Go Back  R/C Tech Forums > General Forums > Electric On-Road
Amperage Question >

Amperage Question

Like Tree4Likes

Amperage Question

Old 11-28-2017, 09:56 PM
  #1  
Tech Fanatic
Thread Starter
iTrader: (30)
 
Dobbs's Avatar
 
Join Date: Mar 2006
Location: Oshkosh, WI
Posts: 873
Trader Rating: 30 (100%+)
Default Amperage Question

Question for the electric whizkids out there.
My F1 car with a ratio of 2.97FDR, 63mm diameter tires, trinity d4 25.5, and 4600mah 90c 2s Lipo on a fully charged (8.4v) pack draws 10.92watts @ 1.3amps.
Now with that data, my battery has the potential to put out a maximum of 414 amps if I take 4.6 amps multiplied by 90 as a discharge rate if I am understanding this correctly.

My VTA car with similar data was pulling the same wattage of 10.92 from an MC1 motiv 25.5 with a 65c 5000mah battery and 3.93FDR and 65mm tires.
Given these same outputs of wattage is it safe to assume that the maximum amp draw from any given 25.5 motor is going to peak at around 1.3 amps?

I would have thought the added resistance and weight of a 4 wheel drive train plus the difference in gearing would result in more of an amp draw ergo meaning I need more power to propel the VTA car.
Does this sound correct?
Dobbs is offline  
Old 11-28-2017, 10:23 PM
  #2  
Tech Elite
iTrader: (2)
 
gigaplex's Avatar
 
Join Date: Dec 2015
Location: Melbourne, VIC
Posts: 3,329
Trader Rating: 2 (100%+)
Default

Originally Posted by Dobbs View Post
Question for the electric whizkids out there.
My F1 car with a ratio of 2.97FDR, 63mm diameter tires, trinity d4 25.5, and 4600mah 90c 2s Lipo on a fully charged (8.4v) pack draws 10.92watts @ 1.3amps.
Now with that data, my battery has the potential to put out a maximum of 414 amps if I take 4.6 amps multiplied by 90 as a discharge rate if I am understanding this correctly.

My VTA car with similar data was pulling the same wattage of 10.92 from an MC1 motiv 25.5 with a 65c 5000mah battery and 3.93FDR and 65mm tires.
Given these same outputs of wattage is it safe to assume that the maximum amp draw from any given 25.5 motor is going to peak at around 1.3 amps?

I would have thought the added resistance and weight of a 4 wheel drive train plus the difference in gearing would result in more of an amp draw ergo meaning I need more power to propel the VTA car.
Does this sound correct?
That 1.3A draw sounds like the unloaded steady state current draw. It'll draw a lot more than that while under load while accelerating. How are you measuring the current?

The C ratings on batteries are more of a guideline, they aren't well defined. The solder on the internal wiring would probably melt before you actually hit 414 amps.
gigaplex is offline  
Old 11-28-2017, 10:23 PM
  #3  
Tech Elite
iTrader: (29)
 
R3VoLuTiOn's Avatar
 
Join Date: Jan 2004
Location: Vancouver, Canada
Posts: 2,662
Trader Rating: 29 (100%+)
Default

how are you measuring the current draw?

I'm certain under load it would be MUCH higher.
R3VoLuTiOn is offline  
Old 11-28-2017, 11:00 PM
  #4  
Tech Fanatic
Thread Starter
iTrader: (30)
 
Dobbs's Avatar
 
Join Date: Mar 2006
Location: Oshkosh, WI
Posts: 873
Trader Rating: 30 (100%+)
Default

I had my PA 0101 wattmeter setup and was pulling full throttle at time of recording data.
I used this meter for electric airplane setups to determine wattage for motor systems. I figured I could use it to check wattages and amp draw on the cars too
Dobbs is offline  
Old 11-29-2017, 12:19 AM
  #5  
Tech Elite
iTrader: (2)
 
gigaplex's Avatar
 
Join Date: Dec 2015
Location: Melbourne, VIC
Posts: 3,329
Trader Rating: 2 (100%+)
Default

Originally Posted by Dobbs View Post
I had my PA 0101 wattmeter setup and was pulling full throttle at time of recording data.
I used this meter for electric airplane setups to determine wattage for motor systems. I figured I could use it to check wattages and amp draw on the cars too
Were you driving it or was this on the bench with the wheels off the ground? If the latter, thats not representative of actual use. I'd expect peak currents of at least 20 amps, if not a lot higher.
gigaplex is offline  
Old 11-29-2017, 05:08 AM
  #6  
Tech Fanatic
Thread Starter
iTrader: (30)
 
Dobbs's Avatar
 
Join Date: Mar 2006
Location: Oshkosh, WI
Posts: 873
Trader Rating: 30 (100%+)
Default

