RC India

dear all,
if u are in Electrics, this is a must to have instrument.
Here is a low cost unit i had made 2- 3 years back and still using. Found it extremely usefull.

The unit is made from a 3.5 digit display micro module from Digital technology Mumbai.  This is a 200mv unit. this is available for rs250,.00

Put this in to a metal casing (Photo enclosed), add a shunt for current measurement and a resistor devider for the voltage. Add a toggle switch to switch between voltage and current.

Schematics/photos/ vdeo attached.
http://www.youtube.com/watch?v=L8DeZEBB2fY

ashta

one more photo

One question for the benefit of everyone.  Measuring current and voltage allows you to calculate the power consumed (wattage) by multiplying them. 

The issue is, doing it on the ground would inflate the values, right ?  During actual flights, the dynamics are different.  How does one account for the difference, especially if they are close to the tolerances of the power system used ?

correct me if i am wrong, since what i am commenting is from my experience and common sense.

1. Ground test/ static test will show slightly inflated value and generally one can take it as the worst case.
For example, under static test if a motor/ prop/ battery combination is found to be taking say 11V/ 15 Amps under full thtrottle, then the wattage in = 165 Watts. If the motor spec says Max 165 Watts and Max current is 15 amps, we can consider that we are safe. Since under actual flying conditions, this will be lesser  (10%??)
2. Any way in actual flying conditions, the wattage will vary depending on air pressure/ height/ upwind/ down wind/ type of flying, cruising/ aerobatics etc.
3. Static test will give a reasonable idea and is very usefull in selecting the Motor/ prop/ battery combination.

To directly answer the question of how do we account, my feeling is that since in actual flight the no of variables are so many,  it may be difficult to factorise. In a common sense approach, can we assume a 10% reduction in actual flight?
more experts pl.......
ashta

What is the max current this unit can measure? By the time you posted this thread, I had already booked a

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10080  :-X Still waiting for it to arrive  :violent:

Actually that was what I was looking to figure out.  Is it 10% or 20% or 30% ?  What is the margin, from anyone who has done any sort of formal testing.

Anwar, it would not be easy, if not impractical, to measure and log current drain 'in flight".

50Amps and 50 Volts

Yes, that is generally true.  However, there are many remote telemetry systems that can give you inflight load readings.  Would be expensive though.  I was looking for anyone who has read about such tests, so that we can get a fair idea of what the real world numbers would be.

If its possible to Log the cell Voltage Drop, then is it possible to Get the appropriate current drain? I mean by comparing it to the static Voltage Drops measured on the Ground? :headscratch:

One could get a fair idea of the AVERAGE current drain by taking off with a fully charged battery, flying for a specific time and then re-charging the battery. The charge into the battery, less say 5%, would be indicative of the power consumed.

Anwar,
u can get the answers here.
http://www.rcgroups.com/forums/showthread.php?t=376054&highlight=prop+unloading

I do not worry about the actual, since there is no point. As long as the static is within the Tolerance of my battery/ motor prop combination. If it is not then i adjust the prop/ battery/ motor combination. Any way i know that it will be less in actual flight and hence i am safe.
ashta
ashta

hello ashta

new member on this site however was following this thread of yours. a very good tool you done for the electric. could you please specify the product details apart from the name of company . the compay has so many products . any product no or reference no for mentioning.

thanks

True.  But it is the extremes that kill most of the time (like flying or hovering at close to full throttle for a minute or two).  In such cases, measuring "average"s would not prevent mishaps, right ?

Nice thread.  What I was expecting was inline with this post (the 3rd one) in that thread :

http://www.rcgroups.com/forums/showpost.php?p=3813408&postcount=3

So hard numbers like 10% (or whatever the number is) would be misleading.

Extreme cases will ALWAYS remain. One minute or two is a big difference.

My suggestion was for anyone to get a general idea of the consumption in the general flying style and duration of the individual person and aircraft. And that too without any additional measuring equipment.

The same, incidentally, would apply for IC powered models. Simple enough to check fuel left after a normal  flight and get an idea of how much "run time" you could get on a full tank.

My discussion was not about consumption, you are right from that perspective.  My question was how much unloading happens in flight versus testing for power consumed on the ground, and "average"s does not work in that case.  It is the "maximum"s (actually the "sustained maximums") that matter in this case.

This is not a ready made product. It is a voltage/ current measuring unit made using parts.
1. Digital voltmeter: form Linear technologies mumbai: rs 250.00
2. Wires and connectrors: Locally bought. say rs 50.00
3. Shunt: Made from normal wire, and calibrated.
4. BOX: sheetmetal box.
Build: Built as per the schematics given.
Skill: will need a little knowledge on electrics, like making a shunt, How to measure current. how to measure voltage etc.
thanks
ashta

Would "kill" be referring to the battery, ESC or motor?

I have only case of experience where my setup was wrong, and in my case the motor and ESC both were lost as the soldering itself came out due to the heat.  Strange as it is, my lipo survived !  Must be because it was one of the better ones claimed to be "no-puff", a brand named "Outrage XP".

But your question is a larger one. What you are asking is, what dies when you overdraw with a wrong electric setup; right ?  I have read  about and seen people who lost ESCs or motors or batteries (or a combination of these).

hi,

i read through the forums and evaluated various options to make a shunt resistor.



Then i tried with local Electrical shops for the 14 gauge wire and found surprise on their faces.

