jib

We are moving component from a (RIP) trainer to another plane and considering upgrading the battery pack for more flights in a day without recharging. The current battery pack is 4 NiCad’s and I’m considering 8 NiMH (4x2) in parallel, so we have the same voltage, but more current. NiMH are lighter for the same current, but we will have 8 instead of 4. The new plane is lighter, so we are offsetting some of the weight gain. I'm just about ready to balance the plane, so I need to select and buy the battery pack, so it can be located correctly.

Any concerns, issues? What should I be looking for or be aware of?

Thanks in advance,

Jack

bruce88123

You don't want to use cells in parallel. I won't get into the technical reasons but suffice it to say - not a good idea in a battery pack. Stick with 4 cells but get cells with larger capacity. I'd say try NiMH of larger capacity in each cell.
This http://www3.towerhobbies.com/cgi-bin...&I=LXNRH6&P=ML is just one of many available and don't limit your search to Tower or any other single dealer.

Remember that bigger 4.8 volt packs will take longer to charge and 6 volt packs would definitely require a different charger.

Jetdesign

My Feedback: (8)

I use 4.8v 2000mah nimh batteries. I can fly for 2 days with standard analog servos without recharging. No need for anything fancy.

http://www3.towerhobbies.com/cgi-bin...?&I=LXNRH6&P=0

jib

Great info! Thanks a lot. I also have standard analog servos.

Is there any reason I would want to upgrade from 4.8 to 6 volts? I suspect faster, stronger servo movement. Anything else?

Jack

dragnbye

you got faster strong you can still use your wall charger but it just takes longer

bruce88123

If you are trying to say that you can use the orig wall-wart charger with a 6 volt pack - WRONG! It will never fully charge. Oh, maybe in a couple of months but doubtful.

Missileman

6 volts= faster and stronger servos BUT unless you really need the extra speed or strength, you will never notice a difference.
On the negative side, a higher voltage battery of the same capacity will not run as long due to the higher current draw by the servos.
On the plus side, a 6 volt battery may be safer if a cell is lost in flight, This is only if the lost cell shorts and can still pass current from the remaining 4 cells.
Cost, of course, is higher on the 5 cell pack as is weight.

jib

I've been reading a lot, but still cannot tell for sure if I can use my current wall wart 4.8v NiCad charger on the NiMH, as long as I give the larger pack sufficient time to recharge? I understand V=iR and C, C/10, etc.

Yes, I know a NiMH specific charger would be better, but why spend the $40-$100, if I don't have to. Don't hesistate to let me know if I am being short sighted.

Jack

bruce88123

You can use your 4.8 NiCad charger for your 4 cell 4.8 volt NiMH batteries even if much bigger capacity. It will take longer to charge them. If bigger than @ 2000 Mah I'd recommend a better charger also. IF you go to 5 cells (6 volts) you MUST get a new charger, no option.

jib

Perfect. I figured that if the voltages matched, it was just a matter of time.

Great sig file, BTW,

Jack

bruce88123

As with ALL batteries you should monitor them between flights for safety and NEVER assume they are OK.

opjose

No...

Your assuming that the charge voltage & current MUST match the battery voltage exactly, which is not the case.

In fact in many chargers like my Accucycle, the voltage is stepped DOWN as is the amperage output as the battery nears a full charge.

I've taken 3000mAh 6V packs and changed them for a few days on a 4.8v 100mA charger. When I subsequently discharged them to test capacity I found it little different than what my computer controlled chargers will do when set to "full" ( 100% ) charges.

opjose

Incorrect...

I charge most of my 6v 2000-3800mAh packs using a stock wall wart supplied with my JR radios, since I have so darned many of them.

I've never had any problems in spite of the fact that I'm demanding a lot from those batteries with 8-9 servos or more on the planes.

alfredbmor

When charging batteries please note this:
When charging a 4.8 volts battery with a capacity of 2,000Ma, then check you wal wart charger which many of them are rated to charge at 50 mAh, then divide 2,000 ma in 50 ma increments, the result is: 40 hours then you should add a 20% for energy lost in the charging process. so the final answer is 48 hours of charging time with a traditional wal wart charger.

The new NEC-222 JR charger will charge the 4.8 volts batteries at a 150 mA rate, then using the same battery of the prior example, with 2,000 mAh capacities, the time now will be reduced to 13.3 hours plus a 20% of time for energy lost in the charge process, then we have a result of 16 hours.

The normal charger is rated at 5.8 V output so it is impossible to fully charge a 6 v. battery with the normal wal wart charger, unless that you are thinking that they are fully charged when they really don't.

For a 6v battery with a capacity of 2000 or 3800 mAh I would suggest a better charger than the normal wal wart, and the battery should be capable of charging at 1C which means that you can charge the battery at a 2,000 mAh rate with out stressing the battery (getting hot) which indicates that you are ruining the cells.

Regards.

Alfred.

opjose

Yup, the norminal wall warts DO produce a higher voltage than they are rated at, which is one reason you can get away with the wall warts ( with caveats! )

However this is close enough that I'm getting ample capacity out of the pack. My peak chargers obviously do much better and can purposely charge a battery to 110% capacity, but the wall warts get within 90-96% percent of a full charge.

