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# How can I measure AMPS that my solar panels put out ?

SOLAR POWER
User ID: 703067
United States
06/15/2009 09:51 AM
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How can I measure AMPS that my solar panels put out ?
I want to accurately measure how many amps my two solar panels are putting out . Can I do this with a multimeter and if so, how do I do it ?
Anonymous Coward
User ID: 703090
United States
06/15/2009 09:55 AM
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Re: How can I measure AMPS that my solar panels put out ?
I want to accurately measure how many amps my two solar panels are putting out . Can I do this with a multimeter and if so, how do I do it ?
Quoting: SOLAR POWER 703067

Most of them will not do it. Only the high dollar ones will.
You need something like an Astro Whatt Meter or you can use a shunt resistor to measure current using a common voltmeter.

As Ohm's law states:

I = V/R

Where:

I = Current
V = Voltage
R = Resistance

To implement the formula, simply put a low-value resistor in series with the power or ground connection to the ESC, then measure the voltage difference between each lead of the resistor. The difference can be plugged into the formula to yield a current.

For example, a .05 ohm shunt resistor reads "0.17V" across the two terminals. We simply replace the variables with our known values and solve the equation

1: I = 0.17/.05

2: I = 3.4A

When using this though, take care that the shunt resistor is of the lowest possible value to minimize voltage losses, and by minimizing voltage losses, you are also minimizing power dissipation, as:

W = VI

Therefore:

W = I x I x R

Using this formula we can calculate power dissipation of the given resistor. Suppose the conditions of the above example, 3.4A and 0.05 ohms.

1: W = 3.4 x 3.4 x 0.05

2: W = .578W

Keep in mind that the resistor power rating of your shunt must be a higher number than your calculated dissipation at max continuous current draw you plan to measure.
Anonymous Coward
User ID: 703113
United States
06/15/2009 09:57 AM
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Re: How can I measure AMPS that my solar panels put out ?
By a charge controller from SunForce for \$150 and it will give you real time readings in both amps and voltage.

Connects easily between your panels and the batteries.
Anonymous Coward
User ID: 684422
United States
06/15/2009 09:57 AM
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Re: How can I measure AMPS that my solar panels put out ?
You would have to select the ameter function and insert the meter in series with the panels. In other words all the current has to flow through the meter. The other way would be to put a known load across the panel output and measure the voltage drop.
Anonymous Coward (OP)
User ID: 703067
United States
06/15/2009 10:00 AM
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Re: How can I measure AMPS that my solar panels put out ?
You would have to select the ameter function and insert the meter in series with the panels. In other words all the current has to flow through the meter. The other way would be to put a known load across the panel output and measure the voltage drop.
Quoting: Anonymous Coward 684422

so a regular multi meter can be used ?

just connect positive solar panel wire to positive meter clip and negative solar paenl wire to negative meter clip and makes sure positive input clip of meter is in the amp input hole of the multimeter ?
Anonymous Coward
User ID: 702829
United States
06/15/2009 10:01 AM
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Re: How can I measure AMPS that my solar panels put out ?
First you must start with either direct sunlight perpendicular to the solar cell, or use a light source that mimics the spectrum of the sun. Then you can use resistors to load the cell and measure the voltage and current. Ensure the resistors can handle the expected or estimated power. Gradually increase the load(amount of resistance) until the voltage begins to drop. The point this drop in voltage occurs is called the "knee" of the IV Curve(Current to Voltage Curve). Once you hit the point where the voltage begins to sag, you have hit the maximum stable current.
Anonymous Coward
User ID: 456756
United States
06/15/2009 10:01 AM
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Re: How can I measure AMPS that my solar panels put out ?
You need to see if you can measure DC or AC amps on your multimeter. Usually, you have to move the probes hooked into the multimeter into different jacks on the meter's body. Consult your owners manual. Get some alligator clips to add to the other end (testing point) of the probes.

Now, if you are measuring in DC amps, make sure the polarity of the probes is correct. What you are going to be doing is put the probes IN SERIES with the DC power coming from the panel.

Make sure the black probe is clamped onto the negative terminal and the red probe is clamped onto the positive terminal. Make sure your meter is set up for the proper amperage range.

If you are measuring AC amps, make sure the black probe is clamped to the neutral (white wire) and the red probe is clamped to the black wire.

SETUP METER BEFORE YOU TURN POWER ON!!!!!!!!!!!!!!
Galaxy

User ID: 701959
Netherlands
06/15/2009 10:17 AM
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Re: How can I measure AMPS that my solar panels put out ?
so a regular multi meter can be used ?
Quoting: Anonymous Coward 703067

As long as the solar current doesn't exeed the multimeter range.
Most multimeters can handle 10- or 20 A.

This way you measure the short circuit current.
After you've done that, you can measure open voltage.

Now you can calculate the power in watts with the formula

P = U x I

Where P=watts, U=open voltage, I=short circuit current.
Luctor et Emergo.
Enigma

User ID: 700809
United States
06/15/2009 10:23 AM
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Re: How can I measure AMPS that my solar panels put out ?
so a regular multi meter can be used ?

As long as the solar current doesn't exeed the multimeter range.
Most multimeters can handle 10- or 20 A.

This way you measure the short circuit current.
After you've done that, you can measure open voltage.

