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how do I measure the amperage?
By strider3700, Section Newbies Posted on Mon Mar 19, 2007 at 06:03:51 AM MST
up, wired and finally wind but I couldn't get a measurement on the current

Friday I finally wired up my turbine using the 25 Amp bridge rectifier dumping power into an old dead 12 Volt motorcycle battery.
It took until today for the wind to come back so that I could try some measurements. First thing I did was measure the voltage of the battery. 11.2 Volts. T
hen I went to measure the current the turbine was putting out so I took the positive to the battery and disconnected it and ran it in to the multimeter on the red line plugged into the 10A port specifically for testing current up to 10 amps. The black com line then connected back to the battery where the rectifier used to connect.
I then waited for a good blast of wind. I never got any reading at all. It was always locked in at zero. so I switched over to the milliamp settings and even at the smallest 2 milliamp setting I got .000 amps. So I'm assuming I did something wrong.
A few hours later I checked and the voltage on the battery was up to 11.5 Volts so I'm assuming it was charging slowly.
How do I measure the current correctly? It could be my $10 multimeter sucks for this but I want to be sure.

how do I measure the amperage? | 8 comments (8 topical)

Re: how do I measure the amperage? (3.00 / 0) (#1)
by Flux on Mon Mar 19, 2007 at 12:31:28 AM MST

You connected the meter correctly, did you set it on the right range ( 10A DC)

Try again but this time short out the series diode when it is spinning fast. If you see a reverse current from the battery then your meter is working correctly. If not you may have trouble with blown fuses on the current range.

If you get a reverse current from the battery, this current should reduce as the wind blows harder. If it reduces but doesn't change direction then you are not turning it fast enough.

Flux

Re: how do I measure the amperage? (3.00 / 0) (#2)
by AbyssUnderground on Mon Mar 19, 2007 at 12:41:36 AM MST

Check the fuse inside the meter has not blown. If you exceed a certain amount of current (15A maybe?) the fuse should blow to protect it.

http://www.repowered.co.uk - My Renewable Energy site.
msn[at]m3ezw.co.uk - my msn if you want a chat.

Re: how do I measure the amperage? (3.00 / 0) (#3)
by dinges on Mon Mar 19, 2007 at 04:09:10 AM MST

No portable DMM I have seen yet is fused on the 10-20A range. In fact, mine use a special input connector which is clearly labeled as being 'unfused'.

The lower current ranges (up to 200mA or so) are fused (in my case).

In the high current range, it's most likely the test leads will act as de facto fuse. Don't ask how I know...

Finally, read the manual of the multimeter. It should give you a complete explanation on how to measure current (amongst other things) with your DMM.

[ Parent ]

Re: how do I measure the amperage? (3.00 / 0) (#4)
by finnsawyer on Mon Mar 19, 2007 at 07:14:36 AM MST

Well, I guess the next thing would be to put a resistance in series with one battery terminal and measure the voltage across it, since you know the meter measures voltage. V (or is it E) = IxR. (Voltage in volts equals Current in amperes times Resistance in Ohms.)
GeoM

Re: how do I measure the amperage? (3.00 / 0) (#5)
by TomW on Mon Mar 19, 2007 at 09:04:23 AM MST

An Easy "shunt" to do what flux suggests 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.

Good Luck.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

[ Parent ]

Re: how do I measure the amperage? (3.00 / 0) (#6)
by gordon01639 on Mon Mar 19, 2007 at 04:52:42 PM MST

it sounds from your explanation of how you connected your meter that it may be wrong. you need to connect your meter between the battery and the output from the rectifier on only iether the positive or the negative line the meter should not be connected to pos and neg to read current. ie break the wire between the out from the rectifier and the battery and connect the red lead from the meter to 1 end and the black lead from the meter to the other end so that the meter is just a continuation of the lead to the battery.

kind of difficult to explain without a drawing.

hope this helps

Gordon.

Re: how do I measure the amperage? (3.00 / 0) (#7)
by strider3700 on Wed Mar 21, 2007 at 06:59:27 PM MST

Thanks for the help guys. It got windy again today and I tried again. I managed to record 0.4 amps at 11.7 Volts during one really strong gust. I'll have to do a diary entry showing picks of the blades and some info on the generator I guess. I think it's got too high of a cut in speed. The blades are really moving almost scary to be around when It finally gets going fast enough. I'm not sure that faster blades are the answer, perhaps I can find a way to gear things up somehow? I know that it will loose some efficiency but that is probably going to be easier then building my first genny isn't it?

Re: how do I measure the amperage? (3.00 / 0) (#8)
by Norm on Sat Mar 24, 2007 at 05:42:18 AM MST

What is a really strong gust?
Do a diary entry....pics and stuff...
( :>) Norm

( :>) Norm
[ Parent ]

how do I measure the amperage? | 8 comments (8 topical)

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