All Day Dan

My Feedback: (5)

I am constantly getting more capacity out of my NiCad and NiMH packs when I use a constant current charger instead of my peak charger. I am charging them at one tenth their rated capacity. Even with sensitivity set at 20millivolts the peak chargers are peaking off at barely the battery packs capacity at fewer hours than the 12 to 14 hours I can charge the packs at a constant rate. It would be great if there was a constant current rate in the peak chargers and I can use the time or capacity cutoff function. Is there anything out there that can do it? Dan.

chuckk2

"I am charging them at one tenth their rated capacity"
That's about the optimum charge rate for many of the batteries you are using.
Do you know what the typical discharge rate might be?
Peak charging is really intended for a faster turnaround, and the measurement of fully charged vs
a partial charge will not be as accurate.

All Day Dan

My Feedback: (5)

Chuck, I discharge the batteries at the rate that I have calculated them being consumed in my models. After a little math, it appears that I have an average consumption of 500ma. I discharge them at that rate every three months to monitor their health. It also tells me what the margin of safety I have considering the amount of time I fly. I stick with three to one. Dan.

chuckk2

I don't know what your battery capacity is, but the smallest I remember was 600mah. A 500mah rate, even for this battery is lower than the 1C rate used to calculate the battery capacity.
I recently cycled several TX & RX batteries that were of the older NiCad types, used in Futaba TX and RX's. After cycling, the available capacity increased, and at less than 1C discharge rates,
was also higher than the rated capacity. A NMIH battery intended for use on a spectrum TX behaved similarly, although the change in usable capacity was much smaller, and the rated capacity
much greater. (2000mah)

All Day Dan

My Feedback: (5)

Chuck, I discharge the batteries at 500ma because that is the load on them in flight. This way I can tell how much flight time I can get from them by noting the minutes in the cycler. It works out real easy. 180 minutes on the cycler means I have a two to one margin on the batteries since I fly for 90 minutes a session. As soon as the batteries get to be less than that, they are replaced. When their capacity gets less that 20 percent of their origin capacity they are replaced. When they get to be two years old I start thinking about replacing them. They are never used when they approach three years old. Like the guys who sell us the batteries say, batteries are cheap. The planes are not. Dan

chuckk2

From what I've seen, the battery quality and treatment/use over time is as or more important than age.
The charger's characteristics also have a major role, based upon my usage of NMIH/NiCad power tools and the chargers used.
The individual cells in many of the power tools are not the best!

JPMacG

My Feedback: (2)

My experience is that batteries will charge to a slightly higher capacity and last longer (more charge/discharge cycles) with constant current charging at C/10. In my opinion, peak detect charging should be avoided.

chuckk2

Some food for thought - - - As I remember, sometime in the 70's, Honeywell made battery powered strobe lights for cameras. Pulse charging
was used to charge the batteries, simply because it put a usable charge on the batteries faster than a constant charge rate.
The reasoning was that the duty cycle could be used to allow the batteries to cool slightly between pulses, thus allowing a higher rate than a constant charge.
There was some fancy language about surface charge dissipating between pulses, but, I always doubted that as a significant factor.
It's also remotely possible that the pulse charging circuitry might have been cheaper to make than a decent continuous charger,
or it was seen as a selling point at the time.

Truckracer

My Feedback: (19)

There were quite a few unique Nixx chargers back in the day. Pulse charging was also suppose to reduce the occurrence of internal cell separator shorts which were so common at the time.

I only know of one method of Nixx charging that gives predictable and repeatable results when recharging from any state of discharge. That is a constant current charge that terminates the charge when cell temperature starts to rise above a certain point. In many hundreds of commercial Nixx applications, I've never seen a more reliable charge method but it is / was seldom used for RC applications. Those commercial applications, much like most of our RC applications have largely switched to Lixx batteries these days and all those old batteries and their strange, expensive chargers were trashed (recycled for our green friends) long ago.

chuckk2

There are charger than can chage at a constant current, until a specific voltage is reached. But, then it is necessary to complete the charge at a lower rate, or terminate the charge.

