Yesterday I did a first fly on a rebuild from a battery failure crash. After the crash, I bought a cycling charger [Accu Cycle] and installed a new 1,400 MIL amp battery in the plane. Friday night I discharged both the transmitter battery and the receiver battery and gave them a full charge [ 15 hours at 125 for the 1,400 and 50 for the 700] per instructions with the new charger, [I had previously cycled both batteries 3 times and found the 1,400 Mil amp to take a charge well over 1,300 mil amp and the 700 mil amp transmitter was well above an 80% chg.] Well, I flew for no more than 40 or 50 minutes total on air time and the receiver battery was down to 4.6 volts. When cycling, it took 6 hours to go from full chg to the 1.05 recharge level, this should have given me at least 2 hours of flying as I calculate. The only thing I can think of is that the amp draw on this old equipment must be higher than 125mil amp. How would I test for the amp draw for the servos and receiver?

Gary

I find that the draw is usually around 250mA for the typical "small" model.

Use one of these. You can even control the servo and check the draw.

Cheers

Nathan, even at 250 with approx 1/2 of 1,400 / 750, I'd think I shuld have gotten at least 2 hours?

Ghostt, how do you hook up the tester? Do you have to remove the leads,eyc?

Gary

Roo,

I have absolutely no concrete evidence to back up my claim but, here is what I think I've found.

I had a hangar 9 double vision charger that i've used for years. I traded my father for his Accu-cycle Elite since he didn't want to fuss with the additional doo-dads and buttons. The Double Vision is almost plug and charge. soon afterward, I started to feel that my batteries were not giving me the same amount of use and I felt that after a couple of years, they might be going bad. I didn't think this was a problem as many gave me years of service. I went out and purchased two new batteries (6v and 4.8v, both 2700 mah) and a new Tx battery (1500 mah). Even the new batteries didn't give me the service I was expecting. After a few flights, they were down to 4.7 or 4.8, lower than I care to fly with, especially if they're dropping that fast.

Well, I borrowed dad's Double Vision and started using that to charge the batteries. I'm finding (again, with no concrete evidence, I admit) that the batteries are lasting longer. Now I'm getting an entire day of flying with them and they're still at 5.0 or close to that. I'm at the point now where I'm planning on buying my own Double Vision. It's a fraction of the cost and, in my opinion, it does a better job. It just doesn't have all the bells and whistles. but, at the end of the day, if you're not happy with how the charger charges the batteries, what's it worth? Just my two cents and like I said, only my perception. Take it for what you will.

Just wiggling the sticks doesn't nessesarily make a servo pull full current, even if you move it at maximum rate. If you really want the servo to pull maximum amps, grab its control surface and force it away from its commanded position.

You would have to make up adapter leads, but then you get volts and amps draw from the servo. Good to test suspect servos, you may also have a faulty cell in the battery pack or binding linkages or stalling servos with to much travel.

Cheers

Crafty, do you think that perhaps the H9 charger is just overcharging the batteries. W/ the A Cycle you give it the specific mAh and it charges accordingly. Try charging it with the A C, then check the voltage. then discharge. charge with H9 charger and check the voltage. I'm guessing that the H9 is just cutting off at a higher voltage. By the way, most good batteries have no problem with what I called "overcharging". I'd rather be able to fly longer at the field and replace the batteries more often anyway.

I have considered that Dixieland. When I check my batteries right after charging with the H9 charger, the 6v reads 6.6v. I don't believe the Accu-cycle obtained this number. If I remember correctly, it was close, at 6.5v most of the time. That's with a loaded H9 tester.

I understand that if the voltage is lower, you'll have less "energy" to work with but it seemed (again, I've not documented all this stuff) that the batteries lasted longer and dropped voltage slower, when charged on the H9 Double vision charger. Is there something to "packing in the voltage tighter" to get a few more points on the voltage? I'm sure that there are those who can explain the situation at nauseum, but that's not me... all I know is that I feel I get more flight time. That's really all we're looking for in a battery anyway. If it weren't for me noticing a difference when I first went to the other charger, and noticing the same difference in reverse, when I went back to the first charger, I would think it were not true. But, I had no bias when going to the fancier charger and, in fact, had high hopes for that charger.

If you stopped at a voltage of 4.6 volts, you still had over half the battery capacity left in the battery. You could probably have safely gotten another 50 minutes of flight time.

Thanks all.

For now, I think I will fly till I get below 4.8 and then do a field charge.

Gary

It was my understanding that on a 4.8 volt battery, you shouldn't go under that number. What IS a safe voltage to still fly? The only way to really find the definitive number would be to exceed it and I'd rather not do that!

Here's the thing about these batteries, you need to understand the discharge curve of the batteries to understand what you can safely use. The chart I provided doesn't contain any voltages because it can represent any voltage pack, I am using it to demonstrate my point. Also, even though the diagram says it's for Ni-CAD batteries the same discharge curve applies for Ni-MH's as well.

