A friend of mine has pignose amp at his vacation home, but only uses it once a year, so every year the lead battery is dead. I decided to replace it by 4 lifepo4 cells 32650 5Ah each. I added an UVLO based on a seiko voltage detector chip at 1.3uA, with a big fet, and active balancer based on the ETA300 chip, good for 2uA standby.
parts:
ABLIC (seiko) : S-80851CLY-B2-U voltage detector 5.1V mouser or digikey
TE Connectivity .250 FAST TAB various suppliers
parts:
3.2V 32700 6500mAh LiFePO4 Battery aliexpress
1.2A Li-ion Lifepo4 Lithium Battery Active Equalizer Balance Board 4S aliexpress
IRFB7440PBF Nchfet 40V 120AABLIC (seiko) : S-80851CLY-B2-U voltage detector 5.1V mouser or digikey
TE Connectivity .250 FAST TAB various suppliers
the schematic is depicted below. I have used the stackable battery retainers, in an 1x2 format , similar to this 2x3 plastics.
the voltage detector trips on a double cell voltage such there is sufficient drive for the fet. The undervoltage threshold is thus set to 2.55V per cell, giving many years of storage without charging. the cellbalancer maintains that all cells have the same voltage.
the voltage detector trips on a double cell voltage such there is sufficient drive for the fet. The undervoltage threshold is thus set to 2.55V per cell, giving many years of storage without charging. the cellbalancer maintains that all cells have the same voltage.
Attachments
How is your friend going to charge his new lithium battery?
Please do not let him plug in his old lead-acid battery charger. 😱 That is very dangerous, unless you've added safe lithium charging circuitry. Maybe you did, but I didn't see anything about it in your post.
You need a lithium-compatible charger, that is designed to limit maximum charging current to a safe value, and that is also designed to prevent the pack from ever charging to more than more than 16.8 volts DC. (Limiting charge to 16.4V or even 16.0 V is safer.)
Without a properly designed lithium-compatible charger, there is a high risk of fire, caused by charging the battery too fast, or too far.
Lithium fires are very hot, and very dangerous. Many homes and garages and cars have been destroyed as the result of lithium battery fires (Google for "lipo fire" if you don't believe me.) Please don't let this happen to your friend!
I recently built a powered speaker which can run either from an AC wall-wart, or from a built-in a 5S lithium-ion pack. I won't post any construction details on this forum, precisely because of the enormous risk of fire if someone without sufficient knowledge tries to build the same thing.
In many parts of the world, liability laws are now extremely stupid; you can be held legally liable for providing battery charging advice on the Internet, if that advice results in someone burning down their house, garage, car, or even worse, causing injury or death due to the fire. Even if your advice was perfectly correct, and the other person misunderstood, you might still be found at fault in a court of law.
I personally knew three people who burned down their own vehicles to the ground, by ignoring the necessary safety precautions. In the same time frame, I also read about a lot of RC hobbyists who burned down their toys, their garages, and even their homes, by not being sufficiently paranoid about the dangers of lithium batteries, most particularly "lipo" packs. (Hard-cased lithium-ion cells are still dangerous, but less so.)
This warning video might be useful:
-Gnobuddy
Please do not let him plug in his old lead-acid battery charger. 😱 That is very dangerous, unless you've added safe lithium charging circuitry. Maybe you did, but I didn't see anything about it in your post.
You need a lithium-compatible charger, that is designed to limit maximum charging current to a safe value, and that is also designed to prevent the pack from ever charging to more than more than 16.8 volts DC. (Limiting charge to 16.4V or even 16.0 V is safer.)
Without a properly designed lithium-compatible charger, there is a high risk of fire, caused by charging the battery too fast, or too far.
Lithium fires are very hot, and very dangerous. Many homes and garages and cars have been destroyed as the result of lithium battery fires (Google for "lipo fire" if you don't believe me.) Please don't let this happen to your friend!
I recently built a powered speaker which can run either from an AC wall-wart, or from a built-in a 5S lithium-ion pack. I won't post any construction details on this forum, precisely because of the enormous risk of fire if someone without sufficient knowledge tries to build the same thing.
In many parts of the world, liability laws are now extremely stupid; you can be held legally liable for providing battery charging advice on the Internet, if that advice results in someone burning down their house, garage, car, or even worse, causing injury or death due to the fire. Even if your advice was perfectly correct, and the other person misunderstood, you might still be found at fault in a court of law.
