opAmp suggestions

can anybody help me out with suggesting some opAmp models or part numbers.

it needs to run on 5VDC and be able to step up 50mVDC to 5V and another changing 1000VDC to 5VDC.

It might help if you tell us what you are trying to do. More specifics are needed. 1000Vdc isn’t exactly a beginners thing.

My hazy crystal ball sees a locomotive and a current shunt. Leo..

Any op-amp can be used to make an [u]amplifier[/u] with a gain of 100. Most op-amps will require dual (positive and negative) power supplies to operate near 0V, and more than the +5V required output.

To reduce voltage you don't need an op-amp, just a [u]voltage divider[/u] (2 resistors) and a [u]over-voltage protection circuit[/u], and a careful design/layout to prevent arching.

You should also have an voltage protection circuit between the op-amp and your Arduino if your op-amp is powered by dual power supplies and/or more than +5V.

I think OP is trying to measure voltage across a 50mV shunt.
A single supply INA196, with a common mode range of -16volt to +80volt could do.
Measuring 1000volt is easy. Just use a string of resistors on the dangerous side of your voltage divider.
We should wait until OP gives us more info.
Leo…

LandonW:
can anybody help me out with suggesting some opAmp models or part numbers.

it needs to run on 5VDC and be able to step up 50mVDC to 5V and another changing
1000VDC to 5VDC.

You want a precision true rail-to-rail opamp for the 100x gain circuit. Is this in a bridge
configuration or relative to ground? Small analog signals close to ground require careful
attention to grounding to avoid ground loops.

For the 1000V this is a divider circuit, no opamp needed, but if the 1000V is dangerous (more than
hundreds of microamps), then a keen understanding of high voltage techniques is needed to make
a safe voltage divider - in particular multiple high-voltage resistors in series are needed (yes resistors
have a voltage spec). High current 1000Vdc is lethal, no second chances, never take risks with it.

@ WAWA. you are correct sir! good guess.

The voltage drop resistors im using are rated for 50W since im not pulling much of a load I figured those would work. im also fusing the circuit for safety reasons.

A voltmeter doesn't have nearly as big resistors in them and they can take it. (if im wrong please enlighten me) (if a volt meter can read 1000vdc then why cant the input circuit be tricked into displaying 5vdc)

But all im doing is making a horse power calculator. I've made the code and I tested it with simulation circuits I built on a bread board.

I'm just trying to get my ducks in a row for building the real-life circuits.

At 1kV DC at anything but tiny current levels you have to know about flashover and ensure it cannot happen - DC arcs do not self-extinguish. Since you appear to be measuring current I assume this is not tiny current levels but lethal current levels, and enough power available to sustain a fireball.

The safest high voltage voltage-divider circuit is entirely potted in suitable insulating compound so no air can get to the high voltages.

Ok that's good info.

i'm taking two measurements.

A) voltage. I set the circuit to knock down 1kVdc to 5vdc however it probably wont get past 800vdc

B) amps. measured in mVDC across a shunt on the high side. (before load) the ratio across the shunt is 1mVDC = 80amps (application only gets to about 35mVdc)

the reason I want to bump the voltage from mvdc to vdc is to get a wider sensing span from the analog inputs on the Arduino.

I just needed some help on how to wire the opAmp in this application. would I put positive to pos and neg to neg on the shunt? would a differential set up be the way to go for shunt readings? and also would I need large resistors for it? a volt meter has no problem with it so I guess what im asking is how does a voltmeter read it?

A voltmeter draws very little current and uses power line integrating to eliminate line noise. You need to draw current for the arduino since its impedance is not as high, and to keep the impedance low enough to not pick up line noise.

B) amps. measured in mVDC across a shunt on the high side. (before load) the ratio across the shunt is 1mVDC = 80amps (application only gets to about 35mVdc)

Shunt on the high side? At ~800V? Really???

yeah really. its on a locomotive

1000volt is not that high if you know what you’re doing (I sure hope so).
To measure that, you need a special high-voltage resistor on the “hot” side of your voltage divider.

Normal 1/4watt resistors should not see more than 100volt across, so you should use 10 or so in series.
I would put a string of ten 330k resistors inside a length of heatshrink.
Keep the “hot” side well away from everything.

The resistor to ground could be 3k3. That would result in <=1volt, and can be measured with 1.1volt Aref enabled.

A big NO for the high-side curent measurement at these voltage levels.
Current should be measured low-side.
The solution depends on what’s already there now.
Leo…

the high side current is off a shunt that's already there. that's where the company put it to be used to test with a volt meter.

the resisters I have for the voltage divider is one 50Kohm and then into a 250ohm. both are rated for use up to 50 watts.

if you'd like a pic of the locomotive schematic I can send it

LandonW: the high side current is off a shunt that's already there. that's where the company put it to be used to test with a volt meter.

the resisters I have for the voltage divider is one 50Kohm and then into a 250ohm. both are rated for use up to 50 watts.

No chance to measure that with an Arduino then, unless you power/use someting with a wireless link high-side.

50k:250ohm is a 4-20mA industrial link. Not very safe for 1000volt. If the 250ohm and/or connections fail, you will have 1000volt through 50k on your Arduino. The 50k resistor has to be rated for 1000volt, and needlessly burns 20watt. The 250ohm resistor only uses 0.1watt. Leo..

ok. also I should mention that in this project anything to the Arduino will be fused to keep the smoke in.

I guess I could install something on the low side for current sensing.. any suggestions for that?

LandonW: ok. also I should mention that in this project anything to the Arduino will be fused to keep the smoke in.

I guess I could install something on the low side for current sensing.. any suggestions for that?

Electronics blows faster than a fuse.

How much current. Can you move that 50mV shunt. Somebody could have put it high-side for a reason. Leo..

Why not punt and use something like this: http://www.vishay.com/docs/83622/il300.pdf

That would require an opamp on the high voltage side, and that has to be powered somehow. Leo..