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Posted: 10/12/2004 8:35:48 AM EST
In researching alternative power sources for my house, one thing that stood out is the high cost of the inverter and voltage regulator. Here's my idea, please tell me why it wouldn't work in concept:

Intead of one large expensive inverter, use 10 or 20 cheap car inverters. They are 400 watts/800 watt surge. modified sine wave form, 90% effeciency, with low voltage shutdown at 10 volts.

My concept involves a bank of 10-20 car 12 volt car type batteries with each one being independantly connected to an inverter. All of the 120 volt AC output wires go into one line that goes into the home power supply/fusebox.

A ten battery system should give me 4000 watts for less than $1000. I know it can't be that easy. What am I missing guys?
Link Posted: 10/12/2004 8:37:28 AM EST
With multiple A/C sources you would have phase issues.
Link Posted: 10/12/2004 8:39:09 AM EST
[Last Edit: 10/12/2004 8:41:23 AM EST by mjohn3006]
Try using a flux capasitor. Those things are awsome.
Link Posted: 10/12/2004 8:40:59 AM EST
how do you sync them?
AC is a sin wave. you have to have all inverters functioning at exactly the same frequency and at the same curve.

if you are off a little they smoke each other.
a better bet is buy an inverter for each appliance.
Link Posted: 10/12/2004 9:24:51 AM EST
Thanks guys. I knew there had to be a catch. You just saved me $1000...and a house.

Regarding putting each appliance on an inverter, is there any reason why you could not hook up the inverter to a bunch of batteries in parallel
Link Posted: 10/12/2004 9:38:19 AM EST
As hk940 mentioned, getting them all to synchronize their waveforms would be a major problem. Each one would be producing voltage that rose and fell based on its own timebase – when you connected them together, the waveforms would "fight" each other. Even if you could solve this problem, you'd probably have headaches with getting them all to share the load equally (a few would be overloaded and shut themselves down, causing the others to overload and shut down in short succession).

There are a few inverters that have a "strapping" option which solves these problems, but they cost a lot more than what you're trying to do.

BTW, you'd probably want something more durable than car batteries for this application, since they aren't designed for deep-cycle service and will become useless after just a few heavy discharges. Generally, the best bang for the buck is 6-volt golf cart batteries (two connected in series to produce 12 volts). They'll tolerate 500 to 750 nearly-total discharges before expiring, have a lot of storage capacity, and yet only cost $60-$75 apiece. Most golf cart shops sell them (the Trojan brand is strongly recommended).

If you're looking for a cheap inverter, consider buying a large used UPS at a thrift store or from e-bay. Many folks throw them out after they discover how much it costs to replace the gell batteries (which wear out every few years). However, you can use a bank of large, Deep-Cycle batteries to power them instead, resulting in a UPS that will produce rated output for many hours or days (instead of minutes). If you buy one on e-bay, ask the seller to remove and discard the gell-cells before shipping it, so you won't be paying the shipping costs on a lot of useless weight.
Link Posted: 10/12/2004 9:40:08 AM EST

Originally Posted By BillofRights:
Regarding putting each appliance on an inverter, is there any reason why you could not hook up the inverter to a bunch of batteries in parallel



I have no experience with these small, cheap inverters - but reading the manual for one might indicate that there are limits to the amount of input current you are allowed to safely apply. There's definately a limit as to how much current you can get out of them.

Remember, buying quality means only having to cry once. Cheap invererters are cheap for a reason.
Link Posted: 10/12/2004 9:45:07 AM EST

Originally Posted By BillofRights:
Thanks guys. I knew there had to be a catch. You just saved me $1000...and a house.

Regarding putting each appliance on an inverter, is there any reason why you could not hook up the inverter to a bunch of batteries in parallel



You can, in PARALLEL, but make sure you use deep cycle batteries such as Optima Marine batteries. They aren't cheap though. Also, you NEED to have some way to cut off power from the service lines. You don't want to be feeding your neighbors or zapping your electrical serviceman when he works on a 'dead' line.

