EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: jancelot on July 13, 2015, 04:05:30 pm
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Do you think these two inline power meters are the same? There's a huge difference in price.
(http://img.dxcdn.com/productimages/sku_183523_1.jpg)
http://www.dx.com/p/g-t-power-130a-2-4-lcd-high-precision-watt-meter-power-analyzer-for-rc-helicopter-black-183523 (http://www.dx.com/p/g-t-power-130a-2-4-lcd-high-precision-watt-meter-power-analyzer-for-rc-helicopter-black-183523)
(http://www.powerwerx.com/_images/products/Watt-Meter-Bare_xlrg.jpg)
http://www.powerwerx.com/digital-meters/dc-inline-watt-meter-power-analyzer-bare-wire.html (http://www.powerwerx.com/digital-meters/dc-inline-watt-meter-power-analyzer-bare-wire.html)
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One major issue I've found (at least with the generic cheap units) is that their resolution/accuracy is quite pitiful at lower currents since there is no auto-ranging. i.e. they just use the 10 bit adc inside the uC to measure from 0mA to 10A (or 20A or 50A or whatever). Of course not mentioned in the 'specs'.
So, "maybe" the expensive units do something "smarter"...
cheers,
george.
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Yeah I saw the Lorton comparison on youtube, the What's Up power meter catches also about 1 watt where the other show 0, but only happens on a very short range.
Review: Turnigy vs GT Power vs Watts Up Power Met…: https://youtu.be/Lxv9Rozs774
None of them are meant to measure miliwatts so anyway to measure several amps the GT Power is good alike and much cheaper (13€ versus 60). Furthermore the what's up meter is missing the detailed specs about the minimal wattage that can read accurately.
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Here are some captures from youtube video. You can see that even at 1 watt the What's Up meter struggles to read fine, and I really doubt it could measure half a watt within any spec. For such low measurements one should get a wattage meter with accuracy from 1 miliwatt to say 1 watt to be withing spec.
(http://i58.tinypic.com/ek2otv.jpg)
GT Power 130A measuring 1 watt
(http://i59.tinypic.com/2s1633s.jpg)
GT Power 130A measuring 2 watt
(http://i61.tinypic.com/2s0o0hy.jpg)
GT Power 130A measuring 5 watt
(http://i61.tinypic.com/73ibeh.jpg)
GT Power 130A and What's Up meter comparison measuring 1 watt
(http://i61.tinypic.com/20icq9w.jpg)
GT Power 130A and What's Up meter comparison measuring 2 watt
(http://i58.tinypic.com/345cu13.jpg)
GT Power 130A and What's Up meter comparison measuring 4 watt
(http://i60.tinypic.com/v823hx.jpg)
GT Power 130A and What's Up meter comparison measuring 129 watt
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I have about four different makes of these and there is quite a difference in the displays. Favorite for all around reading is the Turnigy. All the rest are hard to read except in sunlight. One isn't even backlit. There is a pin for contrast on the 1602 display that I would suggest adding a pot to to make them more readable inside. They actually have a decent shunt, not a length of wire. The older Turnigy actually had a pot to adjust V & I. Number one complaint in the hobby world is the wires become unsoldered from too much current.
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I added four trim pots to my GT Power unit to adjust both gain and zero for V and A. Without the zero adjustment on the current, the offset was about -0.05 (it would read 0.01 for 0.06, and 0.00 for 0.05), just as seen in the video review. That added considerable error at lower currents, but the relative error diminished as the current increased. There was also an offset for V, but since the voltage being read is usually over 10 V, the relative error due to this was small. With the trim pots, the accuracy is within +- 1 digits, 2 max. The linearity of the ADC seems quite good, certainly good enough for the ~4 digits readout on the device. Unfortunately, I used really cheap Chinese pots whose tempco was worse than expected. It drifts quite a bit with temperature, although it is still better than without the trims.
I also needed to adjust the contrast with a resistor to ground, otherwise the display was too faded to read except at an extreme angle. The LCD is soldered to the main board. I clipped the leads and placed a SIP socket on the board and mating pins on the LCD to allow easy disassembly for mods.
