Running a DS615 servo on higher than spec voltage

[Thestructured]

I'm trying to come up with a good power setup for my 700N.

Since It came to me with a dead throttle servo, I've replaced it with a spare DS615 I found in my parts bin. The problem is, the heli was set up with HV servos (7.4v, NOT 8.4v), and the DS615 is not HV.

I have an align step down regulator, and ordered some LiFe rx packs. Even running a LiFe pack and the 0.7v step down on the DS615, it's going to get around 6.7 volts on a full pack at 7.4v. I don't want to kill the servo, especially since it's running the throttle.

I've heard of people running DS610's and 615's on higher than the 6v they're rated for, but I don't know if it's worth the risk.

The other option is to take the BEC off of one of my other heli's where it's not really necessary and put it on the 700N. I was thinking if I can regulate the voltage down to 6.7v then everything should work, the drawback would be stuffing more things and wiring into the heli.

[HarryTheCaptain]

Mine runs fine on 2s

[Thestructured]

2s as in 8.4v/7.4n standard 2s, or a LiFe 2s 7.4v/6.6n rx pack?

[jharkin]

You will be fine using the lipo and a step down.

The voltage ratings on servos are nominal ratings based on battery types, they are not hard limits.

• 4.8v servos are rated for 4 cell NiCD/NiMH. These packs could be up to 6.0v at full charge and the servo will take it.
• 6.0v servos are rated for 5 cell NiCD/NIMH. These packs could be up to 7.2v at full charge and the servo will take it. 2S LIFE also falls within the voltage spec of a 6.0 ovlt servo.
• 7.4v servos are rated for 2S Lipo. These packs could be up to 8.4v at full charge and the servo will take it.

[Number]

Originally Posted by HarryTheCaptain

Mine runs fine on 2s

+1
I run my DS615 in my 600 on 8.4v BEC, works well and do not run more warm than on 6v, just faster..

[Atomic Skull]

Originally Posted by Thestructured

Since It came to me with a dead throttle servo, I've replaced it with a spare DS615 I found in my parts bin. The problem is, the heli was set up with HV servos (7.4v, NOT 8.4v), and the DS615 is not HV.

All HV servos have to be able to take 8.4v btw because that is the fully charged voltage of a 2S lipo.

Originally Posted by jharkin

• 6.0v servos are rated for 5 cell NiCD/NIMH. These packs could be up to 7.2v at full charge and the servo will take it. 2S LIFE also falls within the voltage spec of a 6.0 ovlt servo.

NiMH can actually go to 7.4v (1.5v per cell) but that is pushing the limit and most chargers will stop at around 1.4v to1.45v per cell.

A fully charged LiFe is 7.2v fully charged with a nominal voltage of 6.6v so performance will be slightly better than with an NiMH which has a nominal voltage of 6v.

[Thestructured]

Well that's good to know. So why do older HV servos give specs for 6v and 7.4v but not 8.4? While newer, or high end HV servos give specs for all three?

[Yfbb]

Originally Posted by Thestructured

Well that's good to know. So why do older HV servos give specs for 6v and 7.4v but not 8.4? While newer, or high end HV servos give specs for all three?

Manufacturer preference. The design requirement for them is to work with a 2s lipo, so they can survive at 8.4, but in use, that spec is kind of irrelevant because the lipo voltage drops immediately after it is plugged in.

[cyclenut]

I run all my helis larger than 550 on life packs and all are ds610/615 for cyclics. All work fine. I usually charge the life packs before heading out to the field, so the voltage drops a bit from when they are straight off the charger.

[Atomic Skull]

I recommend something like this if you are using a receiver pack:



I use these ones:

http://hobbyking.com/hobbyking/store...e_Battery.html

They're cheap as beans and work great. I cover the whole thing with 24mm transparent PVC heat shrink tubing to protect it. (if you take off the double back tape then I would put a blob of hot glue on the wires where they are soldered to the board first)

PVC is more conformal than polyolefin and won't crush the item and it sets hard like blister pack materiel. It's the same stuff they use to cover battery packs and it's also what the Hobbywing RPM sensor is covered with. Before shrinking it's thinner and feels "crispy", basically it's softer than polyolefin when heated but harder when cool.

[rhodesengr]

2S LiFe is 7.2V coming off the charger but they spend essentially zero time at that voltage. As soon as you draw any load at all, they drop to around 6.6 and stay there until near the end of their capacity. Their discharge curve is very different than a LiPo which drops linearly from full charge. You can google "LiFe discharge curve" and see what I mean.

With 2S LiFe, I would not bother with a diode voltage dropper. Lots of guys, including me, run Ds615 and other 6V servos directly from 2S LiFe.

