Charging video camera battery

**DONOTDELETE** · Aug 19, 2002

snakebite, care to tackle the forward voltage question? are you too of the opinion that "voltage doesn't matter" ? If you think voltage does matter, then how much forward voltage do you think Craig should see when charging his 9.6 volt nicad pack? I know this matters a whole lot to my lead-acid bank. A couple volts too high, and all the water will fizz away , because the increased voltage breaks apart the water molecules into oxygen and hydrogen
gas..if your voltage stays only a couple volts higher than 13.8 on a 12 volt battery, you eventually end up with dry, dead batteries..of course when equalizing your lead-acids you want voltage in the 15-16 volt range to cause this bubbling, which also serves to stir the electrolyte which can sometimes stratify into water and acid over time if they are sitting on the ground, but not if they are bouncing around in a car..

**DONOTDELETE** · Aug 19, 2002

Coherence, just double checked it with a C nimh cell. With the current held at 20 ma I can change the forward voltage by several volts up and down by twisting the voltage knob, while the current stays the same...

snakebite · Aug 19, 2002

in a nicad cell the overcharge will just cause heat.
iirc the neg plate is longer and contains a material that absorbs gas generated by the overcharge.sets up a recombination cycle.that way it can be sealed.if you overcharge severely the vent will open to prevent explosion.
if craig sets the voltage at 12v and limits current he will be ok.

**DONOTDELETE** · Aug 19, 2002

That's what I thought. Voltage does matter. Voltage heats the batteries. forward voltage of around 10% of battery pack nominal voltage seems to be an effective, safe area...?

Coherence · Aug 19, 2002

just double checked it with a C nimh cell. With the current held at 20 ma I can change the forward voltage by several volts up and down by twisting the voltage knob, while the current stays the same...

Maybe I misunderstand, but if you have another meter can you measure the actual voltage to the load, and does that vary? Maybe the voltage you are reading is the *potential* voltage, if current were not an obstacle.

That's what I thought. Voltage does matter. Voltage heats the batteries.

Voltage alone cannot heat batteries. It is power = watts = volts*Amperes that does it.

Yes voltage does matter, but only in the sense that it determines the current in the circuit. It is the current you are trying to control, using whatever volts needed to do it.

**DONOTDELETE** · Aug 20, 2002

amps being equal, increased voltage increases heat, or 'gassing' of lead-acid batteries.
" but if you have another meter can you measure the actual voltage to the load, and does that vary?"

not sure what you mean here. could you tell me where to put the probes and I'll try it.
tomorrow..;>)

Coherence · Aug 20, 2002

not sure what you mean here. could you tell me where to put the probes and I'll try it.
tomorrow..;>)

I mean to connect the red probe of the meter to the + of the output of the supply and black probe to - of supply.

Goodnight ;>)

**DONOTDELETE** · Aug 20, 2002

oh and about the 'Ted the Led' name, people have often before mistaken it as an acronym for "Light emitting diode" -- an understandable error. But the 'Led' is pronounced "lead" as in "you can lead a horse to water but a pencil must be lead" --

lightlover · Aug 20, 2002

I suppose I could post "something" here, but it's all getting a little bit too *technical* for me.

Frank,
maybe if things were explained patiently, I could possibly learn a little.

Jahn

Wingerr · Aug 20, 2002

If you're using a lab regulated power supply, you could set the open circuit voltage (with it unconnected) to some safe maximum for the pack, just as a safety in case you forget to disconnect it in time, and then hook up the batteries, and set the current limit to the value you want. This leaves it up to you, however, just how long it should charge for, and it's not going to be that easy to determine just how long it should be, since you probably wouldn't know the exact state of charge. You're better off monitoring the voltage and temperature to make sure you don't exceed the limits.
From the chargers I've used, the terminal voltage right at the end of charge generally is about 1.4 to 1.45V for my NiMH batteries, so if not you're using a charger that monitors for the voltage droop for the end of charge, setting your open circuit voltage setting on the supply would at least let it taper off the charge current at full charge, where it switches off from current limit mode to voltage limit mode (the two modes mentioned by Coherence).

