OT - Generator Loading

"Mark Jerde" wrote in news:Br4Bh.3935$Aa5.3355@trnddc01:

As an FYI computer UPS's do not like generators, or at least the smaller 'consumer' generators and will trip out if you try to supply them from a generator..

You are right.

Not quite twice as much, but fuel use goes up with load. Not as significantly as for diesels.

i

Thanks for the quick reply.

The UPSs are very "unloaded." The "internet UPS" normally powers the DSL modem, router, hub, a "workstation class PC" and a 21" monitor. Currently the PC and monitor are off until the power comes back on so the UPS only has

3 wall-warts hanging off it. The other two UPSs are similarily operating at a fraction of their normal use. No problems so far... ;-)

-- Mark

Thanks, I'll use this. ;-)

Thanks.

-- Mark

Forgot this one.

1. Suggestions for making the generator hard to steal? I'm thinking of padlocking a couple of 2"x12"x10' planks at right angles to it.

-- Mark

A lot depends on the UPS innards, some have wider tolerance for voltage and frequency variations than others. I'm a little leary of running any computer equipment directly off just any generator since a high-line blew down in a storm at my last job and we tried to make do with a 50 KW diesel running the computer room. Managed to knock out 5 expensive hard drives and a big chunk of mainframe trying to do that.

UPSes vary, some are a charger hooked to a battery hooked to an inverter, the inverter is always making juice no matter what's going on at the other side. Some just charge the battery until the power goes off, then switch to the inverter. This type is the one liable to give the most problems, any fluctuation in voltage and the thing will switch back and forth giving switching transients that the computer power supplies may not like. Also is the cheapest sort.

Consumer generators tend not to have very expensive voltage regulators, I've seen some that use inverter technology, though, for better voltage and frequency control. You have to be careful with that sort, the modified square waveform a lot put out isn't really compatible with electronics. Motors and resistance devices, sure. Just be careful.

Motors can take 2-3x their running current when starting, refrigerators in particular since they start under load. Switching transients like that can play hob with connected electronics, too.

Make sure you change oil when the engine manual says, it was like 8 hours of running to break in the b-in-l's standby generator before first oil(and filter) change. No time at all if you're using it continuously.

As far as long lasting, that's totally dependent on generator and engine design. There's at least three levels out there, lowest is cheapie consumer generators with plated engine bores and all-alloy construction, they'll probably self-destruct in a couple of hundred hours, but very light. Next up is the semi-portable type, "contractor grade", those will usually have a cast-in iron sleeve in an alloy body and maybe a cast iron head, usually on a wheeled frame, might last

1000 hours. Top of the line is the all-iron engine that will run several thousand hours or more before overhaul is needed, engine HP is usually higher, at least a twin cylinder, weight is definitely higher. Usually skid- or trailer-mounted.

Stan

Sounds like a good idea.

i

Thanks for your detailed reply. I just heard the generator slow down for about 1.5 seconds and I don't have a clue why. I'll use your post as I investigate.

-- Mark

I use line Conditioners on my system... Something like this one...

If you have a "frost-free" fridge - most are these days - there is a heating element built into it that, depending upon how frequently the door(s) gets opened, will be activated for a couple of minutes.

That heating element will draw about 1500 Watts - about the same as an electric space heater.

BTW, don't forget the wattage total of all those light bulbs...

Not necessarily true. On a good generator, a decent UPS will work. Frequency has to be close, and voltage within range. A ground is a good idea.

Frequency and voltage will NOT be within range if fully loaded or too lightly loaded on "cheap" generators.

I always use a dual conversion UPS on stuff that's critical, because it doesn't care how nasty the input power is, within very broad limits.

Switching power supplies have no issues with modified sine wave - most computer grade UPS units provide that kind of power. Motors are actually more particular, believe it or not.

Obviously running the generator at 100% or near it is going to take its wear on the engine. Running it at 5 percent is going to cause problems too. 50% is a good load, but common sense, don't needless load the thing down. If you are running house hold stuff on it it should be ok.

As for fuel consumption, the higher the load the more it eats, but it's not a linear progression, ie 1000 watts uses 1 gallon 2000 watts uses 2 gal etc isn't quite true, most engines will have a 'sweet spot' where they will be most efficient, diesels tend to find this at around 70 to 80 percent load. after that they suck down fuel really bad.

For the electronics. UPS' vary significantly from total crap to really good units. APC tends to have more tolerant ups systems. As bigger loads switch on and off, heating elements, and especially inductive loads like a compressor motor in a fridge for example, the generator will surge as it's governor reacts to the sudden demand on it. This frequency and voltage shift might very well be enough to make your ups shift to battery power for a few seconds until things settle out again. Most ups' come with computer software that you can hook it up to communicate with your computer and you can adjust the settings at when the ups will do what.

