R90s Voltmeter ...again!

[Hoof]

I understand that is an analog meter (what else!) - many of which can be adjusted for accuracy.....Mine works just fine but reads consistently high. Anyone know if there an adjuster on the meter somewhere?

[Kurt in S.A.]

Don't know about an adjustment...likely there's no way inside, either. I have an old voltmeter and don't see anything that suggests adjustment and/or access. What about V=I*R? Use a resistor of some magnitude in series and see what happens?? I googled this and saw some discussions along these lines.

Kurt in S.A.

[Duane Ausherman]

Did you put another volt meter across that one to confirm that it is reading high? I would then be concerned that the charge voltage is also high. Neither is typical, so I am suspicious.

On a high quality old fashioned volt meter one can only adjust the centering screw for the needle.

[Hoof]

I am sure that It is the BMW meter reading high ....It reads nearly 17v on the voltmeter when it is really c.13.5v across the battery (Checked with two different meters to be sure!)

As I also cannot find an adjuster I'll look at the resistor option.

Thanks everyone

[Ken in Oklahoma]

I am sure that It is the BMW meter reading high ....It reads nearly 17v on the voltmeter when it is really c.13.5v across the battery (Checked with two different meters to be sure!)

As I also cannot find an adjuster I'll look at the resistor option.

Thanks everyone

The stock BMW voltmeters, in the pods or dash, aren't noted for their accuracy. And even if you should stumble upon the right resistor (presuming the meter is known to be reading high, the stability of the fix would be dubious.

What I have done instead is to check the bike's voltmeter with a digital multimeter for accuracy. With the bike's rpm's up if the digital multimeter is reading what I think it should read, that is a fully charged known good battery, then I put a dot of white paint on the glass just above the needle tip. Seeing that needle pointing at the paint dot gives me all of the assurance I need about the charging system. (Note, lights on vs off and idling charging vs at higher rpm charging will make a difference. I like to have the rpms set at, say, 2,000 rpm with headlights on.

(editing) I have found the cheapo Harbor Freight multimeters to be accurate and sonsistent with each other. And smetimes Harbor Freight offers a coupon for a free multimeter with purchase. Yep, I'm not much of a fan of Harbor Freight but their multimeters have proven wonderfully accurate and durable for me.

Ken

[Edward]

I don't know the volt meter in the 90S in particular, but typically there is an internal variable pot to trim the response and a mech control for zero. But a mass produced meter intended as a simple fail light replacement may not have any adjustments.
But you can use a variable pot in line or in place of the existing multiplier resistor or in parallel and do the math for the circuit. Depends if your reading low or high.

Once you find the correct deflection, just measure the setting on the pot and replace with resistor.

Caveat,I haven't worked as an EE in 25years, got sucked in to the dark side of SW But analog meters are pretty straight forward.

Good luck,

Edward

[jimmyg]

Hoof, you can adjust them. I've done it on my '74 S. (stock Motometer gauge), as it reads about 14.1vdc, engine running.

Its not easy as you'll have to remove the gauge cover to get to the innards. But once inside there is a mechanical peotentiometer.

I synched mine up to read battery voltage as they're notoriously lower than batt. voltage.

Mine's been working fine for 15+ years with that adjustment.

jimmyg

[Rob]

Hoof, you can adjust them. I've done it on my '74 S. (stock Motometer gauge), as it reads about 14.1vdc, engine running.

Its not easy as you'll have to remove the gauge cover to get to the innards. But once inside there is a mechanical peotentiometer.

I synched mine up to read battery voltage as they're notoriously lower than batt. voltage.

Mine's been working fine for 15+ years with that adjustment.

jimmyg

Along with a good, dedicated + & - wires running from the battery? (I think I have heard of this being done.)

[jimmyg]

you can wire it directly to the battery but then it's powered constantly, which isn't desirable.

Like I said, you can carefully pry off the cover of the voltmeter which allows disassembly.

Then you can adjust it to match battery voltage.

[Hoof]

Wonderful - Thanks for all the help - I'll pry off the cover and adjust the pot. It is much more satisfying to have a meter providing accurate information rather than constantly applying a correction!