Ted, in your test with the C battery, if you set the current limit at 20mA, the supply dynamically sets the voltage at whatever is required to deliver 20mA to the battery, so your tweaking of the voltage knob shouldn't have affected the voltage being supplied to the battery. It's only when you have the current limit set higher that the voltage knob will start being able to vary the voltage. Each of the knobs really just set a ceiling on the current or the voltage, if either one is hit, the other knob will no longer have any effect.
If you were to set the current limit at 1A, you should be able to crank the voltage up until you hit 1A at which point the voltage will just stop increasing, because the current limit takes over. The voltage knob shouldn't affect the output even if you turn it up further.
Similarly, if you set the voltage to 5V and set the current limit to 5A, it should maintain that 5V output with all different loads, unless you put a load on that would draw more than 5A at a 5V input, in which case it would just top out at whatever voltage corresponds to a 5A draw, on that load.

**DONOTDELETE** · Aug 20, 2002

on one chosen setting of power supply:

analogue meter on power supply shows apx. 4.2 v olts / and shows 0 amps ( nothing connected) / short circuit across powersupply outputs= 200 ma. and 4.6 volts / then, with 3 aa connected to powersupply : (nimh I think) Amp reading in series at + battery terminal= 200 ma. / forward voltage at + batt. terminal .58 volts
--------------------------------
with analogue meter on power supply turned up to 10 volts:

nothing connected analogue powersupply meter= 0 amps. / short circuit across supply terminals=200ma and 10 volts / now with batteries connected: fwd current at + battery terminal= 200ma. / fwd voltage at + battery terminal 5.87 volts

that's it! ... seems to me tweaking the voltage knob does affect the voltage at the battery ...so it would seem I can charge just about any voltage battery, a single cell or a dozen, at a low foward voltage and a 'customized ' current...

Jonathan · Aug 20, 2002

Originally posted by Ted the Led:
on one chosen setting of power supply:

analogue meter on power supply shows apx. 4.2 v olts / and shows 0 amps ( nothing connected) / short circuit across powersupply outputs= 200 ma. and 4.6 volts / then, with 3 aa connected to powersupply : (nimh I think) Amp reading in series at + battery terminal= 200 ma. / forward voltage at + batt. terminal .58 volts

Ted,

I think that you are on the right track to understanding what is going on, but there is something not quite right with your measurement....ahh, it is in your definition of 'forward voltage'.

You are using 'forward voltage' as a measure of the difference between the power supply open circuit voltage and the battery pack open circuit voltage. You get this by disconnecting your power supply from the battery pack and connecting your meter between the battery pack and the power supply. This is a useful measurement, generally not called 'forward voltage'. I'd use a term like 'available compliance voltage' or something similar. The term 'forward voltage' is usually used to describe the voltage measured _across_ a diode when it is biased in the forward direction and carrying current.

You will find an additional measurement _very_ informative. Adjust the power supply to read 10V, and set it (as above) so that you get 200mA when you short circuit the output. Connect your volt meter to the output terminals of your power supply.

With the power supply 'open circuited', the _external_ volt meter should read 10V. Now short circuit the supply. The internal meters on the power supply will read about 10V and 200mA, but the external volt meter should read something close to zero volts.

Instead of a short circuit, try a 1 ohm resistor. The external meter should read about 200mV. With a 10ohm resistor, it should read about 2V. With the 3AA pack, you should read something between 4 and 6V, slowly rising.

As I think you will see, the 'voltage' reading on your power supply is not the voltage placed on its output terminals. Rather it is the maximum voltage that it will place on its output terminals, provided that the current limit is not reached. If the current limit is reached, then the voltage on the output terminals will drop in order to properly control the current.

What does this say about battery charging? Well, for charging a battery, what matters is reversing some chemical reactions. This means that a _quantity_ of atoms needs to be moved around, and this will take a _quantity_ of electrons. So for charging a battery, what matters is the total _number_ of electrons delivered, and this means current. _Voltage_ is not what you need to control, _current_ and total _charge_ are what you need to control. But this is not to say that voltage is unimportant; it is quite important.

