2Sunny

I brought this up a few months ago and there were lots of ideas and concerns. Today was a rainy day with some free time so I did some experimenting with parts I had on hand. I put the setup shown below together on the bench with a rx and 6 servos. Amazingly, I found it did exactly what I have been wanting and I've had these parts at home all along. The key being both the BEC and the regulator were designed to be run in parallel with another BEC/regulator so by simply off-setting the voltage between the BEC and the regulator by .1 volts it caused the higher set BEC to be primary while the secondary regulated Lipo unit never showed any current draw until I unplugged the BEC's battery pack to simulate a failure. Even though I wasn't able to simulate a draw large enough on the bench to overwhelm the BEC, the regulated Lipo should kick in the moment the BEC falls below 5.9 volts if it is over taxed, so that means this setup is good for 5 amps even though the BEC is only rated to 2.5 amps, but as the vast majority of F3A work is done at a draw much less than 2 amps this should rarely happen and never meaningfully drain the battery. Obviously there is no internal monitor for the backup battery, so one should check the voltage before each flight. I have already put this in my Delro and will be sure to give an ongoing report during the coming season. I have several servo current sensors that I intend to put in series with the BEC and the regulator so I can keep track of what's going on for the first several dozen flights. The best part is that with a 250 mAh battery rated for 10 amps this setup weighs 49g which is less than the weight of most rx batteries+regulator setups in use today, and no the BEC can not charge the Lipo as Ed's regulator design is top notch and includes a blocking diode so current doesn't flow backwards through the regulator.




To copy this setup you'll need:

[link=http://www.dimensionengineering.com/VHVBEC.htm]Dimension Engineering VHVBEC[/link]

[link=http://www.tech-aero.net/plr5-e]Tech-Aero PLR5-E[/link]

[link=http://www.hobby-lobby.com/pro_lite_v2_2_cell_250_mah_7.4v_20c_lipoly_w_jst_c onnector_323357_prd1.htm]250 mAh 7.4 volt Thunder Power Pro Lite V2[/link]










Cheers!



Joe

KeithB

My Feedback: (1)

2Sunny

Keith,

I'm a little surprised myself, as I would think a redundant power supply for the rx plus the ability to eliminate the need for rx battery recharging would be attracting a lot more interest, but none the less, I am excited to get this out and fly tomorrow. Been rainy last couple of days so lots of tinkering in the basement, but no flying yet. Also of some minor interest, prior to making this change my plane weighed exactly 3720g (minus main batteries, but with the rx battery installed) and now with a BEC and a 250 mAh rx battery the plane weighs 3721g. Go figure!


Its not like I'm worried about weight in this plane so actually I'm thinking of taking this setup one step further by paralleling two BECs as extra-extra insurance. If I join their outputs through a y connection into the same rx power input, I'll have 5 amps of power on both the primary and the secondary power source plus if one BEC failed the second should be capable of handling the job all by its lonesome. I'd really love to find a small electrical board and put it all on that so I could make it "look" tidy. Guess I'll have to do some Radio Shack shopping



Joe

cmoulder

Joe, I think I will use the CC pro and a Tech-Aero on the next install. I have the CC program link and Ed's programming box so I am set to go.

OhD

Here is my plan for my next plane. All high voltage servos. Tap the low end 5S at the 3S pin on the balance connector and feed it to a Jaccio Perfect Switch Harness/regulator set to 8.2 volts. This is connected to the receiver. Connect a small 2S LiPo directly to the receiver through a conventional switch that allows current to flow in both directions. The system essentially runs off the motor power pack. This also keeps the small LiPo charged to 8.2 volts. The small LiPo, in addition to being a backup also serves as a large capacitor to keep the voltage constant. What do you think?

Jim O

Don McCullough

My Feedback: (1)

Bob, I have thought of doing similar dual BEC setups. However, I note on the description page of Castle Creations for the BEC/BEC Pro they have the following warning:

NOTE: CC BEC Pro should never be operated in series or parallel with another BEC or backup receiver pack connected to the RX/Servo side of the circuit.

Any idea what the real-life limitations are for dual switching BECs or a switching BEC with battery backup?

Don

cmoulder

Jim, I think you know far more than I do, so I will just stick with the tried-and-true dual regs and Rx batteries.[&o]

Sometimes I know just enough to get myself into trouble.

Don, I had not seen that warning from CC. Thanks.

nonstoprc

My Feedback: (90)

I would go with double lipo RX battery and double regulator route, if I want on-board electronics super safe. The extra weight is about 1.2oz: 250ma TP lite Pro is 0.6oz, and the smartfly regulator is 0.6oz.

Si-F3a

Double RX battery and regulator. Does this require 2 switches as well. Considering puting redundant systems in my planes, wonder if you could give more details (photos) of the components and install.

