John_M_

That's because you're running a dual battery redundancy buss, like from Smartfly or PowerBox, which have battery share, load balancing, and bad pack isolation... those type of boards clearly state in their manual which type of batteries to use with their product... some brand power boards claim you can mix and match chemistry's and capacities.

I run just a straight up basic servo buss which separates the servo power supply from the receiver power supply... the servo power stops at the buss and doesn't pass through to the receiver and vise versa, so I can run two different voltages, 6 volts to the servos and 6.6 -7.4 volts to the receivers... if I got into something more expensive like a jet, or much larger scale model, I probably would run with one of those full redundancy power boards.





John M,

dirtybird

My Feedback: (5)

If a servo shorts out and you have A123's you will lose the wires to that servo. But then in the fifty years I have flown these things I never had a servo short out. Have you?

dirtybird

My Feedback: (5)

What servo board is that? I don't see how the servos get + voltage

John_M_

Well that is my Inlaw's own design, I believe it is based of the ones from servo city.

Those two large black circles are where you would solder in your servo switch and battery harness... up to eight servos can be plugged into the right side pin connector block... the left side pin connector block are where you connect each channel from the buss board to the receiver; the signal wire is carried through the buss board to each servo.

Then you plug directly into the receiver its own switch and battery pack harness.


I'm bought two of the servo city boards, to lazy to make my own.

https://www.servocity.com/html/servo_power_boards.html



John M,

John_M_

This is the face board if it helps discern things.





John M,

dirtybird

My Feedback: (5)

OK but you can do the same thing with the servocity board if you just bring the signal wires over and connect the negatives together.
What I do is take a female to female extender and turn it 90 degrees and plug it into the signal pins.. On extender brings over Ail,Elev, and throttle. Then another extender brings over the rudder and two aux signals. That is all I usually need.
Then you plug one battery to the receiver and the other to the servo board

rcyoucando

All I want to do is to insure that the receiver is isolated from power spikes the can cause a brown out. Dritybird and john M seem to be on the same train of thought as me.
I have gotten all the info thanks to all that have responded to my post. I am waiting for my order from servo city I am going to use a plug in style switch and am still looking for a balance style plug that can be mounted outside the fuselage to monitor and charge the batteries. I want to make a board that can hold the receiver the power board and the plug in switch on the negative side to power up the receiver and the power board at the same time. I know there is a deans style plug that can be mounted outside of the fuselage. The main thing I am looking for is power spikes that cause brown outs. If a 500mah battery can power the receiver for even 2hrs with out worry is great. ​

dirtybird

My Feedback: (5)

You will need two female to female servo connectors

John_M_

The servo city boards are done that way... the red power conductors on the jumper wires to the receiver side goes nowhere (not connected through the buss).

Theirs is a 3 layer PCB, where as the one by my Inlaw is a 2 layer, his is a bit tidier with the two pin connector blocks... the servo city has the receiver jumper wires soldered directly into the board... if you buy the un-assembled kit, you can make up your own length jumper wires to suit your particular install location... it works well, my inlaw has been running with his setup for over 3 years without a hiccup... I've been using my setup with the servo city boards for over 3 months, with zero issues,


John M,

dirtybird

My Feedback: (5)

OK I was not familiar with the servocity board.You sure dont need all those wires though. All you need is the signal wires.

John_M_

Right, all the signal wires and at least one common ground should be carried through ... the other wires do add some strain relief to the connections to the board.




John M,

TOPGUN WINNER

My Feedback: (27)

I flew on 4.8V with my old Futabas for over thirty years. However, I would not dream of using anything but a 6V NMHI today. In the past year I have seen two of my friends have one of the cells in their battery packs reverse polarity.
I know you can take a 12v battery and shock that cell back but if it did it once it will do it again.

If you discharge your 5 cell 6V pack on a dis- charger after each days flying and then charge it to 99% you should have no problems.

Keep coming with those good questions.

.

dirtybird

My Feedback: (5)

The only way a cell is going to reverse is the pack has been discharged too far.
Battery manufacturers all agree that the less depth of discharge the better.
Discharging everytime after a flying session is not a good idea. It could very well be the cause of your cell reversal.

rcyoucando

I have a charger from BP hobbies that charges using only the balance lead. That is why I am looking for a balance lead charge port.
I can charge and check the life battery without removing the hatch. Also is it ok to use a lipo 2 cell without reducing the voltage on any Spektrum receiver DSM2 or DSMX.
If I have to I would use the diode method to reduce the voltage. just less parts to fail if I do not have to. When it comes to charging the Lipo I will remove it from the Plane for safety.
And from what I have been told per the thread and 8hr uptime on the lipo would be at least twice the fly time that I normally would fly. But I can still check the battery when I chose to.

rcyoucando

Just checked online Horizon hobbies Specs for DSM2 DSMX 3.5 to 9.6 volts That was a 6 channel dsm2 and a 8 channel DSMX.
There was also a tech support article that you can add a second battery using and open servo port or an aux battery port and the receiver can handle 30amps.
I am not sure how to supply the links that I read But it was on the Horizon site. I would still like to isolate the receiver from the servo demands by using separate batteries.

