Prevening the NiMh overcharge or discharge with a LiIon or LiPo Protection Circuit

[nuambenzina]

As regarding NiMh and Solar Panels I have some questions in my mind and I can not find the answer by myself, and I had browsing the web from about 6-8 moths now for nimh+solar panels comobo, circuits, devices, but I haven’t found the answers to my questions.
If you know the answer, please have patience to write a reply…
Thank You in advance!

Using Solar Panel, NiMh battery and PCB from Li-Ion/LiPo


As I know, Li-Ion, Li-Po, LeadAcid, PbGell, charging relays/charging controllers are using Voltage to Stop the battery from overcharging. For example the Auto Relay for the car battery and the Protection Circuit from the Li-Ion/LiPo.

But, on the NiMh I saw that the controlling the charging and overcharging, is more difficult as the relay/charging controller/charger is NOT using the Voltage but, instead is using one or a combination of these:
- Time Control
- Temperature control
- Minus Delta V -Δ v
- Microprocesor for different stages of charging, discharging etc.

Note: *In all the charging process I have left out the charging rate as I don’t know how to calculate it or what the parameters for various chemistry are.

I have these question in my mind am curious about:

1) (A & B & C)

What will happen If the Voltage will be used to stop the charging and potect the NiMh being overcharged instead of time, Minus Delta V -Δ v, or temperature control?
Are they kind of / in some degree protected?

1.A)

Using 3 Nimh in series with a Li-Ion Protection circuit, On small solar panel, they will slowly absorb power and will be overcharged and damaged or will be like trickle charging? What about on a bigger solar panel?
A Li-Po/Li-Ion protection circuit will be better than nothing? Will this work, or will be this like a “semi-protection”, or will not work at all?
The nimh will be overcharged in this combination if will be left in the sun long periods of time and no consumer?
How it will perform on a solar panel rated at 5-6V with output of 110mAh-400 mAh (0.6-1.8 Watt), a Zener diode IN5819, the Li-Ion Protection circuit on a 3 AAA NiMh 1.2V @ 500 mAh cells in series ( 1.2V x3 = 3.6V @ 500 mAh, 1.8 W)?
But how about if the solar panel will be 4.8V and 10 mAh?

1.B)

What will happen if I will use 3 NiMh Cells in series with a Li-Ion Protection circuit when the charging current can be from 10 mAh to 10Ah? As the protection circuit will cut of at 4.2 Volt, will the NiMh be overcharged? Are they kind of / in some degree protected?
I can have a pack with 3 cells of 1.2V connected in series, protected by a LiIon/LiPo , and various power sources like:
- Transformer from the grid 5V 10 Ah
- Transformer from the grid 5V 550 mAh
- Transformer from the grid 5V 1A
- Transformer from the grid 5V 2A
- Usb devices like a Laptop, Pc, etc. 5V, 500-1000 mAh
- Usb Chargers with output of 5V 150 mAh
- Various solar panels of 5V-6V @5mAh, 10mAh, 30mAh, 100mAh, 900mAh, or even 6000 mAh (6Ah)

1.C)

If there is a need to charge and discharge NiMh individually and not in pair (2,3,4 pieces in series) Can they be protected in this way?
The power supply can be a Solar Panel+diode which charge more NiMh’s that are connected in parallel, and left there for an undefined period of time, with various size like AA, AAA, C, D, ranging from 100 to 8000 mAh and there could be a protection circuit on every one cell of NiMh, which will disconnect the current within the range of 0.7V-1.4V for preventing the over-discharge and over-charging.
I have found some circuit which disconnects the nimh battery when it reaches at 0.7V somewhere on the internet but I can’t remember or find it again anymore, as regarding the 1.4V limit maybe something like Zener diode will help.

