Can I charge two 4.8 battery packs on a Y harness?

What chemistry?

I think it's a very good question,

Let's suppose if the charger provides 110 Mah, and charges for around 16 to 20 hours, my wild guess it would be load balanced, like 55 Mah per battery pack and the time would be doubled. I think it's possible, I can be wrong, so lets wait on the experienced people's opinion.

Mody

I've wondered the same thing. Using a Y cord, you would double the voltage and the mA would remain the same. The battery packs would have to be the same mA. And 2 - 4.8 battery packs in parallel would double the voltage to 9.6v. I think.

I too will wait for someone to say if its right or wrong. Scoot

Actually, putting the two packs in series would double the voltage. In parallel, as on a Y, the voltage would not change, the capacity would. If two packs were charged together that were not equally discharged, They probably would not charge evenly, one would either be undercharged or the other overcharged. If you post this in the batteries and chargers forum, there are some people over there that can explain it alot better than I can. But it general, I don't think it's a good plan.

What I want to do, is install 2 small (AAA size) packs in plane. instead of buying a normal (AA) size batt. pack .<div>Any suggestions?</div>

Copied from http://www.hangtimes.com/id33.html

"Parallel charging of Ni-Cds is not recommended due to the tendency of the cells to have the voltage drop off after they reach full charge."
..........

"The use of redundant parallel fight packs (packs may be of different capacity but MUST be of an equal number of cells) is an excellent way to increase the available flight time and significantly improve the reliability of the on power system."
..........

"Summary: Diodes are not required. Packs must be of the same number of cells. Packs may be of different capacities. Individual charge jacks must be provided for each pack (and not interconnected). Total capacity available will be the sum of the individual capacities. Specialized chargers are not required since standard packs (600-800 mAh AA packs)can be charged employing regular system wall chargers (1200 to 1600 mAh should cover most giant size projects)."

I wouldn't do it I don't think......not because of the voltage, because crossman is correct, voltage in parallel is the same...but because of the condition of the individual cells. Which you wouldn't know......now be careful using rechargable batteries instead of regular AA batteries which are rated at 1.5 V a cell.....rechargable batteries are rated at 1.2V a cell....
So to make 2 packs...each pack's cells wired in series (voltage additive)(current the same) then each pack in parallel (voltage the same and current additive) on a 4 cell pack using regular AA's you have 6.0V on a 4 cell recharable pack you're at 4.8V

Form a engineering standpoint, there's something I'm still missing here: What is the real result you're looking to achieve?

If it's a space limitation, I'd try and deal with it by using higher capacity batteries of the same size.

If it's reliability, you can forget it. Today's batteries are extremely reliable if treated properly certainly WAY more than 99.5% good.... so even if you got absolute maximum benefit from the redundant batteries (which is not even close to possible), you'd only raise a 99.5% reliability to 99.9975% for an improvement of less than 1/2%... Remember, that's the maximum theoretical benefit from redundant batteries, and isn't really attainable in the real world.

So, there'd be very little reliability benefit. BUT and this is more important, most power failures don't happen in the batteries they happen in the connections, and in fitting redundant batteries, you may be tripling the number of connections. So you get minimal improvement in the already reliable part of the system, while you create two or three times as many of failure points where systems usually do have problems.

Oh, and then there's the charging issue... improper charging is also a MUCH bigger cause of failure than actual battery failure even for a single pack. Managing parallel batteries imposes some technical requirements, which means either careful compliance with good practice or adding more electronic gear to manage it for you... again creating greater chance of failure in an already more failure-prone part of the system than the actual batteries.

So, redundant batteries is certainly doable, but if doing it for reliability reasons, personally, I wouldn't.

It is not advisable to charge any Nixx based group of cells in parallel unless you want to ruin them. Due to the nature of how the voltage changes as they near full charge, the ones needing the charge most will not get it and the current into the already charged cell(s) will increase instead of decrease. In short, DO NOT CHARGE IN PARALLEL if using NiCad or NiMh. Parallel charging works fine with LiPo's or Pb cells though.

I have done this with two 2/3A NiMh 6 volt packs. I needed capacity and there were space limitations. I started with two new identical packs and with both packs at the exact same state of charge/voltage. I used a heavy duty Y harness and placed the connectors to each pack so that I could monitor individual voltages from time to time. Combined capacity discharge test were ran about 4 times and the results were very good. I did this for several years in that plane and never had a problem the packs are now in two different planes. There may be problems that I didn't foresee or experience.

In my experience, from what I've seen and done, you can fly with parallel battery packs as long as they are exactly alike, ie: same current rating, and same number of cells. Now, as far as charging is concerned, well, I charge my redundant setups separately, either with two chargers or one at a time, depending on what I have available. Since I have four field chargers, well, that takes care of the redundancy..

But, safely, I would advise you do them by the each rather than trying to do them in parallel. I is pretty much absolute that they are not exactly the same so there will be some inbalance in the charging if you use something like a Y cable... of course, that's my opinion.

CGr.

Sorry guys, I have been at work.<div>The Batt. are the same .HydriMax 750 mAh  NiMH 4.8 V . that I need to put in tail for C.G.</div><div>My fear is how small this pack is . And how NiMH batteries can go from full charge to dead before plane can be landed. </div><div>The plane is a  ARF  Kyosho  540 Edge with a 55 OS engine that I am setting up for someone else . </div>

By the way, the owner requested 2 batteries. So what do I do?

Regular packs were 600 mAh for long time, and I still use some, which give more than four flights.

The worst that can happen is that one pack goes belly up in the middle of a flight; you still will have plenty of juice.

Review these FAQ's (look for questions regarding NiMH performance under strong loads):

http://www.hangtimes.com/rcbattery_faq.html

In a perfect circuit....with 2 packs wired in parallel....you will have 4.8 volts at 1500 mAh.... The drain from both batteries would be equal.....(voltage in parallel is the same and current is additive)....With 2 packs you want to have 2 switches....so you can charge each pack individually and isolate each battery to make sure both can power the aircraft...
So you go from each battery pack to seperate switches to receiver...one lead in the battery port and the other in any open channel...this will put the packs in parallel....
To check the battery packs make sure you turn on switch 1 and see the airplane power up then turn on switch 2....now when you shut down make sure you turn switch 1 off first and make sure that the airplane remains powered until you shut off switch 2

And here is the schematic: