amp meters

[Propwash]

Has anyone had any luck with this style of amp meter. I bought three of them on ebay and two of them don't seem to be working. I thought that if I put an amp meter on each rectifier of my mill I would be able to tell if a rectifier quit working. These amp meters felt kind of light and chinksy when I was handling them but I didn't think much of it at the time. They don't have any markings on them at all.

                                   Kevin

[TomW]

Kevin;

Do they have internal or external shunts?

Many of those EbaY meters require a current shunt to be an ammeter. As is they are simply millivoltmeters in the 50 millivolt range. Hooked up in line without the appropriate shunt will likely damage them.

I used to have an extensive webpage on ammeters and shunts but was lost in a hard drive crash awhile back.

Cheers.

TomW

[Propwash]

They do say dc amps on the face. I assumed they had internal shunts. The add for them didn't mention shunts at all. I guess I shunt have bought them. LOL. I emailed the seller and explained my situation. If I am stuck with them I'll find out exactly what they got in them.

                       Kevin

                     

[TomW]

Kevin;

Unless they are relatively low current meters they probably require external shunts.

Maybe describe whats going on when you feed current thru them?

Here is a little experiment you can do if you have a battery charger and a hunk of #10 copper wire.

Strip a length of #10 copper about 14 or 15 inches long.

connect one end to the + battery terminal in series with a battery charger positive lead.

near the charger end of this wire wrap or clip the + lead from the meter to test.

Attach the other lead about 12 inches from the + lead of the meter.

If the meter is a millivolt range meter you should see some deflection of the meter and by adjusting the - meter lead to match the ammeter on the charger you can calibrate the #10 copper wire shunt you just created. If it goes the wrong way when connected just reverse the meter leads.

Note that this will work with most external shunt amp meters that run in the 50 millivolt [mv] range but some are different.

If this works and you do get it calibrated simply solder the meter leads to the copper wire and you have a permanent home made current shunt good to around 30 amps of current. And it costs some time and a few pennies. Other sizes of wire will also work but #10 is handy because it just works out to very close to 1 millivolt drop across one foot per amp of current flowing in the circuit.

Just something I do to avoid buying commercial shunts. Other options exist but this is cheap and easy.

Cheers.

TomW

[Propwash]

One of the meters works fine and gives the same readings as a 20-0-20 test meter that I have been using during testing process . The other two don't even wiggle with 5-8 amps going through them. Test meter confirms current. Seller says somtimes needles stick. I'm going to lay them over a rock and tap them with a 20pound sledge hammer and see if they free up. He He. My test meter came from a junked out riding lawn mower that was parked in a swamp for 10 years and it would probably out live a bushel basket ot those chinese!@#$%^&*().

      Anyhow thanks Tom. I often see meters on ebay that require shunts but don't include them. Thats a great tip. I am quite sure that these have internal shunts but as mentiond I'll find out.

                             Kevin

[Jerry]

Hey Tom.

Could you perelell 4 of the 10 ga. shunts for 120 amps? What would be the MV per amp with that shunt?

                          JK TAS Jerry

[sPuDd]

Call me silly Propwash - but are you trying to measure

AC current using DC current meters ?

[Propwash]

The meters are between the output side of the rectifiers and the battery. I am using a meter on each rectifier rather than one large meter. I thought it would be good to moniter each rectifier and field output individually. Maybe i'm doing something wrong here but it seemed like a great idea at the time. Maybe I've got tunnel vision and I'm overlooking the obvious. Thanks for the input guys.

                                       Kevin

     

[TomW]

Jerry;

Oh, I am sure you could but then you need to do the math for parrallel resistances to get the resistance / mv relationship.

My math sucks but it seems that 4 1 ft lengths would show a 1/4 mv drop per foot so seems you could use 4 4 ft strands to still use the 50 mv meters. Without my calculator and sheet of paper my math and numbers will likely be off so you should do it yourself.

"The inverse of the sum of the inverses"gives parallel resistance.

If you are pulling big current you could simply build your own shunts with brass or copper bar stock some screws and a tap and die set. simply tap off for the meter leads in appropriate places to get the range for your display meter. Use another meter to calibrate it. Set up a known load and position meter leads on the shunt where it agrees with the reading from the other meter. Drilling holes in the bar stock will alter its resistance as will cross cutting slots. Seems both increase end to end resistance which will increase meter deflection per amp of current. Your a sharp guy you should be able to get it from that info.

10% is probably fine for accuracy on the stuff most of us do.

Good Luck!

Cheers.

TomW

[ghurd]

Is it using 6 diodes instead of 2 bridges?

