Noobie Question: How Do I Know What Size Receiver Battery Pack to Get?

[dmt]

Hi,

This will be for an Easy Glider (non-electric), that I plan to use for general fun flying, with an emphasis on thermal flight. No contests or anything like that! I'll be going with NiMh batteries -- but I have no idea what size to get (or even what factors determine what size one would choose). Any advice?

I'll probably get the pack next week, but in the meantime, I have a switch harness hooked up to a 4 AA-cell battery holder in my parts box -- how would you feel about using something like this on a temporary basis? I'd probably put alkalines in there for a few practice flights to get my new Easy Glider trimmed out correctly. Reaction?

Finally, when I have my NiMh pack, how would I know when it has to be recharged? From some threads I've been reading, it seems like you guys go mostly based on a timer. How do you know how much time to give yourself?

Thanks,
-- David

[BMatthews]

For the Easy 4 AA's is likely a pretty good choice since you need the noseweight anyway. But if someone chimes in that you don't need that much then go with what they say.

If you stay in the hobby long enough it's good to get a charger that lets you discharge your packs as well. Measuring how much capacity that is left at the end of the day now and then helps you monitor the pack's condition. But for now all you need to use is the little wall wart charger that came with the radio.

Using a holder with 4 alkalines in it will be fine and the pack will easily last for around 2.5 to 3 hours of total flying and fiddling time. That's probably a couple of days at least of playing around for you.

We don't really go on a timer at all. Just that after a few seasons of flying we get a feel for how long a pack will last. But these days with AA Nimh cells being up around 2000 mah there's so much capacity in the pack that you could literally turn on the airborne pack in the morning and leave it on all day and it would still be fine at the end of the day. We USED to fly for an accumlated 2 hours just on the old 500 mah nicd packs.

As for telling when it's getting down this is where a voltmeter or load tester comes in. A little adapter cord that lets you plug your meter into the battery leads while the radio is on can help you test the pack voltage. When you find the voltage dropping to 4.6 to 4.7 with the radio on and both servos moving at the same time (stir the Tx stick) then it's time to call a halt to the day. A pack is considered dead when it's down to 1.1 volts/cell or 4.4 in this case. But once it starts hitting 4.6 under load it has turned down onto the knee at the end of the discharging curve and headed for 4.4 pretty soon.

Keep in mind though that because the new packs are often such a high capacity and that the old wall wart chargers are set to around 50 or 60 ma rate of charge it can take a lot of hours to bring up a fully dead pack if it's around the 2000 mah capacity.

Many folks tend to go with a smaller weight 600 to 800 mah pack and add some noseweight. It keeps your options open for the next model. You may want to consider the same.

[dmt]

Thanks, BMatthews -- that explained a lot.

[LVsoaring]

dmt, just to clarify, when you say what size battery, I assume you mean what mAh.... as for physical size, what you have is perfect, and any similar 4 AA size arrangement will fit properly in the EG. IIRC, the pre-formed cutout in the EG accomodates this size battery pack. Anything else, and you'll be cutting some EPP!

[dmt]

LVsoaring, yes I meant more about the mAh than the physical size, though that brings up another aspect that I hadn't really thought about! I was just assuming that AA size was normal. This is actually my second glider, though the first one I never really got going. That first one was/is a Sophisticated Lady, which takes full-size servos and was set up for me with AA-size batteries. That's where I'm getting this battery holder and switch harness from -- I'm [temporarily] cannibalizing the Sophisticated Lady (don't worry, she's not all in one piece anyway!).

Anyway, so I was just assuming that AA was the size to go with, but now I see that maybe AAA is more common? As BMatthews brought up though, with the Easy Glider there are ballast issues, so I would have to just add deadweight to get the CG right (I'm going to go with the specified CG to start). In fact, it's already taking me two coins taped to the end of my battery holder to get it to balance as it is now (probably due to the ball in the tail that comes preinstalled in the Radio Ready kit, which I bought).

[dmt]

So I think the basic idea is that when the Easy Glider, four AA size batteries of pretty much any rated capacity will be fine. The only negative will be that if/when I move on to a lighter glider, I'll have to get a new, lighter receiver pack.

Is that pretty much right?

Also:

about BMatthew's post:

A little adapter cord that lets you plug your meter into the battery leads while the radio is on...

Would that be the same as a charger input for the switch harness?

[Oldcoot2]

Another thing to consider is the new volt watch LED meters. I recently bought 4 of them for my planes and it takes a lot of the stress out of a days flying. I did a quick test on them when I got them and found that when #3 LED starts losing its brightness I'm through until I recharge. Previosly I always used a voltmeter, but these devices are a much quicker way to observe your battery condition. I think I paid close to $7 each for them.
Depending on what I'm flying the AA's and AAA's are very good, especially in the NIMH area. FWIW
Gerald

[rdwoebke]

The AA holder and with the switch will be fine. I used to use that for years.

But, one thing to keep in mind. First, those spring loaded AA holder dudes can have issues with corrosion or "loosing contact" with one of the cells resulting in an open circuit which of course would be bad for controlling the plane.

