Rx with BEC and extra 4.8V NiCd Battery?

[TmMugen]

Hi all:

Just checking if anyone had this on their rx (heli). Rx's battery slot connected to a BEC for lipo (2S) and extra aux connected to a 1500mah NiCd battery for extra precaution in case if the BEC fails us.

Please advise..Cheers.

[baby_zyklon]

It is possible, but a few things you need to take note.

1. I have never experienced it before, but I have read somewhere that some regulator when they fail, they will suck amp from the remaining supply of the redundent setup. How true is it, I really don't know. All I know is 2packs of nicd or nimh will definately not do this.

2. Voltage difference between regulator output and ni-cd. If you are using those align or duralite voltage drop down diode, you will need 6v pack instead of 4.8v because 4.8v-0.7v=4.1v....when the regulator fail....

3. 1x 1500mah can be big, can also be too small for a rx batt. All depends on your flying style and setup. Also depends on state of charge. One thing to note is that the 1500mah sanyo nicd have high ir, giving rise to big voltage drop under big load. My setup is 2x6965hb, 1x 635hb, 1x 9254+tj pro, 1x logictech 6100 and according to volt meter, I am at 4.7-4.8v after half a flight and cycling the sticks. Double confirmed with futaba gyro voltage display. My 6100t gives a much lower display(4.4-4.6v). So with a redundent setup, if the regulator fail with a partially charged 1500pack still work, you might still go into batt-failsafe if unlucky.

4. Weight and c.g. Especially if running 3d carbon fins. Do note that 1 pack of 1500mah 4.8v is already 120g++. The difference is between flying your heli with a canopy or no canopy, definately its there.

Weight and pros and cons before you decide on redundency setup, especially with regulator and lipo. Duralite has a nice regulator call gemini(i think) with dual independent regulator. That way, you probably save a bit of weight, but its not cheap.

[TmMugen]

Hi thanks for your advise..Can i check where selling the dura thingy that you mentioned?

I just wanted something more foolproof to prevent my heli from running away when the lipo or BEC fails me..I am currently running on the Webra BEC from Hobby shack and was thinking if i can have more safety when running it on my 50 titan..

Awaiting for your kind advise please,

[LittleGiant]

I think it is possible but not very efficient.

Current always travel from a higher potential to a lower potential. This mean that if your 4.8V battery has a higher ACTUAL voltage than your Regulator output (which normally is 5.5V without load), your 4.8V battery will get drained by the regulator until the 2 have the same voltage. And if it is the other way round, the regulator will charge the 4.8V battery until they are the same voltage.

[baby_zyklon]

no, connecting two packs to a rx will only give neglible counter-charging. That is true even if 1 pack is 6v and another is 4.8v. Yes, more current will be drawn from the higher voltage one, but so long as the difference is not so big like between 4 and 5cells, then it should be a small difference.

IMHO, the best redundency setup for a nitro heli is two packs of 4/5A packs. 2x 1500mah works good and is almost the same weight as a sub-c pack. There is also a lower voltage drop under load because the batt only have 1/2 the internal resistance when you parrellel them. The newer generation of 4/5a nimh also work great at the same weight and even lower internal resistance.

Regulator at

http://www.duralitebatteries.com/

The best and most reliable regulator is no regulator Chance of heli running away in flight when your battery fail is 0.01%, because the heli will lost control and crash. Even had a servo failure in flight? The same thing will happen when the battery fails

[TmMugen]

Hi:

parallel for 2 pack 1500mah nicd? meaning use a "Y" cable? or one in battery slot and one in aux slot of the rx?

[baby_zyklon]

2packs, two switch plug into two different slot.

[Babylon5]

no, connecting two packs to a rx will only give neglible counter-charging. That is true even if 1 pack is 6v and another is 4.8v. Yes, more current will be drawn from the higher voltage one, but so long as the difference is not so big like between 4 and 5cells, then it should be a small difference.

IMHO, the best redundency setup for a nitro heli is two packs of 4/5A packs. 2x 1500mah works good and is almost the same weight as a sub-c pack. There is also a lower voltage drop under load because the batt only have 1/2 the internal resistance when you parrellel them. The newer generation of 4/5a nimh also work great at the same weight and even lower internal resistance.

Regulator at

http://www.duralitebatteries.com/

The best and most reliable regulator is no regulator Chance of heli running away in flight when your battery fail is 0.01%, because the heli will lost control and crash. Even had a servo failure in flight? The same thing will happen when the battery fails

Hi BabyZ, from the electrical point of view you need two set of rectifier diodes to prevent a current flowback to the packs with the lowest electrical potential. A safer methode is to use two packs of battery of 5 NICAd or NIMH and connect two rectifier diodes .

