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Old 13-07-2016, 10:21   #16
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Re: How to measure solar panel current

I use a Fluke 365 and one extra benefit is that the clamp is detatchable to reach into awkward spaces. This meter does me for everything and is super simple to use.



Quote:
Originally Posted by lindabarzini View Post
Is an amp clamp as accurate/sensitive as measuring amps with a mulitmeter leads? Will the amp clamp work right out of the solar panel even if the solar panel is still connected to the battery?

I want to measure the amps from my solar panel. Can I measure them after the pwm charge controller? And I assume the solar panel has to be disconnected from the battery. Or can I split the wires after the charge controller so I can get the amp clamp around just one of the wires?

If I measure at the battery terminal which has the solar panel wires after the charge controller and inverter attached, what am I measuring here?

If my solar panel is rated at 2.9 amps, with an 80% efficient charge controller, would my maximum be 2.3amps. And does this drop to near 0 on a cloudy day?

Would you normally expect a 50 watt solar panel to charge a 35ah battery fully each sunny day if the only draw is 25 watts for 10 hours?
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Old 13-07-2016, 13:27   #17
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Re: How to measure solar panel current

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Originally Posted by PaulinOz View Post
I may be totally wrong, but are not the clamp style current meters for AC not DC current measurements.

"Just buy one of these AC 0 10A Analog Amp Meter " The AC once again refers to Alternating current not DC as in Direct Current the output from batteries and solar panels..

To measure DC current you need a a known shunt in line and then read the voltage drop across the shunt, thus you can then calculate a current reading.

Or you could just install a Battery Monitor and that will give you everything you want to know.
The meter recommended by El Pinquino is a panel meter, not a clamp. But given the symbol under the A, I concur this is for alternating current. besides that, I wonder how long a $4 meter made in China will last?

Also agree, I've never been able to find a DC clamp - maybe I need to look harder.
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Old 13-07-2016, 14:13   #18
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Re: How to measure solar panel current

Quote:
Originally Posted by Omatako View Post
The meter recommended by El Pinquino is a panel meter, not a clamp. But given the symbol under the A, I concur this is for alternating current. besides that, I wonder how long a $4 meter made in China will last?

Also agree, I've never been able to find a DC clamp - maybe I need to look harder.
Sigh....... that typo was dealt with quite a few posts ago.

How long will a $4 meter made in China last?
Well... mine ( $12 made in China - bought in Australia ) have lasted longer than the $2 digital meter ( made in China) built into my $800 BEP switchboard.

I think you will have to look long and hard before you find one built anywhere else.... Mexico maybe... thats where a lot of the Blue Seas stuff comes from ... as do the circuit breakers on my BEP panel.
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Old 13-07-2016, 14:55   #19
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Re: How to measure solar panel current

Unfortunately, solar panel amperage and wattage ratings are given at the maximum voltage that the panel can produce, which is higher than the voltage needed to charge the batteries. As soon as you connect them, the system voltage is driven by the battery, and the amperage falls well below the rating. You have a PWM controller, which does not compensate for this. What you need to get the maximum output is an MPPT controller. These actually convert the output to AC, through a variable transformer, and back to DC. By doing this, while the wattage stays the same between the input and output, the voltage is dropped to just above what the battery needs to charge, the amperage is increased, and can actually exceed the rated output. Of course, the MPPT controllers are also significantly more expensive... Also keep in mind that the panels need to be pointing directly at full sun for full output. But with the PWM controller, or even directly wired with no controller (for testing purposes only - the controller protects your batteries) you will never see rated amperage
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Old 13-07-2016, 16:00   #20
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Re: How to measure solar panel current

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Originally Posted by steve0h View Post
Unfortunately, solar panel amperage and wattage ratings are given at the maximum voltage that the panel can produce, which is higher than the voltage needed to charge the batteries. As soon as you connect them, the system voltage is driven by the battery, and the amperage falls well below the rating.
You are correct about the wattage for a PWM controller, but at the lower (battery) voltage the amperage is (slightly) increased. The amps produced increases, it does not reduce, when the voltage is reduced.

