Battery mod Devo7e

First, it is not strictly related to Deviation, but I thought the Devo7e users would be interested:

I found the battery that fits in the narrow battery compartment and is close by voltage. It is LiFePo4 battery, 700mAh, 2S, 6.6V, with much less self discharge compared to NiMh, NiCd batteries. I know it less than typical NiMh, but in the long run it is better, because it is ready every time you need it, due to low self discharge current:

www.hobbyking.com/hobbyking/store/uh_vie....asp?idProduct=14075

Now the Tx is even lighter and battery seems to last forever. What needs to be done is: file down the plastic tabs that act as sliders for battery holder, change the connector to JST, change the alarm voltage to 6V.

Typical LiFePo4 discharge characteristic per cell looks like:

blog.cafefoundation.org/?attachment_id=1968

so alarm set to 6V should work OK. I am using this battery over a week now, no issues (some users report problems with LiPo 2S 7.4V being to high and problems with saving during shut down).

Thank you! Buying on!
Can you charge it in the TX or do you have to charge it with Li Po charger?

Edit
Maybe a stupid question.

No, the charger in Tx is designed to charge NiCd an NiMH batteries only. You need charger for LiPoFe4 batteries, you need to take the battery out of Tx. All modern chargers have this mod, like:

www.hobbyking.com/hobbyking/store/__7028...r_w_accessories.html

www.hobbyking.com/hobbyking/store/__5548..._Cells_GENUINE_.html

Mullson wrote: Thank you! Buying on!
Can you charge it in the TX or do you have to charge it with Li Po charger?

Edit
Maybe a stupid question.

No, is not stupid - I want to know it too.
I thought about that for my Devo8 (also uses 4x1.2V NiCad) and have read about the lipo problems here (my older WK24xx/26xx worked without any problem with a 3s-lipo).
I have decided to use NiCads because I do not have to pull them out of the tx for charging. The charging lines are directly connected to the battery plug - no safety / charging electronics in between.

I haven't open the case of Tx yet, but my guess is that charging circuit is only the limitting resistor. It says on case in small letters: "Only for charging NiMh and NiCd batteries".
However, the LiFePo4 batteries are specific and different even to LiPo batteries as their nominal voltage is 3.3V/cell and charging cut-off voltage of 3.6V/cell. Meaning, if you apply 12V as input to Tx charging connector, the LiFePo4 would burst at some point as there is no voltage limiting circuitry.
I've read the problems other users report using Lipo 2S batteries, like hardware problems and especially problems with Tx shut off, since Devo Txs are specific: when you shut off with a switch that only gives command to circuit to shut itself off and during that process it happens that it has problems due to high voltage. I haven't experience that problem.

rbe2012 wrote: No, is not stupid - I want to know it too.
I thought about that for my Devo8 (also uses 4x1.2V NiCad) and have read about the lipo problems here (my older WK24xx/26xx worked without any problem with a 3s-lipo).
I have decided to use NiCads because I do not have to pull them out of the tx for charging. The charging lines are directly connected to the battery plug - no safety / charging electronics in between.

Was afraid of that. Whats the best NiCads you can get for money? Longest use per charge that you can use with TX?

I took the first I got into my hands, laying around for years unused... about 1200mAh, I think. I often let the tx on for hours (but not much flying, more testing/programming, but nearly always with 10mW output) and have never seen a discharged pack (although I always have a fully charged in my flight case...) and I load overnight quite regularly.
What I have seen but not tested: the rechargeable batteries which are tested as the best are Sanyo Eneloop (don't know if it's only the german trading name) as they have high capacity and nearly no self discharge. But the voltage curve drops quite fast after a long time of high level output so it can surprise you. Maybe I can tell more after my next birthday...

I use the Sanyo Eneloop for more then 4 month in my Devo 8s.
The have enough power for a full day of flying.
No problems with the intern charger.

ciao Joshua

The reason I did this mod is I hate NiCd and NiMh batteries because of their high self discharge, meaning even full after couple weeks of not using Tx they are near empty, usually when you need them the most. The only advantage they have is that they can be charged in Tx, so if you maintain them charged all the time you are OK. Hovewer, with LiPoFe4 batteries, the are ready to be used even months after not used. Also, the capacity of LiPoFe4 is spot on to manufacturer spec, while NiCd and NiMh are usually much less and it goes down with the use.

I do not even consider non rechargable alkalines being not economic.

Haven't tried Sanyo Eneloop, but for instance Sanyo HR-3U not good, high self discharge as most others.

Usjak wrote: The reason I did this mod is I hate NiCd and NiMh batteries because of their high self discharge, meaning even full after couple weeks of not using Tx they are near empty, usually when you need them the most. The only advantage they have is that they can be charged in Tx, so if you maintain them charged all the time you are OK. Hovewer, with LiPoFe4 batteries, the are ready to be used even months after not used. Also, the capacity of LiPoFe4 is spot on to manufacturer spec, while NiCd and NiMh are usually much less and it goes down with the use.

I do not even consider non rechargable alkalines being not economic.

I will buy one for backup. And the Sanyo Eneloop for every day use.
I always forget the power adaptor in the TX at bedtime so they should be charged in the morning.

Interesting, I didn't know they are that much improved.

I like all lithium based batteries because they never let me down, they are light, with high energy density. The only downside is they have be taken out to be charged, plus fire hazard if misthreated.

FDR wrote:

Usjak wrote: The reason I did this mod is I hate NiCd and NiMh batteries because of their high self discharge, meaning even full after couple weeks of not using Tx they are near empty, usually when you need them the most.

This is the area for what Sanyo's Eneloop or Varta's Ready2Use are made.
They retain the 75% of their power over a year...

I found this review regarding Sanyo Eneloop

www.stefanv.com/electronics/sanyo_eneloop.html

Not as claimed but ~50% retained over a year, pretty good.

I noticed another advantage of Lithium based batteries: Discharge characteristic. Lithium based batteries hold linear voltage over almost whole cycle, while all others, including Eneloop sharply drop in voltage, translating to sharp drop in transmitting power.

I own a Devo6. And after watching the photos in this topic, it seems very similar to what I have on my Devo6. I think the Devo6, and maybe the Devo8 or other model could be modded the same way, if they need the same power supply.

What about renaming the topic ?

Not necessarily transmit power, but quality of transmition (corrupt data). The RF modules do not stand to any ripple in input voltage. I checked several low drop-out regulators used: LM3940, AZ1117, TDA3663 and TLV2217. Although they talk of low drop-out, other characteristics are specified at 4.5, 4.75, 4.5 and 3.8V respectively. Having higher battery voltage, being more linear appears to be beneficial here.

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 don't know if you read the whole topic, but looks like the consensus here is to go with Sanyo Eneloop or similar low self discharge AA batteries.

Pixel166 wrote: I own a Devo6. And after watching the photos in this topic, it seems very similar to what I have on my Devo6. I think the Devo6, and maybe the Devo8 or other model could be modded the same way, if they need the same power supply.

What about renaming the topic ?

Yes, I saw this and I'm trying to find those Sanyo Eneloop as soon as possible (+ charger as I don't have any).
I was just asking about a rename for those how really want a battery pack instead of AA batteries, but for my devo6, it will be Sanyo AA (Thanks for the tip)