Increase current capacity of wires

Thread Starter

varnco

Joined Feb 28, 2021
7
I am trying to figure out how one could increase carrying capacity of lines run 20' to a DC motor to minimize voltage drop.

12V, 6 amps continuous is roughly what will run for 6 hours, with max amps of 18 for short periods of time (10 min).

I currently have 2 wires of 8GA running. Can I increase current carrying capacity by adding two more lines at 8GA versus replacing 8GA with 6GA or 4GA?

I am trying to minimize voltage drop as well.

Thanks
 

dl324

Joined Mar 30, 2015
12,668
Welcome to AAC!
I currently have 2 wires of 8GA running. Can I increase current carrying capacity by adding two more lines at 8GA versus replacing 8GA with 6GA or 4GA?
You can connect more #8 wire. I'd check any applicable electrical codes to make sure that's allowed. If you do it, make sure they're bonded well at each end and that you get a solid connection to both wires. I'd tape them together at each end to make intent clear.

What amperage is the existing circuit fused for?
 

Papabravo

Joined Feb 24, 2006
15,431
There are charts and tables that can help you answer such questions. It all comes down to cross sectional area of the wires.
The rest is Ohms law. A rule of thumb for wire sizing is that you need about 700 circular mils per ampere to avoid undue temperature rise in the wire. If you can tolerate some temperature rise in the wire then a different number would apply.

https://www.powerstream.com/Wire_Size.htm

AWG#8 has a resistance of 0.6282 Ohms per 1000 feet. So 20 feet will be ≈ 12.56 milli-Ω. therefore 2 x AWG #8 at 20' will be the parallel combination of 12.56 mΩ || 12.56 mΩ = 6.282 mΩ
AWG #6 has a resistance of 0.3951 Ohms per 1000 feet. So 20 feet will be ≈ 7.9 milli-Ω slightly more than the 2 parallel runs of AWG #8. Of course 2 runs of AWG #6 would be 3.951 mΩ

The voltage drop from one run of AWG #8 would be 6 Amperes x 12.56 mΩ = 75.36 millivolts
The voltage drop from one run of AWG #6 would be 6 amperes x 7.9 mΩ = 47.4 millivolts.

IMHO you are dealing with flyspecks in the pepper for a 0.25% improvement in voltage drop

Does that help to clarify things for you?
 
Last edited:

ApacheKid

Joined Jan 12, 2015
376
What you could calculate (as Papabravo has pretty much done) is the % power lost through the cable, so you'd need to compare the power consumed by the motor vs the power consumed by the resistance of the cable.

If the motor is at 12V and passing 6A then it is consuming 72W.

The resistance of the cable at 8AWG leads to a power loss of 0.45W or about 0.7%.

The 6AWG cable leads to about 2/3 of that loss or 0.45%.

Nothing to worry about it seems.
 

andrewmm

Joined Feb 25, 2011
1,127
Definitely twist the each pair together, and tape up, to make it clear the intention, a label or two is also of use.
There is a big difference between what works and what is expected, in 20 years time, will you or some one else know what the aim was if they take different routes ?
 

Papabravo

Joined Feb 24, 2006
15,431
It would be interesting to know the specifications on the motor. If the voltage drop in the wire was a significant concern, like it would be if the wires were longer, then perhaps the source voltage could also be modified. This would of course consume more power, but would raise the voltage at the motor, if that was a problem.
 

ApacheKid

Joined Jan 12, 2015
376
Is there any scope to locate he motor DC supply much closer to the motor, then use some kind of signal to control that? the signal would be tiny and carried on thin wires.
 

MisterBill2

Joined Jan 23, 2018
8,201
If the load is really only six amps, with 10 amps on occasion, then with #8 wire the small voltage drop in the wire will not be a problem. But connections at the ends can be a very big source of voltage drops. That is where most of the problems arise, in the connections at the ends. So while doubling up the wires will cut that portion of the quite small voltage drop in half, poor connections can lead to a much larger voltage drop at the ends. To locate where any problems may be, it is often useful to measure the voltage drop across each connection by using a more sensitive voltmeter, one with a range of one volt or less full scale. I have come across that problem quite a few times. Twice the solution was simply tightening the connection screw.
 