G-

[Propwash]

I am using full wave bridge rectifiers from Radio Shack. I did order some from Otherpower but havn't received them yet. From what I am reading on here you can't have enough spare rectifiers. My amp guages do seem to be working. They are pretty wacky below 10 amps. The needles hang and don't do much untill a 10 amp charge hits them. Above 10 amps they all read the same and work quite well. In the light winds yesterday there wasn't enough charge going through them to wake them up. Some of the gusts today seemed to do the job. The Ebay seller did say that the needles could be stuck so I guess he was right. My 20 pound sledge is not far away in case they need a little help.

   I am learning that tail alignment is quite critical on my machine. Yesterday while tinkering on it I shortened the chain between the genny and tail section one link to make the tail square with the genny. I noticed today the machine was making the sounds it makes when furling while running in the normal position. After a bit of looking I noticed the machine was not running square to the wind. I dropped my tower tonight and lengthened the tail chain out one link. I also tied a piece of caution tape to my tower to act as a tell tale so that I can tell if the machine is running square to the wind or not. I have not noticed much mention of this kind of problem on here but thought I would post my problems however trivial they might be so others like myself can be made aware of these little gremlins. My tower has been up and down like a yo yo the past few days. Its great practice and only takes about 15 minutes from start to finish now that have done it a few times. My mill has only been up for three days now but I felt like a celebrity at the local country store getting coffee this morning. A spinnig mill sure does draw a crowd. Friends are stopping by during the day and sneaking peaks at my guages while I'm at work. It's definately one of the most rewarding projects that I have tackled.

                             Kevin

[TomW]

Kevin;

Rather than the hammer, try tapping them with the handle of a screwdriver on one side of the case they should deflect a bit.

If you are holding them a good D'arsonval [meter] movement should move from moving your hand. Fact is if you shake it some it might loosen up if its sticky. They are very delicate inside in the movement too.

If they have a zeroing adjustment [slot usually centered below needle] they can get misadjusted and prevent movement to the right. Just tossing ideas here any, none or all may apply.

Cheers.

TomW

[jmk]

  Is your tachometer working? Careful with the 20 lbs hamer. I hear they are really fussy with them.

[Propwash]

Tachometer works great. It is a Medalion brand marine tach that I had kicking around. 1000 rpm's on the dial equals 200 on the mill, 500 on dial equals 100 etc. I am running it off from one of the stator wires. The tach is adjustable. I cranked the mill by hand with the blades off untill I found a tach setting that worked some wheres near what I thought the rpms should be. I used a stop watch while hand cranking to calibrate the tach.

                Kevin

[Propwash]

Hey Tom thanks. Just joking about the big hammer. I know what you mean about the tapping. I do it to my barometer all the time. I tapped the hell out of them yesterday and jolted them with a battery charger and they didn't even wiggle. These guages are the strangest acting things I'ver ever seen. Maybe they had to adjust to my time zone before they would work???(more dumb humor) My guess is that they are chinese knock offs of real guages. They are very light compared to my test guage which is the same size. I don't see any adjustment holes in them. I'll keep you posted on thier performance and longevity.

                          Kevin

[dinges]

Propwash,

You must be really desperate to have Goofy for assistant. We all know how he can screw up. Oh wait, now I understand, he's there so if anything goes wrong you can blame it on him ;-) What's the story?

Peter,

The Netherlands.

[hiker]

some of those amp meters don"t like mags near them--screws them up bad--

[Propwash]

Goofy makes a great consultant when things go wrong. He's the one thats always telling me to hit things with a 20 pound sledge hammer. LOL he he he.

   Tail chain has been readjusted, amp meters are working, the sun is rising this morning and my blades are still. Its like Christmas every morning in the world of wind mill experimentation. I'm sure they'll be spinning before the day is over.

                                Kevin

[Propwash]

Since starting this thread I have been in contact with the Ebay seller of these amp meters which by the way cost 7.95 each. I have explained my situation with them and asked for any help he could provide. Being of pessimistic nature I assumed that the meters were junk and I got hood winked. I was wrong and I'll be the first to admit it(goofy agrees). This seller has been honest with me and supportive in any way possible. I received an email from him today notifying me that 3 new meters were tested and being sent to me. I replied saying that my meters were working and other than low wacky readings they were fine. He replied that there was nothing he hated any more than meters that didn't work accuratly and to trash them. I have asked the seller for more details on these meters so that I can include it in this thread. The seller uses the name jjr2001 on Ebay. I noticed other windmill type items for sale as well as meters. This fellow bent over backwards to satisfy me and you can buy with confidence from jjr2001 for sure. Here is a link to his current listings. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7201691194&ssPageName=MERC_VIC_ReBay_Pr4_
PcY_BIN_IT

                            Kevin