Battery mod Devo7e

PhracturedBlue wrote: I don't know why you think a drop in voltage necessarily has anythingto do with transmit power. Every one of the transceivers has a voltage regulator set at 3.3V somewhere in the path. as long as the voltage is > ~3.5V the transmit power should not be affected

I think it is most worthwhile to try out how low a supply voltage till the 7e cease to work. Should it be ~3.5V as PB mentioned, then putting in a single cell of LiPo is most effective in terms of capacity, endurance and weight..

Another low self discharge NiMH I found pretty good are GP Recyko (2100mah). I bought 8 of them cause Eneloops were out of stock and they have been a very nice surprise.

Hi All

I also have been intrigued by the recent stamped to replace TX batteries with Lipo’s and a month ago I started a thread on RC Groups to understand why.

Sufficient to say there are two clear camps, the NiMh/Eneloops supporters and the other swearing by Lipo’s. ( www.rcgroups.com/forums/showthread.php?t=1818832 ).

My conclusion after 50 plus comments was that in almost all cases it comes down to personal choice of how you preferred to charge you TX’s batteries.

Personally I decided to stay with a good brand of AA-2500mAh (for the 8s) as I believe the discharge rate of NiMH is a non-issue - just as I don’t put a 450 size helicopter in the air with Lipo’s which (I think) I charged last week, I don’t fly with a TX which batteries were not charged in the last 24 hours.

Pixel166 wrote: (+ charger as I don't have any)

As charger: for Devo8 I use what Walkera hat labeled near the charging port: a simple wall plug charger with an output between 8 and 12V and with 200mA (I use 9V, 150mA because this is what was laying around here).

Remember to check the +/- config of the charger. Walkera and Esky TX power supplies are for instance not compatible, the +/- is swapped

After all the comments I feel the need to clarify:

Any lithium based battery is far superior compared to any NiMh battery (including Sanyo Eneloop) in every single application, including this one which is specific due to the fact that the current demand is low and weight is not crucial. On top of that they are cheaper, especially compared to highly overpriced Sanyo Eneloops. They are used in almost every battery operated application today because the market is calling for it, with the few exceptions where both can be used. If we are talking about higher current demand applications, today there are no alternatives to lithium based batteries. Actually the whole RC hobby today, owns the growing popularity to invention of lithium battery and brushless motor (which are both invented long time ago, brushless motor is nothing else but three phase asynchronous motor invented by Nikola Tesla). You should see the performance of our helicopters and airplanes, just stripping these two components and returned back to brushed motor and NiCd/NiMH batteries.

I have 5 Txs 2.4GHz, of which 3 are in regular use. Four of them are equipped with different LiPo 3S, 2S or LiFePo4 batteries. All of them operate good, and I feel more confident using them, plus I spend much less time maintaining the batteries. Only one has NiMHs, WLToys v911 transmitter. That one is not in frequent use, secondly, it is used to fly 32gr indestructible helicopter so I decided to leave it that way. It would cost little fortune to replace all of it with Sanyo Eneloop and it is not justifiable, not at all. I wouldn't swap them around because of reliability of contacts and hustle of doing that. We all know how AA battery holders look like, cracked, with curved spine, like they are going to burst due to the fact that manufacturers differently interpret the dimension spec. Some batteries are longer, some wider and that represent real hustle.

I have more than 100 different NiCds, NiMHs collected over the years, used in different devices. More than half of them are junk at this point. None of it were used near close to manufacturers specs of 500-1000 cycles. They usually build high internal resistance, resulting in sharp loss of capacity. They cost a lot of money, most of it thrown away. There are different brands, including respectable ones including Sanyo. As I said in previous posts, have never owned Sanyo Eneloops, heard of them, but never considered them because of past experience, price, non-confidence in manufacturers specs and further points listed bellow.

