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Author Topic: Minimum safe battery capacity margin?  (Read 2621 times)

Offline Target

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Minimum safe battery capacity margin?
« on: September 04, 2015, 03:50:26 PM »
I'm flying my E Oriental with 4S Hyperion 2500 packs and 4S Thunder Power ProLite 2700 packs.
I'm averaging just 18a power draw (1650ma replaced for a 5m30s flight). My CG is a bit forward of where I would like to be, and I still have 3/4oz tail weight in the 48oz bird.

I'm wondering if I could safely move down to the ProLite 2100's. They weigh 197g vice the 250g that the 2700's weight. I would think this could shift my CG back, or if I remove the tail weight, lighten the plane by about 3oz all up.

Is this worth doing? Opinions welcomed.

Thanks,
Chris
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Offline Tim Wescott

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Re: Minimum safe battery capacity margin?
« Reply #1 on: September 04, 2015, 03:58:10 PM »
Hey Chris:

"Safe" as far as "won't burn your house down" -- always, if you store your cells correctly (meaning, store them as if they'll burst into flame at any moment).

If I'm reading my calculator right this'll use 79% of your available capacity on the ProLite cells.  I don't know ProLite cells, but the worst that'll happen is that you'll shorten the battery life.  Personally I think I'd buy one pack and give it a whirl.  You probably want to make sure to give them a storage charge as soon as possible after each flight.
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Offline Target

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Re: Minimum safe battery capacity margin?
« Reply #2 on: September 04, 2015, 04:13:01 PM »
Those were my thoughts as well, Tim.
Although the packs are at a substantial discount this weekend, so maybe a couple packs would be better?

I always charge to storage mode voltage upon return, except that I had to measure a pack to arrive at the usage, so one got charged and then storage "discharged" to its happy 15.4v.

My flying pal says that we should try slowing the OrEEEntal down a bit. Currently at a 5.04s lap, he recommends a click or two off the set RPM. I assume this could lower the amp draw, but might be a wash since I may have to make the duration a bit longer? What says you?

Have a happy Labor Day weekend.
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Offline Tim Wescott

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Re: Minimum safe battery capacity margin?
« Reply #3 on: September 04, 2015, 08:01:47 PM »
Having to be talked down from really short lap times myself, and having enjoyed the extra time to think about what I'm doing -- yes, go for it.  Personally, just the difference between 4.9 and 5.1 is noticeable, and the longer you can make the lap time, the better.

P.S. -- the longer you make your lap times, the more that trim problems will show up.  A fast plane papers over an amazing breadth of trim issues.  So if you slow it down and it flies like crap don't give up on it -- just buckle down and learn how to trim better.
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Offline Randy Powell

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Re: Minimum safe battery capacity margin?
« Reply #4 on: September 04, 2015, 08:12:41 PM »
Weirdly, I was flying 5.7 second laps (according to a guy on the side) at the last contest. Didn't feel that slow, but the plane flew fine so I was happy.
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Offline Alan Resinger

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Re: Minimum safe battery capacity margin?
« Reply #5 on: September 04, 2015, 08:35:43 PM »
Chris,
I wouldn't get overly concerned about battery usage.  I had 6 TP 5s 2700 Pro Lite batteries that I bought in March of 2014 and used them all last year, consistently drawing them down to between 85-90%.  I routinely put 2300 mAh in them after flying.  I talked to one of the guys at TP asking about the amount I was drawing them down.  His comment was basically that the batteries have more storage than the stated value and that the 80% is used by companies to hopefully keep users from abusing batteries.  The 6 batteries I bought last year were used for the entire season and logged just over 350 flights and then started this season as my primary batteries.  After about 100 flights on the 2015 model, I switched to a set of 6S batteries.  After another 60 or so flights on the larger batteries, I decided I didn't like the added 2+ oz. so went back to the 5S batteries.  The still seem to be going strong.  The set has close to 100 charge/ discharge cycles.
Your usage doesn't seem to be much of a problem to me.
Alan Resinger
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Offline Motorman

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Re: Minimum safe battery capacity margin?
« Reply #6 on: September 04, 2015, 09:02:29 PM »
I fly a plane that size with a 2500 4S and I wouldn't want anything less.
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Offline Target

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Re: Minimum safe battery capacity margin?
« Reply #7 on: September 04, 2015, 09:08:42 PM »
Alan-
I'm using about 1650 out of 2700's, but want to switch to 2100's.
It sounds like you're thinking that's fine.
Thanks for that.
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Offline NED-088

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Re: Minimum safe battery capacity margin?
« Reply #8 on: September 05, 2015, 01:07:36 PM »
These must be the batteries you're waiting for.

I'm using the 3100 4s 435 Black label and they are over 3 oz. lighter than the ones I replaced, putting the CG just right.
Still delivering between 2350 and 2400 mAh each flight.

Highly recommended!
« Last Edit: September 05, 2015, 02:20:42 PM by NED-088 »
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Offline Alan Resinger

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Re: Minimum safe battery capacity margin?
« Reply #9 on: September 05, 2015, 06:07:47 PM »
Chris,
With the rate you're using, by going to the 2100 mAh, you would still be under 80% capacity usage.  Cutting the weight by 3 oz. is always a good thing.
Alan
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Offline Target

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Re: Minimum safe battery capacity margin?
« Reply #10 on: September 05, 2015, 06:28:01 PM »
Ned, it's these batteries I'm looking at-
 http://www.thunderpowerrc.com/Products/2100ProlitePlusPower/TP2100-4SP25_2

They are allegedly 197g each.
I am not sure if that includes the wires.
The 2700 4s prolites I have are 255g with the dean's connector, vice 260g for the gen 6 Hyperion hv packs, which cost less....
I'm going to see what Hyperion offers, but the 2100 prolite's have to be lighter than their own 2700's, and with the labor day weekend sale, $33 seems like a great price.
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Offline Kim Doherty

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Re: Minimum safe battery capacity margin?
« Reply #11 on: September 05, 2015, 08:39:39 PM »
Yes, by all means move to the 2100 Prolites. You are nowhere close to abusing the battery.
You need to fly at a speed that will handle all conditions all the time. Flying slow is not a high percentage strategy.

Kim
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