Is Daily Low Self Discharge Rate and Important Factor in RC?

A customer asking about an unusual cell size of ours asks: “Are they are low self discharge?”

They are not Eneloops which would be the only NiMH I would classify as Low self discharge. This is almost a silly thing to consider because we come off the charger and go to the field in this hobby. We do not charge a battery, then start a 1 week hike at the end of which we fly the model. That specification makes sense for a flashlight or an emergency radio, not an RC aircraft. Others may have a different view. I don’t fly unless I’m coming off a fresh charge at the beginning of the day. Other systems are to the choice of the users but reckless in my view. Yet I offer the Eneloops for those seeking this value. There are no Eneloops this small. Also, I don’t like the Eneloop under fast charge “ever” conditions.

For RC, lets go over how silly this is;

Standard self discharge x 2 would be only 2% per day.

After charging, if we let a 500mah pack set for 2 days before flying, it would lose (500x.01) 10mah the first day, (490 x .01) 9.8mah the second day. Value at end of 2 days 500-10-9.8=480.2mah. 19.8ma lost over 48 hours or about .416mah per hour dissipated.

If we come off the charger and go to the field, a trip that takes 2 hours, the same rate of loss would mean our pack would be about 499mah since we loose about .416mah per hour.

So, perhaps, a low discharge pack is good for about a .2% advantage when you get to the field. And, to come up with that .2% I had to exaggerate the loss by double and suggest a very long trip to the flying field.

This is why this specification is essentially moot when it comes to normal day in and day out use of receiver packs in RC aircraft. Is it better? We’ll yes in some microscopic way, but to get it, what are you going to have to do? Accept an Eneloop you can never fast charge? Use a non-Sanyo cell? I see a lot of effort hunting something that has no real measurable benefit in our application.

It’s more arguable in a TX battery because we often use that battery over a number of weeks between charges.

Dave

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“Reflections on the 2004 JR Challenge

Hi Dave, I’ve had a few days to recover from the travel and reflect on the 04 JR Challenge and it occurred to me that one of the most overlooked parts of the trip was the performance I received from my power system. I say overlooked because it was such a non-issue the entire week. I arrived Mon afternoon too late to get any flying in; Tue – 6 12 minute flights plus some time on the ground making system adjustments – at the end of the day both flight packs were still in the 6.2 volt range under load; Wed – a duplicate of Tues. Thurs and Friday competition flights I flew on a single charge. What’s more, the TX pack I installed in my 10x the week before went the entire week un-charged and never dropped below the 10v level! My only regret is that my flying wasn’t up to par with my battery performance. Thanks for great products and great service, keep up the good work, hope to see you in Muncie for NATS!

Ty Lyman
Carden 40% Edge – 2 x 2700 NiMH packs RX, 1 2700 ignition.
JR 10X – 1650 NiMH”
March 2004

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Re: (3800RX packs)
“Hi Dave this is Bruce Swartfager I flew my 35% staudacher yesterday with the 3800 metal pack and it flew great no trim adjustments just couldn’t have done any better. It has Brison 6.4 twin up front and did it sing I am excited as you can tell. I figured up how many oz. of torque i am running and it comes in at 1250 oz. That is a lot and so the question of metal packs not providing enough amps is a myth. I have 612 oz. alone on the wings of torque. Just thought i would pass this on thanks Bruce will looking forward to the Orbit charger. Later Bruce, Altoona Iowa
(Most are flying the 2700 in this application but the 3800 works great too where you want a little extra capacity or nose weight).”

August 2001

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