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Archive for March, 2009
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
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,
Monday, March 30th, 2009
Thanks for offering this service.
I am building my own wind turbine for the home. This will be a grid-tied system that will plug into an outlet to supplement the grid. Can you recommend an affordable converter? I saw the Smart Sine Wave Inverter, but that costs $300. Is there a less expensive alternative?
I think its great that you want to tackle a project like building a wind turbine. If you are going to use it to charge a set of batteries for a backup power system then that would be the way to go, but you will not be able to connect it to the grid.
Just a small point, a “converter” is used to convert AC to DC, and “inverter” is used to invert DC to AC.
First, the voltage and current output from a wind turbine is all over the chart as the wind keeps changing by the minute, which requires a very special DC to AC inverter designed for this type power input, plus be certified to feed power back into the grid. The lowest cost inverter I have seen that is designed for this type application and certified for grid connection costs around $2,500.00, plus circuit breakers and wiring. Your local utility will not allow you to feed power back into the grid unless the inverter has these UL and IEEE certifications, and you will not find this level of quality in any $300 inverter..
Sounds like you are on a tight budget, so I would stick with charging batteries and powering some emergency DC lights.
I will point out that many who ask me these type questions totally ignore my advice and go on and waste a lot of their time and money to find out the hard way, so either way, good luck with your project.
Wednesday, March 25th, 2009
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.
Monday, March 23rd, 2009
Is there a UL product out there similar to a DC grid tie in inverter that would work for an AC generator?
I am aware of how the DC is converted with an inverter to AC and the phase angle is adjusted as well as the phase voltage to maintain proper alignment of electric main power. I have seen wind generators plugged directly into a breaker in the main panel as a grid tie in and initially was confused on how this was causing a dead short. However, I understand how it is possible now (there is an inverter in the wind generator head which adjusts Phase angle and Phase voltage to allow simultaneous feeding), but, haven’t been able to find anything for AC generators.
What I am looking for is something that will go between my AC generator and the main panel that will allow me to directly connect to the panel without a dead short, and allowing back feeding to the main line. Also an automatic shut off or transfer switch that would turn off the generator’s power supply from pumping electric back into the power grid when the main power goes out.
I am looking for an AC grid tie in device that will not cause a dead short.
Your thoughts would be appreciated,
I can’t imagine why anyone in the world would want to do what your are suggesting, although it is technically possible. Yes, there are special “in phase” monitors that will sync a generator with the grid, but this is only dome with very larger generators like you would find in hospitals or military bases. The main reason they do this is they are on a time of day rate and if they are approaching a peak demand period, by running their generators in sync with the grid they can save hundreds of thousands of dollars per year because these rates usually carry over the high penalty for the next 11 months. In addition, this switchgear to sync the generator with the grid costs more than your house and requires all kinds of coordination between the utility engineers and your installer. You will also be required to carry a huge liability insurance policy listing the utility as the insured in case something goes wrong and your power feeds back into a down line and kills a lineman.
Inverters for solar and wind systems have special circuits that make sure power is not fed back into the grid during a power outage, and the inverters must supply this power within a very narrow window of voltage and cycles. Most smaller generators are not that easy to maintain a constant output under varying loads.
Now that you know the legal issues involved with doing this, I will give you the simple reason why nobody in their right mind would ever do this:
If you count the cost of fuel, generator maintenance, repair parts, added oil changes, and annual service, you will be paid about 20% of what your actual costs will be, because you can never ever generate electricity cheaper than a utility. The only reason many of these solar and wind systems are doing this is either they are receiving some type of grant or tax credit, or they have been given a special feed-in tariff rate.
Many people still install solar systems as some systems also offer emergency backup, or at least do not need constant fueling or make noise like a generator. The national average cost today to generate electricity from a solar system is 35 cents/kWh. The national average for grid electricity is 9 cents per kWh. You figure it out.
Thanks for the insight and your knowledge on these subjects is amazing. Everyone at times has an idea and can’t figure out why the situation is the way it is; until they ask an experienced individual.
Thank you again. So if I wanted to have some sort of “economical” unit (and I use that term loosely), we would be best off using a UL device DC based unit (solar, wind, hydro) with an inverter monitoring the phase angle and voltage back to the main panel which would shut off when the main power goes out? If we wanted any sort of power when the main power goes out we would be using a battery system or a separate backup AC generator/transfer switch which would not back feed to the main power until main power comes back on. We would then turn off the generator and manually switch the transfer switch back to main power?
I guess I am in the same boat as most people trying to figure out what will work best for my individual circumstance. Oh, yeah I’m not a millionaire so the in phase monitoring for an AC generator would be out of the question.
