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Old Oct 02, 2011, 10:30 PM
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Question
Silicon "dropping diode" choice for 2S1P LiFePO4 Rx airborne packs??

Dear Fellow RC-Groupers:

The PIPE Here...I've seen a growing number of my fellow RCers considering the use of a pair of lithium iron phosphate (LiFePO4) cells to power an airborne "flight pack" with, and as I complete my college courses to head back to work again, after being laid off since September 2008, I've known that some "flight pack" components, especially receivers and servos, might NOT want the nominal 6.6 volts powering them from a pair of 2S1P-connected A123 1.1 or 2.3 amp-hr LiFePO4 cells in such a pack.

I've got upwards of eight Futaba R168DF 50 MHz band receivers to power up for future flying needs, and a good assortment of servos to use with them (mostly Hitec HS-225s and -77s). I'm quite used to making up ALL my own battery packs, ever since I started in the RC flying hobby in 1977. A123's ever-MORE-popular LiFePO4 cells, now readily available from Radical RC at http://www.radicalrc.com/category/A123-Cells-Packs-199 , certainly seem to be catching on for not only powering RC electric aircraft (the ONLY choice I'd ever make for powering RC electrics!!!) but also to power the flight pack components as well, even for glow & gasoline engined RC aircraft - I'm strictly a four-stroke lover.

Given that I'll HAVE to get some lithium-friendly chargers, like Hitec's X4 units - I've already got a 12 volt, 23 amp AC-powered supply to power the X4s with - I would then have the chargers to get them stoked up with electrons for radio power. But...how feasible would it be to place a silicon semiconductor DIODE, directly in series within the plus power cable coming from the battery pack into the RC system power switch, to DROP that 6.6 volts to a more reasonable 5.0 to 5.5 voltage level to the "flight pack" to keep the radio happy, and NOT burning out components that might be much happier with a four cell nickel-chemistry pack's 4.8 volts instead ???

The usual three-wire balancing charge cable for a two-cell series lithium pack would be there, of course, for hookup to the X4 charger, but has anyone already tried using a fairly hefty-current-rating diode to drop that voltage already, and how did it work out?

One source for such silicon diodes might be NTE's list at http://www.nteinc.com/diodes/general....php?a=12?a=12 , with a diode that could handle at least a 3 amp peak current...I'm just wondering IF anyone else has tried something like this already.

Thanks in advance, and Yours Sincerely,

The PIPE....!!
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Old Oct 03, 2011, 02:23 AM
Registered User
Romania, Dolj, Craiova
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Not tried, because I am confident that all my gear can handle those 6.6V.
Any RC equipment that is rated as "6V" actually is rated for a 5 cell NiMh pack, which can be even up to 7V when fresh charged, and the effective voltage drop at 6.2-6.3V when pack is 50%
But, as a computer engineer, I can tell you that your solution is perfect for your peace of mind. I don't see any negative issues, maybe only the diode mount, do it to ensure the best protection against vibrations. It is a common failure in industrial applications that the diode body plastic fatigue due to the vibrations induced into the leads.
Use hot glue to build a support that embed both the diode case and leads, but let a part of diode case in the airflow to disipate the heat.
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Old Oct 03, 2011, 07:11 AM
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Just use a rectifier from an old PC power supply.
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Old Oct 04, 2011, 11:07 AM
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The "diode IN the pack" idea IS what I was thinking of...

Dear Renatoa & Julez:

The PIPE Here again - for Julez in Deutschland. don't EVER forget to visit Biplanes.de on the 'Net from time to time...my German Email buddy Jens, the site's webmaster, held his "Barnstormer's BBQ" vintage aircraft event at Marburg/Schönstadt this past summer, and I've GOT to find out for Jens-SOMETIME soon-how Old Rhinebeck's AVRO 504 umlaufmotored (Le Rhone 9J 110 PS) reproduction aircraft is doing these days !!!

For Renatoa, the EXACT idea I've got in mind for mounting a series volt-dropping silicon diode onto such a LiFePO4 twin-cell airborne battery pack, IS one mounted directly on the 2S1P A123 pack, with silicone RTV sealant to mount the connected diode onto a finished pack with. I'd be using polyolefin heat shrink tubing to cover up the solder joints right up to the diode's case, and I'd be certain to cut a small "window" in the similar polyolefin heat shrink pack wrap where the diode was mounted, to give it a way of getting cooling air to get to the hard plastic diode device case.

