Power boards/expanders really needed?

[capthis]

That leaves 30 amp for a spike when doing a high speed rifle roll or crankshaft? It sounds like that's a pretty good safety margin?

I've seen capacitors that can be plugged into an unused channel that can help overcome a momentary voltage draw in excess of what the battery can handle?

 

[JAG]

Again I'm a newbie into RC planes, but have an industrial electrical background.

What I don't like is running power through those switches. Looks like they only come with maybe 22AWG wire, which at best if it was 200C silicone would be good for around 13amps, which is a high estimate. That's not silicone wire so it would be even less.

Also a 5C receiver pack at 2500mah is only good for a 12.5 draw. So together that would be 25amps worth of power.

Thats why I went with a power board, and when that didn't pan out I went with a power safe receiver. The spektrum power safe receivers run dual 16AWG battery leads. 16AWG silicone, which it is, is good for around 32amps. So thats 64amps just for the wire. And I went with a higher C rated pack at 30C, 2100mah. So each battery is good for a 63amp draw, and I have 3. So I'm good for instananeous. And like said before, the battery power does not run through a switch that can fail.

I'm sure it is probably fine, but I tend to overbuild my electrical components.

 

[JAG]

Yes a capacitor would I think only be necessary if the batteries cannot handle the instantaneous current draw. So with 5C, 2500's you should be good for around 25amps before the batteries can't keep up. And that is with a new pack.

 

[Robotech]

It unusual for you to have seen a drastic voltage sag with A123. Maybe a lesser quality LIFE, but not A123. A123's can provide more amperage than any other chemistry. I've even heard of a guy that put two packs together and started his truck when it's battery went down.

I run dual 2500 A123's in to a Wolverine switch with 4 out puts to dual RXs. I also have a Cricket monitor on each RX that indicate the lowest voltage the RX has seen during a flight.. I have never seen anything more than a one volt drop after a flight. This is on a 40% IMAC plane with 9 high torque servos. I can safely fly 15 IMAC Sportsman sequences and have done as many as 24 by accident, I thought I had charged the day before. I put 2200 MA back in each pack. Yikes!

 

[jhelber08]

I did not have telemetry logging capabilities other than min/max during flight when I had the A123's. That being said, I don't know if they were fluke voltages, short power spikes, or prolonged power spikes. For me it was a little too close to comfort. Mixed that with the fact that I watched a much more talented pilot than me wring out an individuals plane running A123's and he did have brownout issues (not to start any brand war but this was with a futaba setup and no kind of power safe rx or expander).

Mine were fromeco A123's so I don't think quality was an issue. If I remember right, they used high quality sanyo cells.

I'm still messing with the Jeti setup and am not at home to go back and look at logs but with my violent flying style I don't remember seeing anything over 14 amps being pulled from the rx batteries on either of my 100cc setups that now have telemetry capability. I'm running mks 777's in my demonstrator (2 ea on rudder) and just sitting at idle with engine off the setup pulls around 1 amp, with engine at idle the setup pulls around 3. On my 105 laser I'm running the MKS 599's (brushless). Engine off with servos at idle it pulls about .2 amps (big difference compared to the 777's). Engine at idle it pulls about 1.5-2. I don't really have a whole lot of flights and haven't looked in much detail at the logs but its pretty cool to have the ability to pull this information for comparison in different setups. The radio tells me how much capacity is used from each battery as well, its pretty neat. I know for a 10 minute balls to the wall flight on the demonstrator each battery uses about 500 mah. The laser uses about 400 mah for each flight but I haven't beat as hard on it yet with the engine being new.

 

[Xpress]

A lot of modern receivers have much higher current capabilities and some do have their own battery management systems built in so there is little need for a power expansion system. The system I like to use is PowerBox SRS (Serial Receiver System) components with a pair of single line style receivers to give a better redundancy on bigger airplanes. Basically, you have 2 receivers feeding all the same data into the PowerBox and the PowerBox will automatically switch receivers if one gets shielded or blocked. Gives you the ability to mount your receivers in 2 different spots to spread out your coverage.

As long as your receiver can handle the current loads and provided you have enough power going to the receiver then you should be fine. Spektrum systems give you the ability to mount multiple remote receivers in different locations and orientations on the airplane to give you wide coverage without the need for a SRS style system.

 

[capthis]

Thanks for the insight folks.

I may look into power safe Rx's for 40% size planes as I tend to think that due to their increased size and weight they will draw more current than the same servos in a 35% size airplane. But I think the dual Life Packs through RCExcel Switches and then into the Rx have been working well for me for some time and it appears the weak link being the switch.

I do know I put about 500-700 Mah back in each Life Pack after 3 or 4 flights so I don't quite use 200mah out of each one for each flight?

After watching Jase Dussia Fly a few weeks ago I can see where his power system has to be the best ever as he is hard on airplanes in the air! I can't/don't fly like that! LOL

 

[Xpress]

As long as your power switch is a soft/fail on style switch then I'd say you're golden. I personally like to use Fromeco Wolverine and Badger switches because if anything goes wrong the circuit is designed to automatically turn on and keep the power on to prevent loss of control.

 

[capthis]

As long as your power switch is a soft/fail on style switch then I'd say you're golden. I personally like to use Fromeco Wolverine and Badger switches because if anything goes wrong the circuit is designed to automatically turn on and keep the power on to prevent loss of control.

They are not but that is why there is two of them and I always check to see that both are working before taking off.

 

[Xpress]

They are not but that is why there is two of them and I always check to see that both are working before taking off.

This is just me but I wouldn't use anything but a fail-on style switch. The reason being is if vibration gets to the internals in the switch it can wreak havoc on them. Some people get away with it for years but it's cheap insurance to assure your airplane doesn't lose power if you decided to use switches for power. There are people I know that simply plug the battery directly into their receivers because that's the only way that they feel safe with doing. It's all up to you though, if you feel safe with a mechanical switch with mechanical contacts then by all means keep using them