finewayne

my question too, anyone knows?

Truckracer

My Feedback: (19)

See responses above. 2.5 v/cell is used by some companies and is common but I've seen a range from 2.0 v/cell up to 2.6 v/cell. 2.5 v/cell is certainly a safe and conservative cutoff voltage or 5 volts for a common 2 cell pack.

All Day Dan

My Feedback: (5)

Here’s a clear plot of the discharge voltage of a LiFe battery under different loads. You can see that with a one amp load the voltage is already in a steep decline at three volts. If you are using a cut off voltage to determine the capacity of a LiFe pack for R/C flying it appears that three volts is the absolute lowest with no margin of safety and that something higher would be safer. Dan.

Truckracer

My Feedback: (19)

When recommending cutoff voltages, the values I suggested were for testing purposes, not in service values.

You can see from the curves why I said the cutoff voltage wasn't that critical for measuring purposes. When the discharge gets to that part of the graph, the voltage drops so fast the actual cutoff voltage isn't at all critical. Whatever the selected value, it doesn't stay there very long.

All Day Dan

My Feedback: (5)

Truck, with the wonders of modern electronics I have added .1 volt lines from 3.0 to 3.5 volts. As you can see, below 3.2 volts leaves some margin of safety before the cell voltage completely collapses. That also results in a cell capacity of around 1750 mah which is much lower than the stated value of 2500mah. Now I know why so many guys have dual packs on board. They need them. Dan.

Truckracer

My Feedback: (19)

Dan, is that a curve you compiled or the one that has been floating around online for a number of years? I ask because in my tests, the curves are similar but the values are a bit different resulting in greater capacity. One thing is certain and a reason some people don't like LiFe chemistry batteries .... voltage is not a good indicator of remaining capacity. In addition, A123 maintains capacity much better at high discharge rates than any Nixx based battery I have ever used as noted by the 4 curves being almost parallel regardless of discharge rate. A Nixx based battery would fall on its face at the higher discharge rates.

All Day Dan

My Feedback: (5)

Truck, I found that plot on several websites. The one I used had the best resolution. I added the .1 volt lines using a cad program. I can not verify its accuracy. I tried the A123 site and I don't remember what I found. You're right about the lack of voltage significance. It scares me along with that precipitous drop. Dan.

Truckracer

My Feedback: (19)

Yes it does drop off quickly. Kinda like stepping off a cliff! But that curve is oh so flat. I never use more than 2/3 capacity and feel I have good reserves. Most days I use less than half capacity.

jwrich

My Feedback: (17)

First, let me say I am dumb as dirt when it come to electronics, no matter who tries to explain it to me. It is like I have a mental block understanding how it all works. I have been flying RC since 1976. I always said keep it simple, what is the number I see when I need to recharge.

I think you guys have answered my question that has nagged me since I began using LiFe batteries. Over the last 3 years I have now changed all my planes to LiFe batteries, 2 batteries, 2 switches. going into 2 receiver ports per plane. In the past I used my digital voltmeter to check my nicd or nmh batteries. When they dropped below 4.3 (4.8) or 5.6 (6v) I would quick charge them or go home.

I like the fact that I can leave the LiFe batteries the plane to charge them and not worry about a fire. They seem to be the next improvement in RC battery. So I check them with the digital volt meter, but I have alway questioned myself what is the drop in voltage before recharge. In my planes I have, LiFe batteries 6.6 volt with a range of 1700 mAh to 2500 mAh, 2 in each plane, both batteries the same mAh. I always begin my fights with a full charged batteries. I have 6 (1/4 scale) planes I fly regularly.

Now the question. When I check the battery with my volt meter, what is the number I see the for a unsafe condition and a need to recharge?

