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Power Expander or not -that's the question

Old 12-09-2008, 11:11 PM
  #126  
Hammbone
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Default RE: Power Expander or not -that's the question

I think it is very difficult to figure out exactly how much current flow we need, there are just way too many variables. This is why I simply supply 3 amps to each servo, and then go fly, knowing that this is more than enough. (Sorry for saying it yet again)
It just takes a little thought and planning to make sure that each component you are going to use is up to the task. Check the manufacturers current flow ratings for each individual component.

Jim
Old 12-09-2008, 11:13 PM
  #127  
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Default RE: Power Expander or not -that's the question

ORIGINAL: Hammbone


Think of it like water going through pipes. If you have 4" diameter pipe running 30', but have one small section that is reduced down to 1/2" diameter, you are only going to get as much water as will flow through the 1/2" pipe out the other end. If you had 4" pipe the whole way, you'd get much more water through the pipes. Putting in a section of 6" pipe will not improve your flow if you still have the section of 1/2" pipe inline somewhere.

Jim
BINGO! [sm=thumbup.gif] There you go. That's one of the best analogies I've heard yet of trying to explain what's going on with our power systems. I've raised hogs for 25 years, and I know how much water and how much sh** will go thru a pipe. Block it up some where, and you've got problems! [:@][:@] LOL

That's exactly why I'm replacing the Y's and plugging everything into the power expander. One bottle neck anywhere in the system, and the whole thing is compromised. Will my plane fly better? I don't know, that's why I'm doing this.

Jim,

I really couldn't tell any difference when I added the second battery, and my mAh per flight stayed about the same.
Old 12-09-2008, 11:25 PM
  #128  
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Default RE: Power Expander or not -that's the question

With my setup I'm only going through one connecter for each servo. I have 2 A123's, each going into a 30 amp smartfly switch with a Deans connecter. There are 2 leads coming out of each switch so I have 4 leads going into the reciever. Each servo has it's own port coming out of the reciever.
Old 12-09-2008, 11:53 PM
  #129  
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Default RE: Power Expander or not -that's the question


ORIGINAL: flatspinjim

With my setup I'm only going through one connecter for each servo. I have 2 A123's, each going into a 30 amp smartfly switch with a Deans connecter. There are 2 leads coming out of each switch so I have 4 leads going into the reciever. Each servo has it's own port coming out of the reciever.
That sounds like a pretty good system to me. Four leads going to the receiver will give you 16 amp or so capacity? But if I recall, the darn switches like that are like $30 each.

How many channels are on your receiver to let you plug in that many servo leads?
Old 12-09-2008, 11:55 PM
  #130  
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Default RE: Power Expander or not -that's the question

ORIGINAL: flatspinjim

With my setup I'm only going through one connecter for each servo. I have 2 A123's, each going into a 30 amp smartfly switch with a Deans connecter. There are 2 leads coming out of each switch so I have 4 leads going into the reciever. Each servo has it's own port coming out of the reciever.
I'm only trying to help here, so don't get mad at me.
You might want to check with Smart fly on the rating of those switches. If they are the ones I think they are, the last time I checked, I was told they were rated at 5 amps.
Besides, if it has 2 standard connectors coming out of it, they are rated at 3 amps each. That gives you 6 amps total, so it doesn't really matter if the switch can handle 100 amps, the standard connectors are your weak point.

You have 4 standard connectors going into your rx feeding how many servos? If you only have 4 servos, then you only have one connector per servo, and you have 3 amps per servo. If you have 8 servos, then you are feeding 2 servos with each connector (4 connectors going into rx). See what I mean now? With 8 servos, you have 1.5 amps per servo. This may be fine. It's up to you.

This is why I never use standard connectors anywhere between the battery and the rx / Power Expander. When I say I never have more than one servo downline of any single standard connector, this includes the input side of the rx as well as the output side of the rx.

It's up to you to decide how much current flow you want to provide.

Jim
Old 12-10-2008, 12:25 AM
  #131  
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Default RE: Power Expander or not -that's the question

I don't get mad, not why I'm on here. With 4 leads going into the reciever, I can handle at least a 20 amp spike. The connectors are rated at 3 amps, but I'm pretty sure they could at least handle a 5 amp spike and probably more. With that going into the receiver it's not going to every servo at the same time in most cases, just the one 's that are needing the power. I'm a firm believer that if you setup your servos and linkages right, no binding and the correct geometry, then there is no reason to draw 50 amps in the first place. If you are using A123's and you are using 1000 mah per 10 minute flight, that's when you have problems. If you are using 200 to 400, then I would say you have a pretty good setup. My biggest thing is adding too many components that can fail. If it's electric it can sure enough fail. If a servo, or a single battery in a dual battery setup fails you have a chance of saving your plane
Old 12-10-2008, 12:54 AM
  #132  
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Default RE: Power Expander or not -that's the question

Here's something to think about on this subject.

