incarcator acumulatori defect?

[Vizitator]

Sa traduca cineva de la

http://batteryuniversity.com/learn/arti ... _batteries

 

Full-charge Detection by Temperature

Full-charge detection of sealed nickel-based batteries is more complex than that of lead acid and lithium-ion. Low-cost chargers often use temperature sensing to end the fast-charge, but this can be inaccurate. The core of a cell is several degrees warmer than the skin where the temperature is measured, and the delay that occurs causes over-charge. Charger manufacturers use 50°C (122°F) as temperature cut-off. Although any prolonged temperature above 45°C (113°F) is harmful to the battery, a brief overshoot is acceptable as long as the battery temperature will drop quickly when the “ready” light appears.

 

With microprocessors, advanced chargers no longer rely on a fixed temperature threshold, but sense the rate of temperature increase over time, also known as delta Temperature over delta time, or dT/dt. Rather than waiting for an absolute temperature to occur, this method uses the rapid temperature increase towards the end of charge to trigger the “ready” light. The delta Temperature method keeps the battery cooler than a fixed temperature cut-off, but the cells need to charge reasonably fast to trigger the temperature rise. Charge termination occurs when the temperature rises 1°C (1.8°F) per minute. If the battery cannot achieve the pace of temperature rise, an absolute temperature cut-off set to 60°C (140°F) terminates the charge.

 

Chargers relying on temperature inflict harmful overcharges when a fully charged battery is removed and reinserted. This is the case with chargers in vehicles and desktop stations where a two-way radio is being removed with each use. Every reconnection initiates a fast-charge cycle that raises the battery temperature to the triggering point again. Li‑ion systems have an advantage in that state-of-charge is being detected by voltage. Reinserting a fully charged Li-ion battery pushes the voltage to the full-charge threshold, and the charger turns off shortly without needing to create a temperature signature.

 

 

 

Full-charge Detection by Voltage Signature

Advanced chargers terminate charge when a defined voltage signature occurs. This provides more precise full-charge detection of nickel-based batteries than temperature-based methods. Monitoring time and voltage, a microcontroller in the charger looks for a voltage drop that occurs when the battery has reached full charge. This method is called negative delta V (NDV).

 

NDV is the recommended full-charge detection for “open-lead” nickel-based chargers. “Open-lead” refers to batteries that have no thermistor. NDV offers a quick response time and works well with a partially or fully charged battery. When inserting a fully charged battery, the terminal voltage rises quickly, and then drops sharply to trigger the ready state. The charge in this case lasts only a few minutes and the cells remain cool. NiCd chargers based on the NDV full-charge detection typically respond to a voltage drop of 10mV per cell.

 

To obtain voltage drop of 10mV per cell, the charge rate must be 0.5C and higher. Slower charging produces a less defined voltage drop and this becomes difficult to measure, especially if the cells are mismatched. In this case, each cell in a mismatched pack reaches the full charge at a different time and the voltage curve flattens out.

 

Failing to achieve a sufficient negative slope would allow the fast charge to continue. To prevent this, most chargers combine NDV with a voltage plateau detector that terminates the charge when the voltage remains in a steady state for a given time. For additional safety, most advanced chargers also include delta temperature, absolute temperature and a time-out timer.

 

NDV works best with fast charging. A fast charge also improves charge efficiency. At a 1C charge rate, the charge efficiency of a standard NiCd is 91 percent, and the charge time is about an hour (66 minutes at an assumed charge efficiency of 91 percent). A battery that is partially charged or has reduced capacity due to age will have a shorter charge time because there is less to fill. In comparison, the efficiency on a slow charger drops to 71 percent. At a charge rate of 0.1C, the charge time is about 14 hours.

