Large inverter

[48Rob]

I'm considering a 3000 watt continuous inverter for a work truck.
I realize the truck will need to be running so the alternator will be able to keep up, but am concerned that the standard truck battery will not.

The unit won't get real heavy use, just now and then for 30minutes or so at a time.
Most loads will be 8-10 Amps (a/c).
This should be a 1200 watt draw on my 12 Volt system, right?

Do I need to add a deep cycle battery(s) to provide enough power?
I'd also like to mount the inverter in a tool box, a 12' wire run from the battery, too far, even with heavy #2 stranded copper cables?

And finally, like anything else, you get what you pay for...
I'm looking at an inexpensive inverter that costs a few hundred.
If I spend several thousand dollars, I'll get a much better unit, but for light use, not powering expensive electronics, is there any reason not to get a cheaper unit?

Anything else I'm not thinking of, or general thoughts?

Thanks.

Rob

[Miriam C.]

Go diesel? How's your truck going to like all that running? You might do better with a generater...Again Diesel if you can.

[fromeo]

Rob,

Couple of thoughts come to mind..

I'm assuming you want to run some power tools. Modified sine wave inverters cause some motors to run slower. Some motors also apparently run hotter. This is not necessarily a problem, but something to keep in mind.

A 10A AC load will yield right around a 120A DC load. Percentage wise, mid-80's efficiency is fairly common for inverters. Have to pull up a wire resistance chart and do the math to get hard numbers, but off the top of my head, at 12' I think I would lean towards 0AWG.

Alternators lack current output at idle. Even a fairly beefy 140A or so stock alternator is going to have a hard time keeping up with more than a 30-40A load @ idle. There's ways around this - raise the idle speed (like a pto application does, may not be the greatest thing for your engine, cooling system may have a hard time keeping up sitting still), multiple alternators, battery banks, different diameter pulleys on the alternator, custom wound alternators.. For some ideas, take a look at guys that run very high powered car audio systems, or other high load vehicles like ambulances (the former very easy to find online, but lots of folks with no real clue also).

When considering a high amp installation like this you also need to take a look at the wiring under the hood. Most factory wiring is on the light side. You would want to look at upgrading (bigger gauge) the cabling from the alternator to the battery and the ground cables as well.

The simplest, and probably least expensive way to do this is a small generator. Knowing they have downsides, namely having to haul it, haul extra fuel, risk of theft/hard to hide, the inverter may make sense.

The biggest factor is obviously the load. The next biggest will be your duty cycle. If you're going to drill a hole here and there, you can probably sneak by with just wiring the inverter up using fat cables, and I'd consider beefing up those charging cables under the hood too.

If you are going to be running something 10A AC for a solid half hour (say shop vac) then you are going to have to look at a battery bank in the box with the inverter, and keep it charged through an isolator. If you are finding you are using it a lot, a second or custom alternator might be in order.

- Frank

[48Rob]

Miriam and Frank, thanks!

The general use for the inverter will be 5-10 minutes at a time, once a month on average, with a 15-30 minute run a couple times a year for a trash pump or larger draw tool.
Convenience is the goal, along with relatively low cost.

I have several generators, but they are used so infrequently that they sit in the shop.
When we're on a job and can't borrow power from a neighbor, an inverter already on the truck makes sense, much more so than going back to the shop for a generator.
If in my job I could plan ahead, life would be easier, but I never know what the day might bring.
I've actually had a small one on my truck for years, but wanted to upgrade as a 750 doesn't run much...

I'll read through and absorb your comments Frank, when I get off work tonight.

Thank you for taking the time to spell it all out for me.

Rob

[vreihen]

Rather than having to upgrade the truck's DC system to drive a huge inverter, perhaps a PTO-driven generator might be worth the investment? There is at least one company (Real Power?) that makes PTO-driven generators capable of powering a whole house that permanently mount under the truck, so it will always be with you wherever you drive. If you have to upgrade the truck's alternator, buy batteries, and invest in a huge pure sine wave inverter, stepping up to a PTO generator might not be a huge price jump.....

