What is the disadvantage of Y connecting 2 batteries into the receiver?

I have connected batteries to 2 different channels before and this worked out fine.

I have also read about connecting a servo with a Y connector to a battery and into the receiver. Is this better? Why?

The only real disadvantage is that the Y-harness represents another point of failure. There are two reasons why a 2 battery system is employed in a plane, more battery capacity and redundancy against failure. If you're going for redundency then you need to eliminate any point of failure that will knock out your entire battery system. This means that you need two batteries, two switches, and two separate connections into the receiver. While the chances of a Y-harness failing are slim, they do exist. If the batteries are connected into the receiver on two separate channels then no one component failing will knock out power to your receiver.

Hope this helps

Ken

Another possible problem with using the Y instead of two seperate paths is that many Y's are not of sufficient gage wire or could have a bad solder joint that will cause excessive voltage drop under load. The quality of the switch is also a possible problem here as some switches do not pass high currents without a significant voltage drop. Two switches, two wire paths give 1/2 the impedance to current flow.

What is involved Y connecting through a Servo. Is it just a matter of connecting servo to Y and battery to Y then into the receiver?

Yep. That's exactly what you have to do.

Ken

Of course, then you have no switch.

OK- You got me, I will add the switch.

Ask yourself why you are running two packs. The two most common reasons are backup and current. A “Y� between battery and RX belongs in neither setup.

If using as a backup system, the "Y" represents a single point of failure which was mentioned. Not much point in running redundant batteries if you don't have redundant switches and paths all the way to the RX. A "Y" into the RX from batteries has no use if your goal is redundancy. There are better systems with fail on switches (or no switch) and load balancing systems that prevent failure from both opens and shorts in the system.

If using a second battery because your current loads are too high for a single pack, usnig the "Y" is self defeating because of the wire gauge and current rating of the pins. If in a high current situation, you should be using at least 18ga or larger wire from battery to RX which will be hard to pull of in a "Y", and the standard servo connector is only rated for 3A, which is probably well below what you are expecting to pull if you are putting in a 2nd battery for current reasons.

OK the other disadvantage is that if you store the batteries connected in // they will self discharge much more quickly.

Question for those that know more about our batteries than I: is there a failure mode, such as an internal short, for a battery pack that would suck down the voltage of the second pack, preventing it from maintaining power to the Rx?

Basically, I think the suggestion of the Y-harness connection of a second pack is sound for redundancy (not capacity). This allows you to double up on the switch harness, which is a MUCH more frequent failure mode than a Y-harness. If you are concerned about the failure of a harness and don't have an empty channel connection on the Rx, connect the Y-harness through one of the existing channels. This way the failure of the harness will only kill one pack. Connect through one of the least critical channels, of course. That said, I have never heard of a Y-harness failing.

Bedford

OK, I think there may be confusion, so let me clarify my post. If you use two "Y"s and two batteries to the RX, each battery plugged into a different "Y", then that would be redundant. If both batteries are plugged into one "Y" and then that "Y" has one connection to the RX, it isn't redundant. Seriously, why waste money on two batteries and two switches, only to make one power connection to the RX. Batteries can fail shorted, seen it before. It will suck down a pack really fast, like faster than a typical flight. Closed circuit failures are rare, but they can and do happen. The more likely failure is a open... like pins breaking contact, hopefully not in the single "Y" into the RX.

John,

I believe your failure analysis is flawed. Plugging the two battery packs in separately instead of through a single Y-harness, does not help against a pack failing by short. The bad pack will still pull down the voltage and power of the second pack. There is very little difference (in electric circuit terms) in either arrangement. To avoid problems due to a pack failing, we are better off using 5 cell packs and voltage regulators. This is the best way I know of to isolate the packs.

Plugging both packs through their own switch harness into a single Y-harness will give you switch harness redundancy.

Bedford

No, it is not flawed, read my first post. You can protect against shorts, but you need an intelligent battery balancer, or two voltage regulators would work as you mentioned, same basic idea. I never said a "Y" would protect from shorts, I belive you read something into my post that wasn't there. I was answering two ideas, I probably should have made two paragraphs and not run them together. My premis is that full redundancy all the way up to just before you get to the RX seems, well, not redundant. You said shorts didn't happen enough to worry about... I'll give you they are rare. If all you are really worried about opens in the switches, then I suppose a single "Y" to the RX would be fine, but it seems pointless to me becase you only made part of the system redundant.

John,
Hi, I had set up my secondary battery that was connected to my throttle servo with a Y harness and now found out that my throttle servo has packed it in so to speek it is dead, just wondering if the battery connected to the Y harness did this, and yes it is connected to a secondary switch then to the RX to the throttle channel.

Jason

Jason, I can't think of a reason why using the "Y" as you described would have damaged the servo, unless there was a witring fault in the "Y", which would be pretty easy to check.

Is it better if i just set the battery up streight into the RX on the ex 2 or ex 1.

I have the battery connected to a Y lead that is connected to the throttle servo, from there it is then wired through the switch then to the RX.

Dedicated wiring from battery to RX is always better than a "Y". However, if you don't have enough connections on the RX, then the "Y" is OK.

Thanks John, just reconnected everything, throttle streight to the RX and the only chanel left is the (ex 2) so then the second battery will go into that one with a switch between the battery and the Rx (EX 2). Much cleaner and easier. Dont think I will need a battery indicator as there is one on the other battery 6v.

Jason

Interesting thread.

I am intending to provide redundancy in my latest EP project due to my first foray into 2.4Ghz and concerns (purley personal) about the rx "locking out" if the supply voltage drops momentarily. I appreciate that a lot of fliers regard this redundancy as not required but for the amount of £'s invested in this particular model I do!!! So.....

I will use a 4350 6s Lipo to provide motor power and this will also be connected, via a SmartBEC, to a spare rx channel (I use this setup regularly to provide rx power in my EP fleet but use the batt channel)
I will then add a separate rx Lipo connected via a Voltage regulator to the rx batt channel.
This will provide me with redundancy for;

a/ SmartBEC failure
b/ Voltage Reg failure
c/ Flight Lipo "failure"
d/ RX Lipo "failure"
e/ Pin failure of either rx input

What I'd like to know is how the rx takes power from the two lipos? I presume (probably wrongly!) that the rx takes power from the Lipo with the highest voltage. But as both power "feeds" will be regulated to 5v (one by Smart BEC, one by Voltage Reg), how will the rx decide which to use?!?

Although I appreciate this may be seen as overkill I really want redundancy for all the above and so any thoughts regarding the power draw is gratefully received

If the quote is true, then you always have the servo as a load on the battery, even when the switch is "OFF". Not a good idea.
As to a comment in another reply above, two batteries in parallel DO NOT self discharge any faster than either one will alone. However, the resulting impedance of the power system falls (a good thing).
Most of the above suggestions work, but if you have no way of checking before each flight that both systems are working (with one battery switched off, you should have full control. Now turn the other battery on and the first off, you should still have full control. If both tests are okay, they turn both systems on and fly. However you set them up, make sure you never try to charge the two batteries in parallel. Nixx batteries will not properly charge in parallel without some damage occurring in one of the batteries.