I never had a crash because of this, but I still have that old AA holder I used to use in planes when I first started and now use it as a battery holder to charge NIMH AA rechargables with my Sirius charger, and it this thing now being almost 15 years old it is starting to get really bad. AKA, I put the cells in, hook to charger, nothing happens, then I go and "spin" the cells a bit one at a time till connection is made.

Ryan

[BrianSmith]

Plug your volt watch into an empty servo outlet on your rec. Then with it on, run all your servos back and forth. That'll give you a real reading under load. .. Brian


Another thing to consider is the new volt watch LED meters. I recently bought 4 of them for my planes and it takes a lot of the stress out of a days flying. I did a quick test on them when I got them and found that when #3 LED starts losing its brightness I'm through until I recharge. Previosly I always used a voltmeter, but these devices are a much quicker way to observe your battery condition. I think I paid close to $7 each for them.
Depending on what I'm flying the AA's and AAA's are very good, especially in the NIMH area. FWIW
Gerald

[Hostage-46]

I just picked up an integrated switch, charging jack, voltage indicator by MPI from my LHS. Looks pretty tidy, and claims to indicate voltage under load with a green, yellow or red light.

[dmt]

rdwoebke, I get exactly what you mean -- in my drug store battery charger, I often have to rotate/jiggle a few cells around until they register for charging. That would be less than ideal in the air!

[dmt]

Hostage, I am looking for one of them too. I saw this one online that I might get:

http://www.isthmusmodels.com/product_info.php?products_id=46

[dmt]

Oldcoot2 and Brian Smith, thanks, I'll also be on the lookout for a "volt watch". I'll probably go with either the switch with indicator lights or the volt watch, depending on what's in stock (hopefully, something!) when I go to the hobby shop at the end of this week.

[Hostage-46]

Hostage, I am looking for one of them too. I saw this one online that I might get:

http://www.isthmusmodels.com/product_info.php?products_id=46

Yep that's the one! I'll be flying for the 1st time this weekend if everything goes well in the shop this week...

[BMatthews]

So I think the basic idea is that when the Easy Glider, four AA size batteries of pretty much any rated capacity will be fine. The only negative will be that if/when I move on to a lighter glider, I'll have to get a new, lighter receiver pack.

Is that pretty much right?

Also:

about BMatthew's post:



Would that be the same as a charger input for the switch harness?

Yes to the first part. Fortunetly packs are pretty cheap to buy.

"Sort of" or "it depends" on the plug. In some sets the plug is live when the radio is switched on. On others it goes dead because they join it to the other unsued side of the power switch.

If you modify it so that the plug is always live to the battery side then it becomes an excellent test port.

[dmt]

Great info again, BMatthews.

Thanks to everyone for all their help -- I threw in my old switch harness and battery holder and temporarily borrowed the receiver for my easy glider electric and got the radio and servos set up last night. Then today I got in my test trimming tosses and have it flying pretty straight. I'm pretty excited.

I really wanted to get it trimmed out today, because they're still a bit of snow on the ground. Doing the test tosses over a blanket of snow is so much easier on the airplane (and the nerves)!

So, I'll look for a receiver battery pack and better switch harness when I go to the hobby shop later this week, but otherwise I just have to wait for the perfect day for my first launch.

I may of course still have some more questions though before then!

:)

[lincoln]

I usually solder up my own battery packs. You can get nicads really cheap, and you only need 500 mah to fly for ages. Well, ok, maybe two hours. You may want a cycler. I don't know if you can get the RAM simple cycler anymore, but it's quite cheap (under $20) and works fine if you can stick around to listen for the alarm and time it. No hurry, but if you cycle now and then you can catch batteries going bad before you crash.

[dmt]

I usually solder up my own battery packs. You can get nicads really cheap, and you only need 500 mah to fly for ages. Well, ok, maybe two hours. You may want a cycler. I don't know if you can get the RAM simple cycler anymore, but it's quite cheap (under $20) and works fine if you can stick around to listen for the alarm and time it. No hurry, but if you cycle now and then you can catch batteries going bad before you crash.

Okay, so I just bought a [4-cell] 1,000 mAh (possibly 1,100 mAh, I forget) receiver pack for my Easy Glider. So, if you get two hours from a 500 mAh pack, I should expect about four hours from my new [1,000mAh] pack?

BTW, I was surprised how much heavier a four cell 2,500 mAh pack was, when I compared them side by side at the store! With that in mind, and having read the responses here with people getting 600 and 800 mAh packs, I went for a 1,000 mAh pack over the 2,500 one. On second thought though, with either of the airplanes that I can use it in (my Easy Glider, and possibly my Sophisticated Lady), I'll just have to add ballast in the nose. I guess I should've gotten the 2500 mAh one. Oh well -- as long as the 1000 mAH pack gives me about four hours, that will be plenty of flying time for one day.

[lincoln]

I'd advise using one of those expanded scale voltmeters every once in a while, in case it's not as well charged as you think, a servo has friction, etc.