Go to Post You can take my blocker... but you can never take my cheesecake! - Andrew Schreiber [more]
Home
Go Back   Chief Delphi > Technical > Electrical
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
Thread Tools Rating: Thread Rating: 4 votes, 5.00 average. Display Modes
  #1   Spotlight this post!  
Unread 15-02-2015, 10:32
wireties's Avatar
wireties wireties is offline
Principal Engineer
AKA: Keith Buchanan
FRC #1296 (Full Metal Jackets)
Team Role: Mentor
 
Join Date: Jan 2006
Rookie Year: 2004
Location: Rockwall, TX
Posts: 1,171
wireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond repute
Send a message via AIM to wireties
voltage loss over long runs

Lots of tall robots this year! Several online calculators tell me I lose 1.8V in a 30' long 10 AWG wire with a 30A load.

Question: do I really lose two times 1.8V? 1.8V in the red wire and 1.8V in the black?

TIA
__________________
Fast, cheap or working - pick any two!
  #2   Spotlight this post!  
Unread 15-02-2015, 10:42
RufflesRidge RufflesRidge is offline
Registered User
no team
 
Join Date: Jan 2012
Location: USA
Posts: 992
RufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant futureRufflesRidge has a brilliant future
Re: voltage loss over long runs

Nope, 1.8V is correct if the length of the run is 30ft. (i.e. 30ft. of + and 30ft. of -).

The resistance of 10AWG is .001 Ohms per ft. * 60ft. = .06 Ohms
.06 Ohms * 30A = 1.8V
  #3   Spotlight this post!  
Unread 15-02-2015, 20:15
rich2202 rich2202 is offline
Registered User
FRC #2202 (BEAST Robotics)
Team Role: Mentor
 
Join Date: Jan 2012
Rookie Year: 2012
Location: Wisconsin
Posts: 1,275
rich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond repute
Re: voltage loss over long runs

Basically, you have +12 -> R1 -> load-> R2 -> ground.

But, R2 is sinking a lot of current, which is in essence ground, and not really resisting the current.

However, if you are saturating the wire, then "pushing" power to ground could result in voltage loss needed to push the power to ground.

Just some thoughts from a Math major, and not a EE major.
  #4   Spotlight this post!  
Unread 15-02-2015, 20:22
MrForbes's Avatar
MrForbes MrForbes is offline
Registered User
AKA: Jim
FRC #1726 (N.E.R.D.S.)
Team Role: Mentor
 
Join Date: Feb 2006
Rookie Year: 2006
Location: Sierra Vista AZ
Posts: 6,033
MrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond reputeMrForbes has a reputation beyond repute
Re: voltage loss over long runs

"ground" is not something we really have on FRC robots.

Good question, I think you lose voltage on each wire, but I don't' really know, since I'm a mechanical guy. How about measuring the voltage at both ends of the wire run, under load? or measure the voltage across each of the wires, under load.

This is something we get to deal with on underwater robots. I expect that 148 gets to deal with it on their tether, too. On the underwater robots, with a surface mounted battery, we run a higher system voltage, so a specific voltage drop is a smaller percent of the total voltage available. And with a higher voltage, there is less current for the same amount of power, so the voltage drop is less also.

But they don't let us run four 12v batteries in series in FRC....only NURC let us do that.
  #5   Spotlight this post!  
Unread 15-02-2015, 20:27
Ether's Avatar
Ether Ether is offline
systems engineer (retired)
no team
 
Join Date: Nov 2009
Rookie Year: 1969
Location: US
Posts: 8,125
Ether has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond repute
Re: voltage loss over long runs

Quote:
Originally Posted by rich2202 View Post
Basically, you have +12 -> R1 -> load-> R2 -> ground.

But, R2 is sinking a lot of current, which is in essence ground, and not really resisting the current.
R1=R2, and the current is the same through both because they are in series; so the voltage drop across R2 is the same as the drop across R1. R2 is "resisting" current just as much as R1 is.


  #6   Spotlight this post!  
Unread 15-02-2015, 20:31
Ether's Avatar
Ether Ether is offline
systems engineer (retired)
no team
 
Join Date: Nov 2009
Rookie Year: 1969
Location: US
Posts: 8,125
Ether has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond reputeEther has a reputation beyond repute
Re: voltage loss over long runs

Quote:
Originally Posted by MrForbes View Post
How about measuring the voltage ... across each of the wires, under load...
You'll get then same voltage drop across each one.