Schematic attached. My GT Power seems to follow this schematic exactly with the exception of a 5.0 V regulator in lieu of the 3.3 V one. This means that the lowest usable voltage (without external power) is around 9 V.
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I had a Turnigy given to me that didn't work. I connected it to 12V and carefully folded it open. The 3.3V regulator was shorted and 11V was going into whatever that chip is. Replaced the regulator and it has been working for over two years. Pretty amazed it took that and survived.
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Finally received my GT Power 130A from eBay, here are some comments on it:
- The power consumption with no load (the meter itself) is 25.80 miliamps at both 11.87 volts and 8.79 volts, so it looks like it needs a constant current independent of the voltage (provided is bigger than 5 volt or so).
- It's quite thick
- The blue blacklight can be somewhat unpleasant sometimes. It has no regulation and can be quite bright if you want to put it where dark is required (like a room)
- The additional 3 pin connector for auxiliary power input wasn't included in the box, so I am guessing which one should I buy to be compatible?
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Finally received my GT Power 130A from eBay, here are some comments on it:
- The power consumption with no load (the meter itself) is 25.80 miliamps at both 11.87 volts and 8.79 volts, so it looks like it needs a constant current independent of the voltage (provided is bigger than 5 volt or so).
- It's quite thick
- The blue blacklight can be somewhat unpleasant sometimes. It has no regulation and can be quite bright if you want to put it where dark is required (like a room)
- The additional 3 pin connector for auxiliary power input wasn't included in the box, so I am guessing which one should I buy to be compatible?
The auxiliary power connector is just a standard 0.1" header. Look for "Dupont cable" on eBay.
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Finally received my GT Power 130A from eBay, here are some comments on it:
- The power consumption with no load (the meter itself) is 25.80 miliamps at both 11.87 volts and 8.79 volts, so it looks like it needs a constant current independent of the voltage (provided is bigger than 5 volt or so).
- It's quite thick
- The blue blacklight can be somewhat unpleasant sometimes. It has no regulation and can be quite bright if you want to put it where dark is required (like a room)
- The additional 3 pin connector for auxiliary power input wasn't included in the box, so I am guessing which one should I buy to be compatible?
The auxiliary power connector is just a standard 0.1" header. Look for "Dupont cable" on eBay.
I guess this will do the job?
The 3PIN DuPont line adapter cable #00584571 (http://www.miniinthebox.com/the-3pin-dupont-line-adapter-cable_p584571.html)
3-Pin 20cm 2.54mm DuPont Lines(5 pcs) #02422446 (http://www.miniinthebox.com/3-pin-20cm-2-54mm-dupont-lines-5-pcs_p2422446.html)
70cm 3pin Female - Female Jumper Cable DuPont Line For Arduino (http://www.miniinthebox.com/70cm-3pin-female-female-jumper-cable-dupont-line-for-arduino_p2816739.html)
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Finally received my GT Power 130A from eBay, here are some comments on it:
- The power consumption with no load (the meter itself) is 25.80 miliamps at both 11.87 volts and 8.79 volts, so it looks like it needs a constant current independent of the voltage (provided is bigger than 5 volt or so).
- It's quite thick
- The blue blacklight can be somewhat unpleasant sometimes. It has no regulation and can be quite bright if you want to put it where dark is required (like a room)
- The additional 3 pin connector for auxiliary power input wasn't included in the box, so I am guessing which one should I buy to be compatible?
The auxiliary power connector is just a standard 0.1" header. Look for "Dupont cable" on eBay.
I guess this will do the job?
The 3PIN DuPont line adapter cable #00584571 (http://www.miniinthebox.com/the-3pin-dupont-line-adapter-cable_p584571.html)
3-Pin 20cm 2.54mm DuPont Lines(5 pcs) #02422446 (http://www.miniinthebox.com/3-pin-20cm-2-54mm-dupont-lines-5-pcs_p2422446.html)
70cm 3pin Female - Female Jumper Cable DuPont Line For Arduino (http://www.miniinthebox.com/70cm-3pin-female-female-jumper-cable-dupont-line-for-arduino_p2816739.html)
No, buy one of the 40-pin jobbies for a buck and peel the last 3 wires off the end. That leaves you with 37 for other uses ;)
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No, buy one of the 40-pin jobbies for a buck and peel the last 3 wires off the end. That leaves you with 37 for other uses ;)
Sorry mate, no idea what you are talking about. Could you provide a link at least.