The Smart Fly power expander and the Spektrum AR9100 use basically the same curcuit for input power, it's 4 diodes that pass current through to the servos while isolating the beatteries from each other.

These diodes introduce a voltage drop. The voltage coming out of the servo connectors is about a half volt lower than what is coming out of the batteries.

While this is not the end of the world, you will find that your system consumes less power with the PE or AR9100 because the voltage to the servos is lower. You will also find your servos to be slightly slower and slightly less powerful than when sending power through a pure copper circuit.

TF
Old 12-10-2008, 09:13 AM
  #133  
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Default RE: Power Expander or not -that's the question


ORIGINAL: rctom

Here's something to think about on this subject.

The Smart Fly power expander and the Spektrum AR9100 use basically the same curcuit for input power, it's 4 diodes that pass current through to the servos while isolating the beatteries from each other.

These diodes introduce a voltage drop. The voltage coming out of the servo connectors is about a half volt lower than what is coming out of the batteries.

While this is not the end of the world, you will find that your system consumes less power with the PE or AR9100 because the voltage to the servos is lower. You will also find your servos to be slightly slower and slightly less powerful than when sending power through a pure copper circuit.

TF
I don't know where you got that info, but it's wrong.
It says right on the Smart Fly website that the voltage you put in is the voltage you get out.

I just checked one of my planes. The voltage direct from the battery was 6.6. I turned the Power Expander on and checked the voltage at one of the servo ports............ 6.6.

I took my spare JR R1222 rx out of the box and plugged a battery into it. Battery voltage was 6.6, voltage at one of the servo ports on the rx was 6.6.

Please don't spread bad info on the forums.

Jim
Old 12-10-2008, 09:43 AM
  #134  
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Default RE: Power Expander or not -that's the question

Technically, sure, I guess you can say that a standard servo connector is "rated" at 3 amps continuous, for the sake of argument. But it can surge to double that or more for at least a second or two with little or no voltage loss. I charge my A123's through a standard lead at 3 amps and the lead doesn't even get warm.
I just did a hard, 12.5 minute flight with my 100cc Extra with 6 5955's and an 8711. Flight included a knife edge loop, fast-rolling loops and circles, blow-overs, tumbling maneuvers, etc. Pretty much stress-tested the plane.
I have an AR9000 standard 9-channel receiver, powered by two A123's through a wolverine switch with two standard leads going into the receiver. I then have a Fromeco DC-up plugged into the receiver. The DC-up has a low voltage recorder on it. Lowest voltage encountered was 5.9V. This was the second flight on the batteries' charge, so the voltage had already stabilized at 6.6ish.
Old 12-10-2008, 09:50 AM
  #135  
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Default RE: Power Expander or not -that's the question

What's a blow-over?

Also, I thought the purpose of a DC-up was to make up for the low amp rating of Li Ion batteries. It stores energy to be used when the battery can't keep up with demand. Is there a reason to use it with A123's?

Jim
Old 12-10-2008, 09:54 AM
  #136  
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Default RE: Power Expander or not -that's the question


ORIGINAL: Hammbone


ORIGINAL: rctom

Here's something to think about on this subject.

The Smart Fly power expander and the Spektrum AR9100 use basically the same curcuit for input power, it's 4 diodes that pass current through to the servos while isolating the beatteries from each other.

These diodes introduce a voltage drop. The voltage coming out of the servo connectors is about a half volt lower than what is coming out of the batteries.

While this is not the end of the world, you will find that your system consumes less power with the PE or AR9100 because the voltage to the servos is lower. You will also find your servos to be slightly slower and slightly less powerful than when sending power through a pure copper circuit.

TF
I don't know where you got that info, but it's wrong.
It says right on the Smart Fly website that the voltage you put in is the voltage you get out.

I just checked one of my planes. The voltage direct from the battery was 6.6. I turned the Power Expander on and checked the voltage at one of the servo ports............ 6.6.

I took my spare JR R1222 rx out of the box and plugged a battery into it. Battery voltage was 6.6, voltage at one of the servo ports on the rx was 6.6.

Please don't spread bad info on the forums.

