Rick K

My Feedback: (6)

Hi Guys, I know I'm behind the times (batt wise) but for my current project (the infamous Viking) I decided to pick up new batts all the way around for both my Stylus Tx and get a new Rx set as ALL (8 sets) of my old packs tested 'shot' (you just can't leave them sit for a year or so like I did!) The insert for the Stylus pack I obtained from 'Batteries America' a 1100 NiCad set, no problems there.

I saw in a Hobby People ad they had a 5 cell Rx 1K mah NiMh pack on sale for $15 . . . Sounded good so I made a trip over there yesterday morning and picked it up. Using my 'Accu-cycle charger I' (I have models I & II) that's supposed to be good for NiMh I put the new pack on a 125 mah charge around noon time. When I checked at 11pm it was still charging! Humm... 1000 mah/125=8hrs. ???? When I awoke this morning checked again, done and in the 'trickle' mode. OK now I'll cycle it once with a 250mah load. . . see ya around two. I happend to glance at it a half hour later . . . and it was aready in the charge cycle. Checking the display it showed it had 'flipped' at 17min. Being my first experience with Nimhs I don't know if this is normal or not. The older Accu-cycle I unlike model II doesn't give a reading for voltage or a indication of chg. mah. (how much it took) When it goes into the trickle mode again I'll check voltage with my DVM. I haven't used the model I charger in a few years and am worried that there might be something wrong with it, or at least on the Rx side. Any ideas??? I really can't afford to mess this pack up (funds are kinda limited for hobbies around here of late)

Rick K
LSF 6493

BMatthews

I'm guessing that it only needs to be cycled a couple of times to wake things up. Try again and you should see a big improvement the second time through. This is certainly the case with the older nicads that are left in storage for quite a while.

rscarawa

I was under the impression that Nimh did not need cycling. Is that correct?

BarracudaHockey

My Feedback: (11)

Some things about NiMH they don't need cycling like nicads, infact it reduces thier capacity.

They also have a higher self discharge rate than NiCad's, which means they should be peak charged the night before you go flying. The older ones also have a lower discharge current than NiCad which made them inappropriate for digital servo use. The newer one's dont seem to have that problem.

Lots of battery info at www.rcbatteryclinic.com

Good luck!
Andy

Rick K

My Feedback: (6)

Bruce and others, this is a new pack purchased Sunday morning as in yesterday. I wonder, what problems might I encounter if I used the model II accu-cycle charger? Where would be the problems . . . In the charging cycle or discharing modes? Let me go out there and check what's going on now, be right back. In trickle now, what do you guys think, should I leave it alone a little while? Weather report: Still raining strongly, windy and cold. News says 'Major storm warning' Two inches of water standing in the back yard, one inch more and it'll start coming into my patio room (where I'm sitting) soon if it does't quit . . . Rain storms, forest fires so near and earth quakes, and so many of you wish to live here?
Rick k

rscarawa

One other note. I do not think you are supposed to trickle charge NiMh. Chargers do not fall back to trickle when peak charge is reached. This is supposed to be the difference between charging nicads and nimh.

3dd

My Feedback: (6)

NIMH WILL GET HOT AND SHORT IN LONG TERM TRICKLE.MY NEW 6 VOLT CAME DEAD AND WAS FULLY CHARGED IN 12 HRS BUT I CHARGED AT 300 MIL PER HR AND IT SHOWED 7.2 FIRST CHARGE OF THE WIRES.TAKES FOREVER TO CYCLE A GOOD PACK DOWN

BMatthews

Well, no battery should ever be left on trickle for long terms. But with new NiMH packs I run them up and cycle them down as a test and to check the capacity. On mine, admittedly only two of them so far, that I've done they did show more capacity on the second time through. There's also cell balancing issues so it's always a good idea to trickle them overnight now and then even if you rely on higher rate peak charging most of the time.

Rick, in your case the discharge test time seems VERY short. I'd check the voltage coming off the charger and then let it sit for a few hours and check again. You may have gotten a pack with a bad cell. I've got a motor pack here that I need to dig into that has a brand new bad cell so it can happen.

Rick K

My Feedback: (6)

Good day Bruce, Well on the second cycle things improved some . . . 486mah/121 min. On the third cycle now so I'll have to wait until tonight to see again what's going on. What should be a 'good' ch'd voltage reading? Geez, some here have said don't trickle, you say to ???? As the charger I'm using says it's a NiCad/NiMh capable charger I'd think trickling would be ok? Perhaps I'll call Battires America and ask them even though I didn't get the pack from them (got the NiCad Stylus insert pack from them though) If the have any recommendations/insights I'll pass them on here. Thanks to all for taking the time to respond . . . Wish me happy birthday (49) RCU sent a e-mail doing so.

Rick K
LSF 6493

BMatthews

OK then. Happy Birthday... I'm still a lot worried about that pack. When I said it might take a cycle or two to come up I was thinking more like 800 to 900 mah on the first pass and then up close to the final value of 1100 'ish on the second. I think you must have a bad cell in there or the charge port is set for only 4 cells worth of voltage and with you using a 5 cell pack it's not going to charge properley. Can you get a current meter in there to confirm the 125 ma charge rate if this output is set for specific cell counts? Converseley on charge you should be seeing about 1.3 to 1.35 volts per cell at that charge rate so x5 would equal 6.5 to 6.75 volts at the battery terminals and after a few minutes from coming off the trickle cahrge it'll go down so about 6 to 6.2. If it's appreciably less then you probably have a dead cell. In particular the only proper way to cycle the pack is to add in the cell count so it knows when to switch off so I guess I has to assume that this has all been taken care of. So it comes down to confirming the actual charge current and measureing the on charge and off charge voltages.

