Think I messed up

[tnreefguy]

Well I have done it. I decided to purchase a new reciever battery and went with NiMH without serching for tips. Turned on the trusty computer and went to a site called batteryspace.com and they had a sale on NiMH 3000 mah sub c packs. I bought two for a combo deal and also bought a transmitter pack as well to replace my low capacity stock 9c battery. I slow trickle charged them to capacity then discharged them then charged them again. Should i be worried. I did a test with my futaba battery checker and discharged it for 15 mins at 1.0 amp then checked the voltage. still good. Any imput would be helpful.

[Shortman]

Is there a problem with the packs or are you just making sure your cycling them correctly?

Just remember to cycle your NiMH packs 3-5 times at a C/10 or C/16 rate and repeat. The first few cycles your capacity will not be at 100%, but as you cycle it 3-5 times it gets better and better.

Just curious, what transmitter pack did you get for the 9C?

[tnreefguy]

I was looking at some posts about voltage drops that occur with some Nimh packs. The pack for my 9c was a square 2000 mah AA pack. I bought it to replace my 700 mah stock battery.

[Shortman]

You shouldn't have to worry about any voltage drops with your 2000mah NiMh pack. It sounds like they are speaking of using this cell in the actual rx application of the heli where there can be big spikes of power from the digital servos. Your transmitter hardly pulls that much power, maybe 300mah an hour or so, no where near the max limit discharge of a 2000mah NiMh pack.

Just rememeber to cycle it a few times and then go ahead and have some fun.

[tnreefguy]

I was just worried about the reciever pack. It is a 3000mah 4.8v type battery. My chopper has all digital servos, gv1 and a 601. But after doing more research I found the problem to mostly center around the AA cell on a high discharge rate.

[Shortman]

You really shouldn't have problems with a NiMH pack at all, I am kind of curious as to the others having problems with the "high discharge rate", because I've used them in Giant Scale planes with 10+ digital servos ganged on one single NiMh pack pulling a lot of juice and it works out just fine. As long as you cycle it you should be fine, there should be no reason the helicopter would pull more then about 2-3 amps continuous which is well within todays AA nimh cells.

[tnreefguy]

Thanks for the input.
:D

[Shortman]

Not a problem, please keep me up to date on how your pack performs. I was going to say, another great NiMH pack that can handle more amps than the same capacity Li Poly/Ion packs would be the GP 3300s and 3600/3700s. GP (Gold Peak) makes very high quality NiMH cells.

[DavidH]

tnreefguy,
Your correct about the A and AA size cells with all digital servos. Even the high capacity 2700 mah nimh packs are not up to the task of supplying power to an all digital system. They will supply power for a couple of flights, then they will start going below a safe level. When I was using the 2700 mah pack, I would have the model go into battery fail safe if I was a couple of flights into the charge and I did a maneuver that required the servos to move to there extreme travel range.

You should be OK with the Sub C size cells.
Or if you want to spend a little more money, go with Li-Ion packs and a voltage regulator. Then the voltage is the same from the first flight till the last flight.

David

[WillJames]

I am kind of curious as to the others having problems with the "high discharge rate", because I've used them in Giant Scale planes with 10+ digital servos ganged on one single NiMh pack pulling a lot of juice and it works out just fine. As long as you cycle it you should be fine, there should be no reason the helicopter would pull more then about 2-3 amps continuous which is well within todays AA nimh cells.


Maybe so in theory, but I have also experienced Gyro resets and things similar to David with my R90's when I ran NiMh. You may be running 10+ servos, but you do not have a good idea of the power requirements of a heli. There are MANY people who have experienced AA/A NiMh packs dropping below the point where all kinds of stuff happen and IMHO it has the distinct potential to be dangerous. I would not recommend anything other than SUB-C NiMh packs in helis with all digital servos and I am a little leery of them as I don't have any experience with the SUB-C Cells.