My bet is that you would be best served by good batteries, a good charger and inverter, and a small generator, for a system that works as opposed to a rigged up system for 1/2 price that doesn't work.
Link Posted: 10/12/2004 9:47:30 AM EST

Originally Posted By Dolomite:

Originally Posted By BillofRights:
Regarding putting each appliance on an inverter, is there any reason why you could not hook up the inverter to a bunch of batteries in parallel



I have no experience with these small, cheap inverters - but reading the manual for one might indicate that there are limits to the amount of input current you are allowed to safely apply. There's definately a limit as to how much current you can get out of them.



I don't think there is any 'input current'. 12V is 12V, the current is drawn on the OTHER side of the invertor where you are needing the power. Watts are consumed and Amps are drawn at the DESTINATION. Volts are all that is supplied. It is true that 2 12V batteries will last twice as long as 1 12V battery, in general.
Link Posted: 10/12/2004 9:48:50 AM EST
A generator and a half-dozen good extension cords - what's so hard about that?
Link Posted: 10/12/2004 9:50:17 AM EST
The problem with 'cheap' invertors is that they aren't designed for LONG-TERM use. Their sine-wave isn't usually very smooth which can shorten the life of electrical components. GOOD invertors can be run indefinately, and generate good sine waves which is the only good way to power a dwelling and it's plethora of electrical devices.
Link Posted: 10/12/2004 9:52:43 AM EST

Originally Posted By rayra:
A generator and a half-dozen good extension cords - what's so hard about that?



Generators are very inefficient if they are being run at low capacity. It is far better to run the generator for a couple hours per day at full load, (charging the batteries, running the stove, freezer and fridge, doing the laundry) and then using the batteries and invertor for the light duty work such as small appliances and lighting.

No need at all to run the thing 12-16 hours a day, and you will have a generator last a lot longer as well.
Link Posted: 10/12/2004 10:21:27 AM EST
Putting batteries in parallel can be done but usually with mixed reuslts. If you do this, you probably should diode isolate their individual battery outputs. You will also need separate charging circuits for each battery. You can make it work without these features but it is much less reliable and can actually be problematic.

Deep cycle marine batteries (or equivalent) is the ONLY way to go. Do NOT use car batteries, as they are designed for high output current but shallow discharge cycles.

Synchronizing the output of multiple inverters is required BEFORE paralleling them. Definitely better top distribute higher voltage DC and invert locally.

AC distribution versus DC distribution is one of THE great debates in electrical engineering. It pitted Thomas Alva Edison against Nicolai Tesla. What? Never heard of Tesla? That's because he lost the debate advocating DC distribution.

OVERALL COMMENT:

If you are not a trained electrical engineer and know what you are doing, you will likely hurt yourself or someone you love through fire or explosion. Batteries store LOTS of energy and if not cared forcorrectly can exploded (as in detonate!). Be careful, be wise. Go to those who know what they are doing.
Link Posted: 10/12/2004 10:53:19 AM EST

Originally Posted By Torf:

Originally Posted By Dolomite:

Originally Posted By BillofRights:
Regarding putting each appliance on an inverter, is there any reason why you could not hook up the inverter to a bunch of batteries in parallel



I have no experience with these small, cheap inverters - but reading the manual for one might indicate that there are limits to the amount of input current you are allowed to safely apply. There's definately a limit as to how much current you can get out of them.



I don't think there is any 'input current'. 12V is 12V, the current is drawn on the OTHER side of the invertor where you are needing the power. Watts are consumed and Amps are drawn at the DESTINATION. Volts are all that is supplied. It is true that 2 12V batteries will last twice as long as 1 12V battery, in general.



Oh I'm sure I could scratch up enough DC current from somehwere to blow-up any input protection and turn the inverter SCR or IGBT section into a pretty shower arc display on a cheap inverter.
Link Posted: 10/12/2004 11:09:31 AM EST
[Last Edit: 10/12/2004 11:10:47 AM EST by Torf]

Originally Posted By Dolomite:

Originally Posted By Torf:

Originally Posted By Dolomite:

Originally Posted By BillofRights:
Regarding putting each appliance on an inverter, is there any reason why you could not hook up the inverter to a bunch of batteries in parallel



I have no experience with these small, cheap inverters - but reading the manual for one might indicate that there are limits to the amount of input current you are allowed to safely apply. There's definately a limit as to how much current you can get out of them.



