Good way to measure high (100A+) amperage amps DC

[Red Squirrel]

Typically if I introduce new batteries into the system I ensure their charge rate is fairly equal to avoid sudden current shifts. I also try to avoid connecting at the terminals, that's why I added switches so I can connect stuff first then turn the switches on.  Spark near battery = bad. 

On slightly different note, whatever I end up doing I will need to calibrate it and make sure it's actually the right current. Will a meter like this work for DC amps using the clamp?

http://www.amazon.ca/Sinometer-UT204-True-RMS-Auto-ranging-Clamp/dp/B005G4VKFY/ref=sr_1_1?ie=UTF8&qid=1418324929&sr=8-1&keywords=dc+clamp+meter

It's not clear whether or not the clamp part actually measures DC current. Is it the case?  I know you can measure DC with the leads by inserting as part of the circuit but not what I want, and already have meters that can do that up to 10 amps.

I might even just forget about fixing this for now and buy that meter so I can check manually when needed.  Eventually I want to fully redo this as a -48v rectifier -> batteries -> inverter setup and I can revisit current measurement at that point and redo wiring.  This was done quickly with scrap wire and I was limited by sizes and did not want to cut too short so ended up leaving lot of slack in places that I should not have which made it hard to bend where I needed to.   I don't have tools to work with metal or even know where I'd start as far as what metal based materials to get so wood is the only option for structure.  This is not any different than the fact that 120v wiring is stapled on wood or passes through holes in studs. When using proper wire size the wire should not even be warm let alone hot enough to melt plastic or catch wood on fire.
 

[IanB]

there is zero reason to get an electrician to do 12v wiring

This statement seems to be a major WTF.

The most significant danger from electrical faults is fire, and fire is a risk in all high energy circuits no matter what the voltage.

You hire an electrician to mitigate risk and achieve a safe installation, so your house doesn't burn down.

Brushing off that concern is foolish.

[Red Squirrel]

there is zero reason to get an electrician to do 12v wiring

This statement seems to be a major WTF.

The most significant danger from electrical faults is fire, and fire is a risk in all high energy circuits no matter what the voltage.

You hire an electrician to mitigate risk and achieve a safe installation, so your house doesn't burn down.

Brushing off that concern is foolish.

Do you get an electrician to change your smoke detector battery?  A 9 volt battery can cause a fire in the right conditions.

[LabSpokane]

Mr Squirrel,

The responsible thing for you to do at this point is to disconnect and STOP. IF you want to incinerate yourself like a Vietnamese monk, I guess that's one thing. But crap like this will likely endanger others.

I'd respectfully request others to stop "helping" Mr. Squirrel. You're only validating him at this point.

And for your information, Mr Squirrel, I've spent plenty of time in wiring closets and network centers and we shitcanned installations such as yours, on sight, with extreme prejudice.

<\ToughLove>

[Red Squirrel]

What part of it is dangerous exactly?  Making blanket statements just because the cable management may not be the best does not help at all. This setup has been in operation for over a year and has been fine.      I just decided that I wanted to see if I can get help fixing the meter, but guess I will have to seek help elsewhere or figure something out myself.

[AG6QR]

there is zero reason to get an electrician to do 12v wiring

This statement seems to be a major WTF.

The most significant danger from electrical faults is fire, and fire is a risk in all high energy circuits no matter what the voltage.

You hire an electrician to mitigate risk and achieve a safe installation, so your house doesn't burn down.

Brushing off that concern is foolish.

Do you get an electrician to change your smoke detector battery?  A 9 volt battery can cause a fire in the right conditions.

A transistor radio battery has a lot less energy than a large high current battery bank, so its range of "right conditions" is very much narrower.

You have created a substantial portion of the right conditions for a fire, and we can see those conditions in the picture.  If that narrow gauge Telco wire completes a circuit from positive to negative, it will heat up very quickly and very hot.  Your fuses are apparently sized for the heavy cable, not the narrow gauge wire.  Those fuses will pass more than enough current to heat the narrow wire enough to melt or burn its insulation.  The narrow wires are wrapped around the heavy cables and pass very close to uninsulated portions.

The fact that you think this job is comparable to changing a smoke detector battery speaks for itself.

[Red Squirrel]

there is zero reason to get an electrician to do 12v wiring

This statement seems to be a major WTF.

The most significant danger from electrical faults is fire, and fire is a risk in all high energy circuits no matter what the voltage.

