The Generator and the UPS

An issue I had to deal with recently; was an unstable generator/UPS relationship.  When the generator was running under load, it surged repeatedly causing the UPS to drop out and not recharge.  Eventually, the UPS ran out of juice and shut down, killing the power to the Sine Systems remote control and telephone system.  Of the two, the remote control was the biggest pain to fix, as it lost its timed commands and would not reduce power at sunset for the associated class D AM station.

What went wrong?  This is a chart of typical problems with generators operating UPS loads:

SymptomPotential Problem
Fail to “lock on” to generator powerImproper generator frequency or voltage
Poor generator regulation
Unrealistic performance requirements
Instability of generatorVoltage regulator sensitivity
Control loop compatibility
Filter/control interaction
Governor or AVR problem
Fail to sync bypassMetering errors
Instability at specific load levelsControl loop compatibility
Instability at load changesControl loop compatibility
Metring errorsGenerator output voltage distortion
Loss of voltage controlExcess capacitance in filters vs. load

Table courtesy of Cummins Power Generation.

Generator excitation methods can be the culprit in many of these situations.  Generators often use one of three types of excitation for their field coils:

  • Shunt-excited SCR (silicon-controlled rectifier)
  • Shunt-excited PWM (pulse width modulation)
  • PGM (permanent magnet generator)

Of the three, the permanent magnet generator is the most stable since the AVR (automatic voltage regulator) is powered by a separate small generator which is unaffected by the load on the main generator output.  SCR and PWM both use the generator output windings, which makes them susceptible to load-inducted voltage distortion brought on by non-linear loads.  Therefore, in locations where large UPSs are known to be part of the load, PGM-excited generators are the best choice.

PMG generator diagram
PMG generator diagram

Sometimes, the generator is already in use before the UPS is installed.  In that case, there are some remedial steps that can be taken.  The speed which the voltage regulator reacts to changes in the load is often the culprit in many of these situations.  It may seem counterintuitive, however, the faster the AVR reacts, the more fluctuations there will be in the voltage and frequency.  A UPS can operate under a wide range of voltages and frequency, provided they do not rapidly change.

Depending on other loads, it may be necessary to dampen the gain on the AVR to slow it’s reactions down.  This will work if there are no large intermittent starting loads on the generator such as air conditioning compressors.

Another method would be to delay the UPS transfer to generator power until after all the other loads have been satisfied.  This will ensure that the generator voltage and current fluctuations are damped by the existing load.

The generator’s size needs to account for the equipment attached to the UPS and the battery charging load. With a larger UPS, the battery charging load can be significant. Generators that are improperly sized will not be made to work under any circumstances, hence the “unrealistic performance requirements” noted in the chart above.

You can read the entire Cummins Power white paper on generators powering UPS loads here.

The Onan RS-15000 Generator

It is a cute little thing. This one is being installed at a mountaintop transmitter site for a class A WKIP-FM in Ellenville, NY.  It is way up in the air (at least by local standards) at 2,450 feet AMSL.  As such, the TPO is only 300 watts into a one-bay antenna.  Therefore, even this little generator will be loafing along.  I added all the rack equipment up, both transmitters (main and backup), and the electric resistance heater and came up with a grand total of 6,300 watts.  The working load today was 3,200 watts, which I would assume is about average.

Onan RS-15000 at transmitter site with ice shield
Onan RS-15000 at transmitter site with ice shield

Denis, my sometimes helper, build an ice shield over the top of the unit with pressure-treated wood.  This unit was placed about 40 feet away from the 140-foot tower, next to the concrete block building.  Still, on a windy day, I could see some chunks of ice flying off the tower in this direction.

It has a Lister/Petter 1900 cc engine, 1800 RPM, 240-volt split phase generator.  At 25% load, it burns 1.2 gallons of propane per hour.

Onan RS-15000 gaseous generator
Onan RS-15000 gaseous generator

This is annoying. The gas installer blocked access to one of the through holes in the bottom of the enclosure frame. Actually, more than annoying, downright annoying as it blocked the exact center of the hole.  I had to move the regulator up about two inches so I could run the 1-inch flex under the gas line.  This, in turn, led to some amount of swearing.

Gas supply to generator installed by selfish gas man
Gas supply to a generator installed by selfish gas man or woman

Another side of the engine:

Lister petter 4 cylinder 1900 cc engine
Lister Petter 4 cylinder 1900 cc engine

Pushrods going to rocker’s arms over the cylinders.  Low-tech, under-head cam engine. That’s okay, so long as it works when it is supposed to.