Imp is measured at Vmp which is typically around 18v for a "12v" panel. This is higher than the battery voltage so Imp is more easily achieved at the lower battery voltage. Some allowance needs to made for the temperature effects, but a healthy system should achieve Imp in very good conditions with a PWM controller.

Isc is measured at 0V so at the higher battery voltages this current is not possible.
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Old 13-07-2016, 17:08   #21
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Re: How to measure solar panel current

I have a question/statement to ask/make....
Has anyone got a clamp that has the "+" & "-" marked on the side of the jaws?
Is it a MUST to clamp in the right direction? (+ to pos & etc...)
I get a dif reading if I reverse the direction.
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Old 13-07-2016, 18:48   #22
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Re: How to measure solar panel current

Quote:
Originally Posted by BruceS View Post
I have a question/statement to ask/make....
Has anyone got a clamp that has the "+" & "-" marked on the side of the jaws?
Is it a MUST to clamp in the right direction? (+ to pos & etc...)
I get a dif reading if I reverse the direction.
Yes. My Mastech has "+" and '-' in a circle on the faces of the jaw opposite to the "trigger". You can see the "+" if you zoom in on the illustration here
Products / categories ? Mastech (Build to Precision).

You should get the same "magnitude" for the reading in either direction, but the sign should be different.
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Old 13-07-2016, 19:07   #23
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Re: How to measure solar panel current

you seem to be anticipating the answer/yes split the wires for clamp meter/no wont charge as well on cloudy days/they doo trickle charge from street lighting /most pv controllers have dc amp read out built in
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Old 13-07-2016, 19:34   #24
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How to measure solar panel current

Quote:
Originally Posted by lindabarzini View Post
Is an amp clamp as accurate/sensitive as measuring amps with a mulitmeter leads? Will the amp clamp work right out of the solar panel even if the solar panel is still connected to the battery?



I want to measure the amps from my solar panel. Can I measure them after the pwm charge controller? And I assume the solar panel has to be disconnected from the battery. Or can I split the wires after the charge controller so I can get the amp clamp around just one of the wires?



If I measure at the battery terminal which has the solar panel wires after the charge controller and inverter attached, what am I measuring here?



If my solar panel is rated at 2.9 amps, with an 80% efficient charge controller, would my maximum be 2.3amps. And does this drop to near 0 on a cloudy day?



Would you normally expect a 50 watt solar panel to charge a 35ah battery fully each sunny day if the only draw is 25 watts for 10 hours?

My guess is that the clamp will not be sensitive enough, it will probably read accurately to the nearest 1.0 or 0.5amp but you should be interested in accuracy to the nearest 0.1amp or better. Readings to the nearest 0.1amps may be false precision. Unless you can check the clamp against a known reference ammeter I wouldn't expect that kind of precision.

Where you measure depends on what you want to do with the info. If you want to know how much is going into the battery measure between the battery and the controller. If you want to figure out the efficiency of the controller measure on both sides. If you have only one ammeter measure one side, the the other, the the first side again to make sure output has not changed significantly. Keep in mind efficiency changes with load so you will want to check at several loads. The easiest way to change load might be to adjust panel angle relative to the sun.

2.3a from a 80% efficient controller sounds about right.

If I recall correctly average output in amp-hours is 30% of nameplate capacity of the panel in watts. So for a 50w panel you can expect to get 15a-hr. 25w x 10hr = 250 w-hr, divided by 12v = 21amp-hr. Starting from a full charge you can expect to draw the batter down recharge it some and then start over loosing a little ground with every cycle. Figure about 5d before haunt problems. Tracking the sun with the panel and/or getting an MPPT controller might help enough to break even.

