Panel meters.

[davelectronic]

I have a possible issue I'm not sure about. Recently I purchased a 15 Amp DC analogue panel meter, but I don't see a shunt with it. A previous Amp meter I purchased (larger display) also 15 Amps has a built in current shunt. I have read the instruction leaflet and there's no mention of a current shunt. It only says prewired elumination, and the turret connection terminals. So would I have to add a current shunt external to the meter ? The meter feels quite heavy compared to the same physical size volt meter, I've no idea if it has a built in shunt. The only thing I can think of doing is measure the Amp meters internal resistance, would that tell me if this meter had a built in shunt ? Any help appreciated, thanks for reading. I just didn't want to destroy a perfectly good panel meter.

[jeremy]

Definitely put an ohm-meter on the two terminals and see if the resistance looks like a shunt (ie less than a few ohms, although for a 15A shunt it should be much less!)

[bob91343]

Do not put an ohmmeter on it.  You might push enough current to damage the movement.

Better to connect a power source with high resistance in series to see if the meter deflects.  If not, then it may be safe to increase the current enough to make measurements with ordinary equipment.

[Jwillis]

Is that a Blue sea ammeter . If it is then its internally shunted .   

[davelectronic]

Thanks for your replies, I've got another 15 Amp DC panel meter, that has a shunt clearly across the turrets. This meter has no visible shunt across the turrets. The specifications are meter movement 4 mega ohm's. That surley can't be or represent the shunt. I did thing a small battery and some high resistor to see if I get any deflection, I can slowly increase it depending on results.

[xavier60]

Thanks for your replies, I've got another 15 Amp DC panel meter, that has a shunt clearly across the turrets. This meter has no visible shunt across the turrets. The specifications are meter movement 4 mega ohm's. That surley can't be or represent the shunt. I did thing a small battery and some high resistor to see if I get any deflection, I can slowly increase it depending on results.

4 milliohms maybe?

[james_s]

It would be highly unusual for a modern DMM to pass enough current to damage a meter movement. I wouldn't worry about it unless it's some kind of expensive high precision thing.

[vu2nan]

...The meter feels quite heavy compared to the same physical size volt meter, I've no idea if it has a built in shunt. The only thing I can think of doing is measure the Amp meters internal resistance, would that tell me if this meter had a built in shunt ?

The heavier meter may indicate the existence of a shunt. The terminal bolt size may also be a pointer. A very low resistance across its terminals would confirm it.

It could be measured, using an analogue multimeter, selecting the highest 'kΩ' range that would pass only a few μA of test current.



The range may then be lowered in steps to confirm the existence of a shunt.

[davelectronic]

I do have a small analogue multimeter, never sees much use, I will try and test it using the analogue meter. Sorry I missed a previous comment, it's not a blue sky meter. I will take a couple of pictures of this meter. There are two extra terminals, but I assume it's for a lamp, as it says in the leaflet it's pre wired for a lamp. I thought that was the meter connection, and the turrets where the shunt. But it's for an internal lamp.

[Jwillis]

I did an experiment with a 20A meter . I already know that it is not internally shunted .  I set up the meter in series with a 1K resistor and used a 1.5V AA battery as a source of power.

1.5/1000 = 1.5mA not enough current to damage a meter . And not enough current to deflect an internally shunted 15A or 20A meter.
Connect one of the battery ends to the circuit and just tap the other end to complete the circuit. If there is any deflection , then there is no internal shunt .
On a 20A meter with no shunt  the deflection is 1.5A

[davelectronic]

I will try this, I've got some 1K resistors, I haven't tested with an analogue multimeter, haven't had a chance today. But will report back once I've done this resistor battery test. The pictures are of the meter, I'm certain the top black colour tabs are for elumination..

[Jwillis]

If it requires a shunt .The meter resistance is 4mΩ and the full amperage is 15A  so the voltage for full deflection is 60mV . So it will need a 60mV 15A shunt.

[StuartA]

I think that the safest and easiest way forward with this is to assume it needs a shunt adding. Make one by wrapping 6 inches of thin wire around a pencil just to coil it. Connect the meter with the shunt to a psu and say a car bulb load and slowly raise the volts and then assess what you see.

[davelectronic]

Well I tried the battery and the 1K resistor, nothing moved. So I upped the voltage to 3 Volts and same resistor, nothing moved. So went to 5 Volts, still no movement. So I got fed up with that and put it in series with a 20 watt lamp and 12 Volts, it's got the shunt built in. I increased the lamp load to 50 watts, with a little expected losses, it's measuring current is I'd expect it to be. Why couldn't they just add two lines of text in the instructions, stating the shunt is built in. The other 15 Amp meter is 60mm it's physically bigger, the shunt can be seen on that meter. I prefer the smaller meter that takes a 38mm cut out in the panel. Thank you for all the help, this time at least nothing went pop.

[Terry Bites]

It looks very much like a https://monacor.co.uk/pm-2-15a.html Its an ammeter, it dosent measure amperage What ever the F that is!
https://monacor.co.uk/contact-us

[davelectronic]

Can't see the bit where it says doesn't measure current. I didn't buy it from that site, and it was £9.00 from memory. It measures DC current fine. £20 + I'd never pay that for this type of panel meter.

[Terry Bites]

The price of quality panel meters is high. I love the look of these ones.