A low power ducted fan

[JetPlaneFlyer]

Originally Posted by babylon5

Babylon reply
The arcing will occur depending which connectors are plug last. If the battery side is plug last, arcing will occur at the battery connector.

That is quite likely true, with larger cell counts, but the pertinent point is that the ammeter makes no difference one way or another. If you get arcing you will get at whenever you connect and disconnect the battery, makes no difference if there is an ammeter in the circuit or not.

The only significant advantage of the clamp meter, as I see it, is the ability to measure frequency and so calculate RPM... Which I'd be the first to admit is a great feature to have.

What the clamp on meter cant do but most in-line meters can do is simultaneously measure instantaneous current, instantaneous voltage, instantaneous power in watts.. Plus record peak current, peak voltage, peak power... PLUS.. record total power consumed during the measurement period (which allows you to exactly measure battery capacity).. These are features I would not want to give up.

[quorneng]

Made use of the fine calm but cold (-2) weather to fly the DuctFan for 21 minutes. Still using my old 'test' LiPo and not to LVC either but just to when it required 2 more throttle clicks to maintain height.
It carried the Key Chain cam but the cold got to its LiPo after only 10 minutes despite being in its Depron cosy!

Bring on summer.

[babylon5]

Originally Posted by JetPlaneFlyer

That is quite likely true, with larger cell counts, but the pertinent point is that the ammeter makes no difference one way or another. If you get arcing you will get at whenever you connect and disconnect the battery, makes no difference if there is an ammeter in the circuit or not.

The only significant advantage of the clamp meter, as I see it, is the ability to measure frequency and so calculate RPM... Which I'd be the first to admit is a great feature to have.

What the clamp on meter cant do but most in-line meters can do is simultaneously measure instantaneous current, instantaneous voltage, instantaneous power in watts.. Plus record peak current, peak voltage, peak power... PLUS.. record total power consumed during the measurement period (which allows you to exactly measure battery capacity).. These are features I would not want to give up.

Hi JPF, I did compare the current reading on 4S lipo set up with the clamp on ammeter and the commercial wattmeter. The reading came up
on the clamp on ammeter reads 55amps while the commercial wattmeter reads just under 50amps. At the time I am not sure what was the condition of the additional connector at the wattmeter side. It was a dean connector nor do I know what is the wattmeter internal resistance.

The disadvantage of the clamp on ammeter in terms of power reading is easily solve . just was add another battery checker read out at the balance connector of the battery. There I have power by P=VxI

Meanwhile I will stick to the clamp on ammeter. Nothing beats zero ohms and zero inductance. Yeah I forgot to mentioned the watt meter comes with a about 3-4inches of cable one at the positive and one at the negative side. At high power , inductive component maybe become significant enough to add problem to the accuracies of the read out.

The only advantage of the commercial watt meter is the price when high power/current measurements are needed. Its lower price than the clamp on ammeter in terms of $/ watt.

Cheers and take care

[JetPlaneFlyer]

Originally Posted by babylon5

Hi JPF, I did compare the current reading on 4S lipo set up with the clamp on ammeter and the commercial wattmeter. The reading came up
on the clamp on ammeter reads 55amps while the commercial wattmeter reads just under 50amps. At the time I am not sure what was the condition of the additional connector at the wattmeter side. It was a dean connector nor do I know what is the wattmeter internal resistance.

The difference in readings could be for a whole host of reasons, accuracy errors of the meters being quite likely. To establish if the Wattmeter resistance really was lowering the current (unlikely if you believe the specification) then use the clamp meter twice on the same system; first with the in-line ammeter unconnected and second with the ammeter connected up. Both times with battery fresh from the charger. The difference in readings between the first and second clamp meter measurement should represent the drop in current due to any resistance from the ammeter and additional connector.
It would add to the confidence if the experiment was repeated a few times to make sure that the clamp meter reading is consistent.

It would be good to know if ammeters do in reality lower current significantly (despite their claimed near zero resistance).. the actual resistance could be easily calculated from voltage and change in current.

Steve

[JetPlaneFlyer]

Originally Posted by quorneng

Made use of the fine calm but cold (-2) weather to fly the DuctFan for 21 minutes......

Impressive duration Bill. So what do you put the doubling of flight time down to?.. improved shroud? gentler on the throttle? 'good air'?

[quorneng]

First the improved shroud then my 'test' battery is actually better than the one use on the previous flight, and lastly almost still conditions.
For the flight I launched at half throttle (about 8A), quickly throttled back to a very gentle climb (about 5A) to 100' and then to its 3.5A cruise. I doubt if it ever exceeded 15mph.
Now when I fit a prop I am expecting it to cruise on 1.5A (1C)!

[copterrichie]

This is very interesting. I have also done some work with converting computer fans to EDF for usage on model aircrafts.

[quorneng]

copterrichie
Computer fans are designed to move large quantities of air at low speed so they are only efficient at very low power densities when compared to a commercial EDF This means they only work at all well in very light & slow planes.
Try to run them at high power levels and they are less efficient than an EDF.

I actually went the other way and with a big and light enough plane used a ducted prop.
Still a low power density (3s, 110mm diam prop, 20A full power) but the result is more efficient in terms of thrust/Watt than a computer fan but it does have to light!

[copterrichie]

"Computer fans are designed to move large quantities of air at low speed"

Actually, this is a desired quality that I am seeking for my Multirotor copters.

[copterrichie]

Here are a couple of pictures of my newest conversions.

Here is a video of the previous version, not as much thrust per wattage as I would like, but I am working on it.


http://www.youtube.com/watch?v=fdxLN81h34U

[Bill G]

Originally Posted by JetPlaneFlyer

The difference in readings could be for a whole host of reasons, accuracy errors of the meters being quite likely. To establish if the Wattmeter resistance really was lowering the current (unlikely if you believe the specification) then use the clamp meter twice on the same system; first with the in-line ammeter unconnected and second with the ammeter connected up. Both times with battery fresh from the charger. The difference in readings between the first and second clamp meter measurement should represent the drop in current due to any resistance from the ammeter and additional connector.
It would add to the confidence if the experiment was repeated a few times to make sure that the clamp meter reading is consistent.

It would be good to know if ammeters do in reality lower current significantly (despite their claimed near zero resistance).. the actual resistance could be easily calculated from voltage and change in current.

Steve

Could be resistance in the wattmeter leads. I need to rework mine for 13GA wire. I haven't used it in a while at higher levels, but from what I remember it was causing significant losses at levels as low as 30A, with 16GA wiring even at very short lengths.