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Thread: How to restrict 12v 5amp output

  1. #1
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    How to restrict 12v 5amp output

    Not 100% car related, but I'd like the ability to use an electric wax embedder on the back of the ute instead of doing it at home. I currently use it on the C-Tek at 7amp and it works perfect, maybe slightly hot, 5 -7 amps will work perfectly. The wax embedder as below just shorts out a thin wire to heat it, to melt the wax to it. Ideally I'd like to run it off the Anderson plug but with my little electrical knowledge that will just draw a metric fuckton of amps and melt it too quick and/or start a fire along the way.

    Image from google of how it works:
    https://i.ytimg.com/vi/X9FaYpz9frc/maxresdefault.jpg

    A quick tells me I need a buck converter. Is this all I need to add inline with a fuse for good measure and it should regulated the 14v~ from Anderson plug to 5amp?

    LINKY

    Is there a better way to achieve this?

  2. #2
    Half Shafted. Madhatr's Avatar
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    What is limiting the current at the moment? just the battery charger? there's no external power supply?

    If your wax embedder thing has no external power supply, like, it is literally just a wiring connected to your battery charger, then you are right, if you remove the charger and run it from the battery on your ute, it will try to draw the entire contents of the battery (many, many amps) though your wiring on the embedder as you pretty much just made a dead short. Smoke will come out, followed by fire, so certainly avoid that.

    Those converters you linked are taking a higher voltage and reducing it down to 12v @ 3 amps. If you are starting with a 12v input (ie battery), then it is pretty useless. There are others that have 12V DC input though, but there is a couple of problems.

    1) you want to draw 7amps continuous, which is a pretty heavy duty load for those small modules. 12V to 12V is more like 1-2 amps max.
    2) anything thats not really a regulated power supply wont do 12v to 12v DC properly, the reason being is efficiency, the input voltage usually always has to be higher than the output. So even displaying a 12v input, the output would be more like 9-10v. So you'd need one that would be more like 60-70w to give you the current you need. Seems to be a hard find for such a small module.

    The question is, how is your wax embedder made? if it's literally just wire, you can probably put more than 12v through it. So id be looking at a DC - DC step up module. 12V DC to 24V DC would be fine.

    Edit:
    Something like this would probably work. http://www.ebay.com.au/itm/DC-DC-Boo...oAAOSwGdhZmBxJ

    8A output, 150w max. Quick calculation, based off 150w output of the module

    20V DC Output - 7.5 amps
    21V DC Output - 7.14 amps
    22V DC Output - 6.81 amps
    23V DC Output - 6.52 amps
    24V DC Output - 6.25 amps
    25V DC Output - 6 amps

    How long they will last being a chinese made regulated module is any guess, but it's pretty cheap vs a regulated power supply. The other alternative would be to look at 12V solar battery chargers.
    Last edited by Madhatr; 09-09-17 at 03:00 PM.
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  3. #3
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    Wax embedder comes with alligator clips, which I just clip to the battery charger. Embedder has a switch when using it, you really only do 4 short bursts of 1-2 seconds at a time per a frame.

    Step up module makes more sense, though will say 21v at 7amps heat the wire the same as 12v 7 amps? Is it just the current causing the heat?

  4. #4
    Registered Fatman Dark Orange's Avatar
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    Ohms law states:

    I=V/R

    Where I = Current, V = Voltage and R = Resistance.

    On a purely resistave load, double the voltage, you double the current. The only way to do what you want to do is to run a new circuit that can handle up to 7amps, or get a higher resistance cutting wire.
    Last edited by Dark Orange; 09-09-17 at 06:06 PM.
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  5. #5
    Sidetracked BMWTurbo's Avatar
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    If it's designed to suit 12V just connect it to the battery via the Anderson connector, it will be fine.

    You are over thinking it. It's just a resistance and will draw whatever current it needs (pending resistance) at 12V.

  6. #6
    Unregistered User Permit Roadsailing's Avatar
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    Honeycomb foundation? I'm with bmwturbo. It will either work the same or just work faster. Or blow up.

    EDIT: I forgot how these things worked. as the steel wire in the hive frame is just normal steel wire (and not Nichrome) it will get hot and orange and melt if you put too many currants through it.

    but as it is just steel wire I reckon it would be worth giving it a shot running straight off the battery, I have a ~30 year old memory of my apiarist uncle doing this with just a car battery, most likely an old car battery which could help things.
    Last edited by Roadsailing; 09-09-17 at 11:19 PM.

