what is needed to turn 12 volts ac into 120 dc

This entry was posted on September 23, 1999.

Organization Components for the Homemade AC/DC Generator Arrangement

• Gas (or Propane) powered engine
• Direct drive shaft couplers
• AC generator caput, 3600 RPM
• GM alternator, 12 volt or 24 volt
• Industrial V Belt
• Pulley (similar to shown)
• Horizontal Shaft Alternator bracket (Epicenter's ain!)

SUBSYSTEM Components for the Bootleg AC/DC Generator Organization

Main Components in the AC subsection

The project could cease here if DC is non required*

Components that Add DC charging adequacy

Mountain the alternator to the engine!

Add this bracket — makes it easy! Add cables for the final affect.

* Delight Note: TheEpicenter.com does not sell AC Generator Heads.

Generator Questions

Q: So why would I e'er want to build my own generator when I can just buy one ready to get?

A: That's a darn good question!

In many cases its meliorate to just lay down the cash and buy a quality Ac generator like this Generac model, just in other cases there is really no way to have everything you desire without making it yourself. That is if you need lots of DC charging and besides sine wave AC power equally well.

And then again, it might not cost as much as y'all might think to build your ideal system if yous already accept i of the key components.

You might exist one of those DIY-ers who might accept a spare engine sitting around and could use it to drive a generator caput without needing to purchase an expensive and defended Air-conditioning generator arrangement. In some cases it could be less expensive to purchase the generator head and reuse an engine from something else that you no longer have a need for, or simply need for a few months each year.

A proficient example would be a person who has a pressure washer sitting effectually that has a large engine, perhaps a high quality and expensive one like a Honda.  In that case you could remove the pump assembly from your washer and attach a generator head when needed in the winter, and in the leap you could remove the generator head and reattach the force per unit area washer pump assembly.

A better case could exist made for building a multipurpose ability generation arrangement because it is non something that you tin currently buy. In this awarding you might need to charge of banking concern of batteries as an example at the same fourth dimension equally having some Ac ability available. In this application the aforementioned engine can direct drive a generator head while belt driving an alternator for DC charging purposes.

In full general, when someone wants to charge a bank of batteries there's oft excess horsepower available which could be used to run an Air-conditioning generator caput at the same time. Or on the other manus, yous might demand AC ability to make repairs effectually the firm with power tools, or you might demand to run the microwave, refrigerator or something, and would like to charge your batteries at the same time.

Shown here at the left is a prototype of a project I'm experimenting with for my own use.

The AC generator caput is direct coupled to the Tecumseh 8 HP motor, and has a belt driven 12 volt alternator mounted to our Horizontal generator subclass which is attached to the motor. To get the full rated output of 6,000 W peak from the generator head, this particular motor is nether powered. To develop the full rated output power from this caput, the engine should really be a 10 HP model like the HM100, or better yet an 11 HP model for a bit more headroom. Of course running an alternator exclusively on this engine is an example of overkill just the combination of the lower output of AC at the aforementioned time as DC is available makes for a fairly efficient utilise of fuel and resources.

In my application, I don't require more than than 2500 watts of AC power which would ordinarily require about a v HP engine. The remaining 3 horse ability can be devoted to the DC charging subsystem using the attached alternator.

Here is another view where you tin can see the direct drive and the chugalug bulldoze components.

Permit's take a look at what's really required to make this generator head produce Ac power for specific output current levels.

For full power, an 11 HP motor is specified by the manufacturer merely other motors could be used if you practise not violate the full general rules outlined beneath. Trying to draw more power than shown beneath using an under rated engine horsepower rating will result in the generator producing an AC voltage lower than the specified output. In some cases this could cause a "chocolate-brown out" condition which could result in electrical damage to the devices being powered. Special precautions should be taken to ensure that the example horsepower ratings and output ability or levels below are not violated.

Ac generator output	Engine size required (for example purpose)
6000W elevation, 5000W continuous (full rated Air conditioning output, no DC)	xi Horse power
5000W height, 4000W continuous	8 Equus caballus ability
3000W peak, 2500W continuous	5 Horse power

So, if you lot are using an viii HP motor with this Ac generator head and can insure y'all never will use more say 2500W of Ac ability, and then there is enough horse power left to exist able to belt bulldoze a 12 volt alternator running at say 40 amps (14.iv volts x xl amps = 576 Watts) with some caput room when belt driven off the same shaft.

