93f
I was thinking about getting this....will this be to much for that motor? Or is it the motor that decides how much power it needs and handles itself? The battery says 40A discharge max...

Thanks,
Soninja8

[Fr0stAngel]

Sir?? haha, I'm at my 20ies not that old :-p


The truth is that back EMF is a function of current mainly, but can be of speed also.

EMF = -DΦ/dt and Φ = LI. Where Φ is the magnetic flux through a surface, L is the inductance of the motor coil. I is current and t is time.... ;-)
There are many things you want to consider before building a very good and efficient motor controller ;-)

So yes actually it is a function of speed as DΦ/dt is higher at greater speeds but people miss most of the time is that EMF is not voltage.
It's measured in volts but actually it's current delivering capability... ;-)

haha  im in my early twenties too, i just wrote that out of respect( thats what we use sometimes from where i come from),since i'm sure you must know shitloads more than me when it comes to robotics ( being a supremerobot and all that  )  ...sorry if it felt otherwise 
and yes, i think i may have mis conveyed by saying it was a function of speed.What i really meant was that,generally, the greater the speed, greater the back emf.

I was thinking about getting this....will this be to much for that motor? Or is it the motor that decides how much power it needs and handles itself? The battery says 40A discharge max...

The mAh( milli-amps per hour) rating is the amount of current a battery CAN supply in one hour( in this case 5000 mA), or twice that in half hour or four times that in 15 mins..etc. Its not something the battery will always supply regardless of the load. Motors should only draw the current they need to operate(unless there is a short-circuit).
when they say 40A maximum discharge, it means don't connect anything with the battery that draws more current than that , else it could damage the battery it by overheating .

[TrickyNekro]

haha  im in my early twenties too, i just wrote that out of respect( thats what we use sometimes from where i come from),since i'm sure you must know shitloads more than me when it comes to robotics ( being a supremerobot and all that  )  ...sorry if it felt otherwise 
and yes, i think i may have mis conveyed by saying it was a function of speed.What i really meant was that,generally, the greater the speed, greater the back emf.

No problem at all, I was joking, I usually try to break the ice with people, it's nice being relaxed with people around you. To my books respect isn't earned with nice talking. There are many ways to show respect to someone. But anyhow thank you, even if you didn't need to.
About the back EMF we are probably saying the same thing. ( And I messed up a little what I was trying to say)

I just wanted to say that in a circuit even if the voltage across a terminal is zero, that doesn't mean that EMF is also zero regardless of the fact that EMF is measured in volts ;-)

The mAh( milli-amps per hour) rating is the amount of current a battery CAN supply in one hour( in this case 5000 mA), or twice that in half hour or four times that in 15 mins..etc. Its not something the battery will always supply regardless of the load. Motors should only draw the current they need to operate(unless there is a short-circuit).
when they say 40A maximum discharge, it means don't connect anything with the battery that draws more current than that , else it could damage the battery it by overheating .

That's not very accurate with all chemistries. For example the 1C/h for the NiMh is a lot more accurate when the draw is around 1C. For bigger currents, batteries usually can deliver less charge over time. Don't know if the source I got that from also calculated self resistance
but, at least having self resistance in mind the above I said is accurate. Cause the power wasted on a resistance is P = R*I^2.

[soninja8]

So I should be okay with the 5000mah?