Is it 3 amps or 4 ?

[Jimbo1707820979]

I have just bought a C7024 Power supply (used) to put more power on my track via my Select Controller. I am puzzle as to why the mains plug, apparently original and in good condition has a sticker "FITTED WITH A 3 A FUSE". To me it doesn't make sense, but I am naive in electrical matters. Could someone please light up my darkness ?

Also, is there anything to do when changing the Select to this Power supply ? It does not seem to be working though the 3 amp fuse is OK. Hope I haven't bought a dud ! Caveat emptor.

[morairamike]

The mains plug is for 240Volts. Inside the Power supply is a transformer and other circuitry which will give out the 15V and that will be capable of providing 4.0A Max. If you draw in excess of 4A then the output voltage will either reduce , or the unit will shutdown. Don't mix up your input rating an dyour output ratings. The input side is 1.5A the 3A fuse protects the unit from excess current draw from the mains.

Looking at the spec on this site

http://www.jadlamracingmodels.com/p-563-scalextric-hornby-digital-c7024-p9300-power-supply-r8213-c7042.aspx

the unit is input: 230/240 V 1.5A 50/60Hz : Output DC 15V 4.0A

[Jimbo1707820979]

The mains plug is for 240Volts. Inside the Power supply is a transformer and other circuitry which will give out the 15V and that will be capable of providing 4.0A Max. If you draw in excess of 4A then the output voltage will either reduce , or the unit will shutdown. Don't mix up your input rating an dyour output ratings. The input side is 1.5A the 3A fuse protects the unit from excess current draw from the mains.

Looking at the spec on this site

http://www.jadlamracingmodels.com/p-563-scalextric-hornby-digital-c7024-p9300-power-supply-r8213-c7042.aspx

the unit is input: 230/240 V 1.5A 50/60Hz : Output DC 15V 4.0A

Thanks Morairamike for your quick and clear answer. I now understand. I have been in touch with the seller who is also puzzled as he tested the unit on his own Select and it worked OK. So I am going to seek the advice of my local Hornby shop before I revert to the seller. Hopefully it is not my Select acting up. It worked OK later on the 1 amp transformer.

Kind regards.

 

 

[Chrissaf]

Jimbo,

Input current on the power supply will always be significantly less than the available output current on a low voltage output power supply. So just because the output is rated at 4 amps doesn't mean that the input also has to be 4 amp. The actual input current will be a lot less than 4 amps, but in the UK the minimum standard plug fuse you can get is 3 amp. Hence the 3 amp fuse. If your power supply is not working and the mains plug fuse is OK then it is probably a dud you have been sold.

.

To be accurate the C7024 is a power supply for Scalextric. The P9300 is the correct power supply for Hornby Select. I would think however that as long as the C7204 is 15 volts at 4 amps with the centre pin of the DC connector being positive voltage that it will be an equivalent substitute.

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In the absence of a test meter, connect a 12 volt car light bulb across the output of the power supply, if that doesn't light up, then your power supply is faulty.

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The above was the quick answer. Below is the in-depth answer.

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For any device, power output = power input less power losses.

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If your power supply output is 15 volts at 4 amps, this equates to 60 watts from Ohms Law (Watts = Volts x Current)

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If the power input voltage is 240 volts then from Ohms Law the input current equates to 250mA** (240 x 0.25 = 60 watts). Some additional input current will be used on the input that results from power losses (heat) in the power supply. But even so, the input current should be well less than 1 amp. Since, as stated above, the smallest amp rating for a UK domestic mains plug is 3 amps, then a 3 amp fuse is used in the absence of anything smaller being available.

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Note** this is only a crude estimate as the 240 volts is AC and Ohms Law is only truly accurate for DC, but for the sake of simplicity it is close enough for the purpose of this description.

[Augustus Caesar]

3 amp fuses are more common now in electrical goods but there is another reason for the low ampage fuse use.

If you use a 4 socket extension with a 13 amp fuse fitted you should really only attach 4 plugs each with no more than a 3 amp fuse which would be 12 in total and thus stop a possible overload.

[Blackbird]

Just a correction to Chrissaf, fuses for standard '13 amp' plugs are available in; 1A, 2A, 3A, 5A, 7A, 10A and 13A ratings.

[Chrissaf]

Just a correction to Chrissaf, fuses for standard '13 amp' plugs are available in; 1A, 2A, 3A, 5A, 7A, 10A and 13A ratings.

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Interesting, I've never seen standard UK plug fuses in 1A, 2A, 7A & 10A sizes in any shops. Just checked out an on-line electrical wholesaler and find they are listed as orderable items. Strange that the smaller values 1A & 2A don't seem to get factory fitted in smaller low power electrical items. They always seem to be standardised on 3A fuses.

Thankyou for the correction. 

[Yelrow]

In all my years of diy, never come across anything other than, 3,5 ,13 amp fuses, fascinating. There cannot be much demand, as the uk sheds dont appear to have them. You live and learn. I have, 1,2,and 3 phase here, plus my own ring mains for uk plugs. French, have no fused plugs, and the wiring, is a nightmare. No colour code. Rolls of wire in 13 colours, which you then put into tubular outer, yourself. Roll on standardisation. john

[2e0dtoeric]

People in general do not seem to understand the significance of the fuse, they think it is to protect the piece of equipment.

So - when a small current fuse decides to expire, the unknowing soul sticks in whatever is to hand, usually a 13 Amp one! (or even a cut-down nail!)

I think it is well over time that ALL manufacturers fitted RCD's to equipment, and not the bit of cheap plastic with brass pins. The price difference is negligible - the safety is not!

If you knew how many UK homes still had the 1940's wire fuses in their distribution box, you'd be horrified!

[RDS]

.... French, have no fused plugs, and the wiring, is a nightmare. No colour code...

Hi John

That is amazing.  In the UK we used to have nice to understand colours, Red for Live, Black for Neutral and then some bright spark (pun intended!) decided we would be better with Brown and Blue.  The easiest way I remember now which is which, being colour blind with Reds, I know that Brown and Red look a bit similar!

I had also not heard of anything other than 3A, 5A or 13A fuses in the UK but it also surprised me that new plugs are always supplied with 13A fuses.   I have loads of them spare.

 

 

[Chrissaf]

Yes agree John, as long as the rest of Europe standardises on the UK system (tee-hee). A work colleague of mine had a holiday home in France. He insisted on doing a re-wire himself based on UK specifications. Now I know why.

[Chrissaf]

If you knew how many UK homes still had the 1940's wire fuses in their distribution box, you'd be horrified!

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My sister's house was built in the 60's and still has wired fuses in the consumer unit. Slightly upgraded compared to the 40's version as the fuse connectors are plastic and not white ceramic.

[Yelrow]

Chrissaf, your mate will have to convert wiring back to french system, when he sells. I have been advised of that in writing. You are also, not allowed to do your own electrical work, as in england, My electrician, did my 3 phase and then said, my wiring was same standard as his, so would sign off for me, should need arise. john

[Chrissaf]

Chrissaf, your mate will have to convert wiring back to french system, when he sells.

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John, It was a work colleague as opposed to a mate. The story although true, relates to a period some 25 years ago and with someone I have now completely lost touch with. The reason the story stuck in my mind, was I remember at the time expressing concern that wiring his French house to UK standards did not seem a good long term idea for the very reason you have given.