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HomeTurbineAircraftHelicopterTurbine Helicopters › One battery or two? The need for a second battery?
02-01-2010 08:08 AM  8 years agoPost 1
iandavidson99

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Ipswich, England

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Hi All,

I’ve noticed that most people seem to use two batteries on their turbine systems, one for the receiver and servos, and another for the FADEC, fuel pump and solenoids.

However, other than the warm-cosy feeling of redundancy, is there any electrical reason why the two should be isolated, as I’m trying to work out why I couldn’t simply use a single large capacity 2S 7.4V 5000mAh battery going via a Duralite 5V regulator to power everything?

Many thanks,

Ian

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02-01-2010 11:17 AM  8 years agoPost 2
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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I think for greater reliability , it's better to keep the systems battery wise on their own , the ecu starter wise can draw a huge amperage , not only the start up , but more so if you using a kero start. I even go further , as I think most do use a Power Box battery redundant system or similar , for safety!!! Same with the digital servos of today , they can draw huge amperage , my Helli having 9 of those servos , so most people won't take the chance!!
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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02-01-2010 12:42 PM  8 years agoPost 3
paul999

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ilford essex

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hi

im a novice at turbines but would not recomend useing one battery for the whole system alway have one only for the ecu i strongly agree with ian do not take the chance you have a lot of money flying around in front of you

regards
paul

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02-01-2010 01:26 PM  8 years agoPost 4
iandavidson99

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Ipswich, England

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Many thanks for the feedback so far…

What I’m trying to understand however is “why” two batteries are needed, rather than “it’s just good practice”.

My setup is a very modest one, just 3 servos on the cyclic and GY401 + tail servo, in addition to the FADEC etc. The servos are Futabu BLS451, which I’ve been reliably informed are very power efficient for their size/performance.

An excellent point was made to me in a PM that my Duralite 5V regular might not be up to the job of powering the whole system, so almost certainly I should consider a beefier 5V regular. In line with this, does anyone have any (approx) idea how much current the starter motor and fuel pump draw on a Wren 54?

I’m not averse to using two batteries, but would certainly prefer a neater system using one and would dearly just like to understand the technical justification of using two batteries.

I’m just not aware of any other vehicle (either full size or models) which require two discrete electrical power sources… but no doubt I’ll soon be enlightened on this

Many thanks,

Ian

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02-01-2010 02:21 PM  8 years agoPost 5
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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Well quite simply put if a single battery should fail you will not only loose the turbine , but total control of the helli as well , not even the chance to attempt to auto to save your pride and joy!!
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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02-01-2010 02:24 PM  8 years agoPost 6
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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One other thing , the bearings do jam on occasion , there by causing an abnormally huge draw of current!
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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02-01-2010 02:35 PM  8 years agoPost 7
iandavidson99

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Ipswich, England

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Hi Dave,

But if you have two batteries, what's to say that the battery powering the receiver won't fail?

I promise I'm not trying to be awkward, I simply want to understand the technical reason why people use two batteries and at the moment it seems to be “because it’s good practice”, which isn't a technical reason.

Considering all the extreme mechanical forces going on in a gas turbine helicopter, to my mind the last thing likely to fail is a simple solid-state battery.

Kind regards,

Ian

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02-01-2010 03:05 PM  8 years agoPost 8
hazchem88

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W.Mids UK

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hi
Ian

I understand what you are trying to indicate.
2 batteries as you have it sort of spreads the risk a little, but not truly.

Since as you say if the Rx battery fails for some reason, you've lost the whole heli. So in that sense you might as well just have one battery.

Personally I use 2 batteries just for convenience, more choices adjusting CofG, sometimes it's easier to position 2 smaller batteries in nice places rather than one BIG battery, etc.
Also, once the batteries life starts to go with time, cheaper to replace 1 small lipo than one big fat one.

Ignoring these issues and 'redundancy', purely electrically speaking, one big Lipo will be just as good as 2 small ones - as long as C rating good enough.

Yes, the FADEC and digital servos can take high current, but just think of the guys flying hard 3D with 600 and 700 sized electric helis. A good lipo could take it. Think of the current going through there!

