DX8 LiPo Conversion

Discussion in 'Scratchbuilding!' started by JettaManDan, Jun 6, 2011.

  1. JettaManDan

    JettaManDan Administrator

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    I hadn't seen anyone else try this yet so thought i would post. Bought my DX8 about 2 months back..and really love the radio. Was cool to see it was setup to use a 2s lipo pack. But was horrified to see that Horizon offered one for the radio and it was $70! :eek: With a big capacity and it's internal balancer it makes sense it is that expensive...but way more money than i wanted to spend. I run LiPo's in my DX7 and did in my 6EX (Before i sold it for this) and loved the run-time and the ease of quick charging the batteries on my lipo charger. So started looking around for what i would need to make my own converson work.

    Thankfully Horizon put the spec's of their pack up on the site so i knew the dimension constraints - they are 68x52x19mm - 2s packs are plentiful but finding one the right size and over 1000mah is a bit tough. Hobbyking sells a couple of 700mah packs that would fit but that was too little capacity for me. So i went to the place that has always had packs to fit my applications..and that was www.valuehobby.com. They had a pack that looked perfect. a 1300mah 2s pack with the proper dimensions. •67.6mm X 36mm X 16mm

    link to it..
    http://www.valuehobby.com/product_details.php?category_id=7&item_id=185

    so finding that i knew i had a pack that could work...now i had to find a source for the JR/Spektrum plug for the radio side..i didn't want to hack off the one on the stock battery (still wanted it as a backup) so then i looked around and found Radical RC..and they had exacly what i needed...

    http://www.radicalrc.com/search/RRC2PPIGWMJRTX

    for only $2 i bought 3..just in case i wanted to experiment later...they shipped super fast and have greta service to boot! then all i needed was a JST plug (which i had) basicially what i wanted to do was make the pack have a long enough plug to go into the radio..but also have the JST and the balance plug accesible to charge the pack and not have to disconnect it from the radio itself..i feel as if plugging and unplugging the Spektrum connector a bunch of times is a bad idea. Having found all i wanted i ordered the pack and the pigtials and got them in last week. Making the conversion was very simple if you know how to use a soldering iron.

    So here is what i did...

    Radio :)
    [​IMG]

    Stock Battery (i already added my own JST plug to this for a fast charge and not have to use the stock through transmitter slow charger)
    [​IMG]

    Here is the 2s 1300 pack from Valuehobby
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    The 2 packs side by side...the radio has a foam insert to space out the smaller stock battery and keep it tight...so that was taken out...
    [​IMG]

    checking the fitment of the 1300...perfect!!!
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    wires i'm gonna be using...the JR/Spektrum pigtial and the JST...
    [​IMG]
    [​IMG]

    Start of the wiring..just parallel connection of the 2 pigtails...
    [​IMG]

    cutting the deans off the LiPo..and starting to connect it to the pigtials...soldered the wires and using heatshrink to protect it..
    [​IMG]

    wiring complete!
    [​IMG]

    connecting it to the radio...
    [​IMG]

    plenty of slack to charge the battery outside of the radio yet still have it connected and not unplug it everytime..
    [​IMG]

    Battery in and the wires tucked in..fits perfect....
    [​IMG]

    setting the radio to lipo and the proper low voltage alarm...
    [​IMG]

    Radio happy and showing the new voltage from the pack! (pack was just on a storage charge...will fully charge it later.)
    [​IMG]

    i'm VERY happy I did this. I haven't had a chance to charge the battery yet and see how long the radio will run on it. The radio has a "you left me on" alarm so it won't just let you leave it on for hours and walk away. But I like that the lipo has a higher voltage so even when fully spent, the ending voltage is higher than the NiMh pack at full charge. The lipo is actually lighter than the NiMh pack (A bonus). And i suspect it will hold power for longer than even the stock 2000 pack would. Plus i can use my AC6 to charger it now and get the pack to full power in 40 minutes and be ready to go.

    So there you guys go. Unfortunately the DX8 has a recall on it right now and i have to send mine back for a fix/update. So i won't be able to try this out for a while. But when i do get it back i'll report on how much time i can get out of the 1300 and see if it was worth it. But to me it is already...more power and signal strength...and lighter weight for the transmitter.

    If you have any questions please ask!

