jetster81

I use a Multiplex safety-switch twinbatt unit which is light,compact and reasonably priced

mr_matt

My Feedback: (10)

Why not 2x 1100mAh A123 instead of the bigger cells?

gooseF22

FWIW, I think you are far more likely to have a wiring/switch failure than a battery failure itself.. but no way to predict when something like a connector or switch fails.. Example...

I have twin Lion's on a wolverine with twin regs in a Jet.. we go fly... land, only one light is on on the switch...hmmmmm... No power on one pack... 0 Volts..... Na.... the weld came loose on the battery, but was making intermittent contact until it bounced around on the ground... jet flew fine on one 2600 Lion.. That intermittent contact would have been a total loss w one pack..

Ron101

My Feedback: (22)

Yep I'm liking that idea... I'm running 2100 life packs now in my large planes. But use a single 1100 life in my Comp Arf Spark.

I checked and two 1100's with save me 4 oz over two 2100's.... that's pretty good.

Would you guys feel safe with two 1100 in a plane as big as the yellow twin F-18? or giant scale warbirds?

Should be fine I don't see an issue

Bob_B

My Feedback: (11)

Ron you going to be flying about five minute and use about 200 maH per flight you shoud be good for at least 5 flights

JackD

My Feedback: (4)

Ron,

Redundancy increases reliability only if you can fly with only one battery. I think that 1100 is too little of a yellow F18. Let's say a battery fails after 3 flights, then you are flying with a battery that only has around 600 mah left. Very little I would say. So I completely disagree with the principle of using two small batts instead of one.

I lost my L39 like that. Had 2 batteries, both 1800 mah. theoretically enough for about 6-8 flights. On flight 7, one batt failed (I think i only turned on one... ). when I dropped the flaps for landing, the good battery didnt have enough juice and the plane crashed. What should I have done differently? assume that I had only 1800mah and fly only 4 times. Or, if I want to fly 8 times between flights, put 2x3600mah's batteries

So, the way to do redundancy is: choose the one battery you would use, and put another one of equal power. And fly the number of flights that one would give you. Don't add the 2 (at the most, multiply by 1.5, but not 2)

It is like twin engine aircraft where the plane can't fly with just one (like seneca's and the like).... what was the point of making it twin? just added complexity, doubling the chance of failure

Hope this helps
Jack

k_sonn

My Feedback: (32)

Ron, just my opinion.  If adding a second pack makes you feel comfortable, then by all means do that.  I agree with Jack, don't decrease the mAh because of weight.  An additional 5 oz on that airframe is nothing.  If the fans won't be enough power due to 5 oz added, then put fans in it that can handle the additional weight. 

Kirk

gunradd

My Feedback: (9)

I put in 2 packs and 2 switches.

With the 2 switches I turn one on test all controls then turn it off and turn battery 2 on and test all controls then go to both batteries for flight. This tests the switches and the batteries before each flight.

Not using switches is ok but its not practical if you want to test each bettery by itself before each flight with out fiddiling with the connectors.

mr_matt

My Feedback: (10)

You should size the battery for redundancy. A 1100 mah pack plus the backup. Decide your safety margin with the one pack, charge every flight or 2. You are charging the flight batts anyway. And for a turbine you could top off the 1100 faster than you could pump the kero back in!

Ron101

My Feedback: (22)

All good points guys

I think I'll drop to two 1100's and top off every two flights.... this way I have the lightest setup and I can check battery health on the charger which is the best way with life packs
you can't test the voltage on life packs, they have a flat discharge cruve until the they drop off like a rock. You must charge and see what you put back for saftey. I know there are a few tester on the market that say they can test life, but I wouldn't trust them knowing what a life discharge curve looks like.

Have seen several big planes go in now because guys thought the could test the voltage on a life pack, you can't they hold voltage until they don't

JackD

My Feedback: (4)

Ron,

Sorry, but I don't think that is a good set up. A larg F18 can be drawing around 500mah per flight. So imagine you do one flight. you have 750 left in each bat. Next flight, you forget to turn one on (i know, it wont happen, but lets say it does... a wire breaks, anything). you are going to fly a 500mah flight with 750 in your battery. Likelihood of crashing towards the end of the flight: High

Don't skimp on capacity, not worth it. It is the only thing you cant run off. You can deadstick land, but you can't run out of voltage. It is a mistake..

