# Milliampere - slight difference

Discussion in 'General Electronics Chat' started by ronph, Apr 8, 2013.

1. ### ronph Thread Starter New Member

Feb 4, 2013
25
1
So am building a portable solar kit of two 5 watt solar panels to charge SLA's and 12 volt (10 x 1.2 AA rechargeables) pack. Based on the rated current stated is .32A X 2, I should come out with +/- .64A if connected in parallel. I measured the open circuit and its giving around ~.54A so there is a slight difference. I know the conditions are not always ideal e.g. direct sunlight and PV performance so would the .10A difference really impact the way the batteries are charged say at a constant 14V coming from the charge controller?

Ron

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2. ### MrChips Moderator

Oct 2, 2009
12,624
3,451
You have a number of flaws in logic and measurement:

1) Don't take a rating as an exact value. There will always be manufacturing variances that will result in variations in actual measurements.

2) Solar output is going to vary immensely depending on atmospheric conditions and location.

3) There is no such thing as an open circuit current measurement of anything besides zero amps. Open circuit means the current is zero. If you are putting an ammeter across the output of the solar panels you are in effect creating a short circuit across the panels and that could not be good for the panels.

3. ### ronph Thread Starter New Member

Feb 4, 2013
25
1
Thanks. I agree that there will be variances in each PV so I am with you on #1 & #2 as earlier stated. As for #3 well, am measuring the current coming out of the charge controller (no load/not connected to the battery) and not the PV per se. Which still does not answer my actual question on the impact of .10A (100ma) difference when charging SLA/battery pack.

Last edited: Apr 8, 2013
4. ### kubeek AAC Fanatic!

Sep 20, 2005
4,687
805
This makes no sense. You cannot measure current by sticking your current meter to the + and - output treminals and looking at the current. You are shorting the output, which will probably destroy the charge controller in a short time.

5. ### wmodavis Well-Known Member

Oct 23, 2010
737
150
Yes it will make an impact. How much? You do not provide enough information to provide a complete answer to your question.