[ERV]

Hi Rob
I have a 2000 watt inverter in the back of the truck to run power tools when I build decks. Some of them are at new houses with out power to the back yard yet. And some where the people are not home to let me in for power. I do this as a side job. Right around 10 decks a year.
My first set up was just the inverter in the back of the truck, and a #2 wire running back to it. Worked fine for me. It will put a load on your truck battery and alternator tho.
Now I am running two deep cycle batteries in the back of the truck. I just went to this for camping, can run a hot plate and coffee maker with out worrying about running the truck. And it gives me a battery for running the electric motor for the canoe.
Most inverters have an automatic shut down if it get hot or the battery is getting low. The thing I have found about mine is it wants to be kept cool.
The other thing you need to do is fuse the line going back, one in front and one by the battery. If the wire gets a short in it, this will save your inverter and truck battery, alternator. I also have a switch front and back. The batteries are charged of the truck when it is running, just don't want them to over charge.
This will be the third truck I have setup this way. Same inverter. Thinking of going to a bigger one, but the cost goes up pretty good for them. And from what I am reading, you don't get that much more range. Might even run another one in parallel with the one I have. Still looking into that.
Look on ebay for some pretty far pricing. Hope this helps.

[ERV]

Rob
Just read Franks reply. He is right about the load you put on it. So far I have not been able to out work my inverter. Getting old. About the only thing I run for a long time is my router. I do all the edges on my decks with it. Makes them look a lot nicer.
And this time of year I have to start running lights too. It is getting dark faster, hate this time of year.
From what you are saying, I think you can get away with an inverter if you set it up right.
I use a shop vac all the time to get water out of my post holes so they can be inspected. Some of the cities around here come out to look at my work 3 to 4 times. Just for a deck.

[48Rob]

Thanks for all the replies and help!

I ended up with a 2000 Watt (4000 watt peak) inverter.
I have it connected to a 100 Amp hour deep cycle battery.
I tried it out today on a job using my 10 Amp Sawsall for about ten minutes.
It worked very well, with no problems.

Next, I need to mount the battery and run heavy cable.
I'm going to buy/install a battery isolator so the deep cycle can be recharged by the truck after use.

I found this one, which seems to be a pretty good one.

http://www.powerstream.com/battery-isolator.htm

Any thoughts or opinions with regard to ordering it?

Thanks!

Rob

[ERV]

I looked at those when I started putting mine together. Very good idea. How ever I am old school and use a switch under the hood and one in the back of the truck. I don't like things that can break, or stop working.
Have not had a problem with it yet. But I do use mine a lot, so I guess I just got use to turning it on and off. I also have front to back fused.
The thing I worry about most is the wire grounding out along the frame. I tried to run it so it would not get damaged when I go off road, but you never know.
One thing I can tell you is, if you are using it hard keep your truck running. My alternator is pretty big. I don't like the batteries to get hit with a big charge that heats them up. So I run all three batteries when I am working them hard.
When I have used the inverter, the drive home is usually enough to charge things up. At home I plug the truck in every night. I am setup to charge the batteries and all my Dewalt tool batteries. On the big batteries I have a battery tender. And now that I have a cap on the new truck, I also have a small electric heater in the back just to keep it above freezing. Easier on all my tools.
The other nice thing about switches, I can start the truck off of the back batteries, some times I do forget to turn the lights off, ha.
P.S. The other thing about an inverter in your truck, you can run your furnace, frig. and a few lights when the power goes out. ( not all at the same time) It has come in very handy here in our area. Seems like I have used it every winter so far.

[48Rob]

Erv,

Thanks!

I considered a switch...but reality quickly reminded me that I'm forgetful...

Rob

[fromeo]

Rob,

That should work just fine. You may be able to find a simple continuous duty solenoid/contactor/relay (whatever you want to call it) without the little control module for less money. Wire the coil to a source in the truck that is hot in run but not start. Just an option.

- Frank

[48Rob]

Thank you Frank!

Rob