unclecrash

Need Help With Dual Switch Dual Battery Power System I could'nt figure where to put this so here it is.
Something is not right with my setup. I am running a Dual battery Dual Switch system into a airtronics 2.4 reciever. The setup is 2- 5 cell Tenergy 2000AA Nickel Metal Batteries run into 2- 5470 MPI switches with the 3 leds One battery into each switch. Run into 2 seperate channels on the reciever. I cut the loops on the back of the switches like the directions say to run them on 5 cells. When I turn one switch on it is back feeding to the other switch and lights the leads. That is one problem. But I figure that would happen. I am running 2- aileron servo's, 2-elevator servo's, 1-flap servo, 1-rudder servo. and throttle. After running for a while I checked like the directions say by moveing all flight controls at the same time and if the leds start flickering it says time to recharge. Well I did but Im only putting back 300mah back into each pack. I even checked the packs under load with a hangar nine load tester and they were in the green. The packs are new am I in need of going to an A cell to power the 7 standard size servo's. Or am I possibly having a problem with the switches feeding into each other. Because when I start with a full batteries the led's stay solid like they are suppose to. I have another plane on one of these switches and on a single 5 cell, A cells and I can run it for it seems like hours before they will start to flicker the led's. letting me know its time to recharge. It is running one less servo though but only one battery pack.

scale only 4 me

My Feedback: (158)

Sounds like you could have a servo that is drawing a lot of current under a load. When you are doing that test are you getting a lot of buzzing from any of the servos?

unclecrash

I don't remember hearing any stalling or buzzing out of the ordinary. Is there a way to test a servo to make sure its not drawing also much. I might also put a 4cell A size in it to see if I get the same problem. And if I do it would let me know the switches are having a problem working on 2 different channels and back feeding.

jetmech05

Your set up is sound...2 batteries 2 switches into 2 ports is a parallel circuit....where voltage stays the same but available current is additive......the problem is how the LED's are wired in your switches.....I suggest you replace one switch with a switch without LED's. or replace both switches and use a voltwatch in a 3rd port of the receiver

unclecrash

So basically you are saying the switches are giving me a false reading. I will try the same setup but change one switch and see if it helps. I really like the switch it has been sound in another plane but it does not have the dual bat dual switch. I do the test and if the led's don't flicker I go fly. So I will try another switch and use one with led's and hope it works. If not I might just bring along my amp meter and check it from time to time. Thanks Dave

unclecrash

Ok here is what I did. I changed one switch out for a no led's switch I turned on the no led switch and I still get flicker through the other. But if I turn both the led and the other switch on it is fine with both batteries. This Makes me believe I might need A size cells. But I would think I should be able to run this setup off of 1aa size 5 cell pack let alone I have 2. I will do another test and put 2 4cell A size cell packs on the setup and see what they do.

tschuy

My Feedback: (1)

I'm not so sure that running two battery packs in parallel without some sort of isolation between the two packs is such a good idea. What if one of the cells in the battery packs should go bad? Won't that cause the other good pack to bleed voltage down? Wouldn't it be better to have one of the commercially available battery backers installed? That is what I did with my turbine and never had a problem. Even lost the primary pack and the receiver and servos continued to function. Didn't notice in flight but when I landed the health indicator LED should that there was. Saved the $7500 I had wrapped up into that one jet...

Just my 2 cents worth...

speedracerntrixie

My Feedback: (29)

I agree with this. You may want to look into a Smart Fly Batt Share.

http://www.smart-fly.com/Products/BatShare/batshare.htm

Steve Percifield

My Feedback: (14)

I have run the same set up you are using for years in many giant scale planes with absolutly no issues. But here is something I have just noticed.

When you use 2 separate battery systems, ie: 2 switches, 2 batteries plugged into separate receiver ports. The current in each will be half of what it would be if only using 1 switch, battery, into the battery port. You can measure this. It is one of the advantages of doing this. I ran some tests, where I used the servo function of my transmitter to cycle all the servos at the same time, and I measured both the amp draw and the voltage drop. I used digital servos. I had 2 5 cell, 2800mah NiMh battery packs. At the moment that all the servos changed dierction, the amp draw momentarily peaked at 5-6 amps, and the voltage droped to under 6 volts. It was very brief and as soon as the servos were moving, everything settled back to normal. I tried it with analog servos, and the same spike occured , but not as high. I, first though the servos were faulty, but upon checking the servo specs, it is normal. I also checked 3 different brands, and , for the digital, high tork servos, this is normal.