The points in which Lithium based batteries are superior to any NiMH batteries, including Eneloops (Li - Lithium based, LSDB - Low self discharge batteries)

Fast charge

Li: are designed for it, no issues with charging at 2C and higher, no heath generated; I can decide to go flying and in ten minutes of charge I'll have half day of flying
LSDB: Not very fast, there are big issues with it, not going into details (I could, if you really want it), like overcharge, heat generation etc.

Charge state

Li: Battery voltage shows the state of charge reliably, so you know the state of you battery before actual use
LSDB: Battery voltage not tied to charge state, determining charge state not possible without loading the cell and even than not reliable, this is the biggest single problem of this battery for use in RC. You don't know the charge state and you always have to charge to the top to have a starting reference point.

Charge power going into battery indicates the quality and capacity of the cells

Li: By AmpHours given by charger you can determine actual battery capacity, subtracting the minimal losses. This way you can follow every pack's behaviour and remaining capacity
LSDB: Not possible or very hard, due to heath loss, so you actually do not know which amount of energy from charger turns into useful battery capacity

Battery contacts

Li: Battery packs have their individual cells soldered together internally, so no issue
LSDB: Lot of issues with contact on actual cell and contacts in Tx

Charge in Tx

Li: Charge outside Tx, not an issue to take it out
LSDB: Charge inside Tx, risk of overcharging batteries especially because of need to have the max charged all the time; Tx have simple limiting resistor as charging circuit; Manufacturers have dilemma: if they make charging current too low (trickle charging) it will take forever to charge batteries, if you make it higher you are at risk to overcharge the batteries.

Weight

Li: Because of higher energy density much lighter. Important even in Tx, especially in Devo7e portable Tx to carry around and fly. The impact of weight of Tx comes to play with duration of use and style of use (thumb user vs finger tops)
LSDB: Simply heavy, why to carry all that weight around

Discharge curve, Low voltage impact on transmission quality

Li: Another big point of these batteries. The discharge curve is more linear, with strong hold of voltage, much less dependant on load. Meaning, supplying cleaner voltage to the electronics. Due to higher voltage compared to NiMhs, they operate in more favourable voltage area for underlaying electronics
LSDB: The discharge curve is not that linear, not very good hold of voltage, especially under higher loads. In this particular application I suspect that nominal 4.8V drop to 4.5V at some point introducing problems in transmission and data corruption, because it is at lower limit of operation of Low drop regulators. Even if higher quality regulators are used, if you go down with input voltage, at certain point there is no regulation any more but output follows input, where high ripple is introduced.

Price

Li: Affordable
LSDB: Highly overpriced for what they are, especially Sanyo Eneloop

Capacity

Li: I can easily make 1400mAh pack to fit in battery space inside 7e, by just connecting two packs in parallel. This is actually like having 6.6/4.8*1400mAH = 1925mAh NiMhs due to higher voltage. Also, in future you can expect the manufacturers to jump into this market making dedicated packs. The capacity holds during time and I don't have a pack that lost more than 20% of original capacity
LSDB: Most of these batteries do not hold charge and more than half I own went to 0. Secondly, many are sold with very enthusiastic capacity label.


After knowing all this, I would never fly big, expensive, dangerous model using any kind of NiMH batteries including Sanyo Eneloop. Only, maybe, if they were charged over night before flight, plus I would have to be 100% confident in battery contacts on battery and inside the Tx, also would have to be 100% confident in the previous behavior of battery.

I stand open to clarify every point with more details, if needed.

Usjak wrote: After all the comments I feel the need to clarify:

Any lithium based battery is far superior compared to any NiMh battery (including Sanyo Eneloop) in every single application,

Have you spoken to the Boeing 787 passengers that had an emergency declared due to a LiPO fire?

Usjak wrote: After knowing all this, I would never fly big, expensive, dangerous model using any kind of NiMH batteries including Sanyo Eneloop.

I stand open to clarify every point with more details, if needed.

I am sure we have managed to fly these big, expensive, dangerous models for the more than 30 years using NiHM (and other types) in our TXs and controllers

Usjak wrote: After all the comments I feel the need to clarify:

Wow, I can see you know what you are speaking about. But it seems to me as if you look at it from another point as we "normal rc users" do.