The primary 22 AWG stranded red-black wires going from the pack to the switch harness for DC power to the model's radio gear would have the diode inline with the red "plus" wire to do the dropping. Of course, a separate triple-conductor cable gets connected to EVERY electrical connection in the pack for charging, as the cells making up a lithium celled pack of any sort can't self-balance between themselves like nickel-chemistry (NiMH and NiCad) cell-built packs can, hence the three-wire "balancing" recharge cable for a charger like the Hitec X4 I mentioned previously, which has its own internal balancing connectors for lithium-celled packs.

Got to get back to my online college coursework that's due today...

Thanks and Yours Sincerely,

The PIPE....!!
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Old Oct 04, 2011, 03:42 PM
Cumulus Altimus
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so if i used a 2cell 7.4 lipo i can put 2 diode on the + and go directly to my RX?
thanks
Ben
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Old Oct 04, 2011, 04:02 PM
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FastBen, PLEASE do a search for "electrochemical grenade" here at RCGroups...

Dear FastBen:

The PIPE Here again...and please, before you do ANYTHING else, as the heading of this reply suggests, do a search for the terms...

electrochemical grenade

here at RCGroups...you'll quickly find out that I want absolutely NOTHING to do with a type of lithium cell technology that IS literally an ELECTROCHEMICAL GRENADE waiting to go off, with ANY sort of inattention, and sometimes even with perfect care and attention being paid to them...

...lithium-POLYMER battery packs !!!

The SAFER option to go with for lithium battery cell technology for ANYTHING in aeromodeling, IS lithium IRON PHOSPHATE, as A123 has created, and as Dave Thacker has available at http://www.radicalrc.com/category/A123-Cells-Packs-199 ...!!!

Thise damned LiPos have NO place in any RC radio gear, anywhere, and I'd certainly NEVER use them in any radio gear I'm using, or in any of the future electric-powered RC aircraft I'd ever consider building or flying. There will ONLY be LiFePO4 lithium cells in radios & aircraft for any possible use of lithium cell technology in my own RC hangar, charged up with, of course, a real lithium-capable charger like the Hitec X4.

Please...KEEP IT SAFER...just do it with lithium iron phosphate cells !!!

Thanks and Yours Sincerely,

The PIPE....!!
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Old Oct 04, 2011, 04:09 PM
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Quote:
Originally Posted by The PIPE View Post
Dear FastBen:

The PIPE Here again...and please, before you do ANYTHING else, as the heading of this reply suggests, do a search for the terms...

electrochemical grenade
The PIPE - you will have a hard sale here with that thought. LiPo batteries rock - they are not small bombs as you elude. Bet your cell phone has one of those electrochecmical grenade's in it right now. How many of the billions of cell phones around the world have suddenly exploded?

MOST of us use those cells - they are certainly not unsafe to use. Again - hard sale with the LiPo's are unsafe here - we just know better.

I too am right up there with 6.6v club on the LiFe packs. Been using them for over a year now without burning anything up. Very happy, no diodes.

Mike
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Old Oct 04, 2011, 04:30 PM
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Sorry, but I am NOT using LiPos for ANYTHING in RC...period!

Dear pda4you:

The PIPE here again - and very sorry to disappoint you, but I REFUSE to use any form of battery cell technology that HAS to be "watched like a hawk", and is recommended to be charged in what amounts to a "flak jacket" OR "ballistic crockery" ...

...from what I've read about LiPo battery FIRES, and even disabling damage to them even from proper charging, I will NOT be made - by ANYONE - to use something, that I have absolutely NO intention of using.

When I can get back to work, most likely after I earn my business administration degree by the end of next Spring, and I can get back to RC flying once more, any of the SAM "Old Timer" type of aircraft that I DO intend to fly with electric power are going to be exclusively "brushless & A123" powered. I certainly intend to give two cell A123 Rx packs with diodes to cut their voltage down just that small bit a serious tryout as airborne battery packs, as well as strongly considering three cell "3S1P" configuration A123 LiFePO4 cell packs with nothing special on them for use in RC "knobby box" transmitters I'll be building for my own needs. That's because a 3-cell LiFePO4 pack DOES operate at practically the same voltage (9.9V) as the 9.6 volt normal voltage for an eight cell nickel-chemistry (NiCad or NiMH) regular Tx battery pack.

Again...SORRY, but LiFePO4 cells are ALL that I'll ever use for lithium celled batteries in the hobby, and "nuttin' else"...