Onan RS-15000 generator wired to transmitter building
Onan RS-15000 generator wired to the transmitter building

PVC conduit running into the transfer switch.  The final connection is made with a liquid-tight flexible metal conduit (FMC).  The control wiring is run in a separate 1/2-inch conduit, as required by NEC.

Overhaul of the Onan 12JC4R generator

I was fortunate enough to acquire this generator last fall.  It was new in 1969 and has unknown hours on it, but it appears in decent shape.  I am going to do a level two overhaul and install it as backup power for my house/shop.  The first order of business is a complete inspection.  I discovered a few problems; the starter didn’t crank, the distributor was loose, and the carburetor had some burned-out chunk of metal attached to it.

Onan 12JC4R generator
Onan 12JC4R generator

First, the starter:  These units use a Prestolite MEO3006 starter, which is common to several Chrysler products from the late ’60s and early ’70s.  This is obviously a replacement unit, as it is not “Onan Green.”  When I hooked a battery up and tried to turn the motor over, the start relay clicked but nothing else happened.  I dismounted the starter and removed the starter solenoid.  The interior of the starter motor looked in good condition, which points to the solenoid.  Sure enough, I removed the back of that unit and found two wires burned through and a large blackened area.  While I had the starter off, I hooked it up to a 12-volt battery and it worked fine.  A new starter costs $469.00, and a new solenoid cost $59.00.  I opted for the solenoid.

Onan 12JC4R burned out generator starter solenoid
Onan 12JC4R burned out generator starter solenoid

The next thing is the distributor.  I was checking the points and contemplating replacing the breaker points with an electronic ignition when I discovered the distributor could turn 1/8 of a turn in each direction, as when making timing adjustments.

Onan 12JC 4R distributor clamp
Onan 12JC 4R distributor clamp

I used a 3/8 box wrench and tighten up the clamp holding the distributor shaft.  It took several turns and makes me wonder why it was loose.  I will have to check the timing with a light once I get it running.  This also could be why the generator was not running when we took it out of service.

Onan 12JC 4R rotor and breaker points
Onan 12JC 4R rotor and breaker points

As for the points, they look brand new, as do the rotor and distributor cap.

Onan 12JC 4R generator spark plug, champion H8C
Onan 12JC 4R generator spark plug, champion H8C

The spark plugs look well used and the plug wires look original.

Finally, there was an electric choke mechanism on the carburetor which is completely unnecessary for a propane-fueled unit.  The choke plate itself was wired open.  The electric choke was burned open, so I removed the assembly.  I then spent some time at the local NAPA cross-referencing parts.  Here is a tune-up list:

NomenclatureOnan part (old)Onan part (new)Napa PartAlternate
Oil Filter122A185122-01931084Fram PH16
Distributor cap166B307166-0235AL91 
Ignition Coil**166B310166-0859-02701002PRX 405011
Plug wire #1167A1410167-1602701064 
Plug wire 2,3,4167A1409167-1602701063 
Spark Plug167-4167- Champ H8C***
Air Filter140B640140-19077-02241 
Starter191C324191-0324 Prestolite MEO3006
*Electronic ignition setN/A166-0825 Pertronics 1545**
**Ignition coil W/PRX 1545   PRX 405011

*Condenser and breaker points can be substituted for an electronic ignition kit, either Onan 166-0825 or Pertronics 1545 with Pertronics PRX 405011 coil.
**Pertronics electronic ignition must be used with Pertronics coil
***Champion RH8C plugs should be used with replacement wires without noise suppression plug boots.

This is for an Onan 12JC generator circa 1969 with a Studebaker engine. Other models/years may vary.  The other issue with this unit is there is no supervisory monitoring and control.  There is no oil pressure loss, overheating, or over-crank faults.  This is why the starter solenoid failed.  To remedy that situation, I started to design a better control circuit.  Then I looked around on the inner tubes and found somebody had already done this.  DynaGen makes the GSC400p which can monitor oil pressure, engine temperature, frequency, engine RPM, hours, voltage, and current.  It can fault for any out-of-tolerance condition, as programmed by the user.

Retrofit generator controller
Retrofit generator controller

I plan to install this in the original control box, leaving the original control circuit intact by using the remote start/stop connections.  I keep the original remote/start/stop switch and hand crank switch in place for use if the fancy controller fails.

Better Times at WICC transmitter site

The WICC transmitter site, Pleasure Beach in Bridgeport, has been cut off from normal access since the bridge to the island burned in 1996.  Since that time, access has been by boat with a 0.93-mile walk from the dock to the transmitter building.

