Trouble with ammeters shunt

[fezder]

Right, i perhaps bought wrong type of ammeter for my car, it doesn't have external shunt and i don't feel confortable dragging high-caliber cable to passengers site....So, it is 60-0-60 amps meter, is it possible to use this with external shunt resistor? of course that would effect reading, but you guys have any idea?

 

[chemelec]

You Need to Determine the Sensitivity of the Meter.
Than Determine the Require Shunt Resistance.
After doing this, It is Possible to put the Shunt Down in the Motor Area and Run Small Wires up to the Meter.

 

[MikeMl]

No, you are stuck routing the heavy wire to the driver's compartment.

 

[MikeMl]

You Need to Determine the Sensitivity of the Meter.
Than Determine the Require Shunt Resistance.
After doing this, It is Possible to put the Shunt Down in the Motor Area and Run Small Wires up to the Meter.

Only by opening up the meter and removing the internal shunt. The meter is likely made in a way which makes it very difficult to open it up...

 

[chemelec]

Usually you can open these up.
Than just Cut a Break in the Existing Shunt and determine the Meters Sensitivity.

 

[fezder]

hmm, thing is, even if i could crack this open, how do i determine sensitity? if i understand correclty, very small current goes to meter but huge current throught shunt?
I talked with my buddy and he pointed out i should place meter's shunt so startup current doesn't go throught it, good point, would have blown up meter if i would have wired it up...

 

[chemelec]

To Determine the Meters Sensitivity, You Need a regulated power supply of a known voltage (12 Volts would be Good.) and a Few Potentiometers.
Start with Pot set to a High Resistance Pot. Possibly 50K
If No Reading on the meter as you get down to the last Quarter of Turn, Than remove it and try a 10K pot.

Set the Pot to its Highest Resistance and Connect it in Series with the Supply and Meter.
Than SLOWLY adjust the Pot till you get a Full Scale Reading.
Now Disconnect the Pot and Measure its Resistance.

Lastly, Divide the Volts by this Resistance to get the Meter Current.

Also, If you put Two Diodes, Back To Back, Across the Meter Terminals, It can give you some Protection against Damaging the meter.

Want to TALK?
If you have a LAND BASED PHONE, Finland is a FREE CALL for Me.

 

[fezder]

ah, if i got it right i adjust current with potentiometers so it doesn't at least right away short out power supply?

Now Disconnect the Pot and Measure its Resistance.

Ah, since it's series circuit, same current goes throught potentiometer as well as ammeter.
No, i don't have land based phone anymore

 

[chemelec]

Once you Know the Meters Current Rating, Here is a Basic FINAL CIRCUIT.

Making an EXACT Value of Shunt is Difficult.
Make a Shunt of a Slightly Higher Resistance, than Using this Pot, It can Correct for Errors.

 

[fezder]

Thanks, too bad these meters aren't opened at all easily, they are same as these:
http://images.biltema.com/PAXToImageService.svc/product/large/2000028458

 

[chemelec]

Thanks, too bad these meters aren't opened at all easily, they are same as these:
http://images.biltema.com/PAXToImageService.svc/product/large/2000028458

OK, These Meters do Not have a Normal, Parallel type of Shunt.
More like This and not easily Changed.

Just a Shunt and a Needle with a Magnet on it.

 

[fezder]

bugger, well thankfully i didn't open it all the way....are there any this fashion meters (60-0-60) with external shunt? i can't find them anywhere.....except perhaps ebay but i tend nowadays buy from elsewhere (first you wair 30-60 days and finally get wrong product....)

 

[fezder]

OK, These Meters do Not have a Normal, Parallel type of Shunt

missed that one....so seems i'm stuck with bigger wires, oh well....unless i setlle with one-polarity ammeter but that doesn't like if/when current goes other way which i'd like to monitor in case alternator goes toast

 

[chemelec]

Probably NOT.
It would Require a Zero Center Meter Movement.

 

[chemelec]

Doesn't you car have a VOLT METER?
MOST CARS DO, If Not you can Easily Add One.
As Long as your Voltage is Normal, About 14 to 14.6 Volts, It is DOUBTFUL you have a Problem.

 

[MikeMl]

Here is how I have done it:

Get one of these:

Two small gauge wires from the meter, through the car's firewall to the engine compartment. Find the wire that goes from the positive pole of the battery to the car's fuse box. Connect the sense wires from the meter to the opposite ends of this wire. The wire becomes the shunt for a the uAmmeter,

Avoid the wire that goes to the starter motor. Usually there is a separate wire that goes from the battery post to either the alternator and/or the fuse box. You want to use the section between the battery positive post and whereever it goes, but avoid the section that carries the cranking current.

 

[fezder]

only voltmeter my car has is digital and i hate it, i must scroll menu on computer to see it....
Alternator is too old technology and doesn't output enought voltage for modern batteries, others too have rigged it with diode to fool it (completely safe)
I had such rigging but seems some wire went loose on some dark corner as computer says low voltage, about 11 volts but battery shows almost 13 volts.
I've checked cables and mechanic too agreed that diode-trick is the way to go, bigger cables and/or better alternator haven't helped anyone with this car

 

[fezder]

hmm, never thought of using micro-ammeter as currents can be quite huge
care to draw schematic just for sure Mike?

 

[chemelec]

I would just get Another VoltMeter and Add it in.

How About This 30 Volt one.
NOTE: the 30 on the meter is Distorted Just because of the Angle that I took the picture on.
FREE, Just Pay the Shipping Cost.

 

[chemelec]

hmm, never thought of using micro-ammeter as currents can be quite huge
care to draw schematic just for sure Mike?

Same as the Schematic I Posted in #9, a few Minutes ago