sodbuster 1

is there a way of testing total amperage draw under load in a receiver/servo/switch setup??
by load I mean with control surfaces moving

Sean C

My Feedback: (25)

place a watt meter between your battery and switch

bruce88123

Or better yet, use an ammeter which will actually measure amps and NOT watts.

tkilwein

The Eagletree monitor works nice. Make sure you read the doc file as there is a voltage limit without a ext battery.
I have one and it is nice as you can record actual inflight numbers and play back also.
They have several attachments to go with. one is a servo current/amp monitor.
If you plan on a lot of functions check out their big guy. I forget the name but it is on the website.

Do a search on eagletree systems, if I remember right.

pilotpete2

Bruce,
A wattmeter is an Ammeter that calculates Watts based on the measured current and voltage for you. Perfect for this purpose
Pete

bruce88123

I know what they are, I use them both at work. Most on this forum get confused enough talking about amps and volts. No need to throw in watts. Besides, he did ask how to measure amps so that is the question that needs to be answered IMO.

sodbuster 1

Ok. I know this is gonna sound stupid.Do I take my readings in series with the positive leg for amps?
As you can tell, I'm extremely rusty on my electrical theory.
Just spent the last 5 minutes triing to remember the calculation for Watts and now my head hurts.[&:]

Sean C

My Feedback: (25)

Or better yet, spare me your condescending corrections. The devices used in this hobby are marketed at WATTmeters.

sodbuster 1

ok,ok, take it easy boys.
remember we''re here to have fun and help each other.

can one of you guys tell me how to go about hooking up the ammeter?
What I'm trying to accomplish here is to conduct a test to determine what amperage battery pack I should be using under actual load with surfaces moving.
I might even go as far as to clamp the airframe in a test stand and create some kind of wind tunnel

Sean C

My Feedback: (25)

On the meter will be a source and load connection - battery plugs into source; switch plugs into load. I use an E-Flite watt meter (which also displays voltage and AMPS) but it only has one decimal place of accuracy compared to others which have two.

Watt meter discussion:
http://www.wattflyer.com/forums/showthread.php?t=6740

BillS

I sacrificed a servo extension and put the ammeter (digital voltmeter) in series in the black wire. Red wire will work also. Banana jacks make it easier to use.

Bill

bruce88123

If measuring power for an electrical motor you are correct. He wants to read simple battery amps to a RX and related servos. Forgive me for wanting him to use the correct equipment for the task HE stipulated.

vicman

My Feedback: (10)

OK you two sources of brilliance how about you post a pic of your given methods and tools to eliminate the poor languange skills and make this simple for the simple.[8D]

bruce88123

Buy this http://www3.towerhobbies.com/cgi-bin...&I=LXWW16&P=ML or similar and using http://www3.towerhobbies.com/cgi-bin...?&I=LXL332&P=M (or similar) to plug in to the charge jack of the RX read the loaded voltage after selecting proper scale. Many TX's have a diode in them which will not allow ANY readings through charge jack. An adaptor lead would then need to be made to check battery out of the TX. I don't recommend modifying your radio unless you know what you are doing. The meters/indicators built into most modern TXs really make this unnecessary.
Oops sorry, just realized that is for checking battery under load, still a good practice.
For the current you need a basic cheap digital multi-meter you can get at Radio Shack, Auto-Zone or many other places. Take a spare extension and approx mid-point cut EITHER the positive OR negative wire. Attach extensions to each cut wire end that are long enough to reach the meter jacks comfortably (Not too long or you can add a drop due to resistance). Set the meter to Amps or MA and plug leads into appropriate jacks (see owners manual) and read the current on the display. Note: it doesn't really matter if you get the leads plugged in backward or not as you are only concerned with the number at this point and not + or - flow.

Sean C

My Feedback: (25)

Can you explain to me the exact difference between current drawn by a radio system versus current drawn by an electric motor? You seem to be set on proving my *simple* method wrong, so please enlighten me.

bruce88123

Not WRONG but excessive. Wattmeters tend to cost more and are un-needed unless flying electric IMO.

bruce88123

If you were running electric then something like this http://www.rc-cars-planes.com/rc-watt-meter_n.html WOULD be a good investment IMO.

modeltronics

My Feedback: (27)

I've been reading this thread with interest and need to ask questions and comment.

If you want to look at the real current draw for any finite portion of time you need to use a scope looking accross a shunt. I would think this to be most true if you want to look at the inrush current of a servo under load just being told to move. I know you can not see this with a amp meter. Is the watt meter fast enough to do this? Or does it average it out over a time period or just miss it?

I have looked at the voltage drop of a RX system and servos under load and have seen things you would never see with a voltage meter.

Now this may not be much help because most do not have a scope to look at what is going on. I just want to make a point that using just a meter might not tell you the real truth.

Happy Friday,
Pete

Sean C

My Feedback: (25)

I provided a working solution and a drawing, which is what the thread starter asked for.

My apologies for suggesting such an inferior testing method.

bruce88123

Well said. Again we are trying to stick with BASIC testers IMO that are available to the average R/C pilot. This could reveal a more COMPLETE truth as you call it. We can even step it up to a storage scope if you'd like to give better analysis time. I've got those too here at work. Let's face it, we can always improve on what tests we run but again lets keep it at a realistic level for the general consumer.

Sean C

My Feedback: (25)

I'm not sure if it uses a sampling rate or works in real-time. Some units may provide averages, I'm not sure but most all will record peak values.

modeltronics

My Feedback: (27)

Bruce,
I agree with you about keeping the test to something that the average RCer can do. In some cases a meter will do just fine. I do not want to bog down this tread but reading this reminded me of a problem a friend was having with a model that had 7 servos, 4 in the wing. At times all the servos would would just go nuts. My friend could not find the problem with a meter. We started to look at things with a scope and found the V drop at the switch was high enough at times to reset the decoder in the RX when the 4 wing servos were under load.

A meter will do fine for getting some average idea of what is going on in the system in some cases.


felice Viernes
Pete

pilotpete2

I hafta ask, what is the number and type of servos you are planning on using. The Idle and stall current is usually published for the servos, receivers also have a published current drain and is usually insignificant.
Pete

sodbuster 1

How insulting!!
OF COURSE I HAVE A SCOPE!!!
will a Leupold 6.5 x 25 work???

just kidding! but figured I'd throw a little comedic relief in to break up what's become a little bit of a Donnybrook

you've all given me very workable answers to my question.


Unless I want to go to the expense (which I don't) of installing something that will take real time readings and record them then make a few flights I won't be able to be 100% accurate and I'm fine with that.
Just want a general idea of what should work ok so I can know I can get a few flights without worrying about charging once the system has been fully charged .

sodbuster 1

am running : 1 JR ls4001 (older and don't even know the pecs) for throttle
4 Hitec 625MG's 2 on ailerons 1 on elev 1 on rudd
Spektum AR7000 revceiver
JR heavy duty switch with charge jack (18ga)

idle and stall current specs mean nothing in this case though because published stall definition (according to Hitec and for that matter ALL manufacturers) is at no load.Meaning nothing connected to the servos ie:control rods,control surfaces,and really doesn't give you a proper idea of what the actual current drain would be under flying conditions to give you guidance as to what you should be using for power.

So what I was hoping to do was create a worst case environment, take some draw readings both in extreme (3D) and normal flying conditions