I will probably be investing in a solar or wind powered DC unit with an inverter for my needs. Would you recommend any companies that you have had a positive experience working with for these devices. Probably, a 2KW-5KW max output would be what my financial situation will allow.
Jeff I can’t thank you enough,
Any inverter designed for grid tie in the US should have the automatic transfer function built in. If you select a battery based inverter, it will also include a built-in transfer switch to disconnect from the grid. Some battery based inverters include a “second” transfer switch to allow also connecting a generator and the grid, and will switch to the generator when the grid is down and the battery charge is low. If you select an inverter that does not have the second transfer switch, then you will need a generator that includes its own transfer switch panel.
Sunday, March 22nd, 2009
I purchased a Central model 2300 wood boiler with propane backup.
I am located in Butte, Montana and the normal wood of choice is Pine.
The wood burning part seems to work sort of adequate, although the fire frequently goes out. The main problem is the creosote that collects on everything inside the fire box. The propane gas nozzle has an electrode on the end of the gas nozzle which sticks inside the firebox. However, due to the creosote collecting on the end of the gas nozzle, it normally does not work after a week or so after I clean it.
In other words, it is pretty iffy, if the gas backup is going to fire or not. The creosote is so thick is makes a black sticky mass that covers the entire end of the gas nozzle.
Central has worked with me to correct the problem. They had me install a larger combustion fan that they felt wood keep the coals alive which should keep the creosote down plus they sent a new gas burner nozzle with electrode. All of these are nice but it fails to permanently fix the problem. It is hard to work with Central Boiler directly as they want you to work through the distributor that I bought it from.
I paid a little over 13,000 for the unit and I cannot count on the gas to backup the wood.
I have only had it in operation since November 2008 and have worked on it and worked on it. It has been a disaster.
I would like to get my money back and buy just a normal boiler but not sure how to approach that subject. If it would work, I would love to keep it, but this is almost ridiculous. I have asked my distributor for names of others that may have similar problems so that I could contact and possibly find solutions, but they have not and will not provide that info.
I do not want to get into the middle of any problems you are having with your wood fired boiler. However, I will be glad to review several choices that you might consider.
1. There is still the chance you may be able to at least turn the boiler back in for some type of partial credit, especially if you made it clear that you were going to be burning only pine and the dealer indicated this was not going to be a problem. A written letter to the manufacturer works far better than an email or phone call. I would make them aware of the problems you are having and include some photos, and explain you are not receiving any assistance from their local rep. At a minimum I would insist on the dealer coming out and checking all the controls and combustion chamber for proper operation.
2. I have a feeling that the written literature on the boiler advised that these were mainly intended for hardwood like oak, which do not have anywhere the problems with creosote buildup that you are experiencing. If this was the case, you might want to offer it for sale on the Internet in like new condition to someone located where hardwood is easier to find.
3. You could install a standard high efficiency propane boiler for “normal” home heating, and leave the wood boiler for when you can get a better mix of wood to burn, or use only for emergencies like when you run out of propane.
Hope this helps,
Wednesday, March 18th, 2009
I, with my small team, am designing a solar system for our senior engineering project. We are all electrical and electronics major students at Oklahoma Christian University. I was researching online for all the information I could find for the project and I came across your website. I could see you have a lot of experience regarding this topic so I wanted to ask you few questions. My questions are:
1. What are the basic problems that people get into while building a solar system?
2. Since we are doing an engineering project, we don’t want it to be just something we bought the parts for and installed. We want some features and some engineering stuff that other people can see. So, is there anything you can suggest for our team that we can work on as engineers and not just installation guys. May be some common problems people face that we can solve.
3. Also since we have a tight budget, can you give us an idea how we can minimize the budget. I mean is it better to buy all the required parts from a single seller or shop around for cheap parts individually.
Thank you very much for your advice.
Sounds like you guys are moving in the right direction for these changing times.
1. Most newbie installers think this stuff is “plug and play” and many systems are, if you understand wire sizing, the National Electric Code, and a hundred other design issues that can bite you if the selected “plug and play” equipment was not what your design needed. Many things in this life that look easy are usually not as they seem. I see and hear people everyday saying in press releases that solar is easy to install without any special training, and I assure you these are the people who will burn down somebody’s home someday. There are no short cuts, if you want to design and size solar systems, you must learn the basics and the code.
2. The solar industry is still young and there are many new discoveries yet to be made. There are still problems with battery life and battery loss of water; we need solar mounting systems that are easier to install and adjust for different module sizes and roof types; we need field equipment that makes it easy to test a new solar array and related wiring safety and ground faults; and I am sure there are many more. You might send some type of easy to reply to questionnaire to many in the field for their suggestions. I would start with the certified installers, listed with NABCEP.
