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Which expanded scale loaded voltmeter to use

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Old 02-09-2003, 04:54 PM
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aftcg
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Default Which expanded scale loaded voltmeter to use

I'm flying a gasser with 5 highpower servos and one regular servo for throttle. What kind of loaded voltmeter should I use to check the strength of the 2000mah battery?

If I use the same loaded voltmeter that I use for my .40 size planes, will it be accurate (300mah load)?
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Old 02-09-2003, 06:10 PM
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arlyn3
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Default Which expanded scale loaded voltmeter to use

aftcg This is just my opinion, and everyone has one but I think you should go to at least a 500mah load.I use a Ace Voltmaster 11 ESV that has 300 and 500 load. Arlyn
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Old 02-09-2003, 07:11 PM
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Default Which expanded scale loaded voltmeter to use

Thanks, that is the kind of info I'm looking for. Where do you buy one of those?
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Old 02-10-2003, 02:21 AM
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Default Which expanded scale loaded voltmeter to use

You could also build your own "load" for any digital meter. Check Red's battery clinic website for information. You can build any load you want.

www.rcbatteryclinic.com

Mike
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Old 02-10-2003, 02:27 AM
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arlyn3
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Default Which expanded scale loaded voltmeter to use

I picked mine up at a Rc swap meet. But I saw on the ACE web site they are making a newer version of the ESV. Arlyn
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Old 02-10-2003, 03:06 AM
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Default Which expanded scale loaded voltmeter to use

Originally posted by aftcg
Thanks, that is the kind of info I'm looking for. Where do you buy one of those?
You can easily get a multimeter either digital or analogue and simply solder accross the leads a 2 watt, 10 ohm resistor. This will give you a load of 600 ma on a 6 volt battery.
Simply divide the voltage (6) by the load you want e.g. 600 ma (.6) which will give you 10 ohm.

Or 6/.5 = 12 ohm or 6/.8 = 7.5 ohm etc....
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Old 02-10-2003, 12:59 PM
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Default Which expanded scale loaded voltmeter to use

Roger, do you have a photo of how you soldered the resister?
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Old 02-10-2003, 01:45 PM
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Default Which expanded scale loaded voltmeter to use

Originally posted by aftcg
Roger, do you have a photo of how you soldered the resister?
Here is a sketch I have done
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Old 02-10-2003, 01:54 PM
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Default Which expanded scale loaded voltmeter to use

Some great information here.
Why do people use and expanded scale analog instead of a much more accurate digital meter ?. I use a Fluke digital meter with a 300 ohm load across it to check my 4.8v cells in my 40 size planes. Am I missing something by not using an anolg meter ?. Kind of new at this
Thanks
Roger
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Old 02-10-2003, 02:06 PM
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Default Which expanded scale loaded voltmeter to use

Originally posted by IronCross
Some great information here.
Why do people use and expanded scale analog instead of a much more accurate digital meter ?. I use a Fluke digital meter with a 300 ohm load across it to check my 4.8v cells in my 40 size planes. Am I missing something by not using an anolg meter ?. Kind of new at this
Thanks
Roger
To check a 5 volt pack with 300 ohms, your only getting 20ma, not very high. You should have a 12.5 ohm resistor to get about 400ma load to be accurate.

As for the units used, I use a Fluke also, but not everyone is willing to spend this amount of money. Today you can get a decent digital meter for about $25.00
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Old 02-10-2003, 02:58 PM
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Default Which expanded scale loaded voltmeter to use

Thanks Roger.
After reading the above I can see where you are right about the load.
Why is everyone talking expaned scale anolog though. I have heard some guys talk about looking for a voltage "bounce" and battery recovery time on the bigger models. Can't believe they would fly something that bounces the voltage everytime the servo's kick in. Kind of like the lights dimming when the air comes on or something.
Just curious
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Old 02-11-2003, 12:48 AM
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Default Which expanded scale loaded voltmeter to use

If I were to use a battery discharger(Triton) and set the rate at what I want, would that give an accurate voltage? Thanks
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Old 02-11-2003, 01:22 AM
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Default Which expanded scale loaded voltmeter to use

The voltage on any battery is gonna bounce if you hit it with a high load (like a series of servos) no matter what you do. If you really want you can put big capacitors on the battery to help, but it's hard to find caps big enough to make a difference. SuperCaps are out there but they're hard to find in high enough voltages to use with 5volt packs. Standard super caps are only rated for a couple volts.
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Old 02-11-2003, 02:01 AM
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Default Which expanded scale loaded voltmeter to use

If you don't want to build your own I4C sells a digital meter with a .5amp, 1.0amp, and 1.5amp load depending on the buttons pressed. Fairly small, compact, and easy to use. I think Duralite also sells the same one, yet I don't know who designed it and who is reselling it.

The Biggest factor in measuring your voltage is to have some load on it, and use it as a calibration point against previous data from your capacity/cycle logs. Its only a reading that you use to balance against other known facts, such as previous capacity checks. So the most important part is consistency. If you use a .5amp or 1amp isn't as important as always using the same load when you compare it against your past capacity checks. You don't want to start with a .5amp load, then later change to a 1amp load. If you do, you should go back and re-do your capacity checks so that your readings are accurate.

