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Author Topic: Generator current vs. RPM?  (Read 8721 times)

Joshua Doremire

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Generator current vs. RPM?
« on: April 18, 2013, 11:32:16 AM »

What is the generator amp output at the calculated lowest 900 engine RPM? What minimum RPM gives you the full current limited 50 Amp output? Would the crew have used this higher RPM to transmit on dry land? Are there engine heating issues with 0 pitch on the props? 

Looking through the research on battery life, capacity, radio current requirements, generator output limits... I find this unanswered question.

Idle RPM has the generator kicking in and useable voltage at 900 engine RPM per your research and testing. I doubt it had full current available. Takeoff engine RPM is listed as 2200. (Variable props make me ask what cruise RPM would be as it isn't listed.) This is a wide RPM spread because generator voltage and amperage vary with RPM. Specifically more Amps with higher RPM. 

Regulators can control the field for voltage as soon as enough RPM is made to make minimum voltage required. Maximum current is also regulated by the regulator at 50 Amps. But there has to be a minimum RPM that will generate the full 50 Amps. Automotive engines have a wider RPM spread and this is the experience I ask the question from. 

Full output is not needed for battery charging. It is needed for radio transmission otherwise you pull more current from the battery when transmitting. With the 'undersized' generator there is a large power management burden placed on the crew. It would also limit the total time they could transmit and keep the batteries up to start the engines again. 
 
Depending on the % of full output at 900 RPM it may not make a statistical difference to the overall picture. 
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Joshua Doremire

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Re: Generator current vs. RPM?
« Reply #1 on: July 15, 2013, 11:57:15 AM »

Try this for a start.  There is more information among TIGHAR's archives of data and bulletins on this site.

Thanks. Ric already shared lots of info on this down to the generator drive type and ratio to fit the RPM range. Best I can tell full amp load was not part of the fuel consumption tests. Regardless with the amount of evidence, from witnesses that lived on the island and RDF logs this is just a curiosity anyway. 
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