Li-ion charging

I've used the 3R3 convention myself for at least 30 years. It's odd looking at first, but I find that it helps avoid blunders, which to me is a fairly compelling advantage. Of course my drawings are all freehand, which makes it more useful than if I were using a letter template.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
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hobbs at electrooptical dot net 
http://electrooptical.net

Reminds me of Soviet resistors I saw late 1960s-early 1970s without colorcodes but using 3 chars (1 apha, 2 numeric). e.g. 47R 3K3 1M0 etc seeing M22 always made me stop to convert to 220k. Constant length, very logical even if a bit strange to western eyes. I cannot remember now if

100k was 0M1 or M10 - both give the same value.

piglet

[...]

I like the idea very much. It's a bit of a pain to get used to, but the decimal point often disappears with different fonts.

LTspice accepts the 3R3 convention, but I have not found a list of symbols to designate the entire range of engineering values. For example, how do you designate the following:

Resistors in Ohms

0.33 3.3 That's the 3R3 under discussion 33 330 3.3K 3K3? 33K 330K 3.3 MEG 3M3 is dangerous. It could be 3m3 which is 3.3 milliohms 33 MEG All the megohm values are risky 330 MEG 3.3G 33G 330G 3.3T 33T

Capacitors in Farads or Inductors in Henrys

3.3ff 33ff 330ff 3.3pf 33pf 3.3nf 33nf 330nf 3.3uf 33uf 330uf 3.3mf Again, we hit the M vs m problem 33mf 330mf 3.3f 33f 330f 3300f

Voltage in Volts or Current in Amps

3.3nV 33nV 330nV 3.3uV 33uV 330uV 3.3mV Again, the M vs m problem 33mV 330mV 3.3V 33V 330V 3.3kV 33kV 330kV 3.3MEGV This is really bad

Yes. ^^^

It seems to me that 3M3/3.3m is no different than 3.3M/3.3m. Since resistors in the milliohms are fairly uncommon, just identify them as

0.0033. It's a lot of characters but it is uncommon.

0R33

That's the 3R3 under discussion

33R 330 3k3 33k 330k 3M3 (the mega/milli thing is specific to SPICE) 3G3 0p33 3p3 3n3 3u3 3300u

Doesn't come in 0603. ;)

I don't generally use it for that, except for supplies, e.g. 3V3. And of course 6V6 is a pentode. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

You really have to be an old-timer to know that one! We could have fun with that - 6K5, 6G6, 5R4, 1V6, 1N3, 6U8...

OK, I think I get it. You simply replace the decimal with a letter corresponding to the value. Very simple, and effective.

Thanks!

or 0V0042. (We do say 0R47 and similar)

No, 330R

copying what was then common practice on schematics glued into the back covers of TV and sets, in magazines etc., decimal points were the norm. I never saw units used as separators. When I later took Radio Shop (building actual toob radios) in High School (ca. 1968), same same.

know my instructor. Decimal points had to be as legible as any other drawing element- a poorly indicated one would drop you a full grade on a drawing.

the mimeograph, which was part of the reason decimal points had to be easily legible.

are separated by commas.

separate integers from decimal fractions IMO.

should impress anyone).

I am about your age with reasonably similar early experience. Just the first stereo that i designed (about 1966) was transistors and ICs, uA741s as a matter of fact. Hand drawn PCB single sided etched using FeCl3. Hand drilled. But it worked as advertised after i built well regulated power supplies for it. I first started seeing 4k7 resistors in the 1990s and simply got used to it. 2m4 V would weird me a bit though.

?-)

me

the

That becomes more difficult when you are strictly limited to 3 characters. Still reasonably easy at 4 characters limit.

?-)

Or even k33 or 0k33 ?

piglet

A sensible precaution

I've had a chance to look at the unit today. The battery does include a protection circuit and I checked the voltage on the cell itself. Cut-off voltage is 4V25. I agree that this is too high for comfort, as the cell is continuously maintained at this level. Also discharge cut-off is set at 2V8, whereas ~3V2 is more the recommended value. Obviously they are trying to push as much charge into the battery as possible.

I'm not much impressed with the charger either. The control chip is set to maintain the charging current at ~125mA. It also holds the base pin of a PNP high to keep it switched off. When a power outage occurs, the base voltage goes low and the PNP is switched on, connecting the battery to the power LED. There is no current limiting circuit, so initially the current is higher than necessary and diminishes as the battery voltage goes down. Cut-off occurs at 2V8 after a little over 3 hours. A basic current limiter(1 transistor, 2 diodes and 2 resistors) will maintain an acceptable level of light output for about 6 hours, so I would have thought that the expense incurred by including a few extra components would ensure that the battery wasn't overly stressed and likely to fail prematurely.

The present design requires maximum charge capacity, whereas a current limiter would only require the battery to be charged to 60%(for example) capacity to adequately power the LED for 3-4 hours. Ie - the control pcb built into the battery could be set to, say, a range of 3V2 to 4V0.

The reason why I am reading 4V9 on the output of the battery seems to be a feature of the inbuilt control chip. This is because when the battery is charged (cell at 4V25) and the input current flow is switched off, the charger supply voltage settles at 5V1. This difference in voltage seems to be held in the control chip as capacitive charge, which the high input impedance of the voltmeter doesn't disturb. Application of any sort of load clears the condition.

I am not inclined to recommend purchase of this particular unit.

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On a sunny day (Wed, 4 Jun 2014 23:04:46 +0100) it happened Steve B wrote in :

Current is limited by beta of transistor x base current (base resistor?).

The transistor (B772) is just used as an on/off switch, the base resistor is sourced from the charging voltage on the battery, when charging it is held at this voltage so is hard off, with (mains)power loss it goes to ground potential(hard on). Initially, when the B772 is conducting it dissipates about 300 mW, compared with 1500 mW consumed by the LED. This is wasting 16% of battery capacity, I can't think why an FET wasn't used.

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On a sunny day (Thu, 5 Jun 2014 23:03:31 +0100) it happened Steve B wrote in :

Do you have a circuit diagram online? I thought you were talking about charge current limiting. In that case if I envision your circuit correctly, then the voltage across the base resistor when on, divided by the value of the base resistor, multiplied by beta, is the charge current. In that case you do not want it full on, as then there is no current limit. But if the transistor is in the output to the LEDs, then I completely agree with you.

A device that relies on a safety mechanism for normal, safe operation has no safety mechanism.

Cheers, James Arthur

On a sunny day (Fri, 6 Jun 2014 11:32:28 -0700 (PDT)) it happened snipped-for-privacy@yahoo.com wrote in :

What is in a name. Over - and under voltage protection, and current limiting, wether in - or outside a battery do the same. At least you know if it is IN the battery it is properly designed.

It might be properly designed, but that's not a safety.

A safety system is a redundant, independent system meant to provide safe operation when things go wrong. If the device depends on it, it's a regulator, not a safety.

Applying over-voltage to a LiIon cell is inherently unsafe--that's bad form. Interposing an over-voltage disconnect doesn't save it if the disconnect fails.

Cheers, James Arthur

On a sunny day (Fri, 6 Jun 2014 11:56:12 -0700 (PDT)) it happened snipped-for-privacy@yahoo.com wrote in :

So, you have a pressure cooker with a safety valve. Does that mean there is no safety? Plenty of other things. It is just a freaking chip, and if the chip is IN - or OUTSIDE the battery makes no difference.

But nobody is stopping you from adding your own protection, that then probably or possibly never works because it is just a few mV above the battery one. Say 4.025 and yours 4.026 Tolerances.

:-)