kc31406

Will this volt meter put a drain on my batteries when I use it to check the voltage?

http://www2.towerhobbies.com/cgi-bin...?&I=LXNK81&P=0

spiral_72

Well, yes.

The meter simulates the load of a radio system to more accurately judge the charge level of the batteries.

If your question is, will it suck em' dry the moment you plug it in? Then no. You CAN use it to completely discharge the Rx battery (for cycling) if you like. It'll take about 4 hours or so.

bruce88123

Normally the term is "load". And yes it will apply the proper "load" for checking your batteries before flying. Typically it is only left plugged in for a few seconds and therefore does no harm but will "drain" the battery pack if left plugged in for a prolonged period.

Technito20

They all will use a little of your battery power but as spiral_72 said it won't kill your battery. This is the one I use, it don't' seem to use much power at all.

http://www2.towerhobbies.com/cgi-bin...&I=LXHDJ2&P=ML


It's just a rule of thumb to charge before you fly and don't fly without a volt monitor

-pkh-

My Feedback: (2)

There are two types of "voltmeters" that are typically used in our hobby...

1) loaded voltmeters that provide a simulated load (~250mA) while the voltage is measured
( http://www2.towerhobbies.com/cgi-bin...?&I=LXNK81&P=0 )

2) High impedance or no load voltmeters or "voltage monitors"
( http://www2.towerhobbies.com/cgi-bin...&I=LXHDJ2&P=ML )

The loaded meter is typically connected to your battery via the charger connection on your switch harness. The switch must be in the OFF/Charge position, and the receiver and all the servos are unpowered. Your battery voltage drops under load, so the simulated load built into this type of meter gives you a more realistic measure of the amount of charge left in your battery pack.

The voltage monitor is connected to the receiver via a servo plug, and continuously displays your battery packs voltage while the receiver switch is ON. Since the receiver and servos are powered while this voltage monitor is on, there is already a realistic load on the battery, so no simulated load is required to get a good reading. I usually move both transmitter sticks around rapidly (at the same time) to put a little larger load on the batt, and watch the voltage monitor to see what I get.

Personally I use a Voltwatch battery monitor in all of my planes. I've seen at least two guys loose their planes due to low battery voltage. Both guys had a loaded voltmeter to use, but neither of them used it because they had just taken their plane off of the charger and assumed it was good to go! With a voltage monitor, you always see the batt pack voltage when you turn your plane on... before and after each flight.
Some guys argue the loaded meter more accurately simulates the load you get while flying, than just banging the servos around on the ground, but I don't think that makes much difference. The main thing is the voltage monitors are always on, displaying your batt voltage, but you have to remember to use loaded meter to check your batt, and most guys don't use loaded meters before every flight, it's just a hassle, so they assume the batt is good for a few flights before they check it again!

Alex7403

Hi

Im installing the second one right now through a polyester window i cut off the fuse and glue the window with canopy glue

http://www2.towerhobbies.com/cgi-bin...&I=LXHDJ2&P=ML

Good luck

Alex

felixone

I have a question related to this topic. When using a loaded voltmeter what is a safe voltage before you recharge. I know the meter I am looking will say Ok or Recharge but I would like to know what a good range is just in case that process fails.

spiral_72

I think a better idea would be see what the run time is for that battery in that system. The reason I say this is: Nicads and LiPo's pretty much output a steady voltage and current up until the very last. Then it drops off sharply. I'd figure my run time and give it a 25% safety window. 4 hours run time, fly for 3 hours... or whatever.

The loaded voltmeter is a quick check, it won't predict 5 minutes from now.

AIRDEL

How do you check run time without running your batteries until you loose control? I don't see how this is accomplished.

Del

opjose

Several ways.

1 - You can leave the plane on the ground and twiddle the controls until the power runs down, then back off a little from the measured time.

2 - You can turn off your plane and plug in the voltmeter with load, and watch to see how long it takes to drop to the unsafe area.

3 - You can measure the typical draw of the electronics with a meter, then enter this as a discharge rate quantity into an intelligent charger/cycler, then let the cycler tell you how long the battery will last.

