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Old 07-02-2019, 09:28 AM
superleccy68 is offline
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Question
Measuring current draw

Having been used to using aircraft electric power set ups as per manufacturers' recommendations, I thought I would like to measure current draw.
I guess I need to measure amps draw at full throttle using a multimeter. I guess the probes should go on the ESC (opto) wires to the lipos. Is that correct and can I use this meter given I imagine I will be drawing over 80-90amps (60cc equivalent aircraft) ?
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Old 07-02-2019, 10:14 AM
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You need a watt meter that is in-line
https://hobbyking.com/en_us/turnigy-...-analyzer.html
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Old 07-02-2019, 10:19 AM
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You are a gent thanks BH. My ignorance is much reduced!
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Old 07-02-2019, 10:53 AM
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My pleasure, you can rig up a contraption to put the meter inline but buying the right tool for the job is the easiest bet.
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Old 07-02-2019, 11:29 AM
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The issue using the MultiMeter is that it is only capable of testing upto 10A.

The MultiMeter is helpful in testing inline for your servo amp draws. But you can still is the Watt Meter to get the same result.

I use the Watts Up, Watt Meter. Astro Flight made one, but not sure if they still do, today... They could.
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Old 07-02-2019, 11:49 AM
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I use the Watts Up meter also, a very wicked tool, especially when running electric. I still use it for setting a plane up but have started using the Eagle Tree telemetry recorder as it does so much more for inflight information.
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Old 07-02-2019, 01:45 PM
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Yes Bunky I did wonder if a multimeter was only capable of 10A recording.
I have ordered from HK the inline 180A analyser which seems a good solution. Thanks for all your comments.
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Old 07-02-2019, 02:28 PM
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You will find it a great tool to have in your bag if you're going to mess with larger electric models
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Old 07-02-2019, 06:14 PM
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Quote:
Originally Posted by superleccy68 View Post
... I thought I would like to measure current draw. ...
Without a watt-meter you are in the dark.
Until something starts to glow

Quote:
Originally Posted by superleccy68 View Post
... I guess the probes should go on the ESC (opto) wires to the lipos. ...
That's how you would measure voltage, i.e. across the battery plus and minus wires/terminals.
To measure current, you have to disconnect one of the battery wires, either plus or minus wire, and serie the meter between battery and controller. All the current must flow through the meter.

Watery analogy to explain current and voltage:
Water circuit analogy to electric circuit - Hyperphysics
(Great site, for all physics)


Quote:
Originally Posted by superleccy68 View Post
Having been used to using aircraft electric power set ups as per manufacturers' recommendations ...
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Old 07-02-2019, 06:21 PM
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uomo ludens modellesticus
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Quote:
Originally Posted by BarracudaHockey View Post
You need a watt meter that is in-line ...
You can also go for a DC clampmeter, that way you don't have to disconnect one of the battery wires for inserting watt/multi/current-meter inline/inseries.

Clampmeter must have DC capability, duh, but not all clampmeters can do DC current.
See this article, lots of good current measuremts info:
www.wattflyer.com/forums/attachment.php?attachmentid=117297 (by Denny Vollrath, developed for 10k+ amps)
&
How to measure motor current using clamp meter? - RCG
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Old 07-02-2019, 06:45 PM
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uomo ludens modellesticus
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For inflight data, apart from the Hyperion Emeter II remote logger mentioned in message #9:
DIY recording electric model amp meter - RCG

And also by Denny Vollrath, for measuring even higher currents, or in case you want to take up welding
DIY high power wattmeter - RCG

Quote:
... Rated for 200 Amps, and as high as you want for battery voltage. That's 10,000 + Watts with a 14S LiPo at 200 Amps. (Skip over to the final design on page two using a 200 Amp Hall effect current sensor.) Parts cost is under $20.00. ...
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Old 07-03-2019, 08:03 AM
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Much food for thought for me, Ron. I appreciate the time you spent explaining it all. Cheers.
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Old 07-03-2019, 05:30 PM
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uomo ludens modellesticus
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Quote:
Originally Posted by ron_van_sommeren View Post
To calculate is better ...
General rules for current and power, they give a relative indication:
Motorcurrent is proportional to pitch¹, voltage², Kv³ and diameter⁴.
Power-drawn is proportional to pitch¹, voltage³, Kv³ and diameter⁴.
(Note the difference between current and power for voltage: squared respectively cubed.)

So, changes in setup (and lousy Kv specifications!) can have surprisingly huge effects.
E.g. doubling voltage would four(2²)fold current, doubling Kv would eight(2³)fold current, and doubling prop diameter would sixteen(2⁴)fold current.
Even a small 10% change/difference in Kv will already lead to a 30% difference in current.

Voltage effect without the exponentiation
extra current drawn with one or two cells added, simple table
For extra power drawn multiply current and voltage.
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Old 07-06-2019, 04:52 PM
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Excellent watt-meter instructions and explanations, about charge, current, voltage, resistance, power, energy
www.rc-cars-planes.com/docs/wu100v2_user_manual.pdf

Watt-meter simulator, lets you play with throtle, voltage, current, resistance, power, capacity (Ah), load etc.
www.rc-electronics-usa.com/ammeter-simulator.html


Prettig weekend Ron
• Without a watt-meter you are in the dark ... until something starts to glow •
e-flight calculatorswatt-metersdiy motor tips&tricksCumulus MFC
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Old 07-25-2019, 09:56 PM
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I use the eLogger from Eagle Tree to measure current draw in flight. I have some current/wattmeters too. But I like the inflight measurements much more. I usually set it up for current, battery voltage, watts, and mah used or consumed. One could add other things like RPMs, airspeed, GPS, etc, but I don't bother with the extras.

https://www.eagletreesystems.com/ind...tegory&path=62
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