Field battery checkers - waste of money?

A number of club members have started using Hitec Battery Checkers at the field and using the readings to decide whether there is enough pack capacity to risk another flight.The meter appears to be a voltmeter presumably with some electronics to give an expanded display around 4v to 5v and a load for the battery.

I am thinking this is a dangerous practice to depend on a single reading. I was always told the discharge curve for NiCd and NiMh was almost flat right up until the last few minutes where it drops off rapidly.

If this is the case how can these meters be of any use when they have no idea where along 'the curve' they are sampling. They could be near the just charged end or they could be just a few moments before the curve drops away and the battery is flat. The latter being real bad news if you used one of these to decide whether to fly or not.

Would be interested to hear from other users and the battery experts on this one.

regards

Bob

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a
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Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

I am no battery expert, however, I have been flying for a "few" years.

A fully charged 4.8 volt battery will read about 5.0 - 5.2 on the meter. If the voltage reading gets much below 4.6 or 4.7, I recommend you recharge the battery. Depending on the number of servos and how often you are using them (aerobatics use the servos quite a bit more than just "putting around) this should come out to ABOUT three or four 10 - 12 minute flights, and still have a safety margin at the end of the last flight. I have seen people run their battery packs as low 4.4 volts and fly, but then there are people who play Russian Roulette also.

I would suggest checking the battery after the 3rd flight, and then every flight there after. This will give you an idea of the number of flights you can get from a pack with your individual style of flying before needing to recharge.

I would not be concerned about where you are "on the curve". For our purposes, the voltage reading is accurate enough.

Reply to
Ted Campanelli

Reply to
Jonneybravo

Reply to
Ken Day

What about those onboard LED meters that fly with the plane itself?

Regards.

- Michael

Reply to
Michael

| I've done it this way for years and so have most of the other club | members. I've never had a battery fail in the air. Don't need to | worry about the 'curve'. The voltage tells the story.

The voltage tells much of the story, but it's not the whole story.

A key part of having the voltage tell the story that you want is to have the battery be fully charged before flying that day. If you charge the battery only a little bit, the voltage won't tell the right story.

Take a totally dead battery. Zero volts. Charge it for 5 minutes at

1/5C -- it's now about 4% charged. Put it on the ESV, and it'll read like an almost full battery -- for a little while, anyways. Take it up for a flight, and you probably won't ever get to land that plane.

ESVs don't tell the whole story -- you need to fill in some details yourself. But they're pretty good in helping you decide if you should go up one more time or not.

| >A number of club members have started using Hitec Battery Checkers at | >the field and using the readings to decide whether there is enough | >pack capacity to risk another flight.The meter appears to be a | >voltmeter presumably with some electronics to give an expanded display | >around 4v to 5v and a load for the battery.

No electronics needed. It's just a resistor in parallel with the meter to give you a 250 mA or so load. (Without that load, the voltmeter will read around 1.4 volts/cell even for an almost empty pack.)

Actually, you can make a fully functional ESV with a $3 multimeter from Harbor Freight Tools and a 16 ohm resistor for receiver packs and a 32 ohm resistor for transmitter packs. Make sure the resistors are rated for at least about one and two watts respectively -- lower rated ones would be fine for the usual few seconds, but if you ever want to use your ESV to discharge a battery, you'll want the proper resistors or you'll risk burning them up.

| >I am thinking this is a dangerous practice to depend on a single | >reading.

It is, but it's better than nothing.

| >I was always told the discharge curve for NiCd and NiMh was almost | >flat right up until the last few minutes where it drops off | >rapidly.

There's some truth to that, but it's not really _that_ flat. And if you're smart, you charge LONG before get gets to the point where it drops off quickly. If you stop when your battery read 1.2 volts/cell, and you fully charged your battery previously, then you've still got quite a bit of power left in that battery. You could probably make a few more flights, but it's smart to charge now.

| >If this is the case how can these meters be of any use when they have | >no idea where along 'the curve' they are sampling. They could be near | >the just charged end or they could be just a few moments before the | >curve drops away and the battery is flat. The latter being real bad | >news if you used one of these to decide whether to fly or not.

