tony0707

HI FOR VERY GREAT INFO ON ALL TYPES OF BATTERY CARE GO TO -radicalrc.com THE INFO THERE WILL HELP YOU A LOT REGARDS ENJOY TONY

TFF

I had a good page to post, but it would not have been worth it unless I could see your eyes glaze over.
http://shdesigns.org/batts/battcyc.html has some charts to look at. If you look at the curve from the top voltage to the 4.8 spot, that is the usable voltage curve for your xxmah battery pack. When you go past 4.8v, you are in no mans land of usable power, and you can see that the voltage will drop fast if you try to use the last bit of power.

abufletcher

Charts are ok. I can deal with charts.

RCHubbub

Though they don't focus on RC specifically, Battery University is an excellent source of information.

http://www.batteryuniversity.com/index.htm

jaka

Hi!
First of all ...get a Voltwatch! I have one of these in all my planes. The simplest ones are just two diods (one red and one green). If the green one shines...it's okay to fly! If both shines ...beware.If the red one shines. Don't fly!
There are more elaborate ones out there with multi diods but the simpler types works as good too.

Second! Get a Multimeter so you can check each cell (the voltage) in your battery pack.

Third ! Get rid of that old 600mAh NiCad battery!
Over here in Europe no one uses NICad batteries any more! We use 1500-2800mAh NiMH cells in our radios. (same weight and seize as your 600mAh NiCad)....or Lipos.

summerwind

NiMH batteries if well monitored..............they will however dump on you at the worst time and when they do, they dump fast.
NiCad will outlast NiMH 5-1.

NiCad can be made to hold more capacity than NiMH as well.

abufletcher

The Voltwatch sure seems like a no-brainer for knowing how much juice is left at the field. Though technically, I guess it just tells you that you have enough juice "now" and not necessarily how much "more" there is. Figuring out how to hide the thing on a good scale model might be tricky. I see that the Hobbico one suggests I tape it to the outside of the fuselage! [X(]

BobH

My Feedback: (2)

Just remember this.. You can get lots of volts from a decent sized battery. The smaller the battery the less available. A decent volt meter (plug in type) is sufficient. It'll tell you how much you have remaining in the battery. If its suspect (below the recommend level) you dont fly. Pretty simple.

summerwind

that's too simple Bob

abufletcher

Here are my battery related purchases from my trip to Osaka. I picked up one Futaba 4.8V 1000mAh battery (4 cells, quick charge in 1 hour) just to have as a simple option for long flying sessions. This is the same battery I have in the Puppeteer and it gives me a full hour in the air (and probably more). At the moment an hour of air time, flying the same model, is about all I want. And I'd say I fly more than anyone else at the club. Most guys just put in a couple of flights and go home.

They did have the 5-cell Futaba battery that Summerwind recommended but I can buy them cheaper through Tower (even including the shipping). I did pick up an additional switch so the 2-battery/2-switch setup is definitely in the future. I also bought a "pig tail" for charging with my ParkFlyer peak charger.

Finally, they were having a special on these Chinese-made 5-cell, 6V 600mAh NiCd packs...for a bit more than a dollar a piece (100 yen)! They don't have the right connector but I can swap those out. I don't know if I'd trust these in a model but for a buck they'll sure do for bench work. BTW, what would be the difference between a "cheap" pack and an expensive, name-brand one?

What I need now, probably more than any other piece of equipment, is a little log book to keep track of what's going on with each battery.

abufletcher

Yikes! The Sanwa 4.8/700mAh pack, which was reading 635 after the last recycle (and then had a 14 hour charge cycle), reads just 18mAh after just three 10 minutes flights on a 6 servo ARF (Aileron x 2, E, R, T, retract servo). Does that mean I absolutely would have crashed on the next flight...or for that matter just dodged the bullet on the third flight? That seems like a pretty heavy use for just three flights!!! []

I was flying fast and hard with a lot of maneuvers, but still....just three short flights??? My voltmeter reads it as having 5.32V and 4.08 under load (1A). I would never in a million years have guessed that it was that low.

BTW, I don't get the voltmeter. I mean what's the point of knowing that the battery is putting out X amount of voltage, if you don't know how long it will continue to put out that amount. Seems sort of like a gas gauge that only tells you the amount of octane is the remaining gas but not how much actual gas is left.

I feel like I'm back to square one.

abufletcher

I must not be understanding the basic relationship between volts and mAh. I have a plug-in volt meter (from Hanger9). When I plug it in, it tells me the pack's voltage pre-load and under load. If the battery falls below 4.8 (under load) then it isn't safe to fly. It doesn't tell me anything about mAh. Are volts and mAh just flip sides of each other, i.e. less volts remaining means less mAh? If so, why do we need to care about mAh? Seriously, this makes absolutely no sense to me.

