Help with shunt meters.

[offgirdonhydro]

I'm in the process of getting a DC disconnects with bus built for my system.  It will have a shunt on the negative site for my batteries.  I'm planning on having a 2000 amp shunt and the most that will be going through the shunt should be 1200 amps.

I need a digital meter that will tell me how low or full my battery bank is.  I need to know what meter I'm using so I can tell them what resistance I need in the shunt.  They need this information on Thursday (8-23-07).

My system is 48 volts.

I have searched the net but I don't know what exactly what I'm looking for.

[Volvo farmer]

I would ordinarily recommend a Trimetric, but I'm not sure it will measure that many instantaneous amps.

What I want to know is what kind of monster system are you building where you're going to be putting in or taking out over 50KW into lead acid batteries? On the charging side, it would take over 10 DanB 20' turbines, or over $225,000 in solar panels .If you're planning on removing 1200 amps @ 48 volts, it would take more than ten 5KW inverters running full tilt.

[offgirdonhydro]

My current set up is

6. outback inverters
   
100. amps PV
     
104. amps hydro
     
     

I'm planning on adding 2 more inverters and installing the rest of my PV panels.  This will get me up to another 100 amps of PV.

The max output of the 8 inverters would be 950 amps at 48 volts.  I always go to the safe side so I upped it a bit.  I know it sounds like I'm running a village; I need to down size, and be more energy smart.  My issue is peak power with my farm.  Currently I do dump power every morning and if sunny about 1 PM.  I only have 4 of the inverters that I use.  The other 2 do not have power to them.

My house will be expanding soon to 6 people.  It will be 4 adults, a 5 year old, and one on the way.

[rossw]

Wow, that sounds um... "excessive".

I live in a "largish" house - some 8800 square feet (88 squares, 820 sq m), running quite a lot of computer equipment, all the usual "mod cons" - microwave oven, 42" plasma TV, dishwasher, washing machine, clothes dryer TV in every room etc, teenage daughter and all that goes with that. My wife works from home all the time (graphic artist), I work from home about half the time (40-50 hours/week).

We use plenty of power tools - big drills, angle grinders, sawbench, router etc.

I even use the arc welder off the inverter (although I start the generator for when its more than just a quick job)

All this, and I make do quite adequately with a 5KW inverter. Yes, one. Singular.

Using your energy smarter is going to save you HEAPS in resources to cater for the once in a blue moon peak (which you could probably manage with scheduling and a second genset anyway!)

That said, I don't know your situation and it may not be an option..... so.....

Most shunts seem to be 1mV/A, but that is going to be a lot of loss for you at 1000A+

Rather than using a seperate shunt (and deliberately wasting power), have you thought about perhaps using one of your battery cables itself AS the shunt?

Depending on the cables and length, you would probably only need to tweek the meter calibration a little, or at most, make yourself a small op-amp meter driver to give you the required (variable) gain (may be less than unity if you have long battery leads). Would be the "least wasted power" solution IMO.

[wphfl]

Good Morning,

Your system sounds quite impressive.  On my system, I monitor current flow by the voltage drop across the fuse.  For me, it is a consistent 3mV/A.  In your case that would be a 3.6V drop at 1200A if your fuse is comparable.  This is well within the range of any DVM.  You could use this method until a more appropriate shunt can be secured.  Just a thought.

Regards

Kevin

[fungus]

'in your case that would be a 3.6V drop at 1200A '.. This would lead to 4320 watts dissipated in the fuse....would have to be pretty huge. You might get away with 10A/mv, would lead to 120mv at full load being dissipated, this would still be 144w, not trivial but could be dealt with... that could bring it to high temperatures and since copper's resistance changes with temperature, it wouldnt be too accurate over the full range. 1200A is a -lot- to deal with...

[Nando]

My first question: why the fuses are in the negative side of the battery ?.

My second : why more than 60 KW are flowing through the shunt ?.

For you to have a reduce power dissipation, one must do some calculations, if the shunt is for the standard 50 mv drop the power dissipate would be 1200 *0.05 = 60 watts.

So for your case, it would be better to get a Hall effect clamp type ammeter which you could get it digital and arrange the battery replacement with a small isolated power supply, this way the 60 watts dissipated will become around less than a watt I( the ammeter power and the losses caused by the hall effect clamp).

Also, you could get a universal hall effect clamp that can be connected to the standard either 200 millivolts or 2 volts setting of a Digital volt meter

Your first reply indicating the PV and Hydro currents and the 6 ( 4 in use) inverters were not well displayed so I can not comment on them.

The PV panel shows 00, and the hydro 04 amps

Normally, PV and Hydro currents go into the battery and the inverters out of the battery and they cancel out to a net value, being the inverters the greater sinking current if all are maximized.

Can you describe each inverter and its use with time parameters usage ?.

It seems to me that your system may be over-built and over powered without need, because a good electric power management was not implemented.

Can you describe in detail your power usage, with time parameters included, to see where you could optimize your system and minimize it for greater efficiencies and lower losses. ?.

