selnekav

Hi,
I never used voltmeter to check my receiver battery. i am using woltwatch instead.
is there any reason to use both ?

Thanks,

airbusdrvr

Most modelers after a while realize that just checking voltage is not the best indicator of your battery condition/capacity. There are several voltmeters that check your battery under a one amp(varies with brand) load. Futaba and Hobbico models are available on Tower Hobbies. Other brands may be available.

selnekav

Hi,
I guess what you meant by saying "just checking voltage is not..." is that the voltmenter check is under load.
but also the voltwatch is under load ( playing with the servo's simulate a similar load ) so what's the real diffrence ?

rcairflr

My Feedback: (44)

There is no chance in this world I would trust my batteries to Voltwatch. I check my batteries under load each and every flight.

When checking your battery underload, you have a known condition and after awhile you get to know your batteries very well and can tell the condition of them at any given point.

I've seen threads here on RCU where people used a voltwatch and crased there airplane due to dead battery. All you have is a bunch of lights that may or may not tell you the condition of your battery. If you insist on trusting your batteries to a Votwatch, all I've got to say is good luck.

Where I fly there are a lot of Giant Scale Flyers including myself, no one uses Voltwatch, we all use battery checkers of some sort under load. When the guys with the little airplanes are out, that is when you see the Voltwatch. There is a reason giant scale guys for the most part do not use Voltwatch. We don't trust them.

selnekav

Sorry of being hard on that issue...
i understand that every flyer has his own preferences based on his experience knowledge etc, but is there any real logical
or electrical reason for why not using only the voltwatch ?

as i said before when you "play" with more then one servo it will simulate the actual load.

Thanks,

BuschBarber

My Feedback: (2)

If you want to use Lights to warn you of a pending Low Voltage problem, OK, but I use a Digital Expanded Scale Voltmeter (ESV) with a .5a load for Nicads and NiMh and 1a load for LiPo and LithIons.

You need to put a load on the batteries and if you are close to the lower limit, leave the ESV on the battery for 30sec to 1min just to make sure the voltage does not drop quickly.

I am using a Hangar9 ESV that has a .5a, 1a, and 1.5a load switch.

Before each flight, I check the voltage and after a few flights, I get a feel for how the battery is holding up. If the voltage is dropping too fast, I cycle the battery (Charge/Discharge), using my DC Cycle Charger.

rcairflr

My Feedback: (44)

It appears to me that you insist on using and defending your Voltwatch, use it be happy, but you've been warned.

So tell me how you are monitoring your battery voltage/ current load while moving the servos so that you can tell the condition of your batteries.

vasek

My Feedback: (4)

Hi drvr, can you post a link for the Futaba voltmeter at TH please? I tried to look it up without success.

Thanks

airbusdrvr

I didn't have time earlier to get you the links to a couple of the battery load/volt testers. Hobbico has one that only has a preset load of 250mah, http://www3.towerhobbies.com/cgi-bin...&I=LXWW16&P=ML . I use the Futaba BR 2000 where you can adjust the load from 1 to 3 amps(more realistic of all servos moving). The Futaba one is here, http://www3.towerhobbies.com/cgi-bin...&I=LXEYM6&P=ML . As BuschBarber stated, I also check my battery before each flight with a load capable voltmeter (Futaba BR 2000). Just a couple days ago I charged an airplane I hadn't flown in several months. It checked good with a voltmeter after charging, but before flight with a 1 amp load the four-cell pack dropped down to 4.1 volts. Needless to say, it did not fly and is awaiting a new battery pack.

airbusdrvr

You have it in the post above. I to could not find it by searching Futaba voltmeter. I just went to my garage and looked at its name. I then did a "BR 2000" search and there it is.

BillS

I prefer a voltmeter and a known load.

But I would much prefer that the manufacturers use the technology to downlink the RX voltage and display it on the transmitter screen.

Bill

selnekav

Hi rcairflr
belive me i am not trying to defend my voltwatch... the only thing that i am trying is to understand exactly what is the risk of using the voltwatch.

Correct me if i worng but it's very simple to know what is your battery condition by using the voltwatch, i always move 2 or 3 servo's simultaneously to thier max through ( back and forth several times ) and then at the same time i watch on the voltwatch ( i do it before and after landing ) if the only flickering lights are the green ones then it means the battery voltage is at least 4.8v under load.

now can you tell what is wrong in that test ?

Thanks,

Rodney

As an electrical engineer with many years experience in instrumentation and testing, IMHO the Voltwatch is far superior to a loaded voltmeter if you are limited to one or the other. The loaded voltmeter checks only one thing, voltage under a constant load. A Voltwatch acts very similar to an oscilloscope if you know how to use it. If you cycle the sticks while looking at the Voltwatch and you see momentary dips down into the yellow or red, it is telling you that you have a potential problem; may be dirty contacts somewhere between the battery and where the Voltwatch is plugged in, a servo or two that is drawing excessive current for a fraction of a second (causing negative voltage glitches which can be deadly on 2.4GHz systems) or binding hinges or to small a gage wireing or some other defect causing negative voltage glitches. A loaded voltmeter will not give you that information. Unfortunately more crashes are caused by electrical problems other than low batteries. The Voltwatch also gives you that low battery indication if you always read it at the end of the previous flight and does it with actual loads you have just experienced. Plus, the Voltwatch is always there to read, no having to remember to plug it in everytime you want to use it.

selnekav

Thanks Rodney
This is great explanation !

rcairflr

My Feedback: (44)

You have no idea what current load you are putting on the battery or the voltage of the battery under load, all you have is a row of lights.

Regardless of what Rodney says, I will trust my voltmeter and a known load on my batteries any day. I know and work with many electical engineers, just because they have a degree in engineering does not mean they know anything more about battery use than anyone else.

