Power inverter for Flex VRG 3401--will this one work?

A

amcdonal86

New member
I have a 2012 Mustang V6 that I plan to polish in my garage bay. Unfortunately, there is no electrical hookup and I have no place to store a gas generator, even if I wanted to.



Does anyone have any idea if this one (below) will be able to run my Flex VRG 3401 and perhaps one halogen lamp (500 watts, I believe) for a few hours with my car idling without causing any problems?



Amazon.com: Roadpro RPPI-1500W 1200/3000 Watt DC to AC Power Inverter: Automotive
 
short answer no. it would run one or the other but not both at one time. flex is 900w and lamp is 500w so you need 1300w continuous minimum. i would look for on that puts out about 2000w continuous. you will have to wire directly to the battery.
 
You mean 1400W continuous minimum!



I imagine I would use the halogen lamp only for inspection. But you are probably right, I should find one that is 1500W continuous or more.



As far as destroying my car's battery, if I only do this once or twice a year, will it destroy my car's battery/alternator?
 
while a car battery is not really rated for this type of thing doing it once or twice year you'll probably be alright. don't know how big your alternator is so can't really say if it can keep up. at idle your alternator will not be able to keep up, so you'll need to fig out how to get your car to say in high mode while your doing it. if you do it while the car is at normal idle you'll need to charge the battery with a battery charger when you done.
 
wascallyrabbit said:
while a car battery is not really rated for this type of thing doing it once or twice year you'll probably be alright. don't know how big your alternator is so can't really say if it can keep up. at idle your alternator will not be able to keep up, so you'll need to fig out how to get your car to say in high mode while your doing it. if you do it while the car is at normal idle you'll need to charge the battery with a battery charger when you done.
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:werd: That's just another reason I like deep cycle batteries and, if possible, dual battery setups that have a transfer switch to guarantee one of the two never gets drained.
 
ya, i hear you, but a true deep cycle shouldn't real be used for starting your car. thats why you need a good battery that is mix of the two starting and deep cycle. optima is probably the most recognized but there others that are better (ie. life line).



my truck has dual batteries and alternators with a pto take off and pto idle circuit.
 
DaGonz said:
Wouldn't it be easier and cheaper to run a heavy duty extension cord from the house?
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Assuming this a home situation, then this recommendation is a no-brainer. When I lived in an apartment, I was in a similar situation to the OP - disconnected garage without any electrical outlets. I ended up stringing an extension cord from my second floor balcony down to the parking spot in front of my apartment. It was definitely a little awkward, but I only needed to polish once every year or two so thankfully it was not a re-occurring need.
 
DaGonz said:
Wouldn't it be easier and cheaper to run a heavy duty extension cord from the house?
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Yeah, it would be if I could find one that's 1000 feet long. My garage spot is actually a breezeway located underneath another apartment building down the street. I also live on the 7th floor of my building which is about 100-200 feet laterally from the nearest parking spot. Not to mention all the stupid looks I'd get.



As far as running a generator--I'd do it, but generators are nosier than just running my car at idle and I have no place to store a generator (my garage spot is really a breezeway). I certainly don't want unspent fuel in my apartment. I want to make as little noise as possible when working on my car, because I want to respect my neighbors--especially those who live right next to my car and are walking by it all the time. Wouldn't want them to vandalize it!
 
amcdonal86 said:
Yeah, it would be if I could find one that's 1000 feet long. My garage spot is actually a breezeway located underneath another apartment building down the street. I also live on the 7th floor of my building which is about 100-200 feet laterally from the nearest parking spot. Not to mention all the stupid looks I'd get.



As far as running a generator--I'd do it, but generators are nosier than just running my car at idle and I have no place to store a generator (my garage spot is really a breezeway). I certainly don't want unspent fuel in my apartment. I want to make as little noise as possible when working on my car, because I want to respect my neighbors--especially those who live right next to my car and are walking by it all the time. Wouldn't want them to vandalize it!
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Don't stress the looks. You get used to it after a while.



Any chance you could rent a generator? Some large rental outfits have them.



I'd be concerned about the car's electrical system/battery... might want to tell a Ford mechanic what you want to do and get his opinion on it.
 
Too late! I bought the inverter! And a stool! And a chrome cart to push all my stuff to the garage.