But apart from pure interest, might just as well keep 2 smaller ones and take advantage of the small advantages they give

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02-01-2010 03:17 PM  8 years agoPost 9
WIRLYBIRD

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CAPE TOWN / SOUTH AFRICA.

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Ian the biggest cause of crashes IMHO , has always been a battery failing , hence we most all use the battery redundancy system. It's quite possible that a new battery can fail in a very short time , believe me it's good to have two on board. I throw away my NH90's batteries every 18 - 24 months no matter how good they seem , or how many charges they've had , this gives me peace of mind. I'm not a show flyer , but fly very gentle scale , maybe that's why I've so far only had one crash in 25 years , but not due to a battery failing. How ever at the club I belong to , there seems to be one every other weekend or so , loss of battery power is very common , and very expensive in money and time.
Dave.

WHAT GOES UP MUST SURELY COME DOWN.

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02-01-2010 03:58 PM  8 years agoPost 10
MattJen

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UK

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i agree with dave

piece of mind when flying is a good thing to have.

I have gone over the top on both of my turbines at the advice of a flyer who is so paranoid about methods and backs ups.

i have 2 batteries via 2 seperate switches going to my radio gear, and i have 2 batteries to the fadec, and i have a further 2 batteries powering the oil feed pump. it is well over the top i agree but in a nice scale machine it is nice to have that backup, but it does make for a mass of wiring.

On my predator i just have 2 NIMH as they are known for being unpredictable wired via 2 seperate switches.

i have tried to make it as bullett proof possible.. but nothing as we all know is 100% reliable.

in my case it is purely for redundancy.

Matt

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02-01-2010 05:20 PM  8 years agoPost 11
iandavidson99

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Ipswich, England

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Thanks again for everyone’s feedback – I have to say, I find this most interesting. Hazchem88 you make a lot of goods points; I think you’re on my wave-length

MattJen your system sounds immense! You must need a turbine just to get your batteries airbourne

In my mind ‘dual redundancy’ is only ‘dual redundancy’ if one system (i.e. the battery) can completely replace the functionality of another system (i.e. another battery). If this is the case, having one battery to your RX and another battery to your FADEC isn’t dual redundancy, if anything it’s surely increasing the likely-hood of failure?

The MTBF (Mean Time Before Failure) of any system is less than that of the individual parts. i.e. if you have two batteries and each one had an MTBF of 1000 hours, then the MTBF of a system which relied on both batteries being operable would actually be 500 hours.

Also, personally speaking I've never had a battery fail (although I appreciate others might), but a battery connection fail I think is far more likely, ergo the less connectors...

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02-01-2010 06:46 PM  8 years agoPost 12
MattJen

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UK

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but a battery connection fail I think is far more likely,

+1

I know mine is well over kill, ha ha ha.. they are lypos on the zealous where there is multiple backups. but you are right it is backup, and often its the link between what the battery is supplying is where the failure occurs.

I appreciate we are talking about lypos, but some are afraid of using regulators with the thinking it adds another break in the circuit, i have found particular with NIMH batteries due to their unpredictable nature i have seen pilots go out and fly with what they thought was a full battery as on the volt spy readout it is green, but half way through a flight they fall out of the sky, and by process of elimination they find it is was the battery, and the first thing you think is " well it was fully charged before i went out" i did the same, it was only i put a load tester on it i realized i was on minimum voltage,the battery gave the charger a false reading of full, so i always recycle once a month my nimh and monitor what goes out and what goes back in,and before the first flight of the day i will connect my load tester to the battery terminal to check the voltage,
lypos are so much better at keeping their charge and are more accurate as i have found on my zealous, but i haven't made the change on the predator as of yet and that is the main reason i have 2 4300mps on my predator.

interesting thread with some good info..

Matt

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02-01-2010 08:30 PM  8 years agoPost 13
Chris Bergen

rrElite Veteran

cassopolis, MI USA

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Something not mentioned (maybe I missed it), but the ECU battery is also powering the fuel pump, starter, and glow plug. Now obviously during normal flight the starter and glow plug are NOT powered, so only the fuel pump is being powered by the ECU battery.

The fuel pump is a constant draw on the battery, it is ALWAYS running, and in certain manufacturers systems, is fluctuating dependign on the fuel needs of the engine. I submit that this is a LARGE drain on that battery.

