dignlivn

I am thinking of using a 3 cell (11.1 v) lipo to
power my Rx. (Futaba 2.4, 6 channel)

I have been reading alot about V regulators and
read in another thread about using a Bec.

Is anyone using a Bec to power thier Rx's from a
Lipo ?
It sounds simple from what I learned about them ,with
my electric heli. But I am not sure about the use
for fixed wing AC.

Bob

-pkh-

My Feedback: (2)

BEC (Battery Eliminator Circuit) is a voltage regulator. When the voltage regulator is built into an ESC (Electronic Speed Controller), it is usually called a "BEC", while standalone/external voltage regulators are often called by either name (voltage regulator or BEC).

If you have a small electric plane running on a 3 cell LiPo pack, then typically the BEC built into the ESC will work fine. If you have a larger electric plane, and/or are using a 4+ cell LiPo pack, then you probably need to go with an external switching regulator/BEC, or a separate receiver pack.

If you have a nitro plane and want to use a 3-cell LiPo for the RX, then you just need to get a standalone switching regulator/BEC. I believe most guys just use 2 cell LiPo packs with a regulator, though, since a 2-cell pack's voltage is 6-8.4V, and you typically regulate down to 5-6V. A linear regulator will waste more power than a switching regulator, especially if you go with a 3 cell LiPo pack, since you have to drop quite a bit of voltage to regulate down to 5-6V for the RX.

dignlivn

PKH


I guess I need to learn the difference between
a Linear regulator and a Switching regulator ?

The reason for the 3 cell lipo, is I already have
them on hand and a electrifly 45 amp esc w/bec

Bob

dignlivn

PKH

BTW,

This is pertains to use with my GP 40 Stick
with a Saito 82a. I lost my Trainer due to
a LOW 4.8 nMhi Rx pac with a voltwatch
on board.

Bob

JohnW

My Feedback: (6)

"LOW 4.8 nMhi Rx pac with a voltwatch" I am sorry to hear that. The problem with the voltwatch is it doesn't load the battery, so it tells you nothing useful. This has been brought up before, but I think some still don't understand.

You realize it is even more difficult to tell if a LiPo is close to the end of its charge compared to NiMh? Just changing the battery chemistry won’t prevent a battery failure in flight due to low battery, you need to properly test the battery before every flight.

BEC/voltage regulator (VR), same thing as mentioned, I'll just call it VR. Switching VRs are more efficient, which is why the poster suggested their use. You don't really need to know the ins and outs of why that is, just look for a switching VR.

One thing you do need to pay attention to is the current rating for the VR. Too small and the VR will drop out, or worse, go up in smoke... just as bad as a dead battery. For a 40 sized plane, I’d suggest maybe in the 3-5A range. But, 10A VRs are pretty cheap, so I’d just go that route if getting one.

Another thing to consider, the VR is a single device that if it fails, you plane is probably going to be totally destroyed… get a good one.

dignlivn

John


Great advice, I now own a good loaded volt meter and
no volt watches. I know lipo's drop off in voltage quickly
when they reach a certain point in voltage. However I
could re charge it or top it off if need be between flights.

I know a VR is also another failure point in the chain.
I also check my rx pac before each and every flight
with my lvm. I'm just gun shy now.

Bob

BadSplice

My Feedback: (1)

Pardon me if Im off here..... but I thought that the reason so many people like and use the Voltwatch is that unlike a regular meter it Does load the system. And rather than a random load, it uses the exact load of the planes radio system? So not only will it tell you the condition of your battery pack (ok, maybe not as exactly as a good loaded meter, but good enough to see if youre near the danger zone) but it can also let you know if you have a servo binding, or some other linkage problem. (which a loaded meter cant do)

-pkh-

My Feedback: (2)

I use a VoltWatch in all my planes and helis. It's always on and always telling you the status of your receiver pack. A loaded meter is good, but you have to remember to use it to check your pack before every flight, and you have to have a charge jack or lead accessible all the time (most of my planes just have a charge lead inside the fuse, which is not accessible with the wing installed).

To each his own. With my VoltWatch monitors, I've never lost a plane due to low voltage on a batt pack, but I have seen at least two guys loose their planes because they did not check their pack with their loaded meter before every flight!

