1.5 volt battery over charge protection circuit needed.

[gary350]

I need a circuit that will charge all of my 1.5 volt AA batteries but will not over charge the battery once it is fully charged.

I am wondering if a circuit board from a Yard Mushroom light will work to charge batteries? The solar cell is connected to the PC board and 2 wires go to the battery but I have no clue if this will stop charging once the battery is charged. If so I will need to build a 120 vac to 1.5 vdc power supply and remove the LED.

I have over charged and killed all my batteries again. I just bought new camera batteries a few months ago, good quality batteries from Wal Greens. I have my Wal Green battery charger on a 24 hour timer set to come on 1 hour every day. 1 hour is the shortest time I can set it for. I put batteries in the charger then do not remember to remove them until i need to use the batteries by then they are over charged.

I did an online search and found several circuit drawings but none of these show the voltage for the battery being charged. Ebay has pre built over charge circuit PCBs from china they are all designed for specific battery voltage and current.

I tried to charge my batteries in Mushroom lights but they all discharge after dark. LOL. Days are now short only 8 hours of daylight batteries never get fully charged.

 

[audioguru]

What chemistry is in your batteries?
Nobody makes a 1.5V rechargeable battery. Years ago they made rechargeable alkaline batteries that were no good and are not made anymore.
Some people try charging 1.5V disposable alkaline cells but it does not work well.

A Ni-Cad or Ni-MH cell is about 1.4V when fully charged but still charging then the voltage drops to about 1.3V when they are removed from the charger.
Ni-Cad cells short and do not last long. Solar garden lights use cheap old Chinese Ni-Cad cells that rust away in 6 months. I replace the Ni-Cad cells with Ni-MH cells made in the West that last for years.
A lithium rechargeable cell is much higher at 4.2V when fully charged.

 

[gary350]

I call all AAA, AA, C and D batteries 1.5 volts but my AA batteries say, 1,2v 2050mAh. I have Energizer and Duracell both are NiMh.

 

[cct314]

Properly charging NiCd or NiMH cells is rather tricky since it is rather difficult to tell when they are fully charged unless they are watched VERY closely.

Here are a few GENERAL observations that I have made over the years concerning NiCds and NiMH cells:

- "Quick charge" circuits (e.g. anything that will charge a NiCd/NiMH in less than 6 hours) will likely reduce its lifetime significantly
- A "normal" charge circuit (e.g. at 1/10th "C") at 14-16 hours for a DEAD cell is the best and safest way to go.
- When doing a "normal" charge, if the cell has perceptively warmed above ambient (often only a few degrees - and one should be able to differentiate this warming from that caused by heat produced by the charger) it should be removed from the charger IMMEDIATELY!
- If you get above 1.6-1.65 volts for any length of time (more than 4-6 hours) then the cell in question probably well-charged.
- NiMH cells will tolerate overcharge/reverse charge abuse far better than NiCds.
- If not abused, NiCds will far outlast NiMH cells (e.g. strict avoidance of gross overcharging and charge reversal).


In an application such as a yard light where a SINGLE cell is used, a NiCd is arguably more suitable than an NiMH since the former can tolerate more frequent, deep discharge cycles than the latter, and with a only single cell, there is zero chance of cell reversal, perhaps the single thing that kills more NiCds than anything else! Unfortunately (or fortunately, depending on your point of view) NiCds are getting more difficult to find (and banned outright in some locales for all but certain critical applications such as medical and aerospace - which tells you something!)

Fortunately, from the viewpoint of the NiMH cell in a yard light, they typically use a buck-type converter, often something akin to a "Joule Thief" (Google it if you are unfamiliar) using either discrete components or a COB (Chip-On-Board) IC that is under a black epoxy blob, which is likely a similar, simple circuit. Typically, these circuits go inert by the time you get down to 0.4-0.8 volts and the battery discharge stops there, but this is likely too deep discharge to keep the longevity of NiMH cells which, for long life, should probably not be discharged below 50%-70% if repeatedly discharged. (I believe that hybrid/electric cars that use NiMHs never discharge below "mostly charged" to assure longevity.)

In dancing around an answer to your original question:

"How do I prevent from overcharging my cells" - which I presume are NiMH, only because NiCds are difficult to find these days? I would recommend that they be charged MUCH more slowly to minimize the damage. If you were to charge them at no more than 1/10th C for the maximum of 14-16 hours (for a "dead" cell) then you are likely to get pretty good life out of them. If you can drop this even more and tolerate even longer charge time (e.g. 1/20th C for approx. twice as long) then the chemistry of the NiMH can more readily reabsorb excess hydrogen when overcharge (produced at a lower rate at the lower charge current) and be much less likely to vent the cell and lose capacity.

There is yet another problem that I've run across: Cell quality. Having equipment to measure the internal resistance of cells and their actual amp-hour capacity, I find the name brands (e.g. Energizer, Duracell, etc.) to be generally pretty good and consistent, but the "off" brand names to be all over the map. What is worse, the cheap AA cells are sometimes really AAA cells in AA cases - something immediately apparent by weight (if you have a "calibrated" hand - particularly if you compare the weight of "X" number AA cells versus "X" number AAA cells and find their heft to be very similar) or by inspection of the amp-hour rating if it is printed on the label: If it is an off-brand and there is no sign of amp-hour rating, don't even think about buying them! Even so, I find that the "off" brands rarely live up to their amp-hour rating. (Never buy an AA NiMH if its stated Amp-hour rating is much below 1.8 amp-hours as it is probably an AAA in disguise!)