To give you an example of the kind of current draw that can take place on a heli. Lets use myself as an example. My Bergen Observer Camera Ship. I had never setup Push-Pull linkage on a heli before just flew helis without them. I have it equipped with all 9252's/601/GV-1&Stator Gator/149DP. etc. I am running a 4000mah Duralite Pack and 5.1 volt regulator. With my first setup I had enough binding to make my 601 reset on the second flight about 5 minutes in. The first flight was ~20 minutes. I had 2 servos binding and it sucked down a Duralite 2p pack that quick or over amped it or something. Once I solved the binding on elevator and pitch, no more trouble, getting 5 20 minute flights no problem with NO resets and still voltage to spare after the 5th flight. The ironic thing about this situation is I am a dumbass enough to do this TWICE before I realized it was binding servos that caused the problem. I blamed my regulator the first time, changed it out and went out and did the same thing again, but this time I made it about 14 minutes into the second flight before the 601 reset...another forced auto with a 20 pound machine! I have no idea just how much amperage a Duralite setup can provide, (certainly WAY more than a A/AA 4.8v NiMh Pack) but I was obviously exceeding it for my gyro to reset like this. My Rev Lock Governor also reset long before the 601 both times and I was to stupid to realize what was going on even then. David Harkey and Clint are who finally clude me in on what was happening.

You are very much underestimating the potential current draw of an all digital heli flight pack in my opinion. You know what happens when your gyro resets in flight right? Forced auto with piros, not fun at all, but definitely exciting. :arggg: If everything is setup right on teh heli, they still seem to draw a whole lot more current than any plane I have ever owned. I run all NiMh in the planks I still have. I love planks as well as helis!!

[Shortman]

Very interesting.. the amp draw on most current helis with all digitals from some previous testing posted on one of these forums was 3-4amps continuous with spikes possible of over 20amps fairly easy. GS planes typically draw between 3-4amps in flight and spikes of up to 30-40amps when thrown into a hard manuever. I failed to consider that most GS planes use a redundant battery set up cutting the load in half whereas the heli's use just one receiver pack, DOH! That would explain the drastic cut in flight times.

[DavidH]

Very interesting.. the amp draw on most current helis with all digitals from some previous testing posted on one of these forums was 3-4amps continuous with spikes possible of over 20amps fairly easy.

With 20 amp spikes there is going to be lots of regulators shutting off. Most of the regulators I have seen on the market are rated for 7.5 amps continous with 10 amp surges. The top amperage on a heli with all digitals is about 3-4 amp surges.
Most of the time the system is drawing about 1 amp maybe a little more.

David

[Shortman]

Gosh darnit, again sorry, let me see if I can redeem myself. Even if the helicopter itself could not put 20amps spikes, airplanes themselves can push 30amp spikes (IM POSITIVE on this), I was mixing my electric brushless heli with gas here. They use the same regulators heli pilots use with no problems, in fact, I would even venture to say they have less failures and they are being pushed by more servos, but because the draw is not continuous you will find they can handle these surges. Just like a receiver can handle about 50-55amps before it goes bye bye, but some think 5-10 digital servos will kill it from overloading it with power.

As far as how well a regulator can handle surges, I would have to ask Kurt on that as he has far more knowledge on them then I.

[DavidH]

I failed to consider that most GS planes use a redundant battery set up cutting the load in half whereas the heli's use just one receiver pack, DOH!

Using two separate battery systems makes a difference. The larger planes may have 30 amp spikes. But they don't have it on one battery. Most of them I have been around use a separate power system to operate the servos on each side of the plane. Also most of the IMAC pilots I have been around use a power box in the plane. Items like the above makes a big difference in what a system can do.

David

[300wby]

There is way to much worring about this, I have used 4000mah 6V packs for the last two summers on a Raptor 70 all digital setup and have not had any problems. I cant help but wander if some of the problems people have had were blamed on the battery for lack of another explanation. I get 6-8 flights before the batt drops below 5.1, if you are that worried get a y and hook both up.