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Author Topic: Short-lived Zippys -  (Read 4666 times)

Offline Keith Miller

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Short-lived Zippys -
« on: December 03, 2016, 03:37:47 PM »
I'm using Zippy 5 cell 3700 mAh 35C packs (I have 3 packs) with an Arrowwind 2832-05 turning an APC-EP 12x6 at 9600 RPM. On average it pulls 480W, 25A (Castle data logger over a few flights). That's <10C.
I've flown these packs 4 flights each with about 27% capacity remaining (per my LiPo checker) after each flight (pulling about 2300 mAh out per flight).
The cells drop to about 3.7v/cell (no-load).
On my last flight attempts, I checked all 3 packs at between 4.15 and 4.18 v/cell before flight, but they all immediately went to the low-voltage ESC cutout of 3.2 v/cell (15.9 v/pack per the Castle logging ESC).
It really sucks waiting for 5.5 minutes for the timer to finish while your model keeps slowing down. ~^

I'd not charged the packs for 2 weeks, but they were all up in the 4.15v/cell range immediately before flight.

1. Do LiPos perform better if "freshly" charged?
2. Could this break-in process I've read about help recover packs that appear to have gone to s**t?

I do have three brandy-new Nano-tech packs that I'll break in at ~3C for a few 5 minute cycles, but I really don't want to be blowing $60/pack to get only 4 good flights HB~>.
Maybe it's just the Zippys being cheap...  ???
I'm thinking that all three have at least one cell with a really high internal resistance, but I don't have a fancy charger to measure cell IR (or even pack IR).

Any comments?

Offline pmackenzie

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Re: Short-lived Zippys -
« Reply #1 on: December 03, 2016, 03:49:17 PM »
The one thing that seems to be universally bad for Lipos is to leave them charged.
You should always put them to storage charge between uses.
I don't think the two weeks you mention (one time) is enough to cause a problem, but if you have been doing this often it will.
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Offline Fred Underwood

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Re: Short-lived Zippys -
« Reply #2 on: December 03, 2016, 04:13:51 PM »
Many charge only the day of use, and storage at the end of the day.  Chargers are slow dischargers, thus the threads on dischargers.  In addition, you didn't mention temperatures and I don't see where you are located to know. Cold can have a significant affect.

Break in now will not likely help recovery, but the process may help you find the capacity.  

I had about 100+ cycles on each Zippy pack before they begin to fail.  Capacity dropped from 2700 to about 2500 long before they were bad.

When you hit low volt of 3.2 and then run for a slow flight for the remainder of 5 minutes, what was the landing voltage and capacity?
Fred
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Offline Keith Renecle

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Re: Short-lived Zippys -
« Reply #3 on: December 03, 2016, 09:42:06 PM »
You can also set the esc's low battery cut-off setting to the higher limit and this will prevent the motor waiting for the timer to time out. Most esc's allow this. The only low cost one that I know that cannot do this is the Hobbywing Skywalker series. If it is indeed an internal resistance issue then a few sharp turns like a quick up and down elevator should help to shut the motor down. You should obviously not get the nose up too much! Some esc's also allow for a sharp cut-off, or a slow down process which is a better option.

Keith R
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Offline Motorman

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Re: Short-lived Zippys -
« Reply #4 on: December 04, 2016, 07:14:18 AM »
You left your batteries fully charged for 2 weeks?! Storing at cold temps will kill a battery too.

I've been successful at taking the batteries apart and building them back together using the good cells.

MM

Offline Keith Miller

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Re: Short-lived Zippys -
« Reply #5 on: December 04, 2016, 09:02:14 AM »

When you hit low volt of 3.2 and then run for a slow flight for the remainder of 5 minutes, what was the landing voltage and capacity?

Hi Fred -
Well, I suppose that the capacity when I landed was zero. But the capacity was zero when I took off because as I said, the packs reached the low-voltage cutoff immediately on start-up.
On one pack (pictured) pPre-launch, voltage was 20.6 ((4.12v/c) and 17.8v (3.56 v/c) after landing.
But note the immediate flat-line to 15.9v (3.2v/c) during the entire flight. All 3 Zippy packs do essentially the same thing.

Do you see any significance? The only thing I can think of is that once cell went bad in all 3 packs. I'll do some ground runs with a cell monitor so find out.

Offline Keith Miller

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Re: Short-lived Zippys -
« Reply #6 on: December 04, 2016, 09:13:26 AM »
You left your batteries fully charged for 2 weeks?! Storing at cold temps will kill a battery too.

I've been successful at taking the batteries apart and building them back together using the good cells.

MM

Sure - I've been leaving batteries charged for years. I'm in San Diego - it just doesn't get that cold here.
I generally don't have a lot of time to run packs to storage mode, then more time to charge them the day before a flight. I fly RC too and fly up to 10 flights a week. I usually re-charge at the field (outdoors, no risk of burning the house down). Babysitting batteries during storage cycles and pre-fly-day charging periods requires a lot of time in the man-cave that I usually don't have.

