Using power from an alternator

TEG is also a passive system like a thermocouple that generates power through the differential of heat an cold

 

1. Most alternators made up until the late 80's had an internal standalone voltage regulator. Some did not, using an external regulator instead. This limited the field current going into the alternator based on existing system voltage, which in turn limits the electromagnetic force and thus the output of the alternator. Low system voltage would allow more current into the rotor, creating more electromagnetic force, as well as higher amperage output. This in turn raises the system voltage, which then reduces power going into the rotor, also reducing power output of the alternator accordingly. Power output and voltage are also affected by rpm, with some alternators not producing much output at typical idle speeds. There are tradeoffs in designs that make some alternators(or modifications), more desirable for a particular use than others.

For better or worse, nearly all vehicles made since the late 80's have been equipped with charging systems that depend on the vehicle's on board computer for voltage regulation and power output. This change occurred, in part, because automakers discovered that when the voltage regulators failed and voltage went well above the roughly 14 volts it should be, the computers got fried. The other change that occurred was a switch of the rectifier diodes from standard type to avalanche type. The latter are designed to fail quickly if voltage is too high. An alternator actually produces AC power...but at hundreds or thousands of cycles per second versus the 60 cycle AC that we are accustomed to in the U.S.. The diodes change that to DC...but I'm digressing. Remember the avalanche diodes versus standard though, cuz there is another use for an alternator that I'll get to later.

2. Read the spec sheet for the inverter. It should list the acceptable input voltage range. I'm going to say that if you're pushing 16v into a battery on anything approaching a regular basis, it will live a very short life, which will probably end with lots of sulfuric acid on anything near the battery. There's also something wrong with the alternator or voltage regulator if it's producing that much voltage.

You could very easily set up a system as you describe. Many have done so with GM Delco 10SI and 12SI alternators, some of which were set up as "one wire" units. I wouldn't use a "one wire" setup except on the most basic of systems, mostly because they are incapable of sensing voltage at the load which is where it actually matters. In other words, if you wanted accurately maintained system voltage with a 30 amp load, at that load, then the "one wire" system is not suitable. The typical two or three wire 10/12Si is a much better choice because the voltage sense wire can be connected at the load. For your application, this probably doesn't matter, but it is something to consider. The main reason I mention these particular alternators is that they are incredibly common and cheap. I looked a while back, and if I remember correctly, a 94 amp 12SI from a mid 80's gm car/truck was around $30 from O'reilly's. With only 1-3 wires to connect, they're simple to connect up too.

You might want to set up an alternator with a fully adjustable, external, voltage regulator so that you can set the maximum voltage to whatever you desire. This would be beneficial if you wanted to run a deliberate overcharge to desulfate a standard lead/acid battery, for example.

Despite what I mentioned about the particular GM alternators above, they may not be your best choice. They won't produce rated amperage until spun up to several thousand rpm(rotor speed, not engine speed), which is a drawback. Most car/truck alternators are not designed to continuously output their rated amperage either....they will fail as they aren't built to dissipate heat well enough. More modern alternators have been improved tremendously on output at low rpm versus the older units, with some producing 80% or more of their rated output at typical automotive idle speed. This changes when you get into alternators designed especially for industrial/commercial, high demand applications. I have in my possession a Leece-Neville alternator that likely came from a bus, which is rated for 320 amps. That is a continuous rating. It dwarfs a 10/12SI in size, and the latter feel like feathers after hefting the L-N. It also needs a lot less rpm to make real power than the 10/12SI. I will try to remember to post a pic of them side by side. The biggest downside is cost.....I found prices on the unit I have to be around the $1k mark. I didn't pay anywhere near that though. A better bet for getting your hands on a similar unit is a visit to a large truck/bus scrapyard, and then having the unit gone through by an alternator/starter shop(or doing it yourself, easy enough). Sometimes there will be a few in the scrap bins in the repair area of a truck stop, or heavy equipment mechanic shop. You'll need a lot more horsepower to get full power out of one of these though....be warned.

I've rambled enough for now I suppose, so I'll get on with the other use for an alternator. Most alternators can be modified, quite easily in fact, to serve as a power source for welding. The problem with using a newer alternator for this is the avalanche diodes I mentioned earlier. Since they are designed to fail at a low open circuit voltage, they are useless for this purpose and if an alternator has them they must be changed to standard diodes. Several companies offer alternator based on board welders for the off road community, but they are costly. Your proposed battery charging unit, set up with an external voltage regulator and a few extra(very inexpensive) bits could serve double duty. Yet another bonus is that you can run incandescent lights, or single speed(on/off) brushed power tools from 110-120v DC just the same as if they were plugged into the grid. Just food for thought.

One other thing of note is that automotive V belts and industrial V belts are not the same...nor are the pulleys. Automotive belts won't seat or grip correctly in industrial pulleys, and the reverse is equally true. They will work, but belt life will be reduced, as will pulley life. Serpentine(flat, ribbed belt) pulleys are pretty expensive and hard to find(for the engine). There is a company that offers an industrial V belt pulleys for the 10/12SI alternators...and parts/pieces to build what you want. I have no affiliation with them, just something I found when researching the idea myself. Build Your Own Generator | DIY Gas Powered Generator | TheEpicenter.com

 

It's simple enough to get a GM one wire alternator and go from there.
Start small and learn as you go .
Have the appropriate meters to read the results and monitor the progress rather then assuming ratings are fact.
Polly grove belts are more efficient in that it takes horse power to bend the belt and the faster you bend it the more horse power it takes. I worked in the air compressor industry, and many companies went to the polly grove belt to improve their out put.
Personally I don't like pushing things to their limits , so even if something is only working to 30% of their rated capacity I'm happy .
If I need more I build/provide bigger .

