3A Cable Enough?

[scottiecb19]

Hi guys,

I have a 12V tyre inflator, which plugs into the 12V cigarette lighter in a car. The power cable for this is not very long, so I've made myself an extension cable, which is about 10 meters long.

When I plug the inflator into a power source using the extension lead I've made, the LED's on the inflator light up, indicating there is power going to it, but when I turn the pump on, the lights flash and I hear a ticking noise - but the pump won't run.

I'm wondering whether the problem might be the fact that the cable I used for the extension has a 3 amp rating, but I would have thought that this would be enough. Even if the pump needs a bit more current to run, wouldn't this cabling still work?

I note from the inflators' user manual that the 12V plug houses "up to" a 15A fuse.

I should add that the pump runs fine without the extension lead (it just won't reach all the tyres!!)

Any help and advice would be greatly appreciated!

Thanks

 

[DiscoDave]

your tyre inflator is likely to use 15A. With out getting too technical, the wire you have used to make an extension is too small for the current required. you will need a cable that is at least 2mm in cross section.

On a safety note do not use your extension as it is likely to melt or catch fire as it is too small.

 

[scottiecb19]

Thanks for the reply.

The cable itself (insulation n all) is about 4mm diameter, I just know that it is rated at 3 amps.

I accept your comments about it not being safe, and so won't use it, but why won't it power the inflator even if there is a risk to using it?

 

[DiscoDave]

Cable is measured in the cross sectional area of each conductor so 2mm refers to the cross section of the copper inside the insulation and not the size of the cable physically.

For example an item of current using equipment needs 15 amps. if you have a cable that will carry 3 amps maximum then there is not enough room for the current to flow. some voltage gets through but not enough to operate the inflator.

look at it as if it were a water pipe, if the pipe diameter is small not much water can flow, if the diameter is large lots can flow. your inflator needs lots of water to work but the pipe supplying it is too small!

 

[scottiecb19]

Thanks for the explanation, very much appreciated!!!

 

[scottiecb19]

Just a thought, would it be ok to use 240V rated cable as long as it was a 15A one?

Thanks again for your advice!

 

[scottiecb19]

Sorry, does anyone know if it would it be ok to use 240V rated cable as long as it was a 15A one?

Thanks!

 

[DurhamSparky]

yes thats fine

but DONT USE TWIN AND EARTH!!!

 

[scottiecb19]

Twin and Earth?? What's this?

 

[DurhamSparky]

excellent you dont know what it is so thats fine!!! lol

its the cable used to wire property's in! grey in colour and sold in reels with 2 cores and an Earth in side

 

[scottiecb19]

Lol, sorry bout that. I did know what you were talking about after all, just wasn't quite there with the name of the cable. In fact, I only bought some of it a few weeks back to do some wiring jobs round the house.

Back to the original issue, I wanted something a bit more flexible anyway, so wouldn't have gone for the twin one anyways!

Thanks for your reply, much appreciated!

 

[GStueyXR]

if you have a cable that will carry 3 amps maximum then there is not enough room for the current to flow. some voltage gets through but not enough to operate the inflator.

This has gotta be the most inacurate explanation I ever seen.

Voltage is the potential for current to flow, it never "gets through". If a conductor is connected to a voltage/potential, then it's potential rises to that of the origin. If a return path is offered to that conductor, only then will current flow.

Current dosent need "room to get through", it forces it's way through and creates heat in the process. The danger in using under rated cable is from combustion of the insulation and surrounding items.

OP, there is a good chance your pump is knackered.

 

[scottiecb19]

Hey, thanks for your comments, however, when you say...

OP, there is a good chance your pump is knackered.

...if you had read my original post, you would have seen that I did state...

I should add that the pump runs fine without the extension lead (it just won't reach all the tyres!!)

 

[DurhamSparky]

1.5mm 3 Core PVC Flex White 100M

will do just fine!!!

pick it up from any electrical retailer!!! (B&Q charge a premium though)

 

[DiscoDave]

This has gotta be the most inacurate explanation I ever seen.

Voltage is the potential for current to flow, it never "gets through". If a conductor is connected to a voltage/potential, then it's potential rises to that of the origin. If a return path is offered to that conductor, only then will current flow.

Current dosent need "room to get through", it forces it's way through and creates heat in the process. The danger in using under rated cable is from combustion of the insulation and surrounding items.

OP, there is a good chance your pump is knackered.

OP needed a simple explanation to steer him in the right direction and not set anything on fire!

The reason the pump is not working with the extension is that the cable size is too small, it is not able to carry the required current at the correct voltage to operate. Volt drop applies to 12v circuits too!