JNorton

My Feedback: (2)

Mine works flawlessly also. But I never just top off the battery.
John

Geistware

My Feedback: (16)

After reading this thread, I took my 2700maH pack that was competely charged and set it to a 200ma charge. It timed out and shut off after a couple of hours with no damage to the pack. It was hot but not damaged.

3D Joy

200 ma is not even C/10 witha 2700 mah pack. You will never fry a pack at less than C/10.

As for me not using the charger correctly, that is true, knowing what I know today. But from the instructions, nothing is mentionned. The instructions say that I should charge a pack that has not been charged for a few days (Nimh packs have a high self-discharge rate). That is exactly what I did and it resulted in a 50$ pack that is now useless.

I just looked at the instructions. It is not said that I should not "top off" a battery with it so I did and my pack is dead and cooked. They even recommend to charge if the battery has not been charged for a few days (for Nimh only).

Anyway, I know now what I should have known from the beginning. I would have liked some precisions as to how the charger "decides" the voltage it uses to charge a battery. This is an entry level charger and should be usable by entry level users (I am not expert in battery technology and charging technology).

Wayne Miller

Hi Giestware,

The Hobbico MKii normally terminates the charge itself, that is, if the batteries are fully charged, or if the batteries do not charge withing a specified time frame. I think 2hrs. for NiCd or NiMh, and 3 hrs for LiIo or LiPo.

When you selected 270 mah, it may or may not have detected the correct number of cells, but you were being safe with the 270 mah rate, and it should have automatically have timed out after a couple of hours anyway. Since the charge rate was 270 mah or C/10, the batteries should be OK.

Hope this helps.

Fly4Fun,

Wayne Miller

MHawker

My Feedback: (16)

Hey guys,

I'm in the market for a fast field charger. Flying larger planes with more servos, I find I need to recharge after a couple of flights.

How do you check the voltage output? Is a DVM needed or is it readable on the charger. And, if it's charging at too high a voltage, can you override it and set it manually?

Thanks.

MHawker

My Feedback: (16)

Oh, on a different note, I was talking with George at Peak (Sirius) who said their Pro "PLUS" charger can be used to charge two RX packs with the adapter (looks like a simple plug type change adapter). The Plus is a higher output than the standard.

It's a little pricey at $165, though, but Sirius products have a great reputation.

Chevelleflyer

This will probably sound like a stupid question, but since I'm a newbee, too, I have to ask.

I just bought the Hobbico MKII, thanks to many of your recommendations, and before I use it, I want to make sure I don't mess up. I have a new JR radio that (according to the specs. in the manual) has a 600 MA tx and 1100 MA receiver battery. So, when recharging the receiver battery, do I turn the dial to 1.1 amps and when recharging the tx, put the dial at 0.6 amps? I did read the instructions with the charger, but I think it assumes that you know what you're doing already.

I guess I'm a little confused because I thought that a tx has 8 AA size batteries in it, but the receiver battery is a small 4 or 5 cell pack. If so, why would the smaller pack have more power? I would think that the tx would require a higher charge rate.

Thanks.

Highflight

My Feedback: (4)

The number of cells of the pack determines the voltage, and the capacity of the individual cell determines the capacity of the pack. You'll probably notice that the cells in your transmitter are probably AA or AAA, and the cells of the RX pack are probably C.

If you don't NEED to fast charge, don't. The batteries will last longer.
Fast charge only at the field to get more flight time when you need to.

Highflight

vicman

My Feedback: (10)

You are correct in your settings. Voltage and mah are different.

Geistware

My Feedback: (16)

Wayne, you are 100% correct.
If I am going to top of my pack, the most I will put in it is 400maH and that allows me to top off my 2700maH pack.