 

During the first 70 percent of charge, the efficiency of a NiCd is close to 100 percent; the battery absorbs almost all energy and the pack remains cool. NiCd batteries designed for fast charging can be charged with currents that are several times the C-rating without much heat buildup. Ultra-fast chargers use this quality and charge to 70 percent in minutes. Read more about Ultra-fast Chargers. The full charge must be done with a reduced current

 

 

 

Ultra-high-capacity NiCd batteries tend to heat up more than standard NiCds when charging at 1C and higher, and this is partly due to the higher internal resistance. Applying a high current at the initial charge and then tapering to a lower rate as the charge acceptance decreases achieves good results with all nickel-based batteries. This moderates excess temperature rise while assuring fully charged batteries.

 

Interspersing discharge pulses between charge pulses is known to improve charge acceptance of nickel-based batteries. Commonly referred to as a “burp” or “reverseload” charge, this method assists in the recombination of gases generated during charge. The result is a cooler and more effective charge than with conventional DC chargers. There is also the believed benefit of reduced “memory” effect, as the battery is being exercised while charging with pulses. Read about Memory: Myth or Fact? While pulse charging may be valuable for NiCd and NiMH batteries, this type of charge does not apply to lead- and lithium-based systems. These batteries work best with a pure DC charge voltage.

 

After full charge, the NiCd battery receives a trickle charge of between 0.05C and 0.1C to compensate for the self-discharge. To reduce possible overcharge, charger designers aim for the lowest possible trickle charge current. Even though the trickle charge is carefully measured, it is best not to leave nickel-based batteries in a charger for more than a few days. Remove them and recharge before use.

 

Charging Flooded Nickel-cadmium Batteries

The flooded NiCd is charged with a constant voltage to about 1.55V/cell. The current is then reduced to 0.1C-rate and the charge continues until 1.55V/cell is reached again. At this point, a trickle charge is applied and the voltage is allowed to float freely. Higher charge voltages are possible but this generates excess gas and causes rapid water depletion.

[validae]

E frumos ce scrie acolo....repet, cate incarcatoare fac asta....si cat costa unul care tine cont de toti parametrii aia, sa fim seriosi...Cat dai pe un incarcator din ala supermegadestept, cumperi acumulatori toata viata. Am acumulatori de vre-o 5-8 ani si nici macar nu-s de cine stie ce firma.I-am incarcat si cu un incarcator cu decuplare la tensiune maxima Varta (fara detectie de temperatura) si cu incarcator simplu, cu limitare prin rezistienta (fara cc).

Cred ca nu m-au costat toti acumulatorii cumparati pana acum, cat am dat pe acel incarcator ,,destept,, la vremea lui. Cu mintea de acum, n-as mai da atatia bani pe un incarcator supermegadestept, mai bine as cumpara acumulatori de banii aia.

[Vizitator]

Eu am postat din alt motiv: de cate ori cineva deschide un subiect tangential cu incarcarea acumulatorilor apar noi intrebari, noi "teorii', sfaturi ciudate date de pe genunchi.

Am mai spus, fiind o mana de oameni ce raspundem, hai sa incercam ceva unitar, un loc unde sa fie trimisi noii doritori care nu au reusit prin functia cautare sa gaseasca raspunsul.Si abia apoi ajutati daca problema lor este speciala.

Nu am pus documentul ca sa faca un incarcator inteligent ci sa inteleaga complexitatea abordarii si apoi sa aleaga varianta ce i se potriveste.

Scrie apoi despre incarcarea in pulsuri cum am inteles ca are si incarcatorul din poza.Deci ei cam respecta teoria.

Si apoi cunoscatorii sa mai lamureasca un lucru: cineva afirma ca incarcarea in impulsuri este indicata la acum. cu plumb.Parca aici scrie ca incarcarea in curent continuu este cea mai indicata.

 

Interspersing discharge pulses between charge pulses is known to improve charge acceptance of nickel-based batteries. Commonly referred to as a “burp” or “reverseload” charge, this method assists in the recombination of gases generated during charge. The result is a cooler and more effective charge than with conventional DC chargers. There is also the believed benefit of reduced “memory” effect, as the battery is being exercised while charging with pulses. Read about Memory: Myth or Fact? While pulse charging may be valuable for NiCd and NiMH batteries, this type of charge does not apply to lead- and lithium-based systems. These batteries work best with a pure DC charge voltage.

