Espritmodel.com Telemetry Radio
Reply
Thread Tools
Old Jun 21, 2014, 06:34 PM
Registered User
Joined Dec 2013
20 Posts
Question
Length of the battery wires

Hello RCGroups members,
I have a 6s5p battery I made with 18650 cells (24v, ~11Ah).

I use it for an electric bike build with peak current draw of 15 amps and continuous draw of 5 to 11 amps (250w motor brushed).

I use 16AWG wire, and my question is, how long can I make the wires?
What I mean is from the solder tabs on the batteries to the connector at the other end, what is the maximum length allowed?

also, does it matter if I cut the battery cable short but make the wires from the controller to the battery longer?

Thank you!
Dman12 is offline Find More Posts by Dman12
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 21, 2014, 07:24 PM
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,527 Posts
Quote:
Originally Posted by Dman12 View Post
Hello RCGroups members,
I have a 6s5p battery I made with 18650 cells (24v, ~11Ah).

I use it for an electric bike build with peak current draw of 15 amps and continuous draw of 5 to 11 amps (250w motor brushed).

I use 16AWG wire, and my question is, how long can I make the wires?
What I mean is from the solder tabs on the batteries to the connector at the other end, what is the maximum length allowed?

I think that 16AWG is much to small. I don't have numbers to back me up but just off hand I would be thinking more like 12AWG.

What kind of length are you contemplating? More than a foot? If much more than that I would go to even bigger wire. The longer the wire the greater the loss. Bigger wire will mitigate the loss.


also, does it matter if I cut the battery cable short but make the wires from the controller to the battery longer?

Probably not. At least for brushless motors in aircraft that is the correct method. I don't know if the applies to your brushed controller or not.

Thank you!
Glen
ggcrandall1 is online now Find More Posts by ggcrandall1
Reply With Quote
Old Jun 21, 2014, 08:18 PM
PGR
Low AltiDude
PGR's Avatar
United States, CA, Costa Mesa
Joined Jun 2004
7,834 Posts
I don't understand all the science behind it, but it's a well-established fact that long wires between a battery pack and the ESC puts a LOT of stress on the ESC. If you must have long wires you're better off keeping the wires between the battery and ESC short and making the ESC to motor wires longer.

Ron van Sommeren knows about as much as anyone about this subject and he has a thread about it HERE.

Pete

BTW, I agree completely with Glen that 16ga is too small for 15A, especially if the wires are long.

rePete
PGR is online now Find More Posts by PGR
Last edited by PGR; Jun 21, 2014 at 08:24 PM.
Reply With Quote
Old Jun 21, 2014, 10:29 PM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
20,638 Posts
This might help you figure out the right size wire to use.
http://www.solar-wind.co.uk/cable-sizing-DC-cables.html
hoppy is offline Find More Posts by hoppy
Reply With Quote
Old Jun 25, 2014, 06:45 AM
Registered User
Joined Dec 2013
20 Posts
Thanks. I run the wire for 50cm (less than 2ft) and the site say it is possible to use 16AWG wire with only 1% loss, however I changed it to 12AWG just in case.

putting the ESC closer to the battery cant be done the way the bike is built right now, maybe later I will change it, it is a cheap ESC anyways.
Dman12 is offline Find More Posts by Dman12
Reply With Quote
Old Jun 25, 2014, 07:03 AM
Retired in NC
Rich in ILM's Avatar
USA, NC, Wilmington
Joined Sep 2010
1,954 Posts
Quote:
Originally Posted by Dman12 View Post
Thanks. I run the wire for 50cm (less than 2ft) and the site say it is possible to use 16AWG wire with only 1% loss, however I changed it to 12AWG just in case.

putting the ESC closer to the battery cant be done the way the bike is built right now, maybe later I will change it, it is a cheap ESC anyways.

Just run longer wires from the ESC to the motor, if possible.
There is no dc "ringing" on the motor side.
Rich in ILM is offline Find More Posts by Rich in ILM
Reply With Quote
Old Jun 25, 2014, 07:09 AM
Unregistered User
vimy g eaou's Avatar
Australia, SA, Adelaide
Joined Feb 2014
10 Posts
I have no idea of Imperial measurements, but here is a table of resisitance if that helps:

http://www.cirris.com/testing/resistance/wire.html

Here is the formula for resistance:

http://hyperphysics.phy-astr.gsu.edu...ric/resis.html
vimy g eaou is offline Find More Posts by vimy g eaou
Reply With Quote
Old Jun 25, 2014, 07:21 AM
Registered User
tacx's Avatar
United States, MI, Macomb
Joined Apr 2009
2,463 Posts
Your 16 ga. Would have been ok. At only 15 amps max, the 12 ga. Is more than plenty. The national electrical code allows 20 amps for 12 ga. and that rating is very conservative. At 15 amps your #12 is plenty.

