Minimum voltage to safely fly
 

I have a 2600mah lithium ion battery (with regulator but I check voltage before the regulator) and want to know what's the minimum voltage I can go down to with a 1amp load while at the field to safely fly. I have a dig voltmeter with .5, 1 and 2 amp load settings and check with 1amp as I don't think my servos will use more than that on average, especially the way I fly, very little throttle management, very little rudder, mostly aileron, then elevator.

I was told by one fella that 6.6 volts would be the absolute minimum so I put a label on my plane "6.6v min" to remind me.

Yesterday, while flying, another guy says, what's that mean? I said that's my minimum voltage to fly at. He says, 'NO WAY! You shouldn't go any lower than 7volts with a 1amp load!" I pointed out without a load I was up to 7.7V and with a .5 amp load I was over 7.1V. But at 1amp, I was reading just about 6.8V and with a 2amp load I was at 6.4, and he said it wasn't safe to fly, so I stopped flying for the day.

What amp rate should I use and what's the lowest voltage I should fly at safely at that amperage? The servos are five JR DS821 and a single small servo for throttle.

RE: Minimum voltage to safely fly
 

On my gassers that i use 7.4 volt litium ion batteries i just use a standard hobbico volt meter with a built in load, and if i see it is under 7.2 i dont fly... if i take more than one plane i can usually fly both saturday and sunday and be ok ... Ill have to recharge my ignition battery before i have to recharge the receiver battery

RE: Minimum voltage to safely fly
 

Fromeco recommend stop flying when the 8-ball show 7,0V at 1A load. I guess there is a lot of margins here... In addition the 8-ball work with LiIon too, which often have a lower nominal voltage. Thus I would fly until I read 7,0V without hesitating ;)

RE: Minimum voltage to safely fly
 

When the nominal voltage is 6.6V -Fly- It will stay at this for quite some time, but once it shows below 6.6 look at a recharge. That said, you will get a LOT of flying in between charges.
-Snuts-

RE: Minimum voltage to safely fly
 

I just checked Fromeco site and their manual states:

When to Recharge
Fromeco recommends 7.0 volts as a NO-FLY voltage under a 1 amp load. Batteries should be charged if this voltage is reached while testing at a 1 amp load.

Based on that I guess my friend was right. I'm going to go by that from now on.

RE: Minimum voltage to safely fly
 

I agree with this. The question is about the minimum voltage with which you can safely fly. It is not the same as "what should I run my batteries down to before I recharge". RadicalRC suggests never letting the voltage get below 3.0 volts per cell, which would be 6 volts on your two cell battery. Because you are running a lithium battery which is very efficient, flying the plane at 6.6 volts for one flight will NOT bring the battery to a dangerous level. I believe this is the lowest point with which you can safely fly the plane AND not damage the battery.

That being said, a fully charged 2600mah lithium battery should never get close to that point after one day flying, no matter how much you fly the plane. I don't even think it would get close to that after two full days of flying. So, while 6.6 could be the absolute minimum voltage to fly safely, you really shouldn't even be getting close to that number.

http://www.radicalrc.com/lipolyinstructions2.html

RE: Minimum voltage to safely fly
 

I just did a little more research at TBM site and it pretty much agrees with Fromeco's info that NO FLY voltage is 7.0 Volts under a 1amp load, but goes into more detail. Here's what it says (I've bolded some of it):

= = = = = = = = = = = =


- When a 2-cell pack reads 6.8v under a 1 amp load on a new pack, it has no capacity left.

- When a 2-cell pack reads 6.9v under a 1 amp load on a new pack, there is about 25% of the capacity left.

- Each 15 minute flight on an average 35% airplane uses about 400 mah. This offers 12 flights on two 2-cell packs. When you test the batteries and they show 6.9v, you have enough battery life for a few more flights, but don't do it!!

Be safe. When either battery reads 6.9v (or higher), stop flying and recharge.

= = = = = = = = = = = = = =

Again, with a 1 amp load, I'm going to stop flying when I get down to 7.0V. I'll charge before each day's flying and should be set for the day. Of course, I'll check voltage under a 1 amp load between flights to make sure I don't get down to 7 volts.

RE: Minimum voltage to safely fly
 

to be on the safe side follow manufactures recommendations..... My 7.4 5200 mah packs are 8.3 or so volts fully charged If you charge them friday night you should be able to fly a lot .. Since i dont have a one amp load,( i think the its a 250 mah load built in my volt meter) i stop flying at 7.2

Check them after every flight for a few flight sessions to better assess your batteries..

RE: Minimum voltage to safely fly
 

It's frustrating that there's so much information that doesn't quite line up out there. Obviously the higher number you found is safer, so that's what I would go with.

Radical RC is a well known and trusted resource for battery information. I don't doubt their knowledge but it is not a bad idea to take the safer recommendation.

I'll go back to my corner now[&o] :D

RE: Minimum voltage to safely fly
 

I used my balancing charger to charge the 2600mah Li-ion battery from the original question and it finished after 1.5 hours.

After charging, I read 8.5V without a load and 7.45V with a 1amp load. This is well above my new 7.0V NO FLY voltage with a 1amp load, so I should be able to fly several 10 minute flights in a day without going down to 7.0 but I'll check between flights to make sure, then charge before each flying day.

RE: Minimum voltage to safely fly
 

The man said -LITHIUM/ION-
-Snuts-

RE: Minimum voltage to safely fly
 

Yes, it is a lithium Ion battery.