Bus bar current calculations

Brian D

Brian D

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Has anyone ever have to look for DC current data for a bus bar that does not have any? I have access to bus bars that are 7/16" (11mm) wide, 5" (127mm) long, and 1/16" (1.6mm) thick. I am not sure how to calculate the cross section or which values to use. If anyone know the current handling capabilities at 12 VDC 30° C would appreciate the numbers. Thanks
 
Brian D

Brian D

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
That is one of the many pages I visited. I just found another site that uses a very simple, albeit not all parameters considered, calculation of WxHx1000. 1000 is based on the value of 1000 amps/sq in. That give one an estimate or in-the-ball-park value to work with. So that 7/16 x 1/16 x 1000 came up to around 27 amps. The site you showed me showed between 100 and 150 amps. Big difference there. I would feel comfortable to error on the low side for safety reasons.

I will keep searching. Thanks C
 
centerline

centerline

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Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
Brian D said:
That is one of the many pages I visited. I just found another site that uses a very simple, albeit not all parameters considered, calculation of WxHx1000. 1000 is based on the value of 1000 amps/sq in. That give one an estimate or in-the-ball-park value to work with. So that 7/16 x 1/16 x 1000 came up to around 27 amps. The site you showed me showed between 100 and 150 amps. Big difference there. I would feel comfortable to error on the low side for safety reasons.

I will keep searching. Thanks C
Click to expand
from what I know, It looks very reasonable to me... 27 amps it a very very small wire about the size that a fuse has... a copper plate/strip of the size you mention can carry a lot of amps...there are other pages on the site that you can use to double check the information if you have doubts.
 
F

Fred Villiard

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Dec 28, 2009
397
Macgregor M25 trailer
If you can tell me the material I can run it thru my program at work tomorrow. These calculations are what I do for a living
 
J

JohnShannon

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Jan 4, 2010
1,037
Farr 30 San Francisco
Shouldn't Brian post a pic of himself in a bikini? Perhaps this isn't the right forum.
Volts has nothing to do with it amps is all that matters. Looking at the link 1/16 by 1/2 is 103A for 30C rise. So this is a tick smaller call it 95 we are good. How much current you got?
 
Brian D

Brian D

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
In some calculations, voltage is called for so that is why I presented both voltage and nominal operating temperature. If they are not needed, it is all good.

As for how much current I will be using is not known at this time. I am thinking maybe up to 200 amps inrush. But for normal everyday ops, possibly up to 100 if every thing is running. Yeah, overkill, but a safe overkill. The seller couldn't answer the question so that is why I am asking here.

And... no one wants to see me in a Bikini, or Speedo for that matter. LOL
 
Brian D

Brian D

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
Rewiring the boat and adding HF SSB. The wiring is a mess with wires every which way. Main DC/AC panel in the cabin is fine but the batteries need attention. I am building a distro board like Maine has done so everything is tied into one board. ACR (planned) and bus bars for both batteries, ground, and BOTH side of the switch. Hence the question about bus bar ampacity. Again, might be overkill but to err on the side of safe is best.
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
Brian D said:
... I am not sure how to calculate the cross section or which values to use....
Click to expand
The West Bible shows the circular mills, and square mm for wire, so maybe convert your fractions to mm to figure cross section area. That's what I did for buss bars. So, you have 17.6 sq mm, which equates to about #5 wire, or 140 amps. You could always double up the bars for 1/8 thickness.
 
Brian D

Brian D

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
I do appreciate everyone's input. Most of the tables say the same thing so I guess I should rely on the tables. Wonder what Fred will come up with? It will be interesting to see if a program estimates the same values as the tables. Guess I should learn to trust tables. LOL
 
centerline

centerline

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Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
Brian D said:
I do appreciate everyone's input. Most of the tables say the same thing so I guess I should rely on the tables. Wonder what Fred will come up with? It will be interesting to see if a program estimates the same values as the tables. Guess I should learn to trust tables. LOL
Click to expand
the tables have been calculated and arent just some bodys pipe dreams:biggrin::biggrin:.. there may be some small variation in the numbers depending on how many digits after the decimal point are used in the equation, but I think anyone who understands electricity well enough to work up a table, is not the guy that is going to be liberal with the numbers, to where it could be unsafe.
 
Brian D

Brian D

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
That is a very valid point Centerline. Sometimes we just look too hard or read too deep that it messes with our heads. LOL
 
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Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Pretty simple to determine what your shunt will handle. take an ohm metter and measure across the high current terminals. Alternatly look at the meter and see what its highest reading is. Using the ohms measurment across the terminals and assuming a 1% acceptable voltage drop (14.4 * 0.01=0.144 volts). We take our old friend V=IR and solve for I(=V/R) or in this case .144/(resistance you measured). The resistance will be quite low as you might expect so use the lowest setting on the ohm meter. Only use the first three digits and prudent engineering would tell us to round the anwser down.
 
F

Fred Villiard

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Dec 28, 2009
397
Macgregor M25 trailer
Hi Brian,
I ran the numbers, the straight 5 inch bar in free air 20 deg C rise = 137.2 amps 13.5 VDC
running it as a buss bar with .250 stud in .375 in from each end, 5 #8 screws equal spaced in the middle, and one side against an insulator, used .250 G10/FR4, 20 deg C rise = 47.58 amps 13.5 VDC
This modeling program is for calculating mill spec buss bars and power connectors, also show.s all of the E& H fields and took about 30 minutes of mainframe computer time.
Also the cad plating costs you about .9471 amp over clean copper or silver plated, I used ETP Copper, because that is the most common.
 
J

JohnShannon

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Jan 4, 2010
1,037
Farr 30 San Francisco
Wow! How did you take the current out of the buss bar? Input was on the stud outputs were worst case all at the far end, or evenly spaced?
 
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