Power inverters and their uses

drchefscott · 02-06-2009, 10:31 AM

Ok Skoolies..

What size power inverters do you use? What do you have connected to them (appliances, lighting, etc)?? And what supplies power to your inverter: Generator, solar/wind, shore power, bur batteries??

I would love to see some pics here if you would share.

Thanks.

Scott

the_experience03 · 02-06-2009, 10:37 PM

Quite a few of us have the same inverters, actually, thanks to a deal on eBay a couple years ago. I run a pair of them myself. I think they are 700 or 750 watts apiece. I run one heavier circuit (fridge and TV, etc) on one and then my other two circuits (mostly lighting and other misc. outlets) on the other inverter. My power comes from a pair of golf cart 6 volt batteries wired in series which I charge using one of several methods. First, I can run all my 120 volt stuff separate of the inverters using shore power or a generator. When I'm doing that I can put my maintenance charger on the batteries just to top them off. I also charge them using the bus alternator when necessary. The last route I take is charging them is my tractornator which is a hacked up old lawn tractor that spins an alternator providing a much more cost effective way of getting 12 volt charging voltage than running a 6.6 liter turbodiesel.

drchefscott · 02-07-2009, 06:56 AM

Thanks. I would love to a picture and a better explaination on your "tractornator". Sounds pretty cool. And maybe a cheaper alternative to a generator. You said you run multiple invertors. I never thought of doing that. A few years ago I was in Jacksonville, Fl. at a pawn shop and picked up a 900w/1800w inverter for $80. It was placed in a van I had until I sold it (van) and took it our. Now it sits in garage awaiting its next home. A few times the wife asked me if I was ever going to install it in something. When we agreed on the bus,m that was her first thought: THE BUS!! I was thinking of upgrading to a larger one but wanted to bend a few ears here and see what everybody else did. Maybe I will add a larger one, instead of just upgrading.

Thanks.

Scott

the_experience03 · 02-07-2009, 05:22 PM

Behold, the mighty tractornator.

A 6.6 gallon boat gas tank sits in the top rack and the jumper cables clipped to it go to the house batteries.

It really is a simple setup using a GM 1 wire alternator, a 34 inch long A-belt, a pivot bolt on the frame, and a turnbuckle to tension it.

And these are the controls. The throttle also contains the choke linkage. Flicking the switch off grounds the engine's coil and will kill it at 1/2 throttle or less. The starter button actuates the starter solenoid. The engine actually cranks off the power in the batteries you're going to be charging so you can't run them too low. Once it fires you rev it up to full throttle for a few seconds to excite the alternator and then you can idle it way back down and it will output just fine.

drchefscott · 02-08-2009, 07:56 AM

Thats pretty neat!! I like it I do....!! Gave me a few ideas at something I'm looking into developing for another method of keeping a bank of batteries charged. Waiting for my friend to get back to me with a few technical ideas. The main components: A low amp (Harbor freight tools) 110v motor, an auto or bus alternator, a tensioner pulley, a power disconnect, a power inverter and another piece. Thats what I'm waiting on the technical advice on... the other piece. It would be set up as follows: The alternator, tensioner pulley and 110v motor woould be connected with a belt. The motor would be connected to the power inverter (via plug) and the alternator to the battery bank. The battery bank would be connected to the disconnect and the disconnect to the inverter. Basically a completed loop. The missing link would be a sensor that would determine when the battery gets to a low level and would activate the motor to recharge. And automated system sorta without the need for monitoring or outside fuel. He mentioned a surge guard but didn't have time to talk. Maybe Monday. He did say that nice thing about a loop like that is as you add batteries, you could add a larger belt and additional alternators for more charging power to different battery bank sections. And the motors are pretty quiet compared to a generator so if it was done in an insulated box, it may not even be heard in the cabin, or very little.

Ray_WA · 02-08-2009, 11:28 AM

This'll work, if you order the 110 motor that puts out more power than it consumes!

Seriously... you're not serious! Are you?

-Ray

crazyidea · 02-08-2009, 12:13 PM

If I understand this correctly then it wouldn't work. You convert energy with a loss and you can't get something for nothing.

lapeer20m · 02-08-2009, 02:21 PM

i agree that it won't work. there is always a loss when you convert energy from one form to another. using a battery to power a motor to charge the same batteries is just like going back to the concept of running your engine from "an hho generator"

drchefscott · 02-08-2009, 07:11 PM

Oh well. Back to the creative drawing board. Gotta give me credit for trying. And like I've said before, many heads are better than 1... especially when they are experienced Skoolie Heads!!

Thanks.

Scott

Anomalous · 02-08-2009, 09:09 PM

Whenever you have a novel idea for a power system, take some time to step back and evaluate it from a high level perspective.

Forget about all the details of how it works, and look at the system in terms of energy. The amount of energy going into a system is always exactly equal to the amount of energy coming out of a system. There is no way to either create or destroy energy. It is possible to store energy of course.

Don't be fooled by efficiency numbers. If you see that an inverter is 90% efficient, all that means is that 90% of the incoming 12V electricity is converted into 120V electricity, and the other 10% is turned into heat. Energy in is still exactly equal to energy out when you count both the output electricity and output heat. It's just not all necessarily in the form that you would prefer.