I don't think there is any 'input current'. 12V is 12V, the current is drawn on the OTHER side of the invertor where you are needing the power. Watts are consumed and Amps are drawn at the DESTINATION. Volts are all that is supplied. It is true that 2 12V batteries will last twice as long as 1 12V battery, in general.



Oh I'm sure I could scratch up enough DC current from somehwere to blow-up any input protection and turn the inverter SCR or IGBT section into a pretty shower arc display on a cheap inverter.



I'm confused about what 12V power source you can use that will burn up a 12V inverter.

12V is 12V. Batteries don't produce amps or watts, excepting that they store an electrical supply for other devices to use. Most DC transformers have a maximum listed mAh that they can support, but the input voltage is 120V more or less.
Link Posted: 10/12/2004 11:19:30 AM EST
[Last Edit: 10/12/2004 11:32:06 AM EST by Nozzleman]
Torf, rethink your second post. Excluding efficiency losses, watts in = watts out. Assuming a 120 watt load, the output current required is 1 amp at 120 volts, but the input current is 10 amps at 12V. 1A x 120v = 120W 10A x 12V = 120W. There really is an input current that is sucking your batteries dry!

BTW, a microwave oven uses 1200 watts. That means an input current of 100 amps at 12 volts. On top of that, it will require an inverter that can handle 1800 watts as there is a 50% increase in power required as the micro starts up. Consider this 50% as required for all inductive (motor or transformer) appliances.
Link Posted: 10/12/2004 12:18:57 PM EST


A Schaffner Surge Generator. Like the one sitting in the lab 20 feet from me.

Up to 2kA at 200V. Used in new product certification for UL, CE, IEC and others. We blow up stuff all the time with it.
Link Posted: 10/12/2004 12:31:20 PM EST
What would you be trying to run on these batteries, and how would they be recharged? The batteries would not last long at all with a constant high current drain on them.

Link Posted: 10/12/2004 12:32:43 PM EST
What was Hart and Marx doing while Schaffner was off building this??
Link Posted: 10/12/2004 12:37:37 PM EST

Originally Posted By hk940:
how do you sync them?
AC is a sin wave. you have to have all inverters functioning at exactly the same frequency and at the same curve.

if you are off a little they smoke each other.
a better bet is buy an inverter for each appliance.



This is closer to what I have thought of in the past. Wire the house DC. Use DC appliances where possible to avoid the loss throught the inverter and use individual inverters at each appliance that requires AC. You can get away with more that way if you are building a house from scratch as the lights and such could be wired for DC from the get-go. Planerench out.
Link Posted: 10/12/2004 12:43:16 PM EST

Originally Posted By Mike_Mills:
Putting batteries in parallel can be done but usually with mixed reuslts. If you do this, you probably should diode isolate their individual battery outputs. You will also need separate charging circuits for each battery. You can make it work without these features but it is much less reliable and can actually be problematic.

Deep cycle marine batteries (or equivalent) is the ONLY way to go. Do NOT use car batteries, as they are designed for high output current but shallow discharge cycles.

Synchronizing the output of multiple inverters is required BEFORE paralleling them. Definitely better top distribute higher voltage DC and invert locally.

AC distribution versus DC distribution is one of THE great debates in electrical engineering. It pitted Thomas Alva Edison against Nicolai Tesla. What? Never heard of Tesla? That's because he lost the debate advocating DC distribution.

