An electrical question for any experts out there

[retroenduro Member Find all posts View Profile Close retroenduro]

Hi all im in need of some expertise...i will admit right now that my electrical knowledge (amps/volts/watts etc) is very limited.

My compressor packed up the other day. The in line fuse melted and took the fuse housing with it. The compressor is a portable one and worked very well up until then so im hoping i can fix/upgrade it.

The max amperage on the compressor says 45 amps however the fuse in the housing was a 30 amp fuse(it came like that)? What does this mean? was the fuse too weak?it always used to get very hot when the compressor was going and if i ran it for too long it started to melt...... The cabling also looks a bit cheap/weak so im not sure if its up to the job of transferring the current. The cables attach to the battery via crocodile clips. I was thinking i could get a new cable length and in line fuse holder more up to the task. Would this work? Or should i just change the in line fuse holder and then use a 45amp fuse (if they exist?)?

Or do i need to keep the 30 amp fuse as anything more would damage the compressor? Help i have no idea about this stuff!:shock: but i dont want to chuck away a perfectly good compressor for the sake of a $5 fuse holder...

Some other specs that might help...(printed on the compressor)
voltage 12 volts
max pressure 150 psi
max duty cycle @ 72 degrees Fahrenheit and 40 psi 30 mins
max air flow 150 litres per minute

its an outbac brand one

Thanks in advance

[Leethal Advanced Member Find all posts View Profile Close Leethal]

A couple of questions and then we may be able to offer advice.

"In-line fuse melted" did the fuse blow or did the housing melt? If the fuse blew then you have excessive load, if the housing melted without blowing the fuse I would sugest the wire size and/or the fuse holder were not the correct size for the load.

What size was the original wiring, and I mean the wire not the insulation as I have seen a lot of cheap wire that has thick insulation and thin wire (conductor).
Also what length was the loom? The longer the loom the heavier the wire needs to be.

Lee

[retroenduro Member Find all posts View Profile Close retroenduro]

it looks like the fuse holder melted and then the heat melted the fuse too? it was a clear fuse that is now opaque..

the wire core size is 2mm ish and the length of that loom is 2 m approx with the in line fuse holder about 30 cm from the compressor on that loom.

[Fozzy Senior Member Find all posts View Profile Close Fozzy]

It's possible that over time the cable worked itself loose in the connector then got hot because of the high resistance joint, causing the meltdown. I had a Typhoon that came to grief in the same manner.

If the thing is new-ish and this happened it might be undersized cabling etc, but if its been working well for x number of months/years I would try replacing the inline fuseholder, stand back and observe so to speak.

Cheers,

Dave

[Ozpat Advanced Member Find all posts View Profile Close Ozpat]

How long was it running before it got too hot? The duty cycle claims 30 mins but that's usually optimistic. You need to let it cool down for the same period. Was the engine running or was it struggling on a low battery. Upgrading the cable will help but don't overrun the duty cycle and keep to the same fuse rating. Compressor pistons will get tighter with the heat buildup and only a cooling off period will save them.

Cheers Jim

[AJ120 Out of control poster! Find all posts View Profile Close AJ120]

I had the same thing happen to mine recently, the fuse didn't blow but the cable melted the fuse holder. I had 6mm cable and the run was only around 200mm, so I wonder about the quality of the fuse holder. I replaced it with a maxi fuse, so we will see how it goes.

Cheers Andrew

[yowie Advanced Member Find all posts View Profile Close yowie]

Have a Big Red compressor, since 1994. Wiring is 4mm.

I added a glass fuse and holder, with 6mm wire and 30 amp fuse, also an on/off switch. Fuse holder runs hot, and has blown 2 or 3 times in it's life.

Maybe it needs heavier wire, but that 4mm wire is as supplied when new.

[retroenduro Member Find all posts View Profile Close retroenduro]

Ok well i think im going to go with 6mm twin core wire with a run of about 1.5m as its a portable unit, not fixed to the car. Ill put a Narva maxi blade fuse in for 30 amps. hopefully this should work. I have a feeling that the fuse holder supllied just wasnt up to the job...cost cutting by the manufacturer. Now to fleabay to order the bits!

Ozpat i had it running for literally less than a minute before the fuse holder melted, taking the fuse with it. Usually i would run it for one wheel (about 2 mins?) and then let it cool for about a minute before doing the next one. Well inside the 30 mins.

[Cuvier100 Member Find all posts View Profile Close Cuvier100]

With these compressors they have a fairly light duty cycle at a certain ambient temperature. This is typically 20 deg C. So expect a shorter cycle at greater than 20 deg C temperature. Also to protect the compressor they derate the fuse (as all fuses will hold full load current plus 45% for at least and hour). For example if they fit a 30 ampere fuse it will hold before operating a current of 30 x 1.45 = 43.5 amperes. The fuse curve is a straight line so if you increase the current if will operate quicker. Similarly if the current is decreased it will take longer to operate. Therefore, if you ran the compressor on a 20 deg C day for just short of 1 hour the fuse will operate (and its holder may melt).

Also the fuse will heat to its melting point which for a copper fuse is 1085 deg C. So unless the holder if procelain expect it to melt.

A heaver cable connected to the fuse will help the fuse holder as it will disipate its heat. Fuses are not made to hold small overload currents (1.45x) but rather heavy currents (short circuits) where they operate quickly. Therefore, to the find the right type of fuse holder for the job my take some trial and error and testing on hot days.

A better way of protecting the motor would have been to fit a resetable thermal cut out in the motor windings - but these cost money.

[vk2ss55 Senior Member Find all posts View Profile Close vk2ss55]

I've found that it's best to start the compressor and then connect it to the tyre's valve . The compressor can stall if it's got the load of the tyre against it which will blow the fuse . My experience with those in line blade fuse holders is that they're very optomistically rated and just can't handle full load for any decent time .
Even the 5AG plastic fuse holders melt if loaded heavily for extended times . I'm now using those little metal overloads which seem to handle the loads ok .
cheers Ross

[retroenduro Member Find all posts View Profile Close retroenduro]

well re wired the thing with proper 6mm wire and a maxi fuse from narva (30 amp - the same rating as what was in it before) and it runs fine....for a compressor ha ha. It works perfectly but most importantly i ran it for a while and the fuse holder did not get hot at all. mission accomplished! Thanks for all the advice guys.

[yowie Advanced Member Find all posts View Profile Close yowie]

well re wired the thing with proper 6mm wire and a maxi fuse from narva (30 amp - the same rating as what was in it before) and it runs fine....for a compressor ha ha. It works perfectly but most importantly i ran it for a while and the fuse holder did not get hot at all. mission accomplished! Thanks for all the advice guys.

Looks like I might have to upgrade my Big Red wiring from the 4mm that is on it.