Tehben Dean wrote:
> I just checked on the price of 2/0 AWG marine battery cable at my
> local marine equipment shop and they are charging $7.?? a foot.
> The stuff that they sell is made for the marine environment and is tin
> plated or something to resist corrosion. I figure I don't need this
> feature and hoped that there was a cheaper option.
> What is a reasonable price for the 2/0 cable?
> Where is a good place if I decide to order it?
> '90 Toyota 4x4 Pickup
> 'hElix EV'
> Website: www.helixev.com
> evalbum: http://www.austinev.org/evalbum/1225
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Dave Delman wrote:
> Is 2/0 heavy enough?
Heavy enough for what? ;^>
Your message referred to a Warp9 arriving, so I infer you are building a
DC conversion. 2/0 is a fairly common choice for the battery loop wiring
in DC vehicles. You might want to use heavier cable (or double runs of
2/0) for the short run between the controller and motor if you are
planning to run a Z1K or Z2K controller.
In the context of the original message, I think 2/0 is considerably too
heavy for Tebhen's AC conversion. His controller is limited to about
280A peak and we don't size our cables based on peak current, but rather
the average. I would expect that a better choice for his application is
something in the 1ga to 4ga range, and this will be considerably cheaper
than the 2/0.
Personally, if in Tehben's position, I'd probably go with the 4ga cable
and choose batteries with threaded inserts or studs to allow the use of
the much cheaper lug terminals instead of SAE post battery clamps. The
lower current of the AC system doesn't require the use of the
higher-current capable SAE clamps. Browsing the EV Parts catalog, if
one goes with the good stuff (MagnaLugs), the 4ga lugs are $1.50 ea and
4ga cable is $3.30/ft. Assuming about a 1ft interconnect length, the
cost savings on the 4ga lugs vs 2/0 lugs pretty much pays for the cable
used per interconnect (the savings over 4ga or 2/0 battery clamps more
than pays for the cable). If one insisted on 2/0, the cost savings
associated with using lugs instead of clamp terminals knocks a good
chunk off the cable cost.
While I advocate supporting our EV parts suppliers whenever possible, I
would check locally with an electrical supply house to see what welding
cable they carry before having something as heavy as welding cable
Fastenal appears to be a distributor with an Alaskan presence, and while
I don't know if their online catalog prices are current, they do appear
to have #4 cable in 50 or 100ft lengths in stock for reasonable prices:
(While they also offer it in 25ft lengths, I rather doubt Tehben can
wire his pack with less than 25ft ;^)
Fastenal carries cable from Direct Wire and Cable, and while they don't
state which line it is, the 30AWG stranding suggests it is the standard
"Flex-o-prene". If Tehben can get Fastenal to supply Direct's
"Ultra-flex" cable instead, it comes in nice orange jacketing:
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Tehben Dean wrote:
> Before I actually purchase, would there be any benefit to
> using #2 if I found deal?
I suppose that depends on the cost of the #2 terminals you would need vs
the #4 you could use. A deal on the cable could actually be offset by
the difference in terminal cost!
The #2 will run a bit cooler than the #4, but that's really the only
Quoted below is a gem from Bill Dube explaining the wire size issue more
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]
> Sent: Tuesday, June 04, 2002 6:11 AM
> To: [email protected]
> Subject: Re: cable amp ratings - The Facts
> >Arthur Matteson wrote:
> >> So do the wire rules not apply to cars?
> >Actually they still apply, but use the degrees C rise for cross
> >section, and current flow equation. Then take into account how
> >fast you can disipate the heat away from the conductor bundle.
> >>From that you then can figure out the minimum wire size needed
> >then double to quadruple it to handle individual strand breakage
> >and unexpected conditions. No, I don't know the actual equations
> >off the top of my head and those books are packed.
> It is all about heat transfer.
> First, you determine how hot the insulation can get
> before it is damaged.
> This can be 60 C (or less) for thermoplastic (like vinyl)
> insulation. (An example is the pretty stereo wire that
> turns to goo when the wires get even slightly warm.) Some
> of the Silicone or Teflon insulated wiring can take as
> much as 200 C without a problem. It is just as pretty as
> stereo wire, but costs quite a bit more. Welding wire is
> typically 75 C or 90 C insulation.
> There are two operating regimes, intermittent and
> continuous. The continuous rating is what you will find
> in the National Electrical Code, Section 70, Tables 310-16
> through 310-19. For DC use, the formula is
> I = Squareroot( ----------------)
> RDC * RCA
> TC = conductor temperature, C (what the insulation will
> TA = The ambient temperature, C
> RDC = The DC resistance of the conductor at TC
> RCA = Effective thermal resistance between the
> conductor and it's surroundings. (Typically
> 450 to 650 C-cm/watt)
> 2/0 welding cable works out to be 200 amps continuous.
> The intermittent rating is what seems to confuse most
> folks. From Beeman's "Industrial Power Systems Handbook"
> page 183, we have the formula for copper conductors:
> 1 (T2 + 234)
> t = ----------------- log10 (---------------)
> I (T1 + 234)
> (33) * (-------) ^2
> t = time, seconds
> I = RMS current, amperes
> CM = Conductor cross section, circular mils
> T1 = Initial conductor current, Celsius
> T2 = Final conductor temperature, Celsius
> Eye-balled from the chart on page 184,
> 2/0, 75 C rise,
> RMS Amps t, seconds
> 8,000 1
> 3,300 5
> 2,200 10
> 1,400 30
> 900 60
> 30 second duration for 75 C rise (This would be for a "peppy" EV)
> Gauge RMS Amps
> 10 120
> 8 170
> 6 280
> 4 530
> 2 700
> 1 800
> 1/0 1100
> 2/0 1300
> 3/0 1700
> 4/0 2100
> This formula assumes that all the heat is absorbed by
> the copper and none is transferred to the air. This is a
> pretty good assumption for short time intermittent loads
> like this. This assumed temperature rise (75 C) would be
> good for welding wire type insulation, but way off for goofy
> vinyl insulation.
> You can see that there are no simple answers.
> The keys are the "cruising" amperage and the duration
> and magnitude of the intermittent amperage. If you have a
> very light EV and a huge controller, the duration of maximum
> current will be very low, perhaps 15 seconds or so.
> A heavy EV with a smallish controller will have max current
> durations of perhaps 10 minutes or more.
> The KillaCycle has a max motor current of 1400 amps
> that lasts about 10 seconds. I use #2/0, but #1/0 welding
> cable would more than thick enough for the motor leads.
> #1 might get a little warm.
> Since the battery current is essentially a ramp from
> zero with a peak of 1400 amps, the RMS current during that
> time is 808 amps. (To find the RMS value of a ramp, divide
> by the square root of 3.) This mean that the minimum wire
> size would be about #3 (from the chart.) I use two #6 flat
> copper braids in parallel for battery interconnects and they
> work just fine.
> These calculations will give you the minimum wire
> diameter based on allowable insulation temperature. It turns
> out that for acceleration performance, like on the drag strip,
> the optimal wire diameter typically comes out a little smaller!
> I haven't done the calculation for optimal range, but
> it probably close to the NEC size for the cruise current.
> You still have to do the temperature-limit calculation above
> for the max current to make sure that you don't damage the
> wire during max throttle accelerations.
> _ /| Bill "Wisenheimer" Dube'
> \'' <[email protected]>
> Check out the bike -> http://www.KillaCycle.com
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