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Old 08-03-2018, 10:02 AM   #1
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Portable air compressor w/ alligator clips – connect to starter battery or aux bat?

In my case, the aux battery is mounted under the van and so the terminals are not easily accessible.

Will running the compressor off of the starter battery cause material starter battery drain (or otherwise shorten its life), assuming I have engine running while the compressor is on?

Here is the compressor:
https://www.amazon.com/VIAIR-400P-Au.../dp/B000X9B32M

the other idea is that I could get a compressor that runs on A/C, and power it via the Magnum inverter connected to my aux battery. But, this seems like a lot of continuous load for the inverter and all of the associated wiring.

Any thoughts/ideas appreciated. Thanks!
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Old 08-03-2018, 10:10 AM   #2
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Should be fine to run off the starting battery with the motor running. Those units are made to be used under those conditions.
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Old 08-03-2018, 10:14 AM   #3
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My only concern with that compressor is that the 33% duty cycle might limit you. Are you just looking for a compressed air source, are you planning on airing down the tires considerably, what size tires will you be running, how much time do you want to spend airing back up? All these questions come into play.


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Old 08-03-2018, 10:16 AM   #4
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Just connect to the starter battery. Have the engine running, start compressor, and then connect it to the tire. This will make it much easier for the compressor to start. If you connect the compressor first to a tire that has 65-70psi in it, you may cause the compressor to blow a fuse. The higher voltage from the running engine also makes it easier on the compressor motor. These are really good compressors, but don't expect much out of the case. However, these do fit perfectly in a 50 cal ammo can.
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Old 08-03-2018, 10:59 AM   #5
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Quote:
Originally Posted by BroncoHauler View Post
My only concern with that compressor is that the 33% duty cycle might limit you. Are you just looking for a compressed air source, are you planning on airing down the tires considerably, what size tires will you be running, how much time do you want to spend airing back up? All these questions come into play.


Herb

Good questions, Herb. I'm a noob when it comes to off-road driving. Tires are 245/75/16 (around 30.5" diameter). My van is a Quigley 4WD Transit (low roof, 148" WB)

My goal is to have the capability to deflate/reflate the the tires so that I can drive on sand (beaches of Baja) with low odds of getting stuck. Also, I'll be driving a fair amount of washboard road getting to/from certain areas in Baja. So, I'm not planning to go rock-crawling, but rather just getting to my destination without incident.

I'm not going to be *constantly* airing down/up, so maybe I can live with the 33% duty cycle. I'm not sure, though. With the compressor I'm considering, do you have a sense of how long it would take to bring all 4 tires back to "road" (normal) PSI from "off-road" PSI?
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Old 08-03-2018, 11:44 AM   #6
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I have this exact unit and it fits my purpose of checking and maintaining, no serious ups and downs. I use the starter battery simply because I thought the house batteries were not made for power surges, the starter battery terminals are easy to access and you eliminate going through all the other electrical components. This is just my amateur opinion.
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Old 08-03-2018, 12:35 PM   #7
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I don't air down on my van but I do on my Jeep. The duty cycle limitation will mean the compressor may overheat and shut off if used for too long.

That's it.

After it cools down you can air up the others. You may shorten the life of the compressor letting it overheat and shut down, but the worst that is going to happen is you waiting (and wondering) for your compressor to cool off enough to air up the rest of the tires.

On my Jeep my old compressor would shut off after the third tire, going from 18 psi to 44 psi, then I'd have to wait for it to cool off before airing up the fourth. Or I'd borrow my buddies superior compressor. The air compressor I had back then was not your Viair so how many tires you can reinflate may vary.

If you do buy a new compressor, I would discourage buying one that requires you to run the inverter. Inverters waste power creating 110V. With an inverters typical efficiency of 80-85%, that would mean you would use around 115 amps of 12V power to create 100 amps of 110V. When you can buy products that run natively on 12V, it doesn't make sense to use a power wasting inverter, even if you have the amps to waste. Your batteries will last longer the closer to fully charged you can keep them.

You're better off running the engine and connecting the compressor to main battery. For peace of mind, try it before you get out on the trail and buy a better 12V compressor if the Viair isn't up to the task.

Good luck
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Old 08-03-2018, 01:06 PM   #8
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Based on the experience my buddy has had with his (which inspired me to buy one as well), the 400P is a pretty darn good compressor. I wouldn't worry too much about that 33% duty cycle either.

As an "in the field" example of what the 400P performance is:
After a recent trip out of Anza Borrego, we aired back up three rigs in a row, non-stop, all using the friend's one 400P compressor. That was two SMB's on 33" tires and one Jeep on 31" tires, with an average of perhaps 6 minutes per tire for the SMB's alone (Total of 48 minutes there already....plus the added air-up time for the Jeep....).

Yep. 12 tires in a row. 400P didn't skip a beat or overheat once.

Unless you're running seriously-significantly-larger tires, (37's?? 40s??) or pushing fairly massive pressure differentials (between aired-down and aired-up), this compressor sure seems like it would do just fine for almost any single SMB's airing requirements.

Seems like its already been discussed adequately, but yep -- my buddy hooks the alligator clips straight to the starter battery with engine running.
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Old 08-03-2018, 08:01 PM   #9
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Thanks, all. Very helpful replies.
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Old 08-04-2018, 11:09 AM   #10
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Quote:
Originally Posted by JT87 View Post
My goal is to have the capability to deflate/reflate the the tires so that I can drive on sand (beaches of Baja) with low odds of getting stuck.

A little off subject here, and I'm no expert, but I've been stuck in sand a few times and have seen lots of others stuck too. Since you seem to have little experience in sand, I would recommend that your first attempts are with at least one or two other vehicles. You also should have recovery equipment, such as sand ladders, a winch, shovel, pull pal, kinetic energy recovery strap etc. If you go it alone, prior to getting stuck, have a game plan for extraction. As for the OP's question, I have an ARB twin air, with a 100% duty cycle (it's fan cooled) and I connect it to the house battery's with alligator clamps. I've done 8 tires in a row with no problems, but make sure the engine is running. Someone here mentioned they overheated the alternator and cooked the diodes from extended compressor use, something I never thought of before, so perhaps its a good idea to give the system a rest between vehicles.
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