Jim
I have heard the same thing that Tom talks about, but I get the same voltage as you reported. I think you only see this voltage drop if the diodes are flowing current differently, like when one battery in the system fails, shorts, or its voltage drops.
Tom is just repeating what he heard. I bet if you plug a 4.8v battery into one input and a 6v battery into the other you will see this voltage drop that he talks about, because the diodes are sensing the lower voltage and switching to run off of just the 6v battery. It takes a voltage drop on one side to see this - it can't just be an open circuit.
Old 12-10-2008, 10:02 AM
  #137  
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Default RE: Power Expander or not -that's the question

I recognize that while a standard connector is rated at 3 amps, it can pass more current than that. The problem is that as current flow increases, resistance increases and voltage drops.

As I understand it, a manufacturer rates his product as to how much current it can pass while maintaining an "acceptable" amount of voltage drop. If you go above this rated amount of current flow, you will get an "unacceptable" drop in voltage. I don't want that excess voltage drop.

Jim
Old 12-10-2008, 10:02 AM
  #138  
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Default RE: Power Expander or not -that's the question


ORIGINAL: Hammbone

What's a blow-over?

Also, I thought the purpose of a DC-up was to make up for the low amp rating of Li Ion batteries. It stores energy to be used when the battery can't keep up with demand. Is there a reason to use it with A123's?

Jim
Blow-over is kinda like a waterfall, which I also did during that flight. The blow over is just pushing hard over top and dropping in to a harrier or harrier roll, so it probably doesn't demand as much of the servos as a waterfall.
The DC-up is a temporary power back-up. It is great for li-ions for the reason you say, but it is also like adding an additional source of current through an additional lead plugged into the receiver. The A123's don't have a problem delivering current, but as you say, the leads are limited. So it's like having 1/3 more current carrying ability in the most demanding situations, albeit momentarily.
I imagine that the 5.9v that I saw was either during the KE loop or the blender, which are two maneuvers that I don't much care for anyway and rarely do them.
Old 12-10-2008, 10:04 AM
  #139  
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Default RE: Power Expander or not -that's the question


ORIGINAL: bodywerks


ORIGINAL: Hammbone

What's a blow-over?

Also, I thought the purpose of a DC-up was to make up for the low amp rating of Li Ion batteries. It stores energy to be used when the battery can't keep up with demand. Is there a reason to use it with A123's?

Jim
Blow-over is kinda like a waterfall, which I also did during that flight. The blow over is just pushing hard over top and dropping in to a harrier or harrier roll, so it probably doesn't demand as much of the servos as a waterfall.
The DC-up is a temporary power back-up. It is great for li-ions for the reason you say, but it is also like adding an additional source of current through an additional lead plugged into the receiver. The A123's don't have a problem delivering current, but as you say, the leads are limited. So it's like having 1/3 more current carrying ability in the most demanding situations, albeit momentarily.
I imagine that the 5.9v that I saw was either during the KE loop or the blender, which are two maneuvers that I don't much care for anyway and rarely do them.
So does this mean that you actually have 3 leads going into the rx?

Jim
Old 12-10-2008, 10:22 AM
  #140  
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Default RE: Power Expander or not -that's the question

ORIGINAL: bodywerks


ORIGINAL: Hammbone


ORIGINAL: rctom

Here's something to think about on this subject.

The Smart Fly power expander and the Spektrum AR9100 use basically the same curcuit for input power, it's 4 diodes that pass current through to the servos while isolating the beatteries from each other.

These diodes introduce a voltage drop. The voltage coming out of the servo connectors is about a half volt lower than what is coming out of the batteries.

While this is not the end of the world, you will find that your system consumes less power with the PE or AR9100 because the voltage to the servos is lower. You will also find your servos to be slightly slower and slightly less powerful than when sending power through a pure copper circuit.

TF
I don't know where you got that info, but it's wrong.
It says right on the Smart Fly website that the voltage you put in is the voltage you get out.

I just checked one of my planes. The voltage direct from the battery was 6.6. I turned the Power Expander on and checked the voltage at one of the servo ports............ 6.6.

I took my spare JR R1222 rx out of the box and plugged a battery into it. Battery voltage was 6.6, voltage at one of the servo ports on the rx was 6.6.

Please don't spread bad info on the forums.