MaxHeadRoom

Joined Jul 18, 2013
22,623
Another way if concerned with Volt drop, but may be overkill for a simple project.
That is a 12V supply that has sense inputs, this involves a couple of small gauge conductors ran alongside the main ones and terminated at the load end.
The load end voltage is sensed and the source increases the output accordingly to maintain the source supply in order to maintain the load voltage..
Also with this method you would only require 14g conductors Maximum.
Max.
 

Thread Starter

varnco

Joined Feb 28, 2021
7
What amperage is the existing circuit fused for?
Thanks for the welcome! The current 8GA wire has a 30 amp manual resetting breaker on it, and my plan would be for the 2nd positive 8GA strand to have the same breaker, running in parallel, then joining back up at the motor.
 

Thread Starter

varnco

Joined Feb 28, 2021
7
There are charts and tables that can help you answer such questions. It all comes down to cross sectional area of the wires.
The rest is Ohms law. A rule of thumb for wire sizing is that you need about 700 circular mils per ampere to avoid undue temperature rise in the wire. If you can tolerate some temperature rise in the wire then a different number would apply.

https://www.powerstream.com/Wire_Size.htm

AWG#8 has a resistance of 0.6282 Ohms per 1000 feet. So 20 feet will be ≈ 12.56 milli-Ω. therefore 2 x AWG #8 at 20' will be the parallel combination of 12.56 mΩ || 12.56 mΩ = 6.282 mΩ
AWG #6 has a resistance of 0.3951 Ohms per 1000 feet. So 20 feet will be ≈ 7.9 milli-Ω slightly more than the 2 parallel runs of AWG #8. Of course 2 runs of AWG #6 would be 3.951 mΩ

The voltage drop from one run of AWG #8 would be 6 Amperes x 12.56 mΩ = 75.36 millivolts
The voltage drop from one run of AWG #6 would be 6 amperes x 7.9 mΩ = 47.4 millivolts.

IMHO you are dealing with flyspecks in the pepper for a 0.25% improvement in voltage drop

Does that help to clarify things for you?
Thank you... yes, it helps answer. The motor is connected to a controller board, and apparently, the controller board is somewhat sensitive to voltage drop and it's run off a 12V battery, so as the motor is running, the 12.62 volts continues to drop over hours, so it's important. The improvement over today (with only 1 run of wire) would be reducing the voltage drop to 37.7 millivolts vs today at 75.36 (basically, a 50% improvement). I would assume it would run cooler as well, and less resistance, if the amperage were to run at 18A on occassion.
 

Thread Starter

varnco

Joined Feb 28, 2021
7
If the load is really only six amps, with 10 amps on occasion, then with #8 wire the small voltage drop in the wire will not be a problem. But connections at the ends can be a very big source of voltage drops. That is where most of the problems arise, in the connections at the ends. So while doubling up the wires will cut that portion of the quite small voltage drop in half, poor connections can lead to a much larger voltage drop at the ends. To locate where any problems may be, it is often useful to measure the voltage drop across each connection by using a more sensitive voltmeter, one with a range of one volt or less full scale. I have come across that problem quite a few times. Twice the solution was simply tightening the connection screw.
It would be 18amps on occassion for maybe 10 minutes. Definitely will double-check the connections. Is there a best way of terminating the 2 positives and 2 negatives wires at the end? I was considering a power distribution block to take the 2 positives and 2 negatives down to 1 output each to the motor.
 

MisterBill2

Joined Jan 23, 2018
8,201
Some blocks are better tha others, and many of them are aluminum, which is able to dissipate the heat from an imperfect connection. But most blocks do mot make 100% connection to all of the strands of the conductor. Are the #8 wires solid, course stranded, or fine stranded like welding cables? That affects the connections as well.Putting all 3 wires into one opening of the distribution block can work, but it is tedious to get it right.

So another question is just exactly how critical is the speed control of the motor? Only you can know that, we are clueless on the application.
 

