Help me figure this one out.

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gsjames
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Joined: Wed Jul 11, 2007 10:26 am
Location: Weatherford, TX
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Help me figure this one out.

Post by gsjames »

For quite awhile now, I've been having intermittent radio problems with BOTH my Hitec Eclipse 7 on 72 and an Eclipse 7 converted to 2.4 with the ASSAN 2.4 system. I "may" have FINALLY figured out what has been going wrong, but want to bounce this off of anyone with electronics experience.

I "upgraded' the stock transmitter battery packs with 8-cell, AA, 2200 mAh NiMH packs from one of the numerous on-line battery vendors. They don't make 'spec' but usually they test out at about 1500-1900 mAh so they have LOTS of capacity. What I noticed last week when out sport flying is that when the transmitter battery is freshly charged, it puts out a pretty high voltage, around 11.3 or so. When I was 'stirring the sticks' on the bench before test fights, trying to mimic the rapid servo movements during a combat match, I noticed the voltage reading on the TRANSMITTER LCD started flickering and the transmitter module and receiver unlocked. After a few seconds of inactivity, they relocked until I stirred the sticks again and then the same thing happened all over again. Note that the receiver is also being powered by a 5-cell AA 2200 mAh NiMH battery. Now the strange part. After the initial high voltage of the transmitter battery had drained down a bit, say to about 10.6 v or so, everything seems to be working fine. I flew in last weekends contest without a single "glitch". I intentionally didn't top-off the batteries prior to the contest.

I've seen discharge graphs of NiMH batteries from one of those computerized battery analyzers and they have different characteristics than NiCads. The NiMH starts out with a high voltage and shortly there after drops off to a "sustained" voltage that stays fairly constant for a long time. Toward the end of it's charge, the voltage drops off quickly rather than gradually like a NiCad does. So I'm wondering if perhaps my problem has been that a high demand during the initial high voltage period is causing a drop off in voltage to the sustainable level and the module is interpreting this as a voltage drop out and disconnecting? It seems from last weeks results that if I use a battery that is not topped off, then the problem goes away. Does this make sense to anybody?
Gary James
Weatherford, TX
RCCA #908
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Which_way_is_up
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Joined: Tue Feb 12, 2002 8:54 am
Location: Dallas, Texas

Re: Help me figure this one out.

Post by Which_way_is_up »

Yes, that could very well be the case in which the Assan transmitter module is either intentionally (designed that way) or unintentionally (poor design) dropping sync when it see a relatively large drop in voltage regardless of what the voltage level is, that is, the voltage is still well above minimum operating voltage. The receivers come with a filter capacitor to smooth out voltage fluctuations for that same reason, that a heavy load will cause a down spike in the receiver's voltage and cause a drop of the sync lock.
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