Jim
I have heard the same thing that Tom talks about, but I get the same voltage as you reported. I think you only see this voltage drop if the diodes are flowing current differently, like when one battery in the system fails, shorts, or its voltage drops.
Tom is just repeating what he heard. I bet if you plug a 4.8v battery into one input and a 6v battery into the other you will see this voltage drop that he talks about, because the diodes are sensing the lower voltage and switching to run off of just the 6v battery. It takes a voltage drop on one side to see this - it can't just be an open circuit.
I don't have a 4.8v battery, but I do have a Li ion laying around. The voltage on my Li ion was right at about 8v. I just plugged it into my Power Expander along with one of the A123 batteries at 6.6v, so there was a definite voltage difference and only one side of lights came on on the Power Expander showing that it was only drawing current from the higher voltage battery. I got a voltage drop of .07v at one of the servo output ports. Less than 1/10th of a volt.

Power Expanders do not reduce voltage unless you buy one with a built in reg.

Jim
Old 12-10-2008, 10:52 AM
  #141  
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Default RE: Power Expander or not -that's the question

I'm getting ready to start a 33% TTOC Yak with SF PE Sport(I think), dual 2600mah Li Ion/switches& regulators. I'm still not sure how much current the 8 7955TG's will draw, even though Hitec says 2 amps each. If my set-up only has 8 amps total battery capacity(4 amps each battery)wont I be seeing large voltage drops? At 2 amps each, thats 16 amps, more than the batteries could sustain. Yet, this same set-up has worked for a friends 35% planes?? There is something I'm missing here, I can only assume that 2 A rating is assuming very heavy loading(large surfaces & speed)??
Old 12-10-2008, 11:39 AM
  #142  
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Default RE: Power Expander or not -that's the question


ORIGINAL: MIXMASTER

I'm getting ready to start a 33% TTOC Yak with SF PE Sport(I think), dual 2600mah Li Ion/switches& regulators. I'm still not sure how much current the 8 7955TG's will draw, even though Hitec says 2 amps each. If my set-up only has 8 amps total battery capacity(4 amps each battery)wont I be seeing large voltage drops? At 2 amps each, thats 16 amps, more than the batteries could sustain. Yet, this same set-up has worked for a friends 35% planes?? There is something I'm missing here, I can only assume that 2 A rating is assuming very heavy loading(large surfaces & speed)??

Why not skip the li-ions and regulators and go with a A123 battery?

For my 35% I am building I am going with all of the servos plugged directly into an AR9100 and two batteries plugged directly into the receiver. I think once you start needing to Y multiple, high current servo then a power expander becomes more viable. Given enough ports on the receiver however you could Y the signal portion of the servo leads.

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Old 12-10-2008, 12:49 PM
  #143  
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Default RE: Power Expander or not -that's the question

I've been tossing that around in my brain, I would have to buy new charger,batts(A123). I have Li Ion charger now and can get PE & new L Ions & regulators at a good price. From what I've seen here, that set-up has worked well(Li Ions) in several 35%, but I know the A123 would not drop voltage like the Li Ions would. This is whats confusing me, how could the Li Ions have worked so well in a 35% with only 4 Amps each, 8 2-amp servos would have loaded the batts down, you would think anyway.
Old 12-10-2008, 01:08 PM
  #144  
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Default RE: Power Expander or not -that's the question

Quote:Hammbone "I don't know where you got that info, but it's wrong.
It says right on the Smart Fly website that the voltage you put in is the voltage you get out.

I just checked one of my planes. The voltage direct from the battery was 6.6. I turned the Power Expander on and checked the voltage at one of the servo ports............ 6.6.
"
I took my spare JR R1222 rx out of the box and plugged a battery into it. Battery voltage was 6.6, voltage at one of the servo ports on the rx was 6.6."



Diodes are silcone based electrical "gates" Only allowing CURRENT to flow in one direction, wich can be set up in various ways to get a two way(or more) "shuttle vavle" Meaning it will only allow flow from a higher source. I dont have a PE yet to check this out but , Try this. When testing the Drop before and after the PE be sure to dynamically test them. Your readings will only be acurate if a load is placed on the circuit. Some drop is normal and expected however this reading is what should be compared to one not going through a PE. Static voltages will always be source voltage now matter how much impedance. The circuit must be operating in the manner at wich it is operated normally.
Old 12-10-2008, 01:24 PM
  #145  
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Default RE: Power Expander or not -that's the question

I sent another e-mail to Hitec regarding "normal" current draw from 7955TG. They came back with 1-1.5 amps is what they would call normal load, and spikes up to 2 amps or more under heavy loads. That makes more sense to me now, that number explains why my 30% and friends 35% are not failing, they are set-up and flown to handle normal loads, probably never seeing 2 amps, not for long anyway. I know its better to have a set-up that can handle the worst case current, peace of mind.
Old 12-10-2008, 01:52 PM
  #146  
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Default RE: Power Expander or not -that's the question

ORIGINAL: houdinimkii

Quote:Hammbone "I don't know where you got that info, but it's wrong.
It says right on the Smart Fly website that the voltage you put in is the voltage you get out.