I personally knew three people who burned down their own vehicles to the ground, by ignoring the necessary safety precautions. In the same time frame, I also read about a lot of RC hobbyists who burned down their toys, their garages, and even their homes, by not being sufficiently paranoid about the dangers of lithium batteries, most particularly "lipo" packs. (Hard-cased lithium-ion cells are still dangerous, but less so.)
This warning video might be useful:
-Gnobuddy
A solar panel trickle charger may be considered.
There are circuits on the net with 339 or 358 circuits, with presets to cut in and cut out the charge for lead acid batteries.
There are Zener circuits as well.
Best, bring the thing home.
And please, a battery that is used once a year will have corrosion issues.Use it the rest of the year, keep it cycling.
A Tesla caught fire, and basically was dumped in a large tank / swimming pool to contain the Lithium battery fire.
I did not see the above video, but many sober people do not leave them unattended while charging.
There are circuits on the net with 339 or 358 circuits, with presets to cut in and cut out the charge for lead acid batteries.
There are Zener circuits as well.
Best, bring the thing home.
And please, a battery that is used once a year will have corrosion issues.Use it the rest of the year, keep it cycling.
A Tesla caught fire, and basically was dumped in a large tank / swimming pool to contain the Lithium battery fire.
I did not see the above video, but many sober people do not leave them unattended while charging.
sorry , I forgot to mention that I used a special lithium charger for this, and threw his old Pb charger away. the charger takes care of the voltage and currrent to charge. The max load current is determined by the amplifier and the fuse when it fails.
I modified one charger in a UPS application where the charger is always connected to the battery. There the voltage is reduced to 13.8V and only once a month it is increased to 14.6V for 8 hours to reduce fading. I used a silego programmable chip for that.
I modified one charger in a UPS application where the charger is always connected to the battery. There the voltage is reduced to 13.8V and only once a month it is increased to 14.6V for 8 hours to reduce fading. I used a silego programmable chip for that.
Was "lead acid" a typo? Lead acid batteries have fairly simple charge requirements. In fact you can simply trickle-charge them with a power supply with a very high internal resistance, and they will tolerate that sort of crude charging without damage for a very long time.
Lithium batteries, on the other hand, are extremely sensitive to charging. A lead-acid trickle charger connected to a lithium battery is a sure-fire recipe for disaster - you will almost certainly start a dangerous high-temperature fire, along with an eruption of noxious, toxic, and very stinky chemical fumes.
Zener diodes are nowhere near accurate enough for use in a lithium-safe charger. A lithium cell is typically charged to 4.20 volts. But if you charge it to 4.25 volts instead, metallic lithium begins to plate out of the electrolyte. A dangerous high-temperature fire will follow shortly.
Note that 4.25 V and 4.20 V are only 50 mV apart. Yet, the first voltage is safe, the second will cause a lithium fire! The difference is a tiny 1.2% - but that tiny difference is enough to burn down your house.
Let me restate that: An overvoltage of only 1.2% puts you at high risk of a lithium battery fire.
Zener diodes are nowhere near 1% accurate, nor do they have sufficient temperature stability (voltage can change by several percent with temperature changes). You need a much more sophisticated voltage reference, such as a band-gap voltage reference.
These days the usual approach is to use a microcontroller, with a built-in analogue to digital converter to measure cell voltage, and a precision bandgap voltage reference so that the cell can be fully charged, but very precisely, so it doesn't catch fire.
I agree with you on that. Lithium batteries have a variety of failure modes (some have burst into flames simply from being placed on the dashboard of a vehicle parked in direct sunlight on a hot day.) Why risk that in your cabin/vacation home, where you're not even around to stop a fire if it does start?
Agreed. Also, lithium batteries have a finite lifespan - after a few years, they become essentially useless, even if lightly used.
Many Teslas have caught fire. This is another enormous can of worms, which I'm not going to open here...
This is a good safety rule. But if you are in attendance, and a fire starts, what will you do? You need a plan, and a good one. Lithium fires are extremely hot, and spew stinking black smoke, and spray flaming embers around. What will you do if this happens inside your house? You cannot grab the battery without suffering severe burns, you cannot run through your house with a burning battery spraying flaming embers, and inhaling those stinking fumes might cause severe lung damage. So what are you going to do, if you see that fire starting?