Voltage is important because it is what causes the current to flow. The charge current flowing through the battery is _directly_ related to the charge voltage applied to the battery. _Not_ the voltage setting on your power supply, but the actual voltage at the power supply terminals.

What your power supply will do when you set it to 200mA and any sufficiently high voltage, is that it will adjust the voltage at the output terminals so that 200mA flows through the battery. The voltage at the output terminals will be _less_ that the voltage setting of the supply, and as the battery charges up, this voltage will change.

With some types of battery, notably lead acid batteries, there is a very nice, steady relation between state of charge and battery voltage. If you connect these types of battery to a voltage source of the proper voltage, then the voltage will rise as they charge up, and when the battery voltage reaches the supply voltage, then charge current will stop flowing. This means that you can 'float charge' lead acid batteries with a constant voltage supply. With your power supply, you set the voltage setting to the 'float voltage', set the current limit to some comfortable value, and let it go. With a flat battery, the voltage will be low, the supply will hit current limit, and the maximum current will flow into the battery. As it charges up, the battery voltage starts to hit the output voltage setting, and the current drops.

This technique _will not work_ with NiCd and NiMH cells. The problem is that there isn't a nice steady relation between voltage and state of charge. Instead what you need to do is continue feeding current into the battery until you get some indication that the battery is fully charged. If you simply use the max current until a certain voltage is reached technique, then you will very likely overcharge or undercharge the battery, and only if you are very lucky will the charge current taper off just as the battery reaches full charge.

Regards,
Jonathan Edelson

Jonathan · Aug 20, 2002

Originally posted by Ted the Led:
<blockquote>quote:<hr />Originally posted by Jonathan:
(okay, the mixed case stuff is by Jonathan, and the all caps stuff is by Ted)
What your power supply will do when you set it to 200mA and any sufficiently high voltage, is that it will adjust the voltage at the output terminals so that 200mA flows through the battery. The voltage at the output terminals will be _less_ that the voltage setting of the supply, and as the battery charges up, this voltage will change.
NO MATTER, I CAN STILL CHOOSE THE VOLTAGE THE BATTERY SEES, AND AT THE SAME AMPERAGE.

<hr /></blockquote>No, this is the exact point that many of us are trying to get across. You _cannot_ set both the voltage placed across the battery terminals _and_ the current through the battery arbitrarily. If you set the voltage across the battery terminals to a particular value, then a particular current will flow (how much? It depends upon the temperature, the internal resistance of the battery, the state of charge of the battery, etc. The exact current which will flow when a particular voltage is applied is not easily predictable for a random battery) You _can_ adjust the supply maximum output voltage, and you _can_ adjust the supply maximum output current, however at any given point in time, only _one_ of those settings will actually have an effect on the output.

If you short circuit the supply, then the current limit circuit will kick in, and whatever setting you selected will flow. The voltage measured between the terminals will be very close to _zero_, no matter what voltage you dialed in.

When you adjust the voltage knob, but the supply is at the 200mA current limit, then the voltage that the battery sees will be essentially constant, and set by the voltage that the battery requires in order that the 200mA will flow.

Originally posted by Ted the Led:
<blockquote>quote:<hr />Originally posted by Jonathan:

then the voltage will rise as they charge up, and when the battery voltage reaches the supply voltage, then charge current will stop flowing.
IN FACT YOU HAVE JUST DESCRIBLED WHAT HAPPENS TO THE AA PACK IF I SET THE "'available compliance voltage' " AS YOU CALL IT, OR 'FORWARD VOLTAGE' AS I INCORRECTLY CALL IT, LOW ENOUGH WITH A LOW BATTERY, THE VOLTAGE OF THE BATTERY 'CATCHES UP' TO THE POWER SUPPLY VOLTAGE AND THE CURRENT SWITCHES OFF -- (I STILL NEED TO CONFIRM THAT WITH A MEASUREMENT THOUGH.)

<hr /></blockquote>This sounds reasonable for many cases; you are adjusting the maximum output voltage at the time you are charging the battery, which will compensate for many of the variables involved. With this sort of manual adjustment, I would expect the charge to gently taper off. However you would still be at risk if, for example, the ambient temperature changed and caused the battery voltage to drop and the battery to start sucking more current.

