Safe Minimum Flying Voltage
 

What is considered the safe minimum flying voltage for 4.8v and 6v batteries. I never let mine get low, but I've always wondered about the actual low safe voltage. thanks

RE: Safe Minimum Flying Voltage
 

I believe if you get below 1.2V per cell, you're flying on borrowed time. I won't take off if a 4 cell pack is down to 4.9V and a 6 cell pack is down to 6.2. Actually, I tend to field charge them at 5.0V and 6.3V. I'm sure there's a lot of usable current left, but better safe than sorry.

RE: Safe Minimum Flying Voltage
 

Jim

Do you mean 7.2 V for the 6 cell????

Ross

RE: Safe Minimum Flying Voltage
 

think he meant 6v, 5 cell pack...

RE: Safe Minimum Flying Voltage
 

I would like to hear other comments on this. Is this correct? The pack is rated at 4.8 volts, so at 4.9 it is still in an overcharge state...

I really have no idea, just want other opinions.

RE: Safe Minimum Flying Voltage
 

Yes, I was referring to 4 cell and 5 cell packs.

RE: Safe Minimum Flying Voltage
 

4.8v and 6.0v are conservative readings for a 4cell and 5 cell pack. At these readings, if taken with a good ESV meter with a 250ma load, there would be more than 50% of the capacity remaining in a normal pack under normal flying conditions.

I typically fly mine to 4.7v and 5.9v, which leaves about 3 flights in reserve. I arrived at 4.7v and 5.9v from bench testing and then field testing with constant monitoring to verify that I am actually leaving about 1/3rd of the rated capacity and a 3 flight reserve for safety. If you are not consistent enough to monitor your packs, or don't want to take the time to do capacity checking, just fly to 4.8V and 6.0V. This will put you at the start of the flat portion of the discharge curve, or leave you with about 50% remaining capacity. In essence, a very conservative and safe cut off voltage.

The attached chart shows the discharge curve for one of my 5cell packs. You can see that at 6.0v, you are only about 1/3rd of the way into the total capacity. Very conservative. At 5.9v, you would be about 2/3rds into the capacity, with about 1/3rd remaining capacity. Still more than enough of a safety buffer if you have verified your ESV meter with a capacity cycle to verify its reading properly and at 5.9v, you do indeed have 33% remaining capacity.

The pack below was a well used NiMh 2700mah pack taken from a 40% Giles 300. However, it is typical with any of the other packs I use, both 4 cell and 5 cell. The discharge curves are very similar.

RE: Safe Minimum Flying Voltage
 

I second SFAUST.

After extensive research and practice; I check with a loaded voltmeter and stop flying when 4.8 volt batteries are down to 4.7 and 6 volt batteries are down to 5.9 volt.

-ZM

RE: Safe Minimum Flying Voltage
 

Speaking of loaded voltmeters, when do you use 0.5A, 1.0A, and 1.5A with respect to the battery capacity ?

RE: Safe Minimum Flying Voltage
 

I try to base the loaded ESV meter reading to minic the potential load on the battery from the airplane. Basically, I use 250ma for my smaller airplanes (typically 4 or 5 channels, under 80" wing span), and use 1amp for the larger airplanes (8-10 channels, 10-12 servos, etc), and .5amp for those inbetween. I stick with that loaded ESV value for all measurements, be it capacity testing, discharging, plotting the battery curve, and measurements at the field. Consistency is probably far more important that the actual loaded value used, as your readings will be more predictable with a consistent procedure. If in doubt what to use, error toward a higher reading, but no need to go overboard either.