    Dan
     
  2. archie

    archie Cadet

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    Godd stuff JMD, Do you recon the same setup would work to power my DX6i?
    Thanks
     
  3. JettaManDan

    JettaManDan Administrator

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    it may..i know the DX8 was designed to run the higher voltage...so it is safe...i'm running my DX7 off of 3s pack...the stock battery is 9.6 volts..and mine is 12.6 at full charge...and i've had no isses...so i would assume it would be ok..and saw other places that people were running 2s packs on the DX6i..so i guess it is a matter of space and the wire coversion...
     
  4. archie

    archie Cadet

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    I have quite a few lipos to experiment with so i'll give it a shot
    Thanks
     
  5. JettaManDan

    JettaManDan Administrator

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    does the DX6i have a reciever pack like the 7 and the 8? or does it have the AA battery holder? if it is a seperate pack then i think this will work fine..if the AA system is in it i think you need to remove that tray..which is more of a hassle...
     
  6. archie

    archie Cadet

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    It has a tray but I think it isn't too hard to remove as it is supposed to have either
     
  7. JettaManDan

    JettaManDan Administrator

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    ok cool..then shouldn't be too bad...
     
  8. dtribby

    dtribby Top Gun

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    Hmmm.. my 2nd hand DX6i looks like it was made in '05. The 4xAA tray is formed into the back cover. Would take some modification to squeeze a lipo in there. But the Spektrum NiMH batteries charge to 1.43V each, for roughy 5.7V. With 1800mah each, that's 6400mah between the 4 batteries. My Energizer NiMH AAs run about 1.3V each, but they're 2200mah apiece, for a total of 8800mah. How does a lipo get longer battery life than that? I understand the higher voltage, but it seems to come at a fraction of the battery life of NiMH. Mine also doesn't have a Lipo battery menu option either, so are there any risks with running a higher-than-normal voltage?
     
  9. JettaManDan

    JettaManDan Administrator

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    the Mah rating is not addition..it is the same..so your pack would only be 1800...shouldn't be any risks as long as you keep it ot 2s...
     
  10. dtribby

    dtribby Top Gun

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    As I understood it, C-rating was not additive because it is a rate capacity - the ability to support flow, but Mah is a quantity of energy. It I have bottle full of electrons, C-rating is the size of the nozzle, voltage is how fast the electrons move through the nozzle (pressure), and the Mah is how much liquid is in the bottle. If I get more than one of these bottles in series, I can't make the nozzles any bigger, but the cumulative pressure will really move the electrons at the front end, and there will still be more electrons to move than just one bottle's worth. Does that make sense?
     
  11. JettaManDan

    JettaManDan Administrator

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    think of it this way....the Volts added together is the boost of your turbo...one turbo...just a little power....add 3 more turbos? then 4 turbo power! lol! Mah is the size of your gas tank...one battery is 2 gallons...at 3 more to that and you have 3 more times the distance you can travel...your car won't go any faster..soo...we'll make this easy...

    Series: One battery is 1.2 volts and 1000mah (AA's) in series (you connecting the positive of one battery to the negative to another and then that postive to a negative) etc (sausage links lol) you are adding voltage...but the same storage capacity exists...so every battery you add, add's 1.2 volts...so 2 AA's in series are 2.4 volts..but the same 1000mah capacity....

    Parallel: Same batteries..but this time the positive of both batteries are connected togther..and the negatives are connected together...now..you still have 1.2 volts..but your storage capacity is doubled...so you have a 2 cell pack that is 1.2Volts...but now 2000mah capacity....

    so let's use the lipo's you use as an example....if you have two 3s packs...each pack is 2200 mah....so one pack is 11.1v and 2200mah...if you conenct them in series....the positive lead on one to the negative on the other....then you make a 6S pack that is 22.2 volts..but the same 2200 mah rating...(4 turbos but the same size tank!)

    if you connect them in parallel...both positive leads tied together and both negatives tied together..then you still have a 3s pack but with 4400mah of run time...(one turbo but a mega huge gas tank)

    make sense?
     
  12. Jbirky

    Jbirky Ace Pilot

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    Think of it this way...

    The stock battery is 4.8volts.. that is like 5.6 volts when fully charged...

    You are dropping in a 2S lipo 7.4 volts that is 8.4 volts when fully charged...


    Are you sure the DX8 is rated to handle the extra voltage? Obviously, it has a voltage regulator of some kind, but it might get hot and degrade or eventually melt if it has to work too hard.


    Also, you went from a 2000 to a 1300 pack... The old pack had 1.53x the capacity of this one, which can deliver its capacity at 1.5x the voltage of the old one...