In your proposed system, you have electricity coming from a battery. That electricity first runs through an inverter, which outputs perhaps 90% electricity and 10% heat. Then your electricity goes through a motor, which is perhaps 90% efficient in converting electricity to motion. Then you have an alternator, which seem to be around 60% efficient in converting motion into electricity. Finally, you put the power back into the battery, which charges at perhaps 90% efficiency.

So for each 'loop' through the system, you've converted a given quantity of electricity into approximately 56% heat, and 44% electricity which is put back into the battery. So what you've designed is really just a complicated electric heater.

Note that to evaluate the feasibility of this system, you really don't have to look at all the components like that. You can lump everything together, and look at it as a whole. So you have this black box with a battery, inverter, motor, and alternator in it. What energy is coming into the system? None at all. So what energy is going out? At best, it could only output whatever stored energy it started with, which would be the charge of the battery.

Or you can consider the inverter, motor, and alternator as one system, and the battery as separate. So what energy is going into the system? Just power from the battery. And what energy can come out of the system? Well, there's no stored energy in there, so the energy coming out will always be equal to the energy going in from the battery. So even without knowing the details of the components, you could see that you're not going to be generating electricity using this. In reality, a large portion of the energy you put into it in the form of electricity will instead come out as heat, so overall you will lose electricity.

I want to point out that I'm not going into all this detail in order to say that your idea is stupid. I'm trying to show how you can step back and evaluate things from a higher level perspective, instead of getting wrapped up in the details. There are a lot of alternate energy schemes that can be easily discredited by considering them in terms of energy in and out.

Redbear · 02-08-2009, 09:39 PM

We actually did this, sorta-kinda, in a State motor home with Flintstone-era teleconference equipment. It had 2 Sony TV's - a VCR - one or two DirecTV modems - an industrial cube Windows 3.1 PC with tele-conference PC board - and a 'web cam' type camera.

All this was mounted in a corner cabinet. There was a small UPS added inside to prevent power hiccups from losing sync on video signals. With all the power and signal cords, and the cramped space, one of the other techs had managed to plug the UPS into itself. It worked fine for quite a while, as the battery slowly discharged. The UPS finally sounded an alarm, which seemed to be for "no apparent reason." Tearing into the wiring, I found the OOPS on the UPS.

Seriously, If you hooked up your closed loop to fully charged batteries, with nothing else connected, it would sooner or later drain off the entire charge. The efficiency loss of the inverter, the heat generated in the motor, alternator, and wires, and the friction of the V-belt would each take a little bit of the energy stored in the batteries, without putting it back. Any outside load would draw additional power out of the batteries, with no replacement.

drchefscott · 02-09-2009, 07:41 AM

Being I'm far from an Edison or a Franklin when it comes to electricity, I think of something and draw it out. I figured most of you Skoolie Veterans have either tried it yourselves or seen others make these same mistakes. I will figure out something that will work for me eventually. I don't need to reinvent the wheel just need to keep as much cabbage in my pocket as I can so I would rather talk about it here and look a lil foolish than talk about it here already having been a financial fool.

Thanks everybody.

Scott

Ray_WA · 02-09-2009, 11:17 AM

Absolutely the right attitude to have!

-Ray

newbusser · 04-12-2009, 07:38 PM

I absolutely LOVE your idea! Even though it won't work, it is the thought process that you went through that impressed the daylights out of me

I learned a lot from the various responses and am gratefull to you for your original posting, keep them comming...btw, you don't look foolish when you post an idea, just when you keep them to yourself.

the_experience03 · 04-12-2009, 10:37 PM

A person COULD use the electric motor hooked to shorepower to spin up an alternator to chrage the batteries. You would never have to worry about overcharging the batteries which is great. Unfortunately you would never fully charge them either...and it would probably take about a 3-4 horsepower motor to spin the alternator that fast by the time you calculate all the loses.

lapeer20m · 04-13-2009, 01:15 AM

Quote:

Originally Posted by the_experience03

A person COULD use the electric motor hooked to shorepower to spin up an alternator to chrage the batteries. You would never have to worry about overcharging the batteries which is great. Unfortunately you would never fully charge them either...and it would probably take about a 3-4 horsepower motor to spin the alternator that fast by the time you calculate all the loses.

would never fully charge batteries with an alternator? i don't understand

the_experience03 · 04-13-2009, 07:38 PM

Alternators base current output on sensed voltage. As the voltage of a battery approaches it's fully charged state an alternator will trickle it's current down to nearly nothing. For starting cars and such it's not a problem at all. The batteries are easily charged to a 90-95% state of charge all the time. However, with a deep cycle application things can get a little dicey doing that. The electrolyte might become stratified. Sulfation of that last 5% or so will occur. The problem with that is that then that last 5% basically gets taken out of the picture...so now we're charging 95% of our original battery capacity to a 95% state of charge. And so the cycle continues...

I really like alternators as a form of battery charging. I just wouldn't count on one as my primary means of charging unless I knew the small, but certainly existent limitations.

nickverge · 04-16-2009, 08:46 AM

Does anyone have any experience with this model:

http://cgi.ebay.com/NEW-VECTOR-3000-600 ... 1|294%3A50

I am thinking about ordering one.

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