UBEC question

[ekripper]

Guys,
What would your best guess be on max amp draw from our radio systems with 4 hi-speed digi's and a 601 gyro. I have an SBEC, a HVUBEC, and a reciever pack. My SBEC apperently couldn't handle the load put on it and I believed cause my crash a few weeks back. It worked fine for 4 or 5 flights where I was just tooling around doing easy stuff while getting some cycles on the packs. During a quick succesive tick-tock with some rudder bein fed in the gryo seemed to reset as if the voltage had dropped to low. I hit throttle hold but I was too low and the rudder reset to full lock one direction so it ended baddly. It is said that the SBEC can handle 2.5a continuous with 5a burst. The 601 sreen only read 4.8v while sitting on the ground I noticed. What are your guys thoughts on this. I have since switched to 1100mah nicds and not had any trouble. I have a couple of HVUBEC's that I would like to try just to save weight. I would LOVE to run the SBEC's cuz they're so small but I'm a bit leary now. If anyone has any insight into this please share with me. Thanks a bunch.

Regards,
Eric K.

[Russ McC]

If your running Futaba gear your looking at about 300mah for a ten minuet flight, I am running the HVUBEC in both my Ions no trouble, don’t know about the SBEC. I am only using one of the flight batteries to power the UBEC and it is working great. The extra weight of a receiver battery sucks!

[AlanMcSwain]

Pretty much all the battery eliminator circuits out there use voltage regulator ICs. Virtually all of these regulators have thermal overload circuitry built into the chip. These regulators also have a max current rating that is closely coupled with the max thermal dissapation rating. What this means is that you can rarely draw the max rated curent unless the IC is properly heat sinked, which given the small package application of these kind of electronics, never is the case.

I seriously discourage anyone from running digital or hi-torque servos off of ic regulators without doing some serious stall current testing on the servos and making sure you have TWICE the available current rating to stall current.

Oh..those built-in thermal cutoffs...they don't turn the regulator back on until the chip cools off significantly, usually a minimum of several seconds under ideal, heat sinked conditions.

[DavidH]

It is said that the SBEC can handle 2.5a continuous with 5a burst.

That is not enough of a load carrying capacity. Especially with using all digital servos. Most of the upper end regulators are rated at least 7.5 amp with 10 amp or more burst. I would think you was drawing too much current thru the BEC and it shut down for a second and then reset.
I have seen voltage regulators that were rated at 5amps shut down when they were being used with a heli with all digital servos.

David

[Tabbytabb]

Ekripper, another lightweight alternative is to run a 2 cell lipo pack with a 5.1 regulator. Weighs very little and will definately provide the amp draw capacity. That said tons of people are running the UBEC without problems. I even know of some running the regular voltage UBEC on 10s without problems.

It is nice to install as Russ has suggested though so you can arm servos and gyro without the motor being "live"

I tend to stay away from the UBEC/SBEC solutions on such high dollar machines, that is just me and I am probably paranoid.

I dont need every last drop of performance and a 1200mah lipo with regulator is nice insurance IMO.

Besided, those flightpower 10s2p packs you are running are so stinking light you should have to run a huge receiver battery to even the field :)


Tabb

[misskimo]

hey , The Sbec has a new one coming out soon that can handle more cells , but I do think the Bec can handle it but maybe you need to do what Chris S is doing , he hooks his up to 1 of packs, the the voltage is lower , if the voltage is lower going into the bec then it can dish out more .

Tony

[ekripper]

Tabb...I need the power to whoop on these boys still flyin the 90 slimmers!! :mrgreen:
Tony, I wasn't aware that lower voltage going into the BEC would allow it to dish out more...I had the SBEC hooked up so it was pulling off of both packs. Maybe that was part of the problem. I am going to hook up the watt meter in between the bec and the reciever tonight just to see what kind of amps I can get it to pull just sitting here moving everything at once.

[misskimo]

yeh the higher the voltage the less amps it will pull , theres a trade off , thats what I was going to use in my fury , but 13s was too much for that , but I did invite Gregory over here to check this out ,


Tony

[Tabbytabb]

yeah if you tap into only one pack the SBEC or UBEC wont have such a huge margin to step down the voltage. on the full 10s it has to step down 44v to 5.1, with only one pack it only has to convert 22 down to 5.1. You should be fine with the standard UBEC tapped off one half of the 2 pack setup.

Also, I want to hear more about the Fpex-c packs! I am in the market for some new packs and would love to hear your thoughts.

Later
Tabb

[ScotY]

Hmmm...I thought the UBEC and SBEC were switching type BECs and weren't affected by input voltages as much as, say, a Duralite regulator would be. I could be wrong, but I think the input voltage should not matter (and lower input voltage should not allow a higher current rating), provided it's within spec.

[ChrisS]

The UBEC is a switching regulator as Scot says. The biggest reason I tap from only one pack to run mine is that that way I don't have to have another Y harness going to the other pack. I just run a Futaba plug on one of my packs and a mating jack on the UBEC, this acts as my switch too. I plug the radio in first, wait for the gyro to boot, then plug in the speed control. I have been using the UBEC's in this way for a couple of years now.

Chris

[misskimo]

hey , well I recieved a PM from Gregory that makes the Sbec. heres what he said

Hi Tony,

I have been so busy, I haven't had time to get in the air for ages. Gotta get back into soon cos I'm getting withdrawal symptoms ;-)

About the thread - I'd need to register to comment but you can copy this in if you like. one is mistaken about the SBEC's using regulator ICs. Some do and those are the ones that are susceptible to thermal shutdown especially if there is a big difference between your input and output voltage. There is an example on our website at www.firmtronics.com/sbec.htm which gives an illustration of this - scroll down to "Why use a switch-mode BEC?". SBEC and UBEC use switch-mode technology which is MUCH better at converting very high voltages to lower voltages but (unfortunately as a trade-off) have more ripple voltage and more interference than linear regulators and therefore sometimes require a bit more caution when mounting (eg. don't mount them right next to the receiver). There's also something which we've recently discovered about our SBEC called "common mode noise" which some Rx's don't like and users get symptoms very similar to intereference. You have to wrap the output lead around a ferrite ring (about 5 times) to fix this. Some Rx's have good input filtering and don't need it. Also 2.5A is generally more than enough for most setups. The true test is to use a fully charged Rx pack, fly for a timed period, recharge with a charger that tells you the mAh going back into the pack and calculate the average current draw. We've never found (through our customers) this to be more than 1.5A even with aggressive flying but if you're using winch-servos, it may be different! Most people using 1A linear regulators (that can easily overheat) built-into the ESC's don't bat an eyelid even when using digital servos (and there're many who are).

Cheers
Greg

I been know Gregory since he first posted the product on rcgroups , well I was the first to reply and to try for free this product , I told him I would run it on my eco 8 and ended up trying after a debate on ezone on my new joker just to take the heat off of him to see if it would handle it , digi servos 502 gyro and a fan , ran my Joker fine . I have 2 other becs that I plan on useing in other helis if I get time dangit , but it is very light and not a complaint

Tony