| Author |
Message |
Guest
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 Posted:
Tue Dec 06, 2005 12:59 am Post subject:
Battery voltage as indicator of charge level |
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Is no-load voltage a reliable indicator of charge condition ? Are there
universal voltage levels for a particular type of cell (e.g. NiCd,
NiMH, Li-ion, lead-acid, etc.) that can be taken to indicate
full-charge and full-discharge conditions ?
There are gadzillion articles that discuss the general characteristics
of various types of rechargeable cells, but I have not found any that
specifically says that an X-type cell reaches Y Volts at full charge,
and should not be discharged below Z Volts.
Is it at all possible to specify voltage levels this way ? Temperature
and internal resistance (and therefore charge and discharge currents)
must play a part, but standard voltage levels under no-load,
no-charging at standard room temperature would be very helpful.
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PeteS
Guest
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| Posted:
Tue Dec 06, 2005 1:36 am Post subject:
Re: Battery voltage as indicator of charge level |
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pjdd@rediffmail.com wrote:
| Quote: | Is no-load voltage a reliable indicator of charge condition ? Are there
universal voltage levels for a particular type of cell (e.g. NiCd,
NiMH, Li-ion, lead-acid, etc.) that can be taken to indicate
full-charge and full-discharge conditions ?
|
Lead Acid battery noload terminal voltage can be used as an indicator
of charge level (See other comment above). Other cells are not quite as
easy.
Li+. Fully charged : 4.2V per cell. Discharged 3.0V per cell (nominal).
Nominal cell voltage: 3.7V. There are charts available, and maybe I'll
dig out the links tomorrow at work. Fairly linear, but as with NiMH
somewhat susceptible to ambient conditions.
NiMH. 1.2V per cell. More difficult, but 1.1V is nominally discharged,
1.3V (roughly) is fully charged. Fairly linear betwen these especially
for the 20-8% range. Varies somewhat, see the manufacturers data
sheets.
NiCad. The noload voltage for a particular cell has zero bearing on the
charge state of a NiCad. A discharged battery might read anywhere
between 1.1V and 1.3V. The loaded voltage likewise has little bearing.
I spent many years with these, and the only method I know that actually
works is measuring the recovery time of the cell postload.
Details: Measure the noload voltage. Load the cell at some arbitrary
current (but well below the max load rating) for sufficient time for
the loaded voltage to stabilise (perhaps 100millisec). Release the
load. Measure the recovery curve (which is very close to a RC charge
curve). The shorter the curve, the higher the charge. For the
mathematical details, you'll have to wait until I dig out some books
from 15 years ago (when I did those experiments and filed patent
disclosure).
So the general answer is --No--, there is no universal voltage for most
cells. Indeed, we used to determine the charge of a lead acid battery
by electrolyte specific gravity (that was quite a while ago).
| Quote: |
There are gadzillion articles that discuss the general characteristics
of various types of rechargeable cells, but I have not found any that
specifically says that an X-type cell reaches Y Volts at full charge,
and should not be discharged below Z Volts.
Is it at all possible to specify voltage levels this way ? Temperature
and internal resistance (and therefore charge and discharge currents)
must play a part, but standard voltage levels under no-load,
no-charging at standard room temperature would be very helpful.
|
Not really very helpful - an indicator, nothing more. For anything
approaching reasonable accuracy, noload voltage is not much use for
most solid battery types.
Cheers
PeteS |
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Bill Bowden
Guest
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| Posted:
Tue Dec 06, 2005 1:36 am Post subject:
Re: Battery voltage as indicator of charge level |
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pjdd@rediffmail.com wrote:
| Quote: | Is no-load voltage a reliable indicator of charge condition ? Are there
universal voltage levels for a particular type of cell (e.g. NiCd,
NiMH, Li-ion, lead-acid, etc.) that can be taken to indicate
full-charge and full-discharge conditions ?
There are gadzillion articles that discuss the general characteristics
of various types of rechargeable cells, but I have not found any that
specifically says that an X-type cell reaches Y Volts at full charge,
and should not be discharged below Z Volts.
Is it at all possible to specify voltage levels this way ? Temperature
and internal resistance (and therefore charge and discharge currents)
must play a part, but standard voltage levels under no-load,
no-charging at standard room temperature would be very helpful.
|
For lead acid batteries, there are some no-load voltage vs capacity
charts here:
http://www.uuhome.de/william.darden/carfaq4.htm#load
For li-ion, I believe full charge is 4.2 volts and should not be
discharged below 3 volts. But don't know what represents 50% capacity.
-Bill
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quietguy
Guest
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| Posted:
Tue Dec 06, 2005 1:36 am Post subject:
Re: Battery voltage as indicator of charge level |
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You will find lots of info re these topics at
http://www.rcbatteryclinic.com/
David
pjdd@rediffmail.com wrote:
| Quote: | Is no-load voltage a reliable indicator of charge condition ? Are there
universal voltage levels for a particular type of cell (e.g. NiCd,
NiMH, Li-ion, lead-acid, etc.) that can be taken to indicate
full-charge and full-discharge conditions ?
There are gadzillion articles that discuss the general characteristics
of various types of rechargeable cells, but I have not found any that
specifically says that an X-type cell reaches Y Volts at full charge,
and should not be discharged below Z Volts.
Is it at all possible to specify voltage levels this way ? Temperature
and internal resistance (and therefore charge and discharge currents)
must play a part, but standard voltage levels under no-load,
no-charging at standard room temperature would be very helpful. |
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not i
Guest
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| Posted:
Tue Dec 06, 2005 8:15 pm Post subject:
Re: Battery voltage as indicator of charge level |
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pjdd@rediffmail.com wrote:
| Quote: | Is no-load voltage a reliable indicator of charge condition ? Are there
universal voltage levels for a particular type of cell (e.g. NiCd,
NiMH, Li-ion, lead-acid, etc.) that can be taken to indicate
full-charge and full-discharge conditions ?
There are gadzillion articles that discuss the general characteristics
of various types of rechargeable cells, but I have not found any that
specifically says that an X-type cell reaches Y Volts at full charge,
and should not be discharged below Z Volts.
Is it at all possible to specify voltage levels this way ? Temperature
and internal resistance (and therefore charge and discharge currents)
must play a part, but standard voltage levels under no-load,
no-charging at standard room temperature would be very helpful.
|
It depends what you are doing. Simply measuring no-load voltage is most
likely not reliable on most batteries. However, you can probably get a
crude state of charge by looking at the voltage. All battery chemistries
will have their own unique voltage versus state of charge per cell. But
again, in most cases the best you can hope for is just an estimate and if
the battery isn't functioning properly the estimate could be *WAY* off.
That said, if you are trying to charge a battery and want to know when to
stop the correct algorithm varies wildly with battery chemistry, and you
should never attempt to charge any battery without understanding what the
correct behavior is for that algorithm. In particular, NiMH and Lithium
based batteries require careful attention to proper charging or it can
have... unfortunate... consequences. NiCd and lead acid are generally
safer from that perspective.
dan |
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neon
Joined: 25 Feb 2006
Posts: 570
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| Posted:
Wed Jul 26, 2006 10:28 am Post subject:
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| No battery no matter who try to explain can say voltage is a good power capability indicator. Actualy a battery that has failed and has bad current source capability will show above normal voltage until a load is applied. batteries can only be tested under full load no other way. |
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