Jan 7 2011 Email of the day, Generator Mods, notes on AVRs, and know your loads.

Question of the Day: Jan 7, 2011

Randy's Arc

Randy's Arc







—–Original Message—–
Sent: Saturday, January 07, 2012 3:17 AM
To: georgeatutterpower.com
Subject: UtterPower.com Contact Form: generator full power

Name: Ernie M.

Subject: Generator, full power

Message: I’m going to convert my generator to get full power @ 120v.

[My 120v wire feed welder burns up the AVR’s of my 7Kw gen.]

On your explanation page, and another that I looked at, it is demonstrated that some cutting and soldering needs to be done.

However, I believe that the taps on my generator are simple spade connectors. These are labeled 1 through 4.

So, do I actually need to dig into the gen head and cut, solder, etc… or can I simply use these connectors to achieve what I need to do?

This may be one of those questions that give occasion to the statement: “There’s no such thing as a stupid question.”

My answer:  Far from a dumb question!  And perhaps once you find that PAGE you REFERENCE, you’ll comment below and share the page LINKS in comments.

First off, opinions vary, but I think that 120 Volt Wire Feed Welders  are a poor choice because it is often difficult to find an outlet that will deliver the current necessary to run one properly.  If we consider that many outlets are wired with 14 gauge wire and equipped with 15 amp breakers, we are starving for power from the start. Consider that a standard breaker is only rated to carry  80% of the rating continuously What this means is you might be trying to weld on a circuit that has trouble delivering adequate current to the coffee pot yet alone a wire feed welder!

When I added a generator transfer switch to Zach’s house, I also added a new 20 amp breaker, 12 gauge wire, and a heavy duty outlet just below the fuse panel for electric power washers, small wire feeds, or other high current loads, as there wasn’t a decent outlet in the whole house outside the one designed for the garbage disposal under the sink in the kitchen!

So we need recognize you have the 120 volt load from hell (IMHO), there’s a few worse, but not many. We need understand our loads, and that’s why I will ramble on after answering  your  basic question, my readers cal it a rant, but what follows is an education for some.

MOST generators capable of producing 120/240 have two separate windings in the STATOR and they do terminate both ends of both windings on binding posts where you can re-configure the output of the generator for 120V only, (stators windings in Parallel) or 120V,220V where Stator windings are in series with a center tap. Of course you need understand that 120V loads are carried at one half generator power capacity.

If this is your case, both ends of both stator windings appearing on posts or spade clips,  then you have no reason to take the generator head apart and make cuts or splices in or near the windings.

End of Answer:

Following are musings of Generator design and why I think the ‘Hands ON DIYer’ is a totally different customer, and may have far different equipment requirements than the average person who shops for a backup generator. Know your loads, There are other loads that can challenge us, and cost us some money if we don’t address their requirements.

As for the AVRs (automatic Voltage Regulators),  I’ve commented on these in the past and said that many small generators fail to provide service when needed BECAUSE of failures directly related to the implementation of the AVR itself!

It’s my belief that the DIYer is far more capable of managing voltage droop and understanding the pros and cons of running an AVR head or a head without one. All that really counts is the percent of voltage droop and whether it is acceptable in your use. If your generator head droops a few volts at the maximum power you’ll be using, and you have a properly functioning governor, you’ll likely be fine, same as millions of generator owners before you, but there are special circumstances you need to understand.

IF you are selling generators with an AVR, you might be inclined to tell the other side of the story, and there certainly is one, the AVR can help ‘prop up’ the voltage when a larger load hits the generator, and it normally does so by increasing the current in the field.

Here’s where we get into trouble, the Electrical Engineer who is given the budget and a free hand might design the ‘Rolex Watch’ version of an AVR, but most Engineers find that their solutions must sell in the market place, and people need buy the product to keep their paychecks coming. If your generator is a dime more than the next guys, and the buyer doesn’t know the difference, you may be out of business over night.  AVRs that address all of the things that can go wrong add expense to the generator head, and seldom do you find the better voltage regulator with current limiting, and the robust parts that go along with it on the more affordable generators or Generator heads.

