HI folks,
My PV and battery system is 12V, not a great choice I grant you but it just sort of evolved and changing it involve essentially new everything, well apart from a few PV's that match and could be reconfigured in series.
Basically it is what it is for now, 12V and occasionally silly amps.
That said the problem would still be the same if the voltage were higher and the current lower as in the potential range would be big.
What I need ...
Accurate measurement with a resolution of 1% or 0.1A whichever is larger, IE. If I am drawing/charging anything between 0.1A and 10A I want a resolution of 0.1A however above that 1% is good enough IE at 200A a resolution of 2A will be just fine. (Better would be nice but not necessary)
Brief surge currents of circa 1000A are possible, starting motors and the like, and as I don't want to drop more than 0.5V across a shunt at any time that would demand a shunt at 500uV / A which would make measuring 1A a little tricky to say the least.
What I have ...
The inverter is a cheap model and is supposed to be capable of 20kW surge but I have always assumed this was just silly and that 10 was probably pushing it. My biggest loads to date is a chop saw at 1600W and the microwave which is about 1800W, which it has absolutely no problem with.
I havent actually measured the surge current but the saw will have a starting load of at least 5000W which is likely to be circa 500A when you take the dip in terminal voltage into account. Having just done that calc I think I could get away with a shunt at 1mV/A but no more.
The batteries are 450Ah@C20 and hooked up with 50mm, 2 X 25mm in parallel, which is good for 200A, going by general specs, but in practice could be pushed well beyond that without suffering any thermal issues.
So...
Can I reliably measure down to 1uV or less with a relatively easily constructed amplifier that will stay linear?
I appreciate that I would have to have some sort of gain control to change the range and resolution as the resolution of the DAC would be an issue otherwise.
I also appreciate that a, probably some, hall effect devices would be good but I am amusing I would need several so \i could ignore the saturated ones as the current went up. The problem here is cost... I want to measure at at least 2 points, preferably 3 although the last on is fused at 100A and will never see more than about 50.
I had wondered about an active system ... Essentially using a hall sensor but adding biasing coils to the core.
The thought process was to have perhaps 200 turns on the same core as the battery cable passes through. I wouldn't worry about having a linear output from the hall sensor but would always maintain it at 0 and whatever current it took to do that would be 1/200th of the current in the target cable.
I would appreciate any and all thoughts or ideas about this subject in general as well as comments with respect to my musings.
Thanks for looking,
Al
My PV and battery system is 12V, not a great choice I grant you but it just sort of evolved and changing it involve essentially new everything, well apart from a few PV's that match and could be reconfigured in series.
Basically it is what it is for now, 12V and occasionally silly amps.
That said the problem would still be the same if the voltage were higher and the current lower as in the potential range would be big.
What I need ...
Accurate measurement with a resolution of 1% or 0.1A whichever is larger, IE. If I am drawing/charging anything between 0.1A and 10A I want a resolution of 0.1A however above that 1% is good enough IE at 200A a resolution of 2A will be just fine. (Better would be nice but not necessary)
Brief surge currents of circa 1000A are possible, starting motors and the like, and as I don't want to drop more than 0.5V across a shunt at any time that would demand a shunt at 500uV / A which would make measuring 1A a little tricky to say the least.
What I have ...
The inverter is a cheap model and is supposed to be capable of 20kW surge but I have always assumed this was just silly and that 10 was probably pushing it. My biggest loads to date is a chop saw at 1600W and the microwave which is about 1800W, which it has absolutely no problem with.
I havent actually measured the surge current but the saw will have a starting load of at least 5000W which is likely to be circa 500A when you take the dip in terminal voltage into account. Having just done that calc I think I could get away with a shunt at 1mV/A but no more.
The batteries are 450Ah@C20 and hooked up with 50mm, 2 X 25mm in parallel, which is good for 200A, going by general specs, but in practice could be pushed well beyond that without suffering any thermal issues.
So...
Can I reliably measure down to 1uV or less with a relatively easily constructed amplifier that will stay linear?
I appreciate that I would have to have some sort of gain control to change the range and resolution as the resolution of the DAC would be an issue otherwise.
I also appreciate that a, probably some, hall effect devices would be good but I am amusing I would need several so \i could ignore the saturated ones as the current went up. The problem here is cost... I want to measure at at least 2 points, preferably 3 although the last on is fused at 100A and will never see more than about 50.
I had wondered about an active system ... Essentially using a hall sensor but adding biasing coils to the core.
The thought process was to have perhaps 200 turns on the same core as the battery cable passes through. I wouldn't worry about having a linear output from the hall sensor but would always maintain it at 0 and whatever current it took to do that would be 1/200th of the current in the target cable.
I would appreciate any and all thoughts or ideas about this subject in general as well as comments with respect to my musings.
Thanks for looking,
Al