[ilzul]

Referitor la aceasta discutie, si eu am un incarcator gp powerbank si 4 acumulatori NiMh tot gp de 2500mA...In carticica incarcatorului scria ca are decuplare la terminarea incarcarii. Se pare ca nu a fost asa , tot la fel i-am lasat si eu destul de mult timp nefolositi, dupa care i-am pus la incarcat (probabil mult mai mult decat trebuia, in jur de 16 ore sau mai mult iar la scoaterea din priza erau cam fierbinti ) si am constatat faptul ca nu mai tineau aproape deloc - respectiv faceam cam 10 poze maxim (cu un aparat digital).De curand (acum vreo 2 saptamani) i-am descarcat complet, folosind un bec de 12 volti, pana la o tensiune de ~1V dupa care i-am lasat la incarcat din nou 11 ore... Se pare ca de data asta au tinut mai mult .Ce ar fi indicat sa le fac? Momentan zac pe birou (pentru ca nu prea ma mai omor cu pozatul). Se pare ca trebuie sa folosesc incarcatorul impreuna cu temporizarea de la telefon (ceas), respectiv undeva la 12 ore de incarcare (curentul aparatului fiind undeva la 220mA).

[validae]

El poate o avea decuplare la un timp prestabilit pentru un anume tip de acumulator.Daca acumulatorii tai sunt de capacitate mai mica, incarcatorul decupleaza prea tarziu, supraincarcand acumulatorii.Am avut si eu unul care decupla temporizat si astfel putea sa incarce numai un tip de acumulatori, de o anumita capacitate.

Am cumparat apoi un incarcator Varta cu curent setabil de incarcare si decuplare la atingerea tensiunii maxime (fara masurarea temperaturii) pe care am dat o gramada de bani la vremea aia. Dar incarcatorul cel mai folosit de mine e unul simplu fara niciun control sau decuplare.Are un curent redus de incarcare si-l las la incarcat pana cand acumulatorii sunt calduti.Un timp verificam tensiunea din cand in cand, dupa aceea m-am obisnuit sa-i testez doar dupa temperatura ca sa stiu cand sunt incarcati. Si in telecomenzi am tot acumulatori

[turcu_dan]

Cu ce curent ii incarcati ? Cat % din capacitatea bateriei?

[validae]

10% maxim 20% din capacitatea acumulatorului, dureaza mult mai mult decat ,,quick charge,, dar dorm fara grija.Pusi la incarcat de obicei seara, dimineata sunt gata.

[ilzul]

El poate o avea decuplare la un timp prestabilit pentru un anume tip de acumulator.

Treaba este ca mi-am bagat nasul in el si e un circuit destul simplu in interiorul carcasei.

Are un transformator, 2 diode pentru redresare, 2 diode zener, 4 rezistoare, 2 leduri de stare (am uitat sa precizez ca se pot incarca doar cate 2 baterii).

Deci, din cunostintele mele nu poate fi vorba de nici un fel de circuit de siguranta in caz de supraincarcare .

Hmm, sau respectivele diode zener sa fie "trucul" ?

 

 

Cu ceva timp in urma ma gandeam si eu sa cumpar un incarcator "super destept" dar cum spuneti si dumneavoastra, mai bine cumpar acumulatori si ies mai ieftin .

[validae]

Nu are nicio decuplare din ce ai descris.Supravegheaza temperatura acumulatorilor si va fi bine, sa fie calzi nu fierbinti

[turcu_dan]

Am gasit un set de accu sony 1700mA pe care incarcatorul se pare ca-i accepta, - a durat aprox 45 min incarcarea. Pe cei vechi i-am incarcat separat la un curent de 1/10 din capacitate pana au fost putin calduti. Daca nu tin inseamna ca sunt de aruncat? Exista posibilitatea sa-si revina dupa 2-3 cicluri?

[validae]

Depinde, uneori isi revin, alteori...