An example of a problem might be the AVR that will continue to boost current in the field until the weakest component fails, that might be the field winding that experienced a lot of overheating in past usage finally breaking down the insulation and shorting the field windings, or perhaps causing  a brush to arc on the slip rings to arc and create enough heat to damage a brush spring, or more.  Sometimes, it’s the control board itself, and on that board you find the AVR and more components. Having this board changed out can be VERY expensive.

If you buy an aftermarket AVR with adjustable parameters (like current limiting) you need to know how to setup these parameters, and assure the AVR doesn’t overdrive >your< field.  Some people just install a fuse or breaker in series with the field, and they are in the habit of re-setting it or replacing a fuse instead of buying the new AVR.. I guess it depends on what you have, and knowing what current to fuse your field at.

An example of Kiss Generator Design  might be a 5KW generator head NO AVR, that never sees a load larger than 4kw, and is driven by a prime mover with plenty of power at full load and a decent governor. Measuring the voltage droop at the highest load you expect and knowing it serves your particular requirement might cause you to consider KISS, and steer clear of AVRs. Maybe you fuse it or breaker it to open at 4kw to assure you don’t overload it?

Following is an example of a situation I never anticipated, and you now have an opportunity to see if your experience or Engineering skills can spot the following oversight.  Make notes BEFORE you read the answers below.

A Glass Blowing Operation is called a ‘Hot Shop’ and many of the developments over the years comes from the ‘hands on’ Glass Blowers as they learn what works, and what doesn’t. The typical glass shop uses a 2HP electric motor driving a fan to feed air to a natural gas fueled glass furnace. If this electric motor goes without power for more than a few minutes, bad things can happen to the furnace and the glass. I’ve even heard the glass can even find its way out of the furnace and across a shop floor.

For this reason, Glass Shops put in backup power, and they are concerned about little else that keeping the furnace at temperature. Even a single overhead light in the entire shop is optional, as they’ll gladly use a flashlight if necessary to assure the furnace blower motor has the power to be quickly restarted.

So here’s the situation….The Glass Shop manager calls a Generator Dealer, and explains the need, the generator salesmen consults the technical staff and together they  recommended that the customer consider  an 8KW natural gas-powered auto start Generator as a minimum to start their critical load.

OK… here’s your chance, is there anything wrong with this recommendation?

If you answered that it would be wise to do a power audit, give yourself a star, but if you arrive at the glass shop to do this audit, you’ll find a very nervous owner reluctant to turn off that motor and allow you to restart it, so perhaps you’ll leave with name plate data at best.

Once the backup generator was installed, there was an actual test, the tripping the main breaker, simulating a power failure, and watching the backup power come online and   restart the two horse power blower motor, and everything looked great!

OK… here’s another chance, was anything overlooked?

On with the story, one year later, there was reason to remove the glass from the furnace and there was a planned shutdown, eventually the furnace was restarted, or should I say there was an attempt to restart the furnace, and a breaker tripped for the furnace blower motor.  A local Electric Motor Sales and Service Company was called, and it was determined that the start winding was defective. The Technician replaced the motor which included the removal of the fan that was directly connected to the motor shaft and the blower was started and restarted several times to assure breakers wouldn’t not trip out resulting in another failure.

More years passed, and then the replacement 2hp fan motor failed to start.

Your analysis of the problem? write it down before you proceed with the story.

The mystery was solved once someone noted that there had been another power failure and a past restart of the motor on the generator!

The blower was designed and built by Glass Blowers, NOT electrical engineers, and they had chosen to use a higher RPM 3750 Synchronous motor attached to their beautifully crafted, very heavy cast iron master piece of a fan that was very nicely balanced, and fitted into a custom housing that produced just the right amount of flow and pressure for the furnace.

The Mass of this blower fan just barely allowed the motor to start on good (close in) commercial power without cooking the start winding. Apparently there wasn’t adequate thermal protection here, and when the 8KW generator was used to start the motor, the blower did eventually come up to speed, but not before it cooked the start winding or a component in it’s path.

