I hope I chose the correct forum (Moderator, feel free to move the thread if I'm wrong).

I'm curious how an inverter works, and what the benefit is to having one over a 12volt power supply. I can run all my radio equipment off a Saratoga Powerpanel, even have a 3 slot power point that draws its 12 volt juice from the Powerpanel (Powerpanel is basically a fuse box that has 1 point for incoming 12volt, and 5 outgoing 12volt points that can be easily connected and disconnected). What could I possibly (safely) need to use that would require an inverter? How many continuous watts and peak watts is adequate? Do I need to worry about excessive battery drain or ever alternator damage? This would be run off a 2 battery 2005 Powerstroke.

I'm finding that 400w, 500w, 700w, 1000w, 1200w, 1500w and 2000w inverters are commonly available. Other than the price increase the higher that watts, what else do I need to know before I spend my money on a smaller unit and find out I need a couple hundred more watts?

 

I am not sure about what you are asking. You are only talking about DC and an inverter changes DC to AC.
Maybe you want to know about a battery isolator?


Battery Isolators:
Many people listen to their stereo without the engine running. This often leads to dead batteries and a vehicle that won't start. A battery isolator will let you completely discharge one battery without discharging the starting battery.
Different Types of Isolators:
There are 2 main types of battery isolators. The diode based type and the relay (solenoid) type.
Diode Based Isolator:
This type of isolator is basically two very high current diodes in a heat sink. The diode based isolator has the advantage of long life and trouble free operation but many of the diode based isolators cause a .4 to .6 volt loss which means that the batteries will not charge to as high a voltage as when they are connected directly to the alternator. The diagram below shows the connection for the diode based isolator. Some diode type isolators have a fourth terminal which controls the current flow through the device.

 

Coffee maker, curling iron, perhaps?

A coffee maker would require upwards of 1500W continuous, or more.

Most inverters have at least an alarm that will tell you that the battery is getting low and may even have a low battery shut off. Never drain your battery to a level that the vehicle won't start. Boosting a dead battery and letting the alternator charge the battery puts a serious load on the alternator and can burn it out quite rapidly, to know what I mean, next time you see someone boost a dead battery, wait a minute or two and feel the alternator... HOT!

 

Simple inverter circuit shown with an electromechanical switch and with a transistor switch.

Basic inverter designs
In one simple inverter circuit, DC power is connected to a transformer through the center tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.
The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the moveable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator, was once used in automobile radios. A similar mechanism has been used in door bells, buzzers and tattoo guns.
These electromechanical inverters explain the source of the term "inverter". Early AC to DC converters combined a synchronous AC motor with a commutator so that the commutator reversed its connections to the AC line exactly twice per cycle. This results in AC-in, DC-out. If you invert the connections to a converter you put DC in and get AC out. Hence an inverter is an inverted converter. As they became available, transistors and various other types of semiconductor switches have been incorporated into inverter circuit designs.

 

Unless you need AC (or higher DC voltage) power, you don't need an inverter.

Steve

 

Thanks guys, that is the info I was looking for, just the basics. Plus I love toys I don't have a need for! But actually, it would be nice to have the option of plugging in a coffee maker or a hair dryer for the wife.

 

An inverter converts DC to AC.

A converter converts DC to DC, for either higher voltage or isolation.

Other uses of an inverter: To charge batteries for your power tools on job sites with no electricity, or for convenience.

To run small hand tools.

To operate a job site computer, etc. jd

 

Not true, a converter converts AC to DC.

 

I've often heard DC to DC supplies referred to as converters, and AC to DC supplies as rectifiers. But I have heard AC to DC supplies referred to as converters too.

 

It is true, it does both. jd

 

If you had bothered to read what I posted above we would not be having this discussion.

A Voltage Converter is another name for Transformer.
That is why it is called a Converter in an RV because it takes the 120 AC shore power voltage and converts it into 12 VDC for the Lights, recharge the battery, fans and so on. It has a Transformer inside so they started calling them Converters. An Inverter uses a Transformer also so you could call it a Converter but they do not call the Inverter a Converter for the reasons in my post above.