So given two packs, one 4.8V 600mAh and the other 4.8V 1200mAh, the second pack should allow me to fly for twice as long, right?

abufletcher

Maybe I just need to stop trying to understand. [:'(] Just tell me what battery and charger combinations you all use and I'll buy that! Only once in 6 years have I ever lost a model to a dead Rx battery and that was because as I was charging the packing in the model through I had left the switch on so it wasn't really charging. But I can't help feeling that I've just been lucky.

The night before I go to the field, I plug in the battery pack. The next day I fly for 30-60 minutes. I go home. That's all there is to my battery "technique."

RCHubbub

i'll try to help with my opinions. When you said it reads only 18 mAh I presume you mean you went home and discharged it and measured it with only 18 mAh left in the battery before the low voltage cutoff was reached on the discharge cycle. If so, then honestly that doesn't make sense, but there are too many variables here. Have I seen a six servo setup use 200 mAh per flight? Yep. But that doesn't seem normal for this setup for you. Could you have left the receiver on when you packed up and went home? Was the retract servo binding some? Don't know. But with only 18 mAh left in the battery, that is a dead battery. To me, anything less than 15% capacity is a dead battery. If this is the same battery that was discussed before, then I still don't trust the battery as I think it has too much voltage drop under load. I'll be more bold and say the battery is bad. You have a dying cell in that battery. You can tell since the pack only reads 4.08 volts under load (well under nominal voltage of 4.8 unless that was a typo on you part).

RCHubbub

The relationship between volts (potential) and mAh (capacity) is this. For NiCd and NiMH chemistries, as the capacity drops so does the voltage. So unless you have a watt or amp meter hooked up during flight which I know you don't, the only way to have an idea through measurement of how much capacity you have left is by measuring the voltage. Though it is not really standadized, the nominal voltage of a cell is the cell at approxiametly 30 to 60% of its capacity depending on the manufacturer and marketing hype. That is why a fully charged battery measures above its nominal voltage and as capacity is depleted, voltage drops. Now many will use the nominal voltage as a no fly point since just to be safe as there will be a point in time as lower capacities are reached, that the cell begins to die off very fast and could do so in mid flight.

Now there are some chemistries such as A123 and other Li variants that maintain a very constant voltage through most of its capacity discharge especially after the first 10 to 20% is used. Since voltages changes very little during the discharge, it is usually not safe to rely on voltage to estimate how much capacity is left, but it is much more important to "know" the battery in use and its application to know when you need to stop flying with it.

To generally answer your last question. Yes, double the mAh rating (capacity) of the battery doubles the flying time

RCHubbub

I think it's really just too open ended to answer your question. I think you are almost there. You are doing the right things. You are measuring how much the battery discharges in mAh and how much it takes to fully charge back up. You are measuring voltage without a load and with a load and seeing how much of a voltage drop you are getting. Doing the discharge cycle you can watch how the battery voltage drops and how it really drops down in the last 10% of the battery's capacity. Understanding these relationships will help you to make the right choice in battery size and understanding its reliabiltiy/dependabiliity during the life of the battery. Hopes this help some.

abufletcher

Yeah, it read 18mAh after I got home and did a discharge on the Hobbico charger. That's apparently what was left after about 25 minutes of flight time. There was also perhaps 10 minutes of "use" on the ground, when I forgot to turn off the switch and noticed that about 10 minutes later. How much does power gets used just sitting on the ground?

As I said I did leave the switch on between flights for about ten minutes. And I suppose there could have been some binding on the retract servo.

So, you're saying that a battery should NEVER read (much) under 4.8V, even under load, no matter how much use it has had?

Anyway, I think the message is clear. I need to stop using ANY questionable batteries for flying (mark them and put them away for bench use only). AND I need to get myself together and come up with a rigorous set of methods and procedures for charging, maintaining, and checking my batteries.

A big thanks to everyone for all their advice.

RCHubbub

These are general statements for standard setups. If the plane is on the ground doing nothing, there will be very little current used say 20 to 50 mA. The only way to really know is to use a watt or amp meter and measure it. Using one of these tools is helpful in a variety of ways, for example, in determining if you might have a servo binding some where and checked out while on the gournd.

Another general statement. A fully charged healthy four cell receiver battery will never drop more than about 0.5 vdc under normal servo/receiver loads. Can a battery made to have a larger voltage drop? Sure. Just demand more amps then the battery's chemistry can deliver. If you use a 700 mAh battery that also powers a JR 791 retract servo that stalls or binds, well you might get a substantial voltage drop due to the current draw from the stalled servo. That's why many for peace of mind run a dedicated battery for retracts or a larger capacity battery in case the servo stalls.

