OhD

I should have said it is charged during flight if and when the voltage drops below 8.2 volts. At 8.2, no current flows so the pack can never go above 8.2. One cell would have to be below 4.0 for the other to go above 4.2 and into overcharge. If the pack is that unbalanced you better toss it anyway.

Jim O

OhD

Yeah, I do that today (2S lines connected directly) using a PowerSafe Receiver with two lipo inputs. But I agree with others that you really want a regulated voltage so that the servos perform the same before, during and after flight even as the main pack is getting heavily used by the motor. I've wanted to go regulated HV for about a year but haven't found a weight efficient way to do it, was hoping the Jaccio to 8.2v + 3S balance tap would be the answer for the secondary side of my Rx (with the Rx bat on a reg set to something like 8.1v) so that the normal circumstance is pulling from the main pack and the Rx battery is just a backup.

Peter+
[/quote]

Peter, have you got any data that shows what your back up pack is doing? It would seem to me that without isolation you would be draining the small lipo every time you pulled high current in your motor. I know my pack drops to about 35 volts under high loads late in flight, and that says the voltage would be 7.0 volts at the 2s tap. If your small lipo is over two volts current will flow from it into the motor circuit draining the back up. Not good.

Or does a "PowerSafe Receiver" provide the isolation?

Jim O

nonstoprc

My Feedback: (90)

This requires a careful monitoring of the backup pack to make sure the two cells are balanced "almost" during charging phase. A high quality lipo probably can present the characteristics but it may not be a good idea to trust the backup pack to be that 100% ideal state all the time.

Another thing we need to be careful is the charging current limit (e.g. 1c, or 5c).

pvogel

Peter, have you got any data that shows what your back up pack is doing? It would seem to me that without isolation you would be draining the small lipo every time you pulled high current in your motor. I know my pack drops to about 35 volts under high loads late in flight, and that says the voltage would be 7.0 volts at the 2s tap. If your small lipo is over two volts current will flow from it into the motor circuit draining the back up. Not good.

Or does a ''PowerSafe Receiver'' provide the isolation?

Jim O
[/quote]

The powersafe receiver has two power inputs and isolates the two, whichever has higher voltage at any given time will be used, there are blue LEDs showing which of the two power connections is in use at any given time, you can actually see it switch from the balance tap connector to the 2S lipo as the throttle is taken to near full and the voltage drops under load on the main battery and vice-versa. Typically by the end of a flight the 2S battery is in use full-time, I typically change the pack out (450mAh pack) every 3-4 flights. I like the idea of the backup being charged by the main battery when appropriate...

Peter+

OhD

That makes sense. Without the isolation you'd be draining the 2s much faster. How much does the voltage drop across the PowerSafe receiver? Apparently not enough to affect servo performance?

Jim O

pvogel

I have not seen a significant voltage drop due to the isolation circuit, and 8.4v Lipo fully charged is delivering about 8.2v to the servo power bus.

Peter+

vbortone

My Feedback: (2)

Question. I am going to use HV servos next season and I am not planing to use regulator. Can we really feel the diference when voltage drops probably less than 1 volt in the whole practice section?

rm

My Feedback: (27)

There's the $100 question. If your answer is yes, it doesn't make any sense in investing in HV servos.

nonstoprc

My Feedback: (90)

+.

I am hoping that HV servos can be built lighter and delieve at least the same torque as those "low voltage" ones.

Flyer88

The brushless HV servos I just got for my Sbach are very light. It caught me off gaurd........ 1.9oz (no horns)

Comparable Futaba weighs 2.3oz

can773

My Feedback: (1)

Maybe, I could sure notice a difference going from a 5.6V regulator to 7V, mostly in the snaps though.

rm

My Feedback: (27)

What servos are guys finding that are lighter? Most of the HV servos are heavier that I've seen.

OhD

I'm using Futaba BLS171HVs on ailerons and rudder and JR DS3711s on elevators in place of JR8411s and JR3421s. The HVs weigh 1.7and 1.0 oz. respectively with output wheels. The non HVs weigh 1.9 and 0.9 oz. without output wheels.