Highflight

My Feedback: (4)

On the MKII, it can charge two different batteries of different type and capacity and voltage at the same time. If you look at the face of the unit, you'll see that there are FOUR pair of jacks. The additional two pair of jacks next to the charge jacks are specifically for the purpose of plugging in a DVM to monitor the voltage of the pair of charge jacks it's next to.
Using a DVM, it's incredibly simple to figure out what the charger is doing at any given time. In fact, with experience, you'll get to know how close you pack is to being fully charged by seeing where the voltage is at any given time.

Highflight

Geistware

My Feedback: (16)

Chevelleflyer, Their are no stubpid questions in life.
While technically you are correct, the charger can charge a dead pack at a minimum of .5C and a max of 1C.
The minimum is set because the charger has an auto shutoff feature that will stop the charger after 2 hours (0.5C) and the max is set by the manufacturer of 1 hour (1.0C). I would recommend that you set your RX to charge at a minimum of 0.6 amp and the TX at a minimum of 0.3 amp. This will keep your battery's internal temps lower and less stress on the pack. THis is a PERSONAL preference and is not based on any data collected or read.

Superfast

My Feedback: (2)

Interesting post. I also have the MKII charger and really love it. I can charge the reciever and ignition packs of my gas planes at the same time !

We had one of our club members burn up a pack earlier this year with a MKII. It was attributed to the current setting being too high for the pack. He went on the assumption the a reciever pack of 1800 Mah should be charged at 1.8 Amps. Well that is not what the sticker on the charger says. Mine has a sticker on the side of the case that gives cell size (AAA, AA, etc.) and maximum charge rate. Bassed that a standard reciever pack is made up of AA cells the maximun charge rate should be no higher than 1.0A. So if you set the charger per the 1800MAH = 1.8Amps, you will heat up the pack and might even damage the charger. I currently run 1200 and 1800 Mah packs and always charge them at roughly .9 Amps, it usually peaks the pack in about 20 min.

Here is a pic of the sticker I am talking about :



Scott

3D Joy

That is funny.

New AA size Nimh cells are now in the 2400 mah range. If it is fully discharged, and recharged at the 1A max setting, it will not get full charge because the timer will abort the charge before the battery peaks.

I have charged aa cells at up to 1250ma at it was OK. The packs were warm to touch but not too much IMO. I would not charge the same battery more than once a day as it may overheat on successive charges and discharges.

azvmax

No No No on the cell count.
Charger reads internal resistance of Pack.

I arranged 4 AA NiMih cells so I could move the charge probes between them.
This way I could change from 1 cell , 2cell , 3 cell and 4 cell.
This was done while charging was in progress.
The charger instantly changed to the proper voltage.

I also topped the pack off 4 times after full charge was achieved.
Every time it ran for another 10 mins. or so.
Then it terminated on its own, without heating up the pack.
The last time out of 4 the pack got warm not hot.
I also monitored voltage with a Fluke DMM.





FULL SIZE http://www.rcuniverse.com/forum/upfi...78/Cz79723.jpg

Here's a link to my post on this subject.

http://www.rcuniverse.com/forum/m_16...tm.htm#1607487

AZVMAX

Flying Geezer

My Feedback: (14)

Azvmax, how do you know the charger sets the voltage by reading the pack resistance? Is that in the instructions? I am curious as to how you determined this.

Geistware

My Feedback: (16)

I don't know about it reading the pack resistance, but it does some type of continuity check

azvmax

Alot of chargers read the internal resistance of the cells.
Resistance and continuity are sort of opposites, resistance is measured in ohms, conductance is measured in siemens.
Continuity is nothing more than checking if something conducts.
http://www.allaboutcircuits.com/vol_2/chpt_5/5.html
For the answer to your questionsI cannot say for sure what method they used in the design of this charger.
But I did a series of tests, the charger knows how many cell there are whether they are fully charged or not.
Read my link on how I performed the test.
Also simple logic applies here lower internal res. lower voltage higher internal res. higher voltage from charger to force current into the cells. More cells higher internal res. higher voltage.
To top off your quesion I also used a varible resistor(potentiometer)and hooked it up to the charger and tried to charge it.
It tried to charge it and when I changed the value(resistance or conductance) voltage went up when I turned the resistance up.
The charging terminated after 4 second due to the fact that not much curret was going into the potentiometer.
So there is so of my conclusions.
Changed ~~~Before argueing with me please due some research.~~~(Bad choose of words or tense)
To Please due some research to add to what i have allready tested.