Although the manufacturer specifically states that to develop the total rated output an engine size equivalent to eleven horsepower is required, smaller versions of this generator head produce lower continuous ratings shown in the tabular array and require less horsepower. Nosotros have extrapolated the information shown from the specifications for the smaller generator heads, and although the larger 6000W acme caput has more than mass in the rotor, we would realistically wait that it doesn't require that much additional power to spin the rotor especially since sealed ball bearings are used on both ends of the caput.

I guess what I'm trying to say is that if you lot can guarantee that you would never try to pull too much Ac from the generator head, then fifty-fifty a small engine will not bog downwards and at that place would be extra horsepower bachelor for other uses like running an alternator as shown in the prototype.

And so, permit'due south discuss some of the issues

Typical Gas engines rate their horse ability at 3600 RPM.

If the motor is used at speeds below that rating, the engine does non develop total rated output torque and equus caballus ability.

However, running an engine at a lower RPM increases fuel efficiency and decreases wear and tear so in that location are e'er trade offs.

Y'all should also note that these small engines output shaft rotates in counter clock wise direction every bit viewed from the output shaft side of the motor. This is something that will come up up once again!

Because about engines are rated at 3600 RPM, you will notation that many generator heads are likewise designed to exist rotated at 3600 RPM.

If y'all attempt to run the Ac generator caput a speeds beneath the rated RPM of 3600 in this case, the Air conditioning output voltage volition not exist 120 volts, just will be a lower value. Some equipment you intend to power may be more forgiving about the lower voltage, some equipment might be damaged, and so it is critical that you spin the generator at the correct RPM.
More give-and-take on setting the RPM of the engine and generator head can be establish in the adjacent section.

You lot will as well want to note that the generator heads shaft needs to rotate in a clockwise direction as viewed from the shaft side of the generator head. Then, place the shafts facing each other and gauge what? Both the motor and the generator caput rotate in the correct directions. This allows for direct driving the generator head by using a shaft coupler.

Now, let'southward talk about Connecting the Motor to the Generator Head

Q: How do you direct drive a generator head with an engine?

A: Directly bulldoze shaft coupler assembly.

To connect the output shaft of a motor to a generator head input shaft (or anything else), a special shaft coupler is required. Basically, three pieces are needed.

Select a coupler one-half that is the right size to fit the motor shaft (or driving shaft size), so select a coupler half that is the correct size for the generator head (or Driven shaft size).

Then the ii shaft couplers are joined using what is chosen a spider.

Detect that the shaft couplers each take three fingers and the spider has 6 slots. The iii fingers from the motor side fit into iii of the spider slots, and the three fingers from the generator side coupler fit into the other three slots on the spider. This coupler assembly allows for several degrees of misalignment betwixt the two shafts and protect the bearings from seeing side loads that would result from misalignment.

These couplers are available in a agglomeration of sizes. Several sizes are available at TheEpicenter.com.

Q: When you're building your own AC generator using a gas engine and an AC generator head, how practise you set upwards the combination so that the system produces the correct output voltage, and turns the generator head at the correct speed?

A: There are two approaches that can be taken:

Mensurate the Air-conditioning voltage to adjust the engine RPM.

This Ac volt meter plugs directly into any Air conditioning outlet and displays the measured voltage without the demand to use a hand held DVM and jam probes into an AC outlet. The meter features a built-in Air conditioning plug on the back side.

Voltages inside the standard 115 to 125 volts range are highlighted in dark-green indicating acceptable voltage parameters. Voltages out side of those ranges are indicated in red. This meter provides an easy to read indication of the generator output voltage.
Measure the engine RPM with an inductive Tachometer, and also know when to change the oil!
This device allows you to monitor and set up the engine rpm such that it rotates at the specified RPM required by the generator caput. This is an RPM (revolutions per minute) meter or tachometer. It inductively connects to the spark plug wire and senses the rate at which the spark plug fires over a given time period. The resultant measurement is displayed in revolutions per infinitesimal. The engine rpm can then be adapted until the specified RPM of the generator head is achieved. If the RPM is adjusted to the manufacturers specification for the generator head, the rated output of the generator would so be 120/240 volts depending on the construction and specifications of the AC generator caput.

The unit shown too keeps a running total of engine usage and display the number of hours and minutes the engine has operated. While the engine produce a Spark, the RPM is displayed.  Once the engine stops running the total time the engine has operated in terms of hours and minutes is displayed. One matter to note most this Tac is that the hr meter tin can non be reset. However the cumulative run time displayed is extremely useful in deciding when yous need to perform regular maintenance such as oil changes.