Personally, I consider myself to be conservative with batteries. I want to be able to get at least 6, 10 minute flights without hitting nominal voltage, 4.8 for a four cell, 6.0 for a five cell. All of my planes are consistently setup like this, and if on the fourth flight for example, I'm already at nominal voltage, then I need to check why. Is the battery pack getting old, do I have a servo or linkage binding, do I just need a larger capacity battery, etc. Whatever you determine for yourself that works, just stay consistent with it.

TFF

The radio draws power in spurts. When you are not controlling anything the idle draw is around 50-75 mah, so a 600mah battery should run about 8 hours with the radio turned on but doing nothing. When you move the controls, the draw goes through the roof lets say 400mah, but it is only for a few seconds then it goes back to its idle. If you have a binding servo it is drawing its max all the time never getting to idle, sucking down the battery doing no work. If you have 2 binding servos, you can be on borrowed time.

abufletcher

Slowly things seem to be circling around to a consensus in this thread. Looks like, generally, serious flyers have moved towards larger capacity packs (larger than the 500-700mAH packs that come with the radios). I'll be replacing the 700mAh pack I had in the Chipmunk for its maiden with the new 1000mAh Futaba pack I just bought. For a model with 7 servos this seems prudent. Given that this model will probably be doing a fair amount of aerobatics, even a larger 1500 pack (or two batteries) might be better. The 700mAh pack can then go into the smaller 5 servo model and used for 3-4 flights. And I'll probably "retire" all my 600mAh packs for bench use only (or if they are still perfectly good, as back-ups for those rare long days at the field). In terms of numbers of volts, the standard 4-cell packs are much more common but the consensus is that 5-cell (6V) packs provide additional security. Even more security is gained through the use of two-batteries systems.

The other reality now that I'm acquiring more and more models (in actual flying condition) is that I need to have the ability to charge more batteries at the same time. In the past, all I needed was one Tx battery and one Rx battery. Now I might want to take 2-3 transmitters to the field (but could reduce that to two or even one if I get rid of the 72 gear) and might want to charge 3 or more Rx batteries. The Hobbico multi-charger (and assorted banana-plugs) looks like a good inexpensive way of managing this. My current Hanger9 SureCycle seems to be a fine devise but can only do one Tx and one Rx battery at a time. And, of course, if I'm discharging one battery on it, I can't be charging another one.

abufletcher

Curiously, my brand new 1000mAH Futaba battery (after an overnight charge on a wall wart) shows a discharge of 1161mAh.

abufletcher

Unfortunately, batteries and chargers are heavy and a $150 order from Tower would entail over $50 additional dollars in shipping. Or I could pay $15 in shipping here in Japan and slightly higher prices. So it probably all just about evens out. []

summerwind

that's pretty much normal for this pack.
i use the 5 cell version with same cells, and always get more capacity than it's rated for............

abufletcher

OK, Here's what I just ordered from Tower:

1. Two Hobbico Multi-chargers
2. Two sets of three Tx and Rx Airtronics banana plugs (at a quantity discount)
3. One Futaba 4.8V 1000mAh battery (like the one I just bought in Osaka but about $7 cheaper)
4. One Futaba 4.8V 1500mAh battery (about $12 cheaper than in Japan)
5. One banana plug for charging my glow-starter (for use on the multi-charger)

All this cost about $180. With proper care this should give me all the battery equipment I'll need for many years. Thanks everyone!!!

abufletcher

Well, all the numbers just aren't adding up. Today I flew my Kyosho Me109 ARF powered by a fully charged 4.8 volt 700mAh battery (Sanyo, purchased about a year ago, no problems). When I took it off the Hanger9 SureCycle it was reading 5.8V. That's the reading I ALWAYS get on all my 4.8V batteries on this charger. Could this be related to the fact that in Japan household current is 110V but 50 cycles?

I did three flights (with a LOT of aerobatics) for a total of about 40 minutes of airtime. After each flight, I checked the power level with my Hanger9 voltmeter. After the first two flights, the pack was reading a bit over 5.1V or so and 4.9V under load (at the 1A setting). After the third flight, it read 5.1V but dropped to 4.7V under load. I figured better safe than sorry so I packed up and came home.

At home I put the pack back on the Hanger9 charger and ran the discharge function to see how many amps were "left." To my very great surprise, when I checked a couple hours later, the display read 704mah! What's up with that??? [sm=confused.gif]

BTW, I'm assuming that 1A on the voltmeter stands for a load of 1000ma (2A=2000mah and .5A=500). This is a six servo model (T, R, E, 2x A, Retracts) so is the 1A setting ok?