I just checked one of my planes. The voltage direct from the battery was 6.6. I turned the Power Expander on and checked the voltage at one of the servo ports............ 6.6.
"
I took my spare JR R1222 rx out of the box and plugged a battery into it. Battery voltage was 6.6, voltage at one of the servo ports on the rx was 6.6."



Diodes are silcone based electrical "gates" Only allowing CURRENT to flow in one direction, wich can be set up in various ways to get a two way(or more) "shuttle vale" Meaning it will only allow flow from a higher source. I dont have a PE yet to check this out but , Try this. When testing the Drop before and after the PE be sure to dynamically test them. Your readings will only be acurate if a load is placed on the circuit. Some drop is normal and expected however this reading is what should be compared to one not going through a PE. Static voltages will always be source voltage now matter how much impedance. The circuit must be operating in the manner at wich it is operated normally.
I have used A123 batteries on ignitions which are only rated for 6v max. The way I did this was to put a diode inline coming from the battery. The diode dropped the voltage by about .7 amps. I could read this drop with a static voltage, the same way I read no drop this morning.
Plus I was using a voltmeter that gives me the option of putting a load on it. Even with the 1 amp load, there was still no voltage drop.

Jim


Old 12-10-2008, 02:21 PM
  #147  
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Default RE: Power Expander or not -that's the question

ORIGINAL: Hammbone

ORIGINAL: mrbigg

Too bad you can't just swap in the Power Expander without changing the Y's and everything else. That way you'd have a true comparo.
????????????? A Power Expander does not work miracles. You can use a Power Expander and still have limited current flow. It's comments like this that make me feel like I have to keep repeating myself. If you have any one part of your system that limits current flow, then you have limited current flow (even with a Power Expander). A Power Expander in and of itself does not improve current flow if you still have components in your system (like "Y"s, small diameter wire, and standard plugs) that are going to limit the current flow.

Think of it like water going through pipes. If you have 4" diameter pipe running 30', but have one small section that is reduced down to 1/2" diameter, you are only going to get as much water as will flow through the 1/2" pipe out the other end. If you had 4" pipe the whole way, you'd get much more water through the pipes. Putting in a section of 6" pipe will not improve your flow if you still have the section of 1/2" pipe inline somewhere.

If he just put in the Power Expander without changing out the other potential current flow bottlenecks in his system, it wouldn't tell us anything. The way he is doing it will tell us something. He should feel a difference in performance with the new set up. His servos should be stronger with the new set up.

When I started using the A123's / Power Expander set up, I noticed a definite improvenment in both the speed and power of my servos, but I can't say for sure that it was due completely to better current flow, it's probably due to the higher voltage (6.6v) of the A123 batteries without a reg. I used to use Li Ion batteries with a 6v reg.

Jim
Read the first paragraph of your response. Why waste money on a power expander? I posted a long time ago about cutting connectors off of servos, hardwiring/soldering them together, and also taking the battery power wires and tapping them directly into your servo wires before they enter the reciever. Power goes right to your servos, reciever and you've also eliminated at least one connector/failure/amp reducer. Keep wasting your money and maybe someday you'll wake up and smell the coffee.
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Old 12-10-2008, 03:14 PM
  #148  
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Default RE: Power Expander or not -that's the question



Tom is just repeating what he heard. I bet if you plug a 4.8v battery into one input and a 6v battery into the other you will see this voltage drop that he talks about, because the diodes are sensing the lower voltage and switching to run off of just the 6v battery. It takes a voltage drop on one side to see this - it can't just be an open circuit.
NO, Tom knows this because het tested it under load. Please refrain from telling people what I know and don't know and how I know it.

Diodes always cause a voltage drop with current flowing, that's where the term "diode drop" came from.

People use a couple diodes in line with the power to reduce voltage to their ignition when using lithium batteries.

TF
Old 12-10-2008, 03:25 PM
  #149  
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Default RE: Power Expander or not -that's the question

Well I tested it under a load too, but got no drop.

Jim
Old 12-10-2008, 05:20 PM
  #150  
Tony Hallo
 
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Default RE: Power Expander or not -that's the question

Here are photos of a Smart Fly Sport Power Expander. I see no diodes and the resistance is the same between both input plugs measured in the forward and reverse directions, 0.1 ohms. There may be diodes in other models, not this one. The majority of the surface area in photo 1 is positive buss and lighter shaded area in photo 2 is the negative bus.
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