  7. #7
    Half Shafted. Madhatr's Avatar
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    Unless it is basically a big coil, its just an on off switch. Wire is not a load, it doesnt draw what it needs, it tries to carry as much as it can and turns red hot in seconds. Try it, put a length of wire between battery terminals and watch what happens.

    If the op was saying it was good at 7 amps on a battery charger, it wont work the same connected to a battery. The charger was working as the regulated power supply.

    Quote Originally Posted by Dark Orange View Post
    Ohms law states:

    I=V/R

    Where I = Current, V = Voltage and R = Resistance.

    On a purely resistave load, double the voltage, you double the current. The only way to do what you want to do is to run a new circuit that can handle up to 7amps, or get a higher resistance cutting wire.
    We arent talking input or supply voltage. Doesnt work that way as we are using a module to regulate the output. None of the values are fixed though as the module being adjustable so output voltage is trimmed to the desired result. The module has a maximum output of 8amps or 150w which ever you may exceed first.

    Maximum current is achieved when output voltage is 18.75v. Lower the output voltage, the higher the current draw at a fixed wattage.

    Change the value and its still the same. 18.75v output provides maximum of 8amps and 150watts.

    7amps is 7amps. I = p / v. Yes, its the current passing through the wire that is causing it to heat up. The current you know it to work well at becomes a fixed value.

    As i said earlier you cant easily regulate current output with a small module like this with both input and output voltages being the same. High powered circuits are hard to find to do that.

    So if we have a current range, power is fixed at maximum output of module as it simply cant output anymore without melting. So voltage output is altered to adjust the current output to the desired range the OP wanted. The table is there and runs true.

    The only value that is fixed is the resistance of the embedder wiring. So with output power limited by what the module can ouput, voltage dictates current output. Thats the other side of the law, PIV.

    If you had a load like a motor or light source, you would start with the current draw by the load, then work backwards to make sure power output isnt exceeded.

    Edit: heres an example.

    I = P / V
    I= 150W / 24V
    I = 6.25 amps

    I = P/V
    I = 150w / 20V
    I = 7.5amps

    Or

    P = I x V
    P = 7.5a x 20V
    P = 150w

    So you can regulate the amount of current the wire will draw by changing the output voltage, being the current value is all the OP has given as a good operating range.

    In reality, nothing is going to be 100% efficient, itll be more like low to mid 90's. So at 24v its going to be more like 5.94 amps output. Still right in the sweet spot the OP wanted.
    Last edited by Madhatr; 10-09-17 at 12:05 AM.
    Quote Originally Posted by Buford T. Justice
    This happens every time one of these floozies starts poontangin' around with those show folk fags.

  8. #8
    Sidetracked BMWTurbo's Avatar
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    Unless I'm not seeing info in DD's posts.

    He says it's designed with clips to connect straight to a 12V battery, so must have a resistance to suit 12V already. Without testing (or accurate resistance) who knows what current was from the c-tec, may be only drawing 4 Amps.

    Agree with your maths MH, just not the reasoning.

    I'll leave it up to DD as to which way to go as a reg supply can't hurt, just likely may not be required.

  9. #9
    Half Shafted. Madhatr's Avatar
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    Its basically a couple of bolts with a strand of wire between them. There is nothing providing any power regulation at all.

    You apply an unregulated power source to it and the wire will continue to draw an increasing amount of current until it melts or destroys the battery cell.

    The OP was running it on a battery charger which is a regulated power supply. Its not just regulating the voltage, its controlling the amount of available current the wire will see. Its not drawing current like a load, its passing through it. Its being superheated creating ever more resistance and generating more heat until the wire gets so hot it will pop.

    Connecting it direct to a battery instead of the power supply will not see the embedder function the same. Itll heat up vastly quicker and continue heating until it dies.

    The wire might have been able to handle 4-5 second bursts when it was being fed by a regulated maximum of 7 amps. Now it will have hundreds of amps available so itll burn itself up real quickly.