1) Rectifier 1 with the anode side tie to pack1 5xnicad or NIMH +ve side.
2) similarly...Rectifier 2 with the anode side tie to pack2 5xnicad or Nich+ve side

3) The cathode side of rectifier1 and rectifier2 are solder togather see attachment.

Rectifies should rated at least 1amp or even higher rating and a PIV(peak inverse voltage )of 100V or more if your setup with giant servos or lots of servos

Analysis.
4)If pack 1 fails either open or shorted out due to a back cells, Pack 2 takes over and vice versa.
5) If both pack1 and packs2 are electrical balance both will share equal load current.

6) Average voltage of each NICAD or NIMH are 1.2V so 5cell=6V. Rectifier average drop is 0.67V(0.7v) so average voltage is 5.3V still good and safe tofor the RX. Most RX can handle 4.8V to 6.5V without consequences however should still check specification of the RX

However, you need to provide ascessible TAB to charge the NICAD or NIMH packs.



The rectifier diode will drop approximately 0.7 to 1v depending on how much current is drain by the RX and servos.


Cheers and hope this will help.

[baby_zyklon]

babylon5,
battery clinic has an experiment you might be interested in. It involves connecting two rxpack, one charged and one discharged, measuring the current flow between them. You might want to check that out because that shows how neglible the counter charging effect is.

Been using 2 packs with 2 switch and no diode since 2003. Have tried difference of 1x600mah pack and 1x1000mah pack up to 1x1500mah and 1x600mah, with no observable ill effect. So i guess on a budget and kiss viewpoint, two battery and two switch plug into 2 different slot is sufficent.

[Babylon5]

babylon5,
battery clinic has an experiment you might be interested in. It involves connecting two rxpack, one charged and one discharged, measuring the current flow between them. You might want to check that out because that shows how neglible the counter charging effect is.

Been using 2 packs with 2 switch and no diode since 2003. Have tried difference of 1x600mah pack and 1x1000mah pack up to 1x1500mah and 1x600mah, with no observable ill effect. So i guess on a budget and kiss viewpoint, two battery and two switch plug into 2 different slot is sufficent.

Hi Babyzylon, if the 2 packs you are using is LIPO in parallel connection is OK , but not with NICAD , NIMH or lead acid.

In the case of NICAD or NIMH if you connect them in parallel without the the blocking diodes, the battery will self discharge and eventually "konK' out in short order.


Cheers

[baby_zyklon]

babylon5, I am using NI-CD and only ni-cd now.

[TmMugen]

2 lipo in parallel? how to connect?

2 switches with two battery? how to connect?

Anyone please enlighten as i am newbie plus me a nuts when comes to electronics.

[baby_zyklon]

Lipo for flight power system, there are connectors that you can buy to make the packs parrelle or series. For rx power, you need two regulators or you can make harness to join them together to one regulator.

For two nicd/nimh and two switches, you just plug the switch into different slot on the rx. You can plug one into batt channel and other into dsc, or any other avaliable channel. Two switch, two packs setup is just like plugging in two seperate, individual power supply into rx.

[Babylon5]

Lipo for flight power system, there are connectors that you can buy to make the packs parrelle or series. For rx power, you need two regulators or you can make harness to join them together to one regulator.

For two nicd/nimh and two switches, you just plug the switch into different slot on the rx. You can plug one into batt channel and other into dsc, or any other avaliable channel. Two switch, two packs setup is just like plugging in two seperate, individual power supply into rx.

Hi Baby Zyklon,
I see ,if you connect two seperate nicd/nimh in pararellel via switches is ok for a short while . I assume both packs have same number of cells.
In addition , if you have voltage regulator on each packs, it will behave like the two blocking rectifiers . The only differnces is the voltage regulator will output a constant voltage which is better than a rectifiers diode.

I think if you could draw out in a schematics or pictorials on the redundancies power setup , it would made reading easier for all.

Thanks for your effort.

Cheers

[baby_zyklon]

Hi Baby Zyklon,
I see ,if you connect two seperate nicd/nimh in pararellel via switches is ok for a short while . I assume both packs have same number of cells.
In addition , if you have voltage regulator on each packs, it will behave like the two blocking rectifiers . The only differnces is the voltage regulator will output a constant voltage which is better than a rectifiers diode.

I think if you could draw out in a schematics or pictorials on the redundancies power setup , it would made reading easier for all.

Thanks for your effort.

Cheers

links at http://www.rcbatteryclinic.com/ Look under parallel operation. With diagram and text.

No regulator here, just normal switch. I fly cheap cheap. Everything I use is budget de.