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Voltage Converter?

Old 02-08-2013, 09:19 AM
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warbirdfanatic
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Default Voltage Converter?

Hey Guys,

just a quick question, I have a Jetcentral Falcon 100 and it came with a NiCd which I haven't used in yonks! I use 7.4v lipos for all my other jet engines but Eric warned me that it wouldn't be adviseable to connect a 7.4v to an ECU that normally accepts 7.2v from the Nicad, is there a voltage converter about that will just convert to a constant 7.2v source?

The reason I ask is that I took the risk and connected my lipo and upon preheat the leads started to get a bit hot on the starter connection once it span up to max motor RPM.

The ECU is totally fine and no damage, it just appeared that the plastic coating on the wires soldered to the PCB got a little hotter than normal etc and I would like to prevent this.

I've seen that Hobbyking sell some UBECs that convert 11.1V down to 7.2V but didn't know if anyone's had any dealings with such?

If need be, I might just design a converter that will dissipate the .2v as heat through a heatsink but this takes time and I just want to get the engine started!!!!

I don't trust NiCd's like I used to and it's rare to see them about! Plus the memory effect just wound me up (remember power drills before LiPo took over!)
Old 02-08-2013, 10:09 AM
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iflyrcjets
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Default RE: Voltage Converter?

What about one of these. They are fully programable to what ever voltage you want.
http://www.castlecreations.com/products/ccbec.html
Old 02-08-2013, 10:59 AM
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Default RE: Voltage Converter?

Cheers bud!

Just ordered one :-)

It just saves the hassle of losing an ECU over .2 volts!!!
Old 02-08-2013, 11:48 AM
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Default RE: Voltage Converter?

Another 0.2 volts should be no problem. I have a7 year oldFalcon that came with nicads and I've been running it on a 7.4 v Lipo for the past 4 years with no issues. I've also made the same switch on my two Wrens (same ECU as the Falcon). They all work fine.

Joe
Old 02-08-2013, 12:07 PM
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Default RE: Voltage Converter?

A diode soldered to the positive will give you a .7 volt reduction.


Old 02-08-2013, 12:17 PM
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Default RE: Voltage Converter?

Dont overcomplicate it . I think an extra .2 volts will draw a little less current at startup and should help rather than hurt.

A DC-DC converter just adds one more item to fail in the system. I had a buddy loose his Viper because he wanted to run lipos instead of A123's on his Rx. The regulator did a meltdown .. shortly thereafter so did the jet.

If you only want to drop .2 volts a common trick is to put a rectifier diode in series from the battery. They have a voltage drop of about .2 volts. just make sure you use one large enough to handle the starter current.

Steve
Old 02-08-2013, 12:56 PM
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Default RE: Voltage Converter?

Another 0.2 volts should be no problem. I have a 7 year old Falcon that came with nicads and I've been running it on a 7.4 v Lipo for the past 4 years with no issues. I've also made the same switch on my two Wrens (same ECU as the Falcon). They all work fine.
What Joe said.

The only thing that has changed is the lipo is hallf the weight & size. - John.
Old 02-09-2013, 05:33 AM
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warbirdfanatic
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Default RE: Voltage Converter?

Cheers guys,

It was just worrying that the ECU started to smoke so putting two and two together this was the only thing I could think of. The previous owner only put 12 minutes total runtime on the engine of which it's then been sitting in its case for the last 5 years.

Any other reason it would smoke? It happened on preheat when it shot up past 3000RPMs to engage the fuel pump so I just literally yanked the battery!
Old 02-09-2013, 08:01 AM
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Default RE: Voltage Converter?

Is this a kero start?
The Castle regulator is rated for 10 amps max. An ECU battery needs to be able to supply a fair amount of amps during start up. Kero start a lot more Amps than gas start.
You might want to find a Nixx pack to borrow to do a test to see how many Amps your setup needs to start, then you will know what you need to do on the power supply side.

A 6 cell 7.2V NiCd or NiMh fully charged is near 9V, a 2 cell 7.4V LiPo fully charged is 8.4V.

If you have wires getting hot, I would do some checking to be sure that there is not some other issue.
Old 02-09-2013, 10:03 AM
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Default RE: Voltage Converter?

Very true!

It's a gas start (would be handy if they do a Kero start upgrade though)



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