You hire an electrician to mitigate risk and achieve a safe installation, so your house doesn't burn down.

Brushing off that concern is foolish.

Do you get an electrician to change your smoke detector battery?  A 9 volt battery can cause a fire in the right conditions.

A transistor radio battery has a lot less energy than a large high current battery bank, so its range of "right conditions" is very much narrower.

You have created a substantial portion of the right conditions for a fire, and we can see those conditions in the picture.  If that narrow gauge Telco wire completes a circuit from positive to negative, it will heat up very quickly and very hot.  Your fuses are apparently sized for the heavy cable, not the narrow gauge wire.  Those fuses will pass more than enough current to heat the narrow wire enough to melt or burn its insulation.  The narrow wires are wrapped around the heavy cables and pass very close to uninsulated portions.

The fact that you think this job is comparable to changing a smoke detector battery speaks for itself.

If I can find a small value fuse/holder and add it to that wire, it will solve that problem... not really a big deal.   I already acknowledged that I probably should have added one.    The diagram I posted also is accurate.

[LabSpokane]

Mr Squirrel

What you have shown is so far from what would meet any type of code it isn't even worth discussing the details. The fact that you neither see, nor comprehend the failure modes or hazard they pose speaks volumes. I also come away with the distinct impression that you have "liberated" your electrical components from your local telco. Or is it your employer?

[Red Squirrel]

Most of the stuff I got from ebay such as the fuses and meter. The wiring I got for free with permission. Was end of spool, too short for actual use in a work setting. They had a bunch of 000000 gauge too, but complete overkill.   

[jlmoon]

I have to ask if this is in a residential structure. If so, please reconsider disconnecting this instead of "fixing" it. At this point you have a battery system that is almost purposely designed to start a fire.

I hope his insurance company isn't seeing these photos.  If they are, they are sure to cancel a policy!

[richard.cs]

The clamp meter looks like is should work, but a detailed read of the manual would be good. You likely have a very pulse-ey waveform and unless it's entirely square the mean and RMS values will not be equal. To determine battery life you need the mean current not the RMS, this is probably what it will show in "DC" mode but it may have several options. It is also possible it will be confused by the waveform if it's got lots of content at higher frequencies than it can handle, but it'll undoubtably be better than your ebay meter.

Coming back to the safety side, it needs work but not an insurmountable amount. Re-doing the thin stuff, moving the big fuses to earlier in the circuit*, buying a reel of large heatshrink and using it liberally, sorting out the routing and clamping will make a lot of difference without throwing too much of the difficult/expensive bits away or taking more than a few hours work. It's clear that you didn't expect the kind of reaction your photos got, we can't force you to change it but when someone posts something that's clearly dangerous and doesn't appear able to see that it is then that's the natural reaction. It's the kind of setup I might lash-up for charging some batteries or getting the lights back on in a powercut, but it's far from anything I'd leave unattended in the basement while I slept.


*I see you've deleted the photos now, I assure you they do not match up with the schematic, the positive cables go down from the box to the switches, then up to the fuses, then join to go to the inverter.

[Seekonk]

Invariably a poster asks for help and supplies incomplete or inaccurate information.  Often details are not included because in their infinite wisdom seems unimportant to them.  This failure to pay attention to detail is often the reason their stuff doesn't work in the first place.  We ask for a schematic of how the meter is hooked up and your schematic is crap, leaving out all detail of how it is hooked up.  I know for sure it is not hooked up the way the manufacturer told you to do it.  I've been on BB's a long time.  Posts probably number more than ten thousand.  In that time I have probably helped less that a dozen people.  It could be that I don't know anything or my piss poor attitude.  OR it just might be that even given the right answer, the OP never listens or has the ability to comprehend what is being said.  I've seen worse wiring.  I still believe it is not hooked up as is should be.

[Red Squirrel]

Well since I've been wanting to get into electronics I ended up buying a scope.  It's definitely ugly output off the shunt:



Guessing the inverter or some outside factor is causing that.  Though, The last one (testing the voltage between + and - on the bank) is kinda odd, for a big battery plant is it normal to see that on the voltage side?  I would expect a smooth line that very slowly goes down as batteries discharge.  The voltage test was done in discharge mode, so were most of the others, but TBH I kinda lost track, I should have wrote down the tests in order as I took them. The data looked fairly similar either way though.  If anyone wants to see a specific reading I can always go back and take it.  To test I had the probe on the far end of the shunt and the ground on the battery side (shunt is on negative side as per meter's instructions, so I could do that without causing a short through the scope).