JohnW

My Feedback: (6)

... and now you have heard of one that lost a plane with a voltwatch.

IMO, many people like and buy the voltwatch because it has pretty lights. Most people using electronics don't really understand how they work or why, so pretty lights sell. It is unloaded, check the link. http://www.towerhobbies.com/products.../hcap0332.html


I'm not aware of a loaded volt meter that uses a random load. Which meter were you referring too?

If by "exact load of the planes radio system", you mean servos unloaded on the ground, I suppose yeah, but that too is not telling you much as a unloaded setup will have a very low current draw, like 100ma or less in many cases. In flight you can pull considerably more, like 10,000ma on some systems. An onboard test of an idle system really doesn’t mean anything useful. You’d need to load up the servos as they would be in flight to see if the battery is still OK, or at least put a fairly heavy load on the battery, as with a loaded volt meter.

To check for servo binding, you use a current meter, not a voltage meter.

Use and buy want you want, but understand that if you do not apply a decent load to a battery back, you cannot easily tell the battery condition.

BadSplice

My Feedback: (1)

well.... I really didn't mean to start another Voltwatch vs Loaded Meter debate... Sorry....

When I said random load, what I really should have said was arbitrary load. Most Loaded meters that I've seen have 1 or 2 settings, and radio configurations come in all shapes and sizes.

As for the voltwatch itself being loaded or not, I think thats a difference of perception. By itself, the voltwatch doesnt supply much of a load, so by that definition, yes, its not Loaded. On the other hand, the way it was designed to be used, it would be plugged into the RX, which would provide the load, so by that definition, it is Loaded.

You're absolutly right about the load being just the servos at idle or moving unloaded control surfaces. I guess I just figure thats way better than nothing. As others have said, a loaded meter is great, but you have to actually pull it out and use it, whereas the VW is right there to glance at. Also, I dont try to squeeze in every last possible flight based on the voltwatch. If the bttery starts to read at all low, I put it on the charger, or pack up that plane for the day.

And hey, whats wrong with a few pretty lights in the cockpit?

bkdavy

My Feedback: (1)

A linear regulator (nowadays) is generally a single integrated circuit that can be adjusted by use of various resistors to provide a stable, noise free output voltage. Depending on the difference between input and output voltage, they will generate heat.

A switching regulator provides an output voltage that tends to have a noisier signal, and depending on the rise and fall time of the voltage, could produce radio frequency interfernce. It works by turning the input voltage on or off and then allowing the output voltage to rise or fall due to a capacitor. When the output voltage rises above a threshhold value, the input voltage is cut off. The capacitor continues to provide the voltage as the output falls. When it drops below a threshold, it turns on (switches) the input voltage on and the cycle repeats. The result is more efficient than a linear regulator, less heat production, but you get the RF noise component.

A BEC is generally set up such that at a certain preset voltage, the controller will cut off power to the motor, but continue to provide power to the control surfaces allowing you to bring the aircraft safely down.

Brad

dignlivn

Brad,


Thanks for the great explanation.

Bob

JohnW

My Feedback: (6)

Nothing is wrong with pretty lights. I just want to be sure someone doesn't have an accident. Very easy for someone to ask about safe battery voltage and then get quoted a number for a 500ma loaded meter, and not realizing it may not apply is they don't use a similar loaded meter.

-pkh-

My Feedback: (2)

They are all just tools you can use to keep you out of trouble. If you use them improperly, or just forget to use them, then they won't do you much good. John is right, looking at a Voltwatch with the servos idle is not a good indicator, you must move both TX sticks around to exercise all the servos and put a load on the battery while checking the Voltwatch level. I also stop flying and recharge when my pack is down to 1/3 to 1/2 of its full capacity. While most guys at my field typically use 600mAh-1000mAh AA-cell battery packs for their 40-60 sized planes, I use 2200-2400mAh A-cell packs. These packs typically let me get 5-6 flights in while having 1/3-1/2 the total capacity left in my pack. Plus, the A-cells have a much higher current capacity, so at peak current loading, you get less voltage drop.