Engines that don't turn at 3600 RPM

Q: What if I have an engine that doesn't turn at 3600 RPM? Tin a generator head like this be used somehow?

A: Yes! But it's a scrap more than complicated.

Belt Bulldoze Configuration

This generator head is designed with dual ball bearings to allow belt drive applications.

In this configuration, the generator bearings see a high side load and not all generator heads are built with the required bearings to handle this side load. Nonetheless, the generator caput we use is designed to handle the job.

Here is how yous would effigy out what size pulleys to employ:
Ratio of RPM = Ratio of pulley size

In more than detail:
Engine RPM / Generator RPM = Generator pulley size / Engine Pulley size.

So, knowing the generator needs to rotate at 3600 RPM, adjacent define what speed the engine needs to run at. This ratio will make up one's mind the ratio of pulleys required.

Permit's say for example that the engine is a Diesel that needs to run at 1800 RPM for full rated torque. And then plug the values into the equation and you get:

1800 RPM / 3600 RPM = one/two = Generator pulley size / Engine Pulley size.

Then, what always size pulley is selected for the generator, the engine pulley size must be 2 times that size.

The selection of caster size is too complicated by the fact that not all pulleys are available in all shaft diameters. And, the outside bore of pulley sizes is not always the effective bore when using 1 style of belt every bit opposed to using another style of chugalug. Since belts of different styles ride higher or lower in the groove of the pulley, the effective diameter of the pulley tin can change if some other type of belt is used, but the effect is seen on both pulleys then the ratio of caster size is still applicable for most applications.

If you are unable to ascertain a pair of pulleys that are standard, bachelor and requite you lot the verbal ratio, then there are three choices:
one. Yous could utilize what is called a "variable pitch" pulley, which is a pulley that allows the width of the groove to be adjusted. They are very specialized and a flake expensive. Since the chugalug is a stock-still width, adjusting the width of the "variable pitch" caster causes the belt to ride higher or lower in the groove, thus effectively adjusting the "pitch diameter" of the pulley. I mention this only for bookish reasons (so some smart ass out there doesn't beat me to the punch) because the other choices beneath are simpler.

ii. Use the pair that give you the least ratio error, then adjust the throttle of the engine to compensate. This method can not be performed by simply using a tachometer without doing some computations to correct the tac reading. A better pick would be to use a volt meter and adapt the throttle until 120 volts output from the generator is achieved.

3. You could use an intermediate shaft and a combination of two pulley ratios. This option is only needed in Farthermost cases where the ratio is such that no combinations come close, or you don't take access to pulleys that fit one of your shafts. I'm non going to discuss this much equally it gets a chip complicated, but there is an example of an intermediate shaft being used beneath.

Nosotros put together the table beneath to help y'all find pulley sizes that are considered standard in the industry. Nosotros don't stock all these sizes but tin special society one for you if you can't find one locally that fits your need. The cells marked with "X" indicate that a pulley is available in the combination of shaft and bore. Cells that are blank (or black depending on your browser) betoken that a pulley is not typically available in that combination of shaft size and diameter.

Notice that the "pulley size" shown below is the outside diameter. The actual pitch diameter depends on what belt is used. For example if an "A" style chugalug is used, they ride down in the groove such that y'all can subtract 0.25" from the size shown.

Pulley size	Shaft size
	i/2 inch	v/8 inch	3/four inch	vii/8 inch	1 inch
1.75	X	X	-	-	-
2.00	X	10	X	-	-
2.20	X	Ten	X	-	-
2.50	X	X	X	X	-
2.80	Ten	X	X	10	-
3.05	-	X	-	X	-
iii.45	X	Ten	10	X	-
3.75	X	Ten	X	X	10
3.95	Ten	X	10	X	X
iv.25	-	-	-	X	-
four.45	10	X	X	X	10
4.75	-	-	-	X	-
4.95	10	X	X	X	Ten
5.25	-	-	-	X	-
5.45	10	X	X	X	X
five.75	-	-	-	X	-
five.93	-	X	X	X	X
6.25	-	-	-	X	-
vi.93	-	X	X	X	X
7.93	-	Ten	Ten	Ten	10
8.93	-	X	10	X	10
nine.93	-	-	X	X	Ten
x.93	-	-	Ten	Ten	X
xi.93	-	-	-	Ten	Ten
thirteen.25	-	-	-	-	X
xiv.16	-	-	-	Ten	10

Here is a practical example of using intermediate shaft and dual caster arrangement

In the case shown, I was attempting to convert an induction motor into a generator (that'south something that is outlined in the booklet "alternator secrets"). The motor on the left is a one hoarse power motor which turns at 3,450 rpm when powered with 120 VAC and the motor to the right is an induction motor that runs normally at 1725 rpm.