>>>>>><<<<<<

Thoughts:
-The characteristic of one cell of NiMh is rated at 1.2V.
But… in reality while being charged the voltage grows up and up and up then will drop a little bit (this is the mechanism of –delta V method). As I have seen the most of fully charged NiMh have a voltage of 1.4 or 1.5 Volt right out of the grid charger regardless it is a fast, smart, overnight charger, but the fully charged voltage may vary a little bit depending of manufacturer or the cell itself. As regarding discharging they could be fully discharged and they will be harmed by deep-discharging, but will not be so severe as in Li-Ion.
-The characteristic of one cellphone Li-Ion/Li-Po cell is rated at 3.7V.
But… in reality while is empty it is at 3.0V and while full charged is at 4.2 V. The Cellphone battery has an Protection circuit on it for protecting the battery which is cutting the current between the limit of 3.0V and 4.2V.

>>>>>><<<<<<

Now, If I have 3 NiMh (AAA, AA, C or D) connected in series I will have: 1.2V x 3 = 3.6V
The same rated voltage like a LiPo/Li-Ion!
While 3 NiMh fully charged connected in series is about
1.4V x 3 = 4.2 V
The same Voltage like a fully charged LiPo!

>>>>>><<<<<<

Figure 1

Figure 2

Figure 3



2) (A & B)

2.A)

How come that all of the Ni-mh solar charger are with NO overcharging circuit? Browsing the web after nimh solar charger I have found a big diversity of NiMh+solar combo (with warious cell number as 1,2,3,4,6 or 8 etc. with size of nimh battery AAA, AA, C, D, different solar panels with different rated power etc.) but I have NOT seen a overcharge protection circuit on them, why? If I will left the device in sun with no consumer for a year for example, the NiMh battery will be overcharged and damaged this way, right?
2.B)

Even more, I have not seen a device with an “anti-full discharge protection circuit” for preventing reverse polarity or the NiMh battery life. As I understand the NiMh battery life will be longer and will have more recharge cicles if it will be not discharged at the full capacity, and some juice will be lefted in.

Examples:
- Varta NiMh Solar Charger, no Overcharge Ciruit

- Raspberry-pi SolarPowered NiMh, no Overcharge Circuit

- Various Home Made / Do it yourself Nimh solar chargers


- Various Solar Garden Lamps

(I understand that on the solar garden lamps, there has to be some calculation like the solar panel will charge the battery during the day and the led will discharge the battery during the night, but if the led will be removed then the NiMh cells from the solar garden lamp will overcharge in time and will be damaged)

[Sunking]

You are making this more complicated than it needs to be.

NiMh and NiCd are the hardest batteries to charge, unlike lead and lithium batteries is all you need is to regulate voltage to the float level. NiCd and NiMh voltage is irrelevant. For the nickel batteries what you control is the current, and voltage is unknown. The voltage just has to be high enough to push the required current.

Now with that said it is very easy to charge NiMh and NiCd using solar as long as observe a few rules. The most important thing is to keep the charge current at C/10 or less. If you do that, you can leave a NiMh or NiCd on a charger forever. Go above C/10 and now you need some smart control electronics to determine when the battery is charged up by either a delta bump in voltage or by a sudden rise in temperature.

So armed with that lets say you have a 1 AH NiMh battery. To charge it easily is just select a solar panel that has a Imp of 10 ma or less. The only circuitry you need is a simple diode to prevent the battery from discharging itself through the panel if left on overnight or a passing cloud.

The lonly other rule to observe is that the panel has a minimum Vmp of 2 volts for each NiMh cell being charged in series. Never Ever Charge NiMh or NiCd in parallel, only series. So lets say you have 6 NiMh 1 AH cells. You are looking for a panel with an Imp of of 10 ma or less, and a Vmp of more than 12 volts. To make my point lets say you find a thin film panel with an Imp of 10 ma, and a Vmp of 100 volts would work just fine. Such a panel can charge as little as 1 cell at a time, or as many as 50 cells and any number between 1 and 50.

How when you know the batteries are charged up? When they start to feel warm. If you forget and leave them on a week no problem as long as you keep the charge current at C/10 or less.

[inetdog]

So armed with that lets say you have a 1 AH NiMh battery. To charge it easily is just select a solar panel that has a Imp of 10 ma or less. The only circuitry you need is a simple diode to prevent the battery from discharging itself through the panel if left on overnight or a passing cloud.

