drube

Can I use a Lithium Ion 7.4v battery with my Futaba R617FS receiver? I'm looking to go with the digital HS-5585 servos because they're rated for Lipo 7.4v. OR, I'd like to use the Litium Ion 7.4 with a 6v regulator so I can use the Savox 1258TG's. I know the Rx is rated for 4.8 - 6v but, I thought I read somewhere that running a 7.4v would be ok. I also read that using a regulator with the R617FS is a bad idea.
Your thoughts?

Thanks

jester_s1

If the manufacturer rates it for 6v, that means the voltage of a 6v NiCd. That comes 7.2v hot off the charger with no load. Lipo and Li-ion will go to 8.4 and 8.2, which is too high unless Futaba approves it. A 2 cell Life is only 7.4v at full charge, so it will be safe.
On the regulator, it's never a good idea to use one unless you have to since it introduces another failure point in the system. With good Life's on the market, there's no reason to go that route anyway.

DavidAgar

My Feedback: (108)

I am going with no. I use Lipo's with a regulator and have not had any problems at all. I am using a Castle regulator, and while Jester is correct, it is another potential failure point, I have not had any issue's at all. I switched to this a couple of years ago as I had so many NiCad Battery pack failures. I had a couple of brand new packs that failed within a couple of months and these were name brand batteries. I was in a gradual move to electric's so it was an easy choice to switch over. As for the Futaba receivers, They are listed for 6 volt and I am not sure that what higher voltage would do to them. Good Luck, Dave

Pylonracr

I use Lipo batteries and regulators in most of my planes with no problems. I bought a Futaba high voltage receiver to use with high voltage servos in one of my 3D planes. Futaba told me their 2.4 receivers are not rated for above 6 volts unless the specs say otherwise. They have a few high voltage receivers and the spec sheet gives the operating voltage.
Hope this helps

drube

I would like to stay away from using regulators but didn't know what my options were. So if I use a LiFe 1900mAh with the R617FS Rx and these Savox servos www.savoxusa.com/Savox_SC1258TG_Digital_Servo_p/savsc1258tg.htm I should be ok then? Sorry for the questions, i've only used Nicad and NiMH batteries.

Thanks

drube

jester, I forgot to ask. Would I need a 3C or a 10C for those Savox servos?

Thanks

jetmech05

You can always get a smart fly board that allows you to use LiIon batteries. will allow 6.5 V to the servos while keeping the receiver voltage at 5 V. has servo matching, batt share, voltage regulation of course, and optic kill for gassers.

flyinwalenda

My Feedback: (5)

You will be fine using the LiFe pack. If you have a choice between 3C and 10C and you afford to carry the larger pack I would get the 10C.
The 1900mah 3C will provide 5.1 amps and the 10C will provide 19 amps. When using digital servos and if the demand on them is high it's best to have a higher amperage supply.

drube

The Power Expander Pro looks interesting. More than I want to spend at the moment but will consider it when I move up to 50cc.
Thanks for the info

drube

Thanks! Could the 10c also be used with anolog servos like the hi torque Hitec 645's?

flyinwalenda

My Feedback: (5)

The "C" rating of Lithium packs is the maximum current that can safely  be drawn from the pack without damage to the pack. You multiply the milliamp rating by the "C" rating  to obtain the max amp number.   Typically with analog servos you can get away with less amperage than digital servos as the digitals tend to demand more current.

drube

Thanks for the info. I have another plane with 5 645's in it. So it's safe to say that I could use the 1900mah 3c in it.. How many flights do you think I could get out of one charge? Sport flying...

flyinwalenda

My Feedback: (5)

I've been running them in a Hangar 9 Meridian 10CC plane ;one on ignition and one for the receiver and I fly 20 minute flights. I have put around 5 flights on it and checked the packs and they are down to around 40% capacity.  30% capacity is the preferred limit for discharge and then they should be recharged and balanced.

drube

5 20min flights, that's great! Thanks again for your help.

flyinwalenda

My Feedback: (5)

One more very important thing you need to know. LiFe packs discharge differently than LiPo and NiMh/NiCd.. LiPo and NiMi/NiCd packs loose their voltage as they loose their capacity so you can check them with a load tester and have an idea where they are in discharge and know how much time you have left. LiFe packs have a different discharge curve where the voltage stays consistent while the capacity continues to drop. They will continue to show good voltage up to the point the capacity is gone and then both voltage and capacity fall off of the cliff.......so you can't tell where the packs are by using a typical voltage load tester. You have to fly a few times then put the battery pack on a smart charger and see how much capacity you put back into the pack. This will determine a baseline for that plane and you can determine how many more flights you can make before the pack goes flat.