Originally posted by Ted the Led:
<blockquote>quote:<hr />Originally posted by Jonathan:

This means that you can 'float charge' lead acid batteries with a constant voltage supply. With your power supply, you set the voltage setting to the 'float voltage',
OH WE'RE BACK TO MY ORIGINAL QUESTION, HOW DO YOU COMPUTE 'FLOAT VOLTAGE'??

<hr /></blockquote>With lead acid batteries, you pretty much don't have to do any computation at all; the proper float voltages are known and stable, and often printed right on the side of the battery; otherwise just look up the datasheet for the battery.

But for NiMH and NiCd batteries, the 'float voltage' changes so significantly with temperature that voltage controlled charging is not recommended by any battery manufacturer. Especially critical: the battery voltage will _drop_ if the battery heats up, and the battery will heat up as it is being charged, and will heat up especially quickly as it reaches full charge. This can put you in a situation where the current flow will actually _increase_ when the battery reaches full charge. This doesn't always happen, but it is a real possibility with NiMH and NiCd batteries.

Originally posted by Ted the Led:
<blockquote>quote:<hr />Originally posted by Jonathan:

THE VOLTAGE IS ALSO LIMITED, AND HAS TO BE UPPED A BIT TO START THE CHARGING AGAIN WHEN THE SET LEVEL IS REACHED. OR YOU CAN SET THE VOLTAGE A LITTLE ABOVE THE BATTERY MAX POSSIBLE VOLTAGE -- BUT HOW MUCH HIGHER ? .25 VOLTS? .50 VOLTS? 1 VOLT? 9VOLTS?
--TEDTL

<hr /></blockquote>See above. You can do this manually if you know exactly what voltage the battery will peak at when it is fully charged. But this voltage will _change_, so there is no easy way to figure out what max voltage you should set in order to safely and effectively terminate charge. Pick too low a voltage, and you won't fully charge the battery. Pick too high a voltage and you will damage the battery.

Manually adjusting voltage in order to get the desired current flow can work, but it is really not a good technique for charging NiMH or NiCd. The various 'proper' techniques all involve running a constant current through the battery, and then detecting full charge by looking at how the battery voltage changes over time, looking at battery temperature, and looking at how temperature changes with time. The simplest approach to charging these sorts of cells is to run a constant _low_ current into them for 'long enough'. However this technique is known to degrade the useful life of the batteries.

-Jon

Saaby · Aug 20, 2002

You know I've got a novel idea...eBay, maybe we could find a real charger for the batteries...if that fails, maybe we could start another tiny little fund and set Craig up with a MAHA 777.

**DONOTDELETE** · Aug 20, 2002

nah, a Maha charges at 800ma , it'll fry his 1.8 amp battery.

maybe if he can find a wal- wart transformer that when connected to his battery has what I eccentrically call a forward voltage of 3 volts or so, and an amperage of around 100-200 ma, he can just plug it in and go to sleep. (but keep a finger on it the first time it's used, just to be sure it doesn't get hot..maybe will get slightly warm after it's charged..)

**DONOTDELETE** · Aug 20, 2002

+++++++++++++++++++++++++
Ted sed:
oh we're back to my original question, how do you compute 'float voltage'??
------------------------------------------
set the current limit to some comfortable value, and let it go. With a flat battery, the voltage will be low, the supply will hit current limit, and the maximum current will flow into the battery. As it charges up, the battery voltage starts to hit the output voltage setting, and the current drops.
++++++++++++++++++++++++++
Jonathan,
set a "comforatable" amperage value? ok, and what do you set the volt knob at? For what (nominal) voltage battery?

Silviron · Aug 20, 2002

The MAHA C2000 might actually be a better choice for charging camcorder batteries.

The nice thing is that it is cheaper than a 777 or 777+ too.