Rick K

My Feedback: (6)

Hi Bruce, Yes I checked again (3rd time) that the cell selection switch was set to 5 cells. I guess I'm going to have to cut one of the chg. leads to put my DVM into series with the batts in order to get a 'I' (amp) reading. As a thought . . . Would using my O-scope show anything? Today's cycle is not yet complete, well I haven't gone out to check tonight (other priorities tonight) Stay tuned, news at 7 (am, PST)
Rick K

BMatthews

Yes you will have to do that or modify an servo extension cord to provide the same function. If you add a nice connector to the one lead of your cycler or make up a modified servo extension cord you can do such testing more easily in the future so it wouldn't be a bad idea at all.

The scope won't show current unless you add in a sampling resistor to change the current passing through to voltage. Then Ohm's law comes into play. But the resistor will fool the cycler if you leave it in permanently so I don't recomend it.

sawdust

My Feedback: (7)

I gave up on my 'Accu-cycle charger for NIMH batteries a long time ago. I in fact got so feed up with it that I throw it away.
Here is how I charge my NIMH battieries.

Batteries with a capacity of less than 3000 MAH charge at .7 x or 700 mAH for a 1000 MAH battery. If you really want to do it correctly cut it back to .3 x after the battery is 80% charged. For my 3300 MAH NIMH I charge them at 1x or 3300 MAH.

Refresh the charge of each pack before each flight. These charge cells lose their charge very fast.

Never get these cells hot during the charge cycle. Never trickle charge them . Do not cycle them.

This works for me.

bob breese

Rick K

My Feedback: (6)

Well guys, Now what? I caught it around an hour after it went into trickle, my DVM gave me a reading of 7.86V . . . for a five cell pack does that sound ok? How else can I test it? I have a bunch of resistors around, most though are in the 1/8th to 1/4W range. Gosh, I went to a electroins trade school twenty years ago for six mo. after I first hurt my shoulder and could no longer turn wrenches, but as I think as I sit here of how to apply OHM's law to the problem . . . E (V) should = min. discharge V level, with NiMh 1.5V (right?) and I (A) needs lets say to be 250mA. So 1.5 X 5 = 7.5 Then 7.5 / .25 = 30 . . . 30 ohms. So if I place a 30 ohm resistor across the leads of the 1Kmah pack after 4hrs. I should have a 7.5V reading on my DVM correct? Something doesn't seem right with that though. My V number doesn''t sound right. What should the chg'd per cell V be, and the discharged? Besides my Accu-cycle chargers what other ways could I charge?

I guess like alot of other things you learn, if you don't use it, you loose it.

Rick K

BMatthews

That 7.86 volts is just over 1.5 volts per cell so all your cells sound like they are there. But that's the hot of the press voltage. After sitting for a while it should go down to 1.4 or so /cell.

But that's also on the peak of the charge. The nominal voltage for NiMH's is 1.25v/cell just like Nicads. When you discharge the pack you'll see the voltage take a big dive at first until it hit's this midrange voltage and then finally takes a big dive at the end of the cycle where you should cut them off at about 1.1 volts per cell. So the nominal voltage of your pack is actually 5 x 1.25 = 6.25 volts. To cycle it at an average of 250 ma you need a 6.25v/0.25A = 25 ohm resistor and it should cut out at about 5.5v to prevent running any single cell down too far.

While I understand that the NiMH packs do not require cycling to destroy any memory (and for that matter niether do any of the nicads made during the past decade) I still consider a cycle now and then to measure the capacity of the pack a good thing as it'll point out any weakening of the pack.

As for the idea that NiMH should not be trickle charged I'll have to look into that. So far I've been trickling my radio packs using the old nicad chargers without any issues. Electric motor packs are probably a different issue and would appear to be what you guys are reffering to. Yes? No?

sawdust

My Feedback: (7)

I have been in this sport for 4 years. And I have read a lot of articles on how to charge battery packs.

I fast charge all of my packs - motor, transmitter, and receiver. I never trickle charge a pack. Not NICd, not NIMH, and not LIPO.

Just before my flights I refresh the charge in the NICD and NIMH packs via a quick charge to peak them. Never charge NIMH and LIPO at greater than 1 x.

My packs stay in great shape and deliver peak capacity.

The correct method of charging batteries is one area of varying opinions in this sport.

bob breese

sackie

Hey there Rick, after trying to read through your many responses I noticed that no one picked up on one fact. As far as I am aware, the Accucycle I is not rated to charge NiMh, only from the Accucycle II. I have successfully charged 1800 MAh 6V packs on my Accucycle II and have performed the test with peak charging using this charger. For your information it took much more than 12 hours, more like 18 - 24 but then again I was charging 1800 MAh. I read the manual on the Accucycle II and followed their instructions regarding charging NiMh. So if you are still in doubt perform the test using the Accucycle II but as others have stated on this post you are not supposed to perform this too often on NiMh as it is supposed to degrade them.

Rick K

My Feedback: (6)

Geez, Ya think I got it mixed up? I have both chargers and for some reason thought the model I was the one to use . . . hold on, I have a tower cat. that says which does what . . .ok, and . . .yeah, I remembered correctly, it's the Model I (plain Accu-Cycle) not the model II (Accu-Cycle Plus) that says in the cat. is for NiMah. I wonder though, is the chg. cycle or the discharge cycle using the 'plus' that would mess the pack up? I'd sure like to chg. at the faster rates the 'plus' offers. Maybe tomarrow I'll give Hobbico a call, what the heck, I'm paying for unlimited nation wide long distance, might as well use it for something besides my wife calling my mother-in-law!
Rick K