Watt Meters

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MasterE

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Does anyone know of a low cost watt meter(s) that I can put on a portable generator hook-up to help balance the load? I would like something I could mount in a small box or that is already in an enclosure.

MasterE
 
MasterE said:
Does anyone know of a low cost watt meter(s) that I can put on a portable generator hook-up to help balance the load? I would like something I could mount in a small box or that is already in an enclosure.

MasterE
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What voltage and amperage do you need to support? Three phase or 120/240 three wire?
You want more than just an ammeter because you have a wide variety of PF loads?
Usually the PFs are uniform enough that ammeters are good enough for balancing. Especially because it will be the VA not the watts that generate heat in the windings.
The watts determine the size engine you need to move the generator, and that will be the sum of the powers of the phases regardless of how it is distributed.

Mechanical forces in the windings and rotor, and the effectiveness of the voltage regulator might be abnormal if two windings carried the same VA but one had a PF of 1 and the other a PF of 0, but the heating in the two windings would be identical.

Three AC ammeters in one box, or one ammeter with a switch will do what you need, even if it is not what you want.
If you are going to switch the meter, you must either use a fixed multiple CT or multiple shunt type or a very special switch that shorts the terminals before removing the meter and connects the meter to the next phase before removing the short.
 
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Watt Meters

Thank you for the reply. This is for a simple 8800 watt 120/240 portable generator hooked up to a main panel using an interlock kit by interlockkit.com so I guess it is semi permanent. I would like to mount them near the inlet box so that the customer can balance the load between the two 120 legs. I would like them to be cheap enough that we could make these an option when doing similar installations.

Thanks,

MasterE
 
I can see many customers understanding that they can only run so much load, I can not see most customers that have limited electrical knowledge understanding load balancing. If they want to run two loads that are on same line they have an imbalance even if the total wattage of those loads is below the generator capability, but may still have too much load on one side of the source.
 
131017-0836 EDT

MasterE:

GoldDigger's suggestion of ammeters is probably the least cost way. And as he pointed out current is more important than power.

I would think that you want the monitoring in the home, and not at the generator.

How is this customer going to balance load?

If you do not overload current in either side, then balance probably does not matter in your application. Apparently this is for seldom used emergency power.

A TED (The Energy Detective) would work. I liked the system design of the 1000 system better than the 5000 system. The 1000 is no longer made. Both had/have problems with non-unity power factor, but this is not serious in your application. The TED system just can not be used to prove that a power factor correction capacitor is of no value in a home.

The TED 5000 can output both power and VA, but this is only one measurement, both phases are combined into one measurement, not two as might be implied by two current transformers. However, for balancing purposes one current transformer could be shorted at a time to allow monitoring of the other phase.

TED uses PLC (power line communication), a dumb idea, but it can be worked with by the use of filters, and limiting the communication region.

I have to continue to complain about the timeout problem on this forum.

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For one thing, there is no balancing of a load that will be changing. The best you can do is to simulate the most likely scenario and just use an amp clamp to get the loads as close as you can.

It's going to be tough to balance an emergency load. For example, if the customer wants a microwave or a toaster oven on a back up circuit, how are you going to balance that out? If you load up the other side to balance the load, as soon as the appliance is off, the load will become UN-balanced again.

Besides, the generator should be rated to handle it's max load on only one side. Just make sure you don't exceed that rating and just take your best guess at how to distribute the loads.
 
A whole bunch or questions could go round and round, is the service just to small for their desires, is my first one?
If you broke it down to an average hourly summary usage, what does this do to what the Client thinks they need? This alone with set-up some minimum balanced coverage.

I have to side with KW here, but several things need to be stated to the HO.

Why not calculate what the HO needs (think what they need) when they have to use the generator? With a napkin sketch this will help them understand what lifestyle they want to
have while under generator.

Present; your decisions based on the total service demand; make an allotment of circuits required by HO (back to - verses what is really even needed much less available).

My thoughts are the dictation from the HO requirements aren't wholesomely understood by HO.

Take of it what you want, dump the rest or in toto...
 
MasterE said:
Thank you for the reply. This is for a simple 8800 watt 120/240 portable generator hooked up to a main panel using an interlock kit by interlockkit.com so I guess it is semi permanent. I would like to mount them near the inlet box so that the customer can balance the load between the two 120 legs. I would like them to be cheap enough that we could make these an option when doing similar installations.

Thanks,

MasterE
Click to expand...

Some inexpensive multiple-branch circuit type transfer panels for 120/240 have two cheap AC ammeters built in. This is handy because the homeowner will be there at the transfer panel as they switch branch circuits on and off the generator for load management.
There is absolutely no reason to use a wattmeter instead of an ammeter.
Keep the current low enough and the power will be low enough too.
 
K8MHZ said:
Besides, the generator should be rated to handle it's max load on only one side.
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Since when? A generator rated for 30 amps will be able to deliver 30 amps on either side, but with only one side loaded to 30 amps that is still half the kVA rating of the generator. If you tried to get the full kVA rating from just one side that means loading it to 60 amps, probably going to heat up the windings.

GoldDigger said:
Some inexpensive multiple-branch circuit type transfer panels for 120/240 have two cheap AC ammeters built in. This is handy because the homeowner will be there at the transfer panel as they switch branch circuits on and off the generator for load management.
There is absolutely no reason to use a wattmeter instead of an ammeter.
Keep the current low enough and the power will be low enough too.
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I don't know what others do, I have a small generator and manual transfer switch. I turn off breakers to circuits I deem unnecessary or unable to be run by the generator, but leave most other things on. You can then turn on a light in any room, but you need to be smart enough to turn it off when not needed. Refrigerators and freezers cycle on and off as needed and you don't have much control over when that will happen. If you really need the capacity they are using for something else then you will need to turn them off. I'm certainly not going to go the the panel to check the load every time I want to turn something I consider a light load on. If I do end up with too much load the world is not going to end either, just have to go reset the generator breaker and probably remove a little load.

If a person wants to live as if there was no utility power lost then you need a generator big enough to power the connected load, or at least be able to shed some non essentials somehow and power the rest.
 
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