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Sep 18, 2019, 07:01 PM
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BEC Advice


Can I use a BEC to supply power to an electronic ignition on a gasoline powered plane? I can only use 4.8 volts to ignition and do not want to use a Nicad or NiMH battery pack. I would like to use a LiFe 6.6 volt or 3s lipo for battery. Will this work, and if so, what size/type BEC could I use? Thanks.
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Sep 18, 2019, 07:38 PM
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vollrathd's Avatar
Quote:
Originally Posted by GSAV8R
Can I use a BEC to supply power to an electronic ignition on a gasoline powered plane? I can only use 4.8 volts to ignition and do not want to use a Nicad or NiMH battery pack. I would like to use a LiFe 6.6 volt or 3s lipo for battery. Will this work, and if so, what size/type BEC could I use? Thanks.
Good question. Those ignition modules only use an ampere or two at full throttle, well within the capabilities of a Castle Creations 10 Amp Switch mode BEC.

But, those ignition modules also use a switch mode power supply in them to operate its high voltage circuitry. It should work. What I'd do is try one while measuring the 4.8 Volt DC output of the CC SBEC with a digital meter. Then power up the engine. Hopefully, the output of the BEC should be rock solid.

I just programmed one of my spare CC 10 Amp SBEC's to 4.8 Volts DC output, the powered it up with my variable DC power supply. At 6.6 Volts DC input, and no load, it put out 4.8 Volts DC, dropping to 4.4 Volts DC at two Amps.(Likely caused by the lead length of the SBEC plus the servo cable on my break out leads. It still worked just fine with a 3.5 Amp load, double that of the typical ignition module.

I had to drop the input voltage down to 5.1 Volts before the CC SBEC output voltage began to sag with the two Amp load. FYI, the output voltage of those A123's or LiFe's hold 6.6 Volts DC for 90% of the cells milliampere hour capacity.
Last edited by vollrathd; Sep 18, 2019 at 08:04 PM.
Sep 18, 2019, 07:53 PM
If it flies, I can crash it.
rocketsled666's Avatar
If there's an issue, it's nothing a big fat capacitor isn't unlikely to be able to fix...
Sep 18, 2019, 08:33 PM
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Quote:
Originally Posted by vollrathd
Good question. Those ignition modules only use an ampere or two at full throttle, well within the capabilities of a Castle Creations 10 Amp Switch mode BEC.

But, those ignition modules also use a switch mode power supply in them to operate its high voltage circuitry. It should work. What I'd do is try one while measuring the 4.8 Volt DC output of the CC SBEC with a digital meter. Then power up the engine. Hopefully, the output of the BEC should be rock solid.

I just programmed one of my spare CC 10 Amp SBEC's to 4.8 Volts DC output, the powered it up with my variable DC power supply. At 6.6 Volts DC input, and no load, it put out 4.8 Volts DC, dropping to 4.4 Volts DC at two Amps.(Likely caused by the lead length of the SBEC plus the servo cable on my break out leads. It still worked just fine with a 3.5 Amp load, double that of the typical ignition module.

I had to drop the input voltage down to 5.1 Volts before the CC SBEC output voltage began to sag with the two Amp load. FYI, the output voltage of those A123's or LiFe's hold 6.6 Volts DC for 90% of the cells milliampere hour capacity.
OK, I know very little about electric. I checked out Castle Creations 10A BEC and it shows 4.8 to 9v out. How would I get it to be 4.8 only? Don't mean to be a bother, I just don't understand.
Sep 18, 2019, 08:39 PM
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vollrathd's Avatar
Quote:
Originally Posted by GSAV8R
OK, I know very little about electric. I checked out Castle Creations 10A BEC and it shows 4.8 to 9v out. How would I get it to be 4.8 only? Don't mean to be a bother, I just don't understand.
No problem

The CC 10 Amp SBEC is programmable. You need their $20 programmer and a PC computer to program them to any voltage desired.

Those that buy the CC Electronic Speed Controls generally get a coupon for a free programmer.
Sep 19, 2019, 09:30 AM
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Ron van Sommeren's Avatar
No risk of ignition noise propagating into receiver/servos via the SBEC/LBEC?
Wouldn't a completely separate power supply, dedicated battery, be safer?

Vriendelijke groeten Ron
Without a watt-meter you are in the dark ... until something starts to glow
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Sep 19, 2019, 10:10 AM
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Quote:
Originally Posted by Ron van Sommeren
No risk of ignition noise propagating into receiver/servos via the SBEC/LBEC?
Wouldn't a completely separate power supply, dedicated battery, be safer?

