Flyboy1958

My Feedback: (1)

I see voltage regulators for lipo but not LiFe, will a regulator work with the LiFe battery the same? I'm wondering because the newer Hobbico LiFe source battery says a regulator is most likely not needed. But what if you think you need one? I just had a Hitec servo burn up. Hitec servos are only rated for 4.8 volts to 6.0v unless you get a high voltage one. I use a Spektrumreceiver which will handle the volts no problem, but now that I had a servo burn up, I'm thinking I need a voltage regulator. Any thoughts?

daveopam

My Feedback: (9)

You should NOT need a regulator on a LiFe with a Hitec servo. The life puts out a solid 6.6v A 6.0V NiMi or NiCad with a full charge puts out over 7.0V. So the Life is a better choice for your servos IMHO.

David

jester_s1

There is no point in the discharge curve of an LiFe where it goes more than .2 volts above what a NiCd puts out when it's hot off the charger. Any RC component that can handle a 6v NiCd can handle a 2 cell LiFe.

But to answer your question, if you simply must spend money on an unneeded piece of equipment, a regulator sold for Lipos will work just fine with LiFe's too. A switching regulator is just a switch that goes on and off really fast to create a lower average voltage. It doesn't care what the battery chemistry is that supplies its power as long as it doesn't exceed the maximum voltage.

As for your servo, was this a new servo or new plane? Was there any chance it was binding which would make it overheat? Had you noticed any issues with it at all before this happened?

KW_Counter

Voltage regulators don't care where the voltage comes from, it just regulates it.
A switching regulator is best as it doesn't waste the unneeded voltage.

Regulating a LiFe is not a bad idea:
The higher the voltage you use the more current you draw and less time between recharges.
Dropping it to 5V will give you more flying time and less chance of burning up a servo.

However, you have now added an extra device into the mix which means more places for something to go wrong.

You need to decide what is more important to you and what makes the most sense for your application.

Good Luck,
KW_Counter

Edwin

My Feedback: (2)

I use the MPI regulators in my life battery setups, $20/ea. I swap the connectors and use it on a single servo. I use JR791 retract servos in some of my H9 warbirds. The 791 only works on 5.2v or less. Everything else runs off the 6.6v levels.
Edwin

jester_s1

It doesn't change a thing about your chances of burning up a servo at all. If your servos are designed for a 6v NiCd, they are designed to run on the same voltage as a LiFe pack.

jetmech05

As stated a voltage regulator doesn't care where the voltage comes from. If it were me I'd run one it'll keep a good relative constant voltage to your system.

Jetdesign

My Feedback: (8)

I know a lot of people use unregulated LiFe batteries but I've also read about servo issues at max charge. Then again, I think I read the same thing about servos with a fully charged 6 cell nickle battery. No problem running a regulator if that's what you choose to do. I use (two) regulated lipos because it still comes out lighter in weight and I get consistent servo speed and power from the beginning to the end of the day.

jester_s1

The "LiFe hurts your servos" story is about the closest thing we have in RC to an urban myth. I put it right there with fretting over what kind of oil your commercial glow fuel manufacturer uses and Spektrum being a manufacturer of quality products.

But there was a time when I wondered myself too, so I spent a few minutes with a Fluke multimeter and got some answers. A good NiCd hot off the charger plugged straight into my meter gave me 7.1v. Hooked up into the system ready to fly it dropped to 7v, but that could have also been from the little bit of time between the two measurements. It could have also been a difference in how I plugged it in for all I know, but I don't fret about 1/10 of a volt. So 7v is what the system sees and is designed to work with. And, of course, manufacturers build some headroom into that because if you want an electronic component to last you don't design it to run right at the ragged edge of burning up. I went ahead and put a little load on the system by putting moderate pressure on a servo, much like one would see in a big loop. That dropped me to 6.8v which returned to 7v when I released the pressure.
So then I did the same tests with a hot off the charger LiFe. It was Hyperion brand for those who want details. The battery gave me 7.2v plugged straight in, and still 7.2v in the airplane. the loaded test drew it to 7.1v and change.
So the worst case scenario is that your system will see 3/10 of a volt more power than it should under load. This 3/10 of a volt is still less than the system was designed to see from a hot off the charger NiCd. For the mathematically disinclined, 3/10 of a volt is about a 4% difference. It doesn't matter. The only time the system sees more voltage than it was designed for is at rest, when the difference drops to a tick under 3%. That doesn't matter either. If your servos and receiver can handle a 6v NiCd, they can handle a 2 cell LiFe.