With that large drain, I don't want it ALSO trying to power my high drain servos....

Just my .02....

Chris D. Bergen

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02-01-2010 09:10 PM  8 years agoPost 14
iandavidson99

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Ipswich, England

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Good to have your input Chris. I would be surprised however if the fuel pump drew more than 5A when running (if it did I would expect it to feel warm) and so even with a modest 2S 7.4V 20C 5000mAh battery, that’s a very healthy 100A power source you have to play with.

It just seems to me that as long as your battery is up to it, for a simple turbine setup like mine (granted for a scale setup it might be different) a single battery solution has the potential to be more reliable, not forgetting a neater installation and only a single battery to remove, recharge and replace between flying sessions.

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02-01-2010 09:58 PM  8 years agoPost 15
helibeli

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wales.uk

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How many of us give a thought to battery failure when driving our cars?nobody does.How many of us would go driving if there was no alternator fitted to the engine? yet this is what we have done since the year dot with modelling.Would it not be better to have an onboard small alternator on all models to keep the battery fully charged?

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02-01-2010 10:00 PM  8 years agoPost 16
Rappy 60

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Paris, France

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It's funny that no one has mentioned the real reason why. Yes it is good practice to have two batteries for redundancy but that is not the real reason. It has to do with electrical noise. The pump is pulse modulated which puts out huge amounts of electrical noise that back feeds into the battery. If you have one battery then that noise is back feeding into your receiver. That is one reason that the throttle channel is opto isolated.

Dale

Load "*",8,1

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02-02-2010 02:15 PM  8 years agoPost 17
Techflyer

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Palm Bay, FL

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USE TWO PACKS
I can tell you from experience, using a single pack with the Gaspar FADEC is a huge "No-No".
I originally set my T-Rex/Wren 44 up with a single 4000mAh, 2 cell pack. (I use a regulator for my ECU and tail circuits.)
I successfully started the engine a few times (6 or 7) and all appeared well.
The very first time I tried to spool the heli, I initiated the start sequence but once the system was idling, the throttle control never returned. The stick simply had no response. All other radio functions were working fine, just no throttle.

Back at the bench, I discovered that the throttle input to the FADEC was completely dead. Instead, the FADEC was accepting power only from the pump circuit.

After a few calls to Wren the general theory is that using the single pack somehow "confused" the power back-up feature of the FADEC.

After a FADEC change and installing separate packs, I have had no further issues.

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02-02-2010 03:44 PM  8 years agoPost 18
helibeli

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wales.uk

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Surely a well designed power supply can filter out pulses and noises on the power supply line.In a television you can have one line feeding several different circuits via regulators and filters to several different micro processors.

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02-02-2010 05:18 PM  8 years agoPost 19
iandavidson99

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Ipswich, England

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I tend to agree. There’s rarely a time when different parts of an electrical circuit need to have their own discrete power source to eliminate interference.

An ESC + brushless motor combo can be electrically very ‘noisy’, yet I’ve flown many cheap electric R/C helicopters and foam planes which all use a single battery to power the esc/motor and RX without any problems, so it seems strange (but not implausible) that a simple low current fuel pump could interfere with a high-quality 2.4GHz digital receiver. In my experience, even strapping a relatively high-power video TX on to a plane right next to a Spektrum RX hasn’t caused it any concern.

I would have thought that if you went from your main battery to you RX via a quality 5V regulator (which would likely also include some smoothing), then the chance of getting enough interference down the power cable to trip the RX would be negligible. In addition, the Spektrum RX I’m using seems to have quite a wide voltage DC input range (5-10V I think), which would imply that internally it must also be doing another layer of voltage conditioning of its own.

When all said and done, I guess people should just do what they feel confidant with, but nothing (yet) has convinced me that a dual battery solution is a prerequisite

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02-02-2010 05:36 PM  8 years agoPost 20
PETER ROB

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Devon UK

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One battery or 2
iandavidson99, On my turbine heli's the ECU is 7.4V, the receivers now on 2.4, 6V
If I was to power everything off the 7.4V, then in the worst case senario, low battery, the turbine would shut down
With 2 batteries, if the receiver battery went low, I would get an early warning, usually from the tail servo/gyro, failing to operate properly, but the turbine would still be running
Peter R

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