DC ammeter

[fabricator]

Now that my 17 is flying on a test tower I'd like to be able to see what it's doing I guess I'd like to be able to see DC amps and DC volts, I have a DC ammeter that reads 0-750 amps, I think it needs an external shunt, but I don't know if there are different sizes or how to hook it up, it looks like this.





Also, I know if I put my DMM across the DC side of my three phase bridge I'm reading battery voltage, how do I hook up a volt meter to read the voltage going into the batteries?

[TomW]

fab;

That ammeter should have a millivolt rating for full scale deflection. Something like 50 mv 75 mv, etc. They can vary widely.

Once you know that then you can figure out what shunt you need. You can more or less rescale it by tweaking the shunt mv value.

You can even get away with using a hunk of wire the right length for what you want. Not super precise but good enough for seeing what is going on.

I did a post on this wire as a shunt trick on the old board but cannot find it just now.


Tom

[fabricator]

OK, now that FS = 50 MV on the front makes sense, I'd love to see that thread

[Rover]

I imagine your not really ever going to see 750 Amp , maybe you will no idea 

I think finding or making a shunt that will handle 750A full scale, could be a little fun. Analog ammeters are fairly cheap, check out www.alleletronics.com they tend to have ammeters and shunts to match, you might want to pick one that fits your range.

Of course you coud just juggle with the shunt, and work out your own range.

[fabricator]

I might see 750 amps during the end of the world storms in 2012, it's good to be prepared, how would a person  make a wire shunt? And how would you rescale a meter like this?

[Basil]

fabricator
This guy make one in this youtube.
http://www.youtube.com/watch?v=65EiiE4NoDI

[Rover]

I'll let Tom work out creating your own, but if you bought a 75A, 50mV shunt, your actual readings would be 1/10 what you see on the meter (thats the easisest) .

Same would go for other fractions, 150A 50mv ... etc

If I were to build my own  I'd probably go for someting (piece of wire etc) that dropped he requisite number of mv to get to the range I wanted to be in. I'm not a fan of homemade shunts unless you can calibrate, with a known amperage and a meter to support it.

You can read all the voltage drop calculations tables for wire  till you can't see, but in practice, your particular piece of wire might be off , hence the calibration with a known source and meter.

[TomW]

fab;

Here is a snippet I posted some years ago with the basics:

An Easy "shunt"  is a 1 foot long piece of #10 solid copper wire will show 1 millivolt [.001 volt] drop across it for every amp thru it. Not the most precise method but perfectly acceptable for a good idea of the current. I use several wire shunts in my setup. I calibrate mine against a factory shunt / meter combination but you don't need that.

Anyway, if you like to tinker this will work.

What ever happened to "use what you got"?

Anyone can buy a meter / shunt combo but where is the fun in that?

If it was me and it isn't I would start with a hunk of copper wire a couple  feet long and drive a known current through it with a battery charger with an ammeter, whatever attach the wire in the battery + lead. Then attach one lead of your meter to the end nearest the charger ( + in this case). Then test the - lead at different points along the copper wire. With the right length wire you can set the meter to read 1/10 of the current.  If the meter reads backwards, reverse the leads.

If you like to tinker anyway.

Don't let the "buy one" crowd make you think you need factory shunts. They are easy and do work but there is more knowledge to be gained in doing it your own way.

Just my opinion.

I am using factory shunts now but only because they showed up in my junk pile.

Tom

[Shadow]

With your particular meter even with a shunt, with your wind turbine mounted on the hay rack I doubt you would ever see that needle move.

I went through the same thing trying to get amps. I would get a amp meter that reads smaller increments. I got digital ones off Ebay for 9.99. That read from 0-200amps.I use a 50mv 75amp shunt.

But even so I rarely saw more than a amp or 2 until I got my turbine up in the air 60 feet so it could get locked into the wind and make some real power.

As long as its close to the ground in turbulent wind they never make much power.

[Rover]

I just dug through my Junk graveyard, I have a (maybe more) 50a 50 mv shunt that I will never use again.... (it never saw high amperage so it is ok, and I only used it for a short time time comparing accuracy to hall effect sensors)... I bought it from allelectronics so you can see the specs there. If in the US drop me your mailing address (my email is my profile I believe) , and I'll send it off (slow boat to China ups.. chepeast I can get) .. but yours free.

if this too low a range I understand

for metering  with your meter 50A=750A so the meter would read 15A for every amp through the shunt

[Rover]

One more thing , on commercial shunts , you don't want to run them above 60%  continuous of rated capacity or they will start to derate... so figure 30-35 amps continuous is fine for a 50 A shunt

[hiker]

http://otherpower.com/otherpower_experiments_ammeter.html

[fabricator]

lots of good info, Rover I sent you a PM, I have a couple radio shack power supplies of known values so I might just screw around with this just to get some experience, the fabrication I can do blindfolded but the electrical stuff might as well be Chinese arithmetic.

