Melting fuses

[T_Diesel]

I've got an older style RDCKA air compressor which is used to fill a seven litre air tank.

At the moment I have a 30 AMP inline fuse between the battery and the compressor. A few months ago, the compressor stopped working so I checked the fuse and it had melted. No biggy I just replaced it with another 30 AMP fuse.

Two months later and I have melted another one. They only seem to melt after prolonged use aswell.

Looking at the specs of the compressor, the current draw under load is said to be 18 AMPS. Granted the compressor is going to be working harder under load especially once you get a bit of pressure in the air tank.

I have checked resistance across all wiring and all appears to be fine. Is there anything else I should be looking at which might be causing the fuse to melt before I think about trying a 40 AMP fuse?

[PBBIZ2]

I think you will find the issue is to do with duty cycle rating on the motor. The motors are rated for intermittent use, whatever that might mean, but certainly won't be for long periods, say rated for 120secs on every 30 minutes as opposed to say 20 mins on in one hit or 30 mins on every 60 minutes. I run big thick cables up to he compressor motot and connect via alligator clamps to the battery.

The windings will heat up and stay hot, as there isn't enough time for the heat to dissapate. The hotter the windings, the more resistance, the higher the current flow to do the same job - on and on it goes downhill from there. I had the same problem with my 'big red' compressor when pumping 4 tyres up from 14psi to 35psi - wires got so hot they burnt the hands and the fuse holder melted and fell apart.

I now run one of those auto reset bi-metallic fuses rated at 30a. When it gets too hot it trips and I just have to wait. Its effecive to a point, but I find the periods decrease after the first 'trip' and keep getting shorter as the motor doesn't cool effectively between each use, and I also seem to be in a hurry to get the air in, and get going. Only real advantage is I don't have to find more fuses or fix the fuse holder when it melts - I am talking about the cheap white fuse holders not the phenolic black screw types, which last better.

[stuee]

IIRC there was a topic not long ago on melting fuse plastic. It was quite informative. Ill have a search and see if I can dig it up but its well worth looking for if you've got time IMO.

[stuee]

Stays on topic:
http://www.outerlimits4x4.com/ftopic183 ... se+plastic

Goes on to talk about cabling etc but same issue:
http://www.outerlimits4x4.com/ftopic171 ... se+plastic

[T_Diesel]

Thanks for that. I remembered seeing a thread about it a while ago, but couldn't recall which forum it was on!

[T_Diesel]

Just took the passenger seat out and the compressor is actually a VIAIR 40040 - 400C Air compressor. I've only had the vehicle two months and the previous owner put the compressor and tank in.

Reading the specs on the web, current draw is 26A with a max current draw of 30A.

Currently, power is piggy backed off a 12 volt source that is for some merritt sockets behind the centre console so I don't know if the wiring would handle 40A so i'll upgrade the power to the compressor.

If max draw is 30A will 40A fuse be enough or should I be going 50A?

[stuee]

Just took the passenger seat out and the compressor is actually a VIAIR 40040 - 400C Air compressor. I've only had the vehicle two months and the previous owner put the compressor and tank in.

Reading the specs on the web, current draw is 26A with a max current draw of 30A.

Currently, power is piggy backed off a 12 volt source that is for some merritt sockets behind the centre console so I don't know if the wiring would handle 40A so i'll upgrade the power to the compressor.

If max draw is 30A will 40A fuse be enough or should I be going 50A?

You put a fuse in to protect the wire (prevent fires from overheating) so use a fuse that equal to or less than the rated capacity of the wire you use. For a bit of safety it would pay to run cable of at least supporting 40-50 amps, and fuse it suitably (I'd do 50A). My opinion only.

[murcod]

Carefully feel the cabling after an extended period of use- if it's not getting warm then it should be fine. For your fuse go for a 40 Amp- it should be fine given the 30 Amp was lasting for a couple of months.

[bazzle]

Do not use the older syle glass tube type fuses, they get a resistive joint and get too hot as they age.
Use the newer coloured spade type. 40A should be good to go in the correct holder or 2 spades on legs.

Bazzle

[Clanky]

Had exactly the same drama with my older ARB compressor.
30A is not big enough. Go the 40A and the holder melts
I think the small plastic wedge type holder supplied is not that good for the 30A either as it gets pretty hot.
I had heaps of dramas with doing 6 tyres with my old one, overheating, sparking, melting fuses (all ARB supplied wiring etc), melting outlet hoses ( I even went stainless braided teflon in the end and it still went belly up)

In the end I got the vita brits and bought the newer style, moved it closer to the battery and it works a lot better. Gets hot for sure, but not like the oldie

Maybe the older ones are really only rated for lockers.

[-Scott-]

Interesting comments.

I have the older style ARB compressor mounted under the bonnet, and don't have trouble with it.