I've seen a few other "universal" camcorder battery chargers too, some as low as $36.00, and WalMart occasionally has a selection of camera specific chargers for about $28.00

Coherence · Aug 20, 2002

Ted the Led said:
set a "comforatable" amperage value? ok, and what do you set the volt knob at? For what (nominal) voltage battery?

Once you set the current, the supply will vary the voltage until you GET that current in the circuit (or to some lesser current, the amps you get at the voltage knob setting).

This measurement of 'forward voltage' (don't use that term that way) you measure is modifying the circuit. Now you have introduced a device in series which has a HIGH resistance (the meter), when measuring voltage (this is by design, you want to measure voltage by putting the meter in parallel with what you are trying to measure).

(incidently when measuring current, meters are designed to be as LOW resistance as possible, since they are connected in series with the circuit).

So the supply delivers the max voltage (up to where the voltage knob is set) it can, trying to force the amps you have set on the current knob.

Measure the actual voltage at the battery terminals and it will not change if you rotate the voltage knob higher assuming current stays the same.

Sorry if that sounds hostile somehow.

**DONOTDELETE** · Aug 21, 2002

Originally posted by Jonathan:
<blockquote>quote:<hr />Originally posted by Ted the Led:
on one chosen setting of power supply:

analogue meter on power supply shows apx. 4.2 v olts / and shows 0 amps ( nothing connected) / short circuit across powersupply outputs= 200 ma. and 4.6 volts / then, with 3 aa connected to powersupply : (nimh I think) Amp reading in series at + battery terminal= 200 ma. / forward voltage at + batt. terminal .58 volts

Ted,

I think that you are on the right track to understanding what is going on, but there is something not quite right with your measurement....ahh, it is in your definition of 'forward voltage'.
You are using 'forward voltage' as a measure of the difference between the power supply open circuit voltage and the battery pack open circuit voltage. You get this by disconnecting your power supply from the battery pack and connecting your meter between the battery pack and the power supply.
+++++++++++++++++++++++++++++++++
Ted sed:
Jonathon,
i disconnected the positive terminal of the power pack only, otherwise did exactly as you describe.
-----------------------------------------------------------
This is a useful measurement, generally not called 'forward voltage'. I'd use a term like 'available compliance voltage' or something similar.
+++++++++++++++++++++++++++++++
Ted sed:
i think you are just trying to force me to use another acronym,

--------------------------------------------------------
The term 'forward voltage' is usually used to describe the voltage measured _across_ a diode when it is biased in the forward direction and carrying current.

You will find an additional measurement _very_ informative. Adjust the power supply to read 10V, and set it (as above) so that you get 200mA when you short circuit the output. Connect your volt meter to the output terminals of your power supply.

With the power supply 'open circuited', the _external_ volt meter should read 10V. Now short circuit the supply. The internal meters on the power supply will read about 10V and 200mA, but the external volt meter should read something close to zero volts.

Instead of a short circuit, try a 1 ohm resistor. The external meter should read about 200mV. With a 10ohm resistor, it should read about 2V. With the 3AA pack, you should read something between 4 and 6V, slowly rising.

As I think you will see, the 'voltage' reading on your power supply is not the voltage placed on its output terminals. Rather it is the maximum voltage that it will place on its output terminals, provided that the current limit is not reached. If the current limit is reached, then the voltage on the output terminals will drop in order to properly control the current.

What does this say about battery charging? Well, for charging a battery, what matters is reversing some chemical reactions. This means that a _quantity_ of atoms needs to be moved around, and this will take a _quantity_ of electrons. So for charging a battery, what matters is the total _number_ of electrons delivered, and this means current. _Voltage_ is not what you need to control, _current_ and total _charge_ are what you need to control. But this is not to say that voltage is unimportant; it is quite important.
+++++++++++++++++++++++++++++++++++
Ted sed:
It iiiissss??

-------------------------------------------------------------

Voltage is important because it is what causes the current to flow. The charge current flowing through the battery is _directly_ related to the charge voltage applied to the battery. _Not_ the voltage setting on your power supply, but the actual voltage at the power supply terminals.

