Power protection for Ni-Zn battery powered device
EMHmark7
Posts: 93
Hi,
Hi, I am looking for protection on using rechargeable NiZn 4xAA battery packs (nominal voltage is 1.6V for each battery and should not fall billow 1.3V each with possible reverse polarity if too much discharged and would damage life cycle).
I am trying NiZn because rechargeable with a higher voltage than normal rechargeables. It helps because my power regulator already can take about 1.4V an I want 5V for my Propeller QuickStart.
A 4xAA pack gives 1.85V (at full charge) (nominal 1.6V) (1.5V good battery change time before Volt drop) x 4 batteries
So: 7.6V to 6V for the pack.
Protection for both user and device safety.
Anybody has any circuit or component suggestion so it would be safe to use my device?
Right now,
I am looking at PolySwitch that can sustain 300mA at up to 40 Celcius (the app containing a 4D display + an XBEE 1mW needs an estimated 280mA) (this it the remote control side),
but that would safely trip (break the circuit) at even -40C (possible in Canada and in airplane luggage compartments, if batteries left in the device).
TE SMB050F seems a good start 500mA (20C), 430mA (40C), 730mA (-40C) (A bit overdesign, but feel short in the step before (SMD030F) Digikey ASMD050FCT-ND
About an hybrid protection (Both current and voltage) TE LVM2P-035R14431 seems interesting but seems for AC current. I do not know how it behave in DC) Digikey RF2471-000-ND
(it holds 350mA but trips at 750mA, voltage protection is for sparks given the value: 430V, not from normal usage, nor battery source)
I prefer through hole.
Any other suggestion?
Thanks,
Marc
Hi, I am looking for protection on using rechargeable NiZn 4xAA battery packs (nominal voltage is 1.6V for each battery and should not fall billow 1.3V each with possible reverse polarity if too much discharged and would damage life cycle).
I am trying NiZn because rechargeable with a higher voltage than normal rechargeables. It helps because my power regulator already can take about 1.4V an I want 5V for my Propeller QuickStart.
A 4xAA pack gives 1.85V (at full charge) (nominal 1.6V) (1.5V good battery change time before Volt drop) x 4 batteries
So: 7.6V to 6V for the pack.
Protection for both user and device safety.
Anybody has any circuit or component suggestion so it would be safe to use my device?
Right now,
I am looking at PolySwitch that can sustain 300mA at up to 40 Celcius (the app containing a 4D display + an XBEE 1mW needs an estimated 280mA) (this it the remote control side),
but that would safely trip (break the circuit) at even -40C (possible in Canada and in airplane luggage compartments, if batteries left in the device).
TE SMB050F seems a good start 500mA (20C), 430mA (40C), 730mA (-40C) (A bit overdesign, but feel short in the step before (SMD030F) Digikey ASMD050FCT-ND
About an hybrid protection (Both current and voltage) TE LVM2P-035R14431 seems interesting but seems for AC current. I do not know how it behave in DC) Digikey RF2471-000-ND
(it holds 350mA but trips at 750mA, voltage protection is for sparks given the value: 430V, not from normal usage, nor battery source)
I prefer through hole.
Any other suggestion?
Thanks,
Marc
Comments
I have thought quite a bit about this as Ni-Zn are not the only battery chemistry that should have a low voltage cut off to preserve the life of the battery. Lithium ion and NiMH have the same issues and I have already experienced the destruction of one set of Lithium cells on their first use without protection. I do have and use Ni=Zn cells now in my battery operated razor.
In a microcontroller setting, you need a circuit that pull a pin high or low to indicate that the device should shut down for battery replacement. I have fooled around with using a comparator chip and 3.3 volt zener diodes for a 3.7 lithium ion batteries, but never completed the project.
That still seems the best set up to me. The 3.3 volt zener provides a low voltage shut off reference, and the other input is takes in the actual battery voltage that is ranging from 3.7 and lower. When it hits the 3.3 volt mark, the output state changes.
The only trick is to avoid bouncing at 3.3 volt by having code to do an orderly shut down. Another alternative is to have it shut off a MOSfet that feeds power to any device... it doesn't have to be a microcontroller. But if you using a MOSfet, you may have to include a Reset button to restart operation.
I had circuit diagrams, but I will have to dig to locate them.
But you really have two projects combined -- current limiting or current cutout; and low-voltage cutout.
Using a comparator chip does require have it supplied with its minimal voltage; so a source between 3.3 and 5.0 volts must be provided to it.
These chips usually have 4x comparator in a DIP, so you can either insert a cut off for each individual cell (The best for protection against low voltage), or you can do a series.
When you have a series of cells, a peak voltage drain may pull one cell below the damage threshold, while the other cells are not being pulled excessively low. So I would go with checking the voltage levels of each and every cell in a series. And if the comparitor has open-collector or open-drain outputs, I would tie all the outputs together to have one power cutoff via a MOSfet.. unless you want a logic pin to take the signal to start and orderly shut down.