But as others have said. If you are dealing with a ESC there is an issue with length between the ESC and the battery.
tacx is offline Find More Posts by tacx
Reply With Quote
Old Jun 25, 2014, 07:47 AM
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,527 Posts
Quote:
Originally Posted by tacx View Post
Your 16 ga. Would have been ok. At only 15 amps max, the 12 ga. Is more than plenty. The national electrical code allows 20 amps for 12 ga. and that rating is very conservative. At 15 amps your #12 is plenty.

But as others have said. If you are dealing with a ESC there is an issue with length between the ESC and the battery.
The National Electrical Code is dealing with AC. DC is prone to higher line losses than AC. Stick with the 12AWG.

Glen
ggcrandall1 is online now Find More Posts by ggcrandall1
Reply With Quote
Old Jun 25, 2014, 07:59 AM
Retired in NC
Rich in ILM's Avatar
USA, NC, Wilmington
Joined Sep 2010
1,954 Posts
Quote:
Originally Posted by ggcrandall1 View Post
The National Electrical Code is dealing with AC. DC is prone to higher line losses than AC. Stick with the 12AWG.

Glen

???

AC has skin effect that only that travels on the outside of the conductor.
DC use the entire conductor?
Rich in ILM is offline Find More Posts by Rich in ILM
Reply With Quote
Old Jun 25, 2014, 08:14 AM
Space Coast USA
hoppy's Avatar
Space Coast
Joined Oct 2000
20,638 Posts
Don't forget are wiring is multistrand, not a single wire.
Skin effect.
hoppy is offline Find More Posts by hoppy
Reply With Quote
Old Jun 25, 2014, 08:41 AM
Proud to eat Kraut ;-)
Julez's Avatar
Germany
Joined Dec 2003
5,193 Posts
Quote:
Originally Posted by ggcrandall1 View Post
The National Electrical Code is dealing with AC. DC is prone to higher line losses than AC. Stick with the 12AWG.

Glen
Not entirely correct. DC and AC have the same losses at identical voltace and current.


Skin effect does not matter in our applications, where we do not get frequencies above a few kHz.
http://en.wikipedia.org/wiki/Skin_effect#Examples
Julez is offline Find More Posts by Julez
Reply With Quote
Old Jun 25, 2014, 08:49 AM
Retired in NC
Rich in ILM's Avatar
USA, NC, Wilmington
Joined Sep 2010
1,954 Posts
Agree but DC does not have greater losses.
Rich in ILM is offline Find More Posts by Rich in ILM
Reply With Quote
Old Jun 25, 2014, 09:42 AM
Registered User
So. Cal.
Joined Oct 2004
7,826 Posts
Agree that 16 AWG wire will be just fine. Two strands of one foot of 16 AWG wire at 15 amps will have a power loss of 1.8 watts. At 24V / 15A, the OP's power system is producing 360 watts. Thus, a 1.8 watt loss (.5%) is completely negligible and will not be noticed. Going to 12 AWG will not hurt anything, but it will also not help in any way.

Whether stranded or solid makes no difference either as cross-sectional area is the same.

Julez is correct that skin-effect is only applicable to high frequency AC transmission and whether the wire is solid or stranded has no effect here either. In order to reduce skin effect, multi-strand wire can help dramatically, but only if each individual strand is insulated from adjacent strands (litz wire).

Mark
mrforsyth is online now Find More Posts by mrforsyth
RCG Plus Member
Reply With Quote
Old Jun 25, 2014, 11:01 AM
Unregistered User
vimy g eaou's Avatar
Australia, SA, Adelaide
Joined Feb 2014
10 Posts
Quote:
Originally Posted by hoppy View Post
Don't forget are wiring is multistrand, not a single wire.
Skin effect.
Except that charging is DC not high frequency AC as in RF circuits.
vimy g eaou is offline Find More Posts by vimy g eaou
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion ESC/Motor wire length? MikeCr Power Systems 6 Oct 09, 2013 02:45 PM
Question Max effective length for extending PPM singnal wire from Radio? NPatzke Radios 6 Oct 09, 2013 07:00 AM
Question Minimum Wire length between ESC and Motor?? Nucc10 Power Systems 5 Sep 28, 2013 04:35 PM
Battery to ESC wire length? stegla Electric Ducted Fan Jet Talk 4 Jun 04, 2003 10:26 AM
Length of Wire Leads From Battery To ESC? LNL Electric Plane Talk 4 Mar 17, 2003 08:24 PM