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T-REX 600 › Radio Amp Draw in Flight
09-03-2013 09:32 AM  4 years agoPost 21
Craigdieslemac

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Valdosta, Ga USA

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Assuming you are using a 6s 5000mah.. that would give you 2s 15000mah. Maybe overkill? Maybe someone smarter can chime in.

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09-03-2013 09:53 AM  4 years agoPost 22
AWittleWabbit

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O.C., CA

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It's mega overkill. The idea is to prevent what miniscule cell imbalance there is. Also, it would give redundancy so you aren't relying on just 2 puny wires. You'll be relying on 6

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09-03-2013 10:02 AM  4 years agoPost 23
Craigdieslemac

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Valdosta, Ga USA

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thats a lot of amps . I don't mind the little bit of unbalance.. the charger will take care of that.. but I also don't mind all the amps, as long as nothing is going to get fried.

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09-03-2013 10:13 AM  4 years agoPost 24
AWittleWabbit

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thats a lot of amps .

Ya know, I thought about the number for a min. 15 amps for a hour should get it done eh?

Nothing would fry, you would just have a stonkin' no V droop solid 7.4 V. Servos will only eat as much current as they ask for, not what's on tap ( thankfully).

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09-03-2013 10:19 AM  4 years agoPost 25
AWittleWabbit

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Oops Wait a sec
I just thought of something. I'm not sure you can wire in parallel using the existing balance connector. Every other wire is both positive and negative. Only the first and last are either + or -

Its late, I'll revisit this in the late am

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09-03-2013 10:55 AM  4 years agoPost 26
Craigdieslemac

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Valdosta, Ga USA

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you would have to tap 2-4,3-6, 5-7 .. that would make 3 2s packs... You could hook it up some other way as long as 2 cells are combined to get your 7.4 volts.. or 8.whatever fully charged. Those could then be run in parallel to make 7.4V 15000 mah.

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09-03-2013 04:10 PM  4 years agoPost 27
FireNWater

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Collierville, TN

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You would have to be very, very careful adding additional tap wires to the balance port. The reason is that your entire electrical system, ESC main power, regulator, and radio all use a common ground connected to the negative wire on the main pack.
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You can use a voltmeter in continuity mode to check this (without battery connected). Clip one probe of your voltmeter on the black wire that leads into your voltage regulator. Now touch one of the negative pins on your receiver. If your voltmeter beeped or indicated continuity, then the ground is NOT isolated and adding cells that are further upstream will cause a dead short thru either the regulator or your receiver battery bus. The magic smoke will escape in a dollar sign shaped cloud.
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****** What follows is VERY IMPORTANT *******
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When you add the additional cells you need to check for any voltage between the new "ground" wire you want to add and the ground wire that feeds the regulator.
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****** What is written above is VERY IMPORTANT *******
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You want to get the system working as I described previously in this thread using cells 1 and 2 (pins 1 and 3 on balance connector). It is very important that you connect the regulator ground to the battery / balance connector ground (black wire) so you are using the same ground and the rest of the system.
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Now if you feel the need to add additional wires, you would use pins 4 and 6. Check for voltage between pins 4 and 1 before you connect those wires. You must do this with everything plugged in as if you were getting ready to fly, so remove your rotor blades or pinion as you normally would in your shop.
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Now, even though I've written all of this above, the only possible reason you would go through all of that is for redundancy of the balance wires. The radio system draws so little power compared to the motor that the imbalance is nearly immeasureable. Also, there is no need to fear imbalance of your cells during discharge as long as it is corrected during charge. Let me repeat that. There is no need to fear imbalance of your cells during discharge as long as it is corrected during charge. The only time imbalance during discharge would be a problem is if we were placing such a large additional load on those two cells that would drag them below 3.2V/cell or if we were triggering your chargers Safety Mode making it think those cells were bad. Using 3600Mah or 5000Mah cells, even with a dead short your radio system couldn't do that. If it does, then you need to be spinning the rotor with your radio system instead of the other way around.
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As far as capacity, two motor battery cells have more than enough oomph (a technical term) to power whatever your radio system could handle, even with four stalled servos. Adding additional cells in parallel is just way overkill.
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The best solution will be to open up the battery and solder some 20-gauge wire directly onto cells 1 and 2 then re-heat shrink the pack. That way I know there is a solid connection directly to the cells and I'm not relying on the balance connector wire. I'll try to do that this winter after flying season is over.
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Buy Cheap, Buy Twice . . .