Do know that cheaper generators can give you fairly noisy (unclean) power, and this will make any noise / surge supressors you have work overtime and can greatly shorten their lives. Do know that inductive loads switching off, especially if under load, like your fridge compressor for example will send a high voltage spike up the line, and being you are no longer connected to the power grid (infinite bus) the only thing to help absorb this spike is your sensitive electronics. Grounding can be an issue too especially for the noise supression and the supressors might not work well. Avoid GFI's and UPS's together as they absolutely will NOT play well at all with each other.

I have a 4kw inverter / battery setup I run my stuff off when the power goes out and have had no problems at all with it, and it's a modified sinewave output. A squarewave inverter (read cheap) is the one to avoid as it will saturate coils and cause overheating or plain refusal to work with some motors.

As was mentioned, make sure you change the oil regularly in the generator, those engines run hot and hard and many being only air cooled, take a beating. One thing many people totally ignore is the gasoline, gas DOES go bad. I would recommend starting the unit up every month or few months just to make sure it starts, and to keep clean / fresh gas in it. Fuel stabilizers will help the gasoline last longer but won't prolong it forever. When the power goes out, and your generator has not run for a year, is not the time you want to find that it now will not start because your gas went bad and fouled out the carb.

NEVER run the generator indoors, keep it well ventillated, and you can get a chain and padlock and chain around the legs of the thing and wrap the chain around something sturdy to help prevent theft, ie a tree, your truck bumper, a fence post.. you get the idea.

Aaron

Do not load the generator to capacity. As others have stated, starting motors require a serious amount of amperage-----which won't be there if you're already using it for some other purpose. If you must run more things than you capacity of the generator, alternate them. I do that with our 5 kw generator and can even heat water. We run our well, water heater, boiler, freezer and two refrigerators, but not all at the same time. We've gone through two sessions of at least 40 hours on power outage and got by fine, even ran the computer when desired.

Don't know that I've ever noticed much difference, but for sure generating your own power is far more expensive than paying your power bill. My advice is to run the things you need, when you need them, and nothing more. That's what we've been doing and it works well enough.

Harold

The thief just needs a Skillsaw, you've already given him a place to plug it in. Paul

Believe it or not, I actually speak English. I just tried to read what I wrote, in haste, previously.

I certainly hope you guys have better luck deciphering it than I do. I'm not sure what the hell I said, or meant.

Harold

The freezer is trying to tell you something... that's the "8500W starting watts" rating talking. Always leave a little cushion on the load, but if you want you can run one electric heater and camp out around it just fine.

But you'll burn more fuel to make the electricity to make the heat (all the losses in each stage) than you would if you bought a nice propane or kerosene fueled heater and turned the fuel directly into heat. If you have regular fuel available (natural gas, propane, oil) plug in the furnace - the blower doesn't draw as much as a portable electric space heater.

I'd say not quite double, because there are a lot of losses just from running the generator that are static, the rotation speed is still 3600RPM independent of load, which is the engine and generator cooling fans, bearing losses, among other things. But that's how to do the math for a Worst Case.

And you asked about running a Computer off a small generator elsewhere, it all depends on whether the Generator maker claims it's clean enough and whether they lied about it on the packaging or not. You need under 5% Total Harmonic Distortion on the output.

In the last year or so it has become an issue, so if the generator will do it the paperwork will tell you. And there are several new DVOM/Clamp Amps out there that claim to measure the THD and flag "Clean Power" if it passes the test.

If not, my first thought would be to get a SOLA Ferroresonant transformer and clean up the power. (Note that it's only 92% efficient, figure that into your loading.)

But I'd double-check this with the SOLA engineering department before trying it on a computer you care about...

-->--

Im in the UK but totally off the mains grid. So weve had generators for some 35 yrs. Any generator is best run between 30 and 70% rated load, to run at max load is not advised unless its for a very good reason.. Your fridge and freezer have induction motors that draw on start 2 to

3 times the current used to run. So thats another limiting factor. If you want it to last dont overload it. For heating go for a wood burning stove. If you want to think really long term, look out for a diesel powered gen set. the fuel storage is much safer and theres little depreciation if it used only occasionally. there always in demand.

Job #1 this morning for the generator was making a pot of coffee. Mmmm, good! Nothing else, not even the internet UPS, was plugged in until the coffee maker was done & unplugged.

It's the simple creature comforts I really appreciate. ;-)

-- Mark