What your power supply will do when you set it to 200mA and any sufficiently high voltage, is that it will adjust the voltage at the output terminals so that 200mA flows through the battery. The voltage at the output terminals will be _less_ that the voltage setting of the supply, and as the battery charges up, this voltage will change.
++++++++++++++++++
TTL sed:
no matter, i can still choose the voltage the battery sees, and at the same amperage.
----------------------------------
With some types of battery, notably lead acid batteries, there is a very nice, steady relation between state of charge and battery voltage. If you connect these types of battery to a voltage source of the proper voltage, then the voltage will rise as they charge up, and when the battery voltage reaches the supply voltage,
+++++++++++++++++++++++
Ted sed:
which never happens with photovoltaic batteries in the real world, because the power supply from a solar panel is around 19 volts, way to high for a 12 volt battery to think of approaching. (that's what regulators are for.)
------------------------------------------------

This means that you can 'float charge' lead acid batteries with a constant voltage supply. With your power supply, you set the voltage setting to the 'float voltage',
+++++++++++++++++++++++++
Ted sed:

oh we're back to my original question, how do you compute 'float voltage'??
------------------------------------------
set the current limit to some comfortable value, and let it go. With a flat battery, the voltage will be low, the supply will hit current limit, and the maximum current will flow into the battery. As it charges up, the battery voltage starts to hit the output voltage setting, and the current drops.
++++++++++++++++++++++++++
Ted sed:
right, but the supply is always trying to put out the set current, say 200ma, the battery is just less resistant when it's low, so more current flows.
-------------------------------------------------

This technique _will not work_ with NiCd and NiMH cells. The problem is that there isn't a nice steady relation between voltage and state of charge.
++++++++++++++++++++++++++++++
Ted sed:
no, i find with the voltage fine tune knob, i can set the forward voltage a fraction of a volt above the battery while under charge, and the nicad or nimh will rise and the current will switch off..
----------------------------------------------------
Instead what you need to do is continue feeding current into the battery until you get some indication that the battery is fully charged. If you simply use the max current until a certain voltage is reached technique, then you will very likely overcharge or undercharge the battery, and only if you are very lucky will the charge current taper off just as the battery reaches full charge.
+++++++++++++++++++++++++++++++
Ted sed:

maybe it's a great power supply. what you call "max current" is limited to 200ma in this case.
the voltage is also limited, and has to be upped a bit to start the charging again when the set level is reached. or you can set the voltage a little above the battery max possible voltage -- but how much higher ? .25 volts? .50 volts? 1 volt? 9volts?
--tedtl
-------------------------------------

Regards,
Jonathan Edelson<hr /></blockquote>

Jonathan · Aug 21, 2002

Originally posted by Ted the Led:

Jonathan,
set a "comforatable" amperage value? ok, and what do you set the volt knob at? For what (nominal) voltage battery?

To be _very_ clear, this applies specifically to lead acid batteries. Set the current limit to between C/10 and C/2, and set the voltage to about 2.3V/cell. A 'comfortable' current does not depend upon the nominal voltage of the battery at all, but instead depends upon the nominal _ampacity_ of the battery, measured in amp-hours. Set the current to be the capacity in amp hours divided by somewhere between 2 hours and 10 hours. A lead acid cell has a nominal voltage of 2V, so set the voltage to be 2.3/2*(nominal voltage). This will quite reasonably float charge a lead acid battery.

-Jon

Charging video camera battery

**DONOTDELETE**

Guest

**DONOTDELETE**

Guest

Flashlight Enthusiast

**DONOTDELETE**

Guest

Newly Enlightened

**DONOTDELETE**

Guest

Newly Enlightened

**DONOTDELETE**

Guest

Flashlight Enthusiast

Flashlight Enthusiast

**DONOTDELETE**

Guest

Enlightened

Enlightened

Flashaholic

**DONOTDELETE**

Guest

**DONOTDELETE**

Guest

Flashlight Enthusiast

Newly Enlightened

**DONOTDELETE**

Guest

Enlightened

Similar threads

DONOTDELETE

DONOTDELETE

DONOTDELETE

DONOTDELETE

DONOTDELETE

DONOTDELETE

DONOTDELETE

DONOTDELETE

DONOTDELETE