I just got this Hobbico Accu-Cycler (charger)
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXL357

I was wondering if using a servo y-connecter would it be fine to charge two identical batteries at the same time? I have a pair of 4.8V NiMH 750-mAh batteries that I would like to fly with as a pair.

The charger is made to charge a tx and rx battery at the same time but the tx side of the charger is only good for 6,7, and 8 cells, so that is why i was thinking it would be best to use a y-connector and charge the pair from the rx side which handles 1,4, and 5 cells.

thanks.

The AccuCycle is a timed charger. So, it will pump out charge current at the setting you select. Discharge is another issue though. It draws down a pack to a value of 1.1V per cell. Bottom line, is it probably will work for a charger but the I would think the charge would not be equal.

What you could eaisly do though is to to setup an adaptor that would allow you to charge both packs hooked in series. You then would have a 9.6V 750MAH vs a setup with the Y cable where you have a 4.8V pack at 1500MAH.

I've used the Accucycle for a few years now, and I've found that the high MAH packs, IE the NiMh packs of 1500 to 2300 MAH don't charge very well on the accucycle. I've got a couple 1200mah NiCad packs I built and I run into trouble with them also. My field charger that does peak prediction works a lot better. Still not happy with the NiMh charges though as it will over charge them at times. The best bet for these would be the AccuCycle Elite which has a thermal probe to prevent overcharging.

I think you best bet would be to use the Y cable, but cut the red on one female and the black on the other and splice the plug ends together for your series hookup, then charge them as a 9.6V pack.

Don

One other thing just came to mind. If the batteries donn't have a matched load, when it comes time to recharge, you could overcharge on pack and undercharge the other as you will work on the average of the two. This would be a problem with either a parallel or series setup. If you use the series setup, it would be best to discharge each pack on the RX side them plug them together in series for a full charge on the TX side

The simplest answer though is to charge one the the Accucycle and the other with the wall wart from your TX.

Don

Don't try charging two receiver batteries simultaneously if your charger isn't set up to do it, nothing good can come of it.

Ditto.

Just get you another wall charger for them. I have been told the same thing not good to charge two at one time. And it is not cost effective to try and lose lol.

Get a digipulse and you can charge 6 batteries at once, any combination of sizes/amp ratings. From tx to rx, it will charge anything (except the lipo batteries).
Best charger I've ever bought.

Don wonder if that polarity swap is exacty what is done in a servo reverser extension, so connecting a servo reverser to one battery (on the Y) would do the same thing?



Guys I think what Don is describing is exactly how you make a 9.6V battery connecting 8 identical cells in series, no?

So assuming I check the polarity and cofirm I have have combined two 4.8V packs and created a 9.6V 1,500 mAh bundle what can go wrong? My charger would treat this as a 9.6V tx battery, no?

Exactly... although this charger has dual outputs for charging two batteries simultaneously but seperately.

He merely needs the bannana plug to battery connectors for both.

I'd disagree with others here. If your packs are both 4.8V 750mA and you connect them with a y-cable it's exactly the same thing as having a sealed 4.8V 1500mA pack..... The y-cable connects all the cells in exactly the same as you COULD inside a sealed pack. The charger won't know and doesn't care, you're the only one that knows it's two seperate packs.

We do it all the time when we discharge onboard a plane! Two smaller packs on a y-cable, equals the same double capacity pack.

I wouldn't do it on two packs of different capacity however.

Yea, you can cut up the y-cable and charge at 9.6V 750mA, but why sacrafice the cable? It'll work exactly the same.

THe servo reversing extention only changes the logic of the servo control. THe voltage has to remain the same or it will burn out the servo logic. The servo control, the white wire in a futaba or light yellow in JR (not sure about the jr though), Is a series of square wave pulses. If the current matching pulse is the same width of the receiver supplied pulse, the servo doesn't move. It the receiver pulse is shorter, then the servo moves in that direction to match the new pulse width. If the receiver puluse is wider, then the servo moves in the opposite direction to match pulses again. THe servo reversing extention has a logic chip the changes the receiver pulse. IE if the receive puts out an wide puls in relation to null, the reverser translates this to a narrow pluse representing the same amount of travel, but resulting in a direction change. In all cases + to + and - to - or the smoke gennie gets let out.


The trouble with a Y connection paralling two batteries or a series connection of them is that the packs discharge at different rates paralleling them or series connecting them screws up the chargers understanding of the corrent condition of the individual packs, but looks at them as single pack. The reason the the packs work ok is that the cells are matched prior to assembling the pack and as the connection between cells is permanate, what happens to one cell happens equally to the others in the pack.

Look at it this way. You have a flashlight that the batteries are almost dead. You put one new battery in but leave the other in place. The bulb sees a blend of the two batteries. Same as the charger would when looking at the battery condition. If the cells were rechargable, and you tried to charge both the almost dead cell and the fresh charged one in series, before the almost dead one could come to full charge, the fresh charged one would be way over charged. As long as both batteries were started at a matched charge and always charged and discharged at the same time, there is no problem, IE you have a two cell "pack"

Astro Dad, you understood what I was driveing at, but the uneven draw one the batteries woulld cause charging problems, unless you did a full cycle for every charge. Given that my AccuCycle charger can take up to 18 to 20 hours depending on the state of the battery and the capacity of the battery, to do a full cycle on it. Two wall warts still sounds like the best solution or two chargers.

Don

Don do your last comments about uneven charge state of the cells still apply being that this pair of batteries will only be used as a pair running in parallel in my plane? I should have clarifed how I was going to be using these.

Since all cells in both packs will be getting identical use, then I would not expect any cell to be unevenly discharged.

If you charge them slowly, you won't need to worry about cell balance.

Unfortuneately you are very wrong on this. You can not REPEAT CAN NOT charge either NiMh or NiCad in parallel due to the nature of their construction. One will always hog the current and overcharge. You can charge LiPo's or Pb based cells in parallel however.

Ok, why?

I'm not arguing. I don't see the difference, however I'd like to know. And what's the difference between charging a Pb, NiCd or NiMh pack like this? I can't speculate on LiPo/Li-ion because I don't know that much about them.

The cells are never perfectly balanced and depending on the quality of the pack may not be balanced at all. They pick each cell out of a bin and solder em' on! I'm sure each cell is tested before assembly, the good in one bin, the bad in another.

And this is why I just said "no."

Saw this coming from a mile away.