[Number]

Originally Posted by Atomic Skull

I recommend something like this if you are using a receiver pack:



I use these ones:

http://hobbyking.com/hobbyking/store...e_Battery.html

They're cheap as beans and work great. I cover the whole thing with 24mm transparent PVC heat shrink tubing to protect it. (if you take off the double back tape then I would put a blob of hot glue on the wires where they are soldered to the board first)

PVC is more conformal than polyolefin and won't crush the item and it sets hard like blister pack materiel. It's the same stuff they use to cover battery packs and it's also what the Hobbywing RPM sensor is covered with. Before shrinking it's thinner and feels "crispy", basically it's softer than polyolefin when heated but harder when cool.

also here's one in the usa
http://www.ebay.com/itm/Blue-DC-0-30...8AAOSweW5VD07j
but does not have a receiver plug, so u would need to solder one

[getsuyoubi]

Can those "5.1 volts" step down regulators used at, say, 7 volts input to get 6.1 volts for the tail servo, or are they not rated at more than 6 volts input?

[rhodesengr]

Originally Posted by getsuyoubi

Can those "5.1 volts" step down regulators used at, say, 7 volts input to get 6.1 volts for the tail servo, or are they not rated at more than 6 volts input?

well it depends on whether it is a true regulator or just a simple diode.
Most of them are just something like a 1N4001 diode. Most any silicon diode drops about .7 volts when forward biased. So they work on current and not the applied voltage. So the simple answer is yes, they will drop 7.0 volts to about 6.3 volts. The problem is at very low current they don't drop the full .7 volts.

Again, most any 6V servo like DS615 will work fine at the 6.5 volts they get from a 2S LiFe. I'd not bother putting a diode in there.

[Yfbb]

Running a servo at a higher voltage will cause it to wear faster, even if it is spec'ed for that voltage, but there are plenty of other pretty normal things things can make servos wear faster. Application is one of them. Using a 6v tail servo at 7.4v on a 550 may be wearing it less than the same servo at 6v on a 700 just due to the vastly increased loading. Throttle probably isn't the most demanding thing for a servo that can do 700 cyclics, so as long as the servo stays cool, I wouldn't even worry about it at all.

[jharkin]

Originally Posted by Atomic Skull

NiMH can actually go to 7.4v (1.5v per cell) but that is pushing the limit and most chargers will stop at around 1.4v to1.45v per cell.

A fully charged LiFe is 7.2v fully charged with a nominal voltage of 6.6v so performance will be slightly better than with an NiMH which has a nominal voltage of 6v.

Ya got me... it was a typo. Ive been all LiFE for so long its mostly what I think about. I remember when I ran NiMH they would be 7.4 or even 7.5 hot off the charger but once they rest the surface charge burns off so fast that by the time you even get to the field they are down to 7 or so... effectively you are mostly running them in the low to mid 6s under load.

Similarly LiFE come off the charger at 7.2 but almost immediately drop to 6.6 or so under load and stay there since the discharge curve is so flat.

Originally Posted by rhodesengr

well it depends on whether it is a true regulator or just a simple diode.
Most of them are just something like a 1N4001 diode. Most any silicon diode drops about .7 volts when forward biased. So they work on current and not the applied voltage. So the simple answer is yes, they will drop 7.0 volts to about 6.3 volts. The problem is at very low current they don't drop the full .7 volts.

Again, most any 6V servo like DS615 will work fine at the 6.5 volts they get from a 2S LiFe. I'd not bother putting a diode in there.

Agreed, Im pretty sure you are right that Align job just like the Futaba 5v step down are diodes. I was confused and thought he wanted to use a step down with a Lipo, definately not needed on LiFE.

Originally Posted by Yfbb

Running a servo at a higher voltage will cause it to wear faster, even if it is spec'ed for that voltage, but there are plenty of other pretty normal things things can make servos wear faster.

Running a higher voltage thats within the spec range should not make a noticable impact on lifepan we would notice, unless you are forcing things to run hot. An if its running hot while still in spec voltage range its either a poorly designed servo or more likely its being overloaded (either because you need a higher torque or something binding).

I know people with literally thousands of flights on "6 volt" servos running on 6.9v regulators with no problems whatsoever, and many get away with running servos over spec even. In fact I have a bunch of Futaba 3115s, which are rated for 4.8, running overspec on 6.6v life in airplanes and never had an issue in many years of using them this way.

[ddhuans]

Why running a higher voltage to risk your heli like that? A repair cost for single crash of a T700N can buy you a good TORQ or BK HV servo set.
If you dont want to use BEC, so 2S LiFe is the best choice in this case.

[Thestructured]

I'm going to be running a LiFe rx pack with a step down regulator on the DS615 servo, so it should be fine. Once the initial voltage dies, the DS615 should actually be running at around exactly 6v.

[Pard]

Originally Posted by ddhuans

Why running a higher voltage to risk your heli like that? A repair cost for single crash of a T700N can buy you a good TORQ or BK HV servo set.
If you dont want to use BEC, so 2S LiFe is the best choice in this case.

+1

I have had servo failures due to running at higher than rated voltages. The components in a HV servo are not the same as in a servo rated for max 6V. The initial voltage above 6V is enough to cause catastrophic failure.

You are operating outside the envelope where the demons live.

[jharkin]

Originally Posted by Thestructured

I'm going to be running a LiFe rx pack with a step down regulator on the DS615 servo, so it should be fine. Once the initial voltage dies, the DS615 should actually be running at around exactly 6v.

The point we are trying to convey is that LiFE is within spec for a 615. No step down needed.