JR XP8103 PCM TX + Lipo possible?

[pyroM!KE]

Will this Tx handle a Lipo pack..The 3 cell TX packs? This Radio is like 7 years old..Just woundering if it would handle the extra volt or so....

[Troy Newman]

All of the current or past JR and Spektrum radios are recommended NOT to be used with lipo packs. The 3cell voltage is too high for the systems.

No it will not self destruct in your hands, and there are lots of people that say they have been using them for X number of years without issue.

The problem is the output circuit is not designed to operate at the voltage a 3 cell lipo comes off the charger. This is aproximately 12.4V and it stays above 12V for a fairly long time. The cut off voltage to recharge would be down around 11V...

The designed ni-cd / nimh packs that come with the TX's may come off the charger at 11.4V but they only stay there for a short time and quickly find a normal operation around 10.7V down to 9.6V for recharge. So in terms of operating voltage the TX will be operating almost all of its time above or at the full charge voltage of the design pack when using a lipo. This means the heat needs to be disappated all the time its on. The stock batts will run a little warm when they first come off the charger, but the TX will coool off when the voltage drops to the 10.5V or so. The lipo in most cases its 1.5V high. This extra voltage can over heat the components in the output circuitry and risk causing damage. Its a simple fact that heat can cause problems with electric circuits and operating the circuit at a full 1.5V or 15% higher than what its intended to run will cause more heat. The circuits have voltage regulators, and transitors in them that control the voltage and output of the trasmitter. More voltage for a longer period of time means more stress on the electronic components.

The extra heat in the output can make the TX module run extremly hot in the 72mhz systems. This will reduce range over time. Can you run it for a while....probably, but when do you send you module in for repair because of the damage caused by extra voltage? I would say if you are running a lipo you really need to send the module in at least once a year to have the output transitor checked and or replaced. If you are on a 2.4 native system the same holds true. If you insist on running a lipo then I would say you need to send your TX in every year and get it checked out. The Lipo usage will void the warranty.

So the repair bill will be on you, but this is much better than to risk loosing a model. I have direct experience with this and have seen it happen with lipo packs on both 72mhz and 2.4ghz systms.

This is one of the reasons that the JR and Spektrum equipment is recommended to not use the 3 cell lipos.

Troy Newman
Team JR / Horizon Hobby

[c/f]

"The cut off voltage to recharge would be down around 11V"...

HUH???
With a statement like that I wonder how knowledgable you actually are on Lipo use, A Lipo is good down to 3VDC per cell under "ANY" load before recharge, Since a TX is such low of a load you easily can go down to the TX Low voltage alarm of 9.8VDC and have a higher margin of battery reserve than do Nicads/Nmh.

I use Lipo in every JR TX I own, 347, 8103, 9303, 10X................BUT I use (2) 300W rectifier diodes in series, this does two things, each resistor by design drops the VDC by 1.1VDC, so on a fresh charged 1800MAH 3s Lipo I see 11.1VDC which is exaclty what an SR premium Nicad pack will show.

When I get the pack down to 10VDC displayed I use a single diode that once again will raise it back up to 11.1VDC, This pack gets me like 6 hours on time............thats allot of flying.........

The second thing is the Rectifier diode insures you cannot plug a wallwart charger into the charge port of TX as it will not pass as the diode is directional.

Also another trick without diodes is to use a small 3s Lipo pack of 730MAH to 500MAH of 8c-10c ratings, (Blue stripe ThunderPowers are great for this and can be bought CHEAP) both these seem to outlast spektrum and JR 700-900 sized NIMH. do to the higher voltage energy density, The low C rating under load once again will only be 11VDC on a fully charged pack under load. A properly loaded C rated pack is a measure of what the underload voltage will be.

ie ... I prop/thrust a brushless motor to see 3.45VDC (10.35VDC 3s)per cell under load to insure I'm not carrying too much battery weight for a given application of thrust needs.

On the same subject,

The above post agrees that providing more voltage to TX modules the final output resistors work at a higher level. As I see this with my module based JR TX that is a good thing with 2.4G modules, as the higher the ouptut the better the signal link, exampled by JR using a higher output wattages in states than allowed in Europe CE restrictions and have made both available.

This is also confirmed with my Corona 2.4g module as well as my Robbe FASST 2.4G module I use with these JR TX's, in the included instructions , there are also those who believe a Spektrum TX under 10VDC is running at risk.

So in a nut shell if you keep 11VDC or less, the TX has no clue what the available DC power source is and can only tell if a high voltage is ever recorded. This too is bunk in spektrum Lipo use warnings, they could only record or measure high voltage reading, "NOT" a LIPO use type.