OVERALL COMMENT:

If you are not a trained electrical engineer and know what you are doing, you will likely hurt yourself or someone you love through fire or explosion. Batteries store LOTS of energy and if not cared forcorrectly can exploded (as in detonate!). Be careful, be wise. Go to those who know what they are doing.



not quite right. Tesla advocated AC edison advocated DC. Tesla won. But tesla was a poor imigrant and edison bought teslas patents. Tesla designed the AC motors and the AC station in niagra falls. HE was probably the greatest mind in electrical engineering history. Edison was like bill gates, rich enough to buy the other guy out if he was wrong.
Link Posted: 10/12/2004 12:50:42 PM EST
[Last Edit: 10/12/2004 12:57:44 PM EST by Nozzleman]
The fly in the ointment is the higher current resulting from the use of 12 volts. To counteract the I2R losses (voltage drop and heat), very large Ga wire must be used, or you must put the battery right next to the appliance. The higher the voltage, the lower the current. The higher voltage has less drop so smaller Ga wire can be used. We're really talking about spending more time and money than it's worth!!

High end RV's use a pure sine wave 5KW inverter with automatic sensing circuits that turn on the generator to charge the batteries when they get low. $$$$$$$ but works great!

Link Posted: 10/12/2004 1:24:04 PM EST
[Last Edit: 10/12/2004 1:26:50 PM EST by Skibane]

Originally Posted By Mike_Mills:
Putting batteries in parallel can be done but usually with mixed reuslts. If you do this, you probably should diode isolate their individual battery outputs. You will also need separate charging circuits for each battery. You can make it work without these features but it is much less reliable and can actually be problematic.



Not true. In RV, marine and home power applications, several deep-cycle batteries are usually connected in parallel, simply because one battery alone rarely has sufficient storage capacity. Nobody uses isolation diodes, and most banks are recharged simultaneously, using a single charger.

It is true that several parallel-connected batteries of widely differing sizes, ages or plate chemistries will tend to share the load unequally, but this is almost never a consideration (let alone a problem) in a bank of identical batteries.

BTW, if you haven't discovered it already, Home Power Magazine is an excellent resource for info on inverters, batteries, solar panels, regulators, generators, and other alternative energy topics. They have most of their back issues available on CD-ROM – lots of expertise, product reviews and advice.
Link Posted: 10/12/2004 2:04:19 PM EST
nozzleman and skibane know the deal. You pocket protector types are overthinking the problem(as usual).

Grab a West marine catalog, there is an information section that will illustrate what you need to know and how to accomplish it, and products that will do what you want.

big ass boat or Rv can be just like your house, in some cases they are where people spend a great deal of time with all ameneties.
Link Posted: 10/12/2004 2:20:47 PM EST
[Last Edit: 10/12/2004 2:23:25 PM EST by wildearp]

Originally Posted By Torf:

Originally Posted By BillofRights:
Thanks guys. I knew there had to be a catch. You just saved me $1000...and a house.

Regarding putting each appliance on an inverter, is there any reason why you could not hook up the inverter to a bunch of batteries in parallel



You can, in PARALLEL, but make sure you use deep cycle batteries such as Optima Marine batteries. They aren't cheap though. Also, you NEED to have some way to cut off power from the service lines. You don't want to be feeding your neighbors or zapping your electrical serviceman when he works on a 'dead' line.

My bet is that you would be best served by good batteries, a good charger and inverter, and a small generator, for a system that works as opposed to a rigged up system for 1/2 price that doesn't work.



Optima makes a deep cycle RV battery (yellow) and a marine (blue). Not the same.

Your best bang for the buck is getting 6 volt lead/acid golf cart batteries and connecting them in series/parallel. Why, you say? Two 6 volt batteries make one 12 volt battery with huge plates in each cell. This is much more efficient that two 12 volt batteries in parallel with smaller cells and plates. I did this on my RV and can now run my TV and heater all night. The 6V batts are hell cheaper than optimas.
Link Posted: 10/12/2004 2:34:49 PM EST
What are you trying to power? Pure resistive loads like incandescent lights, electric stoves, toasters, water heaters, etc. won't even notice if it's DC. Things that are just motors, or motors with heaters, like refrigerators, air conditioners, washers, dishwashers, etc. MIGHT not notice depending on what kind of motor it has. It's the TVs, computers, stereos and such that will require AC. You might be able to get away with running 10 deep cycle batteries in series to power most of your stuff, with an inverter for a couple of things.