Thanks for your help and advice.
Rich

GR7Racer

I've been using LiFe packs for quite a few years now (typically Spektrum LiFe packs, but also a few NoBS packs). I actually like the "flat" discharge curve as it delivers a consistent voltage to the receiver and servos. Servo power and speed doesn't change much from "fully charged" to "ready to charge" status on the battery. Contrary to what many people believe, the discharge curve really isn't flat and you can use voltage readings to check the status of your LiFe packs. You just need to understand that you are looking for very small voltage changes in the 1/100 of a volt range. A Lipo pack will range from 4.20 volts per cell when fully charged down to 3.70 volts where it should be charged again. A LiFe pack will range from about 3.60 volts per cell fully charged down to 3.00 volts/cell where it falls off the cliff. The LiFe pack will actually fall off quickly from the 3.60 V/cell to about 3.35 V/cell and then slowly drop from there. At 3.30 V/cell you will have roughly 50-60% of your capacity left in the battery, and that is where I recharge. You can get battery voltage checkers that will connect to the balance plug on a LiFe pack that will display individual cell readings down to the 1/100th of a volt (3.30 vs 3.3) from Horizon Hobby (Dynamite, Eflite) and Electro Dynamics. I fly until either of the cells drops below 3.30 volts (no load) and then I recharge. I'm well clear of the drop off "cliff" at that point and for a typical 2200 mah LiFe pack I will put about 800-900mah back into the pack to get them to fully charged status.

One of the other great advantages of LiFe packs is that you can quick charge them inside the airplane as their chemistry is much more safe than Lipos... so when in doubt, just charge!

KennyMac

All Day Dan

My Feedback: (5)

Rich and Kenny, go to the nobs site for all the information you need about the LiFe battery packs. He also has a nice and accurate voltmeter to monitor them at the field. Dan.

GR7Racer

Yes, I've been visiting the Hangtimes/No BS site and Red's battery clinic site for many years. Much of what I have learned about LiFe packs comes from the NoBS site. The tester and procedures that he recommends are pretty much how I have operated with great success.


KennyMac

jwrich

My Feedback: (17)

Thanks Guys, I will check out the Hangtime/NO BS sites. I will read what they have to say, I just hope I can understand it.

Rich

secret_squirrel

So....to throw a wrench into the equation. Telemetry....

I am with you all the way on the charge/no charge scenario without a load.

I have telemetry in one of my radios and set the warning indicator to kick me in the butt when the on board voltage drops below 5.0 volts for more than a second. It really is just a fail safe and something I have been experimenting with. Riddle me this, where should i look if a newly charged A123 pack is giving me a low battery alert with this setup straight out of the shoot. Happened to me last weekend. Plane landed fine, no issues.

Thanks,
Dan

All Day Dan

My Feedback: (5)

Dan, thanks for that input. I don’t use telemetry so I can not comment on its accuracy or value. If it was up to me I would prefer to make the measurements on the ground instead of finding out when I’m flying that the pack voltage is collapsing. Just to change the subject a little, did all you LiFe users switch to high voltage servos and receivers? Any one using a regulator? Dan.

Truckracer

My Feedback: (19)

You didn't say what you are using for power connections, wiring and switches between the battery and the receiver. Most likely, your wiring / switches are not up to the task causing momentary low voltage at the receiver under load triggering your telemetry alert. I know when I got my first telemetry radio some years ago, I was shocked to see how inadequate my wiring and batteries were and I thought I had covered all the bases in this area some years earlier. Not so. Problems were resolved and the voltage became very stable.

Let us know what you are using for wiring - switches, what servos you are using and how many and what battery you are using. Maybe we can help resolve the problem.

Truckracer

My Feedback: (19)

Hi Dan,

I know we've visited about this issue before but maybe we can reopen the discussion. I use A123 batteries almost exclusively with no regulators (I hate regulators) and in a fleet of well over 125 servos, maybe 6 are HV rated. The servos vary from low cost, standard servos on through expensive TI geared, coreless and even brushless servos. The vast majority are rated for 6V operation by the mfgr. which in industry terms means they are rated for use with 5 cell Nixx battery systems. Considering the normal working voltage of a 5 cell Nixx battery is extremely close to that of a LiFe battery, the rating sort of grandfathers in LiFe operation even if not specifically stated. I've never had any kind of servo problem that was voltage related and in fact, servo problems are rare.

