Baldrick,
I noticed that Daerrs now offer the VIAIR compressors as well. Compared to ARB's offering they're actually cheaper.

In their catalogue, Daerr state that the 12 volt VIAIR compressors can easily be run off a 24V vehicle by putting the clamps on one of the two 12V batteries. In theory this should work obviously but I've always been told that this ruins your batteries. Has anyone got experience with this?

cheers,
Camiel

I've done it a handfull of time and got away with it with no problems as long as the engine is running. What's the argument here, why would the batteries go bad?

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A.B.
www.ShortWheelbase.com

I'm no expert, but I think that charging two 12 volt batteries from a 24v source requires the batteries to be of similar capacaties and output rating, that the charge is equally split between the two. Any imbalance would cause one battery to recieve a higher and possibly damaging charge, and theoretically a large enough compressor could cause this imbalance.

I'm no electrical engineer so my theory could be complete rubbish:- Any thoughts?

I am no engineer either so I checked with the garage. They basically confirmed what Baldrick is saying. While it is not too harmful to occasionally tap 12V from a 24V system, it does wear out the battery in the long run.

Camiel

Another option, which might be cheaper for some (though not cheaper than buying used stuff out of the junk yard)--

I bought a 12v compressor, in the US but I think the company is australian. It's called "big red" but it is made by one of the main compressor manufacturers, thomas I think. So I bolted it into the rear of the jeep, ran wires, switch, relay, etc forward to the battery, and everything works great. Add a 25' coil hose and it will pump up all the tires in a few minutes. Not as fast as an engine-driven compressor, and no running of air tools, but installing it was nice and easy, and it supplies enough air for my needs. There are a bunch of companies offering similar products if you don't want to go looking through the junk yards...

(And if you do like junkyards, I am told that older cadillacs had air-controlled suspensions, with nice strong air compressors.)

Just curious, does this thread win the “Most Posts” award? http://www.horizonsunlimited.com/ubb/smile.gif

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A.B.
www.ShortWheelbase.com

I couldn't help but notice that this subject has gone crazy with replys!! Good one Sam! I'm sure Chris Scott will give you a free tee shirt. Although it might be one of his old ones!!

Regarding these compressors, the one I now get is 1.7 cfm (about 48 lpm). These are made by VIAIR, and I sell it with a 50 ft (15m) hose and tyre inflator. Have a look at my web site. www.mattsavage.co.uk

We've just returned from the Land Rover show at Billing. I took 10 of these compressor kits with me expecting to sell maybe 4 or 5 over the three day show. We sold them ALL on the first day!

Cheers,
Matt Savage

Those people with aircon (ie engine-driven) compressors:

How is the pump turned off and on? I'm just thinking about how much power an aircon unit saps from an engine. If it's belt-driven, how do you turn it off when you're driving?

sorry if this is a stupid question!

The York compressor comes with a magnetic clutch controled by an electric switch. This allows the pump to freewheel when not in use, so power consumption is minimal.

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Roman (UK)
www.polandrover.com

The setup works just like Roman explained above. If you have a tank, then you must install a pressure switch to the tank and hook both it’s pole to one of the switch wires. The switch will turn cut electricity when the tank is full no matter the position of the switch itself. And will turn it on when the tank is empty but the compressor clutch will engage and run the compressor only if the switch is on.

I can dig up a wiring diagram if it would help.

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A.B.

OasisPhoto.com – Images from the Magical Sahara.
ShortWheelbase.com – Jeep preparations.

After starting this thread, I figure I may as well tell the end of the story.

I bought a "Grand Erg", with high expectations (given it's impressive cost). It never worked properly from the first moment - see my note approx mid Sept.

I have been told that I will have to pay a further €102 (over £60)(plus postage to Italy) to have it put into working order.

This is not the level of service you should expect for something that costs over £400. I cannot advise anyone to buy this unit - mine didn't work, and now I'm expected to pay more to rectify a factory-original fault.

Just thought I should let you know!

Sam.

Hi Sam,

"Just back from three months in Sahara, grand Erg was just the job many times. In reality, takes a minimum of five minutes to get each tyre back to road pressure (37psi), and sometimes nearer ten. .... Sam"

Thats is worse than the performance of my little Thomas unit (asuming 7.50R16 tyres).

What, according to Grand Erg, is the problem and what do they propose to improove in detail?

GE provides a table with inflation times on their web site: http://www.granderg.com/compressori.htm

So if the compressor does not fit thees promisses, then it should not be your turn to pay the repair!!??

I will observe this thread, it might get interesting for my german site www.sahara-info.ch

Good luck, Yves

Okay,

Took the motor out and sent it off to Grand Erg. It was a 24V motor, no wonder it wasn't very impressive! A replacement motor has just arrived, I will fit it this weekend and see how it goes.

Off to Algeria in three weeks, where the wee beastie will get lots of use and will report back afterwards - expecting to be suitably impressed - we shall see.

Sam.

Adding another option to the menu:

I am currently installing a 12V ExtremeAire compressor, to my Defender 6x6 conversion, after originally planning to use an inverter and a 240V compressor. (I found my 1500Watt inverter tripped out because the AC induction motor pulls a LOT more current on start-up than its nominal power requirement).

The Extremeaire has 100% duty cycle, which is useful (6 tyres can take quite a while to inflate!). They claim a 4 cfm free flow rate, which is supposed to inflate a 33x12.5x15 tyre from 15psi to 30psi in 90 seconds!)

Cost is a bit frightening at £240, plus freight, plus VAT, though.

I will report back when I've used it in anger http://www.horizonsunlimited.com/ubb/smile.gif

Regards,

Michael

Noooooo, NEVER take a 12V feed directly off a 24V system. Lots of ill-informed debate on this issue, but the short answer is that even a trickle feed off of one battery will sooner or later (and usually sooner) ruin one or both batteries.

Yes, you'll get nice clean 12V from the battery, (which is all Daerr care about, apparently) but the 24V charging system will do some nasty things as it tries to replace the charge.

Remember, the batteries are being charged in series. Imagine one is empty, and the other full. This is NOT the same as charging two batteries in parallel - the empty one will never get full, and the full one will be overcharged. They will both die, one slowly and painfully, and other possibly messily and spectacularly.

The website suggested you do this either knows nothing about batteries, or they own shares in a battery manufacturer!

Regards,

Michael...
P.S. You can get some electronic 24V to 12V converters, but it'd be hell of expensive and bulky to cope with, say, 30 or 40 amps (which I would guess might be what these compressors would draw).