Can I use a 600V block with 12V and more Amps?

Discussion in 'OnBoard Electronics & Controls' started by mascip, Jun 2, 2015.

  1. mascip
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    mascip Junior Member

    Hi, I'm thinking of using this Screw terminal block barrier double row on my boat.

    Its specifications say: 600V and 15A.
    Can I instead use it 12V and 60A?

    I am guessing that as an approximation, the temperature of the component depends on the power:
    600V x 15A = 9000W, which is much higher than 12V x 60A = 720W.
    Hence, I think that using it with 12V and 60A is safe.#
    Is it?
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Not a very good idea, the resistance in the connections is calculated for 15A current (no matter what the voltage is) so it may overheat..
     
  3. mascip
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    mascip Junior Member

    Yes, that makes sense thank you!
    R I^2 means that the power will be solely dependent on the current, which will probably be mostly determined by other components in the system. So the current rating is the same, whichever voltage I apply.
     
  4. CDK
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    CDK retired engineer

    Contact cross section determines the current rating, the distance between contacts determines the voltage rating.
     
  5. mascip
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    mascip Junior Member

    Current rating is for avoiding overheating.
    What about voltage rating? Is it related to voltage drop?
     
  6. BertKu
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    BertKu Senior Member

    No, voltage drop is depended on the contact resistance and current. By 60 Ampere and a good contact material,like palladium, you should not have a loss of more than a few milliVolts.
    If it is more, the contacts will get hot and start burning. As a thumb rule not more than 2 to 3 millivolts at 60 ampere.
    Bert
     
  7. BertKu
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    BertKu Senior Member

    Strangely enough I have a different opinion mascip. De golden rule for maximum current density is 6 ampere per square mm2 copper. For aluminium or most other materials, it will be less than 6 Ampere, except material like palladium. Thus by 60 Ampere you need 10 mm2 minimum. That applies to the screw area, connector and the connection between the two screws. Should your product as shown exceed those 15 Ampere, i.e. 2,5 mm2 and are similar the Germans often build, products with 100% safety factor, you could consider to spread the 60 Ampere over 3 screws, by splitting the cable of 4 mm diameter (not 4 mm2) (You stated you need it for 60 Ampere). Most other excess connections would be used probably for lower current application. Everybody will argue, it is not professional, but like anything in life, you have advantages and disadvantages. The disadvantage is, it has not a professional looks, The advantage is that in the event of a bad contact, the law of average is, that only one of the 3 screws is not making good contact after a couple of years, while with a single screw contact, it will be heating up and most likely sparking. Just a few. I do sometimes parallel relays in that way to get 50 to 100 Ampere, but only if the contact is made before the current flows and then to increase the current from 0 to maximum. (In case with P.W.M . circuits) Bert
     
    Last edited: Jun 12, 2015
  8. mertkara
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    mertkara New Member

    mascip, No. I repeat, no. Do not try that. Please don’t even consider that. 60A is a lot of current and your system will just not be able to handle it. There’s not just the current rating limitation of the complete system, there’s also something called voltage rating. At minimal voltage, your system will get loaded and you won’t be able to recover the damage that will be caused by loading of components due to lower voltage.

    Regards,
    Mert Kara
    http://blog.7pcb.com
     
  9. BertKu
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    BertKu Senior Member

    Voltage has nothing to do with current density. You can put a million Volt and 60 Ampere or 12 Volt and 60 Ampere, the heat created on the contact between screw and transfer bridge depends on the TOTAL square mm2 between one point and the opposite point going outwards. If this is in total more than 10 mm2 it is safe and if it is 20 mm2
    you are rating at 50%. I can see you have never worked with parallel circuits. I understand that you are an expert on this subject. Could you please explain why a 110 Ampere International Rectifier MOSFet (peak maximum 2000 Ampere for a very short period of time) can handle this with a connection on not even 1 mm2, refer IRFP064N per example. Not that I do this, I make sure that the connection is at least substantial higher. Or having a 100 Kilowatt Radio transmitter with 4 Valves parallel each transmitter and I can give you hundreds of examples. The OP must verify that the surface/square mm2 from A to B, must be more than total of 10 mm2 minimum, if copper screws and copper transfer bridges to the other side is used. Some other materials can handle higher currents. You get the hint what the reason is why the IRFP064N can handle higher currents/mm2
    Bert
     
    Last edited: Jul 2, 2015

  10. BertKu
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    BertKu Senior Member

    You know Mascip, for future reference it will be good if you could judge for yourself whether something is solid enough to handle high currents or not.

    I had a close look at your terminal block. It is 108 mm long and has estimated of 2 mm x 9 partitions , which leaves you with 9 mm for the contact area. I estimate the thickness at 0.5 mm, but it may very well be 0.8 mm. Thus 9 x 0.5 = 4,5 mm2 throughput area x a maximum of 6 Ampere = 27 Ampere per connection x 4 or x 3 is more than enough for 60 Ampere. The problem is the contact area between screw and cable connector. That has to be equal or more than the 4,5 mm2 per screw and that depends how your cable is split up between the 3 or 4 screws. If your logic and judgment is that it is minimum 3,5 mm2 per screw = 14 mm2 for 4 screws or 10,5 mm2 for 3 screws, you are within the limit. However I would in that case spread it out over 4 screws to have a safety factor. Trust that this will help you in your future decisions. The key is maximum 6 Ampere per square mm. for current and as the block is certified for 600 Volt, any Voltage lower than 600 Volt at 60 Ampere is acceptable. (3 or 4 screws, not 1) Bert
     
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