Now you can calculate the power in watts with the formula

P = U x I

Where P=watts, U=open voltage, I=short circuit current.
Quoting: Galaxy

be careful... if you exceed the amps on your MM, you will blow an internal fuse... ( I did on mine by putting too many panels inline )

use a shunt or get a charge controller with readout...
Anonymous Coward
User ID: 694905
United States
06/15/2009 10:23 AM
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Re: How can I measure AMPS that my solar panels put out ?

Or, you can use your MM in series:

Anonymous Coward (OP)
User ID: 703067
United States
06/15/2009 10:34 AM
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Re: How can I measure AMPS that my solar panels put out ?
ok..jus did it..using my \$1.99 multimeter...

the panels are rated 80 watt - 4.75 amps

they arent in direct sunlight , and they only measured 1 amp at 19 volts . I guess direct sunlight makes all the differnce to get the full amps. Evidenlty they still put out good voltage in non direct sunlight, but low amperage ?
Anonymous Coward
User ID: 694905
United States
06/15/2009 10:45 AM
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Re: How can I measure AMPS that my solar panels put out ?
They'll still charge your battery bank though...Just more slowly...
Anonymous Coward
User ID: 703132
United States
06/15/2009 10:48 AM
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Re: How can I measure AMPS that my solar panels put out ?
btw it doesn't really matter if you have a bank of rechargeable large battery and a power inverter dc to ac then why does it really matter? the capacitor as a safe guard will just bleed excess current off anyways unless you plan on hooking it to a stove
Anonymous Coward (OP)
User ID: 703067
United States
06/15/2009 10:51 AM
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Re: How can I measure AMPS that my solar panels put out ?
They'll still charge your battery bank though...Just more slowly...
Quoting: Anonymous Coward 694905

both my panels measured 2.3 amps together at the source...but by the time I measured it at the b attery bank, it was down to 2 amps

so thats about a 15% drop but my wires coming off the soalr panel travel about 50- 60 ft before reaching the battery banks.

so even if I get max amps out of my panles of about 10 amps, the most that will make it to my battery bank is 8.5 amps
Anonymous Coward
User ID: 694905
United States
06/15/2009 10:55 AM
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Re: How can I measure AMPS that my solar panels put out ?
They'll still charge your battery bank though...Just more slowly...

both my panels measured 2.3 amps together at the source...but by the time I measured it at the b attery bank, it was down to 2 amps

so thats about a 15% drop but my wires coming off the soalr panel travel about 50- 60 ft before reaching the battery banks.

so even if I get max amps out of my panles of about 10 amps, the most that will make it to my battery bank is 8.5 amps
Quoting: Anonymous Coward 703067
Galaxy

User ID: 701959
Netherlands
06/15/2009 10:56 AM
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Re: How can I measure AMPS that my solar panels put out ?
both my panels measured 2.3 amps together at the source...but by the time I measured it at the b attery bank, it was down to 2 amps

so thats about a 15% drop but my wires coming off the soalr panel travel about 50- 60 ft before reaching the battery banks.

so even if I get max amps out of my panles of about 10 amps, the most that will make it to my battery bank is 8.5 amps
Quoting: Anonymous Coward 703067

You cannot connect your solar panels directly to a battery bank. Your batteries are going to die very soon.

You need a charge controller between panel and batteries.
Luctor et Emergo.
Anonymous Coward (OP)
User ID: 703067
United States
06/15/2009 11:00 AM
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Re: How can I measure AMPS that my solar panels put out ?
both my panels measured 2.3 amps together at the source...but by the time I measured it at the b attery bank, it was down to 2 amps

so thats about a 15% drop but my wires coming off the soalr panel travel about 50- 60 ft before reaching the battery banks.

so even if I get max amps out of my panles of about 10 amps, the most that will make it to my battery bank is 8.5 amps

You cannot connect your solar panels directly to a battery bank. Your batteries are going to die very soon.

You need a charge controller between panel and batteries.
Quoting: Galaxy

yes..i know...thanks...im using a charge controller.

but ive also read info that claims every month, its good to charge up the batteries using a fast, high voltage charge of 18 volts or so to bring the batteries up to a voltage of 13.7 volts....supposedly it is good for the batteries and prevents sulfication.
Anonymous Coward
User ID: 669258
06/15/2009 11:00 AM
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Re: How can I measure AMPS that my solar panels put out ?
I want to accurately measure how many amps my two solar panels are putting out . Can I do this with a multimeter and if so, how do I do it ?
Quoting: SOLAR POWER 703067

If your panel is rated at 30 watts then it puts out 15 amps at 2 volts or 2 amps at 15 volts etc. Amps times volts equates to watts.
Wraith1970

User ID: 444477
United States
06/15/2009 11:00 AM
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Re: How can I measure AMPS that my solar panels put out ?
You said "put out".
Anonymous Coward
User ID: 703106
United States
06/15/2009 11:14 AM
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Re: How can I measure AMPS that my solar panels put out ?
ok..jus did it..using my \$1.99 multimeter...

the panels are rated 80 watt - 4.75 amps

they arent in direct sunlight , and they only measured 1 amp at 19 volts . I guess direct sunlight makes all the differnce to get the full amps. Evidenlty they still put out good voltage in non direct sunlight, but low amperage ?
Quoting: Anonymous Coward 703067

1 amp at 19v = 19 watts

P=e*i
Anonymously
User ID: 704960
United States
06/17/2009 04:56 PM
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