Flying Geezer

My Feedback: (14)

AZVMAX,

I am a little confused. I asked you a question. Where is the argument? I'm sorry I stepped on your sensitivity.

Best regards,

azvmax

No, what I ment is if you or others were to respond do some research to add to what I have allready researched.

Flying Geezer

My Feedback: (14)

OK AZVMAX,

Let's agree that this is just a friendly discussion. Let me start by saying that I have several years of research in this matter. I was hoping that you would expand on your conclusions. I have never owned or used a Hobbico Mark II. I did see one at a distance, and I stayed in a Holiday Inn Express last night.

A. I think you are right or partly right.

B. If you think a $50 charger has sohphisticated circuitry in it to measure the resistance of a battery pack in siemans or mhos then I have serious doubts.

C. I theorize that the answer to the question is a simple as I= E/R. For nicad and nimh batteries we are dealing with constant current devices. A simple sensing circuit, monitors the current indirectly and keeps it constant.

If you connect a single cell to the above described constant current device, the resistance of the single cell will be low, so the sensing circuit will lower the voltage output of the charger to keep the current constant. If you connect a 4 cell pack to the charger there will be 4 times the resistance and the sensing circuit will allow a much higher voltage, because it will take about 4 times as much voltage to force the same amount of current through 4 cells, a compared to one.

D. I also theorize that the resistance (and/or reactance) of a cell increases directly with the increasing state of charge, because I have noticed that the voltage goes up progressively when charging until peak. I have also noticed that negative peaking chargers, the Alpha 4 for example drop in voltage output just before peaking.

I'm sure Red can give us some information on cell resistance and, as to whether it changes with state of charge. I am also curious as to how cell resistance is measured in a labratory setting, and the typical resistance range. I have wondered about this since SR batteries has been advertising that they match cells when building battery packs to maintain better balance and effeciency. I hope Red will chime in here, and we can all learn something new.

I'm not putting your research down AZVMAX, mine is just a little different.

Hope you take no offense,

Red Scholefield

My Feedback: (9)

Cell or pack resistance is measure by looking at the voltage of the pack at two different discharge rates. The formula goes something like this:

R= V1-V2/I2-I1, in other words the change in voltage divided by the change in current. You will find that the resistance is essentially constant until you reach the knee on the discharge curve at which time it should be obvious that it goes up.

The pulse that you see in some charge systems is an example of this. They look at the voltage at two different discharge levels and from that determine the internal resistance.

I hope I haven't over simplified this for the battery experts on this forum.

Wayne Miller

With the above information, can you explain why some people have problems with batteries becoming hot during their charging.

I was lead to believe that if they tried to "top up" a charged battery pack that it could missinterpret the number of cells, due to the higher voltage, as having one more cell than it has. The theory is that the higher voltage may sometimes be interpreted as the low end voltage of a pack with one more cell.

I think the answer we are looking for, is how to avoid our battery packs from over heating when charging with this charger?

I found that if I "top off" a pack, I should always discharge a little and it will avoid over heating.

I would appreciate your point of view.

Thanks,

Wayne Miller

Geistware

My Feedback: (16)

Wayne, short of looking at the charge voltage, I don't know how this would be done.

azvmax

I agree with you Flying Geezer.
I was assuming a simalar idea.
I wish someone could fully explain it.
Meaning battery charger design both simple(cheap) and more complex(expensive).
With my test moving the probes to change cell count it reacted very fast.
So it is reading cell resistace indirectly but this is speculation on my part.
You never know with todays technology this senseing circuit could be very cheaply produced.
yes this is a constant current device but you can change the current at any time too.

Please chime in anyone who really knows charger design.