I agree with Roger, that 200mah or even 300ma is on the low side. I would recommend at least .5amp for most 25% to 33%, and 1amp for 35% and 40%.
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Old 02-11-2003, 01:40 PM
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Default Which expanded scale loaded voltmeter to use

Originally posted by aerografixs


You can easily get a multimeter either digital or analogue and simply solder accross the leads a 2 watt, 10 ohm resistor. This will give you a load of 600 ma on a 6 volt battery.
Simply divide the voltage (6) by the load you want e.g. 600 ma (.6) which will give you 10 ohm.

Or 6/.5 = 12 ohm or 6/.8 = 7.5 ohm etc....
So are you saying that if I have a 4.8 volt 1400 mah system and want to check it at say 500 mah load I need a 2 watt 9.6 ohm resister??
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Old 02-11-2003, 01:49 PM
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Default Which expanded scale loaded voltmeter to use

Some great info here thanks.
Couple more questions though if I may.
Is the "bounce" a problem ?. Seems like under the right circumstance it could temporarily drop the voltage below the operating threshold of the receiver...
What is a realistic load to use on a 40 size plane with 5 or 6 servoes.
Thanks for your patience. I am considering a jump into the larger stuff and trying to learn as much as possible first
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Old 02-11-2003, 01:56 PM
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Default Which expanded scale loaded voltmeter to use

Originally posted by robbie


So are you saying that if I have a 4.8 volt 1400 mah system and want to check it at say 500 mah load I need a 2 watt 9.6 ohm resister??
Theoretically yes, but the calculations are allways with 5 volts and not 4.8. They have allways used 4.8 for a 4 cell pack which is not quite right, and I don't know why they still do. A fully charged 4 cell pack NiCd is 1.33 x 4 = 5.32 and usually will stabilize at about 1.25 volts/cell which will give you a more realistic 5 volt pack hence the 10 ohm for 500ma load.
You don't need a 2 watt resistor, you can go lower if you wish as long as you don't leave it plug for very long.

Hope this helps
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Old 02-11-2003, 02:01 PM
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Default Which expanded scale loaded voltmeter to use

Originally posted by IronCross
Some great info here thanks.
Couple more questions though if I may.
Is the "bounce" a problem ?. Seems like under the right circumstance it could temporarily drop the voltage below the operating threshold of the receiver...
What is a realistic load to use on a 40 size plane with 5 or 6 servoes.
Thanks for your patience. I am considering a jump into the larger stuff and trying to learn as much as possible first
When you say 40 size, do you mean .40 size or 40% size?

If its .40 size, don't worry about drawing too much current and getting the receiver below the threshold.

If its 40%, then two things, if you use a PCM receiver, if the voltage goes below a certain value (which I don't remember) it will go into fails safe, which is one of the reasons I don't like and don't recommend connecting the servos directly to the receiver.

With PPM receivers (highly recommended) with the servos on there own batteries, the voltage can go down to about 3 volts and still operate safely. That's the receiver only with no servos connected to it.
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Old 02-11-2003, 02:30 PM
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Default Which expanded scale loaded voltmeter to use

Roger
I was talking 40 engine size, sorry. I am seriously considering the bigger 40% stuff.
So much to learn here though.
If I understand what you said correctly-
PPM is better then PCM for these larger planes ?.
The servoes are connected to there own batteries ?. I take it you then run a ground/common wire and the signal wire back to the receiver ?.
With servoes ganged up. several servoes on the same signal wire it won't pull the output on the receiver down to low ?.

Thanks
Roger
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Old 02-11-2003, 02:34 PM
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Default Which expanded scale loaded voltmeter to use

If you use 5cell packs, even on a 40% aircraft, you're not going to see voltages low enough to hit the receiver clipping point. If you do, you've got other more serious problems. And my using 5cell dual packs in a redundant configuration, you lower the risk even more. You would need an abnormally high load to get dual 5cell packs in good condition to drop anywhere near 3volts.

Futaba is the only PCM receiver I know of that has a battery failsafe feature. If the voltage drops below its set point, the throttle goes to idle regardless of the stick position. You then bring the throttle stick to idle, then back up to power and it resets itself, and you can continue to fly in order land safely.

From what I understand on clipping with receivers is that if the voltage drops below the receivers threshold, the receiver stops working, but does not go into failsafe. Since it stops working, it removes all the load from the servos which removes the load that started the low voltage in the first place. The voltage rises, and the receiver starts working again. It all happens extremely fast, and if the pilot noticed, it would feel much like a sluggish response and not like a failsafe event. Think in terms of something like ABS brakes, where it pulsates on and off rapidly, but doesn't cease to function properly. Even with clipping, the pilot has control of the airplane.

Here are a bunch of recent threads on setting up 40% sized airplanes, PCM and PPM, wiring, etc.

http://www.rcuniverse.com/showthread...hreadid=465411

http://www.rcuniverse.com/showthread...hreadid=436492

http://www.rcuniverse.com/showthread...hreadid=424119

http://www.rcuniverse.com/showthread...hreadid=424119

http://www.rcuniverse.com/showthread...hreadid=289142

http://www.rcuniverse.com/showthread...hreadid=130469

http://www.rcuniverse.com/showthread...hreadid=130687

http://www.rcuniverse.com/showthread...hreadid=473062

http://www.rcuniverse.com/showthread...hreadid=355152

http://www.rcuniverse.com/showthread...hreadid=339931

http://www.rcuniverse.com/showthread...hreadid=246442

http://www.rcuniverse.com/showthread...hreadid=401764]
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Old 02-11-2003, 02:46 PM
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Default Which expanded scale loaded voltmeter to use

Thanks Roger
Very informative.
Thanks for the threads, I will get busy on them
Roger
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