drube

Thanks for that info! I was going to use this charger. www3.towerhobbies.com/cgi-bin/wti0001p The only smart charger that I have is www3.towerhobbies.com/cgi-bin/wti0001p I know it charges Lithium Ion and Poly but not sure if it will charge LiFe.

jester_s1

You're right, the Accucycle Elite will not charge LiFe's. To help things be clear, I want to clear up something it sounds like you're not clear on given your question about using analogs. In electrical systems, current is drawn, not pushed. So if your servo draws say .7 amps at full stall, it will do so whether it's hooked up to a 600mah NiCd or a 5,000 mah LiFe. The motor can't draw more current than its design makes it draw. Now in practical application you would probably see a slight difference in the amp draw between those two packs because the LiFe would do a better job of holding its voltage up instead of letting it sag under load, but that's the only reason.

In choosing the "C" rating, all that really matters is how many amps your system is capable of drawing. Many manufacturers include that spec in their literature, so it's a pretty simple task to figure it out. You'll never come close to *****g out more than two surfaces, so if all of your servos draw an amp at full stall then that makes two, and you'd probably want to allow one more for servos running at less than stalling torque and a bit for your receiver. So that's a minimum need for 3 amps of current capacity from your battery and connectors, which a 3C 1000 mah battery could give you. The conventional wisdom says to not cut it that close, so going to say a 2300 mah battery that can handle 3C discharge gives you a tick over 6 amps of current to work with.

flyinwalenda gave you a good tidbit in that you can't use an ESV made for NiCd's to test LiFe's. There are lithium calibrated ESV's on the market that claim to do the same function, but I haven't used one. My rule of thumb is to fly to half capacity (which I've determined by watching my recharge display and by doing discharge tests when the battery or plane is new) and then do a quick recharge. That way if there is an issue with a servo binding or malfunctioning it's not likely to cost me a plane.

drube

Thanks for clearing that up for me. I'm kinda on the fence about LiFe batteries now considering I'd have to buy a compatable smart charger to check voltage. I like the idea of being able to use my volt meter to check batteries under load. And since I already have a smart charger that can charge Lithium Ions, it seems like the easier and cheaper way to go. But I would be back to dealing with a regulator though...
I just got an email response back from futaba about using Lion with the R617FS Rx.. They said they don't recomend using Lion with that receiver but if I do I need to use a 6v regulator.
So I guess i'm back to where I started..lol Looks like a Lithium Ion and a 6v reg will be in my future. Now I just need to find a reliable reg.

flyinwalenda

My Feedback: (5)

I've used MPI  and a Fromco and  they have worked well.

jester_s1

For what the regulator is going to cost you can have a simple LiFe charger. I don't really see why you wouldn't go that route.

drube

A simple LiFe charger like this one www3.towerhobbies.com/cgi-bin/wti0001p doesn't show readings so how would I know what was used and what's left?

All Day Dan

My Feedback: (5)

Those are excellent questions for Futaba. Get the right answers from them. They know the best way to configure a system since they designed it and their livlihood depends on it. You have now idea what the qualifications are of anyone on RCU to discuss the matter. Dan.

[email protected]

drube

After doing more research about regulators I have decided to go with LiFe batteries and will use this charger www3.towerhobbies.com/cgi-bin/wti0001p I'll do a few flights then recharge and check how much capacity was put back into the pack and go from there. Does a LiFe battery need to be balanced at every charge?

Thanks guys for all your input and help!

sledge_78

My Feedback: (24)

Drube,

I have been using 2s lipo's and a voltage regulator on my Futaba R6i7fs receivers for a few years. I have had nothing but success with this combination. I too, was concerned with over driving the receiver or servo's with 7.4+ volts and so the voltage regulator really fixes that potential problem. After years of using NICD & NIMH batteries I really am satisfied with the performance of the lipo and regulator combination. I use a Associate/Reedy voltage regulator which has a very thin profile and really does not occupy any space or add any additional weight to speak about. Don't be afraid to try this solution it really works well and there is no risk to receiver or servo's. Just remember to put the switch between the voltage regulator and the Lipo otherwise, the voltage regulator will continue to drain the LIPO until it is depleted beyond charging recovery. I learned that one the hard way.

Sledge_78

drube

sledge, check your inbox.