Then another rcgroups search i found an easy way to make a shunt is buy resistance. So the resistance required was supposed to be .001 Ohms. Now most of the electronics shops don't store these kind of low value. So as advised by the forum. i bought 0.01 ohm(2w) X 10 and put them in parallel which means i got 0.001 (20W).  Now this setup should be ok till about 200Amps. Woof. Cost of 10 resistors was only 30 bucks. Also i bought two banana plugs to mount the resister directly on the voltmeter.

Connect this in the series to the Battery and measure the voltage across the shunt. The setting is 200mV and the output will directly show the current consumed.

This setup will cause extremely low loss to the setup and also no confusing Amp calculation.

Thanks to all the forum in and outside india, i am a happy person with a home grown AMP meter.

Regards Especially to Astha ji .

Please post some pictures of your setup IN ACTION.

actully now a days digital multimeter is available in market for just Rs 100.....so except the pleasure of DIY it is of no use.....sorry but no disregard is meant


kartik

Do they work out of the box as ammeters ? Unless you add some load (which is the action taken above) to measure the current (actually by measuring the voltage), I am not sure how this fits in ?

Hi Anwar,

There is way to measure the current. Multimeter having seperate 2 connectors which help in measuring upto 10A. I think, we can connect mutimeter probes in series with load and powersupply for measuring. Experts, please correct me, if I am wrong.

But I feel limitation, because we can measure only 10A.

Regards,
Dileep

Perhaps I should have clarified my question a little.  The standard "amps measurement" capability of DMMs are less than 1A in most cases.  With the name "ammeter", I was referring to meters that can measure the higher amps that are usual in RC applications (10A to 40A is common, can go much higher too). 

So I was wondering about Karthik's suggestion that the need for resister load setup was just a DIY thing which adds no value compared to "out-of-the-box" functionality in common DMMs :headscratch:

with the miltimeter i got for Rs 100/- i can measure DC voltage upto 1kv
current upto 20Amps
AC voltage upto 750v
+ resistance and other miultimeter functions +it has a mode in which it emits sound when the resistances between the leads is less than 100 ohms ,i think a circuit can be made out of it to test the LiPo voltage using it as a LiPo alarm by using ohms law       R=V/I     keeping I(current) constant the resistance will purely depend upon the voltage of battery in our case a LiPo...experts please comment

thanks Mr Anwar but the multimeter i have seen till now measure voltage upto 20amps will search in market for better ones with higher values.....

regards

kartik

Some major points:

1. The "continuity test" actually feeds a voltage through the resistance and sounds an alarm if the resistance is below a certain threshold.

2. If you have a constant current source you will need added circuitry. The voltage drop across the LOAD will be inversely proportional to its resistance. Your meter,   the "load" in the mode above, does not behave like a simple resistance and you may well damage it by the voltage from the LiPo flowing into it!

3. The voltage drop across the terminals in the 20A current mode can be quite high. Also the resistance of the leads themselves can be significant. In short, not recommended to use your meter for this function.

I've already bought a multi meter..Can i use tat?

Pls explain what do you want to use it for.

Copy of my message posted earlier without Pic

i read through the forums and evaluated various options to make a shunt resistor.

Then i tried with local Electrical shops for the 14 gauge wire and found surprise on their faces.

Then another rcgroups search i found an easy way to make a shunt is buy resistance. So the resistance required was supposed to be .001 Ohms. Now most of the electronics shops don't store these kind of low value. So as advised by the forum. i bought 0.01 ohm(2w) X 10 and put them in parallel which means i got 0.001 (20W).  Now this setup should be ok till about 200Amps. Woof. Cost of 10 resistors was only 30 bucks. Also i bought two banana plugs to mount the resister directly on the voltmeter.

Connect this in the series to the Battery and measure the voltage across the shunt. The setting is 200mV and the output will directly show the current consumed.

This setup will cause extremely low loss to the setup and also no confusing Amp calculation.

Thanks to all the forum in and outside india, i am a happy person with a home grown AMP meter.

Regards Especially to Astha ji .

Picture shows a simple setup of 0.001Ohm resistance to measure current in excess of 200amps

Cost
Resistor - 30 ( For 10 nos)
balloon plug - Rs 10
Dean - Own stock
wire - Old Burnt ESC

 

@ hangingtough.

Kewl connector {:)}

Do you have any way to check how accurate the current measurement is with your connector ?

I think this is what you meant. => The full scale when you put your knob to 20mv with this connector would be 200A.

Using the 14 AWG shunt will inc the range. But then there will be calibration issues.
Using 10x0.01 Ohm is a good way of doing I suppose. This may not require any tweaking for the calibration at all.

Using the $3 Wattmeter switch and this connector can have a perfect home RC Wattmeter.

The 14 AWG is approx 2mm-sq. Could not find this in the local market.
I got only 1.5 and 2.5 mm-sq wires.
Using 2.5 mm-sq I think we can go up to 50A.

How much will those banana plugs take ? I think 15A but i'm not sure.
I was thinking of putting a 3.5mm Gold bullet connector if my amps was above 20A.

What fuse does your MM have ?

re living the past as requested by some members

This is with reference to "Drone"s post #32:


Using 10x0.01 Ohm is a good way of doing I suppose. This may not require any tweaking for the calibration at all.

Not quite true. Stray resistances from the wires, connectors could well add a significant amount as compared to the 1 mOhm of the resistance.


The 14 AWG is approx 2mm-sq.

14 AWG is app. 2 sq. mm and NOT 2mm. sq. (which would be 4 sq. mm.)


How much will those banana plugs take ?

The banana plugs are not carrying any of the main current and, therefore, will not make any difference if they  are gold plated or otherwise.


What fuse does your MM have ?

Again, not relevant, since the current is not flowing through the meter wires.