I got this 2000 mAh NiMh battery but I only have the stock charger that came with my radio. it has an output of 80mA, I have another 600 mAh battery that states a 15 hours charge with a 60mA charger, then I'm assuming that to get a full charge on the 2000 mAh battery, I need arround 36 hours of charging with the 80mA charger... am I correct? should I get another charger?

25Hr should do it if its down to 1v per cell.

If you fly for a couple of hours and the battery is only half drained, you will need only 1000 mAh to recharge. Which would be about 12 1/2 hours. I would get a better charger anyway. You could charge your battery's in about an hour. You dont need a expensive charger, just something that will change at a higher rate, like maybe 5 amps. Look at hobbypartz.com for some good deals on chargers.

Maybe something like this??

http://www.hobbypartz.com/60p-dyc-1004.html

Yep, IMO, you need better. May I suggest that you go down to the local Walmart or Radio Shack and check out the stock. I have a number of such chargers. If you have the normal 4 cell, "4.8" battery, you can do very well with a charger that puts out 6-8 volts and 200 - 300 mah, a few up to 500mah. Never read the output of a charger from a hobby radio package. Check the actual output in the fine print on the charger, normally called "power supply" or "converter" in the real world. I have a couple chargers that have adjustable polarity, and 1.5 to 12 Volt output with multiple size selectable polarity transmitter tips. These come in handy.

The good point is if you watch the sales, especially at Radio Shack, you can get them from 50 cents to leass than $5. I think maybe that is where hobby suppliers get theirs and sell to modelers at 3-5 times what they pay.

One other point is that many chargers for NiCads and NiMah batteries list the output as the 4.8V radio standard. These batts charge to 5.5 to 6 volts. You cannot pack the electrics into a batt. with 4.8V charger. You have to have higher voltage to fill the battery.
Don't let deceptive trade practices lead you into not properly charging batteries. [8D]

what about this one? http://www3.towerhobbies.com/cgi-bin...XWTE0&P=ML

by the way, thanks for the replies :P</p>

Yes your 80 ma charger will give your 2000 mah battery a full charge in about 30 hours if it is fully discharged at the start. You can get by fine with this charge rate if you can take that long to charge it each time. In fact, your batteries will last longer (give you more charge/discharge cycles) if you charge at lower rates. Typically around 0.1C (200 milliamperes in your case) for 15 to 16 hours will give you the longest life. Fast charging usually winds up heating the battery a bit and heat definitely lowers the mean time to failure rate; the hotter the lower the lifetime.

With any charger there is overhead. This means that if, for instance, your charger can supply 100 ma per hour charging rate, then that means that in 10 hours, it SHOULD put out 1 ampere or 1000 miliamperes. There is overhead, usually in the form of heat (feel the charger.. it gets warm). So, there is about a 20% factor in charging with this charger, meaning that to get 1000 miliamps will take about 10.2 hours or so.

25 hours may or may not do it for you, but it would be close. Overnight, probably, a bit longer certainly.

As suggested, there are better chargers, however to get the best out of your charge and what's best for the battery is to keep it at or below 0.1C.


CGr.

then charging for about 24 hours everytime wouldn't do any harm to the batteries? what is exactly a full discharge battery? talking about a 4.8 V (4 cell) pack,  if they are at 4.6 or 4.5 V then, can I assume I'll need only  16 hours (or so) to get them fully charged? remember, I'm talking about a 2000 mAh 4.8V pack and a 80 mA output charger.</p>

Only on trickle charge or at a minimum charge rate. Fast charge... a no-no for long term charging.

CGr.

Total discharge for a NiCd battery is usually assumed to be 1.1v per cell. In other words, your 4 cell is totally discharged when the voltage drops to 4.4v while under load. The fastest I would charge a 2000 mAh battery would be at about 200 - 300 mA if getting the longest life possible is your primary concern.

That's roughly 0.1C which is the recommended charge rate for these batteries (for long life). Charging faster will get you back in the air at the possible cost of shortened battery life. It's a trade-off.

Even though I charge at 1C in the field, I usually charge at approximately 0.1C rate. The problem I have is that I usually just replace battery packs when I feel that they are not going to be reliable to me. I value my planes more than what a replacement battery pack costs.

CGr.

this is also a good point, Iuse to "test" my batteries by how many 10 minutes flights I can get before thelow batt alarmstarts beeping. Ithink any 600 to 750 mAh pack should give you at least 5 flights.