MaxHeadRoom

Joined Jul 18, 2013
22,623
Personally I would not mix aluminum and copper conductors, there are a few issues such as different rates of expansion and galvanic and cathodic corrosion between the two where connected
It has been banned in residential wiring for some decades now because of electrical fires.
Max.
 

MisterBill2

Joined Jan 23, 2018
8,201
Iwas referencing the junction blocks, not the wires. An amazing thing is that our power company does use aluminum wires for the drops from pole to house. And then they use crimped on splices to connect them to the copper wires to my meter. And when they installed that new aluminum cabe they stole my split-bolt connectors that allowed me to disconnect the power when doing work on that section of the incoming power. Split bolt connectors for that size wire now run about $ 10 each. Crimps may be OK, but they are not reusable.
 

Thread Starter

varnco

Joined Feb 28, 2021
7
Some blocks are better tha others, and many of them are aluminum, which is able to dissipate the heat from an imperfect connection. But most blocks do mot make 100% connection to all of the strands of the conductor. Are the #8 wires solid, course stranded, or fine stranded like welding cables? That affects the connections as well.Putting all 3 wires into one opening of the distribution block can work, but it is tedious to get it right.

So another question is just exactly how critical is the speed control of the motor? Only you can know that, we are clueless on the application.
It is coarse strand. Its a remote control for speed adjust that has intermittent issues and its related to voltage drop.

I was considering stainless steel block and tinned or copper terminals.
 

MisterBill2

Joined Jan 23, 2018
8,201
Some blocks are plated copper, and they are the best. They have steel screws or possibly stainless screws, and so the very lowest resistance. Stainless is not as good a conductor as either aluminum or copper.
 

LowQCab

Joined Nov 6, 2012
271
NEVER use a "Split-Bolt" Connector to connect Aluminum to Copper, you're just asking for trouble,
and it's Illegal, according to the NEC (National-Electrical-Code),
to use a connector in any configuration that the "Device" is not specifically approved for, in writing.

If you need to disconnect Power, pull the Meter.
It's EXTREMELY DANGEROUS to disconnect live Power-Drop Feed-Wires while they are Hot.
The Power-Company won't "like" the fact that you have cut-off their Security-Tag on the Meter-Can,
but generally, they don't get too jacked-up about it, unless they think you've been stealing Power.

To your original question .........................
It sounds like you are perceiving some kind of a problem that you have not described to any of us.

Exactly what is the problem you are experiencing ???????

14-ga. wire should be more than adequate to run your Motor with insignificant losses.
NEC guidelines are quite conservative on wire gauge, stick with them, YOUR PROBLEM IS ELSEWHERE.
14-ga.=15-A,
12-ga.=20-A,
10-ga.=30-A,
8-ga.=40-A,
6-ga.=55-A,
4-ga.=70-A
2-ga.=95-A,
These are continuous ratings, and are not affected by AC-or-DC, or Voltage Level,
and are for runs of less-than ~100-feet.

Does the measured Current of the Motor ever exceed its Name-Plate Ratings ??
What is the Duty-Cycle-Rating ??
Do you need more "Starting-Torque" ??
Do you experience degraded performance near the end of the normal operating period ??

You probably have an under-rated Motor.
If the Motor gets hotter, FOR ANY REASON, than its rated "Temperature-Rise",
the Resistance of the Windings will start to rise excessively,
you will loose significant Power, and possibly smoke the Windings.

Temperature is critical, don't ignore it.

A Motor that is routinely run at or above its maximum ratings,
for long periods, may do strange things, and will eventually fail.

You really should only need "Remote-Voltage-Sensing", (as noted by MaxHeadRoom),
if you have a machine requiring precision Torque-Control.
If you do require precision Torque-Control,
the Motor should be rated such that it rarely exceeds 50% of its rated maximum current.

So, what is the actual problem you are trying to solve ????
.
.
.
 

boostbuck

Joined Oct 5, 2017
33
Ok, this is a 12V system run off a battery, so a lot of electrical safety considerations are moot - the only real issue is the losses due to the connections terminating the wires. In these applications I use copper crimp lugs bolted directly to the load to minimise interconnection losses. Just make sure everything is copper to copper and well torqued down.
 
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