For testing purposes, I wanted to use the motor on the left to spin the motor on the right at the correct speed then merely I could test the conversion of the induction motor, and verify the output voltage. However, the motor on the correct had a very pocket-sized caster which was frozen on the shaft and there was no mode to remove information technology. My original plan was to remove the caster and put a multi step caster on both motors and so I could accomplish the gear reduction from a 3450 rpm driving motor through 1 belt to the 1725 rpm motor. That would crave having a pulley half the size on the faster motor every bit the pulley size on the slower motor. Similar I said, I couldn't get the pulley off the motor on the right.

So, what I concluded up doing was to drive the motor on the correct through an intermediate shaft which had a multi step pulley on it. The two pulleys were of equal size so the speed on the intermediate shaft would be exactly the aforementioned as the speed of the motor on the right side. Side by side I placed a multi step caster on the motor which normally turns at iii,450 rpm (the left motor) and belt drove that to a caster groove on the intermediate shaft that was twice the size. So for each revolution of the motor on the left, the intermediate shaft would rotate i/2 of a revolution which would crusade the gear reduction from the left motor to the right motor to exist exactly one-half. Thus, when the motor on the left rotated at 3450 rpm the motor on the right would rotate at 1725 rpm.

Permit's pretend that I could have installed the correct size pulley on both motors in the first place. And lets pretend the motor on the left is a gas engine and the motor on the right is a generator caput. Then, the state of affairs is best shown with an equation:

Ratio of RPM = Ratio of pulley size

In more than detail: Engine RPM / Generator RPM = Generator pulley size / Engine Caster size.

Knowing that I needed the engine to run at 3450 rpm and the generator to run at 1725 rpm, so... 3450 RPM / 1725 RPM = ii

Then say I've got a 2" pulley that fits the engine side, that ways that the generator side needs to be twice every bit large, or iv".

Let's Accept Another Chugalug Bulldoze, for example

Here is an one-time Onan Air conditioning generator head. This beast needs to rotate at 1800 rpm to evangelize 120/240 volts AC. Most of the minor gasoline engines you'll find have their rated horsepower output specified at 3600 rpm. Knowing that the engine rpm must be at 3600 to develop full horsepower and also knowing that the Onan generator head needs to rotated 1800 rpm it becomes obvious that we tin can't just direct drive this detail generator with a gasoline engine. Some class of speed reduction is required.

For this application the same formula applies and is shown below:

Engine RPM / Generator RPM = Generator caster size / Engine Pulley size.

Knowing that nosotros would need the engine to run at 3600 RPM, and the generator to run at 1800 rpm, then... 3600 RPM / 1800 RPM = 2

Since I had a three" pulley already for the engine, I needed to decide the pulley size that would be correct or the generator shaft. Over again, from the above equation:

two = Generator pulley size / iii"

So, the Generator pulley size would need to be vi".

Wiring it up

The reward of using the Air conditioning generator caput in this project is that the AC connectors are pre wired to connectors on the back of the caput. At that place are two connectors, ane for 120 volt and one for 220 volt, each having two outlets.

• One 120 volt Duplex (two outlets) 20A Receptacle, 5-20R
• One 240 volt Duplex (two outlets) 15A Receptacle, 6-15R

The DC section tin can exist wired several ways depending on what type of alternator is selected.

The wiring depends on which alternator you choose. All 3 alternator types are shown.

Do non wire the alternator unless you are sure nearly what type you are using. If you make a mistake in the selection of the alternator or wiring diagram you run a very high gamble of damaging your battery, electronic devices, or worse nevertheless causing personal injury! Consult a parts professional for additional information!

This article is intended for educational purposes only. No guarantees are expressed or unsaid as to the accuracy of information presented here! Consult with an automotive wiring expert before attempting to comport out any wiring.

One final note: If you are using an alternator that requires an external switch, you will demand to turn off the switch prior to attempting to showtime the generator. Once the motor is running, the switch tin can be set up to the on position.

Special parts used in many of our power related tips are available here at TheEpicenter.com!

• Parts needed for the Horizontal Shaft Generator Project
• Parts needed for the Vertical Shaft Generator Project
• Parts needed for the Straight Drive Generator Projection

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