Determining the correct ammeters & shunts to buy

[dor]

I have a 500A shunt on my negative side which gives me an overall total current into / out of the batteries. I also have an ammeter on my DC panel (which is on the +ve side) which gives me just the current I'm using that side.

 

Gives me all the information I need. Shows me what my net charging is, and if the engine is not running, the difference between the two tells me what my inverter is using. OK so it doesn't tell me the actual output of the alternator, but it gives me a pretty good idea without getting too complicated. (I also have several voltmeters in various places which helps to know what is going on as well).

[smileypete]

No. Even running them at rated power wrecks them.

 

General opinion in the industry is never to run them past 66% rated power. Not even for a second.

 

I'll agree some are rated to 66% of full power, but these seem to be the more expensive precision ones. A lot of the cheaper 200A shunts appear to be rated to 120%:

 

http://www.ebay.co.uk/itm/200A-75mV-DC-Current-Shunt-For-Amp-Digital-Analog-Meter-/170490927398?pt=LH_DefaultDomain_0&hash=item27b20d1926

 

'Overreacting Capacity 120% (of rate current)'

 

Anyway, the main thing is the bars in the middle of the shunt stay well below 140C at all times. If it's in the the negative next to hull earth stud, extra heat sinking should be fairly easy to arrange.

 

For reference a 200A 75mV shunt puts out 15 watts of heat at 200A. Saying one of the above shunts shouldn't put out more than 7.5 watts even for a second sounds a bit extreme.

 

cheers,

Pete.