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Fergus Kyle
Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada
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 Posted: Tue Jun 08, 2010 6:58 pm Post subject: Battery cable sizing |
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The rear battery mode and such:
I have two batteries behind the second bulkhead in 3/8inch box and run #4CCA through 1/2inch copper tubing. It’s heavier but the batteries are not near the gas tank.......
I worked out the relatives wire sizes of the tubing and will report back once I’ve delved through the records.........!
Cheers Ferg [quote][b]
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Fergus Kyle
Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada
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| Posted: Thu Jun 10, 2010 6:28 am Post subject: Battery Cable sizing |
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Cheers,
Per my message same subject sent late 08JUN¡¯10 (Canada) wherein I
promised backup calcs for aft battery cabling -
These are my calcs for using household copper tubing as container and
ground return for both aft-cited batteries. I wanted to know if I was in
the ¡®ballpark¡¯ for amp-carrying capacity. I suggest following it through
if you plan similar as a phone-call or doorbell might have interrupted the
incredibly complex math. AS for European/Brit equivalents, caveat emptor.
Apologies to most US types but calc¡¯ed in mm for greater accuracy(?):
COPPER TUBING - ¨ö¡± x 96¡± - TYPE ¡®M¡¯ - CURRENT EQUIVALENT
Method #1 - Cross-sectional area
(1) OD=D1=0.624¡±
(2) r1=D1/2=.312¡±=7.9248mm.
(3) A1=197.29956 mm2
(4) ID = 0.570¡±
(5) r2 = D2/2 = .285¡± = 7.239mm
(6) A2 = 164.62912 mm2
(7) A3 = A1-A2 = 197.29956mm2 - 164.62912 mm2 = 32.67044 mm2
( D3 = (¡îA3/¬±)x2 = 6.449599mm
(9) According to POCKET REF manual (Sequoia Publishing, Colorado),
page 113 (or p.810 of the Handbook of Applied
Mathematics), the diameter
in millimetres of AWG2 is 6.544 mm. Therefore the
current-carrying capacity of thin-wall copper tubing is roughly
equivalent to AWG2, which for type T or TW gives an Ampacity of just under
110A at 40deg C. Two tubes electrically-attached should carry the
equivalent of AWG000 cable.
Since this is the design for battery contacts
used, the ground return capabilities satisfy electrical loads very well.
Method #2 - Weight per 1000 feet
(1) Measured weight of tube sample gives equivalent of 87.1 gm/ft
(2) This is equal to 87,100 gm per 1000ft
(3) 87100 gm = 87100 x 0,0022 = 191.62 lb/1000ft
(4) Referring to the reference manual in item (9) above, this gives an
AWG
equivalent to just 4% under AWG2, or about
110A, to 40deg C.
(5) See 2nd paragraph, item (9) above for double tubing.
Both these methods are in general agreement
as to sizing.
Cheers, Ferg
PS: I used #4CCA from Perihelion, with double layer of heatshrink for
security in pipe plus electrical tube end protectors on entry/exit. The
tubing exceeded the CCA capacities.
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