Sorry if you take offense to this Rodney, but you are the one who brought it up.

Like I said earlier, if you are happy with a voltwatch, use it, it is definitely not for me.

In answer to your question " What is wrong with that test?" If you look at every post I've responed to here, I tell you that you don't know the voltage or load on your battery, that is what is wrong with that test.

selnekav

As i explanied before although the voltage measure is not accurate like in the voltmeter it still give you enough information
the only thing you need to know is that your battery is above 4.8v under load. and the lights indication is good enough for that purpose
about the playing with 2,3 servo's is around 0.5A now again i don't think that it's relly matter if it's exactly 0.5A the more important is the fact that the voltwatch test your system voltage on "real time" and not only the battery as stand alone device.

Regards,

Campgems

Man, this question keeps comming up and every time the same old and not very valid arguments get bantered about.

Rodney's explanation is spot on target. The volt watch gives you a dynamic reading of the voltage under the "real" load your system is seeing.. The lights dance because the load is not consistant.

For you loaded voltmeter fans, remember Ohm's law. A fixed resistor can not give an accurate amp reading with variable voltage. SO your 1 Amp load is more like a sorta 1 amp load. In all likely hood, it has 5ohm resistor across the leads and for a 4.8V pack, it will draw around 1 amp.

Don

vasek

My Feedback: (4)

Thanks for the link DRVR,

BTW, since the other link is for the Hobbico Voltmeter I want to WARN everyone that it "self discharges" the 9v battery that powers it EVEN when turned OFF! Don't ask me how i know. When I want to use it, it's always DEAD! very frustrating. The 2 ways to remedy is to take out the battery after use or put another switch on the battery leads itself.

airbusdrvr

I've never used a Voltwatch, however, I have seen them on some airplanes at my field. Not until this "friendly" discussion did I realize that the voltwatch plugs into the receiver and only indicates voltage when the airplane system is powered. I would suppose the only problem using a Voltwatch might be the higher amp useage of the servos when under flight airloads than when sitting on the ground. But assuming the lights display is reasonably accurate, voltage wise, it could be acceptable. And of course, as we see above, some have negative feelings toward a voltmeter with load. Fly safely!

rcairflr

My Feedback: (44)

Please explain to me what a "real Load" is. Also do not try in any way to equate the load the servo is putting on your battery on the ground to the load in the air, they are in no way the same or equal. On the ground the majority of the load is from the DC motor while moving, there is little to no external load on the servo while on the ground. In the air is completely the opposite, the majority of the load is from airloads on the flying surface and minor load from the DC motor moving and the total load will be much higher while flying.

RCAddiction

My Feedback: (87)

I use both. They each have some advantages as everyone has pointed out. Can't we all just get along?[8D]

Voltwatch
The voltwatch and similar devices can be a very convenient reminder that you may have left your RX or IGN switched on. Anyone ever kill a lithium battery because the switch was accidently left on, or perhaps bumped it in transport, etc? I have. They are a cheap, effective way to help avoid killing your batteries. Provided of course that it is mounted so that it is very visible (ie, thru the canopy)

Loaded Meter
For Li-Ion, NiMh, etc I use a loaded voltage checker before each flight. I've found some dying batteries this way. For A123's, loaded meters are pretty useless, so I use a Kodiak switch to monitor battery consumption, and a Cellpro 4S to measure the ma's put back in.

With smaller planes, the $25 MPI charge switch with built-in volt meter is very convenient, since it can be seen outside the plane. With larger planes that require Deans connectors and heavier duty (Fromeco, etc) switches for power, etc, I'll "tee" in a RadioSouth voltage meter to the receiver and a Voltwatch to the Ignition power, making sure they are visible thru the canopy.

It is actually helpful to see the bus voltage at the receiver for the planes where I'm running a regulator. This is something a loaded meter thru a charge switch doesn't do, since it would typically be setup to read the voltage off the battery, not thru the regulator.

my 2 cents only...your mileage may vary.

selnekav

so the question now is how much load each servo produce on the ground ? for example the running current of hitec HS-5625MG is 400ma which means that if i have two servo's on my ailrones, then playing with the right stick produce 800 ma load which is very similar to the voltmeter constant load is that true ?

of course that i can play with the rudder at the same time and get load of 1200ma...

now what is the diffrence between servo load to the voltmeter load ? from what i understand the only diffrence is that in the voltmeter you can set the load for 0.5 , 1 etc, and with the voltwatch you need to know the current drwaing of each one of your servo's and then play with any combination of them to get the required load.

waiting for your comments.

Four Stroker

Why don't you try one of the voltwatch type of things that actually saves the lowest voltage from the previous flight. An example is the VoltMagic available here:

http://www.ronlund.com/

Most guys get the VoltWatch because it is cheap with some rationalization about why the lowest voltage is of no value.

BuschBarber

My Feedback: (2)

Thank you for enlightening me on the other advantages of the Voltwatch type device. I must say though that in 30 years of flying RC, I have NEVER lost a plane do to a battery that I properly checked with an ESV. I also never fly with a battery that is close to the lower voltage limit. I usually top off the charge and keep checking after each flight. I also do not pop the battery off the charger and go off to fly immediately. I usually wait 10 minutes and check the voltage under load. I the voltage drops too fast, from one flight to another, I cycle it before I use it again.

I would have to ease in to that Voltwatch and still use my ESV, but it sounds interesting.

I am using mainly LiPos and LithIons now. I find the charge lasts longer, they are more reliable, they charge faster, they are lighter.

RCAddiction

My Feedback: (87)

...........and they get really unhappy if you forget to shut the power off... ;-)