Considering our technician found it necessary to replace the Motor, it was likely the start winding itself, but doesn’t this beg more questions?

For me, this is all evidence as to why I will always be the student, I would have never thought to question the design of the blower, and this is an example of why we need to take every precaution in checking out our designs and loads. I’m sure all the motor criteria was available, there was no reason the designer couldn’t have placed a power analyzer on that motor and even noted the time and exceedingly high current for all too long caused by the high mass of >their< flywheel like blower design! The inability of the motor to reach operating speed in time to generate the CEMF (counter electro Motive force) to oppose that high current flow was what cooked that start winding! Big flywheels are not always a good idea.

There’s normally plenty of motor data, and I think there’s normally mention of current and time that start winding can be under load.

AS DIYers we need to recognize that there are far larger engineering disasters created by large companies or Governments every day, and some of them cost us taxpayers millions if not billions!

Some of my favorite examples are posted under the title ‘things I hate’. Here’s an example of a coffee pot design from hell. https://www.utterpower.com/kitchen-aid-pro-12/ . And another example of the printer from hell https://www.utterpower.com/epson-sylus-photo-820-printer/

. Of course these are my opinions, and I’m sure the designers would tell a different story. I can imagine a discussion with the Engineers who designed the printer, it might go something like this… “We were told to design a printer that might double the sales of a specific printer cartridge sales outlet. That was a first priority in the design, don’t blame us”

But let’s consider a recent Boeing built Airplane the 787. The Company ‘contracted out’ a lot of the Engineering for this airplane after gutting one the best aviation brain trusts on the planet, (their own engineering department). Sure we all watched as they struggled to build this aircraft but behind the scenes is a story of just how inept sub contractors were and how Boeing management had assumed that these contracted work forces were equal to the internal ones they had down sized or eliminated at Boeing.

Did you know that the 787 required 11 tons of re-enforcement materials added to the original design, and most of that was added in the areas where the wing and fuselage meet! Eleven Tons!

As for the design work contracted out for Boeing.. I can hear the design team that came up with the structural calculations and design for the wing to fuselage joints defending their work. I visualize the reply in broken English… “Don’t blame us, Boeing never told us they wanted to carry passengers or cargo in that airplane, we gave them a very safe design to fly it assuming no loads.

Today we need question near everything, one of the more amazing projects is the Chevy Volt, Billions of Dollars spent on developing a car that only a handful of people want to buy! If you don’t agree, buy one and save the project!

Have a great day! George B.




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7 Responses to Jan 7 2011 Email of the day, Generator Mods, notes on AVRs, and know your loads.

  1. Ernie M. says:

    Here’s the link: XXXXXXXX

    BTW, on your page you’d mentioned that you go into the installation of a full power switch. I couldn’t find mention of it.

    Thanks for the answer.

  2. Peter Ranson says:

    Came across you when looking for some help with my generator – thought u might be able to point me in the right direction. I have a 6.5kw Condor petrol generator ( chinese made ) has been in storage for 3 yrs, I started it up the other day – perfect, runs great but only putting out 120v ( should be 230v ) was told not worth fixing but not prepared to give in yet. Could it be a faulty AVR unit, or does it sound like open circuit on a stator winding ( I have 4 wires coming out of stator ) would flashing the armature help ?? not sure where to start and thought I should email u for your thoughts. cheers Peter

    • George B. says:

      Peter, best to do a visual inspection of your connections, look at how the stator leads are laid down, look for stuff loose, next go to the field, does it have brushes? check them and make sure all looks good.

      Look on the inspection plate for field power figures, voltage and current, then use a voltmeter to see what you have across the field, this si a good place to start..

      Next take resistance readings of the field, and the stators windings, and check resistance to ground.

      Don’t know what to think of the 120 Volts, maybe your rectifer has a diode blown, and you are way down on field power?

      • Peter Ranson says:

        Thanks George – will look over the weekend, have checked voltage at the windings and have 120v – so maybe recifier ?. cheers

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