How to measure load on generator?

[Jason]

Hi everyone,

First post for me, great forums!

I'm curious how folks commonly measure the load on their generators. I've seen a few of the posts here mention a break-in period where you run for 1 hour at 25% load, another hour at 50% load, etc. until you hit full load. My question is how do you know when you are at 25%, 50%, or full load?

I've just had a 10kW Generac model 5281 delivered. It's not hooked up yet, the install will be later this week. At first I was concerned that the 10 circuit ATS wouldn't be enough to power all of the circuits I'd like to have operational during a power outage, so my installer offered to upgrade me to the 16 circuit ATS. He said that more circuits means that I need to be more careful about how I load the generator because I can more easily overload it now. Is there a way for me to check what the actual load on the generator is?

[fara macho]

Kelly, et al, I'm also getting a bit confused on break in procedure. Kelly are you saying my break in procedure should have been running my 16kw 10 hours straight , with or without load (saw in old post) rather than the step load breakin.

p.s. I also read today on another Generac forum (sorry to cheat on you Kelly) that the initial breakin should be with the regualr oil that comes in the generator and not synthetic oil, ( I did breakin w/ synthetic 5w30) Fara

[M Miller]

The easiest and safest way to check the load is to get yourself a digital clamp meter. Do a search on clamp meter to see what they are. Your 16 circuit load center will be a sub panel with probably a 70 amp 240v breaker in the main to power the sub panel. You can check the amps on each leg of this breaker in the main when under utility power. This will show what load you have on these 16 circuits which of course will be the load your generator will need to power.

[Jason]

Thanks, I took a look at clamp meters, and they seem to be more geared toward installers, I'm looking for something more permenant. I found this:

http://nooutage.com/RMK.HTM

Anyone have any opinions on these? Also found this:

http://www.everygenerator.com/Briggs-and-Stratton-6090-BAS1033.html

Though I'm not sure how that Brigg's watt meter can provide you a percentage number if it doesn't know what the generator is rated at. I'm assuming there must be someway to configure it to know what size generator you are using.

Anyone have an experience with these?

[cosmicvoid]

The Nooutage box looks like a pair of current transformers and ammeters. It will tell you the current in each leg of your load.

That Briggs watt meter looks like a scam. "keeps track of the percent of power your generator is using in real time"... my generator doesn't "use" power, it supplies it. That device, plugged into an outlet, would only tell you the line voltage and the power used by something plugged into it.

This is what I have, mounted next to the ATS, to monitor the power used in the breaker panel.
http://pdf.directindustry.com/pdf/crompton-instruments/integra-dms-catalogue/12296-11350-_10.html

Measuring the load is not difficult, its making the load be what you want that's hard. I mean, how do you command your appliances to cycle on simultaneously? Do you even have enough devices on your load to draw 100% power?

[Jason]

Wow, thanks for the link. That's probably a lot more than I need, and at $375, it's a bit more than I was looking to spend.

I was wondering about the Briggs meter too, how can it tell you what percentage of your generator capacity you are using without knowing the rated power of the generator? They sell them in lots of places, so I'm not sure that it's a scam, I'm just really curious how it works.

We are using a 16 circuit ATS with a 10kW generator. Normally the 16 circuit ATS is used with the 16kW generator, so I'll be able to overload the generator much easier. I'm just looking for a simple way to monitor my load so that I don't over do it.

As for making the load what you want it to be, that shouldn't be too difficult with a few high power appliances and some lights that you can turn on individually. I figure Home theater plus computer combined is good for 1kW. Toaster, microwave and hair dryer are good for at least another 1kW each, that puts you at 4kW. An electric clothes dryer is a good 5kW all by itself. Now start turning on lights and it should be easy to hit 10kW (in my case). I just don't want to do that blind ;)

[M Miller]

With a generator running you will need to be prudent about what you run at the same time. In other words don't dry your clothes while you are using your toaster, microwave, hair dryers and a maybe a space heaters. When you lose utility the clothes dryer and microwave will cut off and have to be started again manually so this shouldn't be hard.

The first meter you provided the link for looks like it would do the job. You may want to put the donut transformers around the wires that come out of the actual transfer mechanism and connect to the load center. This way you can monitor your usage while on utility AND generator power to get an idea of your usage.

