Voltmeter/Ammeter Question

[Lurkin]

I have just bought a Voltmeter and Ammeter from ebay, same as this one:- http://www.ebay.com.au/itm/DC-100V-10A-Voltmeter-Ammeter-Blue-Red-LED-Amp-Dual-Digital-Volt-Meter-Gauge-/380984804829?pt=LH_DefaultDomain_15&hash=item58b476c5dd

I have not received any instructions with it. I intend to use it between the charger and the battery to monitor the current/voltage going to it.

It has a shunt bulit in for up to 10a. Some diagrams on the internet suggest the positive should be directly connected (does not pass through the shunt), with the shunt in series on the negative connection. Alternatives suggest the opposite. Which is correct?

 

[amberwolf]

EIDT: Ignore the tiny stuff below; I can't open your link and assumed you meant a regular multimeter type; based on discussion below that must be incorrect.


Doesn't matter.which polarity, as long as it is in series with either positive *or* negative but does not connect to both, it will measure current. Polarity only matters to get the "-" sign correct on the meter.

If you have regen on a bike, then if while riding you get the - sign, then when braking the no - sign means you're seeing regen current.


If you put a lead on each positive and negative of yourpack and have it set to amps you'll melt the meter (or blow it's fuse if it has one).

 

[wesnewell]

The wiring instructions or at the bottom of the product page. But it's only good for up to a 10A load. You could use an external shunt for more load, but then you need to use a multiplier of the displayed amperage. You might should have got a higher amperage meter that comes with an external shunt. I got a 200V 100A one a while back, but too lazy to install it. The shunt is huge and heavy. Just wanted it to test.

 

[speedpower99]

like most wattmeter, the + only show the voltage, the - use to measure current. So the shun must be on the negative side.

 

[Lurkin]

The charger is 42v, 2.5a. 10a should be sufficient. It's only to see what it's drawing whilst charging at my desk, will not be on the bike.

Negative side it is.