Xantos

Hello
I've been following what I thought was universally the best practice for redundant power to the receiver.
I've always plugged in 2 batteries with 2 independant regs and switches to two available ports on the receiver .
The earlier 12ch Spektrum receivers used to come with 2 allocated batt ports "Batt1 and Batt2 "
The newer 12ch versions AR12020 the second Batt2 port has been replaced with a SRXL port , so I sent a query to Horizon Support and heres the reply I got

Thank you for contacting Horizon Hobby's Product Support Department.
*Please do not respond to this email* This email address is not monitored. Please use our inquiry form for any further correspondence.

SRXL should not be used.

The powerbus in this receiver is common and we do not recommend using 2 electronic regulators/bec‚s to power a common power bus.

The Powerbox Gemini is best suited to powersafe receivers which have independent power supply circuitry.

This response is very strange because , its completely contrary to what is stated on Spektrum/Horizon website FAQs
Horizon/Spektrum actually recommend the use of a second battery plugged into any spare port ,
I’m reproducing the statement on the website:

"While all Spektrum 9-channel-and-above receivers have multiple battery ports, you can actually put multiple batteries into any Spektrum receiver. Simply choose two batteries of the same size and capacity with two switches. A common misconception is that one can hurt the receiver with too much current. Wrong. They'll handle over 30 amps. By using 2 batteries, you halve the current on the battery connector, which is the weak link in the system (the reason our engineers developed the AR9100 and R1222 receivers)."

Am I missing something ?

AA5BY

The advice not to use two regulators is good as doing so can set up a battle (oscillation) between the two regulators each trying to establish its voltage setting with the work load of the regulators escalating greatly consuming more current than normal and potentially an oscillation can produce RFI that might get into receiver or servo circuitry causing problems.

Oscillations can produce runaway circuits that overheat and destruct.

AndyKunz

The distinction is "two regulators" vs. "two batteries" - the two batteries are OK (so long as one isn't discharged). AA5BY got it right on why not two regulators.

Andy

raptureboy

The dead battery killing a good battery thing is a myth.Q: Ok, that’s pretty kewl.. but my instructor sez I need diode protection or the packs will cross-talk or try to charge each other. A: Sorry.. your instructor has been gaffed by Under-Informed Magazine Columists or the Battery Mis-Information Committee of your local fields Wives Tale Tag Team. There is NO need for diodes or a 'backup' circuit board (something else that adds weight, complexity and another possible failure point) and in fact there's no flight-safety significant energy transfer between packs at different charge levels.

You can test this yourself.. just plug a discharged pack and a fully charged pack together in a Y-Harness and check the two packs the next day.. You’ll find the system will pass a load test if checked through the ‘Y’, and you’ll also find that less than 20% of the charged packs energy has been ‘used’ by the discharged pack when you separately cycle-test the two of them. Next, consider that your average flight is 10-12 minutes, not 24 hours! The mythical "Energy Transfer Between Packs" scenario is simply NOT a flight safety issue and checking both packs before flight with a loaded ESV will certainly 'pick up' a weak pack before you fly it anyway! Check it out here http://hangtimes.com/rcbattery_faq.html

AndyKunz

The current during the initial part of the charge can exceed the safe limits of the wires, contacts, and traces.

Read up on Ohm's Law.

Andy

fizzwater2

My Feedback: (61)

Well stated, Andy. I wouldn't want to plug a dead battery and a good battery together.. if they're both at a similar charge level, maybe, but not if they're dramatically different.

chuckk2

The "Y" harness is a significant part of any analysis as to what might occur, due to it's resistance.
Besides only conducting in one direction, diodes have a small voltage drop, which also has an impact.
Under "normal" conditions, the diode voltage drop may help equalize the voltages from the multiple batteries or regulators.
Depending on a regulator's circuitry, it may or may not be stable if it sees a diode as the first part of any load.
Regulators do "hunt" slightly, and even two identical ones may have slightly different output voltages, usually due to
component tolerances, etc.
The ancient "rule of thumb" was that 10% of the regulator load should be on the regulator side of the diode, and some filtering
and small additional fixed load used on the receiver side, so that the diode is conducting.
The minor details go on and on, and which are significant or not of concern usually ends up being determined by test and use.