LSDB: Not very fast, there are big issues with it, not going into details (I could, if you really want it), like overcharge, heat generation etc.

If have only two years of experience with LiPo and I still feel uncomfortable because of the warnings I can read everywhere: don't overcharge, don't discharge too far, don't heat, let them cool down, put them in fire proof containers - nothing I have to watch for NiMH in this intensity.

Li: Battery voltage shows the state of charge reliably

I look at the voltage every time I start flying - has never abandoned me. Ok, I do not pull what would be possible and charge too early, but who cares...

Charge power going into battery indicates the quality and capacity of the cells

The absolute value is not in my focus. I will replace them when I feel they discharge too fast - until now with my first set of AA for more than a year I am not at this point.

LSDB: Lot of issues with contact on actual cell and contacts in Tx

Haven't you written somewhere that you take your LiPo out for charching? Then you will have a plug. Mine stay in the tx even while charging except for these few times I change them... no stress for the contacts.

Charge in Tx...LSDB: Charge inside Tx, risk of overcharging batteries

I know that for a good NiMH/NiCD charger you have to pay a lot of money. These include complex electronics with many sensors to apply the very best kind of charging to the AA, but all I know have charging places where the AA have to be put in. So cost and lazyness are two points how I do not use such a tool.
It can not be too wrong because most of the toys / tools ... I have which are driven by NiMH/NiCD have a real simple charging method. Most of them use wall plug charger, some have a resistor in line. I think I have no single tool with a more complex charging built in.

Li: Because of higher energy density much lighter.

So I could use smaller LiPos - but I won't. Why should I go without the additional capacity a bigger LiPo, which fills the space completely, will give me? I would have to charge even less frequent.

Discharge curve, Low voltage impact on transmission quality

This is a point I can accept. It is in the responsibility of the user not to use LSDB over this point. But with some attention this will not really be an issue.
Quality of the voltage regulation circuit between LSDB and tx is a topic in any case, only the LiPo may shift this point.

LSDB: Highly overpriced for what they are, especially Sanyo Eneloop

Maybe, but even one 4-item-pack per year will cost me about 12€ / 16$. This is less then nearly every spare part for my helis will cost me when it crashes because my tx shuts off (or I have made a mistake...). So in my budget this is no really big point.

LSDB: Most of these batteries do not hold charge and more than half I own went to 0. Secondly, many are sold with very enthusiastic capacity label.

Those labels I have seen on LiPos too. You have to buy the high-priced LiPos to have a reliable value printed on it...
Where are the limits for AA? I think I have seen 3.2Ah. Even the half of this would bring me over three flying days (assume backlight is off).

After knowing all this, I would never fly big, expensive, dangerous model using any kind of NiMH batteries including Sanyo Eneloop. Only, maybe, if they were charged over night before flight, plus I would have to be 100% confident in battery contacts on battery and inside the Tx, also would have to be 100% confident in the previous behavior of battery.

This will be true. My biggest heli is a 450, although this will not stay this way in the middle future. The greater the investment for the heli the more I would double check all componentes including the tx batteries. Not only because of the money, but the harm such a big, fast and heavy heli could do even with safety shutdown.

I stand open to clarify every point with more details, if needed.

I am sure you could but the only thing of interest for me would be:
Do you really think that flying with non-LiXX-batteries in the tx is a potential risk for whatever? Or would a careful operation make it as secure as with LiXX?

	NiCd	NiMH	Lead	Li-ion
Energy density (Wh/kg)	45-80	60-120	30-50	110-160
#cycle charge/discharge	1500	300 to 500	200 to 300	500 to 1000
Recharge time	1h	2-4h	8-16h	2-4h
Overload tolerance	Average	Low	High	Very Low
Autodischarge by month	20%	30%	5%	10%
nominal Voltage by cell	1.25V	1.25V	2V	3.6V
Current (pic/nomin)	20C/1C	5C/0.5C	5C/0.2C	+20C/1C
Operation T°	40 to 60°C	20 to 60°C	20 to 60°C	20 to 60°C
Sold since	1950	1990	1970	1991

LiPos are in various airplanes around the globe all the time.

