I am about to switch all my batteries to LiPol in my plane...

This will require 2 x 2S with 2 x voltage regulators and two switches
along with a 3S pack for the ECU...

I don't want to have 2S batteries and a 3S battery in the same plane
because I could easily charge one incorrectly...

So.... I want to put 2 x 3S packs only... From the 3S (12v) I want
to put 2 x voltage regulators to 5.1... but then power the ECU
by (12v) or 3S directly..

I know the ECU can run on 12 volts but recently I plugged a minihobbies
Voltage regulator into 12 volts and well.... uh.... It exploded and
shot smoke all over the shop.....

Does anyone have any advise or can anyone tell my why I should
not do what I am trying to do.. ?

Eddie Weeks

I just confirmed with Jack at Duralite that his regulator can take a 3s pack, but you will get a lot of heat on the regulator. www.duralitebatteries.com

I've used his packs and regulators for over a year now, and about 120 or so flights. I really recommend his stuff although I have not personally tried a 3s pack on his regulator.

Sean

Yea.. I want to stay away from the hot regulators..

Can someone tell me why a regs heats up..

And would this thing work.. ?

http://www.d1international.com/5a.PDF

Thanks

Eddie Weeks

You get heat because essentially you are going through a resistor to get the lower voltage, kind of like a light bulb.
If I'm understanding your pdf file, the 5a series would drop you to a voltage that a normal regulator like the minihobbies could handle, but now you are burning even more "lost" energy from your pack through two resistors.

Electro dynamics makes a regulator with a heat sink that takes up to 12V input.

Contact Andy for details.

The 94% efficiency is where you are losing the energy for what it's worth. I didn't think of Andy, he's got good stuff too. I buy 100% of my leads from him, never had one with a "loose" connection. Actually, now that I think about it, the energy lost in bringing the voltage down is not "more" it's just what it is to get to the voltage you want. 5.1 is more lost than 6.0. I don't know what the efficiency is of the regulators we use, but I could get 7 bonafide flights out of my duralites in the euro (9 minute flights) on one charge.

Hi Eddie:

I posted a while back on another regulator thread that Tony at Minihobbies specifically told me not to run more than a fully charged 5 cell NiCd or NiMh input to his regulators or you will fry them....that about 6.5 to 7.0v on a fresh surface charge.....

Andy makes some nice stuff.......I think his input is up to about 9.0v.......all depends on the dissipation of the components used.....

I just ordered a regulator from www.smart-fly.com ... nice beefy one with a HD heat sink and large output capacitors to keep the voltage well regulated......it is also adjustable output, from about 5.0v up to 6.7v.....also can be wired with a failsafe switch.....and is DSC compatible......

As far as hooking things up wrong, on my Powerflite Lithium Charger, I soldered on different end plugs for 2S vs 3S so as not to confuse them....on my SIRIUS Lithium Charger, there is a sensing circuit that prevents the charge cycle from starting if # of cells is incorrectly selected on the menu.....

Just a quick off topic query.....Do you still have some titanium gear plates for the SuperBandit available.....

Tom

I like all of Andy's stuff but the specs for the Pro Regulator or

http://www.electrodynam.com/cgi-loca...3ff+1116583673

only up to 9 V... I am sure someone one here will tell me what I need.. I don't want to just make more
heat at the regulator because I am using more Voltage..

I have plenty of titanium flex plates for the superbandit... Are you going to Waco.. ?

Eddie

In a linear regulator, that extra voltage is going to make heat no matter what. Get a unit with a very high quality regulator, a very big heatsink and make sure you get airflow over it.