This is why I consider this safety rule (never charge a lithium battery unsupervised) a good one, but it is not sufficient by itself.
As I mentioned before, I knew not one, not two, but three men who burned down their own vehicles by charging lithium packs for their RC toys inside their car, unsupervised, against all advice. In each of the three cases, the pack caught fire, the flames immediately spread to the foam seat-cushions, carpet, and plastic dashboard, and the vehicle became a write-off.
In one case the vehicle (an aging Ford Explorer) burned all the way to a stinking bare metal shell. In a second case, a brand new tall-interior Ford van burned so badly the insurance company wrote it off and totaled it. In the third case, the owner of the older Toyota pickup had no fire insurance; after the fire destroyed the passenger seat, half the dashboard, and half the carpet, the owner had a local shade-tree mechanic patch up the burned under-dash wiring, and kept on driving the vehicle. It stank to high heavens, and made your eyes water if you stuck your head into it for a few minutes.
These fires were caused by careless hobbyists. But even the pros - even the pros with good reputations - have struggled with lithium fires. For example, Sony, Samsung, and Boeing have all had major problems with lithium battery fires in products they manufactured. Google will turn up plenty more if you're interested.
-Gnobuddy
ALso worth mentioning is that I used a 5S LIfePO4 battery with a nominal 3.2V/ cell. These are much more resistant to overcharging, and are generally considered much safer than lipo.
I have designed implantable electronics with lithium batteries and wireless charging at 6.78 and 13.56 Mhz. been there... My favourite battery was built by SAFT, and is also favoured by NASA for space applications. This battery has a pressure safety mechanism built in: when the internal pressure rises, the switch disconnects the battery.
Oh, good. Thank heavens. Whew.
That makes the long post I just typed irrelevant to you - but I'm going to leave it alone, as a warning to other hobbyists who might want to build their own lithium battery packs, without a full understanding of just how @#$%^&! dangerous this can be.
One more suggestion: if that Pignose is going to be left unsupervised for nearly a year at a time, please tell your friend to just bring it home with him. If he absolutely must leave it unattended, tell him to store it in a fire-proof container, with nothing flammable within at least fifteen feet in any direction, including upwards. The container needs to be able to tolerate a rapid pressure spike without exploding, or opening up in any way. If it does open (lid blows off, say), flaming embers can fly out and start a fire.
Legal disclaimer: nothing that I've written in this post should be construed as safety advice. If you choose to charge or store lithium packs, that is entirely at your own risk. I am not liable for the consequences in any way, shape, or form.
-Gnobuddy
In a previous life, I worked with LiFePO4 M1 cells made by A123 Systems. Those were the safest lithium cells I've ever had the good fortune to use. A famous American cordless tool manufacturer had begun using them in its highest-quality range of power tools, and I used to cannibalize those battery packs to get at the cells I needed.
Those M1 cells charged up to 3.6 volts hot off the charger, but that quickly dropped off to about 3.3 volts/cell, and then stayed near that level until nearly fully discharged.
Unfortunately A123 Systems fell on hard times, got sold off for pennies on the dollar, and never regained their original status.
-Gnobuddy
That ETA3000 active balancer chip only consumes 1uA avg, so less than the already small selfdischarge of lithium cells. I can store that pignose away for 5+ years w/o problems
I did mention lead acid batteries, because the circuit I copied off the net, and made about 100+, was for 14.6 / 13.2 V cyclic charger control. Presets are there for high and low volts settings.
Such a circuit could be adapted to Lithium cells, as an alternate to a IC based unit.
If it was not a long vacation, maybe a laptop battery could have been used if the supply volts matched.
Another option that comes to mind is an IC which is a charge controller for 3.7V cells, that can be used to control chargers in hobby use.
Not possibly suited to 3.2V cells.
Long post, for somebody to learn later.
Such a circuit could be adapted to Lithium cells, as an alternate to a IC based unit.
If it was not a long vacation, maybe a laptop battery could have been used if the supply volts matched.
Another option that comes to mind is an IC which is a charge controller for 3.7V cells, that can be used to control chargers in hobby use.
Not possibly suited to 3.2V cells.
Long post, for somebody to learn later.
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We know that now, but it was not evident earlier in the thread.