 

I took some pics, plus some others I already had, to help explain and illustrate parts of my earlier post. The biggest difference between the 10 and 12 SI are the output ratings. The highest output 10si was 63 amps, while the 12si went up to 94 amps. Here are two Delco alternators, a 12SI(left) and a 10SI(right). These are both equipped with standard regulators, making them "three wire" versions.


The physical dimensions are identical between the two, and almost all parts will interchange. Delco was the first to introduce an alternator that was fully self contained...including voltage regulation...back in the 1960's. The SI stands for Systems Integrated. The two tab connectors you see, plus the threaded stud are the three usual connections. A standard 1/4" female quick connect terminal will fit the spades, while the threaded terminal is the output, which you would connect to the battery.

Here is a better view of the terminal markings on the 12si. The 10 is marked the same way.


The battery terminal is clearly marked, but what about the "1" and "2"? The "1" terminal is what supplies power to the fields. This needs to be connected to a fused, switched, power source. The switch is important because cutting power to the fields removes the electromagnetic force, making it easier to start the engine. More importantly, if it isn't switched off when the unit isn't in use, it will drain the battery. The "2" terminal is the voltage sense and can be connected to the battery terminal on the alternator, or to the battery. A one wire alternator won't have this terminal. You might be wondering where the ground connection is. With standard voltage regulators, the alternator housing itself is the ground. There is, however, a threaded(5/16" I think) hole in the back for a ground wire connection.

Here's that Leece-Neville next to the 10si. The former weighs 35 pounds, while the latter is a measly 11 pounds.


Here is a pic of half of the diode rectifier(thing with the red dots) on the LN. Massive and built for real work, with lots of heat dissipation. It also has 12 diodes instead of the usual 6 in a typical automotive alternator. This LN is an isolated ground system, so connecting a negative cable is mandatory.


For comparison, the part circled in red below is the entire diode rectifier in a 10/12SI.


The most likely parts to fail in an alternator are the diodes and the voltage regulator. Pic below shows an almost completely disassembled 12si. Red arrow points to the regulator. Heat kills these parts, and alternators generate a lot of heat when producing at or near their rated output.


I didn't think about it before, but I should mention that your typical lawnmower engine is power rated at(and governed to) 3600 rpm. This means that it produces at or near it's rated hp/torque numbers at 3600 rpm. It will produce less at lower rpms. Running it at lower rpm will yield better fuel economy though. In typical automotive applications, the alternator pulley is well under half the size of the crank pulley. Use a 3" to 5" pulley on the engine to replicate that, and you'll probably have to experiment to figure out the best combination for power output versus fuel consumption.

Ask away if there is anything that isn't clear.

 

Even if that one only produces half of it's rating under real world conditions, it will be more than needed as it's destined to be a welder. The rippled DC produces an arc that is different than a typical rectified 60 cycle ac current, or even a DC only engine drive machine like the Lincoln SA200. Most folks report that the rippled DC from one of these welds like higher amperage than it really is. Have a look at this(not mine, and again no affiliation): http://www.diy-welder.com/

The wife's stepdad gave me a running when pulled 60's model VW engine/trans/axle this evening and I think I've got just the right use for it. It was rebuilt just prior to the bug getting wrecked, but has been sitting a while. I suspect I can have it running again in a couple hours at most. I might go try after work one day this week just for giggles. Just what I needed, another project on a very long list.

 

One of my "to do" projects is to build an air compressor unit with a an alternator driven as well .
Once the compressor comes to pressure the pilot control normally put's the engine at idle , but with a small air piston and micro switch I can engage the alternator to charge the battery bank in stead of just idling . If the bank is full then it would then just kick it down to idle.
I have even set up a gas engine to start and stop like an electric motor driven unit from a pressure switch. it'snot hard ,in fact it's kinda slick, "Pun intended". and nice not to have to listen to the unit running unnecessarily.

 

Not a bad idea. If you're building from scratch and want to save some money, a salvaged A/C compressor from a vehicle can be used. Offroad guys normally use York 210's, but lots use Sanden units too. It's clutched, so there would be less drag on the motor once the pressure switch tripped.

The York is preferred because it has an oil sump. The sandens don't....they depend on the oil in the refrigerant to lube them.

 

Generally refrigeration compressors are not designed for the heat generated by compressing air, I've seen people do it, and the lead head gasket melts out..
it is interesting that those new ones have been made to tolerate that use .
I have unloader controls for gas driven units so that the fly wheel stays spinning at RPM during it's remcycle .
Toying with building a start stop option for that unit, I've done it before using a micro switch on the governor to disengage the starter.

 

If I've been running the A/C in my jeep, the sanden compressor is hot...very hot. Compressing any gas generates heat, and an A/C(automotive anyway) compressor is pumping a lot higher pressure than a typical air compressor. Add to that the heat from the engine. Automotive compressors will handle it just fine.