If you look at the chart you will see that at the beginning of the discharge the battery pretty quickly falls off to the Mid-point voltage. At that point it stays at that voltage for a large portion of the batteries capacity, and then it drops off quickly after that. For a 4 cell battery that mid-point voltage will usually be the 4.8 volt level. So if you are monitoring you battery and stop using it when the battery hits 4.8v you will be wasting a large portion of the batteries capacity (60%-80% of the battery capacity!!!).

So where does this leave you?? It means that you can use the battery while it reads 4.8v, but when it drops below that it's time to stop using the battery. Pretty simple. Follow this and you'll get a lot of usage out of that pack, but if you stop using it at 4.8v you are wasting a lot that you could be flying on. The best way to know how much time you have to fly on is to cycle the battery with a cycler that can measure the capicity of the battery. This will tell you exactly what you can us that battery for. The other advantage of a cycler is that you can tell when a pack is starting to fail. When you first get a pack you need to cycle it to establish it's capacity. Then throughout the life of the battery you should cycle it and refer to the original capacity of the battery. When the pack gets down to 80% of it's original capacity it's time to chuck the pack and get a new one.

Hope this helps

Ken

Very interesting! I'd think that using all the capacity of the battery has got to be better for the battery also. Now, the question again, is how do you know when you're getting close to the rim of the cliff and how do you know if you've gotten too close? I understand about the cycling part but, how does that relate to when you are at the field, wondering if you can get another flight in on the battery? You would have to cycle the battery down from that voltage, to know how much is still in there, wouldn't you? Your chart conveniently shows a "cliff" where the battery's voltage drops significantly. At some point, every battery will get there. My fear is that my plane might be 100 feet high when it gets to that cliff and I'm at ground level. I don't want to beat a dead horse here but I sure don't want to trust blind faith at the fly field either. Any info would be great.

thanks!

T,
You never really know when your getting to the edge of the cliff, the idea here is to stay as far away from the edge of the cliff as you can

With my Accu-Cycle I usually discharge about once a month, set the AC to the 250Mah discharge rate and note the total time. I try to not fly more than 1/3 the total discharge time, which in my case can be up to 120 minutes using a 6 volt 2000 Mah pack. After that just hit it with the field charger.

I made some test leads for my watt meter to test servo and RX draw, I used the ends from my Futaba charger.

Fly for "X" time and cycle the battery down is probably the only method to know how much battery capacity is remaining. Voltage is only a very course indicator of battery capacity remaining, which is why almost everyone stops flying at 4.8 volts.

The starting voltage on a fresh charged pack will be about 5.45 volts or so. The first flight will knock the voltage down to about 5.28 volts. The second flight will reduce the voltage to about 5.18. The third flight will reduce the voltage to 5.12. The fourth to 5.04 volts and the fifth to 4.86.

Cycle the pack down when you get home and hope to have 250ma or more left in a 1100ma pack. Each battery pack and each airplane and your numbers will be a little different.

What you don't want is only 20ma or so in the pack when you get home. Twice over the past 20 years packs have had less than 15ma when cycled down at home. The batteries were discarded.

Bill

The unknown territory is the area near the "cliff". That knee can happen very fast. Typical curves like this show exactly where this would happen, but it differs with each battery pack (slightly) and of course, with different people operating the equipment.

The battery discharge is of course a function of usage of the components. The RX demands a specific amount of current @ a range of voltages to operate. The servo's however, vary their demand on current as useage goes up and down. For each flight, this becomes an average because you won't fly exactly the same way each time, thus the current draw will slightly vary each time you fly.

But, you can figure out your average usage by doing the discharge (via flights) and charge cycle. To do this correctly, of course, you will have to measure your flying time as closely as possible and then add the total times for each flight (remember, flying time starts the instant you turn on your receiver on the bench till the time you power down the receiver). Add all this time up, then when you finish with the cycle charge, read the total current to bring you back up to full charge then calculate your current draw based on time. Do this several times over the course of a couple of weeks, then do an average. This will begin to tell you how long your pack will last and how much current you've used during that time (of course) and then you can work with that to determine your safe flying times.

That's about the best way I can think of to do this. Of course, someone will tell you to put recording equipment on your plane... ok.. that's fine, if you know how, and if you can afford it.

CGr.

Thanks everyone for the input. It definitely gives me something to think about. I'll check a little more inquisitively as I'm charging and cycling.

As B.L.E. mentioned, as the servos strain under the pull/push of the airflow, they draw more current.

Hook up a watt meter, and move the sticks around. You'll get an average "peak" draw on the ground..

Now do the same thing again but "resist" the movement of the surfaces as you do this.

You will be quite surprised at how much current those little servos can draw under load.

On a 40-90oz/in servo it is not uncommon to see max draws of over 1800mA.

Typically the servo draws less than this amount in acutual flight, but the 250mA levels stated are a "best case" situation.

Multiply the higher draws by the number of surfaces being affected at once, plus the effect of any binding.