You could power the LM339 chip with two NI-ZN cells in series, but have it sense the low voltage of each cell by using a 1.5 v zener as your reference diode. I have no idea how to do just one cell. Since my electric razor never worked right will alkaline cells, I switched to Ni-ZN and it works quite well with the voltage boost. Fortunately it seems to stall when the cells get to about 1.5 volts, so no added low-voltage cut out is requried.
An LM339 will accept DC power from 2 to 30 volts, so it seems a reasonable solution. http://www.ti.com/lit/ds/symlink/lm339.pdf
For sensing 4 cells you can't just use 4 thresholds, you have to differentially compare on each cell with the same single-cell
voltage, which means 4 resistors per comparator, which is rather complex. Its possibly easier to use one comparator
for the whole stack and set a conservative lower cut-off. This will increase the life of the pack too I think.
But it seems to get harder as you add more cells to the series. I am tempted to quit at 4 cells in series. And I would prefer not using this scheme if you have extreme instantaneous loads. I suspect that in some situations -- ike R/C airplanes -- the temporary extreme loads are likely to pull one cell down below the safe discharge before the others.
Thanks for the comment about needing a better resistor grid. It is a bit of a nusance to build, but resistors are cheap.
I mentioned in another thread that there are linear voltage regulators with an Enable input. In some cases, the cutoff can use that instead of a MOSfet.
And I really do like the Ni-Zn batteries. For the classic Parallax BOE-bot, they are an excellent recharible cell. Having to switch to a 5-cell battery holder for Ni-Cd recharibles is a bit annoying.
The issue is the same with NiZn, NiMH, and Lithium cells. It seems that all of these are permanently damaged by discharging below a certain voltage.
To avoid the problem, it seems that either Lead acid or NiCad work well.
++++++
The LTC1515 apparently delivers on 50ma of current. I am concerned with loads that might be drawing 5 amps or more in short bursts. Besides, it doesn't protect the battery at all.
They can be damaged or have their life reduced if we discharge them billow 1.3V (manufacturer says 1.1v but wikipedia says1.3V. but these batteries have a long lasting curve above 1.5V, so my limit will be 1.5V)
So, we need to monitor the battery voltage, I am designing it now, based on a MAX1242 AD converter with a voltage divider. about 8-9$ but can work on 3.3v logic.
It will display onscreen the voltage.
The discharging curve for NIZN is flat for a long time before 1.5V (If the data source is sincere...)
I do not know if those more popular in commerce have the same.
If so, in the future, I will maybe use them but put more battery slots in the device in order to have a higher voltage.
But of course, the device is heavier and needs more batteries.
You really have to look at the tails on the manufacturer's curves for your battery chemistry. Wikipedia might say 1.3 Volts and someone else might say 1.5 Volts. I would tend to go with the 1.495 volts as the amount of extra use in the drop from 1.495 to 1.3 is very little while the risk of damage increases greatly. (Keep on the flat portion of the curve as both tails have damage hazards that increase rapidly).
Yes, you can use a MAX1242 AD converter with a micro-controller, but it is a lot of coding for what is essentially a analog cutoff problem. I just want to keep the micro-controller free for other things.
Coding is not a problem, I will write mine this week and can share. We do not need to run it every mseconds, but maybe every sec or every 5-10 sec.
Then, we display the values and we decide when we want to turn OFF. I liked the idea to monitor the behavior of discharge for my specific device, so I endup knowing how it behave.
A possible idea is to log instructions and voltage values. Then we can know exactly power consumption for possible estimations. Of course, it would be better having a thermometer too.But we can just take note of ambiant temp when we logged data.
Other chips were less expensive but seemed not designed to work for 3.3v logic.
It is also less connections.
Doc seems more complicated to understand and not clear we can end up with 3.3v logic.
MAX1242 has its own internal reference at 2.5V, maybe more precise but we are limited to that voltage if we use the internal ref.
All in all, not sure I miss something that justify the big price difference.
There is a lot of coding options when you have 8 ADC inputs on one chip.
Parallax sells it because it can work with either 3.3vdc or 5.0vdc logic without worrying about extra wiring.
The voltage range cannot exceed the power supply, so a Vref would have to be less than or equal to Vcc of either 3.3v or 5.0v (the full range is from 2.7vdc to 5.5vdc0.
An internal voltage range is an interesting feature. Sometime a precision external voltage reference is used as zeners tend to have a larger range of error (One has to test a pile of zeners to know exactly the reference voltage they will provide. I have some that are rated 3.1-3.3 volts. They could be anything between.
Neither the MAX1242 or the MCP3208 is a bad solution, just different.
Thanks,
Marc
Rigns a bell to anybody?
Thanks
Marc
Sounds to me like that cell is dead.