While basreflex certainly knows what he's doing, others who find this thread may not. The level of technical knowledge on diyAudio has been declining for years. Many people here are entirely new to electronics.
Which is great, but we need to make sure they get relevant safety information.
Quite true. But reading a long post is much less painful than burning down your house, garage, or car. 😱
-Gnobudddy
I edited out the reference to @basreflex, because he may not like the attention from newbies.
Sometimes I wonder at the knowledge level of the new members, some questions are very low level stuff.
Makes me wonder about the future in general.
Sometimes I wonder at the knowledge level of the new members, some questions are very low level stuff.
Makes me wonder about the future in general.
I have the same concerns. Humanity is in big trouble, in many ways, from our devastated planetary biosphere, to the way our minds and culture are evolving.
One recent small study found that college students can now focus for only 65 seconds before their brains jump to something else. Smartphones have turned normal brains into ADHD brains, unable to focus on anything for long.
A person who cannot focus for longer than 65 seconds, has a lot of trouble learning anything complicated. Anything that's too complex to understand within 65 seconds, will slip away as your mind leaps to something else (probably the latest notification on your smartphone).
In 65 seconds you can understand how to make a peanut butter and jelly sandwich, but not how to, say, bias a JFET, or do volume integrals in spherical coordinates.
In my entire life, I have never managed to learn anything worthwhile in less than 65 seconds. Everything worthwhile took me hours, days, weeks, or months of concentration to understand. Sometimes it took me years of repeated attempts.
The following excellent article by a very good writer is well worth reading, and it's very disturbing: https://www.theguardian.com/science...n-focus-screens-apps-smartphones-social-media
-Gnobuddy
Argument with electrician at friend's house.
He wanted to put a 10A MCB on a 3kW water heater. We are at 220V here.
I basically threw him out.
He came back with a 16A, so I told him FO.
Then he puts a 20A unit, which is minimum for safety long term.
They are same price from 6-32A, and about $3 at most for a single pole. $2 is average.
Idiot, and dangerous.
Said water entered conduit in rain, there are two more storeys above the apartment!
I left, let them break their heads.
Just an example of what I have to put up with...bit of off topic rant, really. But it shows their level of competence, and insistence that they are right.
He wanted to put a 10A MCB on a 3kW water heater. We are at 220V here.
I basically threw him out.
He came back with a 16A, so I told him FO.
Then he puts a 20A unit, which is minimum for safety long term.
They are same price from 6-32A, and about $3 at most for a single pole. $2 is average.
Idiot, and dangerous.
Said water entered conduit in rain, there are two more storeys above the apartment!
I left, let them break their heads.
Just an example of what I have to put up with...bit of off topic rant, really. But it shows their level of competence, and insistence that they are right.
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A friend did the architectural work for a Cyclotron, he designed it so there was no stray radiation, passed inspection at first attempt from the local nuclear inspection agency.
Then the foreigner engineer came (from supplier) and checked, he was chafing under the collar, and he found nothing either.
He had been insisting on some points which the local hospital people said we will bear it if something goes bad, and he was proved wrong.
That is the level of competence I am used to, and here this kid....
Moderators, your call. Not particularly audio related.
Then the foreigner engineer came (from supplier) and checked, he was chafing under the collar, and he found nothing either.
He had been insisting on some points which the local hospital people said we will bear it if something goes bad, and he was proved wrong.
That is the level of competence I am used to, and here this kid....
Moderators, your call. Not particularly audio related.
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One of the nice features of diyaudio is the highly specialized level of the contributors and the patience and willingness to help those who would like to learn. That is what makes this forum special, and we should cherish that.
I agree, but some days you do an eye roll, the person just does not appreciate how competent the advice offered by the teacher(?) is...unwilling to learn.
It is like shouting at a deaf person, and you need to vent...
But yes, we all have had our share of Thank You! as well, because we saw something which was obvious due to our specialized experience.
The forum users do take the advice seriously, and some have, let us say, totally improbable goals in mind.
But it is mostly to be cherished.
It is like shouting at a deaf person, and you need to vent...
But yes, we all have had our share of Thank You! as well, because we saw something which was obvious due to our specialized experience.
The forum users do take the advice seriously, and some have, let us say, totally improbable goals in mind.
But it is mostly to be cherished.
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