LASTLY: cabling resistance is another solution for your current measurement ( I hope that you have maximized their wire thickness to reduce the losses while operating).

If such GREAT power is being used, then 48 volts may have been a bank too low voltage for such system.

For 10 and 20 KW systems, we have used 140 and 240 volts banks, everything much lower currents and easier to reduce the operating overall losses with a master system using two inverters ( for redundancy), here is the place where one can use commercial UPS systems in a more economical settings.

Nando

[offgirdonhydro]

There are 4 sets of batteries and they each have 300 kcmil that are 7 feet long.

The inverters all connected in to one unit.  The one runs 24/7 because of my computers and my fish tanks.  The systems call for more inverters to start up as needed.  My house is all electric (the bitching will start).  All of my appliances are energy star rated.

As far as my usage goes I have not sat down and tracked it out to be able to post it.  I do think that I use my electricity wisely; there are 2 places that I skimp on.  I use my inverters to power my well (soft start).  I refuse to start a generator to use a 220 20A power tool for a minute.

[Volvo farmer]

Wow, I thought for sure you had made a typo.

It appears that a Trimetric will do 400A continuous@ 48V, maybe you could use two of them? It also appears that a Pentametric will measure across as many as three different shunts as well, so that might also be a good solution.

http://www.bogartengineering.com/

With a system as large as yours, you might want to seek out a professional, experienced installer to solve these kinds of problems. You have a pretty good chunk of money invested there and while there are some smart people on this board, you might not want to jump to conclusions based on something you've read on a DIY based forum on the internet.

[Nando]

now you start to supply the proper "INFORMATION"

With such excess available inverter power, it is logical NOT to run the gas generator for a short time welding job.

You say inverters, can you define them, power and voltage output ?.

In reality you have a single inverter and the rest on need, OK.

4 sets of batteries ( amp hour ?.), how are they interconnected, if so ?.

Can you repeat the PV and the Hydro current capabilities in a way that the yahoo shows them well ( like PV = XX amps).

What type of inverter ONLINE sequence do you have and at what current levels the ON sequence is set for ?.

It may be not necessary to have such special high current digital ammeter.

Also, how often two inverters are ON at the same time, 3 inverters and 4 inverters at the same time ??

Do you run the Air conditioning from the battery bank and what is the power and how it is operated ?.

Can you describe the ON loads and their sequence and load levels ?.

What is the power profile of the Hydro, same thing for the PV and the seasonal amp levels ?.

If you are dumping power by mid morning, then do you really have the system over built or not ?.

Nando

[offgirdonhydro]

The question was about a shun I can under stand a lot of the other questions that were asked but, so you know the day I installed the system I was in green boxers and today in yellow with the smiley faces.  I do feel that I gave the needed info about what I wanted the shunt for and the parameters that it was going to be used.  I hope everyone has at least some since of hummer toady. :-)

Currently my system is...

2. - PS4
   
6. - VFX3648
   
5000. watt hydro; built in control box with dump load
      
4. - 48 volt 850 amp hour Exide fork lift batteries.
   
24. Evergreen Solar Spruce Series - 190W 18 volts Solar Panel
    
    

    Using 2 MX60's

3. DC arresters in an out side enclosures
   
4. AC TVSS units
   
   

I am planning on adding...

2. -VFX3648
   
24. Evergreen Solar Spruce Series - 190W 18 volts Solar Panel
    
2. more 2 MX60's
   
2. DC arresters
   
   

My wiring off my batteries is 300 kcmil about 7 feet long that run into 250 amp T rated fuses.  Each battery has its own fuse and 300 kcmil wires.  After the fuses all of my wires are less than 4 feet so I run 4/0.  So I could use a Trimetric on my batter cable, fuse, or both depending on the resistance.  This would tell me what is needed for one battery witch will work fine for what I need.  So I need to get a Trimetric the 48 volt kit and a few odds and ends and I'm good to go.

The new DC control box (I'm trying to order) will have buss with disconnects for my batteries, hydro, PS4, and a small DC distribution box.

The inverters are set to call for the next one to come on once it is making 25 amps.

So it will be better to use one of the wires off the batteries for resistance instead of a shunt.  As I now under stand that a shunt will cause more voltage drop and "eat" some of my power.

I'm not planning on using more that 6 of my inverters but it would be nice to have a spare for when one dies because of running all of the time, when I send on in for a software update, or if I need more power.

I have looked into UPS but when I was putting my system together witch was small at the time I was told that UPS were not good for starting wells and large motors, or having large fluctuations in power usage.

OutBack stuff with the basics of what it is.  www.outbackpower.com

MX60 (charge controller up to 60 amps for PV)

VFX3648 (up to 3600 watts continuous power)

PS4 (AC and DC distribution boxes for inverters hold 4 inverters)

Mate / hub (system controller and communication for the outback stuff)

[wpowokal]

To tell the state of charge of a flouded lead acid battery acuratly requires a hydrometre, it's not digital and requires a human to obtain a result, but does tell one what the battery state of charge (SOC) is.

It is suficient to check the SOC on only one battery each day, with periodic checks on all batteries.

allan down under