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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 03-14-2011, 06:54 PM   #1
AirmanAirhead
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Default DX 7 (Spektrum) Battery Issues/Question

I've had my DX7 for over three years now. And I have a battery issue that has always been in the background since I got it new.

1. The original battery 1500 mah seemed to drop off quickly and needed to be charged every week or so with about 5-6 days of flying about an 30 mins each day. (Always turn radio off between flights)

2. I finally replaced the battery with Eneloops and I charged them every few days of flying. Those lasted pretty decent but still seemed to need recharging quite often.

3. Finally my eneloops died after over a year of use and I temporarily replaced them with over the counter Alkaline batteries (not-rechargeable). These last about 4 days with flying about 30 mins each day. I'd say the radio is actually on about 15 mins each day of those four days.

My question is.... Am I kidding myself about using the over the counter batteries? Or is my radio drawing more then seems normal?

One of my flying buddies has a DX7 and is still using his stock 1500 ahm battery and needs to charge it considerably less then I do.

Just wondering what might be going on here, if anything.

Thanks,
Jeff

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Old 03-27-2011, 02:05 AM   #2
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I bet your buddy has a newer DX7 that came with a charger that was the correct output (150mA) for charging a 1500mAh pack. The early units came with a charger (50 or 70mA) that was for the older Nicd packs that were around 600mAh. They work fine, but you have to leave the battery on charge for a lot longer.
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Old 03-27-2011, 02:16 AM   #3
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Originally Posted by AirmanAirhead View Post
I've had my DX7 for over three years now. And I have a battery issue that has always been in the background since I got it new.

1. The original battery 1500 mah seemed to drop off quickly and needed to be charged every week or so with about 5-6 days of flying about an 30 mins each day. (Always turn radio off between flights)

2. I finally replaced the battery with Eneloops and I charged them every few days of flying. Those lasted pretty decent but still seemed to need recharging quite often.

3. Finally my eneloops died after over a year of use and I temporarily replaced them with over the counter Alkaline batteries (not-rechargeable). These last about 4 days with flying about 30 mins each day. I'd say the radio is actually on about 15 mins each day of those four days.

My question is.... Am I kidding myself about using the over the counter batteries? Or is my radio drawing more then seems normal?

One of my flying buddies has a DX7 and is still using his stock 1500 ahm battery and needs to charge it considerably less then I do.

Just wondering what might be going on here, if anything.

Thanks,
Jeff
Also got one of the original 3 year old DX7 chargers. They put out 50 milliamperes, so total charging time would by 1500/50 or 30 hours to full charge. Problem is, charging these batteries at less than C/10 or 150 milliamperes can result in low charging efficiency.

So, I built up a charger that puts out 150 milliamperes, and shuts it off after 14 hours. (Nope its microcontroller controlled, plans are not available )

But, as far as the charger itself is concerned, its nothing but a Radio Shack type wall wart charger with a couple of 12 Volt dial lamps in series to set the current at 150 Milliamperes.

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Old 03-27-2011, 03:49 AM   #4
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The discharge curve for alkaline and NiXX are different (study link).
For folks that don't know and understand it this freaks them out.

NiXX loses a up to 10% of it's charge within 24 hours. Then it continues to slowly drop. It levels off about mid-way and can hang in there a good while. It's often right about here that people that don't understand how they work start to fuss that the charge is getting too low. LSD like Eneloop will not do the continual self-discharge but they otherwise behave like NiMh batteries.

Do check your charger output (written on the outside). There are a number of different outputs of these things.
When full your charger should read ~ 11.4 or so. It will not read that level long, rapidly dropping to the mid-10's where it should stabilize and drop slowly. At 9.6 it is at 'nominal voltage level', not almost dead like a lot of people think.

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Old 03-27-2011, 06:21 AM   #5
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Originally Posted by flydiver View Post
The discharge curve for alkaline and NiXX are different (study link)..
Some time ago, I ran a discharge test on a single Alkaline AA cell, and compared it to a Nih AA cell. Was very surprised to find the Nih AA cell had near double the Amp Hours of the Alkaline AA cell, that at a test current of about 200 milliamperes.

But, that was just one Alkaline and one Nih cell. But it was an interesting result.

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