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09-03-2013 04:37 PM  4 years agoPost 28
Craigdieslemac

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Valdosta, Ga USA

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Thank you for your reply. I am stuck deployed with plenty of time to tinker and I was planning on tapping the same wires you tapped to power my vbar. I had thought about the loss of balance and was researching it when I found this thread, which answered all the questions I had. I was just wondering if you had any further success with it.

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09-03-2013 11:05 PM  4 years agoPost 29
AWittleWabbit

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O.C., CA

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That was a great explanation firenwater, thx.

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09-04-2013 03:38 AM  4 years agoPost 30
FireNWater

rrApprentice

Collierville, TN

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I was just wondering if you had any further success with it.
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Yessir, about 20 more flights with zero problems and no receiver battery . . .
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I don't know if I mentioned this earlier in the thread, but I use an identical system on my 2 meter pattern plane. However, in addition to this I use a small 2S-350 Mah LiPo as a standby / emergency backup battery.
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The way this works is by using two regulators, one set to 5.7V output, and the other set to 5.9V output. Both outputs are plugged into the receiver power bus in parallel. The standby / backup battery is connected to the 5.7V output regulator. The 5.9V regulator is powered by the motor battery cells 1 & 2 thru the balance plug.
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The beauty of this system is that when the main 5.9V regulator applies power to the receiver bus, the extra 0.2V shuts off the 5.7V regulator so the little 2S-350 LiPo is not draining. I like to say it sits there "waiting to be a hero". If anything happens to the main system - the backup immediately powers the radio system. You won't even know it switched over. I know that 350 Mah sounds small, but its only there to finish out your flight in the remote chance that something happened to the main power source. And yes, I have operationally checked the backup battery by forgetting to plug in the main battery before a flight. It works. I only did that so you don't have to . .
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You need to develop a pre and post-flight routine of checking each system's integrity. I usually plug in the backup first, then the main, and then after landing unplug the backup first. Unless you are really paranoid you could check each system prior to each flight. I also don't use switches, just the JST plug works fine for the backup. Less moving parts.
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I haven't set up this system on my helicopters yet. Perhaps when the flying season is over I'll take a look at it. Most likely I'll just go with 20-gauge wire directly to the motor battery for a more solid connection for the radio and forgo the backup.
.

Buy Cheap, Buy Twice . . .

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09-04-2013 07:31 AM  4 years agoPost 31
Craigdieslemac

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Valdosta, Ga USA

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I was planning on trying this on a 700 with HV servos.. And no regulator. I already can use a small 300mah 35c on them when tuning the vbar on the bench. I've run through a full setup like this and only run the battery down to 7.2v. That's almost 30 min because I am slow. I have a parallel charge plug for my 130x batts that I used to plug it in.. I wanted to see how small I could go with the batts and still have it operate.

Aut viam inveniam aut faciam

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09-04-2013 02:43 PM  4 years agoPost 32
FireNWater

rrApprentice

Collierville, TN

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Here is why I use a regulator when powering the radio off of the first two motor cells.
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When you look at your Castle data logs there is a parameter called "ripple". Castle explains this as how much the voltage of your motor battery varies during load. The ESC is a switch that turns on and off thousands of times per second, thus making the current that is traveling thru your battery, ESC, and motor do the same. The two cells we're tapping experience this same ripple as the rest of the motor pack.
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The coils in the motor create "back voltage" (for lack of a better term after 1 cup of coffee) each time the current switches from ON to OFF causeing a 1-2 volt "ripple" in the entire motor system that can be measured at the battery. The capacitors absorb and smooth alot of this, that's why they say the spark is your friend. Using a regulator downstream of cells 1 and 2 of the motor battery cuts off that ripple and provides clean voltage to your radio system.
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**** Disclaimer - I haven't tried this with unregulated HV equipment, I'm speculating based on experience so I may be wrong ***
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Your receiver and gyro have regulators installed on the circuit board, so they will probably be OK. Your HV servo electronics probably have the same type regulator. I imagine the problem would come with the HV motor running unregulated on that pulsing voltage while the ESC is powering the motor. However, I could be wrong and it would be perfectly happy.
.

Buy Cheap, Buy Twice . . .

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