Lipo size for 700L Dominator?

[tonycopter]

I have eight Gens Ace 5100 mah 35C lipos which I use on my T Rex 550 and Logo 500SE.
I want to try a 700L Dominator.(RH70E11XT). Will my lipos work OK with the stock electrics, which are:

BL815H head servos
BL855H tail servo
Castle EDGE HV 120
800MX Motor (520KV)

I will also be using a Bavarian Demon 3SX with 2 Spektrum satelites. DX8 radio.

I know I need to connect the lipos in series but I'm not sure about the 35C rating. Will it be enough? Any problems likely either with flight or anything overheating etc? My flying is general aerobatics. I do get confused over topics like "current draw" and have no idea how much power the servos and motor will require. I believe I also need a 2S lipo for something but not sure what!

Any advice very welcome

[Excalibur3]

If your not flying hard 3d it will be fine. You will mostly notice the power diff when it's cold ( like 20 degrees or less) but depends were you live . But 35c is fine for mild acrobatics

[rhodesengr]

Originally Posted by tonycopter

I will also be using a Bavarian Demon 3SX with 2 Spektrum satelites. DX8 radio.

I believe I also need a 2S lipo for something but not sure what!

Any advice very welcome

The 2S LiPo would be an RX battery to run the 3SX and the servos. You can also use a BEC like the Castle BEC Pro.

You might want to consider using an AR8000 or AR7610 instead of the Sat-only setup. Check out this thread.
https://www.helifreak.com/showthread.php?t=675874
and post #14 in particular.

be sure to read in the FAQ for 3SX newcomers
https://www.helifreak.com/showthread.php?t=613552

Also be aware that the DX8 is fine in terms of flying but it is not ideal for the switch programming required for the Rescue and Self level features. It does not have the advanced switch programming of the newer models. There is a sticky on how to set up your DX8.

I have a 700L with a 3SX and it is great. You will love it.

Your batteries should be fine.

[Solmanbandit]

I have been running sats only for quite some time and work fine. I haven't seen any evidence that running two sats are unsafe or even an issue. The main thing is that you are running two of them and not just one. Since you are running HV servos, there is no reason to use a BEC. It is just one less thing for you to worry about.

As for the batteries, they will work. I have been running 45C pulse and 60C eco powers and even after hard flying, they have not been getting anywhere near hot. So if you notice your batteries getting hot, you may want to consider up the C rating.

[HarveyR]

The BEC is to avoid the 2S altogether... the electronics get powered from the 50V PowerPack through the BEC, so no 2S to mess around with !

[atkin]

I think sats can be an issue when you're running a bavarian demon gyro.

Originally Posted by Solmanbandit

I have been running sats only for quite some time and work fine. I haven't seen any evidence that running two sats are unsafe or even an issue. The main thing is that you are running two of them and not just one. Since you are running HV servos, there is no reason to use a BEC. It is just one less thing for you to worry about.

As for the batteries, they will work. I have been running 45C pulse and 60C eco powers and even after hard flying, they have not been getting anywhere near hot. So if you notice your batteries getting hot, you may want to consider up the C rating.

[Solmanbandit]

Originally Posted by atkin

I think sats can be an issue when you're running a bavarian demon gyro.

That I wouldn't know about. I run Beastx and Ikon.

[tonycopter]

Thank you everyone for the advice. I had no idea that two satellites are inferior to a standard RX. My 550 and logo 500 both have 3sx and 2 sats without any trouble but for the 700L I will now consider fitting an AR8000 or similar.

I use spektrum so should I use an external BEC? I found this on RC Universe forum:

Should I use an external BEC?
If you are using digital servos or more than 3S Lipos then yes definitely as the linear mode bec's will overheat trying to provide any useful output.
If you are running spektrum 2.4Ghz receivers then it is highly advisable as they draw significantly more current than a normal receiver and are very susceptible to voltage drops. If your linear bec is trying to provide a lot of current it will overheat and fail to provide the correct voltage causing the spektrum receiver to reboot.

I don't use one on any of my other helis and nothing seems to overheat, but the 700L has a bigger esc and motor and all those posh servos! Also not quite sure now if I need the 2S lipo or not.

I will post again when I've actually got this 700L beast.

[atkin]

I don't use a 2S lipo for my Trex700 HV. I prefer to not charge one more battery. I use this BEC, but there is one from Western Digital that is also fantastic:

http://www.fast-lad.co.uk/store/gryp...5-p-18589.html

arguing BEC vs 2S Lipo might start a holy war.

[semperfib400]

The 35C rating would be over the max amp rating of the ESC by 18 amps. So it's just a little above what the ESC is capable of sustaining.

With gentle flying they should be ok.