Jim O

Flyer88

Oh that's an interesting weight I took their weights 2.3oz right off Futabas website.

Wow thats lite.......

rm

My Feedback: (27)

FWIW, below is the HV system I ran last year. The pos wires run outside the fuse and are connected by 2mm bullets when I'm ready to fly. Redundant and light with no switch or regs. Batts were 2 250mah 2S in parallel to the rx. The change in voltage didn't bother me at all.

can773

My Feedback: (1)

2.3 is for the higher torque ones with metal cases.

All the HV servos I am currently using (BLS 174, 171) are all under 2 oz (1.9 and 1.7 respectively).

I just weighed the servos for my new plane (two BLS174HV, two BLS153, one BLS175HV), total was 224g.

nonstoprc

My Feedback: (90)

By looking at the published specs on HV servos, I did not see a significant reduction in weight, comparing to the standarded pattern servos.

I was hoping that I can drop the regulator in a HV setup to save about 1oz.

What are the other advantages to go with HV servos, other than faster repond speed?

Flyer88

This is dual battery isolator for running two receiver batts.... weighs in at 23 grams (as is with all the wire) and could just go in between a couple 250mah 7.4v batteries direct. And it balances the packs by switching.

Why do we need a regulator...I'm running so many planes direct off 7.4 and never had a problem. More voltage..... less current.... happier HV servos

vbortone

My Feedback: (2)

If using JR servos you need to replace metal with nylon gears. That is a given since metal have too much slop for pattern. Agree that there is not need to use regulator. Looks like you save just the weight of the regulator. .

vbortone

My Feedback: (2)

I am using a RX that already has double redundant battery inputs. Check the picture.

Thomas B

My Feedback: (4)

Another redundant battery system that I recently started using is the new Scorpion Backup Guard:

http://www.scorpionsystem.com/files/...er%20Guide.pdf

It is a 2S 500 mah lipo with a little board on it that senses onboard voltage of the RX power system and does not allow currently to flow out od the 2s500 lipo until the board senses a drop to below 5v on the BEC or other RX power system. Once it sensse a voltage drop below 5v, the board them allows power to be used from the backup battery. Tested it in several ways and it works as advertised.

Unit is good for up to a 10amp draw. Very light at 38 grams.

Would be a very nice improvement if they included an LED (preferably on a long lead) that would indicate whether or not the unit turned itself on in flight, to alert you to RX power supply issues from the primary power system. Also would be nice to be able to get the unit without a battery built into it to use with other batteries.

Not too useful to the folks using HV servos, until another version comes out. One with selectable voltage output, variable battery voltage input and no built in battery would be great.

They are 24.99 each from Scorpion.

You cannot charge them through the RX power lead, due to the board in the pack. They must be charged through the balance plug.

Flyer88

Thats a very nice simple set-up.

Thats great, I like it !

Less is more for me.

OhD

Then you would really like a Jeti Mezon with a built in BEC set to 8 volts plugged into the receiver along with a small 2s LiPo. Redundancy, no single point failure, with a back up pack that is charged during flight. You don't even need to remember to charge it.

Jim O

Flyer88

Sounds like that's the way things are heading ??

This is great for Heli pilots as well as aircraft.

OhD

I asked Western Robotics what the tolerance was on the 8.4 volt output but never got an answer. Castle states that the CC BEC Pro should not be operated in parallel or connected to a receiver with another regulator or battery pack in parallel. I asked them if that applied to the CC BEC and they said yes. I bought one anyway and programmed it to 8.2 volts. So far on bench tests it seems to work just as expected with no problems. It keeps the small 2 cell LiPo charged to 8.2 volts just like my present system. It is very light and inexpensive and looks like a great way to get redundancy in a HV servo set up.

By the way I wasn't correct when I said there were no single point failures in this system. Obviously a short anywhere on the 8.2 volt bus takes out the whole system. Isolated sources would provide a little more safety.

Jim O