Rcpilot

My Feedback: (78)

I need battery help. It's a Kangke Laser with a G-62 on C&H and it has 5 JR digitals on the flight control surfaces and 2 more digitals on throttle and choke.

Okay--28% plane with dual 1900mah MH packs. These things are charging up to about 7.16 or 7.20 volts. These are high discharge packs capable of handling 15amps continuous discharge.


Basically, I wanted to be able to put at least 10 or 12 amps into my RX so I had enough power to drive all these servos. So, I bought the Smart Fly super switches that have the 18ga leads going in with dual 22ga leads coming out.

Here are my switches.
http://www.smart-fly.com/Products/Switch/switch.htm

My batteries have 14ga leads coming out and a Deans to connect up to these Smart Fly switches.

That means--with 2 batteries and dual connectors into the RX from each switch--I got 4 connectors going into my RX for power. If you believe a standard connector with 22ga wires can handle 3 or 4 amps--then I got between 12 and 16 amps going into the RX.

I built my power system like this to avoid a Power Expander AND I wanted to get as many amps into the RX as possible to drive all these digital servos. A Power Expander on a plane this size is just a waste of money IMO and it just makes it too complicated. K.I.S.S.

I was out at the field on Saturday and one of the guys told me that he would NEVER run dual packs in parallel as I've done without some type of diode in each power line to keep the packs from cross charging in the event of one pack failure. He told me that if one pack drops a cell or fails--the other would cross charge through the RX and then BOTH packs end up dead. [] I built my power system like this to avoid just that problem. I thought I was building redundancy and supplying my servos with plenty of amperage. I don't know this guy very well, but he is flying some 31% size planes and he really seams to know what he's talking about. He helpd me pre-flight the plane because it it brand new and not flown yet. He's a really nice guy, and I do put some weight on his experience. He's been flying bigger planes than me for a lot longer period of time--so it's not like the guy is an idiot. He's probably done all this before. [sm=thumbs_up.gif] I just wonder if he's being overly cautious. I do appreciate his help, but not sure if he's on the right track or not.

If I drop a pack or short a cell--will I still have enough power to land after a flight? (I wouldn't know I'd dropped a cell/pack during flight unless the plane started smoking and caught on fire) Or is he right and the good pack is going to cross charge and cook itself trying to charge the dead pack?

If the guy is right, then how do I install this "diode" to prevent my packs from sucking juice out of each other in the event of a major short or failure? Sounds like a simple one-way valve. Only allows power to come OUT of the battery pack and not back into it. How do I know what size diode to install? Does it have to do with how many amps my system will draw at maximum performance level? With 5 JR8411 servos, I'd think I needed at least 10 amps in an absolute worse case scenario.

Does it even matter how much power I draw OUT of each pack?

What I'm asking is:
Do I need a diode?
What size?
Where do I solder it in?

My setup:
Each switch has dual leads coming out. Dual switches. So, I need 4 open ports in the RX to plug them all in. Don't have 4 open ports. So, I used a heavy duty Y-harness on both ailerons and both elevators.

Plug the aileron into the Y and then plug the battery lead into the other side. Plug the Y into the RX.
I did the same thing with the other aileron and both elevators.
4 Y-harness'

Here's a pic of my setup:
The blue squares are the batteries

The purple squares are the Smart-Fly switches

The red lines are battery leads and switch leads into the switch with Deans connectors

The yellow lines are my servo extensions

The green lines are my Y-harness'

The dark blue lines are my dual 22ga leads from the switches to the Y-harness'

Black lines and squares are RX and servos

Flying Geezer

My Feedback: (14)

You don't have a problem RCPILET. If they are 4 cell packs and you drop a cell in one, you should have plenty of juice to get you down. If they are 5 cell packs, you'll probably never notice until you are on the ground and check your battery voltages.

As for diodes, they just lower the voltage going to your RX and servos from the get-go.

Hope this helps,

Panzlflyer

My Feedback: (15)

you worry to much...one pack (1950 ) with 2 leads and 2 switches is more than enough for the Laser.
I had that plane with a ZDZ60 on it and it was a beauty to fly, had to upgrade the landing gear is all and I had hungry Hitec digitals all round on it and much less power than a 1950.

richrd

If they are wired in parallel then it will back feed. If one pack fails then the other pack will dump it’s capacity into it. As said one cell takes both batteries to 4 cell, not what you were thinking but as said could land plane and on meter test show low voltage. Diode isolation is the KISS method cheap and works, but with voltage loss that’s why a). must use 5 cells and b). buy Schokie ?sp? these only drop 0.3V at full current.. Install in series (both batteries) with anode to positive and neg white band to switch. Install after charge input or you can not charge in plane.
Rich

MikeRuth

I disagree with Richrd, but then again he is certainly entitled to his opinion and experience.

