Batteries and chargers

[ragss]

I have a nirvanna II sailboat and am using Energizers AA Mh 2650 ma rechargeable batteries. I bought a Maha 777 plus charger. I'm getting between 7 and 10 hrs of sail time with a single charge if I put it through full conditioning cycle. The difference in the time is the amount of wind against the sail causeing the servo to run. With a normal quick charge I get about 3 to 4 hours sail time. Is this about standard?

Also if I were to go to LIPO's how much more could I expect? I know this has been answered "you have a sailboat it's not needed." But I still want to know.
Also how much weight difference is their?

What charger are you using? Is it a conditioning charger? example: discharges before it charges.

[Shaun Hendricks]

Quick charging a battery reduces both life of the battery and available power. Depending on the quality of the cell, it can be as low as 40% the cell rating. To get full charge out of a NiCd or NiMh battery, they should be fully cycled each charge cycle, however, if you just 'nice' charge NiMh's, you'll get 90-98% rated mah out of the cells each time. NiCd isn't the same, they will steadily decline until you cycle them fully again. I try to fully discharge NiCd's each time before charging them.

There are many automated chargers on the market that can do whatever you want them to do. You are looking for one that does automatic cycling depending on cell chemistry (NiMh, NiCd, LiPo, etc.) and that does delta-v charge cut off. You'll also want a selectable charge rate. Trickle, Normal, Fast or something selectable by amp or "C" value. Always charge a battery at about .5C rate for a nice normal charge. Semi-Fast charge is 1C. Fast charge can be 1.5C or higher.

For your 2650mah batteries, .5C is 1.3Amps per hour. It would take 2 hours to charge them fully. Semi-Fast is an hour charge at 2.65 amps. Fast would be over 3Amps and they'd get hot.

LiPo is an entirely different beast. You should have a significant amount of experience with charging and discharging more forvgiving chemistries (Pb, NiCd and NiMh) before attempting LiPo which is highly efficient but one of the most dangerous chemistries in use for the hobby industry.

If you want longer sail times, just increase your battery pack from being 2650mah to a larger number. There are 2800+mah AA's out there or you can go up to Sub C size packs at 4800+mah. They will be heavier so you might have to re-ballast your boat, but they will last longer.

I'm just trying to imagine 3-4 hours on the water not being enough. Buy another set of AA's, bring the boat in and change out the batteries then relaunch for another 3-4 hours of fun... :D

[Rob_P]

The boat is only half of the story, what run time are you getting out of your Tx cells?

Might be more economic just to get a second set and swap over as needed.

[ragss]

I have a Spektrum dx6i radio. The batteries in it out last the ones in the boat.
The thing I've been trying to do is not recharge/recondition the batteries every time I go sailing. Our club sails for about 3 hours every Saturday. If I condition the batteries then I don't have to recharge them every week.

[Shaun Hendricks]

Ah... well, there's an interesting axiom I've learned to live by:

"Never leave for an RC moment without fully charged batteries"

It also pays to top off your batteries just before you put them in the RC vehicle. It can add about 5% more time than what you get from ones you charged the night before and put into a case for use the next day. It also warms the batteries up to operating temperature.

[mfr02]

With a yacht, practise makes for better run times. Like others have said, just have another pack available.

[Andrew Gilchrist]

in relation to the Nimhs which are a storage rather than apower battery the lipos will deliver more runtime because
they self discharge at a much lower rate
the voltage falls less under load so the currebnt draws are less
the capacity does not fall nealry as much under load

the mass will be lower than your nickels - for a 2000 2s pack 80gm.

[ragss]

Andrew has mentioned the reason that I am considering the Lipo's. One of the problem's with the Nirvanna II's is the lack of power in the servo controlling the sails. As the voltage drops in the batteries the servo will be activated more just trying to hold the sail position as the wind pulls on the line. With the Lipo's this would not happen as soon.

Part of my original question was what kind of chargers are you all using.
Just another meanless survey.

[Rob_P]

Rags,

How many AA cells are you using?
I feed my Futaba 3802 sail winch with five 2100 mA AAs.

Rob

[ragss]

It uses 4 AA's. The ones I use are 2650ma. I'm not sure if the electronics would handle the increased voltage of the 5th battery. I suspect it would but I'm not sure. I know the mh are less voltage that the litimuns. That might also be considered. But with the Lipo's there is also a weight advantage.

[Rob_P]

I got the idea for using 5 cells from one of the forums, apparantly its not un-common when using high drain servos.

The voltage is distributed by the receiver & my Futaba R132JE is rated at 4.8V - 8.4V.

If you look at the sail servo tech specs speed and power is directly proportional to voltage. Plus if your starting at a higher voltage all additional runtime until you get until your down to your four cell pack voltage is a bonus.

[ragss]

Rob I'm going to have to check that out. Sounds sensible.

[Brooks]

It's possible to make up a wiring harness that sends the power directly to the servo, w/o it going through the RX. This way you can use more battery voltage for your high torque requirements. I made such a harness for my barque. Unfortunately, I lost the url showing how, perhaps someone will remember it. I could try to find my diagram, if you are interested.

Post#36 may offer you some options. The SportBEC allowed me to use 3 cell LiPo with the voltage cut down to 6volts for both Rx and 3 servos.
http://www.rcgroups.com/forums/showthread.php?t=743611&page=3

[boater_dave]

Powering the sail servo directly is what is recommended on the bigger units, as the conductive paths inside the smaller rx's are not big enough. A simple Y harness is all that is required. It works just like the BEC feature on an ESC. The Y harness has 2 heavy wires (red/black) from the battery plug to the sail servo, than the normal 3 wires (red/black/white) from the servo to the rx. It should be available at your local hoby shop. It think it comes in the box with the big Futaba sail servo.

Dave

[Stu :)]

I've seen a variation of the Y-harness down here.
One taps an additional battery pack onto the power lines on the servo wire, with a diode on each positive power line before the join; prevents anything spiking back and haunting the receiver.

Also I've seen some skippers mount and plug a 7.2 or 8.4 volt car NiCad pack directly into their receivers.

Stu :)