Feasibility of measuring large DC current with Arduino

Wawa:
80Amp and an opamp gain of 34 gives ~418 A/D values.
Lowering the 1k resistor to e.g. 470ohm could give you twice that resolution.

Right...I imagine it will take some figuring and tinkering to fine tune the circuit to my requirement. Fortunately, the parts are just a few cents each, even the arduino board is just a few bucks.

Wawa:
Are you sure you can safely ground (to USB/computer/mains) the negative wire on the solar cell side?

I am not sure of anything, LOL...this is all new territory for me. What would you suggest? I figured even at 100 amps, the secondary is only .075 volts.....

Wawa:
High-side measurement (shunt in the positive line) could be a safer way.
INA169 Analog DC Current Sensor Breakout - 60V 5A Max : ID 1164 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Leo..

Thanks, I will look into that.

Wawa:
80Amp and an opamp gain of 34 gives ~418 A/D values.
Lowering the 1k resistor to e.g. 470ohm could give you twice that resolution.

Are you sure you can safely ground (to USB/computer/mains) the negative wire on the solar cell side?

High-side measurement (shunt in the positive line) could be a safer way.
INA169 Analog DC Current Sensor Breakout - 60V 5A Max : ID 1164 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Leo..

But using a hall torus would give 'perfect' isolation and be totally "safe"

@Wawa, I looked at that adafruit part you mentioned. It maxes out at 5 amps, how would one use that with the larger shunt?

Please forgive my 1st grade questions. Electronics design is something that has always interested me, but I have little experience and zero formal training; like Arduino programming, it is learn as I go. LOL

jackrae:
But using a hall torus would give 'perfect' isolation and be totally "safe"

I ordered a pair of these, and plan to modify one of them to solder each of the chip traces onto a 1/8" copper strap, bolted to a 4 Ga. lug.

None of the three approaches I have been presented with are expensive, so I plan to try all 3 as time allows. Right now, I am on a fact finding mission. I have already greatly increased my small database of electronics design knowledge!

JohnDeere630:
@Wawa, I looked at that adafruit part you mentioned. It maxes out at 5 amps, how would one use that with the larger shunt?

Just connect it to the larger shunt.

The big shunt is 0.075volt / 100Amp = 0.00075ohm.
The 0.1ohm shunt on that breakout board will be the fly on the elephant.
100Amp through the main shunt is 0.075volt / 0.1ohm = 0.75Amp through the breakout board shunt.
Leo..

Wawa:
Just connect it to the larger shunt.

The big shunt is 0.075volt / 100Amp = 0.00075ohm.
The 0.1ohm shunt on that breakout board will be the fly on the elephant.
100Amp through the main shunt is 0.075volt / 0.1ohm = 0.75Amp through the breakout board shunt.
Leo..

That's what I suspected...Thank you! Just some simple math on the arduino to convert the analog voltages to amp values, and I can change things around with a simple resistor change.

If you decide to use hall sensors...
You could use two 50Amp hall sensors (and two analogue inputs) if you split/divide current over two parallel cables.
Leo..

Wawa:
If you decide to use hall sensors...
You could use two 50Amp hall sensors (and two analogue inputs) if you split/divide current over two parallel cables.
Leo..

In my general practice, I have tried to avoid that if possible. Inevitably over time, one connection gets loose/corroded/etc. and throws the load to the other leg, with spectacular results. 30,000 amps dumped onto a single 4/0 cable is not something you quickly forget. It wasn't my doing, as I was just a helper at that time, but was magnificent....put the 4th of July fireworks to shame. Who knew molten lead and copper could spatter so far and stick to so much?

MCP6002 has 2 amps on the one 8 pin chip, you only need one thus "1/2 MCP6002" it can be had with 1, 2 or 4 amps per chip as MCP6001,2 and4.
BTW since the old timers here seem to know a lot more than me it would be best to listen to them.

JohnDeere630:
In my general practice, I have tried to avoid that if possible. Inevitably over time, one connection gets loose/corroded/etc. and throws the load to the other leg, with spectacular results. 30,000 amps dumped onto a single 4/0 cable is not something you quickly forget. It wasn't my doing, as I was just a helper at that time, but was magnificent....put the 4th of July fireworks to shame. Who knew molten lead and copper could spatter so far and stick to so much?

Sometimes paralleling helps prevent premature failure due to deterioration - if one wire
degrades the other helps, postponing failure to when both are deteriorating. You'll often seen multi-pronged
wipers on switches and potentiometers for this reason, since if one contact point corrodes the other
still has a low resistance and prevents further damage on the corroded one.

Of course if everything is too close to its maximum rating you no longer have diversity/redundancy, and get
cascading failiures, whether one wire or two.

MarkT:
You'll often seen multi-pronged
wipers on switches and potentiometers for this reason, since if one contact point corrodes the other
still has a low resistance and prevents further damage on the corroded one.

Whilst that may well be the case, the real reason for using multi-contact wipers on switching devices is to permit good contact distribution with controlled minimal pressure since a single solid (inflexible) contact wiper surface must inevitably give poorer current distribution as no two sliding surfaces will ever be in perfect contact. As an analogy a brush head with bristles is much better at sweeping than a solid wooden brush head

jackrae:
........As an analogy a brush head with bristles is much better at sweeping than a solid wooden brush head

LOL, I have to remember that one! That pretty much sums up my day, on occasion. Eating soup with a fork is another saying I use; you stay busy, but don't accomplish much.

I don't remember all the details of the incident I was referring to. It was a very, very large bank of 2 volt batteries, on the order of 40k a/h at a biomass powerplant. I was just a helper on another crew and remember asking about the show. I have no idea why such a small cable was anywhere near such a large bank. When it was finished, it was all big copper bars that connected everything.

outsider:
MCP6002 has 2 amps on the one 8 pin chip, you only need one thus "1/2 MCP6002" it can be had with 1, 2 or 4 amps per chip as MCP6001,2 and4.
BTW since the old timers here seem to know a lot more than me it would be best to listen to them.

Gotcha. I have a couple of things I plan to try. All approaches I would not have know about without you folks. Thanks a bunch to all of you that answered!

Gary