    Both packs have the same amount of stored potential energy, so this was pointless!!!:
    Spektrum NiMh 1st: 2 Amps for 1 hour at 4.8 volts ==> 9.6 Watt Hours
    Your Lipo 2nd: 1.3 Amps for 1 hour at 7.4 volts ==> 9.62 Watt Hours.



    You have accomplished nothing besides raising the operational voltage of your radio to a level that may damage its internal voltage regulator(s)...

    The NiMh is much more rugged - you can freeze it, leave it in the hot sun, run it all the way down (or not), not bother balance chargeing it... no worries of it puffing... charge it maybe 500 times... the LiPo would need to be treated better...

    The only advantage to the LiPo in this situation is that its self-discharge rate is lower. I.e. If you let the NiMh sit in your car for about 30 days it will be low or dead and need to be recharged. In contrast, the LiPo can sit for a year and be "Ready" to fly.
     
  13. JettaManDan

    JettaManDan Administrator

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    You obviously didn't read my initial post (sigh)..the DX8 is SETUP FOR LIPO'S...(did you even look at the last 2 pics i posted??? that SHOWS the radio can run lipo's? even for you that is sloppy reading....) and the radio has a menu you can chage to allow it to run and use one..and Horizon offers a very expensive 2s pack for it....so i'm not hurting anything at all..please read 1st before you post....

    and the NiMh pack does lose voltage where the lipo holds a constant charge for a longer period..it drains more evenly..and at it's lowest voltage it is still higher than the NiMh at full.so there is no signal degredation when the pack gets discharged...

    so i did accomplish a few things....and maybe some more information/research on your part would be a good idea...
     
  14. dtribby

    dtribby Top Gun

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    But, JMD, using your gas tank analogy, if I can't go any faster, i.e. burn the fuel any quicker, then there are still 8 gallons of gas to burn. Mah is a quantity of potential energy, that cannot be created or destroyed. We can use it more quickly by upping the voltage (more fuel pressure) or amperage draw (stomp the accelerator), but 2x 1.2 NiMH AAs in parallel will work twice as long (at 1.2V) than one. Put them in series, and the voltage doubles (and your ability to use those electrons doubles too), so you'd only last as long as one AA, but at twice the voltage.

    But I think I see what you meant. It's just that a 2200Mah NiMH AA has the same energy stored in it as a 2200Mah 11.1V Lipo. The difference is how fast you can access it.
     
  15. JettaManDan

    JettaManDan Administrator

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    yes..voltage makes a difference too....but when you add batteries in series technicially it doesn't increase run time..it just increases RPM of the motor you are driving..move volts means a faster motor...if you run an electric motor on 1.2 v and 2200 mah...it will spin at 500 rpm for like 20 minutes...(just an example) if you run it on 2.4v and 2200...it wil lrun at 1000 rpm for 10 minutes....the power consumption is more at the higher RPM due to the voltage...so..it's hard for a direct comparison...i've run one of my planes on a 2s pack wtih 1000mah..it flew at a reduced speed but lasted longer..then ran the same plane on a 3s pack with 1000mah..it flew much faster (more voltage) and a reduced run time becasue it sucked up the capacity at a higher rate..so both values matter...
     
  16. dtribby

    dtribby Top Gun

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    I agree completely, but earlier you said:
    And that is simply not true. Running 4x 1.2V 1800Mah cells in series is the same as having one 4.8V 7200mah battery. What NiMH lacks in raw power delivery, it makes up for in capacity. Running your 7.4V 1300 pack will give you higher voltage, but less run time than the 2000Mah pack you replaced. I don't really have the option of using a lipo, but I'm using 4 AAs that each have a higher capacity than your whole pack, so I'll get 5 or 6 times the run time on a charge over the lipo. My voltage won't be up at 7.4V, but it still works fine.
     
  17. Jbirky

    Jbirky Ace Pilot

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    I saw some video where Spektrum wasn't recommending LiPo packs in their radios stating it could cause damage... not sure it was the DX8 though.

    Yes, I saw your pictures and think you did a good job with the soldering and all, but I still think it is pointless because the radio should fuction just as well at any voltage; since, there is an internal voltage regulator. More voltage just means the regulator has to work harder stepping it down, which creates excess heat (lowering your efficiency more).

    One thing you loose with the LiPo is an accurate fuel guage to some extent... they generally hold their voltage pretty well under load then drop like a rock.


    The only really valid reason to do a LiPo mod is to increase your run-time. In the DX6 for instance, Spektrum included a 600mah battery pack. A LiPo brick the same size as 8 AA batteries can be 2000 mah AND be 11.1 v vs 9.6v nominal... In other words, you can easily 4x the runtime on an older i.e. DX6 radio doing a LiPo mod!