If we get rid of Lipos in our Txs, is the hazard smaller, as we still have to bring our drive LiPos inside our house, car, we have to be in their vicinity?

Or we replace the drive LiPos with NiMHs?

RandMental wrote:

Usjak wrote: After all the comments I feel the need to clarify:

Any lithium based battery is far superior compared to any NiMh battery (including Sanyo Eneloop) in every single application,

Have you spoken to the Boeing 787 passengers that had an emergency declared due to a LiPO fire?

But, why still do it, if there is better solution?

RandMental wrote:

Usjak wrote: After knowing all this, I would never fly big, expensive, dangerous model using any kind of NiMH batteries including Sanyo Eneloop.

I stand open to clarify every point with more details, if needed.

I am sure we have managed to fly these big, expensive, dangerous models for the more than 30 years using NiHM (and other types) in our TXs and controllers

If have only two years of experience with LiPo and I still feel uncomfortable because of the warnings I can read everywhere: don't overcharge, don't discharge too far, don't heat, let them cool down, put them in fire proof containers - nothing I have to watch for NiMH in this intensity.

If we get rid of Lipos in our Txs, is the hazard smaller, as we still have to bring our drive LiPos inside our house, car, we have to be in their vicinity?

Or we replace the drive LiPos with NiMHs?


I look at the voltage every time I start flying - has never abandoned me. Ok, I do not pull what would be possible and charge too early, but who cares...

NiMH battery voltage w/o load recovers and it does not ressemble the charge state at all.
NiMH battery voltage with load does not ressemble the charge state either, as the internal resistance builds up.
So, it can surprise.

The absolute value is not in my focus. I will replace them when I feel they discharge too fast - until now with my first set of AA for more than a year I am not at this point.


Batteries have to be followed during charge and discharge on table, if you want to know their health. That way you use them to their best and feel comfortable at the field.

Haven't you written somewhere that you take your LiPo out for charching? Then you will have a plug. Mine stay in the tx even while charging except for these few times I change them... no stress for the contacts.


We are talking about one connector with 2 golden plated contacts, as oppose to several nickel plated contacts held by plastic. Problems with charging in Tx were covered before.

I know that for a good NiMH/NiCD charger you have to pay a lot of money. These include complex electronics with many sensors to apply the very best kind of charging to the AA, but all I know have charging places where the AA have to be put in. So cost and lazyness are two points how I do not use such a tool.
It can not be too wrong because most of the toys / tools ... I have which are driven by NiMH/NiCD have a real simple charging method. Most of them use wall plug charger, some have a resistor in line. I think I have no single tool with a more complex charging built in.

Trickle charging is not necessarily bad, as long as the current is bellow 1/10C, but it takes 14-16 house to charge. I do it also in some applications.
Fast NiMH chargers are different story: they destroy batteries in most cases as they push batteries above the limits. They apply DeltaV cut off method which is not 100% reliable, so better ones complement it with temperature sensors. Big topic as Electro-chemistry is different story than electrics/electronics and lot of it is empiric.


So I could use smaller LiPos - but I won't. Why should I go without the additional capacity a bigger LiPo, which fills the space completely, will give me? I would have to charge even less frequent.

You have a choice of very light Tx with more frequent charging or little heavier Tx with less charging.


This is a point I can accept. It is in the responsibility of the user not to use LSDB over this point. But with some attention this will not really be an issue.
Quality of the voltage regulation circuit between LSDB and tx is a topic in any case, only the LiPo may shift this point.

I think there is an issue there with NiMhs. I haven't done any measurement, but gut feeling, based on experience, there is potential problem.

Maybe, but even one 4-item-pack per year will cost me about 12€ / 16$. This is less then nearly every spare part for my helis will cost me when it crashes because my tx shuts off (or I have made a mistake...). So in my budget this is no really big point.