Then again, maybe there is some cause for concern. The following PDF I found online seems to state that even with a 130 amp alternator (like the one in my Mustang), I will probably only be putting out 50 amps at idle. It says for that alternator with an OEM battery, I can expect to run the inverter at 1000 watts for about 30 minutes--safely, I assume. I estimate, since I will be doing a one step polish and wax (not a perfectionist), that I will probably be polishing/waxing for maybe 4 hours or so. So maybe the actual run time of the machinery will be about 2 hours, and the rest of the time the car's engine will still be on, and will be charging the battery at maybe 50 amps.



http://dimensions.sensata.com/Application_Notes/130489.pdf
 
Hm.... well I figured out the stock battery has about 40 amp-hours in it when fully charged. The alternator can probably put out 50 amps at idle, but let's assume 40 amps just to be safe. I intend to use an average of 500 watts over the course of 4 hours or so. At 12 volts, 500 watts is about 42 amps. So subtracting 40 amps from 42 amps, I should be able to do what I need to do without draining the battery (or I suppose I will be drawing about 2 amps from the battery, so it would be able to last in such a manner for 20 hours maximum). It will put additional load on the alternator, however.



Does this sound right? Honestly I wouldn't be using an inverter if I had another option that was simple enough for me to do.



I guess of course, I'm forgetting the amperage it takes just to run the engine and mandatory accessories in the car (instrument panel, etc.).
 
Nevermind, it appears that I was basing this on an incorrect assumption--that my devices are running on 12V when in fact they are 120V. So the total amperage at any time ends up being closer to 10 amps instead of almost 40, which means that perhaps I would be OK, given that the alternator provides 30 amps at idle.
 
amcdonal86 said:
Nevermind, it appears that I was basing this on an incorrect assumption--that my devices are running on 12V when in fact they are 120V. So the total amperage at any time ends up being closer to 10 amps instead of almost 40, which means that perhaps I would be OK, given that the alternator provides 30 amps at idle.
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i think your math is backwards.

@ 120v and 8.3a yields 1000w this is coming out of the inverter.

@12v and 83.3a yields 1000w this is what the inverter is drawing from the battery.

these statements make certain assumptions so the actual amps will be different in real life (higher).



renting a generator is probably your best bet or borrowing one from a friend.

would it be possible togo to a friends house and do your car there?
 
wascallyrabbit said:
@12v and 83.3a yields 1000w this is what the inverter is drawing from the battery.

these statements make certain assumptions so the actual amps will be different in real life (higher).
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I don't believe this is correct. I ran this by an electrical engineer at work today, and he says that the draw on the battery will only be 10 amps or so, which is easily handled by a stock alternator at idle engine speeds.



The best way that this can be explained is using the analogy of water:



HowStuffWorks "What are amps, watts, volts and ohms?"



"A neat analogy to help understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size."



What you are saying is that the flow rate going out of the "battery" is not the same flow rate that is coming out of the inverter, which is not the case. I made the same mistake the first time I did the calculations.



A gas generator would be completely unnecessary. The only thing it would do for me is use less gas. But it also produces several times more emissions (no emissions controls on it) and is noisier.
 
amcdonal86 said:
I don't believe this is correct. I ran this by an electrical engineer at work today, and he says that the draw on the battery will only be 10 amps or so, which is easily handled by a stock alternator at idle engine speeds.



What you are saying is that the flow rate going out of the "battery" is not the same flow rate that is coming out of the inverter, which is not the case. I made the same mistake the first time I did the calculations.
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did you inform him of the fact you want 120v from a 12v source and the final load will be 1000w. because the power law formula states that power measured in watts(w), annotated as (p)=voltage measured in volts(v)*current measured in amps(a) annotated as (I). p=i*v so if we now the power 1000w=the voltage 12v*I so 1000=12*I or 1000/12=I (83.3). so you need 83.3a at 12v to power a 1000w load. now for the 120v output. 1000w=120v*I or 1000/120=I (8.3a) so you'll need 8.3a at 120v to power a 1000w load. the inverters job is to provide 120v output from a 12v source. in this case power being constant the voltage is inversely proportional to current. so if voltage go's up current must go down. for these number i've have not taken into account the efficiency of the inverter and just used perfect world numbers. if you factor in the losses created by wiring and components the number will be different. most likely you'll find that you need more.
 
The problem is it's a 1000 watt (actually 1150 watt) load at 120V, not 12V. The incorrect assumption I made in my first set of calculations was that a 1000 watt load was the same at 12V as it is at 120V. (It's actually 1/10th of that.)



The amps at 120V that the polisher and the 250W lamp nominally require is 1150W/120V = 9.583 amps. Assuming 80% efficiency, that number is really closer to 12 amps. The inverter is capable of powering 5000 watts at 120V for startup (40 amps or so), so on the inverter the load is fine. But 12 amps continuous should be no problem for the alternator.
 
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