SCA 12v 750 Amp Jumper Leads $20 + Delivery ($0 C&C) @ BCF

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zuuutoootuuu on 08/05/2023 - 13:06 bcf.com.au (788 clicks)
Last edited 08/05/2023 - 13:13 by 1 other user

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Same leads SCA are selling for $106.99
https://www.supercheapauto.com.au/p/sca-sca-12v-750-amp-jump…

PRODUCT INFO
For a quick fix in a tricky spot, a set of SCA Jumper Leads (or Jumper Cables) are a great companion on your next journey. These car jump leads are perfect for a flat battery when you need to get on the go, and don't have hours to spend attached to a charger. The fully insulated clips and high quality copper and aluminium construction will keep your hands safe from current while connecting cables, and the in-built surge protection will help prevent any damage to the battery on either end during the process. With a handy plastic storage case to prevent any tangling or damage, you can trust they will always be ready when you need them.
These SCA 12V 750 Amp Jumper Leads are numbered near each clip to ensure that you have no issues correcting in the right order. They are suitable for starting petrol engines up to 6.0L (6000cc) and diesel engines up to 5.0L (5000cc), making them a great solution for large-engine vehicles and 4WD's that require a lot of power to turn over.

FEATURES
Suitable for 4, 6 and 8 cylinder petrol engines up to 6L (6000cc), and diesel engines up to 5L (5000cc)
Built-in surge guard protects vehicle electronics and engine management systems
Insulated copper/aluminium cables for quality and durability
3.5m long to make sure you've got the reach when you need it
Handy plastic carry case for neat and tidy storage at home or in the boot

Related Stores

BCF - Boating, Camping, Fishing

• 

  beastontheroad on 08/05/2023 - 13:09

  No c&c near me

  • 

    zuuutoootuuu on 08/05/2023 - 13:11

    Shipping $7.99 or free over $100 spend

• 

  Marty156 on 08/05/2023 - 13:24

  No stock NSW or Qld

• 

  Nugs on 08/05/2023 - 13:33

  only SA metro store with stock is Marion, all others are regional (& Elizabeff)
  .

• 

  Soapdroid on 08/05/2023 - 13:35

  Thanks mate, ordered one delivered

• 

  RubenM on 08/05/2023 - 13:47

  +2

  Sorry, but aluminium cables rated at 750A is just ridiculous. It would be physically impossible to put that through these cables.
  The voltage drop would be more than 12V

  The price might be cheap, but the description is just intentionally deceiving.

  It be good if I could downvote the product only, but not the deal…

  • 

    Bargain4Days on 08/05/2023 - 13:53

    I mean, its probably not a constant load, just enough current to "jump start" the battery, its the reason why you can go over a breaker limit for a very small period of time or when motors start they dont instantly trip breaker due to in rush current

    • 

      RubenM on 08/05/2023 - 13:58

      You're right that it's not a constant current and for quite a short period of time.
      So I'm not looking at it as the continuous rating, but it's impossible to transmit 750A through a copper-coated aluminium cable (the copper is really just there for the colour, so it looks like copper). The reason for this is that at that current, the voltage drop would be more than 12V, which would be the supply voltage (really at 750A it would be more likely 7V or so, due to the Peukert effect in the battery, but we'll ignore that here, to give the cable any benefit of doubt that we can).
      So even if it was just for one picosecond, it couldn't happen.

  • 

    Prong on 08/05/2023 - 15:10

    +1

    Jumper cable ratings are for what peak current they can be exposed to, without failing. It's not a continuous rating.

    This is the normal rating system used for jumper cables. That doesn't mean low quality cables don't fake it, but high quality brands also use the same ratings.

    Electric motors (especially series wound motors typically used to start cars) have a very brief inrush current that only lasts a fraction of a second, but can be many multiples of the normal operating current.

    Car cabling and connectors are specced to handle this inrush current without failing. When jump starting, that includes the jumper cables.

    Like you say, the voltage drop at high amperage is more than 12V. So while 100A - 200A might flow, the rest is turned into heat in the cables and connectors. If not the right spec, or if built with any high resistance spots, then localised heating will melt things, including the cable insulation.

    In this case, the cables are rated to handle 750A of very brief inrush current, mostly turned to heat, without that heat being enough to cause an issue. If exposed to 750A for any significant time, they would of course overheat and fail.

