6.0V servos on LiFe packs - sure, maybe

[Steve P]

Okay, this is not intended to raise everyone's ire, but I know it will. At issue: These days many of us fly 4.8-6.0V servos on straight 6.6V LiFe packs.

I've been talking with some tech folks in our hobby. The general sense is what we're seeing as hobbyists -- 6.0V servos can and do work just fine over time on LiFe packs. Let's be clear on that point. However, the growing sense is that the excess voltage is degrading servo electronics more quickly. Techs are now seeing 6.0V servos returned all the time with bad motors and or amps due to running them on straight LiFe packs (no regulators as many of us use). These are not just some of the newer servos that might have lesser quality components/amps (Radim Horky is upset over the new Hitecs having these issues) but some of the older workhorse servo lines.

As with all things, your mileage may vary. One might never see any issue on occasionally, lightly-flown air frames or sport flying favorites. Others, working those controls long and hard, might lose some servos along the way. Thankfully, we now have HV and wide-voltage servos that are clearly the way to go at the moment on new projects.

For me, I am going to make one shift in my winter build plans. In restoring my old 7-meter Salto, it's loaded with all JR 8611 high torque servos that are working perfectly. But, they ain't no spring chickens, so I have decided not to replace the two existing big Ni-Cd packs with the planned LiFe packs. Instead I'll be going with two new 5-cell 3000 mAh NiMH packs from noBS. That's just me. You might disagree. That's cool. My other stuff will be living on LiFe and LiPo.

Asbestos ready, flame on.

[lenb]

lol.

Interesting and good points Steve.
Having seen exactly what you are talking about its hard to disagree with your assessment.
HOWEVER..... Flame thrower is always ready...

[BobM]

Excellent information and also very helpful to have the observations of the techs on servos they have been servicing.

The range of servos available combined with the range of batteries available continue to make it more complex to get the right pairing so to speak.

Choosing battery packs that are matched to the servos, as you have, works extremely well and is likely to be the most cost effective solution.

While it may be a bit more expensive I have found going the route of using a quality battery regulator to be very successful for keeping my servos from being driven by over voltage. The ones I have found to work very well typically allow the user to set the voltage output themselves. It gives me the ease of switching from one battery chemistry to another without having to worry about what the unregulated output is directly from the battery itself (as long as the output is at least what the regulated voltage is set for).

Bob

[Tom]

Going thru this right now! Both Mr. Wood and the Hemple Ka-6 need new batteries and both are set up with older high torque servos and electric spoilers on the K8.......neither of which “like” fully charged LiFe packs.......not wanting to add voltage regulators.....I went to my old standby www.cheapbatterypacks.com only to find that they are no longer in business! I found these on Horizon Hobby and ordered 4 of them..... https://www.horizonhobby.com/dyn1443

[gunny11]

older high torque servos ......neither of which “like” fully charged LiFe packs.......not wanting to add voltage regulators.....

I agree! On my older models I would plug in my load meter (1 amp) and strip the surface voltage off for 15 seconds. This always worked....
I worked for NoBS batteries and was the beta tester for his A123 LiFe packs in 2010.

[kjkavaney]

Really good points...STeve ...take care of my old Salto for me...miss her dearly actually...
I have been using Castle regulators for years for this reason with my NBs Lifes and have had zero issues...knock on wood of course..
kevin

[John Lueke]

With a lot of planes using long Servo leads has anyone actually measured the voltage at the Servo when using an unregulated Life pack? Traditional advice was to go to heavier gage Servo wire when using long leads to have less voltage drop. So maybe the voltage drop from using 22g wire puts the voltage at the Servo in a safe range.

[ARUP]

I have been using Spectrum VR5203 voltage regulators for my birds using LiFe receiver batteries since they all have lower voltage servos. No worries with 'fresh off the charger' peaks (I hope)!

[Tom]

The problem with that unit is it’s only 2amps......no where’s near enough “juice” flow for a large scale bird......
These are what I have in my Duo..... https://www.horizonhobby.com/vr6007-...--6v-spmvr6007 super nice but at $90 a pop.......and you need 2 for a powersafe receiver......it adds $180 to the build.....not a huge amount in the grand scheme of things but still a chunk of money.

[ARUP]

Tom- you are spot on! My sailplanes are pretty basic, not that large and don't require BIG amp draw since I just float 'em around. For the price of those regulators that I use I can dodge buying higher voltage servos. I did put 5000 mah NiMH packs (with higher voltage servos) in my ASW20, as recommended by Jeremy, (the Swiss cowboy!), because I need the nose weight anyway. I should be able to fly a long time without charging.

[Mark9]

Maybe I missed something, but many people have used and still do use 5 cell NiMh packs prior to LiFe becoming popular. The general consensus is that NiMh cells have a peak voltage of 1.45 V or greater. That would mean a 5 cell pack voltage after getting a full charge would be 7.25 V minimum. My LiFe, A123 cells, packs actually come off charge peaked at about 7.1 V and some of the bagged LiFe packs slightly less.

I would think the duty cycle, application and user environment is a much larger factor in the described servo failure profile than .15 V increase in input power. Still I would agree that adding a voltage regulator if one wishes would add an additional layer of safety protection for the servos. But, one should also consider the additional failure points of adding the regulator. As always everything in aviation is a compromise it seems.

[BobM]

While somewhat expensive I have found the PowerBox BaseLog units to be fantastic. They have dual regulators that are independent of each other, which is very helpful should either pack fail for any reason. Dual battery inputs that are then regulated to 5.9v or 7.4v dual battery output. I have used these on my larger sailplanes (my Duo Discus, Arcus, ASH-31, and Ventus) as I have 6v servos in these airframes. The peak current is 20 amps for each output. This allows me to use any matched pair of battery packs (which must be identical battery packs in terms of chemistry, # of cells, capacity, and voltage output) and know I have a regulated output to my receivers and servos.

I have been using dual Duralite lithium ion packs that are 5200 mAh capacity with a voltage output of 7.4v on all of these sailplanes, regulated by the BaseLog to 5.9V on each output. This gives an effective capacity of 10,400 mAh for the sailplane. Should one of the batteries discharge or fail for any reason it is backed up by the other battery.

While the cost for these units is somewhat high (about $185 each), it offers very good assurance of the voltage output and enough current ability to my receivers and servos as well as allowing digital readout of battery usage on the display. In light of the cost of the sailplanes, the electronics installed, and most importantly safety concerns it seems to me to be a very reasonable investment for the power system to the electronic control system of the sailplanes.