Wattmeters...for beginners - please keep it simple

[Cyclicscooby]

Here...

Makes sense in the diagram, but as it has 'normal' batt wires plus balancer socket (Not joined together like the diagram), I cant see any good reason for it.. !!!

Apart from that tho, it is an essential tool...

 

Luv

Chrisie.. xx

[Malcolm Fisher]

Tim,

Thanks for your reply.

I have used my meter with it's control knob and a radio transmitter to test several set ups - mainly different propellers with one new brushless motor and just out of curiosity with a couple of "can" motors I have.

Having used the meter as a stand alone unit, I thought it just might be possible to do the ESC programming, using the control knob as the throttle stick, hence my question.

Having read through the ESC data several times, I'm not sure that I will need to do any programming apart from enabling or preventing the brake action which leads to another question. Is it essential to have the brake "on" to ensure that a folding prop will fold or will it just continue to windmill when the motor is "off" if the brake is also off?

As for the other readings, I had another look today and your surmise that milliamp consumption is one of the readings - it alternates with the Watts reading, gradually increases, remains when the motor is shut off and is added to when the "throttle"! is opened up again. The other value is MS units and seems to vary with the throttle setting so presumably is something to do with the time the switched power is "on" - just a guess, but it doesn't really matter as the values I need to know (V.A.W), are, at least, meaninglful to me. The total consumption might also be a benefit when I get more used to this form of power and acquire more batteries.

Malcolm

[Tim Mackey]

Yes, you need to set brake "ON" to get a folder to fold.

[Shaunie]

Posted by Vecchio Austriaco on 10/01/2011 09:26:31:

sorry to put in my comment just now - did not see this thread before.

My comment is nothing special - but let's stick to the right letters in the formulas to avoid confusion.

 

Tim writes

"Watts are derived from multipying the volts of the battery ( under load ) by the Amps consumed. W =I x V ( I is the symbol for current, or amps ). "

 

The letter for power is P not W - W stands for the unit watt.

So the formula is P=V x I

 

Cheers VA

 

 

If we wanted to be purists then we should change the V to an E as V is the unit Volts and E represents Electromotive force.. So the formula really is: P=E x I.

Shaun

[Malcolm Fisher]

Many items which deliver power now state the power available in Watts, and that seems to apply to anything using an electric motor for the power or an electric element heat source.

 

Some Ic engines also use Watts wheras it used to be Horse Power or Brake Horse Power.

 

Even mains gas consumption refers to Watts these days where it used to be Therms or British Thermal Units.

 

Just my two pennorth to throw a spanner in the works of the "purists".

 

Malcolm

[Brian Lambert]

So can we settle on W=A*V then?

 

[Erfolg]

As Malcolm has said, the nomenclature for many functions in science changes with time, particularly when units of fundamental measurements change.

 

Personally I find it useful to harmonize the the electrical and mechanical expressions, rather than say 746w = 1hp = 33000ft ib min-1.

 

Not worth getting excited about though

[John Privett]

Malcolm, I'm not sure how your point is throwing a spanner in the purists' works.

 

Your quibble is over the units used. Shaunie and Vecchio were talking about the letters conventionally used to represent the name of things rather than the units they are measured in.

 

So E represents Electromotive Force which is measured in volts.

And P represents Power which is usually measured in Watts - though if you wanted to you could measure power in BTU/h. Or perhaps MJ/fortnight. But that might be getting a little silly...

 

However, on your point about units, I'd suggest that measuring gas in Watts (or more accurately kWh) makes it rather easier to compare 'energy' costs from different sources.

 

For instance, I currently pay a little over 3p per kWh for gas, but a touch under 10p per kWh for electricity (in both cases ignoring the "standing charge" element of the bill.) So if I didn't already know, it would be quite easy to work out that household heating is rather cheaper using gas than electricity. If the gas prices were simply shown in BTUs or cubic feet then a bit of extra maths would be required.

 

It might actually be interesting if petrol was billed in kWhs rather than in litres! (at current prices it would be about 14p per kWh)

[buster prop]

Been thinking. If 746W or 1 hp can lift 1lb to 33,000 feet in 1 minute. I weigh 165lb so 746W could lift me 165/33000 = 200 feet in a minute? Hmm. I have a plane which weighs 2lb so with a motor giving 746 W it could theoretically climb to 16,500 feet in a minute! Now I do have a 2lb plane but with around 300W, so I'd expect it to climb to 300/746 x 16,500 or 6,635 feet in one minute, wow! I suppose prop and motor efficiency comes into it though.

[Tim Mackey]

Excuse me chaps, please note the title and subtitle of this section.