4 - You can measure battery capacity with the intelligent charger, and divide that by the average draw to give you an expected run time.

5 - You can fly the plane and take a measurement after each flight, using the voltmeter. Then once the plane gets into the danger zone use the voltmeter alone to calculate the remaining possible flight time.

etc.

Much like determining what to set your TX's timer to w/o first crashing your plane by letting it run out of fuel.

MikeL

My Feedback: (3)

That's bad advice. It assumes that the power draw on the ground is the same as that in the air, which it most certainly is not. On the ground you're not putting the same physical load on the servos. You're not accounting for vibration nor the power required to move and hold the surfaces when there is considerable airflow over them. The three methods listed above are a fine way to calculated the power drawn in each of those three scenarios, but a very poor way to measure what is actually drawn when flying the model. Following the above advice could very easily result in the loss of a model.

What do I do? If I fly more than three flights, I get out the ESV or I top off the pack with a field charger. Simple, practical, and safe. Why three flights? That's based on my own personal experience. Each person needs to develop that for themselves, and put some thought into matching battery capacity to the electronics inside a model. The tools to do this are cheap and readily available.

kc31406

should the tx and rx be turned on or off when using the ESV ?

MikeL

My Feedback: (3)

The ESV is generally connected through the charging jack of the switch harness. That gives it a line to the battery that sits in front of the switch, so the switch should be off. A loaded ESV is providing its own load, so there's no need or desire (it'd increase the load) to test in a way that leaves the electronics on. There's no need to have the RX on. You wouldn't need your TX on either.

opjose

Bad advice?

Hardly, though I know where you are coming from and do not disagree in that you must be careful.

There was a great article about servos in FlyRC last month which talks about servo draw, etc. The variance between running the servos statically but mounted on the plane with linkages, etc., versus in the air was not that great enough to have a highly significant impact.

Maybe it is not accurate at worst, but like glow fuel run time determinations you ALWAYS allow for error.

e.g. if your ground time is say 2 hours, then it would be quite foolish to fly for 2 hours w/o checking.

In this scenario I would take say 60% of the measured time on the ground as a max and work from there.

Personally I prefer charging the batteries and measuring the amount of charge they took after a day at the field.

Needless to say I never bother with the 600mAh or less TX packs, and I always tend to use at LEAST 1200mAh packs or larger on .40 planes and up.

kc31406

I'm finding this thread very informative for me.

Thanks for the replys.

-pkh-

My Feedback: (2)

What Mike describes is what most guys do at my field too. This works well 99% of the time. However if you have one cell go bad in your pack after the first or second flight, you'd never know it. That's why I feel better with a voltage monitor. I've seen some of my older packs, that normally last 3-5 flights, drop off fast after one flight. Needless to say I chuck them in the garbage and get new ones.

MikeL

My Feedback: (3)

I wouldn't trust that article, then, either. Here's some contradictory evidence: http://www.centralhobbies.com/Engine...s/hydetxt.html If you want to experiment yourself, set up a test. It's not hard to do. Move four or so servos around without a real load on them, then move them around after hanging weights on the servo arms. Time out the difference. A servo simply works harder when it has to use greater force to attain or maintain a position. Hence, the advice you gave about calculating run times by moving the servos around without any appreciable load on them really isn't very good advice.

kc31406

If I gave my 600 mah batteries a full charge with my 50 ma wall wart 1 week ago, would it hurt my batteries if I put a quick charge on them now if I wanted to fly tomorrow?

Or should the batteries be drained more than by just sitting around for a week before I use the quick charger?

I thought I read in a thread it's not good to quick charge batteries if they aren't drained very much.

jetmech05

I was taught by my instructor 3 flight is good, 4 is ok, after that be careful. Now this guy has been in the hobby long enough that I think he taught Orville and Wilbur to fly RC.
Since that time I haven't found anything to change that suggestion. Windy days or when i practice touch and go's i'll fly 3 calm days when I'm being lazy I'll do 4, then I'll check the batterys
Good Luck Have fun

opjose

Maybe your advice isn't very good?

Since the magazine article wasn't really trying to sell me engine soft mounts, I'll stick with the magazine article thank you.