However, charging the whole stack of 10 would require a steady 140 or so volts. A 120 source, like a generator with a good DC converter, could probably only charge 8 at once.
Link Posted: 10/12/2004 2:56:17 PM EST
Ok, Just wanted to touch on a few points here, many of which have been talked about....

Tesla vs. Edison:

Edison was pushing D.C. for power distribution. Tesla(with Mr. Westinghouse) was pushing A.C. .
DC (as was stated before) is a poor choice, due to the large power losses. Edison was by far the more famous personality Who had the backing of friends like Henry Ford, and not the nicest guy in the world. He went around the country electrocuting animals, to show the "dangers" of using A.C. .

AC was shown to be the better choice for power distribution, and eventually won out.

Tesla is the inventor of Our modern AC system, The induction motor, Florescent lights, Radio (nope!, it wasn't Marconi!! Supreme court 1945) and many other things we enjoy today.

Please don't try to use DC for house wiring!

And Please do not follow this line of thinking....
I don't think there is any 'input current'. 12V is 12V, the current is drawn on the OTHER side of the invertor where you are needing the power. Watts are consumed and Amps are drawn at the DESTINATION. Volts are all that is supplied.

A load on the AC side on an inverter(Destination), draws amperage on the DC side of an inverter(Input). Yes you need 12vdc, but you ALSO need large Amp capacity too.

Above all, PLEASE be careful! even a 12v car battery packs a lot of energy, and WILL explode(Big Ba-Da-Boom!).



YMMV,
Tall Shadow
Link Posted: 10/12/2004 3:00:06 PM EST
[Last Edit: 10/12/2004 3:01:21 PM EST by Garand_Shooter]

Originally Posted By Planerench:

Originally Posted By hk940:
how do you sync them?
AC is a sin wave. you have to have all inverters functioning at exactly the same frequency and at the same curve.

if you are off a little they smoke each other.
a better bet is buy an inverter for each appliance.



This is closer to what I have thought of in the past. Wire the house DC. Use DC appliances where possible to avoid the loss throught the inverter and use individual inverters at each appliance that requires AC. You can get away with more that way if you are building a house from scratch as the lights and such could be wired for DC from the get-go. Planerench out.



+1

There are plenty of 12v appliances out there, between them and using propane powered hot water, fridge, and freezer you can do 80% of your load.

Check RV stores for 12v appliances.
Link Posted: 10/12/2004 3:00:12 PM EST
Your paralleled inverters won't load share. One will go into current limit.
Link Posted: 10/12/2004 6:43:06 PM EST
You guys are absolutely correct about my error in the Edison-Tesla debacle. My bad.

The more I read this thread the less I want to participate in it because it is very clear MANY of you have ABSOLUTELY NO CLUE ABOUT ELECTRICITY (DC or AC). Perhaps it's even worse than that, you know enough to do some real damage to yourselves and/or others. Someone is going to get hurt or killed. I'm not kidding.
Link Posted: 10/12/2004 6:47:28 PM EST
plugging capacitors in backwards is always fun too
Link Posted: 10/12/2004 10:04:35 PM EST
Thanks for the tip, Wildearp, I will consider using the Golf cart batts, if I ever get off my ass and do the project. More importantly, I bet a GC batt would work great in my daughters mini jeep.

Thanks Skibane, Mace and the rest. I will eventually get a solar/generator alternate power backup, but will probably just wait until I have the $$ to buy an off the shelf complete system.
Link Posted: 10/12/2004 10:09:15 PM EST
[Last Edit: 10/12/2004 10:10:46 PM EST by gaspain]
those car inverters would never stand up to the current required from most household appliances, it would be a fire hazard. [fire]
Link Posted: 10/12/2004 10:22:21 PM EST

Originally Posted By BillofRights:
Thanks Skibane, Mace and the rest. I will eventually get a solar/generator alternate power backup, but will probably just wait until I have the $$ to buy an off the shelf complete system.