"Little" things can get you! Consider what happens when a filter capacitor is completely discharged, and power is applied.
Is there sufficient resistance in the overall circuitry to prevent a high current surge? If not are the other components in the circuit
stout enough to handle the surge? This might not be the case when the battery or power source has a very low impedance, and capable of very high current.

BarracudaHockey

My Feedback: (11)

I've been fighting that bs about mismatched packs for ages.

As Raptureboy says it's nonsense.

chuckk2

?????? Which nonsense ????

Two batteries of the same nominal voltage will tend to equalize in voltage if connected in parallel. (Hopefully, the at rest voltage is about the same)
If the capacity is not the same, the battery dynamic? internal resistance will have an impact on where the load current
comes from. In any event, other than battery failure, both batteries will contribute to the available output current.

The two regulator scheme obviously has different considerations than two battery setups.
It seems to me that keeping servo current draw out of the receiver is really the intended goal,
along with the other considerations.

Redundancy always has a price.

BarracudaHockey

My Feedback: (11)

Sorry, they actually won't.

Or....they might but it will take so long you wouldn't notice in a single flight, or several for that matter.

You can protest on all you want, but I did avionics for a living <shrug>

AWorrest

My Feedback: (5)

The internal resistance of a NiCd or NiMH battery being charged increases considerably compared to the charged battery’s. The packs will equalize after a very long time. I had the same opinion as you until I did a bench test. I hadn’t taken into account that a battery internal resistance changes according how it is being used. This should also apply to LiPos.
　
Allan

chuckk2

Many of the people at my club using dual batteries that are connected in parallel leave them connected.
Anyway, I'd agree that over a short term, the battery with the lesser charge will, when connected to one with more charge,
tend to increase in voltage, until it equals the other battery. As to how long the two are actually equal, with no current flowing between them,
that's a different story. The 20% number someone mentioned seems about right as to what might be the case if one battery is really lower in charge..

BarracudaHockey

My Feedback: (11)

Lets try one more time.

The batteries won't equalize. Well they might but it would take hours or days. Try it some time.

AndyKunz

The problem isn't the "days" aspect - it's the first 15 seconds.

Andy

BarracudaHockey

My Feedback: (11)

Andy.....as much as I respect you (and that's saying a lot, you're on a short list), hooking a dead battery to a charged battery won't equalize them.

AndyKunz

I agree, it won't. But there WILL be a rush of current, and that current can be quite high depending on the relationship of the charges in the packs.

Andy

Captain John

So who is right here?????????? Different battery types.....does it apply????

jmcowart

As a much more simple issue, which ports on the Spektrum AR12020 should be used if you want to plug two two wire power leads into the receiver from the same battery?
I get it that you don't use the SXRL port, and you don't use the Aileron, Elevator, Rudder, or Throttle ports..... but which other port beside the one BATT port do you use?
I want to power the receiver and several digital servos from one 5000mAh LiFE pack, (with two two wire power leads) and am not sure of the best practice in doing so. Thanks, I appreciate you'all sharing your knowledge..

AndyKunz

You can use any of them. They're all connected in parallel.

Andy

dirtybird

My Feedback: (5)

If the dead battery is shorted you will have a real problem.
In the five years I repaired R/C systems almost all of the failed batteries I found were shorted.(NI-CDs)

jmcowart

Thanks Andy - I take it that means it doesn't matter if SRXL (X-Plus) is activated or not - AUX 4, 5 6, or 7 are all OK. Thanks again. That makes for a very flexible and convenient system.

BarracudaHockey

My Feedback: (11)

Yes, you can use the SRX port if you're not using XPlus.

In fact, I do that with the 9010 because the battery port is actually a 10th channel.

AndyKunz

You can still use it, even if you are using the port. Y connectors work fine.

Andy

rmh

I charge my single cell 150 ma types, in chargers which put the four cells in parallel and they work just fine all top up .
everything else I charge on balancing chargers ( CellPro 10s