[Solmanbandit]

I don't use a 2S lipo for my Trex700 HV. I prefer to not charge one more battery. I use this BEC, but there is one from Western Digital that is also fantastic:

I have had a few issues where if I did not have a separate receiver battery, I would have not been able to auto down safely. I can easily get 3 flights with my 1800 mah receiver battery and charging it doesn't take long. I don't find it to be a nuisance.

The 35C rating would be over the max amp rating of the ESC by 18 amps. So it's just a little above what the ESC is capable of sustaining.

I don't get what you are saying. What does the C rating of the battery have to do with the amp rating of the ESC?

[semperfib400]

You take the C rating of the battery times the capacity to get the total amps the battery is capable of supplying.

So 5100 mah (or 5.1 in this case) X 35 = 178 amps that the battery can supply. The ESC is rated at sustaining 160 amps in the 700L TOP model.

Does that make sense? That just a formula I've always kinda used determine what a battery is capable ... also works to determine a charge rate.

If those batteries have a 5C charge rate... that means you could charge those cells at around 25 amps!!!

[KSHeli]

Originally Posted by Solmanbandit

I have had a few issues where if I did not have a separate receiver battery, I would have not been able to auto down safely. I can easily get 3 flights with my 1800 mah receiver battery and charging it doesn't take long. I don't find it to be a nuisance.


I don't get what you are saying. What does the C rating of the battery have to do with the amp rating of the ESC?

Its referring to how fast the battery will allow charge to flow to the esc. Fly 30C flight pack setup and then fly a 60C setup and you will definitely feel the power difference in the helis response. Plus the esc, motor and battery packs will come down after a comparable flight noticeably cooler and the battery packs will last lots longer if you're flying hard 3d. I have a 30C 12s 5000 mah setup and a 60C setup, the 30C works just fine for general sport flight and working on orientations, the 60C I save for when I really want to push it.

[Excalibur3]

I've seen plenty of new guys fly 35c lipos for over a year. No issues. The only time they ever noticed a problem was in cold weather on hard collective moves it bogs alittle.
Other than that they are fine until you start flying like you stole it.

[rhodesengr]

Originally Posted by tonycopter

Thank you everyone for the advice. I had no idea that two satellites are inferior to a standard RX. My 550 and logo 500 both have 3sx and 2 sats without any trouble but for the 700L I will now consider fitting an AR8000 or similar.

I use spektrum so should I use an external BEC? I found this on RC Universe forum:

Since the HV ESC's do not even have an internal BEC, your only options are to use an external BEC or a battery. It is purely a matter of personal preference. I have been using an LiFe battery on my 700's. I use the Hobbico LIFE Source ones. They put put 6.5V nominal. You can also use 2S LiPo since the 700L comes with HV servos. The BEC vs battery issues has been discussed countless times. Both have pros and cons. The battery has an aspect of redundancy. If the main flight pack fails, you still have control power. Any of the leading 10Amp continuous models would be ok like the Castle BEC pro or equivalent.

The Sats vs Full Rx issue has also been hotly debated. Many people have the Sats-only working with the 3SX as well as other FBL controller. With the 3SX, you need a good stable voltage source of 6V or more and you must also bind in DSMX with 11ms Frame rate so you need to set your TX for 11ms FR.

However, I think think on big powerful models, it is just safer to go with the full RX. It is worth it just to be able to engage SL on Failsafe. You can't do that with sats-only.

[tonycopter]

WOW, there's a lot to this heli business! I'm tempted now to go with the 2S lipo and AR8000 RX.
Interesting to hear what KSHeli said:
Fly 30C flight pack setup and then fly a 60C setup and you will definitely feel the power difference in the helis response. Plus the esc, motor and battery packs will come down after a comparable flight noticeably cooler and the battery packs will last lots longer if you're flying hard 3d. I have a 30C 12s 5000 mah setup and a 60C setup, the 30C works just fine for general sport flight and working on orientations, the 60C I save for when I really want to push it.

So a larger C rating gives the battery an easier time. I have noticed sometimes when I try to increase the idle up throttle setting of my 550, the lipo tends to be warmer after the flight but so far nothing apparently to. I have a large investment in my 6S 35C lipos which is why I want a heli that can be flown with them.
Thanks again for your time to reply.

[rhodesengr]

A 700 will run less current than a 550 in most cases on average. You are getting a 2x increase in the delivered power from the voltage, so the current can be less. My cruising around current is only about 35 Amps on my 700L so that is only about 7C. I see spikes around 60 to 80 amps when I do flips and stuff. I think I had more trouble with the ESC getting hot than the batteries. That 120HV does not like being run at low HS. Runs hotter at 1800 than at 2000 for example. Also the stock PWM setting is "outrunner", at least mine was. You will want to change that to 12 kHz. That will run cooler.

[Solmanbandit]

Does that make sense? That just a formula I've always kinda used determine what a battery is capable ... also works to determine a charge rate.

I understand the concept, just didn't see how it pertained to the post. I think I see what you got going on.