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Problem with the 120v tire pump through 12v inverter in the truck on the road


bostonrob

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My truck tire was very low and I tried to inflate it on the road.

I have a Sears 120v 9amp inflator which continues to work very well. I plugged it into a 12v 300w 30amp max inverter which we use all the time to charge the computer and phones. I plugged the inverter into the 12v AUX adapter beside the cigarette lighter. It has a 20 amp fuse in the fuse box under the hood.

When I turned on the air pump, nothing happened. But the 20 amp fuse in the truck blew and needed replacing. Today, I connected the pump to the 120v house current through a kill-a-watt and it showed 8.5amps when filling the tank.

What am I missing? How can I get this to work if I need to next time?

 

Thanks

 

Rob

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Someone else can give you a more detailed explanation but amps change when you change volts. Watts stay the same so with a bit of math you can figure out what the amps are on the 12v circuit to run your compressor. 120vx9A=1080watts. Then you divide 1080watts by 12V = 90A being pulled on the 12v side. It is actually a bit more since u are losing some power on the conversion thru the inverter as well as other losses.

 

If you are looking for a good 12v inflator, check out the Viair 88p. It is ducking amazing. I bought it because the TV tires need to go up to 72psi and standard 12v compressors I had would take forever to fill to this pressure, if it is possible at all. It is absolutely worth the money IMO, works faster than some of those gas station compressors too!

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Rob, good questions and the answers are fairly easy, lets do the math. I agree with the other fine gents.

 

 

WARNING this is to educate Rob and answer his question. Those who don't like or get irritated with in depth comprehensive answers don't have to read this !!

 

 

You ask "What am I missing? How can I get this to work if I need to next time?"

 

 

1) If the pump requires 9 amps at 120 VAC, it takes 9 x 120 or 1080 Watts of power to operate it. (even if only 8.5 amps that's still 1020 Watts.)

 

2) If you want to use a 12 VDC to 120 VAC Inverter to power a 9 amp 120 VAC compressor, it will require "approximately" 90+ amps of DC current drawn from the battery bank since 1080 Watts divided by 12 volts = 90 amps. And that means you need a 1500 or so watt Inverter NOT a light duty wimpy 200 to 300 Watt Inverter a cigarette lighter type of 12 Volt power outlet might typically supply, which can be fine for charging low power cell phones and tablets and laptops etc.

 

2) NOTE a typical 12 VDC cigarette lighter power outlet may only be rated for 200 to 300 Watts, which is 17 to 25 amps. Such a low power outlet and its associated wiring and fuse (20 or so amps) CANT DELIVER THE REQUIRED 90 AMPS OF 12 VDC CURRENT.

 

SOOOOOOOOOOO if you need to operate a 120 VAC 9 amp compressor using your engine or house batteries, you need a 1500 or so watt 12 VDC to 120 VAC Inverter and a battery bank and/or charging capacity to maintain that 90 amp draw for the required time (battery capacity also enters the equation). THATS A BIG HONKIN INVERTER AND IT TAKES SOME GOOD BATTERY POWER TO DELIVER 90 AMPS FOR VERY LONG, DONT SOUND VERY COST EFFECTIVE TO ME!

 

ALTERNATIVES a) You could use a small portable 120 VAC genset, but a 1000 watt may or may not work??? while a 2000 watt likely will AWFUL EXPENSIVE TO AIR A TIRE!!!. B) They make all sorts of 12 VDC compressors, but many are light duty and wimpy and get hot, you would need a good one PLUS a circuit with big enough wire and plug and receptacle to power it at 12 VDC. c) They make heavy duty 100 and more amp automotive alternators (or you may already have that capacity or more), that could keep a battery charged long enough and good enough to power an Inverter drawing 90 amps, you still need a 1500 or so watt Inverter mind you.

 

So I hope this answers your question, if not let me know.

 

John T

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For emergency road side air one of the cheapest routes to take is to acquire a high pressure scuba tank, 1st stage regulator and attach an air fill host to one of the LP (low pressure 140-150psi) ports of the regulator. All told ~ $200 if you go used gear from a dive shop. Double plus if you go new. A drop in the bucket compared to overhauling your DC systems, upgrading your inverter or purchasing a generator capable of providing the necessary current.