Good decision.
Link Posted: 10/12/2004 10:23:17 PM EST
ebay has some killer deals on this sort of stuff. check it.
Link Posted: 10/12/2004 10:58:16 PM EST
Why Not just Hook A Capicator Up To your Power Meter in your house and Shift The Phase to 55 hz .
Link Posted: 10/12/2004 11:06:54 PM EST

Originally Posted By Rob877:
Why Not just Hook A Capacitor Up To your Power Meter in your house and Shift The Phase to 55 hz .



huh?
Link Posted: 10/12/2004 11:17:53 PM EST
[Last Edit: 10/12/2004 11:25:48 PM EST by Rob877]
I Guess It Works I Have Never Tried It. My Industrial Electricity Instructor Was An Electrical Engineer And He Was Telling Me About How People Steal Electricity. What I Understand IF you Hook a Large Capacitor to Your Service Panel It Will confuse Your Power Meter and Cause the Meter to turn slower. You will Still Have 60 HZ Coming In To your House but the Power Meter Will think You Have 50 HZ or 55HZ.
Link Posted: 10/12/2004 11:22:39 PM EST

Originally Posted By gaspain:

Originally Posted By Rob877:
Why Not just Hook A Capacitor Up To your Power Meter in your house and Shift The Phase to 55 hz .



huh?



For Got To Use Spell Check
Link Posted: 10/12/2004 11:26:50 PM EST
[Last Edit: 10/12/2004 11:28:02 PM EST by gaspain]
yea but thats stealing, and the risk is HIGH!

Have you ever been to jail? LOL

eta: also the wrong cap could overheat and burn your house down
Link Posted: 10/12/2004 11:31:17 PM EST
[Last Edit: 10/12/2004 11:33:22 PM EST by Rob877]

Originally Posted By gaspain:
yea but thats stealing, and the risk is HIGH!

Have you ever been to jail? LOL

eta: also the wrong cap could overheat and burn your house down



Yep stealing Is wrong
cap could overheat = True
Micro Wave Oven Trans Formers Also Over Heat And Burn Houses Down
Link Posted: 10/13/2004 5:12:50 AM EST
Phase is the sin-cos condition of the sinusoidal waveform at any given point in time.
OR relative to a reference point, i.e. another waveform.

55Hz is the frequency of the waveform, not the phase.

The rule: ELI the ICE man

in a inductor, voltage will lag current 90d

in a capacitor, current will lag voltage 90d


What your saying is incorrect. Adding a cap will not change the frequency.

Link Posted: 10/13/2004 6:20:48 AM EST

Putting batteries in parallel can be done but usually with mixed reuslts. If you do this, you probably should diode isolate their individual battery outputs.


Yup. I trashed two deep cycle batteries. I figured to power my Kenwood tranceiver, two in parallel would be better than one. Problem is even in identical pairs of batteries, there will be tiny differences in voltgage. So one battery will always see the other as needing charging. So the two are constantly in a tug of war, draining one to top off the other.

Here's a pointer to pretty comprehensive look at 12 volt power, lighting, communications, refrigeration

http://www.caravanandmotorhomebooks.com/books/motorhome_electrics_caravans_too.htm

Also go to www.homepower.com, resources for anyone off the grid.

Link Posted: 10/13/2004 6:36:59 AM EST

Originally Posted By Tall_Shadow:
Ok, Just wanted to touch on a few points here, many of which have been talked about....

Tesla vs. Edison:

Edison was pushing D.C. for power distribution. Tesla(with Mr. Westinghouse) was pushing A.C. .
DC (as was stated before) is a poor choice, due to the large power losses. Edison was by far the more famous personality Who had the backing of friends like Henry Ford, and not the nicest guy in the world. He went around the country electrocuting animals, to show the "dangers" of using A.C. .

AC was shown to be the better choice for power distribution, and eventually won out.

Tesla is the inventor of Our modern AC system, The induction motor, Florescent lights, Radio (nope!, it wasn't Marconi!! Supreme court 1945) and many other things we enjoy today.

Please don't try to use DC for house wiring!

