Puzzling experience using 12V tyre inflator

[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!

 

[tonyidle]

It's likely that the fuse blows due to the initial surge as the compressor starts. Given that the compressor is protected by its own fuse my preferred solution would be to increase the one on the van to 15A.

 

[Sixty-nine Chevy]

Thanks for the quick comment. I am aware of possible initial surges in things electrical, but the puzzling thing is that the inflator actually ran for at least a minute or so. I have always assumed that initial surges are just a few seconds, but I may be wrong?

 

[tonyidle]

Thanks for the quick comment. I am aware of possible initial surges in things electrical, but the puzzling thing is that the inflator actually ran for at least a minute or so. I have always assumed that initial surges are just a few seconds, but I may be wrong?

They are but enough to warm up the fuse perhaps? Even the best fuses aren't accurate to 10% or so.

 

[David and Sally]

Maybe the contacts on the plug and socket were not good and it drew more than 10a?

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[bigtwin]

Any thoughts or recommendations?

Yes, I’d recommend that you pump your tyres up to the tyre manufacturers recommended pressure; there’s no way that they’ll suggest anything as high as 80 psi. Your current pressures must give a bone jarring ride!

Ian

 

[stevewagner]

I would not recommend increase the fuse size in the van as you could end up with a fuse rated higher than the current capacity of the cable.

 

[Spriddler]

I'll venture to suggest that it's a Chinese inflator and the Chinese 10A fuse in it is out of (higher than) spec'n. I'd be inclined to replace the inflator fuse with one from a reputable source (Halfords?) and uprate the van one to to 15A as suggested by tonyidle That way your van fuse and wiring will be protected by the inflator fuse.

 

[Sixty-nine Chevy]

Yes, I’d recommend that you pump your tyres up to the tyre manufacturers recommended pressure; there’s no way that they’ll suggest anything as high as 80 psi. Your current pressures must give a bone jarring ride!

Ian

Thanks and I know it is high but 80 psi is definitely the recommended pressure for these particular campervan tyres as supplied by Hymer. The ride feels fine, although my only other campervan experience is with a very old hired VW in which smoothness of ride did not figure highly.

 

[Burgo]

A total guess, but could it be the new compressor is running a bit tight, and after a minute (ie when it starts to get warm) it starts to bind, thus drawing more current. If it's internal fuse is a 10A "slow blow" then your van one is going first.

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[Sixty-nine Chevy]

Many thanks to all for the very helpful comments given so far. Much appreciated!

 

[IRHP]

Start the van up and get the alternator pumping out some juice at 14v rather than between 12 and 12.7.
Amps=watts/volts. It might make the difference between blowing the fuse or not.

 

[bigwood]

The tyre inflater from my Landrover days has crocodile clips to fasten direct to the battery terminals. I think it would be too much to run it off the cigarette lighter socket.
I am looking for a replacement due to its age and will look for another with clips again.

 

[SandraL]

My experience of fiat inflator was it blew fuses, so i installed new 20amp fused socket.

Now it worked reliably without blowing fuses but soon the crank went in the compressor.

My view is that it wasnt up to spec when dealing with tyres at 80 psi, stored van in winter at 80 psi but used on road at 55/65.

 

[63720]

I would not recommend increase the fuse size in the van as you could end up with a fuse rated higher than the current capacity of the cable.

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

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[Manic]

I use an RAC 700 and if I don’t start it up before fitting on the valve it will blow the fuse of the socket, so it doesn’t like starting when under load which is no surprise really.

 

[TinaLes]

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

 

[Trevor Wbm]

Yes, I’d recommend that you pump your tyres up to the tyre manufacturers recommended pressure; there’s no way that they’ll suggest anything as high as 80 psi. Your current pressures must give a bone jarring ride!

Ian

Mines 86 psi - Boxer based plated at 3.5 tonne.

 

[bigtwin]

Mines 86 psi - Boxer based plated at 3.5 tonne.

From the tyre manufacturer?

And at what axle weight?

Ian

 

[Blackadder]

I use an RAC 700 and if I don’t start it up before fitting on the valve it will blow the fuse of the socket, so it doesn’t like starting when under load which is no surprise really.

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!"

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[bigtwin]

“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)

That line right there indicates that the pressures should be load related (why else would they state different pressures simply because the load is shared between two axles) and not a straight 80psi?

Michelin’s underlying assumption,clearly, is that the rear axle will ALWAYS be run at its maximum permissible weight (or, more accurately, at the tyre’s maximum rating) and that’s why they are insistent on the single 80psi figure.

Ian

 

[Trevor Wbm]

From the tyre manufacturer?

And at what axle weight?

Ian

The axle weights are 1 - 1750 and 2 - 1350, Tyres Continental Camper, max pressure 5.5 bar, which I now know is 79psi ..... I'll be asking my tame mechanic where he got his numbers from after I've dropped the pressure down!

Never had a problem with the ride being hard, but would be interested to hear what you think I should be using.

 

[SandraL]

That line right there indicates that the pressures should be load related (why else would they state different pressures simply because the load is shared between two axles) and not a straight 80psi?

Michelin’s underlying assumption,clearly, is that the rear axle will ALWAYS be run at its maximum permissible weight (or, more accurately, at the tyre’s maximum rating) and that’s why they are insistent on the single 80psi figure.

Ian

I think also they appreciate the rear axle on a motorhome is more heavily loaded than the front axle.
So they may be concerned that the rear trying to step sideways on cornering puts a greater strain on sidewalls. Keeping pressure high to stiffen sidewalls on cornering.
That was the gist of an exchange I had with michelin about 10 years ago.

 

[bigtwin]

The axle weights are 1 - 1750 and 2 - 1350, Tyres Continental Camper, max pressure 5.5 bar, which I now know is 79psi ..... I'll be asking my tame mechanic where he got his numbers from after I've dropped the pressure down!

Never had a problem with the ride being hard, but would be interested to hear what you think I should be using.

Those are your max axle weights and not your running weights. Those pressures are also the maximum pressures not your recommended pressures.

I would recommend that you contact Continental with your actual weights and they will provide you with their recommended pressures. In the absence of that, you could check here:

Motorhome Tyre Pressure Calculator | TyreSafe

Our motorhome tyre pressure calculator gives you the correct pressures for your motorhome. Check your tyres regularly for your safety.

www.tyresafe.org

Ian

 

[A S R]

2 things =
1. 80psi will give a horrible bone jarring ride. I run my 6 wheels at 55psi.
2. Put a nail in the fuse holder. It’ll never blow again.

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[skodaman]

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

 

[skodaman]

And to answer the OPs question - Ive struggled to find a little electric compressor that can handle 80psi regularly, they get ridiculously hot really quickly then struggle to get to 79psi at all. Given up and bought a small proper compressor - But I do know that you can make an excellent compressor by getting an air suspension compressor from an old range rover connect up a cable to croc clips and screw on the inflator pipe from an old tyre inflator - Will happily blow up to 100psi

 

[Bubba]

The tyre inflater from my Landrover days has crocodile clips to fasten direct to the battery terminals. I think it would be too much to run it off the cigarette lighter socket.
I am looking for a replacement due to its age and will look for another with clips again.

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

 

[Brocksford]

This inflator has worked well for me maintaining 80psi:
TIREWELL 12V Tyre Inflator - Heavy Duty Double Cylinders Direct Drive Metal Pump 150PSI, Air Compressor with Battery Clamp and 5M Extension Air Hose

 

[Podney]

RAC 900. Never had a problem getting to 80psi. Recommended by many on here.