Once I have used these NiMH cells, particularly after a year or so, their self-discharge rates tend to increase, so it is hard to know if they are fully charged if they have just been laying around: It's not a good idea to just plop them in a "fast" charger since there is a good chance that they will be overcharged if they didn't run themselves down very far - and measuring the terminal voltage isn't really much help with this type of chemistry in determining if they are "90%" charged or "25%" charged either since there is likely to be little difference in that voltage.

What to do?

I thought about a float charge, so along these lines I ran across a web page a while ago that described a device that "float charged" NiMH cells (based on manufacturers' recommendations) to keep them topped off, but as a side effect it also allows one to spot those that have gone bad. It took me a while to find this web page via a Google search (there seems to be a "robots.txt" that "breaks" searching at the web site for some reason) but here is the link:

https://www.ka7oei.com/floaty_thingie.html

Note that this is NOT a cell charger, but a "maintainer" as the text says.

Best of luck.

 

[gary350]

Very interesting information about changing batteries.

With the help of old junk TV parts, it took me 3 minutes to build a proto type battery charger. I used a 120 vac to 5 vdc wall battery charger, duel AA battery holder, the 330 ohm junk TV resistor, meter reads exactly 8 ma. Battery maintenance. Next, how to charge the battery for 14 hours with automatic OFF. My factory battery charger is 160 ma.

**broken link removed**

 

[dougy83]

I used a 120 vac to 5 vdc wall battery charger, duel AA battery holder, the 330 ohm junk TV resistor, meter reads exactly 8 ma. I need to read the artical again, not sure if this is maintenance only or to charge the battery?

**broken link removed**

You can trickle charge NiCd/NiMH and they will just warm up when finished. If you want to charge them quickly you'd normally use a timer or an charge controller that detects the end-of-charge condition (normally a drop or plateau of the cell voltage for a constant charge current).

That meter is reading 0.008mA (8uA)

 

[crutschow]

I call all AAA, AA, C and D batteries 1.5 volts .........................

Calling them 1.5V doesn't make them 1.5V.
There are nickel-zinc rechargeable batteries that have a voltage 0f >1.6V but they seem to have problems with limited battery life and suffering damage when discharged below about 1.3V which has limited their usage.

 

[gary350]

Calling them 1.5V doesn't make them 1.5V.
There are nickel-zinc rechargeable batteries that have a voltage 0f >1.6V but they seem to have problems with limited battery life and suffering damage when discharged below about 1.3V which has limited their usage.

It is a Chinese meter......it reads in Chinese. LOL.

I am suffering with Bronchitis & Pneumonia. Got out of bed, ate breakfast, checked email, and forum messages, then read Battery Maintenance while under the infuence of several drugs, bronchitis & pneumonia. Holding on to the furniture, walls, chairs, work bench trying to keep my balalance I built this battery maintenace charger in about 3 minutes. Several hours later I am out of bed again feeling 20% better. I may have made some mistakes. When my brain starts function closer to 90% maybe I can figure this out. I think your right, something appears to be wrong.

 

[ronv]

Are you a micro processor guy?

 

[audioguru]

All of my Ni-Cad cells shorted about 20 years ago and I replaced them with Ni-MH cells ever since. Ni-MH cells do not short, they do not have the "memory effect" of Ni-Cad and their capacity is much higher. Modern Ni-MH cells hold a charge for one year. Energizer and Duracell do not make Ni-Cad cells anymore.

A power supply and a series resistor IS NOT a Ni-MH battery charger. A Ni-MH battery charger is made in an IC that does everything that must be done to properly charge a cell or a few in series, then it detects a full charge and shuts off.

I charge my Energizer AA Ni-MH cells with a cheap Energizer battery charger that came with some cells. It is a very stupid charger, it is simply a timer with current limiting. It over-charges a battery cell that is already charged, but an IC charger would detect it and prevent it. If it is charging and the power fails and returns then it begins its timing from the beginning again which causes overcharging. The IC charger would prevent it. An IC charger detects the voltage hiccup that occurs when a cell becomes fully charged.

You know what? If you charge an old Ni-Cad cell and a Ni-MH cell together then you will feel that a Ni-Cad cell gets cooler as it charges but the Ni-MH cell gets warmer. Then they both get warmer when they approach a full charge.

You showed a 5.3V power supply, a series 330 ohm resistor charging two Ni-MH cells in series. When the cells are low at 1.1V each then they total 2.2V and the 330 ohm resistor has 5.3V - 2.2V= 3.1V across it so the charging current was 3.1V/330 ohms= 9.4mA which is almost nothing. The current drops as the voltage in the cells increases as they charge so 2050mAh cells will take more than one week to fully charge.

 

[gary350]

The meter is correct. I have only had this meter 2 weeks, it came form china with no instructions. Online instructings are writting in chinese. I have been learning how it works.

There is 1 location for the black wire.

There are several locations for the red wire.

If the red wire is plugged into the 20 amp hole it reads 20 amps only if the knob is in the 20 amp location.

If the red wire is plugged into the milliamp hole it reads milli amps on all 3 ma knob settings. All the knob does is move the decimal point. .008 ma is correct for 8ma with the knob in that location. If I turn the knob .008 ma changes to .080 ma and .800 ma. This is confusing to me. I have to look at the knob to determine what meter reading really means. It would be less confusing to have 1 knob ma setting.

The $4 Harbor Freight meter is less confusing. I still favor my 40 year old meter.