Those Red/Yellow/Green 3-LED Battery Level Indicator Voltage State Of Charge

"Wild_Bill"

** No way it will work with rechargeable cells like NiCd or NiMH.

Only good for non-rechargeable like alkaline.

... Phil

This is contrary to my expectation. Please enlighten...

"mike"

** Simple fact is that no voltmeter reading will show the state of charge of a NiCd or NiMH battery.

The discharge curve of the cells is almost flat - ie the terminal voltage does not vary until the cell is nearly exhausted.

This is quite unlike non rechargeable cells like carbon zinc and alkaline.

... Phil

Charge state indicators are used on professional rechargeable packs, and give a quick indication of when they're not suitable for service/need recharged.

LED charge indicators would be useful for sealed lead-acid types and other rechargeable types.

The charge state voltage is what causes intelligent chargers to start and stop charging, or switch to trickle charging.

I don't know about the newer chemistry types, but I spotted a comment a couple of days ago that claimed one type can't be recharged if discharged below a specific level (don't recall if it was lithium or poly-something).

NICD and NIMH types shouldn't be used when discharged to a point below approximately 80% of full charge, some manufacturers claim the limit should be about 0.8V per cell.

SLA types should also be limited to specific discharge levels, or approximately 10.8V for a 12V battery.

So.. if a user can quickly, easily and reliably detect when a battery or pack needs to be recharged, and cautioned wrt further discharge.. they can avoid taking low batteries out in the field and finding themselves without portable power. Additionally, keeping charge levels above minimum levels will result in longer battery life. (ideally, one would take a vehicle out in the field and a charger that would operate from the vehicle's 12V source).

The other option would be to keep all SLAs and rechargeable packs on trickle chargers or automatic maintenance chargers.

Rechargeable batteries wouldn't be very economical if owners needed to own enough chargers for every battery or pack that they might own.

-- Cheers, WB .............

"Wild_Bullshit "

** But do not indicate the actual *state* of charge - only if they are flat or not. ** Separate scenario.

Placing a NiCd or NiMH cell or battery on charge and observing what happens is a way to tell its state.

** Horse poo.

** That equates to 100% discharged.

Fuckwit.

... Phil

My own preference is to stop when the battery hits 1.0 volts per cell... this is usually soon enough to keep the weakest cell in the battery from being over-discharged into a state of voltage reversal, and since there's usually only 5-10% of the battery charge left at that point it isn't really wasteful.

Part of the problem here - and I suspect what Phil was alluding to - is that some types of batteries have a voltage-discharge curve which makes it difficult to measure their charge state accurately over much of their charge range.

Alkaline battery output voltage tends to "droop" quite a bit over the battery's useful discharge lifetime, and the "voltage droop vs. percentage of charge used" curve is fairly flat over much of this range. The voltage per cell (under load) can drop by half a volt or more, between the "10% used" and "90% used" points.

A standard "battery level indicator" intended for use with alkaline batteries will probably use this phenomenon - put a load on the battery, measure the voltage, and show a rough indication of lifetime remaining based on the voltage.

This isn't as easy to do with NiCd and NiMH cells. These chemistries have a much flatter voltage-discharge curve... a bit of droop at the beginning, a nearly constant output voltage over most of the remaining time, and then the voltage "drops off a cliff" when there's only a few percent of the charge remaining.

So, with these batteries, you can probably distinguish "fully charged", "almost entirely dead", and "somewhere in the middle" without too much trouble, but it's difficult to get a more accurate estimate of just *where* in the middle the battery might be. "10% left" and "90% left" don't look very much different, voltage-wise.

A battery measurement tool calibrated for alkaline batteries is likely to give misleading readings when used with NiCd/NiMH batteries.

Take a look at

to see one example of some of the data.

--
Dave Platt                                    AE6EO
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"Dave Platt"

** Most users do not run cells flat in a *single* discharge session - they turn the load on and off many times.

NiCd and NiMH cells recover voltage after a time and if you plotted a curve of typical usage - it would look like a saw tooth wave. At each peak of the wave, the voltage is very similar right up until the cells are quite flat.

Users will switch the device on and *then look* at the 3 LED charge display - and never see any change no matter what the state of charge.

... Phil

Apparently I asked the wrong question again (posted previously in Jan). Maybe because I described what the indicators are typically used for.

What I would like to know is where to buy the indicators.. red/yel/green, miniature bar graph in a compact package.

Usenet.. a greasy spot on the ground where a dead horse once lay.

Thanks

-- Cheers, WB .............

"Wild Bullshitartist "

** China.

Take a slow boat and enjoy the trip.

... Phil

I agree with your comments, Dave.

If I knew where to buy the indicators that would take care of my inquiry. I don't know if they're made for just one specific purpose or not.. it appears that I'd be better off gluing 3 LEDs together.

Discharge rates, gotcha.. (and seriously) good of you to explain it for those who don't know there's any difference from one battery chemistry to another.

I believe the .8V/cell level was stated as the absolute maximum safe discharge level I had read, but neglected to state it exactly (wasn't implying an average safe level).

I've seen the circuit board inside the older "deluxe" Sony camcorder batteries (NP-77HD etc).. about 1.5" x 3" and fully populated on a single side with SM devices to illuminate 1 to 5 LEDs to indicate remaining capacity (press a button and 1-5 of 'em are on, or none). The semis apparently track the amount of charge going into the pack, and monitor the amount of discharge to give a useful indication of remaining capacity. There is a 0.02 ohm ceramic resistor in series with the pack's charging terminal, and 3 micro-sized pots (suggesting there might've been a service manual available at one time), 2 ICs and a couple dozen smaller devices. When this circuit is connected to a set of fully charged cells, no LEDs will lite, because the circuit hasn't tracked and stored the charge level.

This circuit's functions could probably easily be done with one of the many tiny uPs commonly available today.. but it would all be fairly pointless without an indicator.

-- Cheers, WB .............

Something like

??

That's not very nice to Phil... is he dead and really that greasy?

--
Adrian C

That's the closest to what I was referring to, Adrian, and maybe the little pips/nipples could be trimmed off so it would look like 3 rectangular LEDs arranged like a mini bar graph.

Thanks

-- Cheers, WB .............

If you just want the LEDs, Digikey lists four types with R-G-Y LEDs.

350-1755-ND 350-1809-ND 350-1751-ND 350-2208-1-ND

If you're talking about the ones that are a frame with rectangular LEDs pressed into them, I don't think they are widely sold outside of Asia, as Phil implies.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

They do have 10 segment ones available from Mouser.

Jeff

--
"Everything from Crackers to Coffins"

Jeff

you

also have bigger displays with 28 leds red-green or yellow here:

but it's difficult to handle them without a microcontroller...

--
----------
Kripton

the ESR Repository @ http://kripton2035.free.fr/esr-repository.html
the Geiger Repository @ http://kripton2035.free.fr/geiger-repositor.html

Thank you Spehro.. I guess I'll need to investigate all those eBay sellers from Hong Kong and nearby regions.

I didn't imagine that the framed rectangular LED indicators would only find one purpose in consumer equipment, or be difficult to find.

Been a spectacular week for that guy, since a couple of people actually agreed with him. I've gotten used to ignoring the rarely-civil, like so many in RCM.

-- Cheers, WB .............

Kripton wrote in news:4eb65f3b$0$2280$ snipped-for-privacy@news.free.fr:

coupla LM3914's,gives you 20 LED steps,then you need scaling circuitry for the voltage range you want to display.

--
Jim Yanik
jyanik
at
localnet
dot com