In closing I use 3s Lipos in all my JR TX and the TX has never seen anymore than 11.1VDC as a rule......... .02

[Troy Newman]

I am very familiar with Lipo packs, and as a rule when flying my electric models on 3cell packs, I use 11v under no load conditions as my cutoff point to recharge them. This is approximately 75-80% of the battery capacity used. When under load on an electric model this means approximately 10-10.5V depending on the power system. Obviously a TX is not going to draw large current like the electric motors. However running the packs below 75-80% capacity has been seen to show pre-mature reduced life of the packs. Just ask the guys that are running high power systems in their pattern planes. Yes they are drawing big current and a TX is not getting these kind of current draws but the battery chemistry is the same.

This is why I chose the 11v number. As I stated I don't run lipo packs in the TX, and am just giving numbers for reference. There are options to reduce the voltage of the packs as you stated with diodes and other circuits before it goes to the TX. In my opinion this adds other items to the circuit that can fail or cause problems. In addition using these voltage reducing devices will not allow your TX to read the true voltage on the battery. It only reads the voltage that it sees. So there could be, and I stress could be, some risk of over discharging the packs. The voltage displayed is not the actual voltage of the battery pack. The displayed voltage is lower, due the voltage reducing devices installed.



Regardless none of the Lipo companies recommend discharging the packs to 3VDC per cell. This is the lowest you can go without damaging the cells. And that is under a loaded condition. Most recommend recharging at the 80% capacity mark. Which in my experience is about 10.8 to 11volts under no load conditions.

I guess to each his own, I gave the reasons why it is not recommended, and I know there are some experts that have this well in hand. Thats great this hobby has room for everybody and their opinions.

I just am giving the facts as to why its not recommended. Its not that your TX is going to go poof instantly buy using such a battery. As I stated its not recommended......And my personal suggestion is if you insist on doing it, as many have, you should send your equipment in regularly to have it checked out. The simple fact is many folks have found out after a period of time using these pack they have a problem. Some found out by loosing a model. and some found out with a simple failed range check.

So its not recommended, simple as that. I'm not saying you can't do it as many people have done it. It simply is not recommended.

Its amazing to me why some folks seem to take personal offense when a manufacturer gives a recommendation not to do something they want to do. So they jump on the manufacturer like they are trying to keep the guy from having fun and enjoying his product. I have seen results with the lipo packs and experienced them when flying my 10X about 3-4 years ago on a lipo battery pack. I fly a bunch or have in the past several years and saw first hand with my own equipment the results. I have also helped other consumers with their radios having experienced problems after a period of time using the lipos in their TX's.

As Sleepy C tries to portray this environment of Flying Giants Open to all opinions and ideas, I think its a decision that each of makes on our own regarding the equipment we choose to operate.

To shoot a messenger and somebody that has experienced the problems associated with a certain path of action seems almost not FG style.


As a modeler I have a passion like most of you for this hobby, the technology, and enjoyment I glean from it. I'm not the ultimate expert on any subject regarding models. I do have many years of experience, and knowledge both self taught, and passed down from other modelers. I try to share that experience and knowledge to keep the sport alive and knowledge passed down to newer modelers in the hobby. After all I have only been doing this stuff for about 28yrs, I'm just a kid in this thing. Many more experienced modelers are on this site and also share their knowledge. I learn new things everyday from people that have been here for 10 weeks and people that have been doing it for 50years.

Enjoy your radio and the battery you choose. Please fly safe, and my humble advice is to not risk damage to your equipment.

Troy Newman
Team JR / Horizon Hobby

[c/f]

Whew...... Thanx for your explanation of the explanation....... Having been into electrics since 10C as the new kid on block I have never read anywhere of gauging unload voltage as a unit of capacity remaining. Your explanation sure is unique.

I wish Lipo use in TX just be a matter of fact straight forward Warning "Voltages higher than a capable fully charged Nicad pack are not recommended. ie above 11.3VDC"

Battery chemistry really has nothing to do with it. Lipos have the most urban legends of any r/c componenent I have the pleasure of using in my 35 years of modeling.

Team BVM
Team HobbyKing

[Pilotpete]

While it cannot be denied that adding diodes to drop the voltage adds components that could theoretically fail, in practice, two diodes running at a fraction of their rated capacity and being forward biased all the time, are about as reliable as you can get, if one does fail, it would usually fail as a "short", resulting in nothing more than you seeing the higher voltage on the display
Pete

[Troy Newman]

Ok, C/F you win.....

battery chemistry has nothing to do with it. I never said it did. Lipo have the ability to provide too much voltage to the system.

Taken from my first post that bothered you so.

"The problem is the output circuit is not designed to operate at the voltage a 3 cell lipo comes off the charger. This is aproximately 12.4V and it stays above 12V for a fairly long time."


I will keep the answer simple. Since it seems to offend you that my reasons being explained have holes. Reality is that doesn't have any real bearing on the situation. My explaination was my own and obviously you have way more internet arguing time than I.

Directly from the manufacturer:

Its not recommended.

....there are many reasons this one is mine.

Enjoy