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Motors and watts?


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#1 munter

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Posted 30 December 2017 - 01:41 PM

Can anyone explain the relationship and relevance of watts when talking about different slotcar motors?

 

I know a guy who often quotes watts in his motor discussions and as I know little I feel I cannot strongly debate motor related topics with him.

 

I have a feeling he is talking out a hole in his head but there is some sort of correlation between watts and motors isn't there?

 

Keep it simple please.

 

TIA

 

John


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#2 Ramcatlarry

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Posted 30 December 2017 - 02:43 PM

Ohm's Law  Volts X Amps = Watts.   It can vary quite a lot with any motor since the way WE use it the voltage is constantly changing with the controller and track power.

Motor "C" draws 2 amps at full speed.  Will probably draw more amps under acceleration load.

 

Track 'A' uses 12 volt DC power supply.  Motor "C" will use 24 watts at full speed and maybe 30 under load.  This about the normal limits for a single or double barrel (Turbo) resistor controller.

 

Track 'B' uses 14.2 Volt DC power supply.  Wattage used goes up just from increasing the voltage let alone the possible amp load from stressing the motor further.


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Larry D. Kelley, MA
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#3 Klenkes

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Posted 30 December 2017 - 02:48 PM

Watt is the international measuring unit for power. Maybe you are more familiar with the commonly used measuring unit for the power of combustion engines which is hp. You easily can convert watt in hp: 1 hp (horsepower based on lbf and ft) equals 745 Watt.

 

Is this what you wanted to know?


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#4 zipper

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Posted 30 December 2017 - 03:05 PM

Group 7 cars on our King tend to use  average 35 amps at 14 volts. Makes 490 watts average = 0.66 Hp.


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Pekka Sippola

#5 havlicek

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Posted 30 December 2017 - 03:25 PM

To make it simpler (*although Pekka's explanation is prettty danged clear), watts= "power".  I think that, if people used common terms there would less confusion to all this.  Watts= "power".


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John Havlicek

#6 Steve Deiters

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Posted 30 December 2017 - 03:37 PM

When I worked in the industrial mixer business (very big stuff) one of the ways they programmed processes (especially in the pharmaceutical industry) for repeatability was to track the ammeter draws at various stages of the process.  When more accuracy was demanded we switched to watt meters.  The techno-wienies told me that it was 10 time more accurate than ammeters.  I don't know if that is true or not, but I took their word for it.  The important thing to note is we are talking about AC motors (10 HP-25 HP on up) and not low voltage/low horsepower DC motors.  There may be a difference.


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#7 Ecurie Martini

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Posted 30 December 2017 - 03:41 PM

Group 7 cars on our King tend to use  average 35 amps at 14 volts. Makes 490 watts average = 0.66 Hp.

 

Typical DC motor efficiency can be as high as 90% - 49 watts dissipated as heat - must get pretty hot.

 

EM


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Alan Schwartz

#8 munter

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Posted 30 December 2017 - 04:06 PM

Thanks guys some understanding is settling into my neurons.

 

Watts + Power is a pretty simple comparison.

 

The guy in question is involved in 1/32 RTR stuff and the motors are pretty weak. I must ask him where he is getting his ratings from.

 

Thanks again for the input.


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#9 munter

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Posted 30 December 2017 - 04:07 PM

I know I can ask this sort question here and get some sensible knowledgeable answers, appreciate it.


John Warren
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#10 zipper

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Posted 30 December 2017 - 04:37 PM

 

Typical DC motor efficiency can be as high as 90% - 49 watts dissipated as heat - must get pretty hot.

 

EM

Operating temperature is probably nearly 200 C / almost 400 F - I did melt a pinion last time, soldered with a 220 - 230 C solder when pushing too hard..


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Pekka Sippola

#11 gjc2

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Posted 30 December 2017 - 05:56 PM

An electric motor is a transducer. A transducer is a device that converts one form on energy to another.

 

An electric motor turns electrical energy into mechanical energy, and generator does the opposite.

 

In reality an electric motor doesn’t have power unto itself; it just converts the supplied power within a range of capability.  


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George Cappello

#12 zipper

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Posted 30 December 2017 - 06:00 PM

Never seen efficiency figures for modern motors - the old Mabuchis did have a graph on the box showing something like 50 - 60 %.


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Pekka Sippola

#13 Ramcatlarry

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Posted 30 December 2017 - 11:08 PM

If you try to draw powerHP/watts, 12 volts is regular gas and 14+ is aviation gas.  The motor puts out a different value every instant...never a constant value.

 

I did a clamping amp meter test on my King track once and a '64' gp-7 motor pulled over 40 amp - for a peak instant.


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Larry D. Kelley, MA
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#14 Bazzie

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Posted 31 December 2017 - 02:14 PM

A motor's power rating is essentially determined by its efficiency and it's ability to disperse the 'wasted' energy as heat. Power in must equal power out. Power in is just V x A, and power out is made up of the sum of kinetic or mechanical energy (to overcome drag and roll resistance of our cars - useful) and heat (not useful for our slot cars).
I've never heard of DC motors with efficiency as high as 90%, 45-60% is more reasonable. That's why for RC planes we now use almost only brushless motors, as they can get to 90% quite easily, generating more useful power, and do not need to disperse as much heat as DC motors do.


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#15 Dan Miller

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Posted 12 January 2018 - 10:24 AM

John,

 

I have been around slot car motors and motor building for about 50+ years and have wound a reasonable number R/C armatures over a 7 or 8 year period. I even made an R/C lamination die, that made blanks that ran very well. They won some major US R/C National race titles, under various names. But that is another story.

 

If a guy ever quoted a slot car motor watt value to me, I would tell him to shove it up his amperage. We have plenty of never ending power to play with.

 

............ But I bet that Tony P would see value in watts consumed in R/C racing, as you are saddled with carrying your power supply around with you, for a designated time period. That situation calls for some electrical math. Slot racing really illustrates no necessity to do so.

 

Tell your motor guy to Ohm off. That, or just sit there, nodding your head, with a far off look in your eyes, until he switches topics. 

 

.


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#16 munter

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Posted 13 January 2018 - 01:51 PM

Thanks Dan, I appreciate the shared thoughts.

 

This guy is irritating on several fronts but the motors/watts thing is one that stood out.

 

I will shove it all as soon as the chance arises.


John Warren
Slot cars are my preferred reality


#17 Dan Miller

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Posted 13 January 2018 - 04:11 PM

John,

 

For slot cars you want to know that the power is clean with no AC ripple or EMF coming through from the pop machine, air conditioner or cheap battery charger, etc. You have to worry that it is steady and constant through out the whole day, start to finish and that it will not burn up your motors. The last important consideration is if the power is the same on all lanes. This has little to do with what the motor puts out in value terms.

 

Ratings or levels of ohms, watts, amps or animated pectrons is all needless information. You want clean, steady, predictable power. If you are using your motor, with a special attachment, powered by a battery pack, to scramble your morning eggs, electrical value considerations may apply.

 

Taking ohmage, amperage, wattage readings of slot motors is not worth the time and leads nowhere of value.

 

On the other hand, my best buddy built a voice operated, computer controlled, RC dyno, for his 1/12th scale cars, that can be programed to simulate operation on his local track. He enters the shape of the track and runs his car on the dyno. That gives him real solid information. He runs his car through a full race, on the dyno, collecting much useful data. Now if he could only drive like an Ace he would be a  big noise.

 

.


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