Fuse Carrier with L.e.d's

[xeitosaphil]

Electrical Query

I have just bought and fitted a 4 way fuse carrier with fuse failure L.e.d indicators. I thought it was a great piece of kit as it only requires one input cable from the battery, but allows 4 fused outlets, nice neat unit. http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=170781860687&ssPageName=ADME:X:RTQ:GB:1123
It allows a total of 100amps over 4 circuits, each individual circuit capable of 32amp max rating. This is to provide a 15amp fused supply circuit for a new fridge/freezer/cool box conversion + any future power feeds for other items?
When I installed it with the necessary wiring and doing a voltage check of the circuit I had 12.65v at the input stud – but 10.9v at the outputs with no fuses installed?
Being a little concerned at this I contacted the supplier thinking that this was a faulty unit, I thought with no fuses installed the outputs it would be completely isolated? He replied and said that because it had Led indicators there was a bridge link across the fuse block to carry voltage back to the negative to power the led when in indicator mode. He also said that as there was no fuse installed, there could be no current flow and not to worry? Is he right ?
I have not heard of this sort of thing before, standing volts at outputs, but with no ability to transfer current? Is this normal and nothing to worry about?
My concern is, if there is 10.9v on the bare unused outputs and something was to fall on them, is it possible to short something out ?
For my own piece of mind at the moment I have put some insulated female connectors over the bare male output terminals.

As usual I will be grateful for any reassurance provided by forum members with more knowledge than myself.

 

[lw395]

The output carries the current to light the LED, probably 10 to 30mA.
The unit will just be a resistor and LED in series, in parallel with each fuse. When the fuse is intact, the LED does not light because all the current goes through the fuse.
When the load is a short circuit, the fuse blows, then the output is pulled down to 0V by the short and the resistor+LED see 12V, so the LED lights.
you can test it with any 12V bulb as a load, pull the fuse out and the LED will come on.

You can buy fuses with the LED and resistor built in by the way. Expensive if you keep blowing fuses though!

In your test, you are seeing the diode drop of the LED at very low current (microamps), not enough to light it visibly.

Hope that helps?

 

[xeitosaphil]

The output carries the current to light the LED, probably 10 to 30mA.
The unit will just be a resistor and LED in series, in parallel with each fuse. When the fuse is intact, the LED does not light because all the current goes through the fuse.
When the load is a short circuit, the fuse blows, then the output is pulled down to 0V by the short and the resistor+LED see 12V, so the LED lights.
you can test it with any 12V bulb as a load, pull the fuse out and the LED will come on.

You can buy fuses with the LED and resistor built in by the way. Expensive if you keep blowing fuses though!

In your test, you are seeing the diode drop of the LED at very low current (microamps), not enough to light it visibly.

Hope that helps?

Thanks for the quick reply

When checking the output terminal voltage 10.9v I did connect a short lead to it and touched it out on the Negative terminal to simulate a blown fuse and the l.e.d did light. If I now do that and check the terminal voltage at the same time, are you are saying that it should read zero volts, which should suggest everything is in order?

 

[lw395]

Thanks for the quick reply

When checking the output terminal voltage 10.9v I did connect a short lead to it and touched it out on the Negative terminal to simulate a blown fuse and the l.e.d did light. If I now do that and check the terminal voltage at the same time, are you are saying that it should read zero volts, which should suggest everything is in order?

If you short the output to ground, negative, the black wire, it is zero volts. You have shorted it to the point you are measuring voltage relative to.
Voltage is like height, you need to measure it against a reference. Normally that's the -ve terminal of the battery, but not always.

 

[xeitosaphil]

If you short the output to ground, negative, the black wire, it is zero volts. You have shorted it to the point you are measuring voltage relative to.
Voltage is like height, you need to measure it against a reference. Normally that's the -ve terminal of the battery, but not always.

Thanks for your help

I will connect a bulb as you suggest, remove the fuse, and measure the terminal voltage and hopefully it should be zero volts just to be absolutely sure everything is ok.
Something else I have learned. What a great forum this is, with quick responses and so many helpful people.

 

[tim_ber]

I know it allows 100Amps, but isn't it a bit expensive at £12?

Or am I just too much of a DIY-er?

 

[xeitosaphil]

I know it allows 100Amps, but isn't it a bit expensive at £12?

Or am I just too much of a DIY-er?

I am also a DIY-er and try to save as much of the folding stuff as I can, but
It’s the only one of its kind, I could find? - 1 x supply cable in, 4 x fused supplies out.

Seemed like a nice neat solution for me with a small footprint, although a bit expensive

I didn't fancy the extra supply wires involved coupling them to the battery along with all the extra joints that could fail? And to be honest by the time you have bought extra wire, connectors, and a 4 way fuse carrier you can't be that far off the price of this one? And in my mind it’s a neater job.

 

[rhumlady]

I am about to look at building a new switch/fuse unit but I looked throug the site and the 12 way panel with -ve busbar looks as if it would do the job and at £40 I reckon it would be money well spent. I like the idea of the illumination for a blown fuse. These normally go when least convenient so the indication would be welcome. The illuminated switches at £8.50 for 4 would be a good buy as well I think.