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Electronics Discuss radios, chargers, etc...

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Old 08-06-2004, 09:40 PM   #1
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I am: Colin J
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I am told that it is good to cycle your batteries on occasion, or even drain them down before charging, rather than continuously topping them up. The transmitter will drain out on itself quite nicely. Problem is the receiver packs take a long time, unless you are sitting there working the controls (and who wants to do that). I was thinking of hooking the receiver battery pack up to a flashlight light bulb(s) as a means of draining the receiver pack. I'm wondering if anyone else has done this, and if so, what type of light bulb you are using.
Colin Jensen
Regina Windy Flyers
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Old 08-06-2004, 11:38 PM   #2
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Be careful! Do not drain your batteries below 1 volt per cell or you could end up reversing the polarity of the weakest cell. Not a good thing to do Fastest way to kill a pack is to completely discharge it a few times. Don't ask me how I know!!
I strongly recommend you get a device that will shut down when this level is reached. Look for a commercial cycler that will also give you battery capacity. This way you will be alerted when there is a reduction in your battery's performance and you have a chance to replace it before your airplane becomes a re-kit project.
Just my 2c FWIW
Keith J
Secretary-Radio Control Club of Detroit
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Ex-MAAC (Oshawa)
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Old 08-07-2004, 08:15 AM   #3
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The flashlight bulb technique has and still is used with great success on glow-plug lighters ... a 1.5 volt bayonet bulb will fit a heater socket almost exactly. The technique is to let it shine until it just fades out and then recharge the battery for the 12 or 16 hours the little brick charger needs, in the thought that this will "erase memory." For a receiver pack, you'd use a 4.5 or 6 volt lamp, depending on how many cells.

It's a pretty crude technique because the lamp's resistance changes with its temperature

Most expanded scale voltmeters (ESV) use a variant of this ... a resistor loads the battery pack to a couple hundred milliamps and the meter measures the pack voltage. Indeed, you can quite succesfully use your ESV to discharge a pack with modest accuracy to the 1 volt per cell that cjensen suggests.

The problem with both is the human memory, not the battery's "memory". Discharging with these "dumb" loads usually leads to the modeller going for a coffee and forgetting all about the pack, which discharges 'til cell polarity reversal is a possibility. cjensen correctly points out that this is a bad thing.

So the modeller is really left with a couple of choices ... modify the charging regime to suit the use, or get a good battery charger/cycler.

The latter is the better long-term choice, as you'll get a clear picture of how your packs are aging and the "peak detect" feature of the good ones will give you confidence that your pack gets the charge it needs. These days, you'll want to look at one that'll handle lithium batteries as well as nickel cadmium and nickel metal hydride.

If you're minding your pennies, get a cheap ESV and use it. Measure your pack's voltage before and after your flying session and that'll give you an idea of how much you're using. Adjust your charge time accordingly. If you've used half the capacity, give it about 65% of full charge time on the wall charger. This will tend to reduce the risk of reducing the pack's capacity through overcharging.

Use the ESV to discharge a pack to about 1 volt per cell (1.05 is a little safer). Time it to see how long it takes ... be warned, you'll be standing there a while. That'll give you an idea of the pack's actual capacity, although you'll need to know the load current of the ESV ... it may or may not be in the instructions. The formula is load current (milliamps) x minutes/60 to give an approximate mAH rating. You'd then charge the pack with the wall charger for the specified time (usually 14-16 hours -- check the ratings and instructions).

Long answer to a short question, and the bottom line is get a good charger/cycler if you're planning on staying with this hobby for a while. If you're not sure, use a safer alternative.
John, VE1FH
MAAC 50007
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