Edit: Not knowing anything about these batteries I did a quick google around. All the first reviews I come across basically say that these Ni-Zn batteries are pretty useless and don't bother with them. Including the PowerGenix. I might be tempted to try them out if they came from a known brand like Panasonic. Or the Turnigy AA Ni-ZN 1500mAh cells from HobbyKing perhaps.
Ring a bell? Yes, this certainly does.
There seems to be an inherent problem with putting cells in series to gain a higher voltage. Due to the dynamics of internal resistance, they don't discharge equally and one cell may be the first to drop below a safe discharge threshold. So you see the closest to negative (-) suffering damage.
Presuming that it is always the same cell that fails first, one can monitor the voltage of just that cell as the one that would indicate a shut-down for recharge. But I have doubts that will always be reliable.
The problem grows more complex with the more cells you put in series and the ability to start out with a completely matched set of cells is dubious. Also, if you have dramatic loads, such as high amperage motor drains; the hazard is greater.
What to do?
A. Create a system that monitors the voltage of each and every cell in real-time for protective shut down. Don't rely on a total voltage for a cut off.
OR
B. Revert to older battery technologies, such as NiCd, that can tolerate excessive voltage drops.
OR
C. Combine at least parallel pairs of cells with series of cells. In that way, the parallel cells may just protect each other from excessive discharge.
~~~~~~~~~
Li Ion, NiMh, and NiZn seem to have exploited thin films that coat their anodes and cathodes to enhance their performance. It is these thin films that fail drastically when discharged below a certain level and then will never recover. So avoiding the thin films seems the easiest solution.
BTW, I just wasted yet another pair of 16550 Li-Ion cells by excessive discharge. It only takes one excessive discharge to turn them to junk. I have been lazy with figuring out how to provide a low-voltage cut-off when using these. After all, it is a lot of extra circuitry. But I finally have decided that I will deploy voltage regulators with an extra Enable pin that shuts off the battery when a certain low voltage level is used. I think I can get by for 2 cells in series by a total low voltage cut off. I certainly wouldn't try this with 4 cells in series.
It seem pretty obvious that much of the Li-ion success is based on cellular phones only using single cells. Mutiple cells raise a lot of issues. My notebook computers have all used at least 2 Li-ion cells in parallel when they are also configured in series. So that seems to be a necessary protective configuration.
Yep, been reading about the problems of series LiPo cells and others all around the net.
I have no idea what they do on Tesla battery packs but there is a guy in the states who will do an electric conversion of your gas car for 10 or 20 thousand dollars. He describes that development of his battery back. A huge lot of cells in series producing 700v or so. Every cell has a chip monitoring it's voltage, they all communicate back to a controller via a bus, fibre optic for voltage isolation.
It's amazing what you have to do to make a reliable battery of cells like that. Even battery chargers for LiPo batteries used in R/C cars and planes monitor each of the cells in a battery pack when charging.
Seems good quality batteries avoid these series problems in most use cases well enough. Assuming they are not totally abused.
On a whim I bought my first ever NiMh battery pack recently. 5 cells, 6 volts, 1600mAh. The charger for it does not even bother measuring individual cells. I was just curious to see how it goes.
Ya, My intent is to trow away the NiZN Powergenix batteries.
Up to now, my strategy was to put a Maxim MAX1242 ADC and read each battery pack voltage and display their values on the remote control, with a psychological treshold of somewhere above 6V (1.5V) because 1.5V is the end of the horizontal flat discharge, before it drops fast. But seems that it is always the last battery in the pack that falls without notice!
I see the MAX1242 giving fluctuating values (maybe because of my design or other sources of fluctuation, even though this chip has its own internal reference). It passes through a voltage divider 1/3 because it should mesure max the reference 2.5V, for reading expected 1.9V (niZN max 1.84v) x 4 batteries, about total 8V.
Then my idea for future design was to put only one ADC and through an analogic multiplexer, monitor each battery of the pack or only concentrate on the last one.
But reading the web, seems that the problem is the most charged batteries pass through the weakest and even generate Hydrogen gaz. So, does not sound good. That is why, my strategy now, was to go back to more commercialy available rechargeable batteries, and put packs of 6x1.2V.
So, some people say these batteries are only good for application with less than 2 batteries.
And, Powergenix seems to have stopped manufacturing these AA and is not responding to my email, although they did in the past.
I do like them.
A. They will allow the classic Parallax BoeBot to perform well on 4 rechargeable AA cells.
B. My AA battery electric razor works much better with the Ni-Zn than it ever did with other AA cells.
But I am fully aware that somewhere down the line, I will likely slip and discharge too much. This 'sudden death' of costly batteries is quite annoying.
I suspect that proper management will require Both and early warning of low battery and a complete cutoff circuit. The biggest problem with the early warning feature is that the discharge curve is extremely flash, so one might have to measure millivolt differences to decide an optimal point. For instance, 1.49 volts might not be good enough, you might have to shut off at 1.495 volts and have and early warning at 1.498 volts. Tedious stuff.