Amp meter

[dougmcp]

Originally Posted by DOOmsman

Doug have you installed one of these? If you need a shunt across 2 batteries it would form a short it seems.

I haven't installed one in a golf cart but I have installed them in cars and my boat. Installing one in a golf cart is the same.
Voltmeters and ammeters connect in 2 different ways for 2 different functions.

A voltmeter is used in parallel across the positive and negative terminals of a battery to give you a voltage measurement.

An ammeter is used in series to measure the current flow in a particular circuit. It must provide a path for the entire current. It would be difficult to develop a meter that would handle significant amounts of current. With that in mind, the ammeter uses a shunt to allow some of the current to travel through a course parallel to the meter. It a little like a bypass where the meter is only reading a small sample rather than the whole current load.
Generally an ammeter will only measure so much current on its own and after that level is reached a shunt needs to be used. Shunts are available in all sizes but need to be rated as large as the current you're trying to measure.
I hope this helps with an explanation.

[gornoman]

Doug, is there a voltage drop across the shunt? Do they affect the pack voltage at all?

[DOOmsman]

This shows the 100 amp shunt you would use a 200-300 shunt.
That is a good site for meter and such
http://www.lightobject.info/viewtopic.php?f=14&t=187

[dougmcp]

Originally Posted by gornoman

Doug, is there a voltage drop across the shunt? Do they affect the pack voltage at all?

There is a voltage drop but it is extremely small, somewhere in the 75mv range, so for golf cart purposes it would be near 0 loss.
The resistance of a 200a shunt is only .00025 ohms so that should give you an idea.
The shunt and meter wiring looks something like this:



Here's what a typical shut looks like:

[DOOmsman]

If I had a sparkler I would have have two. One for volts and one for amps.

[dougmcp]

Originally Posted by gornoman

Doug, is there a voltage drop across the shunt? Do they affect the pack voltage at all?

Not trying to hijack anything here I just saw your cart in another thread and it seems pertinent.
Is that an ammeter shunt you have on the bottom left #6 battery or is it for something else?

[gornoman]

That would be an inline fuse for the entire pack.

[dougmcp]

Originally Posted by gornoman

That would be an inline fuse for the entire pack.

Thanks, I should have known better, I have the same thing on my boat inverter batteries and forgot all about it.

[adamj12b]

Originally Posted by dougmcp

Here's a 200 amp one for $18 http://cgi.ebay.com/UP8135-BLUE-LED-...item3a4a5d07f7

I actually have both Voltage and Current of these gauges installed in my par car. One thing you have to be very careful of is keeping the current sensor supply isolated from the traction batteries. In the post on page 2 that DOOmsman posted, it shows an isolated DC-Dc converter. If you use this, you will be fine, if you dont, as soon as the gauge is powered up with the shunt inline, the gauge will be destroyed. Dont ask me how I know this....

I have included a picture of the gauges installed. The blue is nice, but some times mess' with your eyes. They are REALLY bright!!

I went with the 500A version. I have seen over 200A loads regularly under working conditions, like pulling a tarp full of leaves. Other then that, Im around 120 max usually. Its not much more for the extra 300A.

-Adam

[DOOmsman]

Ok, Gorno has a fathers day gift sugestion.