    This is what the OP is trying to avoid and wants to limit the available current to the wire so it can still do its job before burning out. Yeah, could you stop it burning by increasing the wire diameter so it can carry more current before burning out? Of course, but youll start talking battery gauges not thin strands. That probably renders the tool useless.

    So the OP wants to take the guess work out and avoid burning out the wire by limiting the current and found a buck converter provides basic voltage regulation. He basically wants it to function exactly like it does on the charger hes used to, so he needs some form of current regulation.
    Last edited by Madhatr; 10-09-17 at 12:28 AM.
    Quote Originally Posted by Buford T. Justice
    This happens every time one of these floozies starts poontangin' around with those show folk fags.

  10. #10
    Sidetracked BMWTurbo's Avatar
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    Okay, agree if that's the case. My research suggested they were designed for 12V car batteries.

  11. #11
    Registered Fatman Dark Orange's Avatar
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    Quote Originally Posted by Madhatr View Post
    Wire is not a load, it doesnt draw what it needs, it tries to carry as much as it can and turns red hot in seconds.
    Everything is a load, especially Nichrome wire. (looked in your toaster lately?)

    It draws 7 amps on a battery charger (14v) and gets "Maybe slightly hotter" - this implies it is drawing slightly more current than its usual maximum, so we can assume it draws slightly less than that at 12v.

    I am still confused as to why the OP thinks he needs a DC/DC converter - if the ute is 12v, and the anderson plug circuit is capable of handling the current (check the fuse - if it's got a 10A fuse, you're sweet) then he can connect the wax embedder up directly to the anderson plug without any extra fucking around.
    Is it crazy how saying sentences backwards creates backwards sentences saying how crazy it is?

  12. #12
    Gas Turbine enthusiast da9jeff's Avatar
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    Madhatr, how do you think an incandescent lightbulb works? If the nichrome wire was an inch thick then it would overload the circuit, the fact that its designed to heat up means it has a resistance to current flow. Plus r goes up as temp increases.

    Sent from my SM-G930F using Tapatalk
    Last edited by da9jeff; 11-09-17 at 01:33 PM.
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  13. #13
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    use a cordless drill battery ?

    ......................

  14. #14
    Registered User burn is weird's Avatar
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    if the wire self-thermally regulates at 12v then just hook it up to the battery. if not, and you need a lower voltage to regulate current to acceptable levels then just buy a couple of these at 11 USD a pop.

    https://www.aliexpress.com/item/1pcs...02.4.92.UdRDlX



    they are a boost converter, but also have current sensing/limiting.

    one of the pots (blue rectangles with the brass screw in the corner) is for voltage boost, the other is current limit.

    will do what you want. just need to hook it up to a car battery or PC power supply or something.

    you'll need a current clamp to calibrate the current limit pot for your heater circuit though, or you can just slowly wind it up to get the heat you need.

    I've been using them as a very cheap current limiting bench power supply. being switch mode and the caps not amazing they are a bit noisy when you are boosing the voltage on loarge loads but for a resistive load and very little inductive boost (Vin ~ Vout) who cares.
    Last edited by burn is weird; 11-09-17 at 01:19 PM.

    Oo___oO


  15. #15
    Registered Fatman Dark Orange's Avatar
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    Neat idea.
    Is it crazy how saying sentences backwards creates backwards sentences saying how crazy it is?

  16. #16
    Registered User burn is weird's Avatar
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    not sure of its current limiting abilities if you're running it at zero-boost though.

    as its a boost converter, it's not capable of bucking voltage to reduce it lower than Vin.

    Oo___oO


  17. #17
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    Cheers everyone. Madhatr is on the money the thing will draw enough current to a) melt the wax until it falls apart - 3 seconds at 7amps does this. b) Melt the frame wire and causing it to snap - 10 amps does this. c) Start a fire somewhere - Trying to avoid.

    I will order a buck switch, put a fuse immediately after the battery and see if it will come to plan. Drill battery may just work, a shame the modern batteries have recessed terminals, but I'll play around with my 5 amp and see what happens.

    Plan Z is to take 12v-240v inverter and then run the C-Tech, I know this will work but thought going from 12v to 240v back to 12v there should be an easy way to skip the middle man.

  18. #18
    arboreal bukkake briney's Avatar
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    it seems like massive overthinking. done heaps of embedding over the years with dad. always just hooked it to a car battery, and got to work. just don't fuck around. lol.
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