So, the end of all this is. I don't think anything is wrong. I think your switches are showing this momentary current peak, and that's all. Run your set up normally for awhile and check the batteries for voltage. And you can cycle them after the test. If they test to voltage and capacity, then you are OK.

tschuy

My Feedback: (1)

I used this one: http://www3.towerhobbies.com/cgi-bin...?&I=LXAFM9&P=0

Probably just as good. It worked fine for me...

speedracerntrixie

My Feedback: (29)

Steve, your analisis is spot on when everything is working as intended. My suggestion of the Batt Share is in the event that one battery fails. With this setup you have a shared power bus between the two batteries. Should one fail, the good battery will try to feed voltage to the bad one. It is possible to drain the good battery while it is feeding the bad battery and the servos. There is no way to know this in flight so one would just continue to fly. With the Batt Share, you have isolation between the two batteries and if one fails it does not affect the other.

unclecrash

I am with you after checking my battery voltage. I believe it is just spiking. I am going to just keep my voltage meter with me and check them . I just don't want to ad more to the system,who's to say the backer does not fail and the plane goes in. That being said another guy says he has never had a battery fail in E on's and even if I get a good spike I still have till what about 3.5 volts till the reciever browns out. Its not like Im using a 4 cell the 5 cell pack has a lot better buffer til it will shut down

jetmech05

You have a parallel circuit so when you turn on the switch without the LED's you are going to see the switch with the LED's flicker. You're going from the battery to the switch without the LED's to the receiver to the switch with the LED's and see them flicker. Now when you turn the switch on with the LED's your seeing the output of both batteries...depending on the wiring of the LED's insde the switch.
In one post above there was concern that this set up could cause problems, If a cell in one battery or the other went bad. Yes it would cause an issue. But anything can fail. You have a better chance of a switch failing than lossing a cell. This set up has been used for years in many types of airplanes. Even alot of full scale runs more than 1 battery. An MD-90 runs three.
So in a nut shell in this parallel circuit. Availiable voltage remains the same, available current (amps) is additive. Doesn't mean your using all the current available. As electricity is lazy, it only gives you the minimum to get the job done.
Another way to see this is everything from both switches is the same circuit...from one switch through the receiver to the other switch is all the same circuit. All the switch does is isolate the batteries from the common circuit

BarracudaHockey

My Feedback: (11)

You don't need battery isolation, two batteries, switches, and ports works just fine.

Don't believe me? Take a fully charged pack and a half dead pack and plug them together and see what happens.

jetmech05

Hi Ya Andy...the fully charged battery will charge the 1/2 charged battery

BarracudaHockey

My Feedback: (11)

Give it a shot, let me know how long it takes.

scale only 4 me

My Feedback: (158)

What if a cell shorts in one of the packs?

We can go on and on with scenarios,, it's amazing these things even fly

Red Scholefield

My Feedback: (9)

See http://www.hangtimes.com/parallel_packs.html for information on parallel packs.

BarracudaHockey

My Feedback: (11)

Thats no fun Red! Let them do the experement and find out that it would take days and still never equalize the packs

Doug, c'mon, I was an AT for 16 years

aerofly0610

You can put diodes in the circuit.  Put them in between the switch and the receiver, that way you can still recharge the bats, but the diodes will prevent reverse charge from a shorted battery.  Unless my understanding of basic electronics is incorrect this should word. 

speedracerntrixie

My Feedback: (29)

That is basically what the Batt Share is. It's just someone else has done the reserch and testing.

unclecrash

I remember someone else telling me this about the diodes. But how do you install them and what size would you use. Because like you say right now I can only charge one at a time through the charge port on the switch. I tried doing both but the charger was going crazy.

jetmech05

You are really over thinking this thing.....as long as the battery switches are off you can charge. As I said the possibility of a cell going bad in flight is minimal. If it really concerns you then get a batt share. Never mind soldering in a pair of diodes..

scflyboy

I was going to use a Batshare on a new 50cc plane. What I consider to be an very highly respected rc figure said it was not needed. He mentioned that it could be a possible failure point, so to just keep it simple. I heeded his advice. 2 new batteries, 2 new switches, plugged into one receiver.

speedracerntrixie

My Feedback: (29)

I tend to agree with this on a 50cc airplane. My last 50cc bird had a single RX battery and did just fine. It met it's end however to a regulator failure. The wires fractured off the PCB. A good preflight on my part would have found this. I had hundreds of trouble free flights on this airplane and got lazy. The airplane I did run a Batt Share on was a Conp ARF 3M 260 with a DA 150. It was first set up without and I found that one battery would always drain faster then the other. I spoke with Bob at Smart Fly and he stated that was normal as the battery with the least internal resistance would carry most of the load. The Batt Share kept the batteries discharge under use almost identical. This was a great aid when recharging as I could gauge when a battery was showing it's age when it had a different charge rate then the other.