Circuit/switch panel for fishing boat

Discussion in 'The Projects Forum' started by karamit, May 22, 2012.

  1. karamit

    Thread Starter New Member

    May 22, 2012
    5
    0
    Hi,

    I am attempting to create a main switch and fuse (breaker) panel for my fishing boat, and have a couple of questions.

    1. I am adding a relay that will power a Trolling motor with a 50Amp max rating (see diagram). Should the fuse I install on the coil ("F_?" in diagram)have a max rating equal to that of the switch that drives the relay ("SW_Trolling", 10Amp max)?

    2. I commonly hear that the fuses should be located as close as possible to the power source, however, the setup I am envisioning does not allow for that (battery is in the rear of the boat, all electronics are in the mid/front). Does this pose a problem?

    3. I am attempting to source a decent LCD battery gauge (recommendations?), and would like to know if I will see inaccurate ratings if it is operating while other high-load devices are operating?

    I am open to all tips and recommendations, so do let me know if I am doing something incorrect. My schematic is not perfect, so I apologize in advance.

    Best,
    Elias

    [​IMG]
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    The relay coil should be fused with a fuse just big enough to survive normal usage, and I suspect your relay coil only needs less than 1A. You'll need to find out its specs. Worst case, if you can't find the specs, you start with maybe a 500mA fuse and see how long it lasts. Or use your multimeter to see how much the relay draws.

    Don't worry about fuse placement. Current flows in a loop, and it doesn't matter where in the loop the fuse sits.

    For a meter, I'd just use a $5 multimeter. Not elegant but this isn't something you need on a permanent basis, is it?

    Thanks for the drawing, BTW. Worth a thousand words.
     
  3. karamit

    Thread Starter New Member

    May 22, 2012
    5
    0
    Hi wayneh, thanks for the quick reply (you must eat, sleep, and drink this stuff!).

    The gauge is permanent, and vital especially if I am on a multi-day excursion, and need to conserve battery seeing that I will not be recharging.

    Regarding the coil, I will try with a 1A and see what happens. The datasheet for the relay I will be using does not mention coil data.

    Thanks!
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    That's odd, it's one of the more important attributes of a relay. Do you have a link or an electronic copy you can post?
     
  5. MBVet05

    New Member

    Jul 21, 2011
    27
    1
    I too am working on a boat project similar to the one mentioned. I have found several nice marine fuse panels on Amazon to replace my aging fuse holders. I am glad this thread was here so that I know how much my trolling motor will draw from the source.

    My boat was built in 1979 so you can see where I might want to do a little upgrading.
     
  6. cork_ie

    Member

    Oct 8, 2011
    348
    58
    The previous posters are correct, the current consumed by the relay coil is miniscule, however with a 1A or less fuse you might get sporadic blowing of the fuse due to the inductance of the coil winding.
    To be honest any fuse rating around 3A is more than adequate protection unless you are using wire the diameter of a human hair or there is electronics involved. You will suffer a lot less from voltage drop, which ensures that the relay will open & close sharply minimising contact burning.
    50A is a fairly hefty relay and it is likely that the coil will be stronger than the bog standard CUBE type relay. Also watch out that the relay you use is continuously rated and that the 50A is not an intermittent rating.
    I would also strongly urge you to use circuit breakers rather than fuses in a boat. Thermo-electric are best (eg ETA) and are a lifetime job.
    Finally for voltage monitoring; Sterling Power Products do a very nice Power Management Panel In Europe see http://www.sterling-power.com/products-pmp.htm If you are in the USA http://sterling-power-usa.com/index.aspx.
    Bluesea Systems in the USA also supply similar products http://bluesea.com/category/94/97/productline/138.
    Good luck

     
  7. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    This is somewhat of a nit but inductance will not cause a surge in the current, only a spike in the voltage when the relay is turned off (and the maximum current from that spike is never more than the normal relay coil current). So if you fuse for, say 50%, over the normal relay coil current, you will be fine.
     
  8. cork_ie

    Member

    Oct 8, 2011
    348
    58
    If you try it sometime and you will find out otherwise. The collapse of the magnetic field in the inductor core is generally much faster than the field build. If the switch is opened, theoretically there should be zero current flow as the circuit is incomplete, however there is a minute period when the back EMF will cause a current to flow due to ionisation. With the faster speed of field collapse , the induced voltage will be higher and hence any current will be higher . Obviously a capacitor across the switch contacts or a freewheel diode will reduce the effect.
    Small relays are rarely an issue but if you switch solenoids, the fuse rating needs to be minimum 4 times the continuous coil current otherwise you will be plagued by nuisance tripping or fuse blowing. Best example of all is to compare the charge current v's the discharge current in the primary winding of a vehicle ignition coil.
     
  9. karamit

    Thread Starter New Member

    May 22, 2012
    5
    0
    Hi cork_ie,

    I will be using eaton push button breakers for everything under 10A. The trolling motor will be either 40A or 50A, depending on the thrust output, and cannot find a push button fuse with that rating.
    Thanks for the links, will check them out.
     
  10. karamit

    Thread Starter New Member

    May 22, 2012
    5
    0
    Hi wayneh, here is the link: http://www.alliedelec.com/search/productdetail.aspx?SKU=70132460

    40A max (which is the trolling motor I've decided to purchase, not the 50A model).
     
  11. karamit

    Thread Starter New Member

    May 22, 2012
    5
    0
    Hi MBVet05,

    Be sure to check the manual for your troller, as they do vary. I know some 33ft pound models take only 30A at max, while 55ft pound will take 50A or more.
     
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