[cosmicvoid]

As for making the load what you want it to be, that shouldn't be too difficult with a few high power appliances and some lights that you can turn on individually. I figure Home theater plus computer combined is good for 1kW. Toaster, microwave and hair dryer are good for at least another 1kW each, that puts you at 4kW. An electric clothes dryer is a good 5kW all by itself. Now start turning on lights and it should be easy to hit 10kW (in my case). I just don't want to do that blind ;)Most people don't put the heavy appliance circuits on the generator panel (e.g. water heater, oven, stove, dryer, space heaters), unless you are feeding the main panel, a la 'whole house' style.

As for the Briggs meter, why don't you buy one, and let us know how it works :rolleyes: .

I got the Crompton meter for $360, plus $15 for the CTs. I wanted the 'demand' recording features, so I could see what the peak demand was, while I wasn't watching. For my panel, the peak demand is about 90 amps; my 16KW gen is good for 65 (maybe 70) amps. I don't know which items were drawing power to cause the 90 amp peak, but it tells me that I may have to do duty cycling during an outage.

[Jason]

I'll have a few heavy items on mine, which is why I'm really interested in monitoring the load. I'll have the following "big" appliances on my transfer panel:

Dishwasher
Microwave
Clothes washer
Clothes dryer
Refigerators (2x)

I already know that when the Dryer is running it can consume around 5.2kW all by itself (I've been out at the power company's meter on my house counting revolutions as big appliances are running).

In my search, I came across some other meters:

http://www.powermeterstore.com/index.php?cPath=550&products_id=3528

This one is designed to monitor commercial power to allow you to better control your consumption. I'm wondering if there is a way to install it such that it would monitor the load of commerical power under normal circumstances, and generator power during an outage?

[cosmicvoid]

I looked around that site during my researches, and considered several models they sell. I ignored the TED and other "billing oriented" monitors, as I was interested in the esoteric technical readings, not cost accumulation. While it would have been nice to get a monitor for less than $200, I decided I need the demand readings more than I needed to save money on the meter.I'm wondering if there is a way to install it such that it would monitor the load of commerical power under normal circumstances, and generator power during an outage?Sure, just put the CTs on the output of your transfer switch, where it feeds the panel. That's how mine's wired.

[Jason]

Thanks for the advice! I think I'll probably get the TED, because it's readable inside the house (vs. out in the garage) and gives the overall load, and will be useful during non-outage periods as well. I'll probably also get one of these:

http://www.electricgeneratorsdirect.com/catalog/product_info.php?products_id=595

As the Gen-Tran meter will allow me to see the individual load on each hot wire from the generator.

You've also peaked my interest, what "deamnd" readings is your meter giving you that the TED won't?

[cosmicvoid]

Now that I go back and look at the TED's capabilities, I see that it does show line voltage and peak demand power. But, for me, it was too consumerish, with too much emphasis on billing info. It doesn't show per-leg current flow either, which is why I guess you're getting the dual ammeter box too. No power factor info either.

The Crompton also has a remote interface (RS422), so I can log data from my computer. Here is a pic of the remote comm utility dialog screen, showing my current (meaning 'now') readings. You can see my recent peak current demand is 63.8 amps (near my gen's max), even though the associated power demand peak is only 7.74KW. So there is more to the picture than just the KW numbers.

[Jason]

I must admit, that looks pretty cool, and I really like the PC integration. But I've also factored in that I want something fairly simple to use so that my wife isn't intimidated by it. In that regard, the T.E.D. is geared more toward what I'm looking for.

Aren't 63.8 amps and 7.74kW virtually the same value?

63.8 amps x 122 volts = 7,783.6 watts = 7.78kW

That's only a 0.5% difference.

[cosmicvoid]

It could be the same, but there is no way of knowing how that 63.8 amps was shared between the two hot legs. Is it a 120 volt load on one leg, or is 32 amps on each leg caused by a 240 volt load device, or somewhere in between. And at low power factors, there can be a disparity between current x voltage and real power (that's why VA is useful).

Any way, I'm a geek for this kind of instrumentation, and I'm not suggesting you should get one.

[Jason]

I can totally appreciate your geekness ;) And I'm very thankful for your advice. Just having this discussion has allowed me to better define what my requirements are, because at first I didn't even know what it was exactly I was trying to do. I just knew that I needed some way to determine the load on my generator. After posting here, reading your comments and those of other folks, that allowed me to understand what's available, so I was able to refine my searches, and ultimately settle on the devices that will do what I'm looking for. So for that, you've been a huge help, and I thank you!