  #7   Spotlight this post!  
Unread 15-02-2015, 23:39
GeeTwo's Avatar
GeeTwo GeeTwo is offline
Technical Director
AKA: Gus Michel II
FRC #3946 (Tiger Robotics)
Team Role: Mentor
 
Join Date: Jan 2014
Rookie Year: 2013
Location: Slidell, LA
Posts: 3,723
GeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond repute
Re: voltage loss over long runs

Quote:
Originally Posted by wireties View Post
Lots of tall robots this year! Several online calculators tell me I lose 1.8V in a 30' long 10 AWG wire with a 30A load.

Question: do I really lose two times 1.8V? 1.8V in the red wire and 1.8V in the black?

TIA
You shouldn't need to run 30' of wire for robot height; 78" each way is the maximum length you'll need due to height, even if you put the PDP at the floor. (Sprawl and routing will add additional length requirements, of course.) We have a robot over 6' tall, but I believe all of our motor runs are less than 3' from the PDP to the motor (and another 3' back), because all of our motors are down low on the chassis; all the electricity above the control board is for lights or limit switches. Keeping the motors low also helps reduce the likelihood of tipping over, as well.
__________________

If you can't find time to do it right, how are you going to find time to do it over?
If you don't pass it on, it never happened.
Robots are great, but inspiration is the reason we're here.
Friends don't let friends use master links.
  #8   Spotlight this post!  
Unread 16-02-2015, 00:18
Mr V's Avatar
Mr V Mr V is offline
FIRST Senior Mentor Washington
FRC #5588 (Reign)
Team Role: Coach
 
Join Date: Feb 2011
Rookie Year: 2009
Location: Maple Valley Wa
Posts: 997
Mr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond reputeMr V has a reputation beyond repute
Re: voltage loss over long runs

The easy way to "see" the voltage drop is with a multimeter. Connect the leads to each end of the wire in the circuit and then operate the circuit. The multimeter will measure the drop across that section of the circuit. Alternatively you can connect the leads at the motor and see the voltage drop that occurs across the motor terminals. Yes it is not easy to do that with a motor or controller that has wires exiting it instead of terminals.
__________________
All statements made on Chief Delphi by me are my own opinions and are not official FIRST rulings or opinions and should not be construed as such.




https://www.facebook.com/pages/Team-...77508782410839
  #9   Spotlight this post!  
Unread 16-02-2015, 07:59
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
Posts: 10,798
Al Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond repute
Re: voltage loss over long runs

Keith,
By now you have gathered that the current flows in both wires so both wires contribute to the voltage drop while running at 30 amps. If your motors stall at a greater current, then the voltage drop changes for that increased current. This was a question on the FCC First Class RadioTelephone License test. You were asked to determine the voltage drop to the tower navigation light at the top of a 1000 ft. tower. One of the answers was the drop in one wire, the correct answer included the voltage drop in both wires.
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Storming the Tower since 1996.
  #10   Spotlight this post!  
Unread 16-02-2015, 08:46
wireties's Avatar
wireties wireties is offline
Principal Engineer
AKA: Keith Buchanan
FRC #1296 (Full Metal Jackets)
Team Role: Mentor
 
Join Date: Jan 2006
Rookie Year: 2004
Location: Rockwall, TX
Posts: 1,171
wireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond repute
Send a message via AIM to wireties
Re: voltage loss over long runs

Thanks all - I appreciate the feedback. I was a little confused that the online calculator were giving an answer close to the observed results but I felt that the loss through the return was to be included. It turns out that those calculators (when you tell them it is a DC voltage) include the return distance by default.
__________________
Fast, cheap or working - pick any two!
  #11   Spotlight this post!  
Unread 16-02-2015, 08:48
wireties's Avatar
wireties wireties is offline
Principal Engineer
AKA: Keith Buchanan
FRC #1296 (Full Metal Jackets)
Team Role: Mentor
 
Join Date: Jan 2006
Rookie Year: 2004
Location: Rockwall, TX
Posts: 1,171
wireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond reputewireties has a reputation beyond repute
Send a message via AIM to wireties
Re: voltage loss over long runs

Quote:
Originally Posted by Mr V View Post
The easy way to "see" the voltage drop is with a multimeter. Connect the leads to each end of the wire in the circuit and then operate the circuit. The multimeter will measure the drop across that section of the circuit. Alternatively you can connect the leads at the motor and see the voltage drop that occurs across the motor terminals. Yes it is not easy to do that with a motor or controller that has wires exiting it instead of terminals.
We set up a test with a TalonSRX (which will tell you the supply voltage) at the end of the wire and clearly saw the drop. Making the results jive with the online calculators was the real question I reckon. Doing the actual math solved all questions and CD opinions verified the results.
__________________
Fast, cheap or working - pick any two!
  #12   Spotlight this post!  
Unread 17-02-2015, 07:42
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
Posts: 10,798
Al Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond reputeAl Skierkiewicz has a reputation beyond repute
Re: voltage loss over long runs

