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Thread: Wire gauge needed for 24amp load per bank

  1. #31
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    Default Re: Wire gauge needed for 24amp load per bank

    well, each output will draw 6amps load. 4 output per bank x 6amp= 24a. The 30amp figure is what I was told for safety to have a little bit of wiggle room. It could be lower of course, but the amp capacity between 12 and 10 gauge is quite a bit

  2. #32
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    Default Re: Wire gauge needed for 24amp load per bank

    Dude, you're wasting time and overthinking this. Sorry to be blunt. Its THIS simple. Connect your power supply to that board using 10gauge flexible wiring. Connect your lights/pigtails to the controller board using 18 gauge wire. You can even use 20 gauge for the lights. cmboard.png

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  4. #33
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    Default Re: Wire gauge needed for 24amp load per bank

    Ok, here is the thing i hate about how wire is rated. Yes a given wire may be rated for 30 Amps, but at what Voltage. Amps and Volt are only part of the story. However the important part is Watts as that is what causes heat. A wire rated for 10 Amps at 115 Volts can carry 1150 Watts. 1150 Watts divided by 12 Volts would be 98.53 Amps. With low voltage wiring using normal line voltage rated wire you can carry a much higher Amperage with out burning up the wire. However Voltage drop is way more crucial with low voltage systems. Generally 10% drop is the max acceptable loss. So what I do is calculate the load and convert it into Watts. The formula is Volts x Amps = Watts. As an example, 12 Volts x 24 Amps = 288 Watts is your real load. Then do the calculations to determine wire size. In the case take your 288 Watts 115 Volts = 2.5 Amps. Every Ampacity charts I have seen is based on normal line Voltage, they just dont advertise it. Once you know the corrected Amp loading (2.5 in this case) you can find out what wire gauge you really need, it's voltage drop (keep in mind that is at 115 Volts so you will want to figure out the percentage and calculate the drop for 12 Volts instead), and resistance per foot (even more helpful to calculate voltage drop).
    All of that being said I would go bigger that calculated for two reasons.
    1) Safety factors are a very good idea since loads can change and calculations can be in error.
    2) Never know what you will add next year.

    Hope this helps.
    Regards,
    John

  5. #34
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    Default Re: Wire gauge needed for 24amp load per bank

    Actually the voltage you can apply to a wire is a function of the insulation (thickness and composition) and the current carrying capacity is a function of the wire composition + number of strands + total circumference of the strands (current is carried by the outer shell of a strand, not in the entire strand). Resistance of a wire is expressed in ohms per foot and the voltage drop is distance x impedance / distance * current.

    The power (watts) calculation is used to calculate the current at each side of a power supply.

    So in summary: The max current through a wire is independent of the voltage across a wire and converting to watts in wire carrying capacity is not a valid calculation. A wire rated for 600v and 10A current capacity still only has a 10A current capacity at 12v.

    2017 adding 2 more candy canes, 7 Mid trees and a Halloween show. Removing most 2812 strips and replacing them with bullet pixel mounting strips. Replacing many buck converter waterproof bags with printed boxes.

  6. #35
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    Default Re: Wire gauge needed for 24amp load per bank

    Voltage is not an issue when choosing wire gauge. Voltage drop is. Wire has resistance. Google "wire resistance per foot". The amount of voltage drop in the wire (which is turned to heat) is due to that resistance and the current flowing through it - Ohm's law. For example, 12AWG wire has a resistance of 0.0016 ohms/foot. Putting your load 10 feet away from the power supply uses 20 feet of wire (10 feet of red, 10 feet of black) for a total resistance of 0.032 ohms. If you draw 20A through the wire, 20 * 0.0032 = 0.64 volts. The wire will dissipate 12.8W as heat, but that's evenly spread over the wire.

    Now for the question - is that drop an issue? If you are looking at 0.64V drop on a 120V source, no. If you are looking at it on a 5V source, yep.

