NiMH or Lipo receiver pack

[jimmyhorns]

Well I collected my new (second hand) bird on Friday night, and all is as should be.

The receiver pack (which wasnt in the listing) is toast, can only get to 4.1V and its a 4 cell NiMH 4300mAH, so im guessing a cell is dead.

So now I need to get me a new receiver pack.....

I would usually buy a 4 cell eneloop (2000ish mAH) NiMH for my 30, however this is a 50. I have seen people on here using 2 cell lipos with a UBEC but worry about reliability

I need the equivilent to a 4.8V pack as it has the futaba S9254 tail servo which isnt HV (nor infact are any of the servos on board).

So which would you do?.. (and why)...high capacity NiMH (like old sub C packs) or Lipo and UBEC...


Thanks in advance

James

[tokenlefty]

Have you looked into the 2S LiFe packs? They will run the 6 volt electronics fine. I run 2S Lipo only when all the electronics can run at 8.4 volts. I don't like the extra point of failure with a BEC.

[jimmyhorns]

Originally Posted by tokenlefty

Have you looked into the 2S LiFe packs? They will run the 6 volt electronics fine. I run 2S Lipo only when all the electronics can run at 8.4 volts. I don't like the extra point of failure with a BEC.

no I havent... yet

Im not sure if my chargers do LiFe... but will look into it.

I too dont like the extra point of failure with a UBEC, which is why I have used NiMH until now.

Thanks for the idea

[jimmyhorns]

so the 6.6V wont be an issue for the servos?/...

[Kneedragger75]

Not if all servos are rated for 6.0 volts.

[jimmyhorns]

Originally Posted by Kneedragger75

Not if all servos are rated for 6.0 volts.

They arnt, thats the problem.

The tail servo is the S9254 which in the instructions states is only for 4.8V

So what is the voltage of the 6.6 LiFe when they are fully charged?..

[tokenlefty]

The LiFe pack will charge to 7.2 and drop to 6.6v very quickly and then pretty much remain at around 6.2 volts before it drops off very quickly. The cutoff is generally around 2.2V per cell. So if you have one of those step down regulators that plugs in line with the tail servo, they are generally just a diode which drops the voltage 0.7 volts so from a fully charge LiFe you will be running the tail at 6.5v for the first minute or so until the battery drops to its operating point. They use to make a dual diode step down which would get you to 5.8v and then a nominal 5.2v. Which would work fine. I know of many people running the 9254 at 6V but it does stress the electronics.

The other problem is finding an LED indicator that works with a LiFe battery since they hold voltage really well and then just drop off quickly.

For smaller Heli's running 4-5S or lower a BEC generally works well with a small failure point since it doesn't need to reduce the voltage as far. I have been running the Align version on my 600 at 6S with no issues for a couple of years. However, with 10S or 12S based systems I install the HV electronics and run the 2S Lipo. That works very well and if you add in the price of a ubec at that voltage level, its pretty much a wash.

The only real difference between the NiMH and the Lipo is the charge time. If charging overnight isn't an issue and you are getting the flights want after a charge your best bet would probably be to get another NiMH.

If your not getting the number of flights in that you want in a day then moving to a uBEC and Lipo will keep you flying all day. Or you can buy 2 of the NiMh and swap them. Since the Lipo is only 2S and the voltage point at 8.4V the uBEC isn't stressed as much regulating to 5-6V and shouldn't fail if its a quality unit. If its still a concern a dual diode step down for the tail servo with a LiFE battery should work without any problems.

[SQRT(-2)]

Originally Posted by jimmyhorns

They arnt, thats the problem.

The tail servo is the S9254 which in the instructions states is only for 4.8V

So what is the voltage of the 6.6 LiFe when they are fully charged?..

You can get a little voltage step down that goes between the gyro and the servo. It is like a BEC just for that servo. They are really cheep.

http://helidirect.com/align-51v-two-...tor-p-7099.hdx
http://helidirect.com/western-roboti...age-p-4665.hdx

Now if you use a BEC, there is an advantage. You will get 6v to your electronics as long as the battery is above 6v. This means they will always be at top speed and power. Going from a 6.6 LiFe or a 7.2 Lipo is not too much of a step down and really, it should not fail if you get a half way decent one.