On a 3000mAh pack, after 2-3 days of charging, there is no problem flying all day long... if not all weekend long.

alfredbmor

I suppose that you own those relatively new NiMh batteries which are great and have better capacities than the old NiCd.

If you really want more flight time here is a hint, some guys at the field now use Lipo Batteries in their 3D and Pattern planes, you just have to add a BEC and you will be rewarded with a battery with less weight and more capacity, those batteries can be charged (with an appropriate charger in an hour).

There is something that I really never do, I just do not like to leave batteries charging at home while I am out, so I do prefer to charge them overnight with my wal wart and if I forgot to charge them then I use my Hyperion field charger which handles many Lipo, NiCd, NiMh and other kind of batteries as well.

Regards.

Alfred.

Missileman

It should be noted that you need a charger specifically designed for lipo batteries and you should never attempt to charge one with a standard wallwart charger. (see the recent thread about lipo fire !!!)

dignlivn

Alfred,


I was thinking of using a voltage regulator and thought
about a BEC the other day. I would like to learn more
about it ? What are your friends doing with the other
wires from the BEC ?


Bob

2slow2matter

My Feedback: (1)

It doesn't matter what the rated voltage output of the charger is. As long as you are physically able to push current through the battery, then it will eventually recharge. Wall-warts will definitely recharge your 5 cell packs, fully, unless they are particularly weak. Most of the ones that come with the name brand radios are sufficient to recharge virtually any RX pack, regardless of voltage. To say that a charger cannot charge a battery past it's rated output is WRONG. Car battery chargers have rated outputs of 12 V, yet are plenty capable of charging the batteries to up over 14V.
Also, if a charger could only charge to it's rated output, then there would be no reason to take a battery off of a charger. Take your 5.8 V walwart for example. If that is all it is capable of taking a battery to, then why worry about how long a 4.8V battery has been on the charger? A 4.8 V battery is plenty cabable of safely handling 5.8 V, so why not just leave the batttery on the charger all week or month long, and just take it off when you are ready to fly? The answer is because if left on long enough, you will put more than 5.8 V of potential back into the battery, which can cause irreversible damage to the pack.
Remember, a charger uses CURRENT to reverse a chemical reaction that took place when the battery was used. It does NOT use voltage. The voltage in the battery pack will go up in response to the reversing of the chemical reaction. Where voltage in a charger comes in is in the fact that the more voltage a charger has, the more current it can push through a battery to more quickly re-charge it.
No, I do not believe that you could use a wal-wart to recharge a 6 or more cell pack, as the voltage potential in the charger isn't enough to coninuously push current through the pack as the pack's voltage increases. However, when we are talking about 4 or 5 cell packs, then there is no problem at all......just give it enough time.
The first time, I would charge it for 20 hours, and then test the battery with a multimeter. Then charge more as you see fit. Keep testing it every 5 hours or so, until you are satisifed that it is fully charged. You will only have to do this once. After that, you will know how long it takes...(of course, this all depends upon how discharged it was to begin with).

opjose

What other wires?

A Bec comes with a normal servo type plug already installed and a pair of loose wires.

The plug goes into the RX to provide power.

The loose wires get connected to your power source.

I use a male and female deans connector wired to make a pass through connector.

That way I can use the BEC by itself with a LiPo pack or I can transfer it to an EP easily if I so choose.

It takes a few more minutes to wire it up this way, but it makes things so much easier later.


I've got several cheap LiPo's which I've discovered that they do not hold voltage at the top end of their "C" ratings...

I've pressed these into service as power sources for the RX/Servos on planes...

The draw from a BEC is much lower than what a typical electric motor pulls.

dignlivn

opjose,

I was thinking he had a Esc w/bec and was wondering
about the 3 motor wires. Does your pass through connector
work like a arming pin ?

Bob

opjose

No, but that's not a bad idea... I could solder in a third connection and bring that out to turn it into an arming device.

Basically I put a male and female deans back to back and solder them together this way.

I then solder the BEC's wires in between so to speak, apply a bit of silicon sealant ( to help prevent shorting ) and then put heat shrink over everything.

The BEC's deans plugs can sit between the battery and the motor connector on an EP plane.

But I can also elect to plug the BEC directly to the battery and use the same setup for glow/gas planes.

A bit more work up front, but much easier to deal with later...

dignlivn

Ok,

I used a arming pin on EP Trainer, made it out
of a pair of Deans. It works great. I'll re read
your last post and see if I can get a mental picture.

Bob

2slow2matter

My Feedback: (1)

Castle Creations makes a BEC that is around 21 bucks. Will take in up to 25 volts, and output is variable from 4.8 to 9 V, with the default set at 5.1 ~10c. I think that is the way to go, then get a 2S or 3S lipo and power your plane for a month without recharging.
However, remember a special charger is needed....
Also, Lipos don't lose charge sitting around, so you can charge them when you return home, then they can pretty much set for a month or more before you use them again, and still be in good shape for flying.

jib

While I don't need a Lipo to run the receiver and servos in our plane, I will look to upgrade the 55mA charger for the new 2000mA battery pack I hope to buy tomorrow. The old 650mA battery charged well overnight and I'd like to be able to continue to charge the battery pack completely in 12 hours +/-, so I'll be looking for a charger with at least 200-500mA capacity.

Thanks,

Jack