Gossen Lunasix 3 Circuit

SMBooth · Nov 17, 2008

The link below is the circuit of the Lunasix meter, I wondering if any electronic minded people could tell me if the description of recalibrating for 1.5V is correct. To me he is only reseting the voltage divider for the battery indicator.

http://flickr.com/photos/93918130@N00/2609042974

Thanks Shane

Anon Ymous · Nov 17, 2008

I'm not an expert, but here's my opinion. PX625 batteries kept voltage level rather straight through their useful life IIRC. Modern batteries like SR44 don't, and they also have slightly higher voltage. Therefore, as the voltage drops, you will have to recalibrate constantly. That's not practical.

From what I remember from electronics I was taught, you need a zener diode and a resistor to make an adapter. The meter's circuit is then fed with the voltage from the edges of the diode which is constant. You may be able to make one, but you'll get Dr Frankenstein's Lunasix 3

SMBooth · Nov 20, 2008

Thanks Anon, there is plenty of options on converting battery holder to suit newer 1.5V batteries. And I know you can recalibrate for 1.5V but I not convinced that what these link is saying is correct.

Andrew Moxom · Nov 20, 2008

Why not just get an adaptor from B&H photo that has a diode to adjust the voltage accordingly and use modern and more importantly, AVAILABLE batteries? Mine works just fine.

Polybun · Nov 20, 2008

Anon Ymous said:
I'm not an expert, but here's my opinion. PX625 batteries kept voltage level rather straight through their useful life IIRC. Modern batteries like SR44 don't, and they also have slightly higher voltage. Therefore, as the voltage drops, you will have to recalibrate constantly. That's not practical.

From what I remember from electronics I was taught, you need a zener diode and a resistor to make an adapter. The meter's circuit is then fed with the voltage from the edges of the diode which is constant. You may be able to make one, but you'll get Dr Frankenstein's Lunasix 3

There is another way too, if you want to really franken one up. It looks to me like there is enough room in there for a very small dc-dc converter. Toss it a 3volt lithium cell, have the converter nock it back to 1.3 volts. The thing should run for like 5 years between cells!

ath · Nov 20, 2008

Polybun said:
There is another way too, if you want to really franken one up. It looks to me like there is enough room in there for a very small dc-dc converter. Toss it a 3volt lithium cell, have the converter nock it back to 1.3 volts. The thing should run for like 5 years between cells!

Thats exactly what I've done with my Weimarlux CDS (GDR). Since the voltage regulator draws a little bit of current a switch is helpful.

ath · Nov 20, 2008

His interpretation of adjustment is correct. However the adjustment range might not be sufficient for 1.55V silver cells.
I'm not sure if the circuit diagram is correct, it looks a little bit weird but could be a neat solution.

Anon Ymous · Nov 20, 2008

SMBooth said:
Thanks Anon, there is plenty of options on converting battery holder to suit newer 1.5V batteries. And I know you can recalibrate for 1.5V but I not convinced that what these link is saying is correct.

The critical detail here is the voltage level a battery delivers to the circuit. As I wrote at my previous post, I think mercury batteries held their voltage at a precise level (1,35V). Modern batteries like LR44 will not keep it as constant, while SR44 hold their voltage level better. That's why I wrote that you can calibrate for the new voltage, but it is a matter of time when you will need to recalibrate. I mean, within the useful life of a battery.

Anyway, If you can buy an adapter at a reasonable price (no idea how much they cost), then get one and forget about that hassle...

BrianShaw · Nov 20, 2008

Andrew Moxom said:
Why not just get an adaptor from B&H photo that has a diode to adjust the voltage accordingly and use modern and more importantly, AVAILABLE batteries? Mine works just fine.

That's the solution I've been succesfully using for a few years now. Most people seem to have a problem withthe high cost and seek alternative solutions.

SMBooth · Nov 21, 2008

Not concern about the cost of the adapter, if i could pick one up a Australia then its a no brainer, trouble is the $50.00 delivery charge that everybody wants to sent OS...

John Koehrer · Nov 21, 2008

You want to buy it & have it sent it to me I'll mail it to you. It shouldn't cost much since it's less than a couple of ounces. Pm if you're interested.

Gossen Lunasix 3 Circuit

Polybun

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