    In your case 4x AA size pack is very small and already 2000 mAh from Spektrum. You are going to be very hard pressed to find a LiPo much bigger than 1300 that fits the battery box of the DX8, and that is the problem.

    Also, 8 gallons of fuel is 8 gallons of fuel... it doesn't matter what the shape of the fuel tank is, if the tank is metal/plastic, or what gas station... i.e. Battery pack and chemistry don't matter; since, the radio is a very very low drain device (compared to a brushless motor). You do not even need a 1 C battery for a radio...

    I found that Spektrum does have a Lipo pack for $70 (you told me), and I am going to buy it for my DX8:

    Here is why their battery makes since and yours doesn't:

    Yours is 1300 mah... theris is 4000 mah and still fits!!!


    That is 1.3 Amps for 1 Hour at 7.4 volts is your setup has 9.62 watt hours of total potential energy (this is like 9 gallons of gas)


    Their Battery

    4 amps for 1 hour at 7.4 volts in their setup is 29.6 watt hours of potential energy (This is like 29 gallons of gas)...

    Clearly the Spektrum Pack WILL run 3x longer than your LiPo pack though both are perfectly safe to the radio.

    $70 is fair! 4000mah packs are NOT cheap!


    The Spektrum pack also has a built-in cell balancer and a built in circuit to prevent over-charging! That's right... My guess is you can charge it right in the radio, but I don't know this for sure yet... I am going to research it.
     
  18. JettaManDan

    JettaManDan Administrator

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    sorry but it is true....if you run cells in series you do not add their Mah ratings together....just their voltage....only in parallel do you add mah ratings... or else we'd have huge capacity packs out there...only when you go across postive to postive and negative to negative do you add capacity or run time...
     
  19. JettaManDan

    JettaManDan Administrator

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    reguardless of what you think of it being pointless i know from the packs i've had in my other radios that even a smaller Mah rated lipo gives me more run time than a larger NiMh...the Nimh drains at a much faster rate....so i feel that this was worth it..i didn't want to spend $70 on a lipo..that yes would give much longer run time..but would take 20+ hours to charge through the radio plug slow charger..not to mention the radio heats up when on the charger...try it with yours when you get it and see...

    what i take issue with is you not looking at the pics..not really knowing what can and can't be done with your own equiptment..and then giving an uniformed opinion...why would horizon offer a lipo if it wasn't safe? and the 1300 fits perfect...no mods necessary..with the 4000 you still have to take out the foam insert...

    so here are the FACTS:

    Stock DX8 - Able to take a 4.8 NiMH Pack OR A 2S lipo - and can be set for each one.
    4000mah LiPo from Horizon is $70 - can only be charged when in the radio..and people are reporting 20+ hours to just charge it once to full, and sometimes longer.. And it heast up the radio a lot for a LONG time...can't be good for it...

    And here are my observations...
    Stock 2000 NiMh drops significant voltage in a short period of time. With the raido being used for one hour i saw the voltage drop from 5.3 to 4.4
    With my 2s lipo the radio started at 8.3 volts...and with similar usage of about an hour it only dropped to 8 volts.
    4.3 volts is the recommended alarm for a Nimh...another 10 minutes of use max and i would have been there...(I beleive)
    6.4 volts is the lipo recommended alarm voltage..and seeing how it was draining i think it would have been another hour till it dropped off. (i beleive)

    so..reguardless of your opinions...the Mah ratigns on the 2 packs are not as equal as they might suggest..am i looking for 15 hours of run time like i get out of my DX7 on it's 2600 pack? of course not. But i feel MUCH safer with the lipo in there that i will have full signal and range right up until the pack drops off...will it be longer? hard to tell..but to me it was worth it...should everyone do this? nope..just what i did for fun and my own thoughts and feelings is all...the radio is lighter....and the pack fits perfect and cost me less than $20 to do it...if you want to spend $70 go right ahead...
     
  20. dtribby

    dtribby Top Gun

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    So, I did the reseach, and discovered you're right, and I'm so very wrong. You can add the voltage or the Mah, but you can't do both. Sorry man!

    But I'm still running 4x 2200mah AAs which should still add up to a 4.8V 2200mah pack. Not too shabby for AAs. They must use some cheap cells in those smaller packs. The Spektrum AAs are 1800mah, but carry a higher voltage (1.4V-ish) that the Energizer 2200Mah AAs (1.33V) I already had. Charging is too easy.
     
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