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HomeAircraftHelicopterMain Discussion › Can I run two RX batteries like this?
05-02-2005 04:36 PM  13 years agoPost 1
reilly13

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Binghamton, NY

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I would like to run two 4.8V 2000mah (NIMH) RX packs in my raptor.
I'm planning on a switch for each pack and then using a Y-wiring harness to run the switch leads together into the battery plug in the receiver. I'm doing this for redundancy and increased capacity.

Any reason why this is a bad idea?
Anything I'm forgetting?

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05-02-2005 05:24 PM  13 years agoPost 2
rckrzy1

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Hurst Texas

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Only down side is the weight and the need to charge the packs separatly.



Wildcat Fuels

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05-02-2005 05:27 PM  13 years agoPost 3
d_wheel

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Deep in the heart of Texas.

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You should be OK as long as you charge them separately. You can go here to see what Red Scholefield has to say about it:

http://www.vencon.com/index.php?page=support_art3#s7

Later;

D.W.

Gettin old aint for sissies!

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05-02-2005 05:27 PM  13 years agoPost 4
flybarless

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Torrington, CT

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batteries
In that set up, you will have neither redundency or increased capacity unless the switch is electronic and detects a low voltage condition that causes it to use the other pack.
You can get the same effect by just carrying a spare fully charged pack and change it at the field, without carrying the extra weight on your helicopter.

Just remember -- if the world didn't suck, we would fall off.

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05-02-2005 05:42 PM  13 years agoPost 5
jhugs

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st charles mo

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Check out this topic. I had the same question. Alot of usefull info here.
After getting all the feedback i decided to go to a 4 cell GP3300 custom made pack. I haven't got it yet but im sure it will be more thatn enough. Two packs adds to much weight compared to a single 3300mah pack that will run for a long time.

http://www.runryder.com/t166686p1/

Had to crash some time

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05-02-2005 05:43 PM  13 years agoPost 6
seattlemack

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Renton Washington

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Ive been running my raptor 50 with the 600mah is all...i get 3 flights. Last week got a JR sub c size pack, 1700mah.
This pack gives me 7 flights. Then i just carry my charged 600mah pack also....so I go out and im good for 10 flights.
Im dizzy looking at the heli in the sky before then.

Start DAMMIT!! START!!!

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05-02-2005 05:45 PM  13 years agoPost 7
DS 8717

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Here wishing i was somewhere else

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You can plug another switch and battery into any unused channel and you will have 2 seperate battery packs with redundency.

YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED

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05-02-2005 06:05 PM  13 years agoPost 8
Helinutnz

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below 42 South

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Wrong flybarless.

There is increased redundancy. Two batteries is better than one. Just not a whole lot better as the failure rate of batteries is fairly low. You don't need an electronic switch. Both batteries as long as they are the same number of cells and mohms rating will supply the rx and cross charging nowadays is less than 10% in 24 hours.

The more likely problem to arise is switch and connection failure. Reilly 13 you have done the right thing with the parallel setup as far as switches go but toss your "y" lead and connect both switch leads to the rx. one into the rx batt port and one into an unused aux port. If you don't have an unused aux port then use your "y" lead on one of those and it will be fine. The "y" lead is another problem area you can eliminate as you really want both switches connected separately into the rx for increased redundancy. The ports on an RX are all connected by a bus and thats why it works. The servo's are simply fed pulses by the third wire to control their movement. (so any spare port on the rx can be used by the battery)

d_wheel has a great site for you to visit. Also visit http://www.hangtimes.com and see what they say about parallel setups.

Good and bad.
Bad.....weight and have to charge sep.

Good...capacity, redundancy, useful nose weight if you need it (better than one pack of bigger dimensions), heres a big one.....lower voltage drop on heavy current draws esp on 4.8 volts. (the resistance is halved by a parallel setup hence the reduced voltage drop)
Get your total resistance below 10mohms. I use two 1950 FAUP's which are 5 mohms each.
Nimhs take a lesser fast charge rate than nicads but some say they can fail open. Thats no problems and infact even a great situation in a parallel setup.
Just make sure you plug in your ESV or check with your onboard voltwatch each battery in turn. Turn one on and the other off. check the volt situation. then swap over and check the other batt. now turn both on and go fly.

If you read the sites indicated you will see another method of one batt using two leads and two switches. Good idea as the switches are more likely to fail as well as connections. BUT....if you do this then don't have a switch on while charging through the other switch or you will feed a lot of power direct into the rx!

The fail on switches are great but you would need to disconnect after flying for the day as they have a continual slight discharge when "off"
Most standard RC connections are not rated for multiple connections and disconnections. Why do you reckon they fail? Once connected I like to leave them connected if possible.

This is only what I have researched and is only my opinion. Hope it may have been helpful to you.
Cheers

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05-02-2005 06:21 PM  13 years agoPost 9
Leif

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USA

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What you're doing is fine as long as the added weight isn't a problem. If the combination is too heavy, then you're better off with smaller packs. I did this with two 1500mAh packs since I needed the extra nose weight on my Evo.

You get the added capacity, reduced internal resistance and redundancy. (Ask those guys who harp about a pack failing what happens in their one-pack configuration when the pack fails).

From an operating standpoint you will need to charge the packs separately (which you can do with your two-switch setup). You should also monitor them separately, which you can do by turning one pack off at a time. The Y-harness is fine as long as you are sure it won't come unplugged.

Just keep an eye on the pack capacities. If one takes significantly longer to charge than the other, then it's time to replace both packs. You want them to be similar in capacity and performance.