Also, I'm wondering if this shunt meter is not unidirectional, could it be an issue or would it just go to 0 when power is going "backwards".  Since it's an inverter charger the source changes direction.  On AC fail the inverter-charger is the load, when AC power is on, the inverter-charger is the supply and the batteries are the load till fully charged.

It seems to me this meter is just garbage though, instead of doing some kind of averaging it just does nn readings per second and displays the literal value of that particular reading so that's why the numbers are all over the place.

I was looking at current transducers on Digikey and found a few interesting ones, this one has the most useful data sheet where I get to know the output voltage range:

http://www.digikey.ca/product-detail/en/L01Z200S05/MT7176-ND/529408
These seem nice, as I don't need a shunt and it is non invasive.  Removes a potential point of failure in the system as well.

Though I'm a little concerned about the actual working range.  According to the graph I basically have .5v of play between 0 and 200a, and my expected load is well under 50a and currently it's a 100a system.  Connecting that to the arduino not sure what the accuracy is going to be like.  I want to be able to read up to 200a though, I may potentially upgrade the system in the future, and it's a good idea to be able to read past the fuse rating so I can set a proper alarm point for a unlikely situation that the fuse does not blow when it should.   

There's a lot of others too but the data sheet is not clear on range, not sure how to interpret them.  Open to ideas with better explanation.  More can be found here:

http://www.digikey.ca/product-search/en?FV=fff4001e%2Cfff801ed%2C564006f%2C5640070%2C56400c0%2C56400c3%2C10d0001a%2C10d0001b%2C12040010%2C12040013%2C1204005b%2C12040091%2C12040096%2C120400b3&k=current+transducer&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=250

They also have stand alone ones that are invasive but much cheaper, just not sure how you'd go about introducing that physically to #2 wiring and I don't even see how those two prongs are rated for 200A.  I'm thinking these may be meant to be used with a shunt and not actually directly.  Not closed to the idea of a shunt though, I think my issue is that the meter is crappy. I can either passively smooth the output or read it with an arduino or similar device and smooth it out with averaging.

I also read about op amps, could I use one in a case like this with the existing shunt?  Perhaps with a potentiometer so I can tweak the range with a known load then introduce it to an arduino.

As for the safety issues, perhaps a few clarifications I need to make:

- Those plastic clips are designed for PEX pipe, it was the most appropriate thing I could find.  In a proper battery bank bus bars would be used to interconnect supply/load/devices but not sure where to find those and don't have equipment to make them.  PEX pipe can handle much more heat than they will ever see there. (think: hot water line)

- The system is rated for 100A but the actual load is about 30 so everything is actually quite oversized.  I want to upgrade to -48v eventually which will quadruple my capacity without increasing amperage.

- RE. Fuses being closer to the battery:  You do not want anything that could potentially create sparks inside the battery cabinet.  I wanted to ensure that each run from the batteries are a single cable with absolutely no junctions.  The purpose of the switches is to turn cut one bank out so they can be disconnected for semi annually maintenance.  Checking connections for any corrosion, checking electrolyte etc...    Though I imagine I could figure out a better way of routing the cabling so that the fuses are near the exit of the hole.  I think I may get rid of that 2x6 and put plywood, it will give me a nice flat surface to mount wires and things on.  I could even put drywall over the plywood for fire rating, but really not needed but guess it would not hurt.  If I keep the shunt method, I need to keep the shunt from touching anything though, or it could alter the reading. That's why it's in mid air like that, but I guess there could be a better way of doing it.

- For those who really think this gets hot enough to cause a fire, while I don't have a thermal imaging camera to prove it I can use a rather non scientific method to prove that it's not: Coconut oil. It melts at about 25C. I can almost guarantee if I put a chunk on those cables it will not melt while the system is under load. (when AC power fails, I can throw the breaker for test for a couple hours)

I do eventually want to redo the wiring though, just so that it looks nicer.   Telco flex is just really tough to work with and I should have taken more time and effort to make nicer routing.  In a telco application the turn radius needed tends to be much larger than a small system like mine where everything is closer together.  It typically travels on cable ladders and held in place with string or tie wraps.   In my case I don't really have anything to tie wrap to so went with the pex clips as the cable fits nicely in there.