Re: 12V Cooler
Posted: Wed Apr 14, 2010 6:45 pm
Looks similiar to astroflight's whattmeter. They are used for checking load on motors(short bursts) with different props, and for battery charging. I have the smaller one, but they do make a larger one for large electric model motors. Not sure how it compares in price. Some of these electric models will easily pull 100 amps from lithium polymer(li-po) batteries. Uses a PIC for the display and calculations.
John
http://www.astroflight.com/index.php?ma ... gtvk54pd8n
Astroflight's does not use an external shunt(shunt=very low resistance metal that has stable resistance when hot). The digital ones that use an external shunt are actually comparators(I built a few before they sold them). Your shunt is rated to have a mV drop(across the shunt) at a certain current flow(we are talking DC).....say 50mV/200amps is a common one. The meter has a precision voltage reference(which is adjustable...but no coffee prior to adjusting
) and a comparator circuit. The voltage drop across the shunt is close to linear, compares that to your vRef, and that gives you an amperage indication. You can adjust for accuracy at rated load, but sometimes will not give you zero.
John
http://www.astroflight.com/index.php?ma ... gtvk54pd8n
Astroflight's does not use an external shunt(shunt=very low resistance metal that has stable resistance when hot). The digital ones that use an external shunt are actually comparators(I built a few before they sold them). Your shunt is rated to have a mV drop(across the shunt) at a certain current flow(we are talking DC).....say 50mV/200amps is a common one. The meter has a precision voltage reference(which is adjustable...but no coffee prior to adjusting
) and a comparator circuit. The voltage drop across the shunt is close to linear, compares that to your vRef, and that gives you an amperage indication. You can adjust for accuracy at rated load, but sometimes will not give you zero.