Your plane though...

Been bitten by this enought times already

PS: Plus, who wants to top off every other flight? I say drop a couple 5000mahs and forget about charging the whole weekend Flying these things is hard enough, don't add more variables that mess up with your brain.

Ron101

My Feedback: (22)

I can run the dual 2100 in the F-18 whenever it's done...lol

this is for all my planes, so I want to try the dual 1100's in my warbirds, 3d and jet legend hawk

FenderBean

I run two 2200 ions in my F-16 plenty of flights

JackD

My Feedback: (4)

OK... that makes more sense. I thought you wanted to run the 1100's on the F18, which sounded like a stretch.

Still, I run 2x2600 on my Electra which uses less than 200mah per flight. But I guess after 3 planes down due to power system failures, you become a little paranoid

Hey, when are we flying together? too much internet talk, not enough airtime

Let me know when are you going out with Eric and I'll join you

Later
Jack

Ron101

My Feedback: (22)

sounds like fun Jack.... you should hit up oakdale with us...
we flew at livermore on Satuday, really nice weather

This weekend looks like it's going to be a hot mother.... but I'll let you know that next time we go out

I want to check out your electra, I might buy and electra kit to build after my F-18 not the arf.... hoping to find one that someone got burnt out trying to build

Thanks for the help and I know what your saying about better safe than sorry

later bud
Ron

PaulD

My Feedback: (39)

The current output of the A123 - 1100's is impressive. Also with 2 packs you have 2200 of capacity feeding the airframe with way more punch than nickel metals. I can remember lots of guys being happy with a couple of 600 mah nicad packs even on giant scale stuff. Granted, servo torque and current draw has really increased ESP with digitals.

I have also been running a wolverine switch with a cricket. Great combination.

PaulD

dubd

I would trust dual 1100 A123s. I am using 2300 mah A123s in my SM F-16 and draw about 220 mah per pack per flight.

dubd

Discharge rate on 2200 ions is pretty low. 5200 or bust for me.

Ragz

Heck, I use 2x4600 A123 liFe in my skygate hawk  Would do anything for redundancy.  When you can have it why not use it?

highhorse

My Feedback: (2)

Discharge rate is low compared to...what? The draw spike is hardly more than a few amps, topping out at a 2 or 3c rate, right? I guess I don't get this one, but am wiling to learn if I'm missing something here.

FalconWings

My Feedback: (57)

Forgot all about my old friend Kirchhoff.

When using a backup pack, does it have to be similar to the primary or can I just use a reliable, smaller capacity NiMh pack?
Primary would be LiFe.

dubd

Discharge rate for a 2600 mah ion is low compared to almost all other batteries, including 5200mah ion packs. The max discharge for 2600 ions is 4 amps. That isn't a problem under normal circumstances, but can be catostrophic if a servo stalls. A stalled servo can pull more than the 2600 mah ion can deliver. A 5200 mah ion can deliver 8 amps, which is why I have no issue using them. My rationale is rooted in my IMAC days where 2600 mah ions were frowned upon for anything above a 50cc plane.

flyinfool1

My Feedback: (2)

Don't forget CG.
Had a member at our club that thought he saved 5 oz by going with smaller batteries. But then added 5oz of lead right next to the battery to get the CG back.
When I need nose weight I just keep trying bigger batteries till it balances. If I have to carry the weight anyhow, I want it useful weight.

dubd

Yes, that is the main reason you see 5000 mah packs in most of my planes. haha

highhorse

My Feedback: (2)

Here are the specs of a Duralite 2600 mah lion:

Flight weight: 3.9oz (110 grams)
Size: 2.75 x 1.5 x .75in (7 x 3.8 x 2cm)
Discharge Amperage: 5.2Amp (2C)
Charge Rate: 1Amp

I'm not saying you don't have a point worth considering. But you are short on the lion amps and assuming a double failure, ie a stalled servo when a pack fails. I'm sure the lion can surge at well over the rated 5.2 amps as well......