Power / Watt Meter Review: RCSky, Watt's Up, Po8er and a little surprise...

[MJLorton]

Hi Folks,

All of Franky's inline power / watt meters arrived very quickly from Hong Kong.

Here is the video review: http://www.youtube.com/watch?v=cCd2DDoz38g

Below are some clips taken from the review. When Franky is ready he'll post some more details and pricing.

Cheers,
Martin.

[retiredcaps]

Regarding the pins and possibility of inserting it incorrectly, a drop of crazy glue on the non used receiver pin/hole is an easy cheap bodge.

PS. You must have dissed someone because I can't understand why you always get one dislike.  He/she must have a grudge against you?

[Maff^]

Hi Martin,

Thank you for yet another interesting video.

I'm still watching it right now, (2nd meter almost done), but to me it seems that these meters have ADC's with insufficient resolution. This would be why even with a stable source voltage it jumps with ~6 counts.

Just out of curiosity, do you have the prices of these meters listed somewhere ? I'm wondering how the price/performance of these meters compares.

[iloveelectronics]

Nice review Martin, as always!

Here are some instructions for calibrating the 3rd meter. It's not documented at all but I found these from a similar DIY kit and tried it myself and it worked.

1. Connect an accurate multimeter at the output end of the meter (the top 2 wires on the right) to measure voltage. Connect the variable power supply to the input wires (the bottom 2).
2. Hold that button on the left while you power up the meter. Release the button after a couple of seconds.
3. The screen shows 0V, make sure your power supply's output is turned off and the multimeter reads 0V.
4. Push the button again. The display now shows 2V.
5. Adjust the input voltage until the multimeter reads 2V.
6. Push the button again. Now the display shows 19V.
7. Adjust the input voltage until the multimeter reads 19V.
8. Push the button again. Now the display shows 0A.
9. Disconnect and reconnect the leads on the multimeter to the Amp range and switch to Amp measurement.
10 Switch off the power supply's output so the multimeter reads 0A.
11. Push the button again. Now the display shows 1.9A.
12. Adjust your power supply's current output until the multimeter reads 1.9A.
13. Push the button again. Done!

[iloveelectronics]

As for pricing, the first 2 meters cost the same to me. You can find the SkyRC meter on eBay (other sellers) for just under $26 (without the temperature probe). I can just about offer the same price to members here, perhaps a buck or 2 less. Temperature probe will be an additional $4. The second meter will be priced the same (obviously it doesn't have the temperature option). However, at this point I'm still not sure I would even "sell" them as I just don't feel like they are worthy of the price given their performance. I do still have a few of those SkyRC's here so I might just go yard sale style to get rid of them

Now the 3rd meter actually costs only 1/3 of the price of the other 2. However, adding shipping and other costs the best that I can do is probably around $14 (shipping included) for forum members.

These prices are not final yet, but I just wanted to give people a rough idea first. I will be adding the 3rd meter in my eBay store next week.

[blankfield]

Hi Martin,

it will be nice if you can teardown these watt meter's, based on MCU ADC it easy to calculate real resolution. For example one with attiny26l have 10bit ADC so maximal resolution is only about 58mV for 60V range (Vrange/2^Nbits). So 3 or more digit after decimal point it's just impractical, unnecessary gadget.

Accuracy is basis on quality of parts used in voltage divider and quality of shunt resistor, cheap parts have significant temperature drift etc. Even if all resistors will be measured used 6.5 digit DMM and these values will be placed in EEPROM to increase measurements accuracy it's not possible to omit ADC resolution and variability under the influence of time and temperature.

[iloveelectronics]

More information about the 3rd meter:

As far as I know this meter was designed and published by a Chinese electronics enthusiast some years ago and has since been made rather popular as DIY kits or semi-product in the Chinese market. After a little research I think I found his original website where he  published the design: http://blog.21ic.com/user1/4577/archives/2007/43308.html It is all in Chinese but there's a schematic for those interested. In the article he also mentions something about how he's using the multiple differential ADC channels with the x1 and x20 gains to do the measurements and improve accuracy, etc. Unfortunately I don't have the technical expertise to understand or translate, but from what I gather he's doing something clever to improve accuracy and resolution meaningfully.

[Fennec]

Hey,

few min ago I have build this on a STK500 quickly. Software 40V/5A and a short ADC test. Without any Hardware. It is very easy to build, but under $US14 I can't competition with you.
btw u mean $US or Hongkong, Canadian, Australian, Bermuda Dollar ? The last four sounds much better for me

Here a few pics of my quick 'n dirty setup.

Sry for this bad quality. Its dark here and LCDs are not easy to shot.

[iloveelectronics]

Nice job Fennec! Do you find the measurements accurate with your setup? EDIT: Just noticed you said there's no hardware, so I guess there wasn't any "real" measurement. But with your software test do you think the ADC is providing a real 3 decimal point resolution?

Oh, BTW, it was US$ I was talking about

[Fennec]

No, I only have checked the ADC if it works.

[GingGangGooly]

@iloveelectronics - I would be interested in buying one of those un-cased Watt meters for $14 (I assume US$?)

Let me know how to pay etc.

Cheers

[iloveelectronics]

@iloveelectronics - I would be interested in buying one of those un-cased Watt meters for $14 (I assume US$?)

Let me know how to pay etc.

Cheers

Thanks for the interest! This meter seems to be getting a lot of interest already, before I even put it up for sale at my eBay store!

I sent you a PM with my PayPal address. Please check.

[flywheelz]

Maybe you can compare this one also.
http://www.hobbyking.com/hobbyking/store/__10080__Turnigy_130A_Watt_Meter_and_Power_Analyzer.html

I use one for charging my electric bike and topping off cars batteries.  I like it.  Seems to show similar Ah reading compared to Cycle Analyst.  One thing I don't like is the hard to read display.  Got to look at it at the right angle.  It has a backlight display.

[MJLorton]

Regarding the pins and possibility of inserting it incorrectly, a drop of crazy glue on the non used receiver pin/hole is an easy cheap bodge.

PS. You must have dissed someone because I can't understand why you always get one dislike.  He/she must have a grudge against you?

Thanks...good idea as I was thinking of ways to avoid that again.

Yup....not sure who or how I have dissed someone...

[MJLorton]

Maybe you can compare this one also.
http://www.hobbyking.com/hobbyking/store/__10080__Turnigy_130A_Watt_Meter_and_Power_Analyzer.html

I use one for charging my electric bike and topping off cars batteries.  I like it.  Seems to show similar Ah reading compared to Cycle Analyst.  One thing I don't like is the hard to read display.  Got to look at it at the right angle.  It has a backlight display.

Not a bad idea, the Turnigy meter has caught my eye before....I'll see if I can get hold of one.
Thanks for the post.