[Dadstoysbg]

As I promised here is the what I have learned so far on the power needs for our GS planes.
Now I'm not a expert by any means, so I picking other peoples brains and i want you all to give me your thoughts.

Our servo plugs can handle anywhere from 2.5 to 5amps depending who you talk too.

The HD switches are rated at 5amp.

Using battery's that have standard plugs with 22ga. wire can loose as much as 1v per connector gong into the receiver. that means to me that if you have a switch in line including the plug at the receiver. the possibily of a 3v drop under heavy load.

On the out side going to the servo's, each connector could be from 1/4 to 1/3v drop.

Only JR/Spektrum makes a power box receiver with heavier battery leads.

I was told that a 40% at idle on the runway was will draw about 2.5 to 3 amp fighting the vibration of the engine. It does go lower in the air because of the airflow over the service.

One man tested his 100cc plane with all 8711 doing 3-d and found 16 to 17 amp peak. with a 40% with larger services that would be higher.

I did lose a 46% bi-plane due to a unknown power failure some time back and now wonder if this was the cause.

I have noticed that my battery wires are getting stiff. I have been told this is called 'brown wire' from high amp loads.

At this point I have to admit that I leaning in the direction of a power box.

If I am truly losing up to 3v to my servo's I'm not getting what I paid for in the 8711's and may be putting my plane at risk.

Please all comments are welcome. Tell me where I am right or wrong.
Dennis

[fullspool]

I've tested my wires and jr style connector for 10 mins at 6amps and it shows no signs of failure but then again I don't use jr wire or plugs unless I count the ones that come off my servos. If you're losing 3v anywhere on a rc airplane I would diffidently rethink my setup.

[Ground Pounder]

Prolly need to double check and verify the connector voltage drop data. There was a thread a few years ago that stated that the drop was .1 volt per connector.

Maybe call the Horizon/Futaba Svc Dept and ask one of the tech's for a specific value based on their internal test data. The 1 volt per connector sounds like a very wonky number to me. Should be more like (.1).

If the value was truely 1 volt there would be a lot more impact craters aroung the club flying field.....

[TManiaci]

Originally Posted by Dadstoysbg

As I promised here is the what I have learned so far on the power needs for our GS planes.
Now I'm not a expert by any means, so I picking other peoples brains and i want you all to give me your thoughts.

Our servo plugs can handle anywhere from 2.5 to 5amps depending who you talk too.

The HD switches are rated at 5amp.

Using battery's that have standard plugs with 22ga. wire can loose as much as 1v per connector gong into the receiver. that means to me that if you have a switch in line including the plug at the receiver. the possibily of a 3v drop under heavy load.

On the out side going to the servo's, each connector could be from 1/4 to 1/3v drop.

Only JR/Spektrum makes a power box receiver with heavier battery leads.

I was told that a 40% at idle on the runway was will draw about 2.5 to 3 amp fighting the vibration of the engine. It does go lower in the air because of the airflow over the service.

One man tested his 100cc plane with all 8711 doing 3-d and found 16 to 17 amp peak. with a 40% with larger services that would be higher.

I did lose a 46% bi-plane due to a unknown power failure some time back and now wonder if this was the cause.

I have noticed that my battery wires are getting stiff. I have been told this is called 'brown wire' from high amp loads.

At this point I have to admit that I leaning in the direction of a power box.

If I am truly losing up to 3v to my servo's I'm not getting what I paid for in the 8711's and may be putting my plane at risk.

Please all comments are welcome. Tell me where I am right or wrong.
Dennis

I think you're perfectly on track... I truly believe MANY giant scale pilots seriously neglect details like this. Considering power load and wiring capacity is as important as any other aspect of a build.

When I built my first 150cc airplane, I was doing it on a firm budget. I bought everything used. When I started analyzing the power system, just like you are, I convinced myself that buying a Powerbox was not a useless fancy bling item, it was an essential. Adequate Power delivery, and Power and Receiver redundancy, all seems real damn important to me. There are cheaper devices, but not by a lot if you rig for worst case probability. I am no great pilot, but I sure don't want to have my big bird go down for some silly problem because I was being cheap.

