12v query

[Robtel]

Electricity and myself don't get on too well so any answers, if you could keep them in simple terms please.
I am experiencing an occasional problem with my 12v compressor pump when using it powered by one of the two 12v sockets in the caravan. The pump is a Ring Automotive model, it's about two years old but seldom used. I use it only with the van either with the Floe system for draining the water pipes or to top up tyre pressures when required. It has what I would term as the normal push in plug socket.
Twice when I have used it the 10amp fuse in the van 12v system has blown, first time it happened I thought it was a one off and changed the fuse. The pump then worked fine again. Just before my recent trip away I was checking tyre pressures when the same happened again. I have used it without problem between these two blown fuses without problem. The pump itself has a 10amp fuse in the plug socket which hasn't blown at any time.
Does the fact that it's the caravan system's 10 amp fuse that is blowing suggest the problem lies within the van's system?

 

[DrZhivago]

Does the fact that it's the caravan system's 10 amp fuse that is blowing suggest the problem lies within the van's system?

No, fuses blow because more current is being drawn than they are rated at, in other words they are doing their job. Fuses are not very accurately made, don't need to be, but the fact that two have blown suggests that your pump is trying to draw more than 10 amps, and its own fuse is more tolerant than the van's fuses. (eg the van's fuses might have blown at 9 amps while the pump's fuse would have blown at 11 amps - yes they can be that innaccurate.)

Assuming that the pump is meant to have a 10 amp fuse, and given that things are generally fused with a significant margin over their normal current, (eg the pump might be expected to draw 5 amps normally), I guess that the pump itself is not all well; perhaps it is getting clogged or the bearings are getting stiff..

 

[Robtel]

Thanks Dr. Z, yes , according to its instruction book the pump is meant to have a 10amp fuse.

 

[emmerson]

The plugs provided on this sort of kit are generally very cheap and nasty. I'd suggest you try changing yours.I make a point of doing this once any of my 12v stuff is out of warranty, always replace with a higher quality one.

 

[Woodentop]

Fuses will typically carry the rated current if it rises slowly, and take twice the rate current to blow more quickly.

The issue here is likely to be surge current at switch on when the motor starts. Remember the fuse is only present to protect the cables, so the best solution would be to get a slow-blow fuse rated 10A and fit this in the compressor plug, then fit a 15A fuse on the caravan feed. That way the 10A fuse (usually marked either T10A or 10A A/S) will blow first.

Having said all that the fact that it works sometimes without a problem highlights another possibility. If the OP looks into the so-called cigar lighter socket on the caravan he will probably see that the centre (positive) connection has a strip of metal that goes across the back of the socket and turns 90deg up the sides for a short distance. The negative is the fairly thick metal plate that forms the inside of the hole into which the plug is pushed. I had this problem and it was due to the plug being used having rather longer than normal negative spring connectors on the sides which were making contact with the positive 'elongated arms' described above. I simply replaced the plug with a type with shorter side connectors and never had the problem again. Note that you will probably have to solder the connections in the replacement plug.

 

[brian_c]

Hello Robtel.
I have the Ring Inflater and I tried three times and each time the 10 amp fuse instantly went.
The pump worked fine with my last van and works fine in the car. I've recently set myself up with a portable battery pack for my Air awning pump and the Inflater works fine with that.
I can only imagine that the Inflater draws a current well in access of ten amps on initial start and then falls back to a working level when actually running.
I'm ok now because of the little portable battery pack I've made up (fitted with a 15 amp fuse)

I was reluctant to increase the caravan fuse rating not wanting to take any risks but I'm sure had I tried 15amp it would have been ok. So whilst my comments are not very helpfull at least you are not alone with the problem.

Best wishes Brian

 

[Robtel]

Thanks to all for the very helpful replies.
Thinking back, when the fuse has blown it has , I think , been when I have switched the pump on, so perhaps the initial draw on power is the problem as someone did suggest.
I have ordered a new and hopefully better quality plug which I will try and see how that goes.
I did go out to the van yesterday armed with a supply of 10amp fuses to see if I could find anything wrong with the van sockets. The pump worked every time I tried it without blowing the fuse once and I did switch it on and off numerous times. It doesn't feel a great fit in the socket as there is what I would term excess slack and play but we will see what happens when I change the plug. Thanks again for your input.