Originally Posted by gigaplex View Post
Were you driving it or was this on the bench with the wheels off the ground? If the latter, thats not representative of actual use. I'd expect peak currents of at least 20 amps, if not a lot higher.
It was on bench, wheels up. I will be testing at the track later today so maybe I can put the car down on the burnout pad and get a better reading with more rolling resistance.
Dobbs is offline  
Old 11-29-2017, 06:57 AM
  #7  
LJH
Tech Master
iTrader: (2)
 
Join Date: Nov 2009
Posts: 1,230
Trader Rating: 2 (100%+)
Default

Running the car off the ground would be like testing a plane motor without a prop. I also fly a lot of e-powered planes and was curious of the amp draw of my cars so to get the average amp draw for a run on my 17.5 turn TC I used the Mah used vs. the time run and it averages right around 15A. Obviously the amps while accelerating are much higher.

Cheers,
Jim
LJH is offline  
Old 11-29-2017, 01:13 PM
  #8  
Tech Fanatic
Thread Starter
iTrader: (30)
 
Dobbs's Avatar
 
Join Date: Mar 2006
Location: Oshkosh, WI
Posts: 873
Trader Rating: 30 (100%+)
Default

Originally Posted by LJH View Post
Running the car off the ground would be like testing a plane motor without a prop. I also fly a lot of e-powered planes and was curious of the amp draw of my cars so to get the average amp draw for a run on my 17.5 turn TC I used the Mah used vs. the time run and it averages right around 15A. Obviously the amps while accelerating are much higher.

Cheers,
Jim
Yeah I never thought about the resistance aspect of the friction from the wheels on the ground much like a prop biting into the air resistance from an airplane motor spinning.
Dobbs is offline  
Old 11-29-2017, 02:49 PM
  #9  
Tech Elite
iTrader: (2)
 
gigaplex's Avatar
 
Join Date: Dec 2015
Location: Melbourne, VIC
Posts: 3,329
Trader Rating: 2 (100%+)
Default

Originally Posted by Dobbs View Post
Yeah I never thought about the resistance aspect of the friction from the wheels on the ground much like a prop biting into the air resistance from an airplane motor spinning.
It's not the friction that adds all the load. Physically moving the mass of the car is where most of the energy goes.
Tim Neja likes this.
gigaplex is offline  
Old 11-29-2017, 06:47 PM
  #10  
Tech Fanatic
Thread Starter
iTrader: (30)
 
Dobbs's Avatar
 
Join Date: Mar 2006
Location: Oshkosh, WI
Posts: 873
Trader Rating: 30 (100%+)
Default

So after testing we were pulling between 15-18 amps at full throttle with 130-150 watts.
Tim Neja likes this.
Dobbs is offline  
Old 11-29-2017, 07:10 PM
  #11  
Tech Elite
iTrader: (2)
 
gigaplex's Avatar
 
Join Date: Dec 2015
Location: Melbourne, VIC
Posts: 3,329
Trader Rating: 2 (100%+)
Default

Yep, that sounds more realistic.
gigaplex is offline  
Old 11-30-2017, 07:34 PM
  #12  
Tech Addict
iTrader: (2)
 
MaxRain's Avatar
 
Join Date: Feb 2007
Location: Calgary, Canada
Posts: 569
Trader Rating: 2 (100%+)
Default

I built a Dyno and found that a 21.5 T can draw 25-30 amps easily under load
MaxRain is offline  
Old 12-01-2017, 06:32 AM
  #13  
Tech Elite
iTrader: (37)
 
howardcano's Avatar
 
Join Date: Jan 2012
Location: Olathe, KS
Posts: 3,783
Trader Rating: 37 (100%+)
Default

The latest ROAR-legal 21.5T motors will draw over 140 amperes peak from a standing start if the battery can handle it.
Tim Neja likes this.
howardcano is offline  
Old 12-01-2017, 04:00 PM
  #14  
Tech Elite
 
Skiddins's Avatar
 
Join Date: Feb 2006
Location: Windsor, UK
Posts: 4,911
Default

Originally Posted by howardcano View Post
The latest ROAR-legal 21.5T motors will draw over 140 amperes peak from a standing start if the battery can handle it.
Are you sure about that?
That's over 1.1KW at 8V

21.5's tend to be rated at a couple of hundred Watts, the 25-30A (whilst accelerating etc) sounds far more reasonable.

I can wheelspin a TC off the line with a 13.5
My F1 (21.5) just pulls away without any drama even if the throttle is buried (Taking 1200mAh out during a run equates to an average of 14A)
Skiddins is offline  
Old 12-01-2017, 04:05 PM
  #15  
Tech Fanatic
iTrader: (2)
 
Adamska27's Avatar
 
Join Date: Apr 2012
Location: The land of cheese and beer
Posts: 919
Trader Rating: 2 (100%+)
Default

https://www.teamassociated.com/pdf/c...Spec-Chart.pdf

I hope this helps
Adamska27 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.