All Day Dan

My Feedback: (5)

Chuck, do you know which one? Dan.

chuckk2

Depends on which type of batteries are used. Remember that the NiCads were traditionally charged with a full charge detected by a voltage dip,
or a temperature increase. My chargers, when set for Lipos, can charge at a constant current, with limits as to current, voltage, and time.
I never bother to set the capacity, but some chargers use it to help calculate charge and balance current settings.
One of the older 50W Bantam BC-6 chargers had some slightly different options, including pulse charging. (I used pulse charging once to see of it worked).
I currently don't have any LiFe batteries, only NMIH and some older NICAD packs.

Another user remarked concerning pulse charging. One of the things I remember was that sometimes you could sometimes clear a short in a cell with a charged capacitor.

Jennifer Curtis

The real problem with peak charging at C10 is that
the peak will be very indistinct and thus difficult or
impossible for a charger to detect. Also the heat
from overcharging will dissipate easily so temperature
detection will not work. A reasonably priced low
current peak charger simply will not exist, and
very few people would be willing to pay as much
as it would cost when a wall wart will do the same
job for only a few dollars.

Jenny

Truckracer

My Feedback: (19)

+1 well stated! The remaining Nixx receiver batteries I still use are all fairly low impedance ones that I charge at a high rate. They peak charge quite well and with dependable results even though they are getting along in years. Cell temps are always just warm to the touch at completion. In this case peak charging or constant current charging to temp rise would equal the same results without overcharging. I wouldn't attempt that on high impedance batteries at a lower current though for reasons quoted above. I'm not patient enough for wall wart rates though. Eneloop batteries in several of my older transmitters seem to be an exception and charged within their specs all my chargers work well with peak charging.

JPMacG

My Feedback: (2)

The nice thing about constant current charging at C/10 is that it doesn't matter if you overcharge. The cells will not be damaged. Just charge for 12 hours and don't worry. You know the cells will be fully charged.

Peak charging sometimes misses the peak and cooks a pack, or stops charging early when the weakest cell of the pack peaks, or responds to noise and terminates early. Peak charging a single cell would work better, but we don't do that.

Truckracer

My Feedback: (19)

Not completely true. For small cells, yes as Jennifer stated above C/10 charging can work quite well as there is very little actual charging wattage being dissipated. As cell capacity increases, wattage increases quite a bit and charging something like a 1600 - 2000 Mah. battery can create a fair amount of heat that can be damaging if it can't dissipate either through a heat sink or into the surrounding air. Of course this is only a problem if the battery being charged has a fair amount of charge when the charge cycle begins which is often the case with RCers. How many people know the state of charge when they plug in their C/10 charger?

I worked with commercial chargers / NiCd - NiMh batteries extensively over the years and frankly I found them a first class pain in the rear to deal with as they just don't behave like PB or Li batteries during charge where once the cells reach full charge with a constant voltage applied, currents reduce to close to zero. Even if a charger could switch to constant voltage (CV) Nixx cells will just continue to accept charge current and cook themselves to death unless additional outside means are employed to stop the charge cycle. Simply stated, no Nixx charge method is foolproof or "the best" and complex chargers usually use a combination of controls to maintain battery health, with temperature playing a large part in the equation. Simple solution, bin the Nixx batteries ...... switch to Lixx based batteries. Their much easier to charge with any good CCCV charger as most current chargers are. CCCV doesn't work at all well with Ni based batteries.

JPMacG

My Feedback: (2)

Correct. I should have made that distinction. Let me rephrase. For the old school transmitter and receiver packs, which are AA sized cells of 500 to 700 mAh capacity, it is fine to overcharge at C/10. But overcharging at C/10 is not fine for higher energy density cells, such as 1100 mAh AA cells and higher. A good indicator is temperature rise.

I like NiCd because of its reliability, simple charge routine, and longevity (5-10 years), but I am using low energy density cells.

P-40 DRIVER

The charger I use is the Revolectrix Multi 4. It is as flexible of a charger as your going to find for the type of thing your trying to do. Normally you would do 1/10C charge and terminate it when the pack begins to warm slightly or reaches a peak voltage and stays there. Using peak detection at 1/10C is pointless. You can also do 1/2C peak charge followed by a 1/10C trickle charge for an hour or so if you want max charge. The Multi 4 Peak detection system is probably the best in the industry and far better then my Triton. All of the Multi 4 charger parameters are adjustable including trickle charge functions and it will graph on your computer. It not very expensive either. The only downside, it does not have a discharge function.