I would need around 20-30 batteries, so it is an issue for me. I would rather spend that money on some other new RC component. Especcialy because old LiPos used for drive and are weak for that purpose can be reused in Tx, so it free.


Those labels I have seen on LiPos too. You have to buy the high-priced LiPos to have a reliable value printed on it...

I haven't. Even the cheap ones like this

www.hobbyking.com/hobbyking/store/__7636...200mAh_3S1P_25C.html

are spot on.

Where are the limits for AA? I think I have seen 3.2Ah. Even the half of this would bring me over three flying days (assume backlight is off).

No way. Marketing trick. Measure it brand new, discharging in charger with 1C. Not even close. Do it after 6 months of normal use. Even much further away.


This will be true. My biggest heli is a 450, although this will not stay this way in the middle future. The greater the investment for the heli the more I would double check all componentes including the tx batteries. Not only because of the money, but the harm such a big, fast and heavy heli could do even with safety shutdown.

I would, only after overnight charge, thorough check, plus I would have to know that batteries' hystory. A lot of battery maintenance time => less time flying/building/doing other more interesting things.

I am sure you could but the only thing of interest for me would be:
Do you really think that flying with non-LiXX-batteries in the tx is a potential risk for whatever? Or would a careful operation make it as secure as with LiXX?

Answered obove.

It is actualy this table which includes LiPo:


batteryuniversity.com/learn/article/whats_the_best_battery


It is outdated info like fast charge for LiPo: 2-4h, while it is actualy >5C, 20 minutes for 2000mAh.

NiCd pick load 20C; Yeah sure. for 2s and it goes to 0.5V per cell.

And so on.

domcars0 wrote:

	NiCd	NiMH	Lead	Li-ion
Energy density (Wh/kg)	45-80	60-120	30-50	110-160
#cycle charge/discharge	1500	300 to 500	200 to 300	500 to 1000
Recharge time	1h	2-4h	8-16h	2-4h
Overload tolerance	Average	Low	High	Very Low
Autodischarge by month	20%	30%	5%	10%
nominal Voltage by cell	1.25V	1.25V	2V	3.6V
Current (pic/nomin)	20C/1C	5C/0.5C	5C/0.2C	+20C/1C
Operation T°	40 to 60°C	20 to 60°C	20 to 60°C	20 to 60°C
Sold since	1950	1990	1970	1991

Tested today the 7e works fine in 1S LiPo right down to 3.3V. Transmitter power maintain the same without dropping.

It is too bad that the voltage indication and battery alarm won't work when the battery voltage runs below 3.8V. Otherwise it is the best choice and the tiny 7e weights lot lighter and more comfortable to carry around..

It is a bit strange that the ADC cannot not working properly in low voltages inputs... now that I have to revert back to NiHM...

vlad_vy wrote: I think it's not ADC problem, but Walkera power circuit with electronic switch, after that reference voltage go to ADC.

If you like LiPo, you can insert two (or three) diodes in series in power wire of 2S LiPo. This way you get 6~7V at Tx. It's close to voltage from 4 dry batteries.

ic..

but using 2S voids the benefit of saving weight... I hesitate to use a switching BEC for efficiency worrying any interferrence it may introduce...

I just wired up a 2s 1200mah lipo for my Devo 8.
I am using 2 diodes in series which gives me a 1.4v drop.
So for a fully charged battery I get 7v at the TX battery terminal.
The discharge rate at 150mw TX output power is .3v per hour.
This rate should give about 6 to 7 hrs of TX time with a final voltage of 4.9v at the TX batt' input, and 6.4v at the Lipo terminal.

I set this up 2 days ago so I don't know for sure how many hours I can get out of a charge, but even if it's 5 hrs that's pretty good for a single charge.

I leave the battery in the TX, with the door open, and charge the battery through the balance port with an extension cord at a slow charge rate, about .5C.

I used the Devo 8 for about 2 hrs of flying today, and it works very well. No problems.