Kill A Watt P4400 on sale

My sister replaced her old (died) fridge this spring. The old was not that old, about 6 years, IIRC. The new was a model considered energy efficient. She did notice a drop in electrical consumption with the new one, and figured that the new one would have paid for itself in about 4 to 6 years.

On 9/5/2009 6:23 AM PeterD spake thus:

He's not *selling* it, you idiot.

Some more...

Photo of the insides of the original and the later P4440 versions. The P4440 is at the bottom:

The original version has no memory (loses history if unplugged) and has only 4 buttons on the front. The later version has 5 buttons and retains usage history until the cap discharges. I don't have a P4460 (EZ) inside photo.

I have about 4 of them, some of which are permanently installed monitoring the power consumption of various devices. I use 3 more for distributing the electric power bill on a mountaintop radio site (with poor weather protection). The main advantage is the low price. However, the operation of the 5 buttons is not very obvious and I have to keep a copy of the instructions nearby.

Costco has the P4460 for $27.

Recently, I've been considering alternatives, which seem to have some advantages, like less button pushing. I have one of these on order:

Black and Decker also makes one, but it's overpriced at about $100.:

As for accuracy, the P4400 models that I have seem fairly accurate, even at low levels. I don't have an easy way to calibrate these, especially with odd power factors. My mechanical disc power meter and the numbers from a P4400 were quite close when I tested both in series running only a refridgerator for a month.

I use both clamp-on and inline meters. The clamp-on is best for troubleshooting while the inline is best for monitoring. My no-name Chinese clamp-on meter does accumulate usage (logging), but does not have the power factor correction I need for dealing with inductive loads (motors), or badly designed switchers. The inline can also do cost calculations, which is something my customers can see and understand.

However, the big advantage is that I can buy the inline meter for about $27, do my song and dance for the customer, and then sell it to him for about twice that. It also give the customer the impression that I'm tryting to save him money by monitoring his electricity usage. It's design makes it acceptable for leaving it in place for monitoring, while a clamp-on meter plus inline cord splitter, would be an ugly mess.

Note: I'm not an electrician. This week, I fix computahs. Computer owners often want to know how much power their PC or monitor is burning. Hmmm... I just bought myself a new desktop and forgot to measure it.

On 9/5/2009 11:50 AM Jeff Liebermann spake thus:

So how does this thing work?

It looks like the power just passes straight through from plug to socket over there on the left. Is there a current transformer in there somewhere? What about that half-loop thingy on top? And what's that semicircular thing doing between the power prongs above the ground connector?

intermittently.

Correct. But I feel my electric bill is too high, and I need some evidence to argue with the utility. I intend to measure everything in my condo.

It works quite well.

The actual device is made by Prodigit in China:

I haven't ripped it apart and traced out a schematic (yet). As near as I can guess(tm), the big half loop near the power jack is a low value series resistor. There's no current xformer inside. The big green capacitor is probably AC line coupling for measuring the voltage. The LM324/LM2902 is probably setup as input sections of an instrumentation amplifier to float and isolate the AC line from the rest of the circuitry:

The chip on the display (right) section is apparently a proprietary ASIC and probably handles some of the analog circuitry, the A/D converters, and display functions.

Series resistor.

It's part of the plastic case. My guess(tm) is that it's to align the power jack connectors to the case. Since there are no mounting screws, and the PCB is attached to the case with hot melt glue, something like that is required. No clue why the strange shape as some round holes would have done as well. My guess(tm) is that if one of the brass power jacks became detached from the PCB, it would not lean into the opposing connector as it is blocked by the plastic thing.

Yes you can with the proper adapter.

The Radio Shock inline current sensor is the device on the right. It's normally NOT sold seperately. It consists of 1 turn and 10 turn loops inside a plastic case, wired in series with the AC line. The clamp-on meter clips into either the 1 turn hole for fairly large currents, or the 10 turn hole for a 10x current multiplier. You could easily build one of these if you can't find one to buy.

However, there's a problem. Your fridge is an inductive load, which will require power factor correction to obtain the same current as measured by the typical disc type electric power meter. You can't do that with a typical clamp-on ammeter. You can do that with a wall mounted inline power meter.

Also, watch out for refrigerators that have self-defrosters. Some are on demand, while others are on a timer. The defroster sucks LOTS of power and will be a big part of the electric bill. Same with on-demand ice cube makers.

On 9/5/2009 12:37 PM Jeff Liebermann spake thus:

Ah, so. So the loop must be connected on one side to the incoming hot line, and on the other side to the outgoing hot line. Then the unit measures the voltage across the loop (resistor) proportional to current. Right?

"Saving energy when using refrigerators and freezers"

What I did initially was:

1. Cleaned the crap out from behind and under the fridge so that the radiator coils can efficiently radiate.
2. Moved the fridge away from the wall to improve air flow.
3. Disarmed the self-defrost timer and defrosted it manually (pull the plug and chisle out the ice).

My guess(tm) is about a 20% decrease in energy costs, mostly because it was running more efficiently.

The above fridge was sufficiently old that the compressor was starting to make noises when running. So, I decided I could live with a much smaller fridge and purchased a small "bar type" cheapo for $120. I haven't bothered to calculate the savings, but I vaguely recall my monthly electric bill at the time dropped about $20.

Exactly. It's quite simple.

There's usually a patent on something like this. Digging....bingo:

"Electric adapter with display unit"

Nice explanation with a blockish diagram. My guess(tm) was wrong about half the instrumentation amp. It's even cruder than I thought.

Some additional drivel on patent litigation:

I'm not sure of the final judgement in the case, but the infringing UPM Marketing device is probably the one I have on order and are being sold again by Smarthome:

Know what you mean. ;-)

No method of getting them to check the meter accurately - IIRC in the UK they fit a second one to check the first.

In my case I hadn't really noticed how much lighting load I had - and leaving lights on - until the price doubled. My house and water heating are gas.

I intend to measure the energy over a week or so. That should average out things.

On 9/4/2009 5:51 AM William Sommerwerck spake thus:

Not quite. Singly they're $21.99. $19.99 ea. for 3 or more.

In an earlier post, I indicated that you need a code...

laces

al.

Wow! I claim that I first met him about 44 years ago.

It's possible. I attended Caltech briefly then (Fall, 1965). I was a total shmuck then, and I apologize.

I apologize for not remembering your name, but it just doesn't ring a bell.

A refridgerator in a natural gas heated/hot water/cooking home is the #1 watt bandit. My 10 something CUF fridge all of 3 years old consumes