Disco 2 Replacing the air compressor with something more useful?

as the title states, has anyone thought about doing it? I go rid of the air suspension so the compressor is a waste of space. I though about using it for a water tank (for showers etc) or, more likely for the secondary battery. Although many people go for a second battery mounted at the front, mounting it in the middle is a great idea as it will allows you to run thinner wire for high power applications at the back, like a fridge or an inverter.

any ideas?

Why would it allow you to run thinner wire?

because there would (probably) be much less length. to run for example a 2000W inverter in the back i would need around 6m of wire from the engine bay... that is a lot, which would mean a very large gauge wire

That is an interesting thought. Under the bonnet is not ideal IMHO. The open spot by the passenger bulkhead is too small for a decent battery and way too close to the turbo for long battery life. You can remove the jack and use that space, but although fairly cool, it is again not huge and bottle jacks are useful things. I'd not considered the compressor space as it is a bit exposed, but you could always put it in a battery box......so why not? At least it would stop me lugging about the useless weight of the disconnected compressor.

mad85 said:

because there would (probably) be much less length. to run for example a 2000W inverter in the back i would need around 6m of wire from the engine bay... that is a lot, which would mean a very large gauge wire

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I've already run cables from the starter battery to the rear (access at the louvered grill on the D post by the tailgate) in anticipation of a Bundutop tent in the short term and a deep cycle battery in the space left by removing one of the fold away seats in the longer term. I used about 4m of both red and black 6mm flexible single core rated to 43 amps. There is protective sheathing and a 35 amp fuse in the engine bay and 6mm cable is easily concealed and protected inside the cab and flexible enough to be worked neatly around corners. The tent is fused at 15 amps and the DC to DC charger I was contemplating draws a max of 25 amps. Why would it need to be thicker than this?

Because a 2000W inverter means close to 200Amp I used 6mm cabling for four new fairly low power 12V sockets in the back. The 43amp is a bit misleading since it depends on how long the cable is. in DC this makes a lot of difference.

Mind you, I am not an expert and stand to be corrected

mad85 said:

Because a 2000W inverter means close to 200Amp

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200 amps! I'm no expert either but that sounds a lot for a device that probably would not put out more than 9 amps per socket and probably has an internal fuse of 30-35 amps.
If it could draw 200 amps that would mean that if you fit a 100Ah secondary battery which will be effectively flat at about 50% charge, it will only run your inverter at max chat for about 15mins.
You could of course only run stuff off the inverter with the engine running, but then the alternate battery is irrelevant. Can I ask why you need a 2000W inverter? I have a tiny 300W one that plugs into a 12v socket and that is good enough to run and charge a laptop and a couple of phones or camera batteries at the same time. The largest projected draw I am contemplating is a Snomaster fridge and that draws less than 1 amp per hr.

I don't think the battery will have a long life with a 200 amp draw, it be ruined fairly quick.

Col

If you are using an inverter to generate 240v AC then the AC amperage will be a lot less as it is inversely proportional to voltage. The DC amperage will be a lot lower than the AC as the voltage is a lot higher. You will need thicker cables going from the battery to the inverter, than fropm the inverter to the appliance.

brianconwy said:

If you are using an inverter to generate 240v AC then the AC amperage will be a lot less as it is inversely proportional to voltage. The DC amperage will be a lot lower than the AC as the voltage is a lot higher. You will need thicker cables going from the battery to the inverter, than fropm the inverter to the appliance.

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Confused. "The AC amperage will be a lot less as it is inversely proportional to voltage" OK I think I understand that, 240v and <13 amps
"The DC amperage will be a lot lower than the AC as the voltage is a lot higher." That I don't understand surely you are saying that the amperage is higher as the voltage is lower?

Si Click said:

the amperage is higher as the voltage is lower?

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Yes cos the formula regardless if it's AC or DC is I(amps) = P(watts) : U(volts) so e.g. for 1200W load will be 5A at 240V and 100A at 12V

sierrafery said:

Yes cos the formula regardless if it's AC or DC is I(amps) = P(watts) : U(volts) so e.g. for 1200W load will be 5A at 240V and 100A at 12V

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I've always wondered why amperage is denoted by the letter I

Col

It comes from "Intensity"

sierrafery said:

Yes cos the formula regardless if it's AC or DC is I(amps) = P(watts) : U(volts) so e.g. for 1200W load will be 5A at 240V and 100A at 12V

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Good. Thank you, I thought I was not going mad.
"The DC amperage will be a lot lower than the AC as the voltage is a lot higher." made no sense at all.
I still think that draws of 100-200 amps is unsustainable on any off-charge lead acid or AGM 12V system without frequently killing the battery. Lead crystal or Lithium batteries might survive longer and give power for longer, but you are still talking minutes rather than hours to flat.

The idea that i will only use the 2000w very rarely if I need to run a powertool. Normally i will use the inverter for something much smaller like a fridge or a laptop charger.

As someone mentioned cables from the battery to the inverter need to be much thicker than cables from the inveter to the appliance

A good 2000W inveter which can drive a power tool is very expensive and heavy(around 5kg), not small either so if you dont use it often it doesnt worth the hassle IMO cos for that load you need min 150AH battery and with engine running it can kill the alternator

Yes, i agree. Ideally one finds one which produces a pure sinewave

I've fused the offtake for a second battery to 35 amps running on 6mm cables rated to 43 amps. Applying Ohms Law gives me a max wattage of 430W. This is more than enough to power the tent motor (fused at 15 amp), and the 6mm cables are in line with the specific recommendations for a run length of < 5m for the Intervolt DC to DC charger I was planning to use (though since heard some mediocre reviews), itself rated to 25 amps continuous. Have I under-spec'd this?

sierrafery said:

It comes from "Intensity"

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Never new that! so are we saying W =Vi?

On another tack, have you considered using a solar panel to generate your DC then storing it in a FO battery and inverting that? (If nec). Also, re powertools, would it not be easier to use a battery power tool that can be charged by your inverter or even straight from a socket rather than trying to run an AC one off an inverter? Not that I know much about electrickery.