jetmech05

What jester said is true.....all a regulator will due is keep voltage lower and a tad bit more constant

Boomerang1

Short answer (not reasons why you don't need one) is yes.

Had the situation where I forgot to take my two 4 cell NiMh battery packs to a jet fly-in.

The closest batteries available from trade vendors at the meet was 2 cell LiFe batteries & a friend bought
two for his helicopter which he lent me for the weekend.

Some of the older servos in my jet weren't happy with the higher voltage of the LiFe batteries so I bought two
Powerbox Digiswitches which have selectable battery types in the menu including LiFe.

Regulated output is 5.9 volts.

John.

http://www.powerbox-systems.com/prod...igiswitch.html

KW_Counter

Jester,

There is not a thing wrong with your testing and conclusion.
However, you are placing a lot of confidence in the headroom built into the servo by the manufacturer.
And, you did not test that headroom.
Additionally, since it is headroom, it is apt to vary from manufacturer to manufacturer and from batch to batch.
Many people have had trouble with servos on five cell Nixx packs as well as 2 cell LiFes, many people have not.

It is a personal preference if you regulate or not, there are pros and cons to both.

KW_Counter

aspeed

Not that it applies to most of the readers here, but there is a step up regulator from H___king more for smaller electric planes that will go from 3.?? volts to 5 or so. So a single cell LiFe or LiPo could be used for that. It will not run a larger servo though, but does save some weight.

jester_s1

KW_Counter- Point taken, I didn't do extensive testing to see if my servos' life span would be shortened by the extra .2 volt that the LiFe battery provides in real world use. I've heard of people having trouble using 5 cell NiCds with servos rated for 4.8v only, which is to be expected since they aren't made to use that much voltage. But I've never seen a thread or heard of someone who found that servos rated for 6v NiCd batteries wouldn't work with 6v NiCd batteries. If that has happened and been verified to be the actual issue, that would be a new one on me.

chip_MG

My Feedback: (14)

Flyboy,
Funny here that most of the reply's the guys don't know anything about electronics or batteries for that matter..
The simples thing to do would be to put a diode or two in series with the positive lead of your battery pack forward biased. Choose a large one like an 1N5400 it can pass lots of current. A silicone diode will drop .7volts each so your 6.6V becomes 5.9V If you use two you'd drop 1.4V or 5.2 V. Only thing is you'll have to go to radio shack to get them plus make up the harness yourself. I have never seem this offered as a option in the hobby stores. But would do the trick, and be very reliable as diodes are simple components.

acerc

Here ya go.
http://pages.suddenlink.net/arlyn/rcvotagedrop.html

radfordc

My Feedback: (14)

Some servos won't work with more than 5 volts. My JR retract servos must have 5v or less or they just stop working. On my new TF P-51 I use LiFe batteries for the Rx and all the other servos. I use a regulator in the lead going to the retracts.

WILDCRASHWILLY

For what it's worth... i have been running A123s for two years unregulated with no issues. All my servos and rxs are Hitec. I'm not sure but I think most Futaba radios are simular and can handel these batteries as well. That being said, I would verify with Futaba or a Futaba user. I know there are some at our club that run them with no issues.

WILDCRASHWILLY

Flyboy, I was just thinking.... dangerous for me... what was the servo that burnt up? It seems like the little hs81s that some people have used as throttle servos may only be rated 5 volts but again, I'm not sure as i havent used any of those in several years except on a trainer i have which is still on 4.8 and 72 fm. Who knows every once in a while a servo will just breakdown, short and give up the magic smoke.