If in doubt, put the meter on the plane and resist the movement by hand on say both aileron servos. Measure the difference. You'll get an instantaneous change which is represented by a short lived increase in load.

In use servos have a relatively light duty cycle... overall the difference is not as much as you seem to be making it out to be when calculating flight pack times.

So performing the test as indicated and backing off from the total measured as I said is certainly a good way to test. You merely never run the pack to the full time...

As I alluded just as if you were timing your plane for glow fuel use.

If on the ground you can run the plane for 20 minutes at 90% throttle, then you are CERTAINLY safe setting your timer for say 15 minutes.

Common sense.

opjose

Better safe than sorry.

It always helps to first establish what the limits are of your equipment as you are doing, and then periodically check just in case.

With the bigger packs ( albeit at an increased but useful weight penalty ) you can fly all day long.

Usually well over 10 or more 15+ minute flights per plane.

bruce88123

You use an ESV with the RX turned off. In fact, with every switch harness I am aware of, if you turn the RX on you disconnect the battery from the charging jack. This would make the ESV not work.

MikeL

My Feedback: (3)

You seem to be taking this personally, and retrenching your position. That's unfortunate for everyone. The reason I referred to Central Hobbies' article is simple--they give real-world current-draw numbers that illustrate the difference in current draw between just running the engine and not running the engine. It's illustrative of the differences between sitting there moving the sticks around until the battery is out of juice and real-world applications. It's great to cite a magazine article, but it's useless to prove a point when you're not providing any real data from it. I don't know the author from Adam, and who's to say he actually knows what he's talking about? In this instance you're off the mark. Big whoop. It happens.

This is the second time you've made the analogy to running a model out of fuel, and it's just not that apt. Nobody should ever get close to "empty" on a battery. The little methods you came up with are simply bad ideas. Why give out such advice, when you yourself say it isn't what should be done in practice?

I'm not at all sure why you quoted me out of context, either. This isn't a contest. If your pride is hurt because I pointed out that you gave bad advice that could result in crashes and injuries, perhaps you shouldn't be giving out such advice. Nobody is perfect, and nobody knows everything. Our flight packs draw variable amounts of current depending on what the servos are doing. When they work harder, they draw more current. You advised people that by measuring run times in very lightly loaded conditions they could calculate their available flight time, and that is simply bad advice. Rather than admit that, you're attempting to condition it. Why not just back off the bad advice?

P-40 DRIVER

KC31406, to answer your question, Generally you would not want to fly if your flight pack go's below 4.8 volts using a loaded meter such as the one you pictured.

opjose

Personally? Hurt pride?

No I in no way consider you to be the, or an authority.

You are however effectively splitting hairs and taking my original post out of context ( strange that is what you've accused me of... ). You seem to have purposely overlooked that I mentioned backing off from whatever is the measured time interval on the ground.

In the grand scheme, even an in flight reading is not going to be accurate. This includes your own "advice" with the "three flight rule".

We could go into how each flight varies and what one reading produces may not be applicable on subsequent conditions.

It is after all a ROUGH estimate.

Sitting the plane on the ground and playing with the servos then backing off a safe percentage is going to be no more accurate or inaccurate than your own technique, when it is applied to further flights or even other days and conditions at the field... which I may add will be just as bad as the "bad advice that could result in crashes and injuries". Gawd what a specious comment.

"Nobody should ever get close to "empty" on a battery. "

Hence the analogy, with fuel to which the same applies. You may time your engine to determine the flight time, but is it ever going to be "accurate", no.

No matter what you use, no one is "safe" running out the battery energy period.

The best you can do is an educated guess, and in lieu or in addition to other techniques, nothing I've given is any "worst" than what you've espoused thus far. Yet you've appointed yourself judge of what I had to say by deeming it "bad advice".

Maybe you may want to assess the ingrained desire you seem to have to attempt bad mouth others simply because you don't agree with them.

Do the servos draw more while in the air, sure, but is it going to greatly impact an attempt to determine a flight pack's run time through an estimate? No it is not going to make much difference.


So yes you CAN do a ground test and back off from what is measured for safety's sake and still be in the ball park.