It's been a while since I last checked the wiring or the fuse holders, but it hasn't missed a beat - even after 40 minutes of continuous use.

Having said that, I'd like a new one. So it doesn't need to run for 40 minutes, and I can continue sooner.

[Clanky]

Very interesting. You just reminded me, my brother had the same compressor, mounted in the tray of his ute and it had no troubles and even had to do my tyres after mine packed it in (which was every trip).

So maybe a fairer comment is, there must have been some quality variances

[T_Diesel]

Interesting comments.

I have the older style ARB compressor mounted under the bonnet, and don't have trouble with it.

I made a mistake. I made an assumption that it was an ARB compressor (have only had the vehicle 2 months). The compressor is under the passenger seat (where I can't see it), and there is another ARB compressor under the bonnet for the air lockers so I assumed they were both the same. It's actually a Viair 40040 400c. The specs on the viair have a max current draw of 30A which is why i'm melting fuses after a while.

The wiring between compressor and pressure switch/relay should be ok as it is what was supplied with it but the permanent power from pressureswitch/relay to battery is under par so i've bought some 8 gauge to wire it in.

If I can't wire the 8 gauge directly into the back of the relay, and I have to join it with the wire supplied, am I best to use spade terminals and crimp or should I try and solder the join?

[tweak'e]

check the fuse holder connections. odds are they are getting hot and causing the fuse to melt. there wa a few comments in other posts about stock fuse holders melting.
make sure wiring is ok (wired direct to battery) and fit decent terminals for the fuses.

[T_Diesel]

check the fuse holder connections. odds are they are getting hot and causing the fuse to melt. there wa a few comments in other posts about stock fuse holders melting.
make sure wiring is ok (wired direct to battery) and fit decent terminals for the fuses.

Wiring is fine. It's melting because the peak draw of the compressor is 30A and so is the fuse.

[stuee]

If I can't wire the 8 gauge directly into the back of the relay, and I have to join it with the wire supplied, am I best to use spade terminals and crimp or should I try and solder the join?

Id be inclined to replace everything on the power circuit - cable, fuse holder, relay etc. You might find the relay is only a standard 30amp jobbie in which case you want to change that too. This way you know everything is going to be up to scratch. Only saying that as it sounds like your going to use the existing relay.

As for connections I find spade connections are fine if done properly but I always get a piece of mind from soldering. I have heard that soldering can cold flow over the years but in the 12 years my cars been in my family we haven't seen that happen yet on any if our connections.

edit* DONT solder directly to the relay as it will be a pain to replace if it breaks and you might damage it with the heat. A relay holder would be the go if your not keen on crimping spades as they have tails which yoou can solder to yoour power cables.

[PBBIZ2]

I ran my 'big red' compressor yesterday to top a 32" tyre up from 25psi to 40psi. Ambient temp was 25 degC. I run 6mm2 copper multistrand cables, crimped and soldered, 500mm in length from compressor to battery, with in line auto reset 30a fuse.
The compressor ran for maybe 5 mins all up, max pressure in the tank was 60psi. Compressor head temp was 91 deg C and motor 54 deg C, cables 68 deg C - measured with IR temp probe.
The fuse didn't blow but I wonder what the limit will be - time will tell. I might increase the cables larger if I get the time and post the comparative results

[tweak'e]

check the fuse holder connections. odds are they are getting hot and causing the fuse to melt. there wa a few comments in other posts about stock fuse holders melting.
make sure wiring is ok (wired direct to battery) and fit decent terminals for the fuses.

Wiring is fine. It's melting because the peak draw of the compressor is 30A and so is the fuse.

i take it then its just poping the fuse rather than melting the sh*t out of it.
just pays to check the fuse holder anyway, especially if using the original one that came with pump.

[T_Diesel]

If I can't wire the 8 gauge directly into the back of the relay, and I have to join it with the wire supplied, am I best to use spade terminals and crimp or should I try and solder the join?

Id be inclined to replace everything on the power circuit - cable, fuse holder, relay etc. You might find the relay is only a standard 30amp jobbie in which case you want to change that too. This way you know everything is going to be up to scratch. Only saying that as it sounds like your going to use the existing relay.

As for connections I find spade connections are fine if done properly but I always get a piece of mind from soldering. I have heard that soldering can cold flow over the years but in the 12 years my cars been in my family we haven't seen that happen yet on any if our connections.

edit* DONT solder directly to the relay as it will be a pain to replace if it breaks and you might damage it with the heat. A relay holder would be the go if your not keen on crimping spades as they have tails which yoou can solder to yoour power cables.

The pressure switch / relay are in the one box / case. I'm not sure if they are moulded connections or interchangable. According to the manual, it's a 40A relay in it.

It's just a bastard to get to it all as it's under the carpet / seats!