You said " A converter converts DC to DC, for either higher voltage or isolation."

A Transformer cannot work with DC at all so this can not be true.

We are also trying to talk about Truck, Vans and RVs here and I do not know of an application for higher DC Voltage in any of them.

 

It might amaze you, smartass, that I did read what you said. Are you any kin to Bob Ayers????
Then explain how an automobile ignition works??????


See the following:

In electronics engineering, a DC to DC converter is a circuit which converts a source of Direct Current from one voltage to another. It is a class of power converter.

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Usage

DC to DC converters are important in portable electronic devices such as cellular phones and laptop computers, which are supplied with power from batteries. Such electronic devices often contain several subcircuits which each require unique voltage levels different from those supplied by the battery (sometimes higher or lower than the battery voltage, or even negative voltage). Additionally, the battery voltage declines as its stored power is drained. DC to DC converters offer a method of generating multiple controlled voltages from a single variable battery voltage, thereby saving space instead of using multiple batteries to supply different parts of the device. jd

 

subford is right. A transformer can only work off of AC. It is called Faraday's Law. Voltage on a transformer is directly proportional to the derivative of flux through the core (the ratio happens to be the number of coil turns). The derivative of a constant current is zero, because there is no change, hence the rate of change is zero. Therefore, if you apply DC to a transformer, you will get zero volts because there is no frequency. It takes the changing magnetic field to generate a voltage, which is what comes from AC.

Now, to answer your question. I am a bit shady here, so hopefully subford can help out, but the voltage applied to a coil is technically not DC. It is constantly being interrupted, be it breaker points, or the Hall effect on solid state ignition. This constant on\off voltage applied to the coil acts like AC in that it constantly changes. It is this change in the coil's magnetic field then that generates the voltage on the secondary side.

In short, it takes a changing magnetic field to induce a voltage, which is why DC will not operate a transformer - Faraday's Law.

 

You obviously do not know how one works.
Try putting a test light on the tachometer (NEG, -) side of the ignition coil and see if does not go on and off while the engine is cranking.
This may give you a clue.
I am sorry I do not know a Bob Ayers, is he a super mechanic like me?

I must be missing something here, where did it say this was used on a truck?
I have not seen it used on any trucks that I have worked in the last 45 years of automotive work.
As was stated in my post above we did use in car radios a vibrator (they call it a buzzer) to change dc to ac then send it to a transformer and then rectify it back to a high DC for plate voltage on the tubes. I used to repair radios and TVs for a while but when on to supervising 15 Electronics Technicians and 30 Mechanics.
When you work on a RVs Converter you are talking about changing AC to DC.

I am trying to help people on this forum, but I do not think that is what you are trying to do. Therefore I do not call other posters names and will not be replying to any more of your posts.

 

In electronics engineering, a DC to DC converter is a circuit which converts a source of Direct Current from one voltage to another. It is a class of power converter.

The last I knew direct current is DC.

You both are preaching to the choir. I know all of this. An automobile ignition is DC or direct current. You stated DC current would not work with a transformer at all. If you had added "unless the output is changed to a waveform of some type", all of this would have been avoided. But your statement infers DC cannot be used at all. It is also used to drive the vibrator you mentioned. Collapsing voltage/current is what excites a transformer, and it can be driven by DC.

"If you had bothered to read what I posted above, we would not be having this discussion."
If you want to help people, why do you insult them? To me this is an insulting remark, talking down like I was a child.

You are the only one talking about trucks and RV's. The inital question was concerning inverters.

I am not impressed with anyone who spews out their credentials. To resort to this to bolster their comments shows a lack of faith in theirselves, and it doesn't change anything. This is especially true when done in a condescending, holier than thou, I'm smarter than anyone manner.

Whether or not you respond to anymore of my posts is your choice, I could care less,and rather you wouldn't if you are going to be a snob about it.