CigarMan

Here's what I need, a simple small box with two 510 connectors, male/female and two led or lcd readouts to accomplish two things. I want to test cartos/attys/batts to find current draw and voltage under load. Pretty simple, right? Madvapes sells the LCD readout voltmeter but it doesn't work on a single eGo type unit I have here, it just blinks so there needs to be a way to accommodate those types of batteries. It needs to handle 3-8volts and up to 5 amps.
So that's it; can be a single multi-line display even, I just want AMPS and VOLTS displayed. Battery on one end, 510 carto on the other.

Anyone up for it? We can discuss it here, but I'd prefer PM's if you are really interested in building for me.

Thanks.

Rocketman

CM,

It's not that difficult to do what you ask but might not be worth the effort.
The under load voltage can be done with a powered voltmeter. Most little LED or LCD meters will run off a separate 5 volt battery. The self powered ones (like the madvapes one) won't reliably read a 3.2 volt eGo. The regulated output voltage of an eGo won't indicate 'state-of-charge' either.

An inline shunt is required to measure Amps. The shunt drops current that another voltmeter reads and is calibrated to read as Amps. For example, a 10 milliohm shunt in the current path will drop 10 millivolts per amp, 5 amps would give 50 millivolts. An LED voltmeter with a 1999 display could connected across the shunt calibrated for 199.9 millivolts full scale and the decimal moved to indicate 19.99. 5 amps would look like 5.00.

Again, this meter would need it's own power source. If only one display was used then switching could change from voltage to current. A DPDT switch would be necessary to also switch in the scaling resistor for a 19.99 volt range, and out for the millivolt range and to connect to ground for voltage measurement, and to the low end of the shunt for current measurement.

To test the resistance of an atty or carto and display resistance would require additional circuitry.

An alternative would be a microprocessor with 2 analog input channels, scaling resistor for the voltage measurement and a shunt for current. But it too would require a power source.

A pair of $4 Harbor Freight voltmeters (self contained 9 volt batteries) in a small shoe box would work if you keep lead length short.

How small a box did you have in mind?

berger

why would you even need to measure the amps anyway if you have the loaded volts and the measured ohms..its calculated and absolute anyway? all you need is the simple connector rig to measure the loaded voltage

Rocketman

I got it !!!


A shoe box with two Digital voltmeters, and a calculator

JohnnyJames

I agree, you are just complicating things. And inexpensive HarborFreight meter should do it. I have also found the DCs to be quite consistent as far as ohms. Just test a five pack, if most of the readings are 1.6Ω the meter is fine.
Measure the ohms, measure the volts, calculate the amps. Good enough.

This is what I clip my meter to, had it for awhile.



In action.



3.74V (measured). 1.6Ω (measured) = 2.34A (calculated).

http://www.onlineconversion.com/ohms_law.htm

Here's a test box Ralph T built a awhile back. He did actually meter the amps.

http://s822.photobucket.com/albums/z...urrent=TS1.jpg

Rocketman

JJ,
You didn't like my shoe box idea?

With the built in calculator?

One thing to watch with amp measurements is path resistance. Lead resistance and internal shunt resistance becomes a larger percentage of path resistance with LR cartos.

When you measure 1.6 ohm, and put test leads, switchs, binding post and meter shunt resistance it can go up to a total path resistance of 1.9 ohms easily. That's a pretty big error.

Steampunk

Geeze, man, we're talking e cigs here, not making friends with Muslims!

CigarMan

You guys are right, I really don't need to 'see' amps when I can calculate it. JJ's little rig is all I need to accomplish the task. Now all i need is some connectors.
Thanks for the input