Battery Voltage

[Bob S.]

I know I need to change out my battery... Today I flew for 30 minutes out to the lake and back and thought my TO voltage was less than 12v but had been on charge for 6 hours this morning and every morning for the last two weeks or so at least...  SO I was a dummy and took off anyway at 11.6V  I got out to the lake (Medina Lake) and noticed that my voltage was down to 7.5V and about 15 miles from home.... Uh oh.... How low will it go now?? so made a bee line to home keeping a close eye on the Voltmeter.... Opened the throttle all the way and gained a few 100's feet of altitude on my way home.... Nothing can replace altitude when you run out of go on your motor, right?   When I got closer to home, I reduced the throttle a bit and the volts went UP (to 7.6V) so then and there I KNEW I was going to get home.... Now the question: What is the lowest voltage the 009 distributor and coil will the 1/2 VW fly on???  I don't know. I got home and shut it off and tomorrow I am going to get a new battery!! Just wondered if anybody has ever tested to see where the coil quits working..... I think I heard that 6.0V is a break off point. Anybody know?

[dz1sfb]

Bob,
If memory serves me correctly, The issue becomes more about how big a plug gap can lower voltage jump. Of course the secondary winding voltage of your coil is directly proportional to the input voltage on the primary side. Glad you made it back without incident. What type of rechargeable battery are you using?

[Bob S.]

I am using the suggested 7.5 AHr 12v sealed lead-acid battery as used in a number of applications Mainly for UPS computer back-up to deer feeders. I have a 2 amp charger that is on a timer to charge the battery for 6 hours every 24 in an attempt to have my battery "ready" when I am to fly....
There has been some talk about using a LiPo battery to save weight but I haven't been sold on that yet.

[joecnc2006]

I was curious about a Lipo battery also, would be interesting to do a load test for each and see the run time, would need to know what the max. draw is from the 1/2 VW. of course with a Lipo i would place it in a fire box or a Lipo bag when testing.

[Steve]

I was curious about a Lipo battery also, would be interesting to do a load test for each and see the run time, would need to know what the max. draw is from the 1/2 VW. of course with a Lipo i would place it in a fire box or a Lipo bag when testing.

A caution on the Lipo batteries as relates to use in a total loss system... The lead acid batteries we use lose their voltage in a fairly smooth downward curve... There is witness to that characteristic in the original post...

The Lipo battery is reported to hold a charge well but has a steep drop in voltage at the end of the charge cycle... There has been constant improvement in these batteries but I'm not aware of any change in their steep voltage drop at the end of the charge cycle... Others have found the 009 distr with points will fire down to 9 volts reliably - Bob got his to go more...

There is a lot to be said for Jim Hardies' air driven generator "trade name 'GeniPod'" combined with a lead acid battery of 3.5 amps - the complete system is almost the same weight as the plans directed 7.5 amp total loss battery...

[Bob S.]

If there is ONE THING I DO NOT want in my Eagle is a FIRE! and I have seen TOO MANY LiPo's puff up, vent and catch fire! 

I am going to stick to the Lead-acid batteries!!  Only I will be a bit more religous in changing mine out!! 

They are 1) cheaper than LiPo's and 2) don't puff up and catch fire!!!!

[leshoman]

Bob
check your voltmeter in the machine with a good voltmeter, I had lots of problems and found the voltmeter in eagle was not always correct. did a lot of worrying for no reason, finally after 4th meter have one that is consistent and seems accurate.