Fuses on Hub...

[Corey872]

Just for future reference...(because these things usually come up when I'm wiring) if one of the small fuses blows on the hub will it be obvious?  By that, I mean will the fuse visually look burned, fried, or otherwise 'blown' - or is the failure an internal event which leaves the outer case unaffected and a person would have to look for voltage across the fuse?

[RJ]

Have not blown one yet.?

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[bcstuff]

I think when it blow it looks like this:
---------- ----------

but in all seriousness, it has a ceramic body, so I do not believe you can tell by just looking at it unless you really juiced it.

[LtKadeo]

You can not tell just from looking at the fuse - unless you realy send alot of current to pop the fuse - can check with ohm meter and power off if you think it is bad.

[Corey872]

RJ - I haven't blown one yet, though I haven't put any power to anything yet either!    So that may not be as grand a claim as it sounds!

OK, so a short at normal power levels would blow the fuse but not make any visual mark.  Good to know.  I suspect the easiest way to check a bad fuse would be to look for voltage across it with everything running?.  Good fuse should show 0V, bad would show 12V.  Or look for resistance with everything off/powered down.

Filing this tidbit away for future reference!

[rrowan]

RJ - I haven't blown one yet, though I haven't put any power to anything yet either!    So that may not be as grand a claim as it sounds!

OK, so a short at normal power levels would blow the fuse but not make any visual mark.  Good to know.  I suspect the easiest way to check a bad fuse would be to look for voltage across it with everything running?.  Good fuse should show 0V, bad would show 12V.  Or look for resistance with everything off/powered down.

Filing this tidbit away for future reference!

Of course if the fuse does blow your nodes won't light up either

Cheers

Rick R.

[JoeFromOzarks]

This goes with 12VDC circuits or 440VAC circuits:  ---statement removed---.

Here’s how I’d do it (as long as the steaks on the grill still have a little cooking time to go):   (note that I’ve only peeked at the PCB, I didn’t reverse engineer it nor do I have schematics)

Disconnect the RJ45 (connection to SSC) from the suspected port (Smart String Output) so the load is not connected to the suspect fuse.  Ensure power is provided to the Smart String Hub.

Looking at the component side of the board with the “( c) Robert Jordan” at the top of the PCB,  place the negative voltmeter probe on one of the COM rails such as the black wire on the 20/24pin connector and the red or positive probe on the RIGHT SIDE of the fuse.   If you read 12V then your fuse is good, if not, it’s replace fuse time.

An alternate method, with the Hub POWERED OFF and the load (RJ45) disconnected from the suspect port would be to use the ohmmeter function (low ohms or diode check/beep setting) of your DVM and place one probe on the RIGHT SIDE of the fuse and the other probe on one of the YELLOW wires of the 20/24pin connector.  If you show zero ohms your fuse is good.  Note: the LEFT SIDE of the fuse connects directly to the positive 12V rail, it should always read zero ohms.

Of course, you could ohmmeter directly across the fuse, but too many times I’ve seen a “good fuse” and the PCB electromechanical connection of the fuse failed – the fuse warms to the point that the link doesn’t fail but the soldering of the fuse mount to the PCB foil has gone cold or crusty or some other failure.  Ohming from a known supply point to a known load point is my usual method.

I hope this helps.

joe

RJ - I haven't blown one yet, though I haven't put any power to anything yet either!    So that may not be as grand a claim as it sounds!

OK, so a short at normal power levels would blow the fuse but not make any visual mark.  Good to know.  I suspect the easiest way to check a bad fuse would be to look for voltage across it with everything running?.  Good fuse should show 0V, bad would show 12V.  Or look for resistance with everything off/powered down.

Filing this tidbit away for future reference!

[tbone321]

This goes with 12VDC circuits or 440VAC circuits:  * - statement removed as requested- *

This is incorrect.  A volt meter by its design is a high impedence device that passes very little current and it WLL NOT act like a fuse.  If that were the case then how could you use it to check the voltage of a battery or any circuit.  Anything that you put it accross would be shorted out.  It is perfectly safe to measure for voltage across the fuse to see if it is OK with the lights connected.

[chrisatpsu]

i think the point he was trying to make is...

if you place multitester leads on each end of a fuse while it's on, then electricity will pass through the multitester whether the fuse is blown or not and you will get a reading. it may not be highly accurate as a testing procedure in all cases.

I would turn everything off, disconnect the nodes in the socket applicable, and test the fuse for continuity.  (with a lead at each end of the fuse)

[tng5737]

Of course if the fuse does blow your nodes won't light up either

Given my sequencing skills - that wouldn't be unusual

[tbone321]

LOL, now that was funny! 

           

[tbone321]

i think the point he was trying to make is...

if you place multitester leads on each end of a fuse while it's on, then electricity will pass through the multitester whether the fuse is blown or not and you will get a reading. it may not be highly accurate as a testing procedure in all cases.

I would turn everything off, disconnect the nodes in the socket applicable, and test the fuse for continuity.  (with a lead at each end of the fuse)

This is again, not true or at least not valid.  The amount of electricity or current that will pass thru a good meter is so small as to have no measurable effect, at least on circuits like these.  Remember that a meter (even a bad one) is simply measuring the voltage drop between two points.  A good fuse has so little voltage drop at is rated currect that the meter should NOT be able to measure it so it will read ZERO volts.  If the fuse is blown, then the voltage drop will be 100% and the meter will show full voltage provided that there is a path to ground (the load). 

As for the current flow, in order for a meter to be worth anything, it can't put any load on the circuit that it is measuring.  To do this, the meter needs to have a high impedence and a high impedence means very little current flow.  It may have 10's or even 100's of thoudands of ohms of resistance so there is no way that it can act as a fuse or alternate current path in the circuit it is measuring.  If it did, then it would be a useless device and would serve no purpose at all.

[JoeFromOzarks]

Okay, I’ll withdraw my statement “This goes with 12VDC circuits or 440VAC circuits:  ...” to follow the intent of the technical TOS of DLA.   I will edit my original post.  I respectfully ask you remove my statement from your replies also.

I was taught to meter each side of the fuse to the common, not across the fuse, but that was the Navy and again in college -- and definitely above a few milliamps.

joe

... statement removed...

This is incorrect.  A volt meter by its design is a high impedence device that passes very little current and it WLL NOT act like a fuse.  If that were the case then how could you use it to check the voltage of a battery or any circuit.  Anything that you put it accross would be shorted out.  It is perfectly safe to measure for voltage across the fuse to see if it is OK with the lights connected.

[tbone321]

I would say that they suggested that so you didn't accidently let your probes touch each other while being across the fuse because then you would be shorting out the fuse and if there was a problem on the load, you just re-powered it without the protection of the fuse and at high voltage, you could weld the probes together and to the fuse.  Gee, wouldn't that be fun. 

[JoeFromOzarks]

I would say that they suggested that so you didn't accidently let your probes touch each other while being across the fuse because then you would be shorting out the fuse and if there was a problem on the load, you just re-powered it without the protection of the fuse and at high voltage, you could weld the probes together and to the fuse.  Gee, wouldn't that be fun.

Naw, I doubt that was the reason.  But I enjoyed the chuckle!

joe