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Old 13-07-2016, 21:21   #25
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Re: How to measure solar panel current

As a fixed long term monitor I have installed a 200 amp shunt on the main busbar from the batteries to the consumption and production busbar. It's readout is through a very accurate ammeter that shows up to 80 amp + or -. I have also attached cheap led voltmeters on the battery busbar and on the panel side of each of the three regulators from the 10 by 80/90 watt panels. This setup allows instant and continuous monitoring of the whole system. If I suspect one panel is out of kilter it is easy to block light to each panel and read the drop in amperage at the main meter. Similarly, device consumption can be read off the ammeter by switching the device on and off. It has worked well for a number of years.
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Old 13-07-2016, 22:46   #26
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Re: How to measure solar panel current

Quote:
Originally Posted by Adelie View Post
My guess is that the clamp will not be sensitive enough, it will probably read accurately to the nearest 1.0 or 0.5amp but you should be interested in accuracy to the nearest 0.1amp or better. Readings to the nearest 0.1amps may be false precision. Unless you can check the clamp against a known reference ammeter I wouldn't expect that kind of precision.
I would expect around 2-3% accuracy. So when reading down around 2-3 Amps you would get around that 0.1A

Quote:
If I recall correctly average output in amp-hours is 30% of nameplate capacity of the panel in watts. So for a 50w panel you can expect to get 15a-hr. 25w x 10hr = 250 w-hr, divided by 12v = 21amp-hr.
Another common rule of thumb is 5 hours of rated output on average per day. 50W x 5 Hrs = 250 Wh = 21 Ah. In which case, ignoring charge/discharge efficiency, the OP is right on the edge.
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Old 13-07-2016, 22:48   #27
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Re: How to measure solar panel current

If you have a battery monitor it will tell you current used or charging. I believe it is an essential item as you really do not know the state of your batteries without one. They typically use a shunt for measurement with an exception or two - Smartgauge being one.

As far as multimeters I have used the Blue Seas 8110 for years and found it very accurate. 400 amps AC or DC in clamp mode.
https://www.bluesea.com/products/811...imeter_-_AC_DC
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Old 14-07-2016, 03:18   #28
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Re: How to measure solar panel current

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Originally Posted by Adelie View Post
Where you measure depends on what you want to do with the info. If you want to know how much is going into the battery measure between the battery and the controller. If you want to figure out the efficiency of the controller measure on both sides. If you have only one ammeter measure one side, the the other, the the first side again to make sure output has not changed significantly. Keep in mind efficiency changes with load so you will want to check at several loads. The easiest way to change load might be to adjust panel angle relative to the sun.

2.3a from a 80% efficient controller sounds about right.
I think the current upstream of a PWM regulator will be the same as downstream. Regulator inefficiency, or self consumption, will result in a voltage rather than a current change.
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Old 14-07-2016, 03:40   #29
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How to measure solar panel current

Uni-t UT210D nice and compact. It's been fantastic to have on board this year

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Name:	ImageUploadedByCruisers Sailing Forum1468489112.191928.jpg
Views:	58
Size:	30.1 KB
ID:	127787

I have a PMW solar controller with a display which I use to monitor solar production.

I just added a Victron battery monitor with Bluetooth connection to my phone. I like the way it works so now I want to upgrade my solar to a Victron MPPT with the Bluetooth. 😃

Sent from my iPhone using Cruisers Sailing Forum
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Old 14-07-2016, 03:58   #30
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Re: How to measure solar panel current

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Originally Posted by hoppy View Post
Uni-t UT210D nice and compact. It's been fantastic to have on board this year

Attachment 127787

I have a PMW solar controller with a display which I use to monitor solar production.

I just added a Victron battery monitor with Bluetooth connection to my phone. I like the way it works so now I want to upgrade my solar to a Victron MPPT with the Bluetooth. 😃

Sent from my iPhone using Cruisers Sailing Forum
You can measure so easily like in your photo? Just need DC clampmeter and clamp ONE SINGLE wire (not two or three inside one cable)? And you are getting 4.97 Amps from that one panel? Really so simple?
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