3. We run into people all the time looking for the lowest prices and buying from different suppliers. But this is not like finding what website has the lowest price. What would a car look like if you ordered all the individual parts from different auto parts stores then tried to put it together? Many of these components are available with different voltage and amp ratings, different style connectors, different control protocols, and different features that do not allow you to just select all these separate parts and plug them together. Buying everything from the same supplier will make it easier for them to match up these features and a larger order size will reduce the total system cost.
Friday, March 13th, 2009
I am a student, and I am planning a solar water pumping system to supply non-potable water to a public bathroom on a Island. I am having a hard time finding a toilet to use in this system.
We are planning on having a large above ground storage tank to hold all the water. My biggest question is what type of toilet can be run on low pressure as the holding tank may only be 5-10 feet above the bathroom. We are trying not to have to install a separate pump to pressurize the system.
We are assuming a gravity feed toilet would be just fine, as most toilets are gravity feed. Most of the literature that I have read on gravity feed toilets suggest a water pressure of about 20PSI, which would require considerably more head.
It sounds like you need more consideration of other options. I can’t design a system on a free web site as we do not have the time and would never know all of the design parameters for the hundreds of request we get. However, I will give you some things to help you fine tune your design process.
1. You say you will have a large water storage tank, which in turn will provide water to flush toilets. It’s a law of nature that for every foot of height you raise any tank, the pressure at the bottom outlet will increase .43 psi per foot of height. You do not need to raise a large heavy tank, you could raise a smaller tank up on a nearby hill and fill it from the larger tank.
2. Consider waterless urinals and cut the total water usage by 50%. http://www.airdelights.com/waterfree_urinal.html
3. Use a second pump and pressure tank feed from the large storage tank. You can get any pressure and flow you want by selecting the right pump, which can be powered from a solar-charged battery. These require clear water entering so you will need some kind of filter between the tank and the pump.
Thursday, March 12th, 2009
A problem has come up in a couple of states involving inverter voltage and frequency limits. Common inverter voltage and frequency limits are +/- 10%, and utility voltage and frequency limits are +/- 5%. This has had more than one utility thinking about limiting the number of acceptable inverters to like one or none.
I have told people that this problem is asking the tail to wag the dog, that the inverter follows the utility, not the other way around. One utility I worked with removed the voltage and frequency limits from its net metering agreement, just leaving the UL 1741 compliance requirement.
What do you think about this problem? Thanks!
David Ryan PE
Normally, inverters control voltage and frequency much tighter than the grid, and I am not aware of any UL1741 certified inverter that can’t hold extremely tight to the grid it “sees” as this is how they control their shoving of amps back onto the grid. Normally this is more a problem with inverters when the local utility cannot hold their voltage in range in a local area. In most cases the utility is not even aware of this issue until somebody installs an inverter, since the inverter is looking for much tighter control by the grid and won’t connect. Most home appliances and lights do not require the grid to be this exact and so nobody reports a problem if it does not affect their appliances and lights. Yes, this could cause long term appliance damage but not short term.
The only time we have ever seen a problem with an inverter not connecting when it was not a problem with the grid is when the line losses between the inverter and point of connection back at the meter was so long that the voltage drop required increasing the voltage output from the inverter. However, even then, the higher inverter output voltage is usually dropped back in line with the grid voltage after passing back through this higher line loss. I have also seen problems when the homeowner or business has a very big load like an AC compressor or large well pump on a panel that was already borderline and that also was the point of connection for the inverter. Every time this large load kicks in, the inverter will see a high voltage sag and drop line. Then after waiting the required 5 minutes it will try to re-connect, and this can cycle so much the inverter will never send much solar power back on the grid.
As you know, it is against code, utility rules, and the inverter manufacturers UL listing for an installer to re-adjust these limits on an inverter, and to do this requires inputting special program key the inverter manufacturer will not provide the installer unless they submit a written form for authorization with the utility. Since this program key will only work for the specific inverter having the problem, I am not aware of any way any installer can go around and change these limits on all of their installations on a whim.
I do not think this is an issue for more utility regulation. I think if the grid can supply power within allowed tolerances to the homeowners site, and if installers install inverters mounted very close to the meter base, and select a wire sized for no more than a 1% loss, than there is no reason for this to be a problem for either party. Any unusual exception to the rule can be handled by existing permission forms that are issued only after review.
You are right that the inverter follows the grid, with the exception of a high resistance in the wire run between the inverter and the meter, and this is normally a reflection on the installers sizing of the installation. Don’t forget, the installer may be connecting the inverter to the grid at an existing sub-panel and think this couldn’t be a problem, but forgot to check that there may be a long wire run back to a main panel, that there may be another line loss back to the meter base, and all this existing wiring was installed years ago based on a 5% wire loss and have many connections that now have a high resistance causing the large voltage drop I am talking about.
Hope this helps,