what are my options for dual batteries for a 72Mhz receiver?

That kinda depends on the goal you have in mind for using dual batteries. Two batteries, two switches and a Y harness would work. There are other ways to do it.

Hooking up 2 batteries is a pretty easy thing to do. This is normally done to get redundancy in batteries in case there is a failure. If this is what you are going for then it's also best to duplicate everything in the battery setup including the switch. This would mean two batteries and two switches.

To accomplish this you would setup each battery on it's own switch and then plug each battery into a separate channel in the receiver. If you don't have 2 open channels on the receiver you can use a Y-harness and plug the harness into a channel of the receiver and then plug the servo for that channel into one side of the harness and the battery into the other side of the harness.

By doing this setup if you have a battery or switch failure the other battery and switch will still provide power to the receiver.

Ken

This is done all the time. I have the exact setup as Ken described in two of my planes. And, believe me, it will save your plane one day. I have a Venus II pattern plane, OS 1.20AX, Spektrum radio setup with five servos. I have two 6 volt battery packs, two switches, plugged into two separate channels on my receiver. As said, you can also do this with a Y cable, two into one. I also have a voltwatch hooked up to a vacant channel.

One day, as usual, I pre-flighted, checked everything, first battery A, turned it off, then battery B, then turned both on. They checked out fine pre-flight. When I was finished, and did a post flight check, I found that one of the batteries was showing down in the red on the Voltwatch, so I checked it with a loading voltmeter.. it showed about .1 volts. The other battery was fine. I replaced the battery that showed .1 volts and continued flying. Had I had a one battery setup, and that battery died in flight, well, I would no longer have a Venus II.

So, yeah, two batteries is a viable setup. It's not absolutely necessary, but is clearly viable.

CGr.

Im curious, do you turn both switches on for flight or just one? If both are on wouldn't that give you twice the voltage?

No. You can have a 100 6v battery's wired in parallel and you would still have 6v. The voltage stays the same, capacity goes up.

Parallel Set Up - 2 packs of 6V 2000mAh wired in parallel would be 6V and 4000mAh.

Series Set Up - 2 packs of 6V 2000mAh wired in series would be 12V and 2000mAh.

Excellent Ken. Love these forums. Great Planes Reactor 160 don't wanna lose the airplane to this.

You can get fancier than RCKen's diagram and use a battery combiner, like the one from Smart Fly, that draws from the stronger battery.

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

Kens design, while simple and reletively inexpensive, draws on both batteries during flight continuously. This fancy do-dad would alternate between battery packs always tapping the stronger pack. At first glance the fancy do-dad was what I was thinking would be the better way to go but upon further contemplation it may just be an extra link in the chain that could fail during flight making the simple way a safer choice.

I agree. Something that my instructor emphasized when I was learning to fly was the good old "keep it simple" method of putting these things together. The more complex things get, the more potential there is for an added point of failure.

CGr.

That being the case I usually opt for a much larger single pack, a voltwatch and a good switch, which is simpler still.

The weakest point of all of these configurations ( assuming you use a good interconnect system with clips, etc. ) always seems to be the switch.

Iagree. The only model Ihave with dual batteries and switches (and Batshare) has nine servos and is already complicated. ;-)

Iusually use plenty if capacity in a battery, aheavy duty switch (like a Cermark)and check it with a ESV when Iget to the field and then progressively between flights. Have had good lock with VoltWatch2s as well.

Well, as I said, the dual battery, simple config, did save my Venus II, so I am convinced that with some planes, it is something worth while. If a single battery quits during flight, well, there is not much you can do about it but pray for a "soft" crash... []

Sense I started flying RC I have had three electric problems, two switches and one battery. Dirt in a switch once and something came loose in the other switch. The soldered wires on the battery pack had a loose connection. I never lost a plane because of it but two very hard uncontrolled landings did do some damage.
If I have a plane I really like and have put a lot of work, time and money into then they have two batteries and switches. My small planes only get one. The plane I just built has three, one for the ignition too but that isn't a big deal. I use the JR heavy duty switches these days. Other then the dirt in one I haven't had one go bad. The dirty one? Well, flying on a dry lake bed for years with the battery port opened is my problem, bad me!! Because of dumb luck the plane told me it was having a problem with controls kicking around so I caught it before I flew it. My lucky!!

Hey Charlie,

Interesting device. Three things though.

1. I see there are two leads in and out...but does the device potentially create a single point of failure thereby negating the dual battery redundancy? If the device fails then what?
2. If it is drawing from one battery at a time (back and forth from what I read), what happens to the higher amperage draw that dual leads make available to high demand digital servos? To get the benefit, the system has to be free to pull from both batteries simultaneously, no?
3. Why do I need a device to decide where to pull power from anyway? I'm thinking right now my dual setups run down the same anyway. In other words, what problem is the device solving...maybe that is what I am not picking up on.

