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Old 05-12-2016, 05:23   #1
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Question Wattage / Voltage = Amperage... Correct?

The reason I ask is because I am not getting the correct amperage out of my solar panels.

This is just as the sun is coming up on a overcast rainy day.
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Old 05-12-2016, 08:07   #2
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Re: Wattage / Voltage = Amperage... Correct?

Yes you are getting about 12watt going to the battery 12vx 1a which isn'5 going to do much of anything

It says you have 10 watt out of panel (probably rounded off as they should match). So since panels at 20v your panels amps to controller will be about .5a

You only get full power with sun at 90 degrees to panel and no clouds. Overcast day on horizon I wouldn'5 expect much.
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Old 05-12-2016, 09:31   #3
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Re: Wattage / Voltage = Amperage... Correct?

You're right.

Now that its noon, the numbers are making more sense.

I just installed these panels so I am new to this.
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Old 05-12-2016, 10:57   #4
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Re: Wattage / Voltage = Amperage... Correct?

The panel's wattage number is most likely an average over some time period.
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Old 05-12-2016, 11:58   #5
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Re: Wattage / Voltage = Amperage... Correct?

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Originally Posted by epiic View Post
The reason I ask is because I am not getting the correct amperage out of my solar panels.

This is just as the sun is coming up on a overcast rainy day.
It would be helful if you coudl share the specs of the panels and how they are connected (series or parallel).

Make sure you do not confuse current upstream of the controller with current downsrtream of the controller. Same with voltage.

When the controller is in bulk mode (as in the photo) , current x voltage downstream of teh controller should be just a bit lower than current x voltage upstream of the controller. "Just a bit" is equal to 1 minus the efficiency of the controller, say 1 minus .

Without looking at your install it is difficult to tell if the 1.0A reading is taken a) at the boatīs main shunt (downstream of the controller but with other things in between) b) at the controllerīs output terminals. I also wonder if the


My first guess is that you have 1.38V x 1.00 A = 12.38W (plus/minus the current taken/put into by other things connected in between the point where current is measured and the batteries. If the 10W is meant to be a live reading of power produced by the panels (as opposed to a statinc reading of nameplate capacity), then I bet that the extra 2.38W come from some other charging source.



Note that the
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Old 05-12-2016, 17:16   #6
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Re: Wattage / Voltage = Amperage... Correct?

Amps x Volts = VA (voltamps). To convert that to Watts you have to multiply VA by power factor (PF). PF is always less than 1. PF basically how efficient your system is at delivering the power and takes into account losses developed at the source.

If you are just doing a rough estimate, then V x A = W is an OK formula. If you have to be fussy, then you need to use (V x A)PF = W.

So if your W/V doesn't give you the watts you were expecting, it could be the PF throwing your expectations off. Most PF should be less than 1 and greater than .85 .

Clear as mud?
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Old 05-12-2016, 17:34   #7
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Re: Wattage / Voltage = Amperage... Correct?

I see nothing suspicious here. Seems you regulator and monitor are fine.

Morning the sun is low the energy is low the stage is bulk, so all fine.

Noon power goes up and so do all the factors and the regulator seems to be doing the job well too.

The number do not have to fit to the last digit. They may be a mixture of points and averages.

b.
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Old 05-12-2016, 18:06   #8
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Re: Wattage / Voltage = Amperage... Correct?

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Amps x Volts = VA (voltamps). To convert that to Watts you have to multiply VA by power factor (PF). PF is always less than 1. PF basically how efficient your system is at delivering the power and takes into account losses developed at the source.

If you are just doing a rough estimate, then V x A = W is an OK formula. If you have to be fussy, then you need to use (V x A)PF = W.

So if your W/V doesn't give you the watts you were expecting, it could be the PF throwing your expectations off. Most PF should be less than 1 and greater than .85 .

Clear as mud?
You are mixing things up. Power Factor is only relevant in AC. OP is talking about DC, which is what there is between solar controller and battery. It does not make make sense to talk about phase, hence Power Factor, in DC.
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Old 05-12-2016, 19:05   #9
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Re: Wattage / Voltage = Amperage... Correct?

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You are mixing things up. Power Factor is only relevant in AC. OP is talking about DC, which is what there is between solar controller and battery. It does not make make sense to talk about phase, hence Power Factor, in DC.
Yes.

Power Factor is *not* the same thing as controller conversion efficiency -- not at all. PF is also *not* loss.

By the way, that second set of readings looks quite good. The conversion efficiency is almost 98%
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Old 05-12-2016, 20:02   #10
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Re: Wattage / Voltage = Amperage... Correct?

Indeed, for DC:

P = I*E

And of course:

E = I*R

(Yup... I learned this when it was E, not V)

And it's not just a good idea..... It's the law.
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Old 05-12-2016, 22:45   #11
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Re: Wattage / Voltage = Amperage... Correct?

I stand corrected. I was indeed crossing over from AC
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Old 06-12-2016, 08:31   #12
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Re: Wattage / Voltage = Amperage... Correct?

My photovoltaic panels have always underperformed manufacturers specs. I attribute this to optimized test manufacturer uses to boost their numbers. But if you have sufficient panels and can fully change your batteries then all is good
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Old 06-12-2016, 09:30   #13
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Re: Wattage / Voltage = Amperage... Correct?

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The panel's wattage number is most likely an average over some time period.
The panel's watt rating is the maximum it can supply, like noon at the equator in full sun, assuming your arch or deck is parallel to the ocean. That's why you need a curved arch (or articulating frames) and an MPPT or two, to get more light down them outside of lunchtime.
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Old 06-12-2016, 09:31   #14
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Re: Wattage / Voltage = Amperage... Correct?

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You're right.

Now that its noon, the numbers are making more sense.

I just installed these panels so I am new to this.
Don't know the size of your bank, but that's a reasonable number.
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