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I'm just going to throw out the Viair 88P out there again as a VERY viable option, in case anyone missed it. It is long enough to connect to my truck batt up front and fill the rear tires on the Silverado, and long enough to connect to my hitch mounted house batts to fill the rear tires on my 30' toyhauler. I should make a video of how fast it pumps, but to give you an idea, I took the TV and trailer tires down to 10 psi all around in order to drive on the beach at Pismo. Before getting back on the road, I filled all 4 truck tires up to 60/72psi (front/rear) and the trailer tires to 65psi, and spent around 3-5 mins per tire. My buddy used a 120v pancake compressor to fill up ONE tire on this truck (70psi) and it took just about as long. I helped him out after I finished with my rig. Now, that 120v pancake was a cheapo Campbell Hausfield, but anyway, i was colored impressed with how fast the 88p worked, for how small it is. I am in no way affiliated with Viair, I am just a very satisfied customer..... Current price is $63, but I did get it cheaper on Amazon. CamelCamelCamel shows it was around $53 in Sept, I think I got it around that time.

 

https://www.amazon.com/Viair-00088-88P-Portable-Compressor/dp/B005ASY23I/ref=sr_1_1?ie=UTF8&qid=1472064671&sr=8-1&keywords=viair+88p

 

http://camelcamelcamel.com/Viair-00088-88P-Portable-Compressor/product/B005ASY23I

 

 

 

 

For emergency road side air one of the cheapest routes to take is to acquire a high pressure scuba tank, 1st stage regulator and attach an air fill host to one of the LP (low pressure 140-150psi) ports of the regulator. All told ~ $200 if you go used gear from a dive shop. Double plus if you go new. A drop in the bucket compared to overhauling your DC systems, upgrading your inverter or purchasing a generator capable of providing the necessary current.

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I'm also a fan of the 12v viairs.. when appropriate. It's important to do your homework as some of the pressure ratings "can" be deceiving and might not be appropriate for all applications. They have limits. Ie., A 150psi unit may only be able to sustain that pressure rating for a limited amount of minutes and may require 15-30 minutes of cooling time between duty cycles.

 

So... if you're trying to achieve 90-110psi in your tires, a "given" unit may not be able to provide a full fill on one go around and may require a significant amount of down time before it's able to complete the job.

 

Just to be aware while shopping.

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I agree completely. The first review on the Amazon page has a good comparison of the other Viair options in this class (I'm copying and pasting). This made the decision super easy for me!

 

70p
15% duty cycle which means you should only run it for 1.5 minutes and let it cool down for 8.5 minutes. Then you can start again.
1.27 cfm @0 ps
20 ft maximum reachi
Cigarette lighter adapter
Kit bag
Overall it's a great little compressor but for light duty.

85p
40% duty cycle which means run for 4 minutes, then cool down for 6 minutes.
1.83cfm@0psi
Fills up to 31" tires
13 ft maximum reach
Cigarette lighter adapter
Kit bag
Overall another good compressor but you will blow fuses like there is no tomorrow unless you have a 20 amp cigarette lighter.
The worst part is the reach. 13 ft iwill make it hard to reach tires for mid sized cars and up.

90p
15% duty cycle which is 1.5 minutes of. Run time and 8.5 minutes of cool down time
1.77 cfm@0psi
Fills up to 31"tires
15ft maximimum reach
No cigarette lighter adapter but available if your cigarette lighter uses 30 amp fuses
Kit bag
Overall, bad run time, bad reach for air hose, uses too much power for what it does. Worst out of them all

88p (Save the Best For Last)
45% duty cycle 4.5 minutes run time and 5.5 minutes cool down time (highest out of all of them)
1.98 cfm@0psi (awesome) more air output means less time filling up tires
Fills up to 33" tires
20 ft maximum reach
No cigarette lighter adapter but available and might not blow your fuse if you have a 20 amp. Not sure though because I have not tried
No kit bag but go buy a cheapo from a big box store. It is probably more durable than the kit bags that come with the other kits.
Overall, the best in the price range. Most powerful and it is still just as small as the others. I have a Chevy 2500hd and it fills my tires up fast. The 88p laughs at my wife's range rover sport tires. I never write reviews but I am so impressed with this thing that I had to.

 

I'm also a fan of the 12v viairs.. when appropriate. It's important to do your homework as some of the pressure ratings "can" be deceiving and might not be appropriate for all applications. They have limits. Ie., A 150psi unit may only be able to sustain that pressure rating for a limited amount of minutes and may require 15-30 minutes of cooling time between duty cycles.

 

So... if you're trying to achieve 90-110psi in your tires, a "given" unit may not be able to provide a full fill on one go around and may require a significant amount of down time before it's able to complete the job.

 

Just to be aware while shopping.

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You say you plugged in to the aux port next to the cig lighter?that is not (large) enough to carry the current needed, go straight off the battery/s with the inverter, we're talking maybe 12/14 ga. wire compared to right from the source.

That would still blow the fuse on his 300W inverter.

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