    How does mixing wire sizes change things? The drop is different on each size. Let's say you use 12AWG wire for the run for 9.66 feet of the distance and 16AWG for 4-inch stubs on both ends to fit the terminals (0.004 ohms/ft) for the same 20A current

    The drop in the 12AWG wire is (20 * 9.66 * 2 * 0.0016) = 0.62 volts
    The drop in the 16AWG wire is (20 * 0.33 * 2 * 2 * 0.004) = 0.11 volts
    Total drop is 0.73 volts. Heat in the 16AWG wire is 0.55 watts per piece. Heat there is too low to be an issue and will make terminating the wires easier.

    Voltage rating on the wire has to do with how good the insulation is. That's why you don't use speaker/sprinkler/cat5 wire for 120V even if the current is low enough

  7. #36
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    Default Re: Wire gauge needed for 24amp load per bank

    Quote Originally Posted by akareaper View Post
    Dude, you're wasting time and overthinking this. Sorry to be blunt. Its THIS simple. Connect your power supply to that board using 10gauge flexible wiring. Connect your lights/pigtails to the controller board using 18 gauge wire. You can even use 20 gauge for the lights. cmboard.png
    No need to apologize. But I'm not overthinking it. Started as a simple clarification/advice request. But what would you think if you were brand spanking new to that, and you had veterans and people whose advice you trust being on completely opposite sides? In some cases, flipping to the other position lol. When you're dealing with possibly frying your equipment you can't afford to replace, you tend to want to be sure. Having said that, as someone said, you can't oversize your wire. So as long as there isn't an issue with the gauge and the controller, go big right? Remember, the original issue was that 10 gauge wasn't fitting or securing properly under the power bank Input. Well, I think I've solved this issue and I can't believe it didn't occur to me before...... Ring and/or fork connectors!! Lightbulb moment looking under my hood. Really hoping I'm not going to find out that it's not safe or good to use, but a dirt cheap ring connector gives a solid connection to the screw terminal on the controller, and the 10 awg wire is pretty damn solid in that crimped section. So basically, consider this solved unless I find out it's a bad idea. The only thing I can think of being an issue is the strain on the psu connections from the 10 awg wire. Even the stranded soft stuff is strong enough to flex it when moved. But hopefully, a little creative mounting should help this

  8. #37
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    Default Re: Wire gauge needed for 24amp load per bank

    No such thing as too big of wire or too little voltage drop as far as I know. Use #10 wire like I suggested to you before you started this thread and you should be good. And yes... you are overthinking it

  9. #38
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    Default Re: Wire gauge needed for 24amp load per bank

    Ring connectors are a great solution.

    2017 adding 2 more candy canes, 7 Mid trees and a Halloween show. Removing most 2812 strips and replacing them with bullet pixel mounting strips. Replacing many buck converter waterproof bags with printed boxes.

  10. #39
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    Default Re: Wire gauge needed for 24amp load per bank

    To the OP, I'm with you I don't know why I didn't think of ring terminals. Great solution I have used many times.
    To the couple of people that somewhat firmly hammered me. You may well be correct. I am trying to get a hold of a friend that is an Electrical Engineer to find out what if anything I missed. He can be hard to get a hold of, but I have always known him to be a solid (if not overly methodical) engineer and I trust his advice. Once I find out I will let y'all know. While I am pretty well versed in a lot of ways I know that I don't know everything and can admit when I am wrong. Have a safe and great holiday season everyone.
    Regards,
    John

  11. #40
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    Default Re: Wire gauge needed for 24amp load per bank

    Hammering you was not my intention. Aligning with what was taught to me a long time ago (or at least as I remember it, which has been known to be a bit out there at times). I look forward to seeing your feedback from an electrician (always good to get latest info from someone who is living this stuff). FYI: I started life as a digital electronics engineer. My data is admittedly 30 years out of date and to be honest, I have forgotten a ton of the formulas that I used to know without thinking about them.

    2017 adding 2 more candy canes, 7 Mid trees and a Halloween show. Removing most 2812 strips and replacing them with bullet pixel mounting strips. Replacing many buck converter waterproof bags with printed boxes.

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