in-line fuse and relay melting

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Gillygirl

New Member
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16
Location
I live at Barnwell, Northants.
Hi Guys hope you can help me.I,ve just fitted a pair of spot lamps on my 110 td5 ( 02 plate ) and have wired them up through fuses,a dash switch and a relay which i have wired up following advise on this site ,so im sure its correct.every thing works ok,however after a few minutes with all the lights on the in-line fuse holder starts to melt and relay gets hot.Its a12v relay but i,m getting over 13 v0lts from the headlight switch.Is there a problem with the electrics giving too many volts or am i doing something wrong ?
would be grateful for any advice,thanks:confused:
 
bet you've got a cheap n cheerfull fuse holder that's prolly rated at about 5 amps - 13 volts is about right
 
Agreed - I guess this voltage is when the engine is running. To charge a 12 volt battery you need more than 12 volts - the alt will put out about 14.5 volts (DO NOT DISCONECT IT TO FIND OUT IT WILL DESTROY THE REGULATOR) which when connected to a battery with an internal resistance (i.e. the force required to drive the power into the battery) you get to around 13 volts.

As for melting fuses and relays what is the wattage of the lamps i bet you have 100 watt ones?

Calculations :

100W x2 at 12V

200w/12V = 16.6A - You must then add in a little bit for resistance through the wires etc and more importantly the surge current (a cold filiment will allow more current through than a hot one (in a cold wire the free electrons are not moving much so not much force is required to make thm move in a single direction --ve --> +ve, in a hot wire they are moving much faster and in randon directions requiring more force to make a current flow in a uniform direction)


Anyway enough of the science - Basicly you will need a fuse (and fuse holder) capable of handling around 25amps and wiring to match and a good 30amp relay (with good conections onto it)

To do my 8 spots i have used one of those big fuse holders you get from car audio shops with a 50amp fuse in for the inverter, and two 40 amp fuses each doing 4 lights (300W - 2 are 50w others are 100W)

There is a bit of 25mm cable comming off the battery to the fuse box and then 6mm cable running to EACH of 3x 30amp relays, and 2.5mm cable going onto EACH light

The inverter then has 18mm cable running to it

The one thing I would change is the fuse holder in my setup as it cant actualy handle the 90A plus that is used with the lights and inverter on at the same time - if your just doing lights then you should be fine - If you want there are many marine products avalible for hadling this amount of power - do a google.

Sorry for the science - but if you understand the principles behind it then it should be easier to design a system to fit you needs - V=RA and I=VA

James
 
what current are the two lamps you are trying to wire in?
where are you taking power from to drive them?
what size fuse do you have in line?
what current handling Relay are you using?
 
jamescronin said:
Agreed - I guess this voltage is when the engine is running. To charge a 12 volt battery you need more than 12 volts - the alt will put out about 14.5 volts (DO NOT DISCONECT IT TO FIND OUT IT WILL DESTROY THE REGULATOR) which when connected to a battery with an internal resistance (i.e. the force required to drive the power into the battery) you get to around 13 volts.

As for melting fuses and relays what is the wattage of the lamps i bet you have 100 watt ones?

Calculations :

100W x2 at 12V

200w/12V = 16.6A - You must then add in a little bit for resistance through the wires etc and more importantly the surge current (a cold filiment will allow more current through than a hot one (in a cold wire the free electrons are not moving much so not much force is required to make thm move in a single direction --ve --> +ve, in a hot wire they are moving much faster and in randon directions requiring more force to make a current flow in a uniform direction)


Anyway enough of the science - Basicly you will need a fuse (and fuse holder) capable of handling around 25amps and wiring to match and a good 30amp relay (with good conections onto it)

To do my 8 spots i have used one of those big fuse holders you get from car audio shops with a 50amp fuse in for the inverter, and two 40 amp fuses each doing 4 lights (300W - 2 are 50w others are 100W)

There is a bit of 25mm cable comming off the battery to the fuse box and then 6mm cable running to EACH of 3x 30amp relays, and 2.5mm cable going onto EACH light

The inverter then has 18mm cable running to it

The one thing I would change is the fuse holder in my setup as it cant actualy handle the 90A plus that is used with the lights and inverter on at the same time - if your just doing lights then you should be fine - If you want there are many marine products avalible for hadling this amount of power - do a google.

Sorry for the science - but if you understand the principles behind it then it should be easier to design a system to fit you needs - V=RA and I=VA

James
Click to expand...


Good answer :D:D:D:D:D:D:D
 
Gillygirl said:
Hi Guys hope you can help me.I,ve just fitted a pair of spot lamps on my 110 td5 ( 02 plate ) and have wired them up through fuses,a dash switch and a relay which i have wired up following advise on this site ,so im sure its correct.every thing works ok,however after a few minutes with all the lights on the in-line fuse holder starts to melt and relay gets hot.Its a12v relay but i,m getting over 13 v0lts from the headlight switch.Is there a problem with the electrics giving too many volts or am i doing something wrong ?
would be grateful for any advice,thanks:confused:
Click to expand...

Put simply you are drawing too much current - the information above is all very useful and will help you find your problem.

When you specified all your components; relay, fuses, wire, what did you use for your max current rating? i.e. what your lights will draw plus some more?

Did you forget you had more than one load on the circuit and forget to multiply the wattage, the voltage will stay the same, but the power of each lamp needs to be added to find your total.
 
Thankyou all for pointing out my miss use of letters - I stand corrected - so to clarify

Power(W) = Current (amps) x Voltage(Volts)

Voltage(Volts) = Current(Amps) x Resistance(Ohms)

therefore

Power(W) = Current(amps)xcurrent(amps)xResistance(Ohms) (sorry i can't work how to raise current to the power 2 on the forum screen)
 
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