And Please do not follow this line of thinking....
I don't think there is any 'input current'. 12V is 12V, the current is drawn on the OTHER side of the invertor where you are needing the power. Watts are consumed and Amps are drawn at the DESTINATION. Volts are all that is supplied.

A load on the AC side on an inverter(Destination), draws amperage on the DC side of an inverter(Input). Yes you need 12vdc, but you ALSO need large Amp capacity too.

Above all, PLEASE be careful! even a 12v car battery packs a lot of energy, and WILL explode(Big Ba-Da-Boom!).



YMMV,
Tall Shadow



You totally misunderstood what I said. Obviously a 12V battery that is rated for 10Kwh will last longer in any application than 8 1.5V that are rated at 1800 mAh.

A 300 Watt invertor will work with any normal 12V source, but it won't work for very long if you are using 8 AAA batteries and running a TV. You'd be lucky to get the thing to start.
Link Posted: 10/13/2004 8:28:56 AM EST

Originally Posted By Mike_Mills:

AC distribution versus DC distribution is one of THE great debates in electrical engineering. It pitted Thomas Alva Edison against Nicolai Tesla. What? Never heard of Tesla? That's because he lost the debate advocating DC distribution.



Actually it was Tesla who won out with AC, and Edison who lost with DC.
Link Posted: 10/13/2004 11:52:25 AM EST
I have already acknowledged my error relative to this historical fact. Move on.
Link Posted: 10/13/2004 12:48:59 PM EST
Torf - There will be current on both sides of the inverter if anything is "running" on the output side.

Ohm's Law E=IR, Voltage = Current xResistance You short that battery and you'll see a lot of current as it welds things together as it is heading to zero resistance

think of it as the transformer in a model RR but going the other way
Link Posted: 10/13/2004 1:01:57 PM EST
[Last Edit: 10/13/2004 1:03:45 PM EST by Torf]

Originally Posted By PaDanby:
Torf - There will be current on both sides of the inverter if anything is "running" on the output side.

Ohm's Law E=IR, Voltage = Current xResistance You short that battery and you'll see a lot of current as it welds things together as it is heading to zero resistance

think of it as the transformer in a model RR but going the other way



I agree with that. This was in context of hooking two or more batteries together for more runtime on a 300W invertor. In that instance, the input voltage is 12V and as long as the current 110V/300W is less than 2.73A, there won't be a problem. The Invertor itself will cut off at extended 300+ watt loads. Most of these invertors will spike up to 600W with no damage either on the input side or the output side.

In this case I am assuming we would need an input cable that is capable of handling 25A correct?
Link Posted: 10/13/2004 2:01:12 PM EST
[Last Edit: 10/13/2004 2:09:09 PM EST by Boomholzer]


And Please do not follow this line of thinking....
I don't think there is any 'input current'. 12V is 12V, the current is drawn on the OTHER side of the invertor where you are needing the power. Watts are consumed and Amps are drawn at the DESTINATION. Volts are all that is supplied.
A load on the AC side on an inverter(Destination), draws amperage on the DC side of an inverter(Input). Yes you need 12vdc, but you ALSO need large Amp capacity too.



Here is how to calculate the current on both sides given a known load.
The input side is 12V and output is 110V in this example.

We want to power a 50W light bulb in your house, I'll add 5W of line loss to even the numbers.

P/V=I

55W/110V=0.5A

First, model it as a 100% efficient unit.

Pin=Pout
VI=VI

ex) 12V*4.6A=110V*0.5A
Low side will be high I, High side will be low I

Now use 75% eff for the conversion efficiency of the inverter
P/n
.......so your 12V load will be 6.1A to run a ~50W light bulb on house juice.
Link Posted: 10/13/2004 2:13:06 PM EST
Ok, not trying to hijack the thread but I have a quick question about a statement on pg 1. My battery is about to give out on my UPS for my computer. Not fitting into the UPS housing aside, can I use a deep cycle marine battery to replace it for a longer run time??
Link Posted: 10/13/2004 2:39:39 PM EST
[Last Edit: 10/13/2004 2:40:52 PM EST by Andrewh]
nevermind
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