I'm an Engineer. I design complex electro-mechanical devices for a living. Reliability is the number-one concern in my work. I design locks for safes, among other goodies. When one of these devices fail, it costs a ton of money to remedy the situation, because the safe must be damaged considerably to open it and make repairs.

Some of top end SmartFly goodies are suitable too, if you're looking to save a little.

[WrongWay]

I have had the 22g JR wires go stiff just from sitting in a box for two years...just sayin'.

Speaking of 22ga.... Had a buddy with a 42% Extra switch over to my batteries after a couple years of his Liion being in service... He said it was time.. His had the typical well known brand name Liions with two HD 22ga switches... think about that... all current going to the receiver was channeled through two 22g Quality Switches. He has 9 flight servos plus separately powered Seiko 12v.

I talked him into the 18ga Smart Fly switches to interface the A123's with the power expander. When he went to take the old switches out one of the power leads was stuck to the balsa side of the plane... It was never glued in that place... but it was....
"Stuck...."

[TManiaci]

Originally Posted by Ground Pounder

Prolly need to double check and verify the connector voltage drop data. There was a thread a few years ago that stated that the drop was .1 volt per connector.

Maybe call the Horizon/Futaba Svc Dept and ask one of the tech's for a specific value based on their internal test data. The 1 volt per connector sounds like a very wonky number to me. Should be more like (.1).

If the value was truely 1 volt there would be a lot more impact craters aroung the club flying field.....

I would agree, 1.0V drop on a connector seems way high. However, not every connection is perfect. A poor crimp or a bent pin can compromise conductivity quite a lot.

I don't have time to run the numbers right now, but we use Servo Wires for power transmission. Technically speaking, our wire systems are undersized considerably already. Google it and you'll see that the "good" wires at 22 gauge are supposed to be limited to less than 1 amp, and at 3 amp loads the voltage drop exceeds the 2% drop standard. The real drops are not huge, but not insignificant. If you use 26 gauge extensions, you are getting significant voltage drop, on the order of 0.12 volts per foot. 22 gauge wire is around 0.05V per ft at 3 amps.

[fullspool]

Someone correct me if I am wrong but I am calling snake oil.

Set up
Using the "17amp load" and a 42" 20awg extension.

VD=(2xLxRxI)/1000
VD=(2x(42"/12")x9.5x17A)/1000
VD=1.1305 volts on 42" 20awg wire @17amps.

[TManiaci]

Originally Posted by fullspool

Someone correct me if I am wrong but I am calling snake oil.

Set up
Using the "17amp load" and a 42" 20awg extension.

VD=(2xLxRxI)/1000
VD=(2x(42"/12")x9.5x17A)/1000
VD=1.1305 volts on 42" 20awg wire @17amps.

Not sure where you got your wire resistance. My table shows 0.01015 ohms per foot for 20 gauge wire. You don't factor by two because it's two wires. 42" = 3.5 ft. R= 3.5 x 0.0102 = 0.036 ohms. V = I x R.

V = 17A x 0.036 Ohms = 0.604 Volts (drop)

[fullspool]

2 conductors and 1 signal wire so why wouldn't you count it as 2 current carry conductors?
9.5kft for 20awg and 8.08kft for 18awg are what my tables show, I will dig up factory spec sheet when I get back to the home pc.
Regardless it's no where near 3volts even with the allowable 3% safety factor.

[TManiaci]

Originally Posted by fullspool

2 conductors and 1 signal wire so why wouldn't you count it as 2 current carry conductors?

The current makes a loop. We are measuring drop at the half way point, where the demand is, where we make the voltage measurement. The drop from the source to the target is one wire carrying current.

I think we agree, the drop to a servo is no where near 3V. Not even at 17 amps.