Leif

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05-02-2005 06:49 PM  13 years agoPost 10
reilly13

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Binghamton, NY

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I weighed 4, 3300 NIMH sub C cells, they weigh the same as the 8 AA cells I'm going to use...which is why I decided to use them.

I'm wondering why one would say this is not redundant? My understanding is that the NIMH's fail open which is like the pack not being there, in which case the second picks up the slack until I check the voltage when I bring it in. Two switches means also means that should one of these fail (open I assume) the other set picks it up.

I will be charging the packs individually using a triton charger which gives a pretty good indication of each packs condition.

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05-02-2005 06:49 PM  13 years agoPost 11
rckrzy1

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Hurst Texas

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In that set up, you will have neither redundency or increased capacity unless the switch is electronic and detects a low voltage condition that causes it to use the other pack.
Sorry but flybarless seems to be clueless also.



Wildcat Fuels

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05-02-2005 07:08 PM  13 years agoPost 12
reilly13

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Binghamton, NY

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Ok, I feel better about this now.

I have no extra channels on the radio (7 channel, all filled) so I'll have to Y a servo lead instead.

I shrink wrap all my connections that aren't plugged directly into the receiver so they can't come apart so I should be ok there.

the weight doesn't really concern me as I've currently got a 4/5A pack that's pretty heavy....flies fine. I've also jammed a 550cc R60 tank in my R50 so that will mean a little extra weight in the rear....til it's empty anyway. Won't know for sure til I balance it all up.

I will monitor my voltage through my GV-1 which I can see through the windshield.

I was mostly concerned about how the two packs would react to each other.

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05-02-2005 07:14 PM  13 years agoPost 13
reilly13

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Binghamton, NY

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In flybar's defense I think he may have thought that, I thought I could leave one switch off, one switch on and still have redundancy.

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05-02-2005 07:18 PM  13 years agoPost 14
wolfdad

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Southern Maryland

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Easiest solution for this is either the JoMar "glitch buster" or the I4C isolator. Either one is about $80 and not only allows the use of two or more batteries, but also allows isolation between batteries and receiver for transient "glitches." I run a single 4 sub-C GP3300mah pack on my nitro's and double 4 sub-C GP3300mah packs through isolators on my gassers and turbine.

wolfdad sends....

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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05-02-2005 08:01 PM  13 years agoPost 15
reilly13

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Binghamton, NY

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I'm not familiar with diodes.
Anyone?

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05-02-2005 08:28 PM  13 years agoPost 16
reilly13

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Binghamton, NY

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I built the packs......$20
Another switch $7
Y harness....just laying around.
Pack Shrink Wrap $1.50

Pretty cheap really!

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05-02-2005 08:58 PM  13 years agoPost 17
Gary

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Crosby, Texas

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I like to keep things real simple. Just get Duralites and be done with it.

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05-02-2005 09:20 PM  13 years agoPost 18
reilly13

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Binghamton, NY

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Resistance? I couldn't tell you!

Is that an indication of a junky cell?
I could measure it when I get home I guess.

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05-03-2005 12:19 AM  13 years agoPost 19
ErichF

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Sutton, NH

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Guys have been doing this in giant scale aerobatic planes for years (me included). Dual power supplies (batts + switches) plugged into separate RX ports.

Switches are the weakest link in our current onboard systems. When they fail, they usually fail open. So, should one fail open, the other is still closed, and you have full power from it's battery. Cross charging won't occur since the other switch has failed open.

Heck, you could even wire two separate switches with one well tested and reliable battery. Wire in Parallel for the same redundancy as above, minus the redundant battery packs. That could save weight.

There are also "failsafe" switches that have a built in SCR or something similar that maintains conduction even if the mechanical part of the switch fails open. When it reverts to this condition, you have to physically disconnect the battery to shut the switch off.

There's a ton of options out there. Chose whatever suits your peace of mind.


Erich

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05-03-2005 12:20 AM  13 years agoPost 20
Helinutnz

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below 42 South

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forget the diodes.
Not needed. The cross charging thing is just not an issue these days. Read up Red schofields article on this. (listen to the experts....not me).If it's only to cover for a direct short??? well if you only had one pack you are definately about to take a dirtnap anyway!!!!!

Yes "y" lead a servo but don't "y" lead the batts together or you are killing some of the benefits. Remember that connections are an issue.

what is your cell? what is the number on the side of it?

Duralites. Here we go again. With much respect does this always have to be mentioned when people talk about nicads or nimh? we are all aware of the benefits of durlites but is it really all that more simple than a redundant setup???? two batts, two switches! not complicated at all.
duralites. one batt, one failsafe switch (with connections!) and one regulator that will kill your bird should it give up the ghost, overheat and shut off or whatever. I hardly think it is simpler than parallel setups. Do you take your duralites out of the bird to charge them? The experts say you should. Do you have a place to put them incase they blow up from operator error while charging etc. Thats less complicated?
I looked into the cost of duralites and the associated charger (that you need if you want warranty) and failsafe switch and regulator. You must be kidding when you say it's only a little bit more!!! My 1950 FAUPS from NOBS batteries were $34 each and switches are $7.95 each. I use gem super rocker switches at $25 each but they are a bit of overkill in a redundant setup.

I am sorry Adrian.law and Gary but this is not meant to upset you and say what you have is wrong. Not at all. I am very sorry if it does. They have a place and yes they are light but the post is about parallel setups.
All setups have some drawbacks.

hope this has helped reilly 13.
cheers

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