Yours Sincerely,

The PIPE....!!
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Old Oct 04, 2011, 04:34 PM
Cumulus Altimus
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Quote:
Originally Posted by The PIPE View Post
Dear FastBen:

The PIPE Here again...and please, before you do ANYTHING else, as the heading of this reply suggests, do a search for the terms...

electrochemical grenade

here at RCGroups...you'll quickly find out that I want absolutely NOTHING to do with a type of lithium cell technology that IS literally an ELECTROCHEMICAL GRENADE waiting to go off, with ANY sort of inattention, and sometimes even with perfect care and attention being paid to them...

...lithium-POLYMER battery packs !!!

The SAFER option to go with for lithium battery cell technology for ANYTHING in aeromodeling, IS lithium IRON PHOSPHATE, as A123 has created, and as Dave Thacker has available at http://www.radicalrc.com/category/A123-Cells-Packs-199 ...!!!

Thise damned LiPos have NO place in any RC radio gear, anywhere, and I'd certainly NEVER use them in any radio gear I'm using, or in any of the future electric-powered RC aircraft I'd ever consider building or flying. There will ONLY be LiFePO4 lithium cells in radios & aircraft for any possible use of lithium cell technology in my own RC hangar, charged up with, of course, a real lithium-capable charger like the Hitec X4.

Please...KEEP IT SAFER...just do it with lithium iron phosphate cells !!!

Thanks and Yours Sincerely,

The PIPE....!!
THE PIPE
Thanks for your post.
i also am using 2s packs in all my hotliner with 3amp 6v regulator and have been for years without any problem...my Q was if i use diode's can i lower a 7.4 2 cell pack to asafe V to connect directly to my RX?without use of voltage regulator.
Ben
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Old Oct 04, 2011, 04:51 PM
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The "E.G." lithium packs DO need at least one diode in there...

Deare FastBen:

The PIPE Here again - if all you've got are so-named "E.G." lithium polymer packs that put out that somewhat higher 3.7 volts per cell, you'd need at least ONE diode, and perhaps even two in series, to drop it down to a safer 5.0 to 5.5 volts for your radio gear, especially IF you've got no way of finding out if they're actually rated for the higher voltage.

Check out what Renatoa was suggesting for mounting the diode(s) on the pack itself, and how I use polyolefin heat shrink tubing on ALL the connections that connect the diodes on the pack, for whatever you're intending to power - remember, those diodes do NOT get inserted into any of the charging/balancing wiring, they ONLY go in series with the plus power wire coming from the pack, to whatever you're powering with it.

Since I've BUILT all my own radio gear, for over three DECADES now - from my absolute need to use ONLY knobby, "single stick" style RC radios, I've spent a LOT of funds on creating the transmitters I've used for the RC hobby ever since I started in it way back in 1977, and I also try to build just about EVERYTHING I use in the hobby as well, just to help save a bit on the hobby's cost...

...so, I've always placed "a lot of myself" in what I fly with, and just about everything else I use in the hobby, and that translates towards my opinion about having a GREAT deal of resistance about using ANYTHING that could wreck something I've built for my own use and enjoyment in RC flying. LiPo "E.G." battery packs represent just such a potential threat for wrecking my hard work, from my viewpoint, so I am simply NOT using them.

Thank you and Yours Sincerely,

The PIPE....!!
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Old Oct 04, 2011, 05:42 PM
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I do respect your openion in this matter.
thanks for the diode post.
Ben
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Old Oct 05, 2011, 04:18 AM
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Cell phones are using LiIon, not LiPo. laptops the same.
Completelly different things.
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Old Oct 05, 2011, 10:29 AM
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Many cell phones use LiPo batteries. For example my LG phones use batteries marked as "Lithium-Ion Polymer". LiPo is short for Lithium Polymer which simply omits "-Ion" from the full name.

Back on topic: I use 2S LiFe in my planes with no diodes or regulators - straight to the receiver and servos (through a switch though). I just make sure the servos are capable of 6V (from their specs).
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Old Oct 05, 2011, 10:32 AM
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Likely even MOST use LiPo.

We all certainly get to pick what we use - but I have a hard time with calling LiPo batteries chemical grenades. Just not accurate.

All batteries store significant power and energy. All should be treated with respect.

Mike
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Old Oct 05, 2011, 10:52 AM
Xtreme Power Systems
Lake Havasu, AZ
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Lion and Lipo are completely different types of batteries. If you see the word "ion" anywhere in the cell name/type, it is a Lion battery. You won't find a single cell phone or laptop using "Lipo" cells (anymore), only Lion. The safety risk is too great with standard Lipo cells.
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