Eddie, I just switched over from Nicads to Lithium Ion batteries, voltage regulators, and heavy duty switches on my JR stuff. Look at www.fromeco.org and/or call them and talk to Mike at (503) 310-5194. There are a couple of us here flying our jets on these batteries, now and really do like them. We can pretty much fly 5 or 6 flights without worrying about recharging, but it helps to top off the batteries occasionally during the day (paranoid holdover from nicads, I guess - the Li-Ions don't seem to need it, but I feel better anyway). Mike is super to work with, and his prices are reasonable. He will advise you in selecting batteries, switches, and regulators to meet your needs. He told me he tested his regulators up to 10 amps and only got warm, but still functioned perfectly. I chose to use a 4800 mah pack which is a series/parallel redundant pack for both ECU (Jetcat) and my flight packs, heavy duty wires/powerpole connectors, heavy duty wire/power pole connectors on the regulator, heavy duty switches, and a redundant JR output from the regulator - about as bulletproof as you can get, it appears. I charge the Lithium Ion batteries at 2.5 amps on either a Triton, or the Shultz charger set for Lithium Ion, 2 cells and they don't even get warm. The Lithium Ions don't have a memory, don't self discharge, and aren't nearly as finicky (dangerous) as the Lithium polymer batteries are.

Give Mike at Fromeco a call and see what he says - I think you'll be very glad you did. So far, I'm very pleased with the service, price, and performance of my new battery sets.

Regards, Les

Like Matt says, if you go with a 3S pack, you just have to dissipate that extra 3.7v or 4.2v with a full charge X the average amps, say 3 amps as heat.....that is up to about 12.6 watts and that's allot of extra heat.......ever pick up a 10 watt light bulb that's been on for a while.....puts an added stress on the output caps as well which may well lead to less stable regulation if they are not of large enough capacity....also, whichever regulator you choose, be sure to get one with 18 ga input and output leads, rather than the 22 ga that some are using......

Tom


Sent you a PM about the flex plates......

Mike over at www.fromeco.org said... instead of going from 12V to 5... Just go from 7.2 up to 12 once...

So instead of using 2 x 3S packs I could use 2 x 2S packs and just step up the voltage to the ECU...

Anyone know how to do that... ? hAHAHA

Eddie

This will come close.

http://www.maxim-ic.com/cookbook/pow...pdfs/CB134.pdf

EDIT Oh wait you wanted a lot of current, right? I forgot you were running an ECU, this circuit is really only good up to a couple of amps.

Eddie,

As mentioned above, the voltage regulators we have available specifically for model use (and proven in jets) are linear regulators and the voltage is dropped from the higher to the lower basically resistively so that the extra energy is dissapated as heat. What is needed for high cell counts is essentially a "switching power supply" which operates much like a switching speed control for electrics. These DC-DC converters have very high efficiency, and can even "up convert" a lower voltage to a higher one, or even a negative one. For example, you can find DC-DC converters that generate +12V and -12V from a 5V power supply.

Unfortunately, not many of these have been adapted or proven in the RC market. Here is one that is capable of supplying 3.5A loads that has been:

http://www.medusaproducts.com/Other/...-BEC-45035.htm

Note that it doesn't have a heat sink. Its efficient enough that it doesn't need one. I have the 2A model in my TRex helicopter and it works flawlessly, however, I'm not sure I'd want to be the first guy to try one in a jet, even if 3.5A was a sufficient current rating for that application...

Bob

You are going to get heat regardless of whether you use a DC-DC convertor or a linear regulator. Energy needs to be dissipated when stepping down voltage. Unfortunately, silicon is not good at dissipating heat. That's why it gets hot. There is not enough surface area on the die to dissipate the heat. This is why the die is bonded to a heat sink in the packaging. This heat sink is usually connected to ground to prevent eddy currents. The heat sink of the package, depending on the energy that needs to be dissipated is connected to an external heat sink that further increases the surface area to help distribute the energy. This causes the regulator to run cooler because your heat dissipation efficency goes up.

Forget about using a DC-DC convertor. These can be a little complicated to setup for good line regulation. You could try a LM1084 which is an adjustable regulator that can supply up to 5A continuous with a maximum input of 8.8A. The maximum input voltage is set by the difference between the input and output. You are well within the 29V max difference. You would need a couple capacitors and resistors to set the cct up on a piece of perf board.

http://www.national.com/ds/LM/LM1084.pdf

You need a switching regulator.

http://www.koolflightsystems.com/ultimatebec.htm

We use these all the time in electrics for up to 10S power systems with the high voltage version - no heat involved. There are thousands in use...

yeah but nowhere near as much with the DC-DC switcher.

Yeah.. BEC... That is perfect... I knew you guys would know how to do this...

Thanks 1000 times...

