Split charge relay

Discussion in 'Tech/Mech General' started by Snowbird, Aug 30, 2011.

  1. Snowbird

    Snowbird Funster Life Member

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    Have fitted a new split charge relay onto the camper. Fused it at both ends with a 15amp fuse,but it blew the fuse so replaced with 20amp fuses. All seems well now. What fuses are recommended on these things.
     
  2. scotjimland

    scotjimland Funster Life Member

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    Hi Dave .. depends on the cable size..

    The function of a fuse is to protect the wiring from overheating and going on fire, (due to a short or overload), so the answer depends on the max current rating of the wire, the insulation class and the ambient temperature.. .. this applies to any circuit ..

    Most probably yours is 2.5mm cable which is rated at 17A ,at 30deg C, so a 20A fuse is on the upper limit, but should be fine.... so check wire size and if it is less than 2.5mm , stick with 15A fuse.
     
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  3. Snowbird

    Snowbird Funster Life Member

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    Ta Jim, the wire is fairly thick heavy duty,the type used for spotlights etc.
    There is a fuse at the relay end and a fuse at the leisure battery end. The original 15amp fuse blew at the relay end so I swapped it for a 20amp. Then the 15amp blew at the battery end so I swapped that also for a 20 amp.Have run it up this morning and all seems well.
     
  4. Wildman

    Wildman Read Only Funster

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    thinking about this, you are getting a lot of current possiblly being drawn when you start up (depends how the relay is switched) or a low battery that takes a boost to charge it. Are your batteries ok? where is the relay powered from?
     
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  5. scotjimland

    scotjimland Funster Life Member

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    yes, that is a good point ..

    the problem is that the standard blade fuse isn't designed for surge loads .. it blows fairly quickly ..
    I had the same issue with a euro van , once every once in a while it blew the 20A charging fuse.. so I up'd it to 25A .. yes, I know that is naughty .. and I don't recommend.

    It would be better if converters fitted a DC MCB or indeed a slow blow fuse, might be worth considering if it's a persistent problem.
     
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  6. Snowbird

    Snowbird Funster Life Member

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    Hy Roger, The relay wont open till it senses power from the alternator,which incidentally is a high output 110amp joby. I think the alternator was trying to push more juice into the batteries than the 15amp fuse would take. The leisure batteries were down as have had little sun,so maybe that was the problem. Since fitting the 20amp fuses all seems well.
     
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  7. Snowbird

    Snowbird Funster Life Member

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    Latest update on this is,the 20 amp fuses have started blowing now.
    Would an auto electrician be recomended or has anyone any thoughts to save me £45 an hour.:Eeek:
     
  8. scotjimland

    scotjimland Funster Life Member

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    Hi Dave..

    do you know what charge is in the batteries.. you mentioned little sun, I rather suspect that they are low and the fuse is blowing due to the high charge current when you start the engine rather than a cable fault .. can you measure the voltage at the battery terminals ?

    edit

    are both fuses blowing ?
     
  9. artona

    artona

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    This happened recently with my split relay. The fuse was actually burnt rather than just gone. It happened after a prolonged stay on site off hook up so I think the batteries demanded a huge supply
     
  10. CHRI$

    CHRI$ Funster

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    if you have fused it on the load side(battery)and its that fuse that's blowing,if it was me i would remove the fuse altogether,and just leave it fused on the switch side,or put the biggest fuse you can in it,an altanator will throw a huge current if it needs to,you say you got an 110amp alt when your switch relay switch's to your hab battery the fuse cannot handle the current and if your hab bats are low the current will be huge,to start with:thumb:
    let the relay take the load thats why you got a switch relay:thumb:
    another thing are you useing a heavy duty switch relay?
     
  11. Snowbird

    Snowbird Funster Life Member

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    Hi Jim, Theres 12.5 in the liesures,have had an amp meter on the relay wire and theres 25 amps going in.Have put 30 amp fuses on and one of them has now blown.
     
  12. Snowbird

    Snowbird Funster Life Member

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    Will try that Chris,have fused it at the relay where the wire comes out to the lesures and just before the leasure bank.Its doung my shed roof in now:Sad:
     
  13. Snowbird

    Snowbird Funster Life Member

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    Hi Stew,I never have hookup so maybe thats the problem,the battery bank is asking to much of the fuse.
     
  14. CHRI$

    CHRI$ Funster

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    the wire from your alt to the cab bat is not fused?if it is it will be a huge fuse around 150 amp,so going on this the wire from your alt to your hab bat has to handle the same load i would use a heavy duty relay (150 amp)and if it worry's you an inline fuse rated at 140 amps.
    what you need is jim to work out what cable size you should run to take a 110 amp load and use this as a starting point,he will need the lenth of the cable run:thumb:
    you say there is 12.5 in the bat,the alt will sence this and only throw out what it needs to replace the lost power out the bats.
    do some thing for me messure your hab bat when the alt is running,if its 13.8 volt the bat's are not fully charged,and will go up to as much as 14.5(with alt running) before you bat's are charged:thumb:
     
  15. CHRI$

    CHRI$ Funster

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    correct:thumb:
     
  16. CHRI$

    CHRI$ Funster

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    ditch the fuses,or put huge fuses in, and only one:thumb:
    my little charger runs 70 amps max,the cable's i use are rated at 800 amp:Eeek:
    no fuse, straight from the alt to the batteries:thumb:6m in lenth:thumb:
     
  17. jonandshell

    jonandshell Funster

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  18. jonandshell

    jonandshell Funster

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    And what happens when that cable gets chaffed and shorts to chassis?

    Hope you have a good fire extinguisher!
     
  19. CHRI$

    CHRI$ Funster

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    so your are saying the cable WILL get chaffed or might get chaffed, and short to the chassis,when fitting any high ampage cable through a motorhome you must ensure it WONT get chaffed,all down to the instalation,do it right,do it once:thumb:
    but i see your point,and as i said put a fuse in it if worried:thumb:
    my cables do not run through the motorhome,so no worry of fire:thumb:
     
  20. CHRI$

    CHRI$ Funster

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