Certainly some servos are rated for 4.8V only, or 4 cell Nixx so these servos should not be used at higher voltages. But unless the servos in question are really old, most anything produced in the last 10 years or so carry a voltage rating. Yes there is also the receiver component but I don't know of a 2.4 GHz receiver that will not work at LiFe voltages and the vast majority are approved for LiPo voltages.

Dan, like you I research things to excess and perhaps worry about things not worth worrying about. When I changed to LiFe batteries some years ago, I did my research and visited with all the companies that I had servos from. Only one expressed concern about using their 6V servos with LiFe batteries and that was MKS. Since then they have a line of servos labeled for LiFe use along with their HV line. The industry doesn't consider LiFe voltages to be HV. At the time of my switch, I only had a handful of servos that were rated at 4.8V only and these were either retired or used in non critical applications with a diode in the (+) lead to drop the voltage.

Not sure if I helped or not but maybe a bit more food for thought.

All Day Dan

My Feedback: (5)

Thanks Truck, your inputs are always informative and much appreciated. How about someone else describing their experience with the LiFe batteries. One of my my flying buddies switched over to the Nobs 2500s and changed all his servos on the control surfaces to HV JRs. He is a mild 50cc 20 pound type of flier like me. His current consumption is so high he has to carry two of the battery packs and is smart enough to monitor the individual cell voltages. Charging at the field is necessary to get in more than a few flights. Dan.

Truckracer

My Feedback: (19)

Dang, that is some high power consumption. Those servos must be way over rated for that size airframe.

My typical consumption for a 10 minute flight on a 55 cc Extra with lots of stick banging, including (4) 300 oz. in coreless servos on Ail and Elev, (1) 400 oz. in on the rudder and (2) smaller torque servos on Thr. and choke plus Ignition power through a Tech Aero IBEC all runs between 280 and 350 MAh, per flight. I usually fly 4 or 5 flights per plane and barely use 2/3 of a single battery's capacity. I usually have (2) batteries on board and could easily fly 10+ flights with reserves to spare. One 61 powered YAK only has a single 2500 battery and I never get close to using over 2/3 of the battery capacity.

On another example, I flew a 1/4 CUB yesterday (3) very aggressive flights (not CUB like at all). That plane has (6) 100 oz. in coreless servos (that are all moving most of the time) plus the IBEC and I didn't use 200 MAh per flight which is typical for that airplane.

Modern brushless servos use quite a bit less power for the same amount of torque than their coreless counterparts. I wonder what your friend's servos are that is causing so much current drain. I never recharge at the field but always check consumption when charging at home.

karolh

About 2 years ago I switched to using Life 1200 - 1500 mA batteries exclusively in my models which are gas powered and in the 70" span range. The models are outfitted with a mixture of budget priced analog and digital servos rated at 6.0v and not exceeding 90 oz of torque and so far I have experienced no problems. As expected the current draw is very low and this arrangement gives me enough power for a full day's flying of 5 or 6 10 - 12 minutes flights with more than 50% battery power remaining. I still use 4.8 v Nicads or NiMH to power the ignitions.

bobbucko

If I use a LIFE battery in one of my new Futaba transmitters and forget to turn it off and put it in my case and run it all he way down will it kill it like a lipo.
Bob

karolh

Possibly eight times out of ten it will kill it. The other two times you might be able to revive it but it's health would always be in question. My suggestion would be to replace any Life battery once it runs down until it's dead flat.

bobbucko

Thanks That was what I thought might happen but do not have much experience with LIFEs

karolh

It took me awhile to switch from using Nicad and Nimh batteries to Life chemistry battery packs both in my Tx and for Rx and servo power and I am glad that I made the change. They have a much longer shelf life than Nicads and Nimh and can be charged in minutes and are not the fire hazard that Lipos can be.

pilotpete2

Which Futaba transmitter?
My trusty old 8FG shuts down when the battery voltage drops to 5.5V according to the manual. So 5.5V should not damage a 2S LiFe. Modern transmitters usually have a cut off that does a proper shutdown before the battery dies. this is to protect the flash memory. The original DX7 was notorious for going brain dead if the battery was allowed to die. the message "Backup Err", meant a trip back to HH
Pete