Power Efficiency and Power Loss Measurements

[Billy Mayo]

At work I have to measure the Power Efficiency of our product

The Product runs off 120 VAC or runs off DC batteries , So we are going to measure the Power Efficiency of AC or DC batteries test, from the power input and power output

Power Output / Power Input X 100 = Power Efficiency or Poss Loss?

1.) I have to measure the Efficiency at load percentage of fully charging current of the battery

What is the formula for this?

2.) I have to measure the Efficiency at load percentage & Trickle Battery Charger

What is the formula for this?

How do you measure the "Trickle" of the battery charging? My manager said that the current should be in the millivolts supplied to the battery bank when measuring the Trickle of a battery or batteries

3.) I have to measure the Efficiency of the Battery

Which the formula is: Power output / Battery Voltage X current = power input X 100 = Efficiency?

 

[ChrisP58]

Efficiency is the ratio of output power to input power. And when measured in real time is fairly strait forward. But a battery changes the dynamics of the measurement immensely.

Why? Because a battery is not a real time device. It takes power in over time, then releases it over time.

The only way to measure the efficiency of a battery is to integrate every watt-second of input power, then integrate every watt-second of output power. You must start the charge process, and end the discharge process, at EXACTLY the same state of charge. THEN calculate the efficiency.

Why do you need to know the efficiency of your battery?

 

[Billy Mayo]

Why do you need to know the efficiency of your battery?

The product/unit can either run on AC or DC batteries

So we need to know the power loss and power efficiency when the product unit is running on DC batteries

How would u calculate the efficiency or power loss of a unit or product? when running on AC or DC batteries?

 

[ChrisP58]

You measure the output power and divide it by the input power. If you have two different operating modes, AC and DC, then you will have two different sets of measurements, and two different efficiency results.

Make sure that your AC measurements are with true RMS meters.

 

[Billy Mayo]

How would you do the Power Efficiency when it's in DC mode? since the Batteries are charging

How do you measure the Trickle charge of the batteries? it should be in milliamps of batteries current

Trickle of the batteries, it not the norminal voltage or cut-off voltage or floating voltage

 

[KeepItSimpleStupid]

Power measurement is not easy. I will refer you to this application note: http://www.lecroy.com/Support/TechLib/registerPDF.aspx?documentID=187

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For your DC measurement of power, your going to have to disable the trickle charging circuitry.
Measuring DC power is straightforward. Just the product of Idc and Vdc at the battery.

Measuring the AC power in and Ac power out is a bit more complicated. See the application note.

It would also be a wise measurement to measure the power factor. There should be regulations concerning the power factor of an appliance.

 

[ericgibbs]

hi Billy,

The more I read the way you are technically phrasing your posts and the words you are using, the more I am convinced that you already have a good working knowledge of electronics.???

Are your questions related to Homework assignments/questions.??

E

 

[Billy Mayo]

your going to have to disable the trickle charging circuitry.

If the product or unit doesn't have a trickle charging circuit , how do you measure the Trickle charging of a battery? it should be in milliamps

 

[KeepItSimpleStupid]

Insert an appropriately sized reistor that doesn't drop much voltage in series with the battery and measure the voltage across it.

e.g. If you expect < 3000 mA and want your output to be 300 mV, the R=300 mV/3000 mA or 0.1 ohm precision resistor.

For greater accuracy get a 4-terminal resistor or a Current Shunt. You can also use an Allegro Hall effect sensor.

 

[ChrisP58]

If the product or unit doesn't have a trickle charging circuit , how do you measure the Trickle charging of a battery? it should be in milliamps

If it doesn't have a trickle charging circuit, how is the trickle charging accomplished?

 

[RCinFLA]

Do you care about power factor and/or harmonic current content on AC side when using AC input?

 

[Billy Mayo]

I don't think so, but our products power factor is 0.7 power factor

 

[ronv]

What is your product a power supply? A battery charger or ?.

 

[KeepItSimpleStupid]

@ronv

Billy has been discussing Uninteruptable Power Supplies for quite a while.

 

[Billy Mayo]

It's a UPS , they either run on AC or DC batteries and output 120 VAC , power factor is either .7 or 1

 

[MrAl]

Hi,

To measure the current into or out of a battery you can use a current meter, or a resistor in series with the battery and measure the voltage across the resistor and then use Ohm's Law to calculate the current. For example, using a 1 ohm resistor (of the correct wattage) if you see a 0.1 volt drop then you have a 0.1 amp current. But usually we use a smaller resistor like 0.1, but then again it depends on the current and how much voltage drop is acceptable.

One catch is when the battery current is very very high like 100 amps or 200 amps. Then we have to be more careful what we use to measure that current. Most likely a current shunt or a clamp on DC ammeter. Clamp on DC ammeters measure current without having to break the circuit and are accurate enough for most battery applications. However, some clamp on ammeters are sold as DC ammeters when really all they measure is AC current, and they can say "DC" because they also measure DC voltage. So if you want to purchase a Clamp On DC Ammeter then you need to make sure the spec's state that it will measure DC current. Most of them also measure AC current too.