Slim357

Im looking into getting a power inverter for my jeep but not sure what I will need. I want to be able to run a grinder sawzal impact and maybe an air compressor nothing big just a 25gal from harbor freight. Im looking at a 900watt constant and 1800watt peak. How can I wire this up to the jeep since I have an amplifier wired up for my subs and will I need a capacitor if so can I get one that is commonly used for an amplifier for adio ise

JayneCobb

Let me start off by saying that I am no electronics expert. All I can tell you is what I have on my Jeep, and what my plans are.

Check out my build thread, I have a 0 gauge wire running from my battery to distribution blocks that are under my rear seat, and I have electronics wired into the block. Right now all I have is an on-board compressor, but my buddy has the same wiring setup with 2 big amps,2 subs and an air compressor and everything runs perfectly. We're both planning on getting Whistler Pro-2500W inverters, but they also sell smaller ones.

I'm pretty sure that if you ran something similar to what we have you'd be fine. I'd recommend upgrading your battery and maybe alternator, but I don't think a capacitor is necessary.

Slim357

Cool I read somewhere there where different waves or something that was needed to start the compressor. Is you compressor running on dc volts?

WTF_LOL

There are different types of waves. What you are referring to is the AC sine wave which the inverter is trying to replicate out of the constant DC power. AC is a "true" alternating sine wave created by the rotating equipment such as generators. Crappy inverters create a square wave. Better inverters create a modified square wave. The better yet are pulse width modulating inverters that better match a true mechanical sine wave...on and one..

The point is, some variable speed motors can not run at full efficiency on a square wave sign. Also dimmers need a true wave sign to work (generally speaking). As for a compressor, even a crappy square wave will be fine.

What you really need to look at is the amp rating. Power (Watts) only tells you so much. We know the Voltage will be 120V, what you need to work out is if the inverter will supply enough Amperage for your device. Pay special attention to motor start up amperage draw. When a induction motor starts, it draws more amps than it does while operating. The motors in hand tools and compressors are induction motors.

So first look at the devices you plan to operate. Find out which one has the highest operating Amperage. The product likely will not list startup Amps. The general rule of thumb is that startup amps will be about 225% of the full operating load amps. Also keep in mind that when a device is bogged down, like a temporarily stuck grinder, amperage can spike.

Next take a look at the inverter specs. Better models will list their operating amperage along with a chart indicating how long it can temporarily operate at a "in rush" level. For example, it might say it has a 20A operating capacity but can do up to 60A for 20 seconds type of thing.

So, sorry about such a long post... Guess I coulda just said look at Ampere ratings of the device and the inverter

EDIT: Chart showing wave signs...didn't see one that also showed PWM but you get the idea

hankthetank

^^^ awesome explanation. i have a 2000w (4000w peak for x seconds) inverter with three outlets, but it can only deliver a maximum of 4 amps. not so good, but hey it was practically free so i'll take it.

Slim357

Awesome explanation thank you very much and btw love the screen name

WTF_LOL

That's why looking at the Amps is key. 4 amps isn't bad though. I had one that was around that amount and was able to find an el cheapo angle grinder that operated at 4 amps that has saved my bacon a couple times. As I mentioned before, if it bogged down it would trip the breaker...

Oh, speaking of which, good idea to see what its over current protection is. Some cheaper inverters have an internal breaker (prolly a bi metal deal) that resets over time and is annoying as ****. Some have a fuse that you would have to replace. Ideally you can find one with a resettable breaker. I have not looked at 12v inverters made for vehicles much so I can not give good advice on a model or anything (just a solar guy so I know inverters)



Thanks Slim

Slim357

I hear that and your welcome wish I woulda thought of something funny like that

JayneCobb

Yea, it's DC. It's a VIAIR, they are designed to be used in a car. I just cut the cig adapter off and hard wired it.

WTF_LOL, great explanation. I've read all that before but I haven't retained enough info to spit it back out like that!

Dan91

Ok so I'm just curious here. Watts are volt amps: watts/volts=amps. 2000watts/120v= 15 amps. So why doesnt the wattage corellate properly to the amperage it should provide? Inefficiency? I'm wondering cause I planned on getting a large inverter and was expecting it to work as I said above.

SDC

Excellent question. Ohms law isn't adding up on the other guys inverter specs. I'm in the marine buisness and only deal with high end stuff. A 2k inverter would cost over $1000 bucks.

Also keep in mind that in order to run a full 2000 watts that you could pull 200 or more dc amps. Your gonna need big cable for that as well as proper dc circuit protection.

WTF_LOL

Thats a good question, generally it is "creative" marketing. When you are dealing with high end inverters, like you would use on your house, the math does line up. For example, a 3.8kW, 240V inverter does produce over 15 Amps

To clear one thing up first, useable Power (Watts) is technically: I (Amps) x E (Volts) x PF (Power Factor) = P (Watts). In other words, you need to consider the devices efficiency to truly know the amount of power you have available to use based on your system specs. Technically speaking E x I = VA. For example you may see a transformer rated at 12kVa.

Anyway, the misleading watt/power rating on portable inverters I have seen derived from the surge rating (based off the highest Volts and amps the device can survive). I have also seen it based off of a 24V connection even though vehicles are generally 12v. Who knows, I am sure there are some other creative ways they can claim that.

They really are not wrong. The inverter could likely invert up to 2000W, the only problem is it may be unlikely to handle the combination of amps and volts to get there based on your system configuration so it is irrelevant. It is the same reason compressors and many other induction motor devices are rated in Horse Power rather than Watts at Home Depot. 1kW = 1.34HP. Most people don't know the conversion and makes it sound more powerful! The big letters on the box read 200W, never mind the fact it will never invert that in a standard 12V vehicle, but it sounds good!

So this all circles around to why you can not look at the biggest letters on the box. You need to know your system specs. We know your DC supply is 12v and some amount of amps. The output will be 120V and some required amount of Amps. To get the right inverter, you need to be sure it is big enough to supply your required amps. The power rating doesn't help us as it is the last thing we need to check. That is, if we know we will need 120v and 5a than we only need to double check that it can invert at least 600w

To dive into this even further, we now know the required AC output Volts, Amps, and Watts. We also know the DC input Volts. We also need to know the vehicles DC Amp capacity. It is possible to have an inverter with a higher ampacity rating than your battery and alternator can deliver. So, again, the inverter capacity may be irrelevant if your battery and alternator can not supply it.

If you go with a very large amp inverter you will need to look at your alternators max amps at idle to be sure you can supply it above and beyond what your vehicle uses in operation. If you want to know if your battery alone can supply the required amps, you need to look at your batteries AH (amp hours) at whatever rate they have listed. If they list a C20 hour rate, you divide the AH rating by the rate (20) to see how many amps are available per hour. For example, if a battery is rated at 100AH @ C20 than this means it can supply: 100AH / 20h = 5A for 20 hrs. An important note is this is normally rated at about 70F so you need to consider temperature effects as well.

Enough book writing again...sorry guys. I could blab about this crap for hours, lol

Slim357

Keep going very useful info bro

hankthetank

my inverter has an auto shut down when it sees a too much of a voltage drop from the battery.