Here's some more information about measurement on low currents.
Using a power supply of 11.87 volts on the source side,
- Connecting 148 ohms on the load side, shows 0.5 watts, when there are 0.95
- Connecting 1k on the load side, shows 0 watts, when there are 0.14
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No, buy one of the 40-pin jobbies for a buck and peel the last 3 wires off the end. That leaves you with 37 for other uses ;)
Sorry mate, no idea what you are talking about. Could you provide a link at least.
Like: http://www.ebay.com/itm/40PCS-Dupont-Wire-Color-Jumper-Cable-2-54mm-1P-1P-Female-to-Female-20cm-DX-/251753896377?hash=item3a9db399b9 (http://www.ebay.com/itm/40PCS-Dupont-Wire-Color-Jumper-Cable-2-54mm-1P-1P-Female-to-Female-20cm-DX-/251753896377?hash=item3a9db399b9) (just an example, not a recommendation).
You can simply peel off as many conductors as you need, so two for just power or three for power plus reset in your case. You can glue the individual ends together with CA/superglue in whatever configuration you need (two or three in line). These things are handy to have around for connecting to all sorts of headers, like serial console ports or programming headers inside many devices. Arduino people use them by the fistful to interconnect boards, sensors, displays, etc.
Here's some more information about measurement on low currents.
Using a power supply of 11.87 volts on the source side,
- Connecting 148 ohms on the load side, shows 0.5 watts, when there are 0.95
- Connecting 1k on the load side, shows 0 watts, when there are 0.14
A 1k load on 11.87 V is about 12 mA, or less than 1/10000 of the full scale current measurement (130 A). What more can you expect?
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Like: http://www.ebay.com/itm/40PCS-Dupont-Wire-Color-Jumper-Cable-2-54mm-1P-1P-Female-to-Female-20cm-DX-/251753896377?hash=item3a9db399b9 (http://www.ebay.com/itm/40PCS-Dupont-Wire-Color-Jumper-Cable-2-54mm-1P-1P-Female-to-Female-20cm-DX-/251753896377?hash=item3a9db399b9) (just an example, not a recommendation).
You can simply peel off as many conductors as you need, so two for just power or three for power plus reset in your case. You can glue the individual ends together with CA/superglue in whatever configuration you need (two or three in line). These things are handy to have around for connecting to all sorts of headers, like serial console ports or programming headers inside many devices. Arduino people use them by the fistful to interconnect boards, sensors, displays, etc.
I see it's not a good recommendation, the seller has only 98.5% positive votes. In case of sticking several pieces together, it starts taking into account the spacing between each piece due to the glue, because the outer pins will be more distant than should on a single piece. For example, if there's 2.5 mm spacing, for 12 connectors it makes 27.5 mm from pin 1 to 12, but if glued together there can be 28 or 28.5 so you will bend the pins.
I think I'll go with dealextreme, some examples
3-Pin 22cm 2.54mm DuPont Lines - Yellow + Red + Black (http://www.dx.com/p/3-pin-22cm-2-54mm-dupont-lines-yellow-red-black-276575#.VbqXOfntmko)
Dupont Line 1P-1P (40-Pack / 20cm Length) (http://www.dx.com/p/dupont-line-1p-1p-40-pack-20cm-length-121338)
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I have about four different makes of these and there is quite a difference in the displays. Favorite for all around reading is the Turnigy. All the rest are hard to read except in sunlight. One isn't even backlit. There is a pin for contrast on the 1602 display that I would suggest adding a pot to to make them more readable inside. They actually have a decent shunt, not a length of wire. The older Turnigy actually had a pot to adjust V & I. Number one complaint in the hobby world is the wires become unsoldered from too much current.
Whats the 'real' continuous current that these meters can sustain @ about 14/15 volts on a charging circuit?