What Cable Do I Need ?

Discussion in 'The Projects Forum' started by pscammp, Apr 21, 2016.

  1. pscammp

    Thread Starter New Member

    Feb 22, 2016
    23
    1
    Hello all,
    I'm mid flow into a project to power multiple pieces of astronomical equipment using a 75Ah 12V leisure battery and x6 buck/boost DC-DC converters which supply XLR connectors for their outputs and I need some advice on cables.

    Here's a rundown on my situation thus far:

    The main fuse directly off the battery is rated at 30A (which is about 10A+ more than I should pull) which is wired up with 36A cable to two 100A distribution blocks (one for + and one for -, 100A is a bit overrated but I happened to have these lying around), these in turn use 16.5A cable from the distribution blocks, through 10A fuses on the +, to power the DC-DC converters. The output of each DC-DC also uses cable rated at 16.5A through individual quick blow fuses and outputted to XLR connectors on the case which contains all this stuff.

    The output voltages of these converters are adjustable to whatever voltage I require and capable of supporting 10A each ( 7A continuous ) on each output although all outputs wont come even close to pulling this kind of amperage.

    Here is a list of the 'Outputs, their required output voltages, quick blow fuse ratings, what their powering and estimated Watt usage:

    No 1 - 12V......3A.......12V 7-way USB 3.0 Hub........Not 100% sure of the Watts for this Hub but mains adaptor is rated at 3A, x4 USB inputs are used
    No 2 - 14V......4A.......Telescope Mount...................Max 18W at full load
    No 3 - 12V......4A.......Astrophotography Camera.....30W absolute max but will pull approx. 12 - 15W under working conditions
    No 4 - 12V......1A.......Telescope Focuser.................Manufacturer estimates 5 - 10W absolute max at 12VDC
    No 5 - 19.5v....6A.......17" Gaming Laptop................Mains Adaptor rated at 19.5V 6.15A 119W but that's under full load, only approx. 35W was
    measured in a test while Laptop was running on internal battery with required software running.
    No 6 - Aux.....??.........Spare

    Here's my problem:
    Each of the above outputs will need a cable to run from the output XLR's to their respective equipment, I need about 3 meters long on each cable. I popped into my local Maplin store and they offered me the following:

    http://www.maplin.co.uk/p/twin-core-15a-figure-8-cable-priced-per-metre-xs72p

    Not 16.5A but almost there at 15A and well capable of handling the absolute max of 6A as stated above. They also wanted to charge me over £40 for 20 meters of this stuff which was ridiculous to say the least.

    After getting home I went on line to get it cheaper but one fact came up which made me a little concerned. I found loads of Figure of 8 twin black & red cable on Ebay like Maplin's have rated at 15 Amps but as you'll see from above I have one output at 14V and one at 19.5v.

    Example:
    http://www.ebay.co.uk/itm/Twin-Core...hash=item2a07772a4d:m:m4faPioneKjuOm9F73jphOA

    Will this cable be a problem if I run 14v and 19.5v down it even though I wont come close to it's 15A rating ???

    Many Thanks for any help
    Paul
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    13,166
    3,632
    The insulation should be well within any of your limits shown, the important feature is the current rating.
    Do you need a cable with a jacket for any protection? if so look at Cab-tire rubber sheathed cable which should be cheap, it can be obtained in 18g, 14g, 12g, it may not have the exact colour you are looking for.
    The other feature to look at is the strand number, if it is required to be used in a flexible application.
    Max.
     
  3. pscammp

    Thread Starter New Member

    Feb 22, 2016
    23
    1
    Thanks MaxHR,

    Protective jacket wont be required, there will be no friction or rubbing going on. Multi strand is important though as the cables will need to be flexible to some degree not solid, they also do the same black and red cable at 20A which may be an even better option.

    So running 19.5V at around 35W down a cable like the one I linked above should be fine............YES ?

    Many Thanks
    Paul
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    13,166
    3,632
    Yes, That is only a couple of amps, the insulation on most cables today is far in excess that you require.
    Max.
     
  5. pscammp

    Thread Starter New Member

    Feb 22, 2016
    23
    1
    Excellent Thank you for your time

    Paul
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    5,082
    1,104
    In general.. Most regular hookup wire insulation is rated for a min of at least 300 volts..
    Sadly the information on the maplin site is just about useless as they don't specify anything about the voltage rating or even the manufacturer of the wire or the UL specs its rated too..
    But I'm sure its fine for your low voltages
     
  7. RichardO

    Well-Known Member

    May 4, 2013
    1,674
    573
    I would recommend a cable with a jacket that is resistant to friction since this sounds like a portable operation. Good strain reliefs are extremely important in a situation where cables will be subject to abuse during set up and operation.

    Also, keep in mind that the cables have to remain flexible at the coldest temperature you will use the equipment. The last thing you want to have happen is a cable failure while you are out in the middle of nowhere in bitter cold.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    13,166
    3,632
    He's in the UK, It doesn't get cold!:p
    Max.
     
  9. RichardO

    Well-Known Member

    May 4, 2013
    1,674
    573
    Same here in Colorado -- except if you are skiing or doing astronomy. ;)

    It _was_ cold while in eastern Colorado trying to see Halley's comet in mid winter. Fingers and toes got numb. Unfortunately, there were too many little towns on the southern horizon for great viewing. But, instead, we saw a lot shooting stars. :D
     
  10. JohnInTX

    Moderator

    Jun 26, 2012
    2,942
    1,406
  11. pscammp

    Thread Starter New Member

    Feb 22, 2016
    23
    1
    Hello all,
    I ordered 25M of this in the end:

    http://www.ebay.co.uk/itm/401076607753?_trksid=p2060353.m2749.l2649&var=670604313073&ssPageName=STRK:MEBIDX:IT

    I have used the 6A version of this stuff with my old power supply for the telescope Mount for over a year and all is fine with that still and shows no sign of ware with it trailing on the ground. The ideal would be flexible sheathed cable but some of the connectors I need to terminate to have small cable entry holes and some wouldn't take the sheath I know. Maybe in the future I can change equipment connector types to allow bigger cable entry but this will do for now.

    :)

    Thanks all
    Paul
     
  12. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    5,653
    1,605
    This sounds like a job for simple lamp cord. Two wires, 16 ga or 18 ga, good for 10 amps minimum, pennies per foot. 25 or 50 foot spools at the local giant hardware store, or buy extension cords at a discount store and cuts the ends off. Am I missing something here?

    ak
     
Loading...