Just trying to understand the products application...embarrassed to say I haven't seenthe device!

Thanks my friend!

Tom

The two outs mean you can plug into the receiver's battery jack plus either "Y"into another jack or into an unused one. Is it a single failure point? Yes. But it's designed to fail open so one (or both)battery(s) will still power the receiver. The receiver being a whole box full of "single failure points."

If your batteries are matched you pull the same voltage whether it's one or two in line at the time (parallel).

If a dual battery system fails in a closed circuit the dead battery will be like adding a big resistor to the good battery and drain it quickly. Granted, a battery failing in a closed fashion is rare, but so is switch failure . . . which is the reason to use two switches.

Yeah, Charlie. I use two switches, two batteries one voltwatch. All set up in parallel so that one does not affect the other, well, unless there is a battery failure. The voltwatch is simply set up on a short leash type Y connector to one of the channels that I don't disconnect on a regular basis (rudder for instance).

But, my contention is that with one battery failure, as I had, it may work to drain the other battery, however, there is (was in my case) sufficient battery power left to finish the flight. Now, granted, I had no idea there was a failure until after I landed, so my assumption is that it worked as desired... must have, because I didn't fill a trash bag that day.

And, with any type of failure with a redundant setup, you won't have any idea.. should not have any idea, (unless some sort of telemetry is used.. yet ANOTHER point of failure.. jeech.. this could to on forever.. ) that a battery had failed until landing.

So, it's up to the pilot as to how he/she wants to set things up. As for me, I really prefer the simple solution for dual battery.. two batts.. two switches, one voltwatch. Chances of such a catastrophic failure during flight as both failing at the same time are... remote??? is that the right word? doesn't seem to give enough 0's in the count.

CGr.

Agree with all of that...and yes, I suppose we can always trace back to some kind of failure point to tank the whole system. We eliminate as mucha s we can and make the system as reliable as possible.

Speaking of that, I'll just share my dual battery setup that I learned here on the forum.

I used to have dual A123's into two switches with one voltmagic. The voltmagic would go into a low voltage reading after one flight (50cc Extra with DA50) on a fresh charge to both batteries. Come to find out...the switches and related extensions were just enough to cause a peak low voltage reading (momentary as it was).

So I switched to a Powersafe receiver and the soft switch. So two batteries with EC 3 connectors going directly into the receiver and the softswitch is tiny, tiny! The voltmagic is so sensitive I just watch those readings, count my flights and after 5 flights (I can probably go to 8 but dont) I pull the canopy and re-charge. I actually like pulling the canopy because it never hurts to take a look at connections and so forth every 5 flights of so anyway.

This set-up makes me most comfortable, is very reliable and I will be using something very similar on a Giant Aeromaster project soon.

With the voltmagic it is bullet proof!

take care guys....

Tom

I have a pair of A123 packs, both, I believe, are 1800 mah (but I could be wrong, and it doesn't matter), but have not run them through the Voltwatch. I am not quite sure if the voltwatch is spec'ed for the slightly higher voltage or not, althogh it isn't that much higher.

I've not used Voltmagic but it sounds interesting. Where did you get them, Tom?

CGr.

This should get you anything you end up needing...and there is a dealer link. I think I got mine from NoBs Batteries....

http://www.voltmagic.com/

Don't let the instructions overwhelmyou. It takes a while to understand it, and interpret it.I got a little mixed around trying to figure it out and even discussed it on RC Universe a bit. Once you understand it, it is a very handy little device.

A simple digital numeric readout is about the only improvement I can see for the device as the series of LED's get a little cryptic at times.

I'd be happy to help you with the device should you run into trouble. Just PM me with your phone number and I'll give you a shout.

I'm taking my 11 year old to fly his Tiger 60 tonight..and probably tomorrow too. Also have a trainer on the chord for my 9 year old daughter. So much fun watching them I'm surprised it's not illegal!

Tom

Tom: Where did you mount it? How did you mount it?

I mounted the voltwatch 2 on the inside of the fuselage by cutting a hole the same size as the voltwatch and put a piece of clear tape over it so I can see it. I put a piece of Blenderm on the inside to hold it in place and that was that.

CGr.

CGr.,

Sorry for the delay in response...

I mounted the voltmagic on a horizontal brace across the fuse and just below the canopy deck (50cc Extra 260 from Aeroworks). Then I cut a hole in the floor of the canopy to line up with where the Voltmagic is so I can see it through the bubble of the canopy. (Another tip I picked up here on RCU!). Plus the little LED lights look pretty cool when you power up.

Can't seem to get the phots uploaded at this point though....I'll try again later when I get some time. {oops...I see the photos AREthere}

Tom

Ah.. Ok. Very cool.

Thanks for the update.

CGr.