That would be C/100, which would be unconditionally safe, but would take several weeks to recharge a totally drained battery.
A current of 100 ma would be more practical, or if you wanted an even better safety margin 50ma. Under some really unusual circumstances a panel can produce more than its rated I_MP.

[Sunking]

That would be C/100

Good catch my bad. Still doped up with meds. I meant C/10 or less so for 1 amp at C/10 is .1 amps.

[nuambenzina]

Thank you for reply! The answers unloads the questions that where on my mind && give birth to others.

My main target is to have an automatic light powered by NiMh which are recharged by small solar panels.

I already have the consumer, an Osram with 3 white led of 5mm with sensor (motion detection, dark detection).

The sensor is draining very slowly the alkaline batteries, and for this I have replaced the 3 alkaline which is using of 1.5V (in series 4.5V) with 3 1.2 NiMh (3.6V) and is accepting the NiMh very well.

But I have to get the NiMh out and put them in the charger every time they are depleted.

And on other way / point of view it will be nice to have at hand an always full and ready to use pack of 3 NiMh for replacement for my headlamp. But this is not a must, the osram-sensor-nimh-solar is a must.

So, what I wish to archive is:

1. Primary: To have the Osram Light connected to a powerbank of 3 in series NiMh, which is recharged every day by small solar panels. I have some good nimh of AA or AAA size with different mAh ratings, eventually I could buy C or D size nimh in time.

2. Secondary: It would be nice if I can power the Osram Led device by a Pack composed by 3 AA/C/D because AA/C/D has more mAh, as sometimes (like now) I have full weeks of clouds.

So, this will be a pack.

The second pack, I would like to keep charged and always ready to use, is composed from 3 AAA.

Because I need an always ready to use 3 NiMh of smaller AAA for replacement, always be ready to use, fully charged for my headlamp which is using 3 smaller AAA.


Consumer:



Scheme:





3.
If the Li-Ion is worthless to use Then can voltage be used to (detect), but to stop the over discharge / prevent the reverse polarity?
If so, what will be a good value per cell, 0.5, 0.7, 1V?

4.
a) How to calculate the charging rate? What is the forumula of calculation?

b) So, a charge rate at C/100 safe to slow charge NiMh but continuous,

But can I go with the charge more than a week like full year (one year)?





5. What does it mean:
a) “a solar panel that has a Imp of 10 ma or less” I don’t understand what Imp is meaning
b) “rated IMP” this is “input/impedance on square meter?”

1. a) “Never Ever Charge NiMh or NiCd in parallel, only series.”

Why is not oky to charge nimh in parallel? Is this because of the balancing of the cells?

This solution is fine for charging/discharging a 3 in series 2 in parallel nimh?

If I make two packs one pack from 3 nimh in series, the other pack from 3 nimh in series, then wiring them in parallel but using two blocking diodes for prevent one pack to charge the other one in the case the one will be weak over the time or in the case that one is composed by AA and the other one composed by AAA.





b) Is there something wrong if I connect different solar panels in parallel and using diodes? For example:
one solar panel is making 4.5 V in shadow @ 5 mAh, and 6 V @ 10 mAh in full sun
the other solar panel is making 3 V in shadow @ 10 mAh and 5 V @ 130 mAh in full sun
Now, I wire them in parallel, connecting the (-) / ground and on each + positive terminal to have a blocking diode, after the diode to connect the (+) from the panels.

[inetdog]

Thank you for reply! The answers unloads the questions that where on my mind && give birth to others.

The .5 volt panel (actually a single cell) will do you no good at all connected in parallel, and the forward voltage drop of the blocking diode could well be more than .5 volts.
You could put that high current cell in series with the parallel combination of the other panels to add .5 to the output. Other than that is is useless to you.

[nuambenzina]

The .5 volt panel (actually a single cell) will do you no good at all connected in parallel, and the forward voltage drop of the blocking diode could well be more than .5 volts.
You could put that high current cell in series with the parallel combination of the other panels to add .5 to the output. Other than that is is useless to you.

I assume that you are reffering to point 1&2, first and second picture.

There could be a 6.8 V panel with Schotty diode In 5819 (400V / 1 A) so the voltage output after the solar cell plus diode will be 6.4-5V