    Mostly it's about the cables avoiding hot spots. The thermal mass is enough to handle the overall heating for a few start attempts.

    The current flowing to the starter once it is turning is much less, so the cables have no issue continuing to supply that without problematic voltage drop. For larger engines, a larger starter motor is used, which has a higher inrush current, and thus higher rated cables are needed.

    • 

      RubenM on 08/05/2023 - 20:48

      If it's the maximum current that can be applied to it without failing, why not just say 1,000,000A? It's just as physically impossible as 750A for 12V
      The voltage drop at 750A through this cable is over 20V, it's just not possible. This current can't go through the cable for a short period of time, not for a nano second, not even for a Planck time (the smallest unit of time possible). It just can't ever happen, ever.

      https://pasteboard.co/ktuHPdSkHJ3m.png

      • 

        Prong on 09/05/2023 - 10:56

        That's not how voltage drop works. It's absolutely possible for 750A (and higher) to flow through these cables.

        That calculator can't really calculate what is needed here - it's a different tool for a different job.

        Over the entire circuit (battery, jumper cables, other cabling, starter motor), voltage drop is 100%. You can't calculate the voltage drop of one section, without knowing more information about the rest of the circuit.

        What determines the amount of current that flows is the total resistance. Ohm's law. V = IR.

        Again, the 750A is a rating, not the actual current that flows. But 750A absolutely could flow through jumper cables.

        Let's say we have jumper cables with 5mm diameter aluminum conductors - ~20mm2 cross section, 7m long. Our total resistance is 0.01 Ohm.

        To simplify, we connect them to a 12V battery with no internal resistance that can output whatever current we need. We assume the resistance of the jumper cables is the same as the resistance of the cable.

        We short out the ends of the jumper cables - how much current flows?

        I = V / R. So current = 1200 amps. Over the circuit, voltage drop is 100% - the full 12V.

        If we drop the cross sectional area of the wire down to about 12mm2, then 750A would flow if short circuited.

        Of course, this is not what is happening when jump starting a car. The 750A is not how much power flows, because there is a key extra bit of resistance in the circuit - the starter motor.

        Again, 750A is not how much current flows over the jump cables. We are not short circuiting them.

        We can consider the 750A rating as being able to start a car with a starter motor that itself is rated for a brief inrush current of 750A. That 750A inrush rating doesn't mean it will actually get 750A in a car - it's just what the motor could draw at a specific voltage, based on it's internal resistance.

        It's more complex, but we can simplify and consider the starter motor as a length of copper wire. (When it starts to spin, it generates back EMF which is why the current flow drops over time).

        So what is the motors resistance if it draws 750A? R = V / I. Resistance = 12V / 750A. Resistance = 0.016 Ohm.

        So if using our 5mm diameter jumper cables, we now have a total resistance of 0.005 Ohm (cable 1) + 0.016 Ohm (starter motor) + 0.005 Ohm (second cable). (Simplified of course - real world all the connectors and other cabling adds resistance)

        I = V / R. Current flow = ~462 amps.

        Now we can examine each individual part of the circuit.

        Jumper Cable 1.
        Voltage drop V = IR. V = 462 x 0.005. = 2.3V voltage drop.
        P=VI. P = 2.3V x 462. So ~1.1 kW of power is dissipated (almost all as heat) in the cable.

        Starter Motor.
        V = 462 x 0.016. = 7.4 V voltage drop.
        Power used by the motor = ~3.42 kW.

        Jumper cable 2.
        Same as jumper cable 1.

        This is just the brief initial start condition. And there are a lot of other sources of resistance in a real world circuit, so the total current will be lower.

        What happens if we use our 12mm cross section cable instead? It's 0.0077 Ohm for each jumper cable. 0.0315 Ohm total with starter motor.

        Current flow is now 380A.

        Each jumper cable now drops 2.93V. And dissipates the same 1.1 kW, but in a much thinner cable, making it much more likely to overheat.

        What if we go up to 10mm cable? 0.0012 Ohm each.

        Current is now 650 amps.

        Each cable drops 0.78 volts, and dissipates ~500W.

        So a higher rated cable dissipates much less of the initial current as as heat. What's important though, is real world, a starter cable is not just a uniform resistance. It's an average resistance, but shorter sections (such as where the cable joins a clamp) might be much higher resistance. So that shorter section will experience proportionally more of the voltage drop, and thus heat dissipation. So even if the cables themselves can handle the current, they need to be built well enough overall to avoid any hot spots that could cause a failure.