I suppose if these LiPos are that fragile and need break-in and special storage practices, I can switch back to nitro. $180 for a set of 3 LiPo packs can buy a lot of nitro fuel!

I like your idea of rebuilding packs from good cells.

Offline Igor Burger

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Re: Short-lived Zippys -
« Reply #7 on: December 04, 2016, 09:49:05 AM »
You not need discharge to storage voltage, enough if you do NOT charge after flight, that does not take any time :- )) Simply charge before you go fly.

I do not think problem is in batteries, if all of them did something wrong and other pilots do not have that problem, you probably do something wrong, it could be probably storing charged, that for sure kills battery, but I would also check if your charger works well (especially balancer), it must do 200 or even 300 flights.

BTW I did not find cycling helpfull at all. It can help if you fly at max C rate, but not if you fly under 10C whole flight, it is cycling all the life time :- P


Offline pmackenzie

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Re: Short-lived Zippys -
« Reply #8 on: December 04, 2016, 12:53:35 PM »
I would look very hard at all the electrical connections. Sort of odd that all three batteries would fail at the same time.
A high resistance somewhere might be the cause. Could even be an ESC issue, any other model you could test the packs in?
Were they hot after the flight? If they have increased a lot in IR then they would also get hotter than normal.

Also odd that the ESC in cuttoff held the voltage so flat. What setting did you use?

As far as not wanting to spend time to go to storage charge, and then recharge, get a paraboard it saves a lot of time.

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Offline Joe Yau

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Re: Short-lived Zippys -
« Reply #9 on: December 04, 2016, 01:56:51 PM »
I notice the motor's Kv is rather high (960Kv) for 5 cell set up.  As usually around 760-820 is the range for 5 cells, and any higher should be 4 cells.  But interestingly they recommend to use with 5 cells.
« Last Edit: December 04, 2016, 02:17:29 PM by Joe Yau »

Offline Fred Underwood

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Re: Short-lived Zippys -
« Reply #10 on: December 04, 2016, 02:46:21 PM »
Keith,
As you suggested, I didn't learn much from the datalog.  I was more curious to the after flight voltage, and should have said % capacity on your cell checker.  I've not seen a datalog like that, thankfully.  I think that as suggested, the voltage cutoff accounts for the flat 3.2 voltage/cell.  That assumes the selection of "slowing" as the cutoff when voltage is reached.  In your case, allowing the system to maintain the 3.2 volts.

I know that ThunderPower suggested the break in cycles.  I found that about 2 cycles evened out the cells, lowered the IR shown on my charger, evened it out, and gave an even charge/voltage per cell.  More cycles are of course just using the battery.  Not everyone may agree with break in, at not all suppliers even mention it.

At the cost of batteries, a good charger is a great investment.  Perhaps yours is fine.  As mentioned the parallel board and enough power to make use of it is a time saver and a great to storage at the end of a day.  I don't know the lowest recommended safe low voltage to leave the batteries, so I storage.  Perhaps not necessary as Igor suggests as long as the batteries are all above the 20% range.  I parallel to storage once I know that the batteries/cells are at about equal voltages, usually the case if used on the same plane.  I don't consider it a time waste as that same energy needs to be replaced whether in a session to storage, and then a session to capacity before flying, or one longer session from discharge to full before flying.  I do occasionally charge each pack separately to keep balanced, and check on that more often with a cell checker.

I have not had luck, or knowledge and skill, to get the 200 - 300 cycles that Igor does.

Fred
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Offline Randy Powell

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Re: Short-lived Zippys -
« Reply #11 on: December 06, 2016, 11:27:15 AM »
I'm no expert at this but, I've had some Zippy batteries I've used for 3 years and seem to be fine. I've lost two of them but that was to damage. I only charge them when I'm ready to fly and always (ALWAYS) discharge them to storage level after flying (unless I'm flying again the next day, then I charge them back up). I've only ever left they fully charged overnight.

Just my two cents.
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Offline Mark Scarborough

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Re: Short-lived Zippys -
« Reply #12 on: December 06, 2016, 11:35:21 AM »
I can promise you, leaving them charged is bad juju!
I have suffered some loss of capacity with my zippy packs, and after conversing with Fred, we came to the conclusion that not only did I damage them leaving them charged ( for a week or two)
but its likely that the zippy packs are margninal on capacity to begin with, IOW, the capacity is perhaps a bit overstated when new let alone after you abuse them by leaving them charged,,
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Offline Russell Bond

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Re: Short-lived Zippys -
« Reply #13 on: December 06, 2016, 02:26:07 PM »
Joe is correct, You should be running 4 cells with a k/v of 960 at those rpm.
At the moment your ESC is running at 60.1% which is way too low. Everything will run hot.
If you use 4s, it will run at 75% which is right in the ball-park.
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Offline Keith Miller

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Re: Short-lived Zippys -
« Reply #14 on: December 07, 2016, 06:37:28 AM »
Joe is correct, You should be running 4 cells with a k/v of 960 at those rpm.
At the moment your ESC is running at 60.1% which is way too low. Everything will run hot.
If you use 4s, it will run at 75% which is right in the ball-park.

