14 replies to this topic

[GreaseMonkey]

Hey,

I'm having problems with my Smiths gauge,

Before it used to register the volts correctly, when testing with a 9v battery the needle used to come to a rest just before the 11 now however it rests on the 11. When connected to a 12v battery the needle swings all the way to 15 if not a little above.

Any ideas?

Thanks

Edited by GreaseMonkey, 16 February 2009 - 08:47 PM.

[miniat40]

Was the battery being charged while you tested it. Such as in a car with engine running or connected to a battery charger.

Ian

[GreaseMonkey]

Hi,

Nope the battery is out of the car

Thanks

[dklawson]

Gauges do go out of calibration and if you're confident that the battery is really not at 15V (be sure to check with at least a multimeter or similar), then it would be time to contact someone like Speedy Cables to inquire about how expensive it is to re-calibrate the gauge.

[jpdgmilan]

Gauges do go out of calibration and if you're confident that the battery is really not at 15V (be sure to check with at least a multimeter or similar), then it would be time to contact someone like Speedy Cables to inquire about how expensive it is to re-calibrate the gauge.

You may be able to recalibrate the gauge yourself, if you have slots in the back of the gauge covered by small bits of cork. Simply apply 12v or (13.8 with the engine running above idle) remove the cork, insert a screwdriver slightly into the slot and twist to move the needle.

[GreaseMonkey]

Aha okay,

I have it roughyl calibrated to read correctly on the 9v battery, will have to wait till tommorow to see what it does with the 12v

What does adjusting the other plate opposite to the needle adjusting one to?

Many thanks

Edit- They both seem to affect the needle

thanks

Edited by GreaseMonkey, 16 February 2009 - 10:59 PM.

[GreaseMonkey]

Adjusting the needle I have it roughly where it should be on a 9v battery, however now with no power the needle rests quite to the left of the red area where it should come to a rest with no power if that makes sense.

Looks abit odd?

[dklawson]

I didn't suggest calibrating it yourself because the process can be a bit frustrating.

One of the two screwdriver slots sets the "zero" of the needle, the other adjusts the span. I can't remember which does which. If you Google using the right keywords you're likely to find a site or two that tells you what order to tweak the adjusters in. You should also plan on making these adjustments with a couple of different applied voltages. That 9V battery is going to be pulled "down" rather quickly. If you have some DC wall adapters you could use them instead. Be sure to compare the voltage displayed on the Smiths gauge with what you measure using a multimeter. Regardless of whether you're using a 9V battery or a wall adapter, don't assume it is delivering the voltage it says on the label.

[GreaseMonkey]

Hi,

Many thanks for all the help so far,

Dklawson, I've tried searching for what you mentioned with all types of keywords but come up with nothing

[dklawson]

You'll find more articles on calibrating the early gauge system (without the voltage stabilizer) than those with it. As I hinted at above, calibration of most later Smiths gauges is a bit of a black art.

However, take a look at this link:
http://www.mgb-stuff.org.uk/fuel.htm
You'll get some of the basics there and you'll see what's inside your gauge. Before you write back and say "Hey, that's a fuel gauge they're working on"... I know that and it doesn't matter. The inside of Smiths bimetallic gauges are all functionally the same. On a volt gauge all they do is change the resistance value of the heating wire and obviously change the calibration to match.

[GreaseMonkey]

Many thanks Lawson,

I have had a little fiddle with the adjustments, I measured the voltage of the 12v battery and it shows about 12.1-12.2 volts and I have the gauge reading just a tick over the 12 and it reads in about the right area with the 9v battery.

Many thanks for all the help

[GreaseMonkey]

Just one last thing,

I now have two holes where the cork circles were, they were damaged on removal and I was wondering what should I plug them with? Should I have a go at trying to make a makeshift cork plug for each or blue tac?

I'm guessing the corks purpose was to stop dust and dirt getting in and not to stop the plates moving inside?

Thanks

[GreaseMonkey]

Ouch my head

[dklawson]

Very few gauges still have the cork disks. I am lazy and would leave them off. If you want to close the holes off, you don't have to use the cork. Small pieces of tape will suffice. If you want them to look nice, take a few pieces of masking tape and layer them on top of each other on a piece of regular paper. Take the paper/tape to a hole punch and make several "disks". Peel off the masking tape disks and apply.

[GreaseMonkey]

Excellent thanks