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Get Powered Up! Certified Energy Manager Jeff Yago answers your alternative energy questions

Wondering about a great new energy-saving device
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Sorry. Jeff no longer answers questions online.
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Archive for the ‘Generator’ Category


Battery charging from a generator

Wednesday, June 17th, 2009


I have a 7500 Watt generator working fairly well except that the DC output to charge the 12 volt battery is ony 8 volts DC due to a problem I am unable to repair.

Will the 8 volt DC to the battery cause any harm to the 12 volt battery? I have been using a portable 12 volt charger to to keep the battery up to par.


Bob Libbon


You should never run a large generator like this just to use the battery charger circuit. Some generators offer this small DC charging power to trickle charge a battery while you are running the generator to power other loads, but you would use up a tank of gas just to charge a small battery like this.

You want to buy a high quality 120 VAC battery charger and plug it into the AC outlet of the generator. Select a charger that lets you select different amp charging rates to match the battery. You could easily power a large capacity charger with this size generator, so the charging process would be much faster and will save fuel.

One caution – cheap battery chargers will not work from most generators as they require the higher peak-to-peak voltage of a generator output, and if the generator voltage drops while under load the charger will stop charging. Be sure the charger specs indicate it can be powered from a generator.

If you have a half-full basketball with 30 PSI pressure inside, you will never add more air to fill it up if your air pump only goes to 20 PSI, even if you ran the pump all day. You cannot charge a 12 volt battery with 8 volts. Regardless of charger type – solar, generator, wind, grid, the charger voltage must be higher than the battery voltage. A 12 volt battery will require a charger that puts out 13 to 14 volts. At 12 volts the battery will be almost discharged.

Good luck,

Jeff Yago


Generator and fluorescent lighting

Friday, April 24th, 2009

Hello, Jeff,

I live in a condominium building consisting of six floors with about 8 units per floor. Since the construction of this building about 40 years ago, we have operated incandescent bulb lighting with about 800 watts per floor, as well as the outdoor lighting and an elevator.

We are now discussing the possibility of converting the incandescent bulbs to fluorescent bulbs which would reduce our energy consumption by about 2/3, thus reducing our energy bill accordingly. It is the opinion of some that our emergency generator (same age as the building) could not or would not operate properly with the conversion to fluorescent lighting. Can you advise if this assumption is correct?

I thank you for any assistance you can provide.

I think this concern goes back to the old style 4-foot 2-tube T-12 style fluorescent lamps that had magnetic ballasts, which were those long black objects inside the fixtures that would get very hot. This type fluorescent ballast “flickered” the lamp on and off 60 times per second, which produced a strobe effect and was hard on your eyes. Also, the ballasts were a form of transformer which altered the “power factor” which is a angle relationship between the voltage and current peaks. If the power factor drops due to lots of transformers on the circuit, this causes the circuit to use more current and can really screw up a lower cost generator.

Compact fluorescent lamps do not have a transformer type ballast so they produce a much smaller power factor drop. Also, the electronic ballasts in these newer fluorescent lamps are “flickering” on and off at many thousands of times per second so there is no “60 cycle” strobe effect that hurts your eyes. Combined, these two features are much easier for a generator to handle and I have installed generators as backup power for on and off grid homes that only used compact fluorescent lamps with no generator problems.

I will suggest that if you re-lamp all at the same time, be sure to document the date as we are finding that many of the most recent compact fluorescent lamps now being made in China are not lasting anywhere near the advertised life, so I would buy them all at the same time from a lighting distributor and let them know you will be monitoring performance.

Good luck,

Jeff Yago


AC or DC generator. What’s the difference or which is better?

Thursday, April 2nd, 2009


I’ve been looking at different generators after reading some of your articles. My goal is to build a home that uses generator power while I slowly shift to solar as it becomes financially effective. That being said I’m looking at using a propane generator so I can have a propane stove, and a propane water heater for radiant floor heating. Using this much propane I figured that a propane generator just made sense in order to stick with one fuel source.

Here’s the problem – all the Kohler generators I look at all output AC power and some output it in single or triple phase. I thought it would be better to get a generator that outputs DC to the batteries then use an inverter to output to AC.

With most examples I would have a generator that outputs AC which would have to get converted to DC which would get reconverted to AC when I use it. Isn’t this an awful lot of energy loss?

Isn’t there a propane generator out there that runs at 1800 rpm and will output DC? I mean after all, a propane motor can have different kinds of generators hooked up to it can’t it?

