I have a JR TX and would usually have the stock 600 or 700 mAh pack near death by the time I had 4 or 5 flights on a fresh charge, I have since switched to a 2200mAh Lipo pack and have had no trouble at all... I have not gotten it anywhere near dead and could probably get 3 or 4 days worth of flights at the field before having to recharge. The JR transmitters show the realtime voltage of the pack making life easier as well. As for the RX packs a loaded volt meter is the way to go. I have a digital meter that accepts bannana plugs so I simply made a loaded lead to plug into my RX packs. I believe it is a 2 watt 10 ohm resistor that I used which gives a 500 mAh load on a 5V pack. A little heat shrink tubing over the resistor makes for a nice clean lead.

Edit: Use a 2.5 watt or greater 10 ohm resistor [8D]

That's pretty much what I do.

With that setup you will be generating 2.1 to 2.5 watts or even slightly more, so I would recommend upping the wattage rating on the resistor. The setup will draw anywhere between 436mA to 533mA depending on the particular resistor (5% tolerance - gold band) in case anybody is wondering.

If you use conservative quitting voltages you will be fine.

What wattage do you recommend? Mine maybe be higher, but I would have to look, it has been a while since I put it together.

You could probably get away with what you have, but the resistor will probably just enjoy a shorter life. It doesn't matter exactly what wattage, just get it over 2.5 watts since that's what the circuit will draw. A three or five watter will do well.

Mine is more than likely a 2.5, but if it ever stops working I will know why. Thanks for the tip!

Could be, but 2.5 is not standard. Glad I could shed some light on things. I have mine attached using a small socket so that I can apply an appropriate load to any type of battery by changing out the resistor value.

Sorry to drag up an old thread. Thought I would ask in this one instead of starting a new one.

I am wondering what % of mAh is it safe to pull out of a NiMH battery?

For instance I have a .40 sized ultimate running 5 standard (HS-311) servo's. The battery is a 5 cell (6v) 1200MaH battery. I get 9 minutes out of a tank and currently do 3x 9 minute flights and then charge the receiver pack.
After the 3x 9 minute flights the RX pack takes between 270 and 300mAh. Should I get say another 2 or 3 flights out of the plane safely or should I continue to do what I am doing?

In short I would like to know the % of total capacity I can use before the battery will drop dead.

A battery pack rarely gives the full rated capacity, so with that in mind, plus a margin for safety, I would assume leaving about 200mAh or more charge in the pack.

In other words 9, 9 minute flights based upon your average would be fine.

However I typically start checking the battery condition when I hit the half way point, and every flight there-after just to be sure.

a lot of people go nuts charging their packs. if you have only used 200-300 mah that means you still have 1000 mah left. why did you buy a bigger pack if you arnt going to use it.
the lowest i would go is 1000 mah discharged. and that still gives you 2-3 flights worth of battery power in case you forgot to check voltage.
if you wanted to be safer recharge at 500 mah.

my point is this. when i go to the field i go to fly (idk about others, some like to socialize more than fly). if you want to fly your plane then do so.
now say you stop for lunch or something. then go ahead and charge them.
just dont waste your flying time charging your packs unless you need to (which you dont when you are only drawing 200 mah from them)


i would cycle your packs, check their actual MAH reading. and recharge when you get to around 800-1000 mah discharged (200 mah left depending on actual compasity)

Thanks opjose and jimmyjames.

I had only ever pulled around 300mah out of the packs because I wasnt sure how much I could use before I was at risk of the pack being depleted enough to cause an issue with my Spektrum RX's.

The pack in the Ultimate is only about 50mah below its 1200mah rating. So I get 1150mah out of it.

I go to the field to both fly and socialise, but was thinking I might be over cautious by charging every 3 flights. I will start doing 5 and will check voltage every flight from the third flight. And then gradually increase the flights til I am using roughly 700mah from it. Or somewhere I feel comfortable anyway.

My other two planes I currently fly have Voltwatch's onboard so will keep an eye on them as well.

Watched a 1.40 sized Katana lawn dart from about 250ft up full throttle the other day at the club. Due to a faulty (or not properly charged) rx pack. Destroyed everything including the 1.20 OS 2 stroke. Want to try and avoid this sort of thing happening by understanding how to properly monitor the packs usage etc.

Just one more quick question.

With the 1200mah pack for example. At what point should the pack be thrown out as capacity drops. Say for instance after a couple of years the pack loses 300mah from its original capacity should the pack be disposed of?

Thanks.

The guidlines that I have seen for discarding a pack range from 70-80% So with your 1200mah packs that would be either 840mah(70%) or 960mah(80%) depending on who you follow. When I cycle my packs, I put a lable on them with the date and the test numbers (both mah and %) so I know how the are holding up.

Excellent info.
Thanks crossman.


Great info from everyone. Cheers