I also have a couple of DSM2 Jr receivers and they have the same voltage specs 3.5 to 9.6.

dirtybird

My Feedback: (5)

I think that specification shows that you don't really have to worry about brownout. Putting in another battery just adds to the complexity and can lead to failures. Just get an A123 battery and forget it. Your receiver can take the voltage.

SkidMan

My Feedback: (17)

Spektrum receivers are perfectly fine with 2-cell LiPo's - As you found. The voltage rating of your servos is what you need to consider.

kurtataltos

Jmiles...for the sheer joy of it, you may want to try stalling the servo (restraining movement) to see if the current draw changes significantly.

init4fun

Your welcome Ken , And Thank You for doing what needed to be done with that other thread .

Something I'd like to see mentioned here , for those that may not be 100% up on electrical theory is ;

I see much talk of Volts , as in how much "better" 6 Volts is than 4.8 , but little talk of Amps . The bottom line in any system is that the power supply has to be capable of delivering every Amp the system draws on it , and if those Amps can't be delivered the end result will be a voltage drop , whether the system is 4.8 , 6 , or 600 volts ! I believe the current carrying capacity of modern RC system's wiring and switches hasn't grown with the increased power draw of modern servos . Couple that with batteries that sag too much under load and there is your classic recipe for a brownout .

Kudos to DirtyBird for mentioning the stalled digital servo issue , I tested this myself and found it to be true , it WILL keep drawing current , assuring the RX never gets a chance to recover (Reboot) .....

deadstickdan

My Feedback: (3)

Just went out and bought a 6v 1600mah NiMH battery. I was also looking at the Spektrum capacitor thinking that may be a good idea but then read where it is not for aircraft use. Anyway, I think 1600mah should be good for my basic 4 channel setup with the HiTec HS322HD servos??

kurtataltos

Init4fun... agree... my weak analogy in post #8 tried to express that if you run out of hot water because too many showers are running at the same time it doesn't matter how big your water tank is as there is just not enough juice...er....hot water to spread around. And a large current draw servo in stall mode will likely do something unpleasant and will continue to do so as it thinks it's just doing it's job. Or trying to.

init4fun

I don't think your analogy was weak at all , many times folks use water as a way to illustrate electrical principles .

So in a practical sense , that pack should deliver 1.6 Amps max if the circuit load is enough to cause it to need to supply that much . If the circuit draws less , then all is well . But if at any time the circuit attempts to draw more than that 1.6 Amps , of if the wiring can't support the amount of power flow that the circuit will draw , then the voltage will sag . The best reliable indicator of how much the system will load the battery would be to use one of those servo current meters in line with the lead coming from the battery , move all the TX sticks , and make sure the draw never hits or exceeds 1.6 Amps . Also don't forget , the wind against the control surfaces while actually in flight is going to raise the servo current draw somewhat as well , with the servo now working against the airflow it didn't see in ground testing , and this additional current needs to be taken into account as well ........

John_M_

You don't need to use one of those electrolytic capacitors... all its doing is smoothing out any variations in the voltage supply to the receiver as the load on the power supply changes... if you plan on separating the servos and receiver power supplies, then you won't need the capacitor... and not to mention, cheap quality electrolytic capacitors can short out, causing the biggest brown out you will ever experience... I'm sure that's why spektum doesn't recommend it for aircraft use.... you usually see filter / smoothing capacitors on DC switching power supplies, or where there is large voltage fluctuation caused by very hi current draws, like with sound systems sub-woofer amplifiers, where the capacitor helps to keep the voltage from sagging on each thump of the woofer.

You'll do just fine with the 1600 mAh without the capacitor.


John M,

TOPGUN WINNER

My Feedback: (27)

I PREFER 6V (5 CELL) IF USING NICD OR NIMH BATTERIES. BOTH HAVE DIFFERENT ADVANTAGES.

From everything I have been told, you should pay attention to the mAh ratings. I use 2300 minimum up to 2700 because of price.

The 2700 gives you 2.7Amps max and the 2300 gives you 2.3 Amps max.

I suggest you see how many Amps your servos require and purchase your battery accordingly. I have A-123 (LIFE) which are 6.6 Volts for my receiver. However, they are 4500mAh which gives me 4.5 Amps max.

Sometimes I run two of those. Depends on the servos draw.

Remember the guy in the CIRCUS that took a million volts and his hair stood on end? He made sure there were no Amps to Electrocute him...great show.

Hope this helps.

dirtybird

My Feedback: (5)

The specification 1600mah does not mean the battery is limited to 1.6 amps max. It means it will put out 1.6 amps for 1 hour.
Depending on its internal resistance it will put out many more amps for a shorter period. The C rating tells you how much current the battery can source. NIMH batteries are not C rated.
A decent digital can draw many more amps than 1.6 depending on the load.