I personally have never seen a cell short that bad unless it was overheating on fast charge, never during flight.

But more importantly I think you should definetly read this [link]http://www.rcbatteryclinic.com/parallel.html[/link]

Mike R

Red Scholefield

My Feedback: (9)

Gee, that's what I was going to tell him. His buddy should read it also.

TampaRCGuy

My Feedback: (282)

I have been running dual 1650 or 2700 5 cell NIMH in my 32.5% Godfrey Extra's (3 of them) for the past 10 years using only 2 batteries, 2 switches, plugged into 2 ports on the rx. Never had an issue.

I agree that is could happen. Highly unlikely though.

I charge each battery separately.

nsmjim

My Feedback: (52)

Hey guys -
I've been running dual packs for many years in my giant scale with no problems. Here is what Red's Battery Clinic says"

"Many pseudo battery "experts" put forth the argument that plugging two battery packs into the same receiver with out blocking diodes is NOT a good thing, claiming that his creates a host of problems and the two packs will end up fighting each other or "cross charging".

These concerns show a lack in the understanding of the charge and discharge potentials involved in Ni-Cd cells"

Or here is information from the NoBS Battery company:

"Q: Ok, that’s pretty kewl.. but my instructor sez I need diode protection or the packs will cross-talk or try to charge each other.



A: Sorry.. your instructor has been gaffed by Under-Informed Magazine Columists or the Battery Mis-Information Committee of your local fields Wives Tale Tag Team. There is NO need for diodes or a 'backup' circuit board (something else that adds weight, complexity and another possible failure point) and in fact there's no flight-safety significant energy transfer between packs at different charge levels.



You can test this yourself.. just plug a discharged pack and a fully charged pack together in a Y-Harness and check the two packs the next day.. You’ll find the system will pass a load test if checked through the ‘Y’, and you’ll also find that less than 20% of the charged packs energy has been ‘used’ by the discharged pack when you separately cycle-test the two of them. Next, consider that your average flight is 10-12 minutes, not 24 hours! The mythical "Energy Transfer Between Packs" scenario is simply NOT a flight safety issue and checking both packs before flight with a loaded ESV will certainly 'pick up' a weak pack before you fly it anyway!

I hope this helps,
Jim

Rcpilot

My Feedback: (78)

Thanks guys.

I'm cutting down to a single pack with a single 14ga lead going into the Switch. Then dual 22ga leads coming out of the switch into the RX.

1900mah high discharge pack should be able to put out all the juice I need.

Flying Geezer

My Feedback: (14)

With all the vibration that G62 will kick up, you might consider both battery packs and two (2) switches. It's a little more insurance.
Switch failures are not uncommon, and it sounds like you have a substantial investment in your aircraft.

Rcpilot

My Feedback: (78)

The G-62 is on C&H ignition and it runs smooth as a Swiss watch. [8D]

I can't just run any old switches. Do you know of any other manufacturer who has a 14ga wire going into the switch with a Deans connector to plug in the battery? If I continue to run the Smart Fly switches, I will have dual 22ga leads coming out. Might as well do the same thing I'm doing right now.

I'm going to drop one switch and battery. I'll use a single switch with dual 22ga output leads to plug into the RX. Single 1900mah 6V MH battery that can handle 15 amps continuous discharge. Thats simpler than the setup I have now. (see my pic in my first post) The single battery and dual output leads will give me 6--8 amps into the RX.

Flying Geezer

My Feedback: (14)

All my gassers are wired with two MPI switches and two packs. This gives me redundancy all the way from the pack leads to the receiver bus. This has worked fine for me.

Just sharing my experiences. I'm sure your system will work fine, too. Like you say in your signature line, "They all crash anyway".

There are a lot of opinions on these things, and a lot of pilots have had good experiences with a lot of different systems.

Sounds like a fun airplane!

Rcpilot

My Feedback: (78)

But, this one's brand new!! I'd like to get a few flights out of it before discovering the expiration date. [&:]

Oh well, it's only $2250 right? [sm=tongue_smile.gif]

Flying Geezer

My Feedback: (14)

That's why we worry about wiring and batteries, radio range, and balance. I usually get all that pretty much right.

Then when I'm get really comfortable with a plane, and I'm really doin' my stuff, I do somethin' stupid on an impulse, and eventuality rises up to slap me down.