Can you explain? If the battery and motor current are lower with 5s as compared to 4s, how does everything run hotter?

Offline Mark Scarborough

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Re: Short-lived Zippys -
« Reply #15 on: December 07, 2016, 08:09:11 AM »
My understanding from reading on here, the ESC has to switch more energy off internally and it builds heat, whereas when using lower voltage, the ESC does not work as hard.

( for the record, I am only reporting what I recall reading and my facts may be askew )
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Offline Igor Burger

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Re: Short-lived Zippys -
« Reply #16 on: December 07, 2016, 08:44:11 AM »
Can you explain? If the battery and motor current are lower with 5s as compared to 4s, how does everything run hotter?

Well .. the curren in motor is linear to torque and since there is the same motor and the same prop, then also the torque is the same and therefore also average curent in motor is the same.

Higher voltage will make current impulses of higher value for shorter time (that is that mentioned percentage) and since the resistance loses are linear to I^2 * R then clearly the same average current will make more heat.

Offline Tim Wescott

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Re: Short-lived Zippys -
« Reply #17 on: December 07, 2016, 10:30:17 AM »
Joe is correct, You should be running 4 cells with a k/v of 960 at those rpm.
At the moment your ESC is running at 60.1% which is way too low. Everything will run hot.
If you use 4s, it will run at 75% which is right in the ball-park.

What Igor and Mark said.  I can't resist tossing in my two bits, because I design motor drivers that are similar to ESCs -- but it all really boils down to is a highly detailed way of saying "more voltage = more energy lost to heat".

The average current (and voltage) at the motor has to be the same -- otherwise it wouldn't generate the same average torque.  The ESC regulates voltage to the motor by chopping the battery voltage.  With a higher voltage battery, the pulses that the ESC sends have to be narrower.

With these larger-voltage, narrower pulses, the current in the ESC goes to a higher peak value and dips to a lower minimum value.  Because of the way that heat is generated in a resistance (I2R losses is the key phrase), this means that more heat is generated in the motor (and energy is consumed to do it).  Also -- and I haven't tested any motors for this so I don't have a good handle on it -- the higher applied voltage on the motor windings will cause more energy to be dissipated in the steel armature of the motor, both from eddy current losses and hysteresis losses.

Higher voltage on the ESC means that there's more switching loss in the ESC transistors.  Whether this is important depends on the detail design of the ESC, so if I wanted to know for sure if this was an issue I'd be measuring temperatures on a real one.  The same higher current peaks and lower troughs that happen in the motor happen in the ESC, which leads to conduction losses in the ESC (and the conduction losses are mostly the same kind of I2R losses as in the motor).

What I have not done, because it takes a lot of picky, detailed, time-consuming work, is to try to quantify how much of this happens in an electric power setup, and how much of it comes from each possible cause.  If I did do it, I'd just end up putting detailed numbers to what Igor is saying.

If batteries didn't fade toward the end of a flight, and if you didn't need some voltage overhead for power in the overhead maneuvers, then you'd want to set the thing up with as little excess voltage as you could -- but it's more important to have plenty of oomph in the clover and overhead 8 than it is to have the Most Efficient Setup.
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Offline Russell Bond

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Re: Short-lived Zippys -
« Reply #18 on: December 07, 2016, 03:34:09 PM »
What they said................... ;D ;D

Keith, buy the 4s 3700mah Zippys and you should have no problems. (Or if your plane is heavy use the 4s 4000mah.)
(My plane is 72oz and I get away with the 4s 3700mah 25c Zippys.)
You'll save some weight by using the correct battery. The ESC will run cooler along with the motor.
In fact you would get away with 25c instead of 35c. However the 35c batteries will be under less stress so will run cooler.
This is ok if the weight of them is ok for you.
Bandolero

Offline Igor Burger

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Re: Short-lived Zippys -
« Reply #19 on: December 08, 2016, 01:44:55 AM »
What they said................... ;D ;D

Keith, buy the 4s 3700mah Zippys and you should have no problems. (Or if your plane is heavy use the 4s 4000mah.)
(My plane is 72oz and I get away with the 4s 3700mah 25c Zippys.)
You'll save some weight by using the correct battery. The ESC will run cooler along with the motor.
In fact you would get away with 25c instead of 35c. However the 35c batteries will be under less stress so will run cooler.
This is ok if the weight of them is ok for you.

OR use motor with lower KV OR prop with lower pitch, it will be far better :- )))


... but still, this is not answer why battery goes dead soon after start : -))


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