Imitation Nightstar - Help with analysing circuit

[i7r7]

I recently got my hands on 20 induction flashlights after a visit to my friend's import warehouse. I reckon that the Chinese manufacturer was copying the design of the way more expensive nightstar flashlight.

I noticed that the beam was relatively bright for a 1 LED light and the focus was quite good. I pulled the whole thing apart:

I can see: small circuit board, magnet shaft, induction coil, LED and lens..... batteries.... BATTERIES!!??

Umm... isn't the point of induction lights to eliminate the need for battteries?? I had a close look at the batteries, 2 lithium CR2032 coin batteries. AFAIK, these are not rechargable batteries.

So, I had a look at the circuitry of this thing... maybe the batteries are there for testing purposes or something.... or not:

It seems that the batteries are very much a permanent part of the circuit. I ask some of the more experienced electricians on CPF, wouldn't the batteries once they run out, be charged by the induction coil? Also, wouldn't the battery, when its still full, be continuously charging the leaky capacitor? Another thing... the markings on the capacitor states that its rated at "5.5V 0.1F". A quick look at a electronics catalogue shows that a much larger capacitor is only rated at "5.5V 0.047F", plus it costs much more than each light cost me.

If the capacitor has that large a capacity, it would provide a good runtime and be very bright. So I removed the batteries, shook the light as long and as hard as possible, turned it on.... it was very, very dim and it only lasted a minute or 2. Since the batteries are connected to the capacitor, inserting the batteries would charge the capacitor to 6V, so it should have been as bright as if the batteries were there if the capacity was as good as it says.

Well, I'm starting to not make sense, so I'll try and end this post now. To all the electricians out there, feel free to insult the poor quality cirucuitry, provide comments on how I could modify this circuitry to improve etc.....

Jeff

 

[paulr]

Re: Imitation Nightstar - Help with analysing circ

Looks to me like it's a dim, cheap, crappy induction light, with a couple of batteries added to make it brighter for the first few hours of operation after the poor sap who buys it gets it back from the store. Most people will never use the light enough to drain the batteries anyway.

A 5 volt 0.1F capacitor can be pretty small these days, and have low leakage though.

Is that a "Forever Flashlight" by any chance? How hard was it to get the thing apart?

 

[MrAl]

Re: Imitation Nightstar - Help with analysing circ

Hi Jeff and paulr,

I guess that big zig zag thing to the left is the inductive
pickup...

This circuit looks like a simple led series resistor circuit
with a charging circuit, except some of the diodes are
drawn backwards, and either the battery is drawn backwards
or the LED is drawn backwards.

Corrections made, the inductive pickup will cause a current
to flow which is basically alternating current. The
bridge rectifier (made up by the diodes) changes this
to pulsing dc which then charges the battery. The small
capacitor filters out high order harmonics in the
inductive waveshape and also gets charged.
The resistor limits current flow to the LED so it doesnt
get too much current and blow out.

It's a little strange since those battery types are
not supposed to be recharged :-)
Perhaps there is another diode in there somewhere
that prevents the battery from charging?

You may want to double check the connections and redraw
the schematic paying close attention to the polarities
of the parts. This may tell us a little more.

An improvement would be to use a rechargable battery,
if you can find one that small.

As a test, you could take the batteries out again and
attach a voltage meter to the capacitor and shake
the light. Then, quickly measure the voltage and
record, then wait 1 minute (stopwatch) and record
the new voltage. Report those two values back here
and we can estimate the 'real' value of the cap.
Double check the value of the resistor too.

I take it it's a white LED right?


Take care,
Al

 

[da_guy2]

Re: Imitation Nightstar - Help with analysing circ

Hey Al,
I hear what your saying bout this circuit but I dont think that would really work. A few reasons for this. First of all, with a battery that is not meant to be recharged (for the most part) it not physicaly possible to recharge it. The batteries undergo no reversable reactions and there no good afterwards. Next, even is it were recharging the batteries, in order to charge a battery you need alot of current maintained for a fairly long period of time. If what Jeff is telling us about the led being dim and not lasting long after having shook the thing for a while, this would inidcate to me that the coil is not producing enough current to keep things going let alone charge batteries. The next thing that I dont like about this situation is the size of the capasitor... .5F?!? Thats a bit too big to be justified as a means of filtering out the input voltage... I mean thats just HUGE especialy for something that being charged by a simple induction coil. Looking at this circuit i'd probably have to agree with paul that this thing is more likley designed to trick the buyer into buying a "very bright" light that only stays bright as long as the batteries last though they can still claim that is human powered. Oh and Jeff about the batteries draining through the cap, that shoudnt be much of an issue, capassitors leak on the order of micro amps. So in the end you might notice some loss from the batteries a year or 2 down the road but still long after the user has bout the battery and can no longer return it /ubbthreads/images/graemlins/wink.gif. I have to admit it is a rather shrude piece of junk though. Anyways have fun with you new flashlight!