Correct that to say "ANY GOOD 600 to 750 mah pack.."

With that, I totally agree.

But, I bought one of the original DX7's and, although I never experienced the "brown-out" that some did, I immediately switched over to 6 volt ( 5 cell ) NiMh packs so that I would never reach that threshold unless I was sleeping or something...

Thus, I have a box full of older 4 cell packs that I have absolutely no idea of their status

CGr.

oh you are right, I forgot to say "good" 

Dreadhea, you wrote: "Total discharge for a NiCd <u><font color="#0000ff">battery</font></u> is usually assumed to be 1.1v per cell. In other words, your 4 cell is totally discharged when the voltage drops to 4.4v while under load." Does that mean this is the lowest (4.4v) I should set the discharge when doing a cycling? I used to use the charger that came with the radio, and I just got a charger/discharger and I don't know how to use it.</p><font face="Arial" size="2"><font face="Arial" size="2"></font></font>

The nice thing (other than longer battery life) about charging at 0.1C or less is that, if you forget and leave the charger on for a 24 hours to long, there is probably no damage done to the battery.

Yes. You should set the discharge limit to 1.1v per cell. I use an Accu-Cycle Elite. It uses the "per cell" voltage. I don't know what other chargers use. You may have to do the math yourself (1.1 times the number of cells). Also, the discharge rate should approximate what the plane does. for a typical 4 or 5 standard servo plane, I use 300 mA. More servos, or high torque/speed servos draw more current so you should adjust the discharge rate accordingly. This will give you a more accurate idea of how much flight time you have.

I agree. Long battery life is not always my primary concern. Since I routinely cycle my NiCd batteries twice a year and monitor their performance, I replace them when they reach about 90% of their stated capacity. If a 600mAh battery only gives 540-550 mAh usable, it's time for it to be replaced. I usually get three to four good years out of a battery. I could get more, but I tend to charge them at 1C many times. Sometimes, getting recharged quickly is more important to me than extending the life of the battery. The one thing that I have noticed, and I wonder if anyone else has also, is that with a peak-detect charger, charging at a high rate does not charge the battery as efficiently as charging at a lower rate. what I mean by this is that if I charge at 500mA, when the charger shuts off I can charge the battery further by setting a lower rate.

Dredhea,

<font size="2">

I don't mean to hijack this thread but maybe my questions can help the one who started it. My battery is a 4-cell 4.8 Nicd with 600 milamps. I did a cycling setting it to a low of 4.4 discharge. It took the charger 1 hour to discharge the fully charged battery to 4.4 at a rate of 0.5 amp. Is 0.5A a good average rate or should I go lower? The charging time was also 1 hour and it went up to 6.2 volts on the charger, but when I used my voltmeter under load (.5a) the voltage was 5.32. Is this more or less what I am supposed to get? Also, one last question, my instructor told me not to fly when my battery shows 4.78 or less under load (using the 0.5A in my voltmeter). Some people are telling I can go much lower. I am curious to know. Thanks.</p></font>

I don't mean to hijack the thread either, but to answer your question, 4.4v is usually considered to be a "totally discharged" state. You never want to fly to that point. Follow your instructor's guidance. If that's the guidance you elect to follow, set your discharger to stop at 1.2 volts per cell (4.8v). You will then know exactly how much time you have to fly.

hey stop hijacking!!!  lol just kidding, all the good information is always welcome :P

That's too much time but if you charge with that time from a fully discharge battery as long as the charging rate is similar to that, the battery is fine. The rate is less 5% of the capacity. That would not heat up your battery internal resistance instead charger internal resistance compensate when battery is fully charged. That is to make sure the battery is fully charged.

BTW, the actual current is based on the actual voltage of the charger less initial battery voltage then devided by their combine resistance.

Depending on the condition of your battery, considering healthy battery at fully drain, devide the mAh capacity by the charging rate of mA will give you time in hours then multiply it with factor that base on your charging rate. Usually 1.25 would give you 20% of energy to compensate loss on charging. Make sure that rate after full charge or charging current would not heat up your battery for a long time.

let's see if I got it right... I have this 2000 mAh battery (it is healty ), then I have this charger that states a 80 mA output, then following your formula, it should be 2000/80 * 1.25 = 31.25
so I have to charge the battery for 32 hours assuming it is discharged at 4.4 V
am I correct?

Yup. Time to invest in a new charger? []