Vriendelijke groeten Ron
Without a watt-meter you are in the dark ... until something starts to glow
e-flight calculators watt-meters diy motor tips&tricks Cumulus MFC
Sure! Do you know of a source for 4.8 volt battery that is not nicad or nimh?
Sep 19, 2019, 10:33 AM
Registered User
Just a point but putting switch mode voltage controlled items is series (or parallel) is not recommended.
Switch mode devices switch the full input voltage on and off very fast to give the desired average output voltage. If this output then directly drives another switch mode device without substantial voltage smoothing (capacitor?) the downstream controller may get confused as to what the input voltage really is and be unable to control the output voltage correctly.
Sep 19, 2019, 10:57 AM
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Thread OP
Quote:
Originally Posted by Quorneng
Just a point but putting switch mode voltage controlled items is series (or parallel) is not recommended.
Switch mode devices switch the full input voltage on and off very fast to give the desired average output voltage. If this output then directly drives another switch mode device without substantial voltage smoothing (capacitor?) the downstream controller may get confused as to what the input voltage really is and be unable to control the output voltage correctly.
Is there not a simple device to reduce higher voltage to 4.8 volts. That is all I am trying to do. I have two older ignition engines with systems that only allow 4.8 volts. The rest of my ignition engines can handle higher voltage. I feel like going out and kissing my old reliable magneto engines
Sep 19, 2019, 11:50 AM
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vollrathd's Avatar
Quote:
Originally Posted by GSAV8R
Is there not a simple device to reduce higher voltage to 4.8 volts. That is all I am trying to do. I have two older ignition engines with systems that only allow 4.8 volts. The rest of my ignition engines can handle higher voltage. I feel like going out and kissing my old reliable magneto engines
One could try putting several 10 Amp silicon diodes in series with the ignition modules red wire. Each diode will drop about 0.7 Volts DC, so two in series will drop 1.4 VDC. That's 5.2 Volts when fed by a LiFe battery.

FYI, my RC club members power their glasses with a pair of A123's, both plugged into the receiver. And the ignition module is plugged into one of the A123's.

No one has had interference problems on their Spektrum receivers. That, after many years and 1000's of flights.
Sep 19, 2019, 06:15 PM
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scirocco's Avatar
Unless the ignition module spec is a hard 4.80V, rather than 4 cell NiCd, it should be fine running off a 5V BEC, as a fully charged 4 cell pack is at about 6V - 4.8V is just the nominal voltage of 4 cells

I use a small 5V BEC running off a 2 cell LiFe, with the rx powered directly from the same pack. No interference issues.

IMO, no need to go to the expense of a programmable CC BEC just to run your ignition

Something like this is all you need for just the ignition https://hobbyking.com/en_us/micro-bec-5v-2a.html
Last edited by scirocco; Sep 19, 2019 at 06:41 PM. Reason: Added link
Sep 19, 2019, 07:32 PM
Registered User
vollrathd's Avatar
Quote:
Originally Posted by scirocco
Unless the ignition module spec is a hard 4.80V, rather than 4 cell NiCd, it should be fine running off a 5V BEC, as a fully charged 4 cell pack is at about 6V - 4.8V is just the nominal voltage of 4 cells

I use a small 5V BEC running off a 2 cell LiFe, with the rx powered directly from the same pack. No interference issues.

IMO, no need to go to the expense of a programmable CC BEC just to run your ignition

Something like this is all you need for just the ignition https://hobbyking.com/en_us/micro-bec-5v-2a.html
By looking at the HobbyKing unit, it IS a switch mode BEC that can likely handle the continuous power requirements of an ignition module. As compared to a linear type regulator that may not be able to handle the continuous power of those ignition modules.

One must verify that the HobbyKing unit can reliably put out the power required by the ignition module while its input is only 6.6 Volts DC from the LiFe battery pack.
Sep 19, 2019, 08:17 PM
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Thread OP
Quote:
Originally Posted by scirocco
Unless the ignition module spec is a hard 4.80V, rather than 4 cell NiCd, it should be fine running off a 5V BEC, as a fully charged 4 cell pack is at about 6V - 4.8V is just the nominal voltage of 4 cells

I use a small 5V BEC running off a 2 cell LiFe, with the rx powered directly from the same pack. No interference issues.

IMO, no need to go to the expense of a programmable CC BEC just to run your ignition

Something like this is all you need for just the ignition https://hobbyking.com/en_us/micro-bec-5v-2a.html
Thank you very much! I will go with your suggestion.


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