Measure high voltage and low amps: 130-200V / .01-2amps

Hi everyone,

I am trying to develop a circuit but I don't have enough experience in Ohms law, or circuit design in general. I was wondering if anyone might be able to point me in the right direction on how I can achieve the goal I stated above. That is to measure 130-200 volts (or 100-200) and .1 - 2.0amps DC current. This is for a car battery system low power charger.

I found a few posts related to measuring solar voltage but there wasn't enough information, and not anything that would work with the high voltage I am looking to measure.

Is there anyway to do this with just resistors, and / or capacitors? I don't have an electronic shop nearby, and I'd like to avoid having to wait for parts to be shipped in. Of course there is radioshack, but besides the cellphone inventory, they don't have much selection.

I would greatly appreciate any help.

Thank you!

This is for a car battery system low power charger.

There is nothing low power about 200V at 2A that is 400 Watts a hefty lump of power in anyone's book.

I have never come across such a high DC voltage in a car charger are you sure you have the figures right?

That is to measure 130-200 volts (or 100-200) and .1 - 2.0amps DC current. This is for a car battery system low power charger.

Good grief! That's 400 Watts at max output. You are nor messing around with nickel metal hydride or LiOn high voltage automotive are you? Very dangerous batteries.

Ray

It's definitely not low power..but its actually only charging at low amps. It's really closer to 35-50 watts. I guess the max I'd want it to handle would be 60watts just for some overhead. My 2amp requirement silly D

This is for a hybrid car grid charger/balancer. I want to be able to use the arduino to monitor the voltage, and use a relay to turn on/off the charger based on the readings off of the charge current.

2amps was a high number. The charger is only charging at 170-250ma. With a max in the 300ma 350ma (possibly going higher for short amount of time), the voltage range is also lower between 160-175 with max of 185-190.

Is this possible somehow using the arduino? Any ideas on something else that I can use as a template, or are there shields for high voltage measurement. I'd prefer to make a shield myself from a custom circuit. I just cant find something at that current. I see smaller examples, but I am not sure how to scale it up..

The best way to measure current is a Hall effect current sensor. There are lots to choose from here:- http://uk.farnell.com/sensors-transducers_current?CMP=KNC-GUK-FUK-GEN-KWL&gclid=CjgKEAjw2KCcBRCQ_6mztcunhEgSJABPxOF1SnWK88gNFQgXRMWRdswuXdn47rwpOnN79KzTLI9qKvD_BwE

However where they are not so good is the lower current range. But they do have the advantage of being safe due to them being totally isolated.

How about this one:- http://uk.farnell.com/honeywell-s-c/cslw6b1/current-sensor-1a-4-5vdc-to-10/dp/2292984

Isolating and measuring DC however is a lot more tricky. One way is to use a voltage to frequency converter, then couple into the Arduino using an opto isolator and then measuring the frequency on the Arduino to see the voltage.

Hey Mike,

Thanks for the input. I checked them out, but not sure about how I'd really use them...

I realized I didn't try searching for "arduino voltmeter", when I did I came up with some interesting results.

Here is an entry in this forum. I am still new to schematics, does this specify the max voltage anywhere: http://forum.arduino.cc/index.php?topic=191964.0

It looks like I goofed, and there are some examples I can work from when looking for" arduino dc voltmeter"...so I'll just post what I find here so the search term I was using "measure x DC voltage" gives someone else a hand, and I can use it as reference.

Thanks again.

It seems a voltage divider would be something I could use to measure the volts at the minimum, correct?

http://startingelectronics.com/projects/arduino-projects/arduino-4-channel-LCD-voltmeter/ That link has someone measuring up to 50V, how would I go about increasing that? Is there a ratio that I compute to get the resistor values?

The problem you will have with a potential divider is that the arduino would not be isolated and that is a very large voltage to attach to such a small controller.

To use a hall current sensor you measure the voltage comming out of it. Down load the data sheet and you will almost certainly see an application circuit.

Okay. I see what you're saying mike. Thanks for your help. I'll post back with my results.

Do not connect >14V to a car battery.

1 MegOhm 1/2 Watt and 10 kOhm resistors would make a 'nice' potential divider for measuring your 130 to 200 V DC within the arduino range.

If you are not sure about your V=IR then I'd expect you'll get a P=I^2R catastrophe somewhere, but that won't happen in the above potential divider.

1 MegOhm 1/2 Watt and 10 kOhm resistors would make a 'nice' potential divider for measuring your 130 to 200 V DC within the arduino range.

Yes but it is not isolated is it? As a rule of thumb you should isolate things if the voltage is over 100V, it could kill.