Puzzling experience using 12V tyre inflator (1 Viewer)

[Sixty-nine Chevy]

Hi. Can anyone out there with a degree of electrical expertise please explain the following to me? For over 2 years I have used a cheap 12V tyre inflator to 'top up' our campervan tyres to the recommended 80 psi. The van has two 12V cigar lighter style sockets on the leisure side and I have used both of these. They are both rated at 120W and protected by 10A fuses. The inflator also has a 10A fuse. Never a problem until yesterday when the inflator died. Opening it up I found that the cylinder had fractured, which I put down to old age given that I also use the inflator on our small hatchback. I then went to Halfords and bought another 12V tyre inflator, again running at a max. of 10A. However, using this on one of the leisure 12V sockets blew the 10A fuse in the van, but not the 10A fuse in the inflator itself. I replaced the van fuse and the same thing happened. Clearly, the van's 12V leisure electrics do not like this new 10A inflator. Have I just been lucky before with the previous inflator, which never blew a fuse? I see that the 12V cigar lighter on the cab side of the van (Fiat Ducato) is protected by a 15A fuse so perhaps I should just use that? This would bring another problem in that the inflator's cable is not long enough to run from the middle of the dashboard to the rear tyres, but I guess I could get some kind of extension cable. Any thoughts or recommendations? Thanks for reading this far!

 

[Sandyt]

Wired inflators are so yesterday. It's far easier to go around with a battery powered one.

Dewalt cordless does the job for me. Uses the same battery as my drill. Can also use mains or 12v. No issues with reaching pressure, just preset required pressure and away she goes, shuts off when desired pressure is reached. Rated to 11 bar.

 

[Sixty-nine Chevy]

I'll second that. At home I now use a small motorcycle battery as it's easier to move around the van. A Land Rover owning nephew told me the RAC inflator is the one they all use when doing "safaris".
Regarding the much & often discussed tyre pressures, I sent my axle weights to Michelin and got the following response which I follow to the letter just in case my insurance company get involved:

"Regarding your query, the recommended tyre pressure, for tyres equipped with metal valves, the rear (single) axle of a motorhome running on the MICHELIN Agilis Camping is 80 PSI (5,5bar) and for twin axle 69PSI (4,75bar)
This is due to the construction of the tyre with 2 casing plies enabling the use of higher pressures. Its construction and the use of higher pressures is designed to cope with continual heavy loads sometimes found on motorhomes and can help with wear pattern issues, if lower pressures are used particularly on the rear axle.
The front tyres however can be adjusted down to a pressure of 65 PSI for a more comfortable ride and optimum performance.
Here are some safety points to be taken into account when it comes to tyre pressures:
1. Always check the pressures when the vehicle tyres are cold. We consider the tyres as being cold if they haven’t been used for at least 2 hours of it they have rolled less than 3 miles at low speed. If the tyres are not under these conditions they are considered to be hot.
2. When the tyres are hot you should always add 4.4 PSI to the recommended pressure.
3. Please remember - Never deflate a hot tyre!"

Thanks for that extra information from Michelin. Their website gives very little!

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[Sixty-nine Chevy]

I believe by the sound of it, that the OP has Michelin Agilis Camping Tyres on his Hymer as we do on our Carthago. There is only one pressure that Michelin recommend for there tyres regardless of Axel Weight and that is 79PSI.
It no use arguing with them,(Michelin) giving specific axel weights, as we have read many, many times on here before they always insist on 79PSI especially on the rear axel because of the way the tyre is designed with extra thick side walls.

I do not run ours at 79PSI on the front though, we run at 65/70, but always 79 on the rear axel, and its OK, not too harsh at all.
However, that is the reason many Funsters change their van tyres, getting away from Michelin Campers to allow lower pressures and if needed a smoother ride.

PS: most 12V tyre pumps will struggle to get tyres all round to 80PSI, not only does it take ages, they need a rest to cool down between tyres, and the good ones that are HD versions only have crock clips to connect to the battery directly, as they draw more than 10amps.
LES

Thanks for that information. Yes, we have Michelin Agilis. The ride is fine, but perhaps I should drop the fronts to 70 psi and see how that is.

 

[IRHP]

Here's my tuppence worth on tyre pressures.

In a former life some years ago I was a ride and handling engineer for a vehicle manufacturer, we regularly tested vehicles at 3500kg, biased to the rear - from a dynamic point of view fairly similar to a motorhome.

A lot of our testing was focused in severe manoeuvres - the stuff the customers don't normally do or experience, except in an emergency. Extreme braking, emergency lane changes, and of course - the 'elk avoidance manoeuvre' or CU Chicane in the US.

So basically manoeuvres you wouldn't think about attempting in your motorhome, unless to avoid a crash.

One of the variables we would play with was tyre pressures. The pattern that develops is that as you lower rear tyre pressures, the rear tyres tend to react slower in building up grip (if anyone is genuinely interested, I'm happy to waffle on about slip angles later) but effectively, the rear tyres take longer to build up lateral grip in response to a swerve, and the rear of the vehicle has to step out further in order to generate the lateral grip.

Take it to the extreme, either in lowering the pressure, or in the aggressiveness of the manoeuvre, and you can turn a vehicle which normally has a 'safe and progressive understeering response' into one which will do it's best to suddenly swop ends when you least need it to.

How far do you need to reduce the tyre pressures to turn a safe vehicle into a dangerous one? It's different for every combination of chassis, load condition, tyre, and speed. But, I have seen reductions of as little as 12 psi (on a recommended pressure of 45psi) make a vehicle dangerous.

You would never know it was dangerous, all you would likely feel is improved ride. You would need a combination of high speed and an extreme manoeuvre to find out, so you won't notice until you swerve while braking from motorway speed. Even then, if your van is quite modern, the stability system will step in and probably save the day, they are very very good.

So you guessed it, my tuppence worth - if conti or michelin want 79psi- then 79 psi they shall have.

As a side note, I rent out campers, even if I wasn't an extremist tyre snob - I wouldn't consider running anything but manufacturers recommended tyre pressures simply because of liability in event of an accident

Very interesting, thanks. Most just seam to think about the ride when talking tyre pressure.

 

[Norman Jones]

I have a Halfords Rapid inflator (which isn't rapid).
But usually plug it in the socket by the Hymer door and use a cigarette lighter extension lead.
Our Hymer is 4.2 tons. Hymer recommend 3.75 front 4.75 bar rear.

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[JohnH17]

When I got Michelin's reply, it started off ""The inflation pressure at the rear is 80psi because the Motorhome manufacturer has chosen to use the ETRTO guidance using CP tyres for stability at the rear. This must be maintained in order to comply with the Manufacturer’s guidance.

However, there is some scope to adjust the front pressure..."
And I heard it was as Skodaman said - about rear handling in a swerve.
For the pump I got an RAC630, nice and small, and hasn't blown a fuse yet. Use it with about 24ft of 5A twin mains cable extension lead as a bit of in-line resistance. And I've also come across these chinese fuses using steel instead of copper. Sooner we go back to making our own over here the better (but don't get me started!). Anyway, more info on the compressor at:

Error Page 404 - Ring automotive

www.ringautomotive.com

 

[tonyidle]

Plus one for this. A fuse is to protect the cables not the appliance.

I'd imagine a few extra amps will make little or no difference.