[Rover]

Got your info, no probs. The fun thing about calibrating is that you need to know the amp draw of your load, (and be able to measure it ) .

[fabricator]

http://otherpower.com/otherpower_experiments_ammeter.html

I've never seen that one before, cool link.

[fabricator]

OK, the next one should be easier but there are still some things I don't understand, the volt meter has to go in line right?  My volt meter has two lugs on the back but I have #4 battery cable from the battery to the DC side of the rectifier, di I just go way to heavy with that wire? could I just use say, 12 ga wire from the rectifier to the battery with my volt meter in line?

[Fused]

http://fieldlines.com/board/index.php/topic,133114.0.html

Heres how I did mine.

Fused

[wooferhound]

Also, I know if I put my DMM across the DC side of my three phase bridge I'm reading battery voltage, how do I hook up a volt meter to read the voltage going into the batteries?

Once your system is connected to the battery, the voltage you read anywhere in the system will be held down to the battery voltage, even the AC voltage on the turbine side of the bridge rectifier.

The battery will always try to keep the voltage going into it, at the voltage level of the battery itself. The battery will be sitting at 13 volts, and your Wind/Solar power will be 22 volts open circuit. As soon as you connect your open circuit Wind/Solar power to the battery, POOF ,everything is now running at 13 volts. It pretty much doesn't matter what voltage you want to charge the battery with, Your genny may be making 65 volts open, but connect it to the battery and then everything is at the battery voltage.


What happens to all that extra voltage? It's converted to amps and that is where you start to worry about your stator burning up. Once your wind genny reaches Cut-In (battery voltage) the measured volts will be the battery voltage which should be increasing slowly as it is charging. As your genny speeds up past cut-in the voltage doesn't increase, but the amps do. Under most circumstances you don't have to worry about the voltage of the device you are connecting to the battery, your worry will be with the ability of the charging device to deliver the Amps without burning up.


When Charging a battery try to keep the current going in to less then 10% of the capacity of the battery. For Example: a 100 amphour battery should be charging at 10 amps or less.

[fabricator]

Thanks guys, excellent explanation Woof, so it's like flow and pressure in a water system, the flow gets necked down so the pressure builds up and it's like cavitation, the amps got no place to go.

[freejuice]

Hi Fabricator,
 Whew was working on my 17 footer blades today....your 17 footer gave me the inspirational boost I needed.....
 Yes, that was a good explantion by Wolf.
 I have seen my 24v 11-footer pumping out 30-35 amps and I would check the voltage at the battery terminal with a meter and it would only be a few volts above the battery bank voltage at best...I guess that's the batteries "clamping" the voltage.
 If you are looking for a simple control box style, per the Dans or others, here is a style I borrowed from VoloFarmer
http://fieldlines.com/board/index.php/topic,143693.0.html

I have bought some 50 amp rectifiers and will have to wire two to each phase ( on my 17 foot upgrade)....probably in parallel so each phase will have 100 amp potential before they blow...it might not even hurt to have 150 amps per phase...or three 50amp rectifiers per phase.

I had my alternator overspeading in some 50-60 mile an hours winds the other day...it was scary...I cant imagine a 17 footer over revving.
 In the photos I'm also going to do away with the fuses.... one blew which tried to put the alternator into orbit.

 Just the other day I was playing around with the 17 foot alternator and spun it by hand, it was connected only to a brige rectifier...no batteries or any kind of load was on the other end of the rectifier, as I revved it up it hit 100 volts dc fairly easy, but like wolf says, once a battery gets hooked up, "bingo-bango" you could spin it at almost any speed ( if you could overcome the torque from the amps its pushing) and it would not get much higher than what you have the battery bank configured for.
 All the best,
 Gavin

[FishbonzWV]

Dale,
Here's a link to BTHumbles meter dial program.
I used it to change the dial range on a couple of meters. Used homemade shunts.
It's a download and is easy to use.

http://www.otherpower.com/images/scimages/236/MeterDial.zip

I've got some 1/4" x 1/8" square magnet 'wire' from a transformer if you want to use it for a shunt.
Let me know and I'll ship it to you.