You also sometimes have a little warning before it goes really flat -- the servos start getting sluggish and sometimes jittery. I don't suggest ever letting it get to this point, but I've seen it happen, and seen people notice it and land really quickly, and find the pack at 4.0 volts ... whew!

Personally, I put these --

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into most of my planes. Mostly for the lost plane alarm functionality, but the low battery alarm is nice too. In a powered plane you won't probably hear it in flight, but you'll hear it while you're refueling and such. (In a glider, you will hear it in flight if the plane is close.) It starts going off when the voltage drops below 4.6 volts -- which generally means that you've got some time left -- maybe 15% or so? -- before it craps out completely. At $15 and 7 grams, it's cheap insurance.

Reply to
Doug McLaren

| What about those onboard LED meters that fly with the plane itself?

They work pretty much exactly the same as a ESV, except that 1) they're always on if the plane is on, 2) they don't provide a load -- they rely on the receiver and servos to provide a load instead, and 3) since they're always on if the plane is, they're always draining the battery a little bit. (Just a little, however.)

I guess that ultimately they're a little more convenient, and a lot more expensive if you have a lot of planes :)

Reply to
Doug McLaren

Reply to
Lyman Slack

The whole idea is to stop flying before it gets to the point where the steep drop off occurs. While the curve is certainly much less steep, it does go down. Knowing where the steep drop begins would in theory let a person fly until just before it begins. For those who are more conservative, staying a couple tenths of a volt above the start of the point where the drop begins ensures safe flying.iu

Testing is better than not testing. It accomplishes two things. First, it confirms that the battery still has adequate voltage to fly. Second, there have been cases where a person noticed a sudden voltage loss due to a bad cell.

I avoid pushing the limit by bringing more than one plane to the field and using 1250 NiMH packs instead of the typical 600 or 650 NiCad packs that come with the radios. The larger NiMH packs weigh the same but give me way more flights.

Reply to
C G

Test

C G wrote:

experts

Second,

Reply to
pcoopy

An ESV is most accurate when its internal load is big enought to match the maxumum current draw, under maximum load, of the particular battery installation. If you have a very large plane with many servos, the load provided by the ESV maker may not give you a very accurate reading. Allow the ESV to remain connected for a full minute before reading to avoid reading surface charge which will build up whenever a nicad is idle for a while. Also, an ESV is not just a meter with a load. It gets its accuracy from a diode regulated voltage divider which reads only the top few volts but with great accuracy. Don't think that a digital meter is accurate just because it is digital. I agree with C.G., use a bigger battery.

Phil AMA609

Reply to
pcoopy

I have these permanently mounted on my planes. Not only do I look at the voltage reading, I start moving all the servos around and watch what it does. When a battery is fully charged the highest green light will stay on the whole time. After a couple flights moving the servos will make the light "move down" the scale a few notches as the control surfaces move, them come back all the way to the top when you stop moving them. I figure that I want to know what the voltage is when I'm actually moving things when I'm flying as opposed to what it is when it's static on the ground. Steve

Reply to
scasko

Phil --

Just for kicks, you might want to investigate the use of a "TTML" -- visit Red's site

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then scroll down to Loaded digital voltmeter, better than an ESV What's a TTML? It's a "Tic Tac Meter Loader" -- and it works great :-)

Cheers -- \_________Lyman Slack________/ \_______Flying Gators R/C___/ \_____AMA 6430 LM____ / \___Gainesville FL_____/ Visit my Web Site at

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Reply to
Lyman Slack

Not a waste of money. Just consider it very cheap insurance. Go here and scroll down to "Loaded Digital Voltmeters..." in the left frame. AAMOF spend a little time reading everything - very good site.

Reply to
Ed Forsythe

Oops! Forgot link :(

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Reply to
Ed Forsythe

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