12v lights

[JohnW2]

From battery through wall 2m right no2 no3 is right no4 sits at 2oclock off no2 no5 sits 10oclock off no4 and no6 sits 12oclock off no5

Is 12 o'clock always 'upwards' in terms of my diagram?

Kind Regards, John.

 

[seabreeze1]

Yes

 

[ban-all-sheds]

The layout of the lights are, battery bank then through wall 2m right no1 light from battery 2m left no2 light from battery 3m left another room no3 light from battery 3m left no4 light from battery 6m left no5 from battery 8m left no6 and last light, All light have own on/off switches. 12v 20w

Could you draw it for us, showing distances and relative positions?

From battery through wall 2m right no2 no3 is right no4 sits at 2oclock off no2 no5 sits 10oclock off no4 and no6 sits 12oclock off no5

This is like pulling teeth.

seebreeze1 - could you draw it for us, showing distances and relative positions?

 

[JohnW2]

From battery through wall 2m right no2 no3 is right no4 sits at 2oclock off no2 no5 sits 10oclock off no4 and no6 sits 12oclock off no5

Any warmer? ......

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• JohnW2
• 14 Sep 2011
• 1

Kind Regards, John.

 

[Stoday]

"The resulting volt drop must then be multiplied by a factor of 1.20. This is the factor from table 9C in the on site guide to correct for the rise in temperature when the circuit is under load."

Table 9C was supposed to adjust the values in table 9A, which provides values of conductor resistance at 20°C.

 

[JohnW2]

"The resulting volt drop must then be multiplied by a factor of 1.20. This is the factor from table 9C in the on site guide to correct for the rise in temperature when the circuit is under load."

Table 9C was supposed to adjust the values in table 9A, which provides values of conductor resistance at 20°C.

There's something seemingly odd about these various Tables, so I presume I'm being silly somewhere. If one takes the 1.20 factor from OSG Table 9C (conductor in a cable, 70°C) and applies it to the 4.61 mΩ/m figure for 4mm² conductors from OSG Table 9A, then multiplies by 2 for a 2-core cable, one indeed gets to the VD of 11 mV/A/m figure given for 2-core 4mm² at 70°C in BRB/BGB Table 4D2B. However, if one has two singles, OSG Table 9C gives a factor of 1.04, which leads to a VD figure of 9.57mV/A/m, whereas BGB Table 4D1B appears to again give 11 mV/A/m. I think I must be missing something here.

Kind Regards, John

 

[ericmark]

Why is anyone looking at an OSG? We have a battery which can be on or off charge so before we look at cable volt drop we have 2.8 volt difference in voltage according to charge state. A standard vehicle is expected to drop battery voltage to 9 volt when starting but only expected to use lights while running so all lamps rated at 13.8 volt approx.

Looking on Labcraft web site the voltage for their 10W halogen down lighters is 10 - 14 volt. Florescent lamps rated 10 - 15 volt. And LED 10 - 14 volt. I think these values are typical so looking at minimum volts of 10 volts. So with battery off charge at 12 volts maximum volt drop is 2 volts.

This leaves the question heavy cable or some form of compensation and with consideration of cost then and the fact individual switched the separate cable to each lamp seems way to go. This would also mean a more direct route can be used.

But still guessing on real spec for lights so I think time to give up.

 

[seabreeze1]

Yes drawing looks good lights are halogen but these could be changed to 8w LED

 

[bernardgreen]

Looking on Labcraft web site

I would reccomend them, their products are good. ( and not because that was my first job in the 1960's)

Alternative idea.

Have a small battery at each lamp location. With small three core cable to each lamp location. Two cores to trickle charge the battery when ever the generator has output and the third core ( with one of the charge cores as return ) to operate a relay at the location to turn the lamp on when needed. No voltage drop between lamp and battery so best efficiency there. Charge current over 24 hours would be less than current to lamp over 8 hours so voltage drop in charging circuit is not so critical to efficiency.

Using a ( Labcraft ) 12 volt flourescent 8 watt lamp with a 12 amp hour 12 volt battery will give well over 10 hours of light.

 

[JohnW2]

Looking on Labcraft web site the voltage for their 10W halogen down lighters is 10 - 14 volt. Florescent lamps rated 10 - 15 volt. And LED 10 - 14 volt. I think these values are typical so looking at minimum volts of 10 volts. So with battery off charge at 12 volts maximum volt drop is 2 volts.

That's a good point. Even BS7671 accepts that one can use device sepcifications for deciding on acceptable voltage drop - the 3% for lighting circuits is simply a figure which is 'deemed to satisfy' in the absence of a stated minimum operating voltage from the manufacturer.

Kind Regards, John.

 

[JohnW2]

Yes drawing looks good lights are halogen but these could be changed to 8w LED

Currents (and hence cable size requirements) would obvioulsy be less with 8w LEDs.

As for the layout/drawing, it looks as if it could theoretically be fairly nicely split into two circuits. Would it be fairly easy to have cables which ran:
(a) from battery to lamp 3 ?
(b) from battery to lamp 5 ?
(c) from lamp 2 to lamp 4 ?

Kind Regards, John.

 

[seabreeze1]

Thank you all for your help, I"ll be intutch let you know how i got on

 

[JohnW2]

Thank you all for your help, I"ll be intutch let you know how i got on

You're welcome. One wiring layout (if it's easy to implement) you might like to consider is as follows - and should facilitate reasonably modest cable sizes, even for 20W lamps. Let us know if you want us to try to do some calculations for you:

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• JohnW2
• 15 Sep 2011
• 1

Kind Regards, John.

 

[ericmark]

Yes drawing looks good lights are halogen but these could be changed to 8w LED

That is the way to go. Three advantages one is volt drop is reduced. two the lamps are better able to handle the volt drop, and last the batteries will last longer.

 

[JohnW2]

Yes drawing looks good lights are halogen but these could be changed to 8w LED

That is the way to go. Three advantages one is volt drop is reduced. two the lamps are better able to handle the volt drop, and last the batteries will last longer.

Indeed. If the OP went with 8W LEDs and adopted the circuit design I suggested in my most recent post (one 2-lamp radial and one 4-lamp ring), I think he could theoretically probably get away with 1mm² for all his cables. If I've got my sums right, that would mean (using 70 degree operating temp as very conservative) VDs of around 0.35V and 0.59V for the two lamps on the radial, and VDs <0.3V for all lamps on the ring. In practice, probably better to use 1.5mm², or even 2.5mm², for the radial circuit, to get brightness/colour of all the lamps roughly the same.

Kind Regards, John.