I will be getting rid of 2 x 5cell x 1650 AAs..... getting rid of 8cell x 2000 AA ECU

and getting 2 x 3S LiPol... around 1600-2000 mah each....

Right now I have 2 receiver switches and 1 ecu switch...

I think I will need an extra switch for the ECU so I can separate the 2 3S packs..

Now I can put all kind of 12v stuff in the plane with out more and more batteries...

Thanks again for all the help..


One more thing.... Can any one see anything wrong with what I am doing.. ?
I will test it before I fly it but is there something wrong with using the same power
for the ECU and receiver.. ?

Eddie Weeks

That's the same freeking regulator everyone else uses (or one with the just about the same specs). As we've all said, a linear regulator dissipates all of the energy from the voltage step-down as heat. A switching DC-DC converter doesn't. If you use any linear regulator to step down a large enough voltage with a large enough current draw, it will get hot unless you have a massive, air-cooled heat sink. I've worked with some guys who have designed a high-cell count supply with linear regulators and to supply the current required by a normal RC system, the heat sinks were massive. If you don't keep it from getting too hot, you will get thermal cutoff and that's the end of the airplane - period. I've seen it happen.

As for all of the rest, silicon is actually a fairly good conductor of heat, its simply that the IC is small and thus the power density is quite high. Getting all of that heat through the small contact area of the back of the IC is a challenge. Then you have to have a large enough heat sink to dissipate it into the air...

I don't fly turbines but I will offer a few cautions:

Make sure the battery is sized to handle the maximum load - does the ECU load involve the electric starter on the motor as well as the normal ECU + fuel pump load? That would make the startup load pretty high, a 2.0 amp 10C pack will handle 20 amps but only for 6 minutes, a failed start or two involves how much start motor on time?

Make sure the motor on your fuel pump and on the turbine are suppressed - caps between the power wire terminals and the motor case. I'd assume that is standard practice - but I don't know! It could be the case for instance that the starter motor is unsupressed but the ECU has an optical coupler which isolates the noise on the ECU battery (which powers at least 1 cheap can motor in the fuel pump) to starter motor circuit from the Rx lead going to your receiver. By adding a UBEC you have re-established that direct connection. Range check!

Treat the UBEC like your ECU - seperate it physically from the Rx, don't tape it to the Rx for instance. A few inches seperation is fine... - RANGE CHECK.

It should work, basically you have a computer and a couple ESC's in the ECU. It is an electric with a turbine added.

BIG WARNING - Lipo performance really sucks wind below 40F. I would not use them if the temps are below 50 degrees in an Rx application on a big dollar turbine just to be safe. Guy in my club stored his Composite ARF 3x% aerobat in his truck overnight. The overnight temps were in the high 20's. Of course the lipo pack was well insulated from vibration by a nice blanket of foam. At 11:00 am it was 40F and he went to fly after checking the voltage which was in the green on the Duralite load checker. 3 minutes into the flight the plane went stupid. It should have been OK at 40F but the pack was cold soaked overnight and well insulated so we figure the pack temp was still down around 30F....

Eddie,

With castle creations BEC on their brushless electric speed controls they use two BEC in parrallel. They state this does not give them double the amperage load as one might think, but allows for a safety margin of thermal shutdown one then the other. Sounds really strange but you could get more info over in rcgroups electrics forums on this subject matter............

Anyone look at the LM338? 5A rating.....

Dave Rigotti

Actually that's because the two regulators won't share the load equally unless they are matched to within 0.1V or less - which is hard to do and even if you get it close, it changes with temperature. If they are not matched that closely, then the one with the higher output voltage will carry 90% of the load.

I've actually set up a system like this with two Duralite regulators and watched its operation. We did it on a NASA research model for redundancy.

Bob

Dave,

Its a linear regulator, so even though its rated a 5A, if you use it with high cell counts, its going to dissipate a lot of heat and a big heat sink is necessary to avoid thermal cutoff.

Bob

I can back up what Chris True says on the UBec, there are lots of them in use in big electrics. I have never had a problem with mine. If I decide to switch to LiPoly in my turbine jet (BoB Cat XL/P-70), I wouldnt be afraid to use them in this application.

Regards, Bill