Thank you

Dean Ash


Up until around 1995 what you are trying to do was very common as most DC to AC inverters were not as reliable and could only produce a modified wave form output which was not very good to power any type of battery charger. There were several manufacturers making a generator that consisted of a gas or propane engine driving a heavy duty truck DC alternator for direct charging large batteries. There are a few still being made, but since todays higher quality inverters now have perfect grid quality (or better!) sinewave output and very high capacity battery chargers built in that are designed to operate from either grid power or a generator, we now design everything around normal 120 or 120/240 home wiring systems.

Since these new inverters are so efficient, the system losses are almost the same when using a high quality inverter to charge a battery bank with a generator to power the inverter, as it would be to use an engine driven alternator to charge the same battery bank. Also, since your generator would be supplying 120/240 volt AC, you can supply larger AC equipment and power tools directly that you could not do with a DC output generator. Unless you are planning a very small battery system and are trying to avoid the cost of an inverter, I would go for a high quality generator like the Kohler which we prefer since it uses a very simple 2-wire start/stop circuit. This makes it very easy to remote control from almost any inverter, while many other generator brands require complex 3 or 5 wire start circuits which sometimes require buying a separate control box to allow remote start/stop control with an inverter.

Good luck,

Jeff Yago


AC generator voltage problem

Tuesday, March 31st, 2009


I have a 7500 Watt AC Generator and have a output voltage problem. If I set speed to 60 cycles my AC voltage climbs to 165 volts. Can you direct me to points of this problem that may help me correct same?

The normal rated output should be 60 cycles and 120 volts AC


Bob Libbon


There are many possible reasons you are having this problem and each generator brand and model have different designs that could cause this. First, what type voltage meter are you using? If you are using a $20 Radio Shack model, then your meter is giving you a good indication that there is a problem. If you are using a high dollar RMS volt meter, then this may be telling you something else. The actual “peak” voltage of the utility grid and a 120 volt nominal generator is actually 169 volts. This is because the voltage is changing every 1/60 of a second from a high of +169 volts to -169 volts and passing through 0 volts twice, so 120 volts is the “average” of this sinewave curve.

As you start adding loads to a lower cost generator, the internal voltage regulator allows the voltage to drop as it tries to maintain current for the load. This means the peak to peak voltage of 169 volts will start to drop. Since all battery chargers use only the “peak” part of the sinewave, as soon as this peak voltage drops, most battery chargers will stop charging, which is why you should not use a low cost generator to charge a battery bank like you would find in a solar home.

Some generator designs are based on a rotating coil that is supplied a DC current, and by varying this DC current the generator can control the AC voltage output from the fixed coil. Sometimes the voltage regulator device used to vary this voltage includes a control that you can adjust.

Some higher cost generators include a special “inverter” electronic circuit connected to the generator output to stabilize this voltage and maintain the 169 volts peak to peak at a perfect 60 cycles per second. For example, most Honda generators add a “i” to the end of the model number if they include this option.

Odds are your generator has a circuit board that is used to maintain the voltage output and something has gone wrong with this control board. Even lower cost generators have some type of control board to regulate the voltage output even if they are not as accurate as the inverter models.

Sorry, but sounds like this is going to cost,

Jeff Yago


Intermittent use cabin

Wednesday, March 25th, 2009

Hi Jeff,

I have a situation not completely unlike Blake McKinney’s cabin (issue 83) in that I am planning an off grid cabin that will only be used once in awhile — in northern Wisconsin! Was considering solar hot water (closed glycol system) that might be able to be integrated into a radiant infloor (also with glycol) system to keep the house/plumbing from freezing when no one there. Do you think this is reasonable? Electric to run the pump would be from PV modules/battery bank. Would you still recommend a propane wall heater as backup?

We would use a high efficiency wood stove to heat home when occupied.

Our solar exposure is considerably better than the McKinney place.

Also, do you know of any remote monitoring system for house temperature, etc that could use cell phone signal to communicate info back to us at our main residence 90 miles away? :)

Finally, is it generally recommended to NOT let your propane generator automatically switch on to recharge the batteries when no one is around?

Thanks a bunch,



That’s a lot of questions!

I would not recommend trying to heat a home with an active solar system for long periods of the winter when nobody is home. There are too many little things that can turn into big things when nobody is there to correct. For example, a big snow can cover the solar array for days if nobody is there to clear them off. A pump could fail, or the system could leak. Even a small leak of a sealed antifreeze system will cause makeup water to enter and could cause the now antifreeze in the loop to freeze.

I would deal with this in one of two ways. Either design a passive solar home that has enough thermal mass to keep from freezing at night, or design all the plumbing to slope to 2 or 3 low points where you can completely drain all the piping before you leave. Blankets and sheets on beds and clothing in closets will become “musty” under these conditions so I would strip the beds and remove anything that could be damaged from the cold and/or dampness.

I would not leave a generator on automatic start if I was going to be gone longer than a weekend as a simple control glitch or battery problem could cause the generator to run until it ran the tank dry.

