Volts, amps, milliamps... and a tyre inflator

[richandjo]

Quick question on the above, due to my ignorance on the matter.

Michelin tyre inflator, powered by in-car 12V supply. Power requirement stated in instructions: 7.5A/96 V under normal usage.

Works fine, no problems.

I'd like to get an adapter for it, the type that plugs into the mains (3-pin) and allows the male lead from the inflator to be inserted. This would avoid having to plug the inflator into the car each time. Useful when pumping up the bike tyres in the shed (where there's mains power).

However, the adapters that I have seen seem to state (fir example) 600mA maximum, for use with 'phones and satnavs.

Does this mean that the above inflator simply wouldn't work via the mains adapter or is there some way around this? Anyone seen such an adapter for use on devices like tyre inflators?

Thanks, in anticipation - and apologies for the ignorance on matters electrical!

 

[Spark123]

Probably 96 Watts, have you considered one of those battery boost packs - they usually have a cigar lighter outlet on them. Some have an inflator too

 

[westie101]

You need something like this: -
http://www.halfords.com/webapp/wcs/...uctId_785261_langId_-1_categoryId_165465#tab1

but with a higher output. This only supplies 5 amp so you compressor would burn it out, you could perhaps try Maplin

 

[echoes]

No, the usual plug-in a.c./d.c. adapters will not deliver 7.5 A / 96W.

100W power supplies are quite beefy compared to the 5-10W plug-in adapters.

A cheap battery charger rated at > 8A might work as a crude power supply.

 

[ericmark]

There are on the market battery replacement units for use with caravans. Zig is most common make. However these units are not cheap and likely the cheapest option is one of the booster packs

at around £70 will likely be a multi-purpose cheap option.

The standard battery charger has a very rough supply and motors don't like the un-smoothed DC using a battery as well could smooth it for you.

All the ready built units like this

are 5A not 7.5A so would be overloaded.

Boat stuff does have what you need but at £262 for a charger I am sure you don't want to pay that.

 

[Adam_151]

Supprised you didn't suggest something like a 13.8v 10Aish ham radio supply, eric...

 

[echoes]

Been googling, and LED power supplies keep coming up, like this one:
http://www.tlc-direct.co.uk/Products/SK660449.html?source=froogle

Replace little plug with cigar-lighter socket.

Thought LED PSUs would be constant-current rather than constant voltage, but there you go...

 

[ericmark]

I have used a ham radio power supply to do exactly what they want. But have you seen the price?

I thought there would be loads of battery replacement units on the market but was surprised when I tried to google.

Remember in the 90's I found a 8A unit for caravan use but again the price was silly.

I used a 6AH battery to smooth the supply and a battery charger with a home made loading unit which would start loading the battery once the voltage exceeded 13.4 volts. Tried at first to regulate battery charger output but the 0.6 threshold voltage resulted in a 12A battery charger giving just 3A into battery.

Working as an away worker living in touring caravan we tried about everything we could to get 12v stuff to run off 230vac. Theory is easy but in practice it was a cost problem.

Standard battery charger around £15 with a power supply at around £80 and when looking at 8A then price sores.

I would say "echoes" find is about the best to date. Full mark to "echoes".

 

[echoes]

Could modify a cheap charger by adding a big (27000μF) capacitor across the output: same principle as eric's 6AH battery. Wouldn't bother even trying to regulate unless the heatsink would be handy for keeping the tea warm. More faffing around though, and such caps aren't small .

Oh, and the output voltage would increase - maybe a bit too much for the motor...

 

[richandjo]

Thanks, everyone, for your replies and efforts to search the right kit.

Seems like I should just plug it into the car! Cheaper!

Again, many thanks for your input.

 

[plugwash]

Use a PC PSU. Cheap and can provide a load of current at 12V. You will have to change the connector on it but that is no big deal.

 

[Monkeh]

I have used a ham radio power supply to do exactly what they want. But have you seen the price?

Fixed 13.8V supplies don't go for much on ebay. Even new they're cheap.