David

 

[MrAl]

Re: Imitation Nightstar - Help with analysing circ

Hi there David,

Yes it *could* work at least to some degree, but probably
not as good as we would want it too :-)
I can not, however, say whether or not the company
made a good product, but i can say that if it was wired
as noted it would work even though the batteries arent
'supposed' to be charged. The batteries voltage will
rise even though they arent rechargeables. That doesnt
mean they will perform as normal rechargeables will,
but the voltage will rise just the same.

If the cap really is that large they might have the
battery isolated with another diode not shown.

Of course im assuming in addition to the induction coil
there is also a moving magnet somewhere in the light.
If he wants to send me one i'll check it out more
carefully. I'll either send it back or purchase it.

Take care,
Al

 

[i7r7]

Re: Imitation Nightstar - Help with analysing circ

My bad.. first of all, I put it in the wrong forum. Second and third things I forgot to mention, there is a pretty large low quality neodymium magnet (can been seen in the photo) and it has a white 5mm LED.

New info:
I have around 20 of these things, I chose another light and 2 diodes are reversed polarity. However, it still doesn't look like a standar bridge rectifier.
The diodes have this marked on them "4.007" with some other letters under "bufan" or something like that
I confirmed with my multimeter that the resistor is exactly 68.0 ohms.
I may or may not have the LED drawn the right way around, I hate polarity.

The diodes in the other light were different to this one, but this one seems to work slightly better without the help of the batteries.
The circuit board is really hard to remove from the light because there's those really thin coil wires attached. I'll try to pull it apart to get a better photo of it.

More later...
Jeff

 

[i7r7]

Re: Imitation Nightstar - Help with analysing circ

A quick runtime test... I shook it for as long around 30-40 sec as quickly as possible while it was switched off.

The initial current reading was as a peak of 18mA but quickly dropped.

Sec mA
0 18.00
6 8.05
12 4.70
18 3.12
24 2.36
30 1.80
36 1.53
42 1.28
48 1.10
54 0.96
60 0.85
66 0.77
72 0.69
78 0.63
84 0.58
90 0.53
96 0.49
102 0.46
108 0.43
114 0.41
120 0.38
126 0.36
132 0.35
138 0.33
144 0.32
150 0.30
156 0.29
162 0.28
168 0.27
174 0.26
180 0.25
186 0.24
192 0.23
198 0.22
204 0.22

Hmm...

Jeff

 

[MrAl]

Re: Imitation Nightstar - Help with analysing circ

Hello there Jeff,

Yes, that looks like a bridge rectifier configuration as
thought, and the inductive pickup is connected where it
would be expected to be connected.

Also, your cap value is close to 0.078 Farad, so its
marked value of 0.1F is correct.

It looks like your light is working at least somewhat
as it would be expected to. I cant explain why the
non rechargeables, but that's life i guess :-)
I dont see any other diodes either, but i also cant make
out the cap.

The diodes are probably 1N4007 type. These are basically
dirt cheap but reliable and can handle 1 amp continuous.

Hope this helps.

Take care,
Al

 

[Steelwolf]

Re: Imitation Nightstar - Help with analysing circ

Hangon, are we sure those are CR2032 cells? I sort of remember seeing a dealer offer rechargeable button cells. I should look it up.

Maybe this Chinese manufacturer is using the rechargeable button cells as the primary storage element and the cap is only there to absorb the pulses? 0.1F isn't very big, since the NightStar uses 1F caps.

 

[paulr]

Re: Imitation Nightstar - Help with analysing circ

The Nightstar runs for several minutes without getting too dim. This thing is below 5 ma at 12 seconds. The smaller cap would explain that. I assume those measurements were taken with the batteries disconnected.

 

[i7r7]

Re: Imitation Nightstar - Help with analysing circ

Yes, those measurements were without the batteries.
The batteries don't have any unusual markings on them which shows that they are rechargable.

Jeff

 

[rdshores]

Re: Imitation Nightstar - Help with analysing circ

How about a close up pic of the battery?

 

[i7r7]

Re: Imitation Nightstar - Help with analysing circ

I'm a bit too lazy/sleepy right now, I might get a pic of battery later. The positive plate of the says:

+
Lithium Cell
CR2032
3V
SC4

Nothing out of the ordinary.

Jeff