What kind of Ammeter do I buy ?

[DigitalMind]

This is a stupid question probably, but electronics isn't really my strong suit so I learn as I go.  

Lets say I have a battery bank that has a total of 800ah, what kind of multimeter do I need to read how much current is being drawn ?? I guess what I mean is, I'm looking at ammeters, and they all have a maximum in amps.  So lets say Ammeter #1 says it can measure up to 300 amps. Would that mean that if I was actually using over 300 amps the multimeter wouldn't read it ??  

I know there's something stupid I don't know about since it seems that the good meters that electricians use don't measure THAT high in amps.  

I don't know if this question made any sense, spent alot of time wondering how to word it.  

If anyone has model numbers of a good ammeter I can use for the rest of my life, it would be great.

Thanks as always for your help.  

[DigitalMind]

I was looking at the Fluke 336, but the DC Current range says 0-600 amps, so from what I understand (and I'm hoping i'm wrong) this would be no good to measure the current of a 800AH batter bank ... ??  

http://us.fluke.com/usen/products/specifications.htm?cs_id=30405(FlukeProducts)&category=ELW

[Flux]

You won't find a multimeter that reads up to 300A.

For currents higher than 10A the normal route is to use shunts and read the millivolts dropped. A multimeter on the 200mV range will cope with the common shunts.

For a permanent display you can use a digital panel meter to display the shunt voltage direct as a current reading. For this purpose the common shunts are 50mV ( or 75mV if you want to go with analogue although with your sign in name you probably don't)

The other option for permanent metering is to use a hall sensor.

As you say, you will not normally be able to read beyond the meter's range but in some cases you can overload a shunt for a short while to measure higher current, they are normally rated continuously at nominal value but they will stand 100% overload for a few seconds to take a reading.

For crude readings you can measure the millivolt drop across a cable if you want to save the cost of a shunt but you need to calibrate and it will not be particularly accurate with resistance changing with temperature.

Flux

[DigitalMind]

That's kind of a bummer.  I was hoping for a meter tool that I can carry around with me  to measure current at a couple of locations, not so much a permanent meter for this one setup only... Hmmmmm ...

Thanks Flux for the information ... !!

[Flux]

The Fluke 336 will probably not measure beyond its claimed fsd.

That is an expensive way to go about things and if you decide to go that way you should decide how many amps you actually are going to want to measure. Knowing the battery bank capacity gives us no idea how many amps you want to measure. You need to think of your loads and any inverters or other things you intend to use.

Start learning something about your requirements before dashing out to buy a rather expensive piece of test equipment. A shunt and a cheapo multimeter may do all you need and save you a lot of money.

Flux

[Flux]

That's fine as long as you decide the maximum current for the worst case. If you really need the 800A there are Flukes with higher dc ranges. There are quite cheap dc clamp meters with ranges to 1000A, not in the Fluke league for accuracy but still good value.

I bought one from J & L in the UK, look at their site to see if they have something in your part of the world.

A clamp meter does seem the simplest option for your needs.

[DigitalMind]

Ok .. I just read up a bit more on Shunts and your explanation makes alot more sense to me now.  I guess it's no big deal to install a Shunt whenever I do solar setups.  Almost every solar set-up i've read about says to put one, I just never understood the point until now.  So, thanks again !

So that meter I put the url for that says it can calculate from 0-600amps, means that WITHOUT the shunt I could see the current being drawn as long as it's not past 600amps at that moment ??

SOOO sorry about these stupid basic questions, but I really appreciate the info !

I'm getting ready to do about 3-4 more or less small Solar set-ups for friends and family's cottages.  I probably won't start until next summer, which is good since I still have lots to learn about, but I know soooo much more than I did 4 months ago.  

[disaray1]

Digital- You might want to look at Fluke multimeters. A Fluke 87 is a fine tool that should last a lifetime, and accessories are available like this clamp..

http://cgi.ebay.com/NEW-Fluke-80i-400-AC-Current-Probe_W0QQitemZ170176978780QQihZ007QQcategoryZ25412
QQtcZphotoQQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 that'll help you read those big amp draws, and a variety of thermal tools...all just plug and play.

 Happy hunting. Ebay is your friend.

 David

[DigitalMind]

Wow you answered my questions while I was asking them in the previous post.  

Thanks alot Flux, I think I understand the concepts now.

I'm in the telecom business, and one of the companies I work for buys hundreds of thousands of dollars worth of equipment from suppliers that re-sell Fluke Products, and I get pretty nice discounts on these things when I buy through that company.  

[ghurd]

That eBay meter attachment is AC only.

"3-4 more or less small Solar set-ups for friends and family's cottages".

Save your money and buy another small PV.  And make it 12V.

Honest? I usually use the $3-on-sale HF meter.  It goes to 10A.

It's not hard or expensive (under $20) to find a meter that goes to 20A.

They measure 'just about as good' as my expensive meters, better than within reason. Close enough and more.  The internal battery being low causes us more problems.  It is more of an irratation than pure pain when one jumps the gutter and does a 35' swan dive onto a cement sidewalk.

Don't trust the thermal probe on a cheap meter.  My last few were off over 10'F at 70'F. I can guess closer than that!

The battery AH has nothing to do with the amps.  A 12V 12W bulb will still read 1A with a 12V 1AH battery or a 12V billion AH battery.  The bulb takes 1A with a 12V battery.

I question WHY it is so important to know what some huge loads take.

Say it takes 600A at 12V (13.8V).  Meaning 8280W, or 11 HP.  Who cares what it takes!  Read the sticker.  If it's off 10%, so what.  If 10% on a battery powered load that size makes any difference, then the whole system is far too small.

If it takes 600A, how big do the meter/shunt cables need to be to measure it within 1%? (Real Big).

I have used a car ammeter ($10) to read high amps at 12V. Close enough for me!

G-

[TomW]

G-

Very well said and to the point.

Not like we are measuring factors for a Martian wing shot rocket launch from earth. Cheap is generally fine for this stuff. plus or minus even 15% is not significant here. In My Opinion.

Cheers.

TomW

[disaray1]

  Ahh yes, the HF meter (of which I have two) will get most everything done, but his last comment about it lasting his lifetime puts the HF cheap chinese thing out to pasture. If you want a quality tool- get a Fluke- if you you want cheap chinese junk- head on over to Harbour Freight.

 I bought a vice at HF not too long ago. Pretty blue one, the largest they had. It broke the second time I used it, right at the front jaw, just above the screw- snapped right off. I returned it and did not get another. They sell disposable tools.

 I prefer quality and non chinese. My opinion.

 David

[DigitalMind]

Hi Ghurd,

  Thanks for the info.  I guess the only reason i'd like it to measure HIGH loads is to confirm the power consumption and to see if it adds up to how I thought it would.  Plus I love tools, and any excuse to get a new one is good.  

[ghurd]

Think car ammeter for the big loads.

Like David said, I prefer quality and non chinese too.  On a bench.

But field use, trust me, it will rain cats-n-dogs when you ran to town to find a 5/16" nut.  About then is when you remember the $250 Fluke is out in the gutter so it wouldn't fall. A minute later is when you wish it was the $3 HF.

Or someone will have it set to amps, then check the battery volts...

Or it is in a nice safe place, right where the drill falls off the ladder... or something.

[DigitalMind]

Hehehehehe, unfortunately Ghurd, I know all too well what you're saying.  I will check out the car ammeters as you suggest to see if it will do the trick for me.  

Thanks!

[DanB]

You are confusing current drawn from the batteries instantaniously with the banks amp hour rating I think.  The amp hour rating of the battery has nothing to do with how much current is going in - or coming out.

As Flux has said - you could use a shunt and a normal ammeter.  If you're messing with different systems all the time and taking lots of readings in different systems I would think that a shunt is tedious.  It is expensive, but the fluke 336 is a good choice/very nice tool for that stuff I think. (I use mine all the time, it's very handy to have a DC clamp meter)  In RE systems, the 600 amp rating of the meter is way more than enough - I cannot think of many applications where you'll need to read higher current than that.

[DigitalMind]

Thanks Danb,

  I was in fact confusing the ah rating of the battery with the actual current being drawn at that moment.  I now see the light.     Thanks for the info DanB, your advise means alot to me.  I think that Fluke will be at the top of my xmas list.  

[DanB]

If you're going to use them frequently - nice tools are a good investment.

Mine is actually the Fluke 337-which is about the same thing with a couple more 'small' features.  Its a nice thing though and it's been reliable.  I like it because I can quickly check current in lots of different places without screwing around with shunts etc...  It's very handy for me.

[wooferhound]

I would say to make an amp meter from a Shunt and a VoltMeter

http://www.fieldlines.com/story/2007/8/21/19914/7054

http://www.fieldlines.com/story/2007/3/28/71210/8066

http://www.fieldlines.com/story/2006/11/17/201828/63

[dinges]

Darn. I find myself agreeing with just about everyone in this thread. Generally good sensible advice.

I'll add that ~5 years ago I bought a small DC current clamp meter (0.1-200 A, AC and DC current). Price was 70 E at the time. One doesn't find DC current clamps with such a low range (<1A, .1 A resolution) often. The only alternative I had was a 400 E piece of equipment. Too expensive for me.

Ever since I have that current clamp I find myself doing a lot more current measurements, simply because it has become so easy and handy, compared to using a DMM where you have take apart wires and insert the meter in the circuit. Less risk of electrocution too.

Not a Fluke, just 'cheap' Chinese stuff, but it does the job fine for me at a fraction of the price. It works fine, just be careful with it (as goes with ALL tools, cheap or expensive). Don't use a screwdriver as prybar, etc.

Unlike Ghurd's, it gets used both on roofs, in swimming pools (when emptied) and on the bench.

I doubt you can buy it in USA (it was bought in NL from a Belgian company, Velleman, but it just puts their own brand label on it; 100% sure it's made in China), but here's the data:

Velleman DCM269

AC/DC clamp meter.

http://www.velleman.be/nl/en/product/view/?id=361666

Hm, on 2nd thought, it may be available in the USA too:

http://www.vellemanusa.com/us/enu/product/view/?id=522365

[Volvo farmer]

I could not find the Velleman for less than $100USD

However, this thing looks exactly the same for only $80. That's a pretty good price for a DC clamp ammeter if you ask me.

http://www.electronicsnmore.com/product_info.php/products_id/3460