[fabricator]

Thanks Fish cool download, I actually have quite a bit of copper flat stock one inch wide from .032 to 1/8" thick, the 1/8 stuff should make a pretty short shunt.

[ghurd]

There will be times when it makes more than 100A.  Might get peaks past 120A?

If using 50A 50mV shunts, would need (at least) 2 in parallel.

If using  two 50A 50mV shunts, the scale will be off.  Should be able to remove the front cover and put permanent adhesive sticker label over the factory numbers.
20A over 150A, 40A over 300A.... 100A over 750A.

Should be pretty easy to make one like Fused did.

Not sure how easy it will be to calibrate with flat stock. 
Maybe connect the mV wires to the flat stock a tiny bit closer together than required, then "adjust" by slowly filing the 1" a bit narrower, one or 2 passes at a time?

G-

[TomW]

Not sure how easy it will be to calibrate with flat stock. 
Maybe connect the mV wires to the flat stock a tiny bit closer together than required, then "adjust" by slowly filing the 1" a bit narrower, one or 2 passes at a time?

G-

Sir Dozenaire;

You could also probably calibrate bar stock by cutting across the flat stock in a few places to alter the amount of copper "in parallel"  or more or less reducing the size of the cross section if that makes sense?

Might take some time to suss out how much to hack.

Seen this done someplace but forget where?

Tom

[ghurd]

Exactly the same idea.
The cut area is smaller, so the heat would be more concentrated between the bottom of the cut and the opposite side of the stock.
I kind of like the idea of filing the whole 1" bar down to 127/128" (whatever) so the heat is more even.
G-

[TomW]

Exactly the same idea.
The cut area is smaller, so the heat would be more concentrated between the bottom of the cut and the opposite side of the stock.
I kind of like the idea of filing the whole 1" bar down to 127/128" (whatever) so the heat is more even.
G-

Sorry, didn't get the entire comment and method into my pea sized noggin.

Just remembered I have some nice copper bus bar I may set up to use a large face meter I have in my pile.

Tom

[Rover]

There will be times when it makes more than 100A.  Might get peaks past 120A?

If using 50A 50mV shunts, would need (at least) 2 in parallel.

G-

Fabricator, if you expect 100+ amps , I probably would not use the comercial shunts that I was going to send you. If I did I would use 3 in parrallel just to be safe about them not getting derated (150A). I do have 3 of them I could send, but really  its going to get a little messy hooking em up, and there will be some inneficiencies when you have to wire em up in parrallel (the parralel wires etc)

Let me know if you still want em, but at this point you may be better off building your own or buying a suitably sized shunt ... 150A/50mV for instance

[fabricator]

There will be times when it makes more than 100A.  Might get peaks past 120A?

If using 50A 50mV shunts, would need (at least) 2 in parallel.

G-

Fabricator, if you expect 100+ amps , I probably would not use the comercial shunts that I was going to send you. If I did I would use 3 in parrallel just to be safe about them not getting derated (150A). I do have 3 of them I could send, but really  its going to get a little messy hooking em up, and there will be some inneficiencies when you have to wire em up in parrallel (the parralel wires etc)

I think you are right, Glen had to come along and throw a reality based monkey wrench in the works, now between him and Tom they are giving me a headache.........

Let me know if you still want em, but at this point you may be better off building your own or buying a suitably sized shunt ... 150A/50mV for instance

[Rover]

Now I remember why I like and use hall effect sensors.

[fabricator]

Now I remember why I like and use hall effect sensors.

You might as well be speaking Chinese

[ghurd]

For something on the order of 125A, might be good to make your own shunt from the CU flat stock.
Could scale it 25-50-75-100-125 Amps.

I doubt flat stock is very pure (electrically speaking), but should not be much of a problem.
Just need to start out with that in mind.
G-

[fabricator]

For something on the order of 125A, might be good to make your own shunt from the CU flat stock.
Could scale it 25-50-75-100-125 Amps.

I doubt flat stock is very pure (electrically speaking), but should not be much of a problem.
Just need to start out with that in mind.
G-

I think I'm gonna give it a try, I'm sure I'm gonna do a lot of stuff wrong but I might come up with something useful.

[TomW]

Now I remember why I like and use hall effect sensors.

You might as well be speaking Chinese

Here it is in English then.

霍尔效应的传感器

Tom