There are now all kinds of remote Internet and wireless phone based controls to allow monitoring of remote homes and businesses. We have inverters that will send an email to the installer if there is a problem, and there are Internet based cameras that will send you live video of inside your home if the alarm is activated or there is a water leak.

I suggest that you keep it simple. If the pipes are dry and you remove anything that can be damaged from the cold, why spend all that money to heat someplace you will not be for months at a time.

Good luck,

Jeff Yago


Hydro generator system

Friday, March 6th, 2009

Hi Jeff:

I purchased DC-512 four alternators over the Internet for a hydro project. I’m taking advantage of an existing irrigation system on a farm, which pumps a steady stream of water with great pressure at a very long distance. It’s like a fire hose in action.

This system is running continuously for 12 hours daily. I’ve designed a special, very light aluminum=blades arrangement and I have adapted it to the DC-512 via belt drive to disrupt the powerful irrigation water stream, moving this blade as when cleaning a painting roll with a pressure hose. This creates a speed in the DC-512 of 1150 RPM as measured with a tachometer. The voltage produced with no load, e.g., disconnected from the batteries, is approximately 25 volts, measured with a Flux digital meter.

The DC-512 were all connected in parallel to a single 12 volts Flex-Charger of 100 amps to charge a battery bank, 4 batteries connected in parallel. Three alternators DC-512 were disconnected from the charger to perform troubleshooting leaving just one connected in parallel. This is what happens; when I connect the positive cable to close the circuit, seems like a short circuit is created in the alternator, which slows down the speed to about 500 RPM stopping the blades and disrupting its function to load the battery bank. The charger light turns on indicating that is charging but, producing only 13 volts, which is not really enough voltage to charge the batteries. I have connected everything precisely as per alternator and charger instructions. Finally, I am tired of getting wet like crazy during test and troubleshooting process. I wonder if you can explain what is happening and how can I make this system work. Your help will be really appreciated.

Thank you in advance.

Carlos Echevarria


As it states on the web site, we can not answer specific design questions as we do not know all of the specifics of your installations, and this is a free site and we have limited time to spend on each email question. However, we can provide general answers that may be of some help.

First, I assume this pressure flow is due to gravity head and not from a pressure pump somewhere. Second, if I had this much “free” water flow I would purchase a quality hydro-generator that is designed to maximize the conversion of energy. Most likely a properly sized and designed unit could replace all four of your home-made units and without all the problems you are having.

If things work fine with all four alternators in the circuit and then when you cut out all but one and it does what you describe, it sounds like it is being over-loaded. This would drop the voltage while appearing to be under load. Also, your wiring switching to one alternator could be causing the remaining alternator to be sending power into the alternators not being used which would be a large current drain on the working unit.

Again, you have a great opportunity to power your home with this much hydro power if you bite the bullet and purchase the correct equipment.

Good luck!

Jeff Yago


Wood Gas Generator

Tuesday, March 3rd, 2009


I have a lot of acreage we are clearing and hate just piling up the wood to be burnt as waste.

I have a large chipper and would like to instead chip the wood and store it for use in a wood gas setup to power a gas generator (25KW) to power the main home and out buildings. Everywhere I look there is a lot of information on wood gas but nothing much on using it with a gas generator. We really only need 8KW but with peak draws and lower output from the wood gas vs real gas I would prefer to be a little oversized.

Any info you can throw my way would be greatly appreciated.

Best Regards,

Bart Young


The reason you are having problems finding information is this is a very complex process to setup and very costly to oeprate and maintain. Most successful systems are large scale with large gasifiers and generators.

Here are a few links to help you get started:

Hope this helps,

Jeff Yago


Generator Powered House

Monday, February 16th, 2009

I have really enjoyed your articles about using a generator for your primary power, and noticed how hard it is to currently get 1800 RPM generators. By accident, I looked up the specs on PTO generators, and found that they were geared for 540 RPM’s and have a continuous runtime. While I would still need to supply the motor for the PTO generators, it also looks to be very cost effective.

What are your opinions on it?




The 540 RPM generators you are talking about are intended to be connected to the rear-mounted PTO shaft of a farm tractor.  Although I cannot say every brand and model are the same, I have had several clients tell me they could not keep an inverter on line to re-charge their batteries because the voltage and cycles from these units were too unstable so their inverters kept disconnecting.  Since even a very small change in tractor RPM gets multiplied by the gearing to the higher operating RPM of the generator, this can really affect generator performance.

Most of these generators were designed to keep farm loads operational during a power outage like lights, motors, and heaters which are far less sensitive to power quality.  I think some of the newer higher cost models may include electronic voltage and cycle regulation, but without it I think you will find it very hard to charge batteries.

Good luck,

Jeff Yago



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