Keith,
I have talked about wire losses and voltage drop for years here on CD. One of the easy to remember items is the "wire foot". Simply this is a simple calculation you can make in your head. As previously stated, #10 wire is .001 ohms per foot. Well, at 100 amps, that one foot chunk of wire will drop exactly 0.1 volts. In terms of 'wire feet' here are some other equivalents.
#6= 0.5 WF/ft.
#12=2 WF/ft.
#14=3 WF/ft.
Victor=6 WF
Talon and Jag=4 WF
Battery=11WF
0.1 volt drop/WF/100 amps
So all you have to do is just add up the losses in WF and that will get you an approximation of the loss (keeping in mind both wires need to be counted).
As an example, #6 wiring from battery to PDP is typically 1 foot from battery to APP connector and 2 feet from there through the main breaker to the PDP. So that is 6 feet of #6 at 0.5 WF=3WF or 0.3 volts at 100 amps. Add 11 WF for the battery and you get 1.4 volts. Typical FRC robots at worse case will draw 500 amps so 5 x 1.4 volts=7 volts drop at the input of the PDP. And yes, that is real, the PDP will only see 5 volts at the input with a fully charged battery. That is why the PD of old had the boost/buck power supplies that were capable of running down to 4.5 volts.
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Storming the Tower since 1996.
  #13   Spotlight this post!  
Unread 17-02-2015, 09:13
rich2202 rich2202 is offline
Registered User
FRC #2202 (BEAST Robotics)
Team Role: Mentor
 
Join Date: Jan 2012
Rookie Year: 2012
Location: Wisconsin
Posts: 1,275
rich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond reputerich2202 has a reputation beyond repute
Re: voltage loss over long runs

Quote:
Originally Posted by GeeTwo View Post
You shouldn't need to run 30' of wire for robot height
Not tall, but go look at Team 148 (batman thread). They have a 30 foot or longer tether. Drive wheels are on the robot with the battery, but the tethered piece has motors for lift.
  #14   Spotlight this post!  
Unread 17-02-2015, 11:01
GeeTwo's Avatar
GeeTwo GeeTwo is offline
Technical Director
AKA: Gus Michel II
FRC #3946 (Tiger Robotics)
Team Role: Mentor
 
Join Date: Jan 2014
Rookie Year: 2013
Location: Slidell, LA
Posts: 3,723
GeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond reputeGeeTwo has a reputation beyond repute
Re: voltage loss over long runs

Quote:
Originally Posted by rich2202 View Post
Not tall, but go look at Team 148 (batman thread). They have a 30 foot or longer tether. Drive wheels are on the robot with the battery, but the tethered piece has motors for lift.
This falls under the heading of sprawl.
Quote:
Originally Posted by GeeTwo View Post
(Sprawl and routing will add additional length requirements, of course.)
__________________

If you can't find time to do it right, how are you going to find time to do it over?
If you don't pass it on, it never happened.
Robots are great, but inspiration is the reason we're here.
Friends don't let friends use master links.
  #15   Spotlight this post!  
Unread 17-02-2015, 11:17
Jon Stratis's Avatar
Jon Stratis Jon Stratis is offline
Mentor, LRI, MN RPC
FRC #2177 (The Robettes)
Team Role: Mentor
 
Join Date: Feb 2007
Rookie Year: 2006
Location: Minnesota
Posts: 3,835
Jon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond reputeJon Stratis has a reputation beyond repute
Re: voltage loss over long runs

In 2008 we saw a significant voltage drop to the motors on the ends of our elevator. There are really two days around this... Go to a larger wire (see Al's post) or double up your wire (two equivalent resistors in parallel cut the voltage drop in half). At the time, we had plenty of the wire we were using, but would have had to buy thicker wire, and didn't want to sacrifice flexibility with the thicker wire (or pay a lot more for high flex wire). So, we doubled up the wire to each motor. Each Victor had 2 positive and two negative wires going from it, and they were then rejoined when they went into the motor. The inspector we got that year was a bit confused by it, and had to call Al over to check it out and make sure it was legal. As it was still on controller powering one motor, it was.
__________________
2007 - Present: Mentor, 2177 The Robettes
LRI: North Star 2012-2016; Lake Superior 2013-2014; MN State Tournament 2013-2014, 2016; Galileo 2016; Iowa 2017
2015: North Star Regional Volunteer of the Year
2016: Lake Superior WFFA
Closed Thread


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 20:31.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi