Analogue moving coil meter range extension?

Yup, that's the thing ... and why many battery meters are calibrated with red, amber and green sections. Now whilst that would work for me re charge (voltage) and loosely therefore charge status, it wouldn't be useful to pin down the discharge / charge status (unlike say a CCA tester) as the terminal volts are a function of load.

Yup and I have some of those. Highly repeatable but always 'out' by some amount. ;-(

And it was the latter thought that I was using when it came to this meter. ;-)

Take something that offers a very 'human' way of displaying something (like an analogue car fuel or specifically, temperature gauge that starts at say 60 DegC) and retain the merits but improve the general meaning / readability.

Mileage / trip counters are more suited to being 'digital' etc. ;-)

Cheers, T i m

With very coarse markings you won't get accurate readings. End of relevant material. I have no motivation to argue over the simple and immaterial.

NT

Yep, that's a good idea.

And, there's NO NONLINEARITY unless you apply bias less than the zener voltage breakdown, because of Norton's theorem: any bunch of resistors and voltage sources (the zener is a voltage source) is identically a current source with a shunt resistance. Offset by a constant, you can get; nonlinearity, you can't. The meter magnetic field is the only source of nonlinearity (and meter manufacturers do pretty well on keeping that uniform).

zener v/i curves vary, some are terrible near zero i, some straighter.

NT

So, if the / any issue to the zener solution is the closeness of any knee to the bottom end of the required voltage range, would the using the / a lower reference and a potential devider to set the fsd on 15 volts be a better idea still (or have I missed something again)? ;-(

Cheers, T i m

Thanks for the follow up Dave.

Well, I have worked with SMD's but a wired device and could use on at a pinch (soldered to the side of the meter contact etc) bit a wired device is probably easier.

Understood. I was thinking more on the idea of when using a lower voltage zener to be well clear of the lower voltage levels being considered and then the potential divider to set the FSD when the input is 15V?

And also, wouldn't the impact of the battery voltage changing from say

That seemed like the best of all worlds (for the KISS solution)?

Cheers, T i m

Doesn't that depend what you are looking for? Say I determine my LVD should be at 11.000 volts then I would appreciate the meter being as accurate as possible (at that point at least)?

Cheers, T i m

You want a zener with a nice straight line at the low current end. One linked to from here has that.

NT

Yeah, ok ... but what about the question re using a lower value zener to get it away from the 'knee', especially as it's no more difficult to do?

Cheers, T i m

Here it is again. The simplest is a 20K resistor in series with a 10v zener diode. Use a low current Zener so the knee works right at low values. Something like this: Note, this is a DO-35 package.

Since we're just trying to be clever, Try this:

The transistor and zener make a temperature compensated ~7V reference (must use 6.2V zener with standard tempco). Two pots set the min and max voltages. Rk allows you to add current to the zener to get it past the most nonlinear portion of it's V-I curve. This circuit has the ability to calibrate out almost any component variation. It's relatively temperature independent. You can use any meter that will make full scale at less than about 7V. Downside is that the pots are vibration sensitive and subject to moisture/corrosion.

Are we having fun yet?

The zeners with the straightest knee are at 9-10v. Go look at the linked data sheets.

NT

I'm not mike, I'm just trying to refine the design of any solution to be as good as possible with the fewest possible components. ;-)

Ok.

Noted.

Understood.

That sounds like the sort of thing I was hoping to hear. ;-)

As long as it will cope with the -10 to +10 DegC range it should be fine here in the UK. ;-)

And that's most small panel meters I'm sure.

Sure, but in my case they won't be subject to any real vibration and will be in a sealed enclosure. Also I would typically use a quality multiturn pot of the smallest value possible to give me sufficient 'trimming' around the end points and quality resistors to do the main bridge / work.

Well, it's certainly bringing some interesting and varied solutions out of the woodwork. ;-)

It might also help me use up my stock of BC107's. ;-)

Cheers, T i m

Ok, so again that helps because I'd go for a 9V zener to get AFA I can from that 10V threshold and still retaining the sharpest knee. ;-)

Too much information (variables) for me in most cases mate. ;-)

Ah, you can use the 9V zener but it only comes in SM and you have to buy 1000. The 10V are easier to get but need a higher current ... etc etc. I don't play chess or poker or any game of chance for that matter (preferring FPS when I can shoot my fellow players in the face). ;-)

The whole point to me of asking those who know is they are the ones who should all agree on a single 'best' solution. ;-)

More than one way to skin a cat? (But for that as long as it does get skinned is good enough for me [1]).

Cheers, T i m

You keep missing it.

Here it is again. The simplest is a 20K resistor in series with a 10v zener diode. Use a low current Zener so the knee works right at low values. Something like this: Note, this is a DO-35 package.

Just use a 10v zener. Job done. There's little point in the rest when the meter is so coarsely marked. You can adjust for 10v mechanically. You should find one in your scraps box.

Catgut is made from sheep, goats etc.

NT

Use a small value pot with a fixed resistor on each end. Easier to set, more stable.