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LIPOLI SET UP FOR SPEED 500

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Old 09-02-2005, 03:54 PM
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afischer
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Default LIPOLI SET UP FOR SPEED 500

I bought a graupner speed 500 8.4V with a speed control Blue Arrow pp-30c (30 amps) and a Li-poly 11.1V 2100mAh. (Is for a 40" wingspan trainer)

The Speed 500 manuals states not to exceed more than 8.4 volts. Do you think guys I will burn the motor with this set up? recomendations, suggestions?

Thanks.
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Old 09-02-2005, 05:36 PM
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DHG
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Default RE: LIPOLI SET UP FOR SPEED 500

Yes, probably. That is, unless you get a wattmeter and reduce the size of the prop (i.e., lighten the load on the motor) so that the total watts are the same as with the original prop and the 8.4V Ni-Cd battery.

I have a Speed 400 setup that I was thinking about trying to use with an 11.1V Li-Po. I haven't done it yet, but this is the approach I was going to take ... I think it makes sense ... try it if you dare.

1. Fire up the motor with the fully charged 8.4V battery and the original prop. Measure the watts using a wattmeter. (Or if you don't have a wattmeter and want to live dangerously, measure the rpms with a tachometer.)

2. Turn everything off and plug in the fully charged 11.1V Li-Po in place of the 8.4V Ni-Cd.

3. Using the transmitter's endpoint adjustment, reduce the "high" throttle setting to about 50%, so that high throttle is really only telling the ESC to go to half throttle.

4. Turn everything on (with the transmitter stick at low throttle) and SLOWLY advance the throttle stick until the watts (or rpm) approach the original reading. If the stick goes all the way to full without matching the original reading, use the endpoint adjustment to gradually increase the "high" throttle setting until it gets there.

As I say, I haven't tried this yet, and I'm not sure it will actually work, but I can't think of a reason why it wouldn't ... if anyone else out there knows better, I'd be glad to know that before I fry something.
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Old 09-07-2005, 11:04 AM
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DHG
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Default RE: LIPOLI SET UP FOR SPEED 500

afischer,

Just a followup note: I assume that the speed control you bought is compatible with the Li-Po battery you bought at the same time ... the supplier should have made sure of that. Reason being, the battery eliminator circuit (BEC) in the speed control needs to shut off power to the motor before the voltage drops below the critical level to prevent battery damage. For a Ni-Cd or Ni-MH battery, that's around 1.1 volts per cell, or 7.7 volts for a 7-cell pack. If you're using a 3-cell Li-Po pack, the critical level is more like 9 or 10 volts. If it goes down to 7.7 volts, your Li-Po will be damaged. So if you have any doubt about where the voltage cutoff is set, read the manual and reprogram your speed control if necessary.

D.
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