        Once the starter motor is moving, it allows much less current to flow, so circuit current drops, and the jumper cables experience less voltage drop, and less power is turned to heat. The cables need to be specced to handle the ongoing current too, but it's the initial startup current that is most likely to cause a failure. If the jumper cables can handle the initial high current, then typically they will be fine for the continuous current flow.

        • 

          RubenM on 09/05/2023 - 13:46

          @Prong: I actually largely agree with you, but I think that it's highly unlikely for the cross sectional area to be 20mm2 or more. Plus the connection points will add a bit to the resistance as well.
          We can both agree, if the resistance of the cable and the clamp contacts is more than 16mΩ, it's completely impossible for 750A to flow at 12V, right? That's exactly what I'm alleging!

          I assumed that the motor had a resistance of 0Ω and it was an ideal power supply with no internal resistance (as you seem to have done as well), to give the cables the best possible chance of getting to 750A. But they (in my opinion) failed even at this hurdle, so I maintain that at 12V it's impossible to ever have a flow of 750A through these cables and even at 24V it's not possible if using lead acid batteries.

          • 

            Prong on 09/05/2023 - 15:13

            @RubenM:

            I maintain that at 12V it's impossible to ever have a flow of 750A through these cables

            You misunderstand what the 750A rating means in this case, and are assigning a meaning to it that is incorrect. The 750A rating does not mean 750A will flow through the cables.

            Essentially, it means the cables are designed for use with starter motors that have up to a 750A inrush current rating.

            Keep in mind that a starter motor rated for 750A of inrush current won't experience that in actual use. It's a idealised rating used for comparison - the real world current flow will depend on varied factors the manufacturer of the motor can't predict.

            Like you misunderstood how voltage drop works, you have misunderstood what the 750A jumper cable rating means, and then assumed it means something that it does not.

            I assumed that the motor had a resistance of 0Ω and it was an ideal power supply with no internal resistance (as you seem to have done as well)

            I used that as an example of how you misunderstood how voltage drop works, and how to calculate the actual current flow. That's a separate issue to what the 750A rating means.

            So again, the 750A rating on the jumper leads is not a rating of how much current the cables are designed to handle. It's a rating for comparison with peak starter motor currents.

  • 

    tunzafun001 on 08/05/2023 - 20:25

    I'll help you out mate. These cables are utter shit and not anywhere near a proper rated 750w cable. Seen them on eBay / Kogan for around $12..

    Second warning - I bought some EV cables, which went cheaper the next day. Got a credit, followed by an email basically saying, spend it soon or lose it. Bought crap I dont need to use it up.

    Then discovered the cable wasn't what it said it was. So returned it. Didn't get the credit bit refunded, they kept that as I had used the credit to buy other stuff. Said fair enough, you can have the other crap back as well, I didn't actually want it, just grabbed it as I would lose the credit. Here's your stuff. I'll just get my cash back I paid for the cable.

    Nup, can only give that $40 difference back as credit on your account as it was bought with credit …to which I said, ok I have the same rule… I bought the cable with cash and I can only accept that back in full cash.

    Store guy couldn't refund me the full amount I paid for the cable. Showed me there was nowhere on the till to do it.

    In summary, I used to have a lot of respect for SCA..but that is fading fast.
    And…
    These cables are far too thin. My 400w cables are at least double the gauge.

  • 

    OzBragain on 09/05/2023 - 21:34

    It be good if I could downvote the product only, but not the deal…

    You most certainly can downvote for issues with the product

• 

  vbt on 08/05/2023 - 13:54

  +2

  750amp LOL
  …for 1.8 seconds.

  • 

    RubenM on 08/05/2023 - 13:58

    +1

    Please see my post above. The cable can do 750A for exactly 0 seconds.

• 

  payless69 on 08/05/2023 - 13:58

  A bit like "dog food" with SUL raising!

• 

  hashtagbargain on 08/05/2023 - 15:28

  +4

  Mother’s Day sorted

• 

  theHMASfriendship on 08/05/2023 - 16:07

  +1

  Can anyone confirm whether these can securely be attached to nipples? Asking for a friend

  • 

    Laserface on 08/05/2023 - 16:15

    might need some meaty nips for them to grab onto.

• 

  rogsamsy on 08/05/2023 - 16:56

  +1

  OOS