Thanks
Simon

Portlandflyer

cmoulder

Actually, you don't need any switches if you plug the batteries into the regs before each flight and unplug afterwards.

klhoard

My Feedback: (10)

.
I think this system works perfectly . . .
.

nonstoprc

My Feedback: (90)

＋1。

The only minor obstacle is that the HV servos (e.g., those from Futaba checked several months back) are a little bit heavier. Do not know why though.

klhoard

My Feedback: (10)

.
I've been flying the system the Jim O mentioned above for well over 100 flights and it has been working great.  No more charging receiver batteries!  The regulator connected to the motor battery cells is at 5.9V, and the 2S-350Mah LiPo regulator is at 5.7V.  The little LiPo stays charged for weeks since it doesn't get used.
.

cmoulder

Just asking...

If it is not good for us to leave our main batteries fully charged for long periods of time, is it okay to leave the back-up RX LiPo battery fully charged?

2Sunny

Morning Bob,

I'm no battery specialist, but my only thought regarding a fully charged LiPo Rx bat is that it will not pose any problem for the 2 or 3 seasons you might expect to use it. However, I would note that the Eneloop Rx pack I am using is purpose built to sit on a shelf fully charged with less than 3 % degradation, and does not require a regulator, and has capacity to produce 10 amps for short bursts, and weighs the same as a 800 mAh Lipo + reg. Also this and a buck might get you a coffee in a diner, but below is a graph of my BEC output during an Intermediate Sequence which corroborates the same experience another fella did with an FAI Sequence servo test. The point is your BEC never sees even 1 amp max which means a CC Pro is way overkill and the Dimension Engineering VHV-BEC is more than adequate, but I know there is "More than one way to skin a cat" and that's what makes the world so interesting.

Anyways, still hoping to catch up with you and Anthony soon!


Joe


[link=http://www.dimensionengineering.com/products/vhvbec]Dimension Engineering VHV-BEC[/link]

klhoard

My Feedback: (10)

.
I'm sure that the little LiPo's degrade the same as the big ones at full charge. At $7-9 each, I look at a 2S-350Mah LiPo as disposable at the end of the season, or give them to an indoor foamy flyer to finish them off. It's a tradeoff I make for the convenience of not having to discharge to storage at the end of every day. I do check the voltage at the start of the day, and top it off if it's not at 8.4V, but I rarely have to put in more than a few Mah.
.
They are "taking one for the team"!!
.

cmoulder

Fair enough, Kieth. I would just check the voltage occasionally with a 1-amp load to make sure the voltage is holding up, and discharge/ recharge now and then to check cell IRs.

cmoulder

Thanks, Joe. It's reassuring to see a lot of headroom in the amps department.

I think I will combine the VHVBEC and a Tech-Aero reg (single, switched) which I already have on hand, along with the programming box.

MalteS

I've been flying a Jeti BEC in a 2x2m pattern ship for >150 flights now. Using the 10s Battery as input, no issues here.

More important and why I'm writing this post:
I've been using a single 200mAh Lipo battery as "emergency" battery for over two years now. This battery is connected to the receiver using a low voltage drop schottky diode (0.2V). In nomal operation the BEC (or whatever your main power supply is) supplys ~ 6V and the single Lipo isn't discharged. If the main power supply fails the Lipo kicks in.
Its important to note that this is not a redundant power supply but an emergency! This means -> immidiate landing. In order to be aware you need working telemetry and a low voltage alarm set in a way (e.g. 5.5V) so you are informed your main power supply is gone.
I've been using this in two planes with many flights now and also did an emergency landing once (poorly installed BEC switch).

For those concerned with the single Lipo voltage:
The single Lipo voltage is close to the Voltage of 4 fully discharged NiCD for which our equipment is designed. All servos that I've tested this with (JR, Futaba, Hitec) work, but you want to try this yourself. The Receiver is more important. Make sure to check the specs and do a testrun also checking the Voltage of the cell when one servo is blocked.

Don't use this without proper ground testing and working telemetry.

klhoard

My Feedback: (10)

.
I accidentally "ops checked" the backup LiPo a few flights ago(forgot to plug in the primary). It works just fine . . .
.

cmoulder

Update: 235 flights later with the VHV BEC, backup lipo and tech aero reg, and I'm still luvvin' it!

This will be my default configuration from now on.

Only thing I changed was to move the lipo batt switch to the side of the fuse so the whole shebang can be armed/disarmed with the canopy on. Ready to fly in 2 seconds!

pvogel

How do you set the Jaccio to 8.2V? I'd been looking for a while for a regulator that could do HV settings...

Thanks,
Peter+

cmoulder

Good question. I just sent an email inquiry to Dimension Engineering to ask if they will soon have a VHV BEC for HV servos.

I guess the same should go for Tech-Aero.

OhD

I don't have 258 flights but I have been flying the setup I described and haven't charged the 2S pack since I put it in the plane. Actually it gets charged all the time when I am flying from the bottom 5S pack. The DVM shown is from Hobby City and costs about 5 bucks. It tells me that my motor power pack is fully charged when I connect the BEC to the balance connector.

Jim O