Last summer, LVI Construction, under contract from the Town of Stratford, put in a temporary road and began removing the burned out cottages.  While that road is in place, the radio station has been able to access the site and get many important things accomplished.  These include:

  • Replacing the vandal damaged top beacon on the South tower
  • Removing several decades worth of stored crap, garbage, obsolete and unused equipment
  • Repair the electrical service to the building
  • Replace the generator transfer switch
  • Repair the Sonitrol building alarm
  • Replace the old Onan Generator
  • Have the power company replace the 3-phase circuit from the point where the underwater cables come ashore to the transmitter building.

All of these projects should greatly improve the reliability of the station.  This should make Bill, happy, who appears to have a WICC chip implanted in his brain because every time the carrier is interrupted he posts about it on the website.

The biggest issue with the site was the utility feed from the shore to the transmitter building.  The original circuit was installed in 1936 when the station moved to the island.  It was old and the poles were all rotting and had horizontal cross arms.  Ospreys especially liked the horizontal cross arms as they made good nesting spots.  That is, until the nest shorts out one of the phases catches on fire and burns the top of the pole off.  This has happened several times over the years causing many hours of off-air time.

WICC new utility service
WICC new utility service

United Illuminating, the local utility company, was very cooperative and installed new utility poles, wires, breakers, and transformers, this time with a vertical phase arrangement, which should keep the Ospreys off of them.  Additionally, the cottage removal project included installing Osprey nesting poles.

Pleasure beach cottages removed
Pleasure beach cottages removed

With almost all of the cottages now removed, the area looks much better than before.  Actually, it should be a nice nature preserve, and hopefully, the absence of the buildings might reduce the number of vandals in the area.  The work is almost done, so the road is about to be taken up. This means we need to wrap up the work out there, so the final push is on.

WICC transmitter building
WICC transmitter building

In the last three weeks, 10 truckloads of junk have been hauled out of the transmitter building and generator shack.   Over 1,500 pounds of scrap steel, 640 pounds of insulated wire, 2,000 pounds of particle board furniture, old t-shirts, and hats (something called “Taste of Bridgeport” which, if anyone knows what that was let me know), old propane tanks, batteries, etc.  We also managed to fix the fence and gate in front of the building and cut down the overgrown yew bushes and bittersweet vines.

Transfer Switch
Transfer Switch

The old Kolher transfer switch was also an issue.  There was no place to mount a new switch inside and mounting one outside is out of the question, so the guts from the Kohler switch were removed and replaced with an ASCO unit.  This was done in the summer of 2009.  The breaker on the right side is the main service disconnect for the building, which was installed in September.

Onan 12JC 4R air cooled generator
Onan 12 KW 12JC 4R air cooled generator, removed from service

Today, it was time to replace the Onan propane generator.  The old generator is an Onan 12JC-4R air-cooled propane unit which was installed on April 4, 1969, at a cost of $1,545.00.  For many years, this unit gave reliable service, but it has many, many hours on it and it lacks the fault/self-control circuits needed for remote (read desolate) operation.  Several times over the last few years, the generator would run out of gas or the propane tank would freeze up and the starter would crank until it burned out.

It was cold out on the island, with temperatures in the twenties and a bitter west wind blowing right into the generator shack.  All of this conspired to make working conditions difficult.  Wind chill readings were in the single digits all day long, and in spite of long johns and extra layers, by 3 pm I was shivering and even several hours after coming inside, I still felt cold.

Using tractor to move new generator
Using tractor to move new generator

The new generator is a Cummins/Onan 20GGMA which is rated for 20 KW.  We used a John Deere bucket tractor to move the generator from the flatbed truck to the generator building, and then push it inside.  The old generator wiring to the transfer switch was reused, but a piece of flex was used to connect to the generator instead of the solid conduit.  The building fan was also wired up so that it would run whenever the generator was running.

The generator load with all possible things switched on and the transmitter running at full power is about 12,000 watts, but this would mean the air conditioner and tower lights were on during the daytime.  More likely, the transmitter will be at low power when the tower lights are on and the AC will be intermittent on/off at night.  At full load, this generator uses slightly less than 2 gallons of propane per hour.  At half load, I’d estimate that to be 1.4 or so gallons.

Cummins Onan generator in new home
100 pound propane gas tanks
100 pound propane gas tanks

HOCON gas came out and connected six 100-pound propane tanks in series, which should prevent tank icing.  Propane weighs about 4.11 pounds per gallon, therefore the fuel supply should last about 100 hours, or 4.5 days, give or take.  Why 100-pound tanks?  Because we will have to shuffle them back and forth between the dock and the generator shed, a journey of about one mile, in a cart.  Anything larger would be impossible to deal with.  Even so, refilling the propane will be a 2 person job and will likely take all day.