Blowing fuse???

Discussion in 'Motorhome Chat' started by Monty1083, Sep 12, 2013.

  1. Monty1083

    Monty1083 Read Only Funster

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    I have a portable air compressor, just a small thing for blowing up tyres, air beds etc. which operates from the cab 12v cigar lighter socket.

    I bought a 5m 12v extension cable so that the compressor would reach the rear tyres on the M/H.


    The compressor seems to work ok when it is plugged into the cab socket but when connected using the extension lead the cigar lighter 10 amp fuse blows.


    I had also intended to use the extension lead to connect a 12v pump to fill the water tank from an Aquaroll but not sure if this is a good idea.


    Any suggestions as to why the extension lead should cause this to happen?
     
  2. pappajohn

    pappajohn Funster Life Member

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    the extension lead is far too long.

    as the length increases the volts drop and the amps rise so you are overloading the 10amp fuse.

    i had the same problem with my mini compressor to the point the compressor could barely turn under load.....but it was extended by 8mtrs and trying to pump 80psi.

    i then went the other route and extended the air hose but had the problem of air compressing in the hose on each piston stroke but as there wasnt enough volume on each piston stroke to push air into the tyre so it merely expanded in the hose on the downward (uncompressed) piston stroke.

    i finally solved the problem using a large motorcycle battery to power the compressor in its normal configuration....3mtr cable and 1mtr hose.
     
    Last edited: Sep 12, 2013
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  3. hilldweller

    hilldweller Funster Life Member

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    Faulty extension lead.

    Some subtle fault with the connectors ?
     
  4. Monty1083

    Monty1083 Read Only Funster

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    Sounds feasible.... Do you think it will be the same then with the water pump idea? (Although my neighbour uses this method without a problem).
    Other than carrying a motorcycle battery is there any way around it other than carrying a foot pump!
     
  5. pappajohn

    pappajohn Funster Life Member

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    I dont think a water pump would be a real problem....not as heavy a load but maybe a little slower than it could be.

    you could try heavy wires to prevent volt drop....maybe 6 or 10mm

    once i abandoned the extension lead and hose idea's and used a second battery the compressor would easily pump 80psi into my tyres.

    i have since modded the compressor to fit on a 24ltr air tank which has an auto cutout switch set at 115psi....no problem getting to 115psi and capable of a higher pressure if needed.

    the compressor wiring is 'as bought' but only 300mm long from compressor to switch and a further 600mm from switch to battery.....doesnt even get warm
     
  6. happypre65

    happypre65 Funster

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    blowing fuse

    :BigGrin:Hi,Same problem for me, so i extended the cable by using two connectors and some more cable and it has now been working for three years,done the same for my daughter and no problem,as the saying goes ,dont make a mountain out of a mole hill,regards H.
     
  7. SomeoneElse

    SomeoneElse Funster

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    I'm with Brian on this one.
    A fault (short) in or caused by the extension lead.

    Does the fuse blow with just the extension lead plugged in the socket?
    or only after the compression is plugged in the lead.
    This may indicate which end of the lead is causing the problem.

    Gordon
     
  8. SC 05 OUT

    SC 05 OUT Funster

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    why not just put your CAR near the m/h wheel where you need to pump up and plug into it,:thumb:
     
  9. estcres

    estcres Read Only Funster

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    This is typical, using a machine to do a job that can be done manually quite easily.

    Get a footpump and get some exercise at the same time,

    I've got a footpump for the vehicle tyres and a hand pump for my bicycle tyres, never had a fuse blow
     
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  10. SuperMike

    SuperMike Read Only Funster

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    Although it is possible that the extension lead is faulty, have you checked it with another device ?

    If the extension lead is ok, then PPJ is spot on with this analysis. If you took a cross section of these extension leads you would find that the amount of copper in them is minimal and they are basically unfit for purpose. :Doh:

    Bloody hell, I'm agreeing with himself, everbody watch out for the pigs. :Rofl1:
     
    Last edited: Sep 13, 2013
  11. JJ

    JJ Funster

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    Resistance.

    That's the problem.

    Cheapo extension cable = increased resistance = more current needed = blown fuse.

    Solution. Fatter (or more conductive) extension cable wire allowing the little electron thingies to move around easier.

    (Or use a big nail for a fuse)

    JJ :Cool:

    PS. Please note. The nail bit was a JOKE.

     
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  12. hilldweller

    hilldweller Funster Life Member

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    Resistance is useless.
    Resistance is useless.
    Resistance is useless.
    Resistance is useless.
    Resistance is useless.
    Resistance is useless.
    Resistance is useless.
    Resistance is useless.
     
  13. rainbow chasers

    rainbow chasers Read Only Funster

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    :Rofl1::Rofl1:......I was hoping it was! Good explanation though!


    Best way to demonstrate this is laymans terms is with a hose.

    Turn on you tap to just a trickle. Wait until the water comes out of the hose at it's trickle rate.

    Now lift the hose into the air. The water supply will stop, as it needs more pressure to reach the end. To do this, you need to open the tap a little more to maintain that trickle and overcome the resistance.

    This is similar to electricity - you need to 'open the tap' a little more. To do this, you need a bigger fuse (opening tap) and a suitable cable to carry that higher 'pressure' (amps).
     
  14. bailey

    bailey

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    I did the very same thing added an extension cable to reach the back wheels and have not had any problems with fuses or drop in preasure

    Bill
     
  15. jonandshell

    jonandshell Funster

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    How can more resistance make more current flow?

    I'd say the extension lead has a dead short inside.
     
  16. JJ

    JJ Funster

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    Fatter wire reduces resistance and allows more current flow. Look at the wires carrying the 12 volts to your starter motor.

    JJ :Cool:
     
  17. hilldweller

    hilldweller Funster Life Member

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    A simple DC brushed motor is virtually a short circuit at low revs. It's back EMF rises with revs and the current drops as does the torque. This is why DC motors are excellent for vehicles, max power for take off.

    The compressor will spin up to revs faster than the fuse will blow.

    Now add a little resistance. The motor can't spin up quickly and can't reach full revs so will as PJ said, draw more current.

    10A is not much of a fuse anyway, some of our sockets are labelled 16A and I think the German ones are on 15A fuses.

    Ill admit PJ 1 : Hilldweller 0 on the first posts.
     
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  18. jonandshell

    jonandshell Funster

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    Even a 16kW motor shows 5 ohms with a multimeter when static. I do buy your explaination of increasing resistance with motor speed but in this case I reckon its a dodgy lead!
    We would have plenty of problems if we only rated fuses at motor running amperages rather than stall currents!:BigGrin:
     
  19. hilldweller

    hilldweller Funster Life Member

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    The lead was my first guess. Those cigarette sockets are as crap as you can get and call them connectors.

    In this case the fuse isn't rated for the motor, we don't have any clues on the motor load so as usual just guessing, intelligently of course.

    I have a cheapo compressor used with a cheapo extension but it's usually plugged into the DIN sockets. It works.
     
  20. Monty1083

    Monty1083 Read Only Funster

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    Thanks for the suggestion but the idea was more for when we were away and don't have the car with us.
     
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