Using Lipo for transmitter

[sonnyk88]

Does anyone know a quick solution to drop a 3s Lipo voltage down to the safe voltage for transmitter?

I heard that some transmitter might get damage with fully charged 3s @ 12.6V.

Thanks,

[Dan Baldwin]

I put 2 diodes in series with my lipo to drop the voltage by about 1.5 volts. I used 4 amp diodes so they would not be operating anywhere near there maximum current. The transmitter even shows undervoltage at about the right voltage for the pack. Of course you have to put a charge lead before the diodes.

Dan

[mrblucor]

I run my spektrums from a 3 cell lipo. I use old tired ones. They won't push high current anymore, but are fine in the TX. I did the dimension engineering mod, this is a dc to dc converter for the 3.3 Volts required for the RF deck. Power consumption was cut in half. I charge my TX about once a month. The only problem is that if you are flying with low lipo battery (9V), the TX low battery alarm won't catch it. Running with 2 or 3 diodes in series as Dan is doing is a good idea. Make an adaptor from your TX plug to your battery plugs with the diodes inline. Charge your lipo outside the TX case. If all else fails, an you forget to charge your TX battery, just pop in one of your other flight batteries. If you are not comfortable doing this work, find someone who is. The last word of caution, if you leave your TX turned on, you will drain and ruin your lipo battery. Hope this helps.

JB

[David Parry]

Try this
http://cgi.ebay.co.uk/RC-TX-transmitter-lipo-battery-11-1v-10C-Futaba-3PK-6EX_W0QQitemZ130232166217QQcmdZViewItem?hash=item1 30232166217&_trkparms=72%3A12%7C39%3A1%7C65%3A12&_trksid=p3286.c0.m14

I use them on my futaba tx and a 35mhz esky type. lasts for ages, no mods needed for voltage as there 11.1 v. but on the esky tx I just had to solder a connector to the + and - terminals so I could unplug the battery.

[jeffs555]

no mods needed for voltage as there 11.1 v

That is just the nominal voltage, they will still be 12.6 volts when fully charged. The nominal voltage for an 8-cell nicad transmitter pack is only 9.6 volts but could be around 11 volts when fully charged. Most transmitters would probably not be damaged by 12.6 volts, but the possibility is there.

[fjintx]

Hello Dan.
Do you have the part number for the diodes you are using to drop your voltage? Can I assume that you are still pleased with the 2 diode set up and it is working fine?
Thanks,
Frank

[Dan Baldwin]

I'm still using a 2500 mahr lipo with 2 diodes in series, and I have had no problems. I only have to charge once a month or so. I think the diodes I'm using are UF5402's which are rated at 3 amps. They are large diodes which helps to dissipate the heat.

I bought mine from Mouser, but Radio Shack also has them http://www.radioshack.com/product/index.jsp?productId=2062578


Dan

[fjintx]

Thanks Dan,
This is excellent and important information. The front of my transmitter case on my Futaba TXAS runs very hot where the RF heat sink or voltage regulator attaches to the case. I'm headed to Radio Shack today for the fix as you have described above. Thanks again for documenting a great, low cost solution and relieve us from constant ni-cad recharging!
Frank

[lazy-b]

Guys, I've also use a 2 Pcs IN4001 Diode (1 amps), this is a Safer way to, I assume you fully charge your Lipoly battery.

Another way, is Not to Fully Charge your Lipoly, charge your Lipoly in STORAGE (3.85 Volts per cell.......3 cell thats 11.55 Volts)MODE , this will works only in Newer Lipoly charger, in Storage mode........the Storage Mode is increase the shelf life of the Battery.

Charging at Storage Mode and 2 Diode will also give 11.55 - 1.5 = 10 Volts which is still Good.

One Nice thing about Lipoly, even after 2 years of not changing it, the Battery is still Good.

[fjintx]

Very interesting. Unfortunately my charger won't stop until the battery is fully charged. I have been flying with the 2 diodes in series and it works great just as you said. Thanks for responding to the question.

Guys, I've also use a 2 Pcs IN4001 Diode (1 amps), this is a Safer way to, I assume you fully charge your Lipoly battery.

Another way, is Not to Fully Charge your Lipoly, charge your Lipoly in STORAGE (3.85 Volts per cell.......3 cell thats 11.55 Volts)MODE , this will works only in Newer Lipoly charger, in Storage mode........the Storage Mode is increase the shelf life of the Battery.

Charging at Storage Mode and 2 Diode will also give 11.55 - 1.5 = 10 Volts which is still Good.

One Nice thing about Lipoly, even after 2 years of not changing it, the Battery is still Good.

[Dan Baldwin]

1N4001's are rated at 1 amp, which is perfectly adequate, but I chose the larger diodes to help dissipate the heat, since they have virtually no air flow hidden in the back of the transmitter.

One of the guys at my local field had his transmitter fail after a few weeks of using a lipo with no diodes. I don't know if it was related to the use of lipos. Could have been a coincidence. I think it was a JR transmitter.

Dan

[BobRCnut]

I use two 1N4003's in series for my Futaba transmitters... when the (8.5 Volt) LV alarm goes off, the LiPo is still at about 10.2 Volts, well above the safe discharge limit. Fusion Pack makes a 3S-2500 LiPo for Tx use that comes with JR and Futaba connectors plus a JST-XH balance tap.

[fjintx]

Hi Dan,
My transmitter now runs cool thanks to your diode recommendation. The two UF5402's seem like overkill but they should be more than enough to dissapate any heat. The current flow is 122mah through the transmitter, so I'm good to go.
Best Regards,
Frank


I'm still using a 2500 mahr lipo with 2 diodes in series, and I have had no problems. I only have to charge once a month or so. I think the diodes I'm using are UF5402's which are rated at 3 amps. They are large diodes which helps to dissipate the heat.

I bought mine from Mouser, but Radio Shack also has them http://www.radioshack.com/product/index.jsp?productId=2062578


Dan