Measuring output from Solar Panels

Submitted: Saturday, Jan 15, 2005 at 19:14

Member - Moggs

Sorry if this sounds stupid but if you never ask you will never know....

...I have recently purchased some solar panels and a digital multimeter. My question is how do I actually (and safely without shorting anything) measure how many Amps the panels are putting out at any given time???

I also have a Waeco fast charge kit wired to the alternator that terminates at a Hella plug in the rear. How do I measure how many amps this is putting back into the battery???

Any info greatly appreciated.
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AnswerID: 93274   Submitted: Saturday, Jan 15, 2005 at 19:45

David Au replied:

It does not matter if you short out the solar panel inputs - that does not hurt the solar panels at all. A solar regulator with a built in volt meter, amps in and amps out are an asset.
Disconnect the one wire from the solar input into the regulator and place the meter on the 10 amp scale into the circuit between the solar panel wire and regulator - does not matter which wire. If you have the multi-meter wires the wrong way around it will just read in the negative and swap the multi-meter wires around.
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FollowupID: 352279   Submitted: Saturday, Jan 15, 2005 at 20:08

Member - Moggs posted:

Thanks David
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AnswerID: 93307   Submitted: Saturday, Jan 15, 2005 at 22:15

Eric Experience. replied:

A very easy way of monitoring battery current is to measure the the voltage on the battery negative terminal compared to the chassis. the voltage will be only milivolts but it is simple and does not require cutting or buying. Eric.
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FollowupID: 352386   Submitted: Sunday, Jan 16, 2005 at 13:53

David Au posted:

Eric Experience you may like to enlighten everybody on this method of yours. Please give a detailed explanation so everybody can understand the methodology.
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FollowupID: 352395   Submitted: Sunday, Jan 16, 2005 at 14:37

Member - Sparkie (QLD) posted:

I am afraid you lost me as well?????????????

Sparkie(IE not Y) ;-)
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FollowupID: 352486   Submitted: Monday, Jan 17, 2005 at 01:28

Mainey... posted:

is Eric Experience a really good mate of yours, I have never seen you be so nice, calm and even polite to a post that is so far off base?

I would want to know what Eric is using to actually measure the battery power with, if (Quote) "and does not require cutting or buying" (end quote) is correct ?

Bugga me I'm in agreement with 0zi....{better pop anutha pill} roflmfao.
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FollowupID: 352495   Submitted: Monday, Jan 17, 2005 at 07:19

Wok posted:


EE suggested this method yonks ago on a post about battery monitors.
It requires measuring the impedance of the ground return, then using [V sq/R] = W or Ohm's Law to get the current.
Problem was a milliohm meter is not a common tool in most kitbags.

It got filed into the 'Too-hard-basket'

EE's method is valid......just hard to implement.

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FollowupID: 352951   Submitted: Wednesday, Jan 19, 2005 at 22:04

Eric Experience. posted:

Gentle men I am happy to give more detials of the easy and safe way to measure battery current. In a comercial amp meter there is a very low value resistor called a shunt and there is a meter that goes on the dash which is wired across this resistor, what the meter on the dash measures is the milivolts drop across the shunt. The major problems with this set up are, 1. fire risk and 2, voltage drop. The fire risk is because you have a high current cct which all the battery current must pass through and therefore you can not fuse it, you then have wires from it to the dash. The inclusion of a common resistor in series with a battery causes a small voltage drop but that voltage with its variations, like for example injector pulses, is imposed on all other ccts. If you measure the voltage across the earth lead of the battery the mili volt meter is near earth so has no fire risk. The voltage drop still exists but it is one that is already there and you are not adding to it. There is no shortage of milivolt meters they are called varius things but a "centre zero 100ma meter" is the cheapest form, To callibrate your meter add resistance in series to reduce the reading or use a slightly longer earth strap to increase the reading. Eric,
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