Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 12-07-2016, 20:25   #1
Registered User
 
lindabarzini's Avatar

Join Date: Jan 2016
Posts: 140
How to measure solar panel current

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?
__________________

__________________
lindabarzini is offline   Reply With Quote
Old 12-07-2016, 21:17   #2
Registered User

Join Date: Apr 2013
Location: So Cal
Boat: Catalina 30
Posts: 863
Re: How to measure solar panel current

If you disconnect the battery, no current will flow.

If you have a clamp-on DC ammeter, yes - you can use that.

You may be able to charge the battery each day, but I doubt it. You'd need 8 to 10 hours of good sunlight to overcome controller losses, charging losses, etc...
__________________

__________________
jeepbluetj is offline   Reply With Quote
Old 12-07-2016, 21:29   #3
Registered User
 
Omatako's Avatar

Join Date: Jul 2008
Location: Auckland
Boat: Morgan 44 Centre cockpit
Posts: 49
Re: How to measure solar panel current

AFAIK the rating of your panels will determine the max output. The calculation is the Watts rating of the panels divided by the battery voltage. And that would be optimistic because the is a % of loss natural to the system.

My array still provides some charge even on a cloudy day. The contention that if shade falls across the panels, they "die" is in my experience, incorrect.

If you're looking to measure the amps incoming at a specific moment, your battery monitor should be able to do that as long as everything is turned off (no consumption). The controller will decide incoming current based on present state of charge. You do have a battery monitor, right?

Perhaps I'm not a really good shopper but I've never been able to find a clamp that measures DC amps and unless you have a giant array, I've also never seen a clamp that measures amps that low. They may be out there, I've just never seen them. The solar array on my boat is 280W and with soft batteries and good sunshine I never get better than 16A maybe 17A.
__________________
Andre

The older one gets, the older one wants to get (Mick Jagger)
Omatako is offline   Reply With Quote
Old 12-07-2016, 21:30   #4
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Tasmania
Boat: VandeStadt IOR 40' - Insatiable
Posts: 2,317
Images: 91
Re: How to measure solar panel current

Without showing my working out, I would expect your 50w solar panel to be able to replace a draw of 25 watt x 10 hours (i.e approx 20 amp hours) only on a very clear very sunny day, i.e. in ideal conditions.

If you measure current flow from solar panel at the battery terminal you should be measuring the current into the battery after any losses from controllers / resistance, etc. Bear in mind though that the current you measure will vary depanding on angle of sun in sky, angle of solar panel to sun, clouds, atmospheric conditions, etc. so if you measure 2 amps now, you might measure 1 amp later.
__________________
Weyalan is offline   Reply With Quote
Old 12-07-2016, 21:50   #5
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: el campo
Boat: 39' Westerly Sealord
Posts: 3,457
Re: How to measure solar panel current

Just buy one of these AC 0 10A Analog Amp Meter Current Panel Meter Ammeter Gauge 85L1 | eBay and wire it in permanently between controller and batts. Then you will always know what is going on.
El Pinguino is online now   Reply With Quote
Old 12-07-2016, 22:03   #6
Registered User
 
PaulinOz's Avatar

Join Date: Jan 2011
Location: East Coast Australia on board L450
Boat: Lagoon 421(2010) & L450(2013)
Posts: 466
Images: 17
Re: How to measure solar panel current

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.
__________________
Life is to short to drink bad wine.
PaulinOz is offline   Reply With Quote
Old 12-07-2016, 22:33   #7
Senior Cruiser
 
StuM's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43
Posts: 5,457
Re: How to measure solar panel current

Quote:
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.
You can buy DC as well as AC clamp meters. Fluke are probably the best known. Fluke Clamp Meters, Amp Meters and Clamp On Ammeters

But there are plenty of others on EBay.
DC Clamp Meter | eBay

Mine's' a Mastech - Products / categories ? Mastech (Build to Precision)
__________________
StuM is online now   Reply With Quote
Old 12-07-2016, 22:58   #8
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: el campo
Boat: 39' Westerly Sealord
Posts: 3,457
Re: How to measure solar panel current

Quote:
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..
.......
OOOOOOPPPPPPSSSSSS! must learn to read and check before posting.

Lets try this one 1×DC 10A Analog Panel Amp Current Meter Ammeter Gauge 85C1 White 0 10A DC | eBay

I have an independent analog ammeter on each of my input sources, shore power, wind,engine, and solar so at a glance ( and from a distance) I know exactly what is going on...
El Pinguino is online now   Reply With Quote
Old 12-07-2016, 22:58   #9
Registered User
 
PaulinOz's Avatar

Join Date: Jan 2011
Location: East Coast Australia on board L450
Boat: Lagoon 421(2010) & L450(2013)
Posts: 466
Images: 17
Re: How to measure solar panel current

As I said I may be totally wrong and looks like I was.
I apologize.

Do any of the battery monitoring systems use this style of current measurement in stead of a shunt ?
Is it a better way to go ?
__________________
Life is to short to drink bad wine.
PaulinOz is offline   Reply With Quote
Old 12-07-2016, 23:25   #10
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Full time cruising. Currently in the Med.
Boat: Aluminium yacht
Posts: 10,214
Re: 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?
The clamp on multimeters are surprisingly accurate. I only have a cheap model but I have checked it against my conventional (not clamp on) Fluke multimeter and the results are very close even for low currents. Of course the clamp on multimeter is much easier. The solar panel needs to be connected to a battery.


Quote:
Originally Posted by lindabarzini View Post
I want to measure the amps from my solar panel. Can I measure them after the pwm charge controller?
Yes.


Quote:
Originally Posted by lindabarzini View Post
And I assume the solar panel has to be disconnected from the battery.
No, it needs to be connected if you want to measure the output you are getting.


Quote:
Originally Posted by lindabarzini View Post
Or can I split the wires after the charge controller so I can get the amp clamp around just one of the wires?
Yes, you need to put just one wire through the jaws. You cannot use both the positive and negative wires together.


Quote:
Originally Posted by lindabarzini View Post
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 I understand your wiring correctly, then with the inverter off the measurement should be accurate. Measuring the current either before or after the PWM controller is fine.


Quote:
Originally Posted by lindabarzini View Post
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?
Solar controllers are near 100% efficient, especially the PWM models. The efficiency loss with solar panels and PWM controllers occurs because the solar panel in most conditions will produce more voltage than the battery. The optimum voltage of the solar panel for maximum output does not match the battery voltage.

If the solar panel has a STC rating of 2.9A in very good conditions (full sun, no shadows) you should see very close to 2.9A. Under exceptional conditions you can even briefly exceed this. However, while 35/12= 2.9A, a 35W panel will not have an STC rating of 2.9A. It will be more like 1.9A.
The STC rating should be on a sticker on the back of the panel. If it is not there, the maximum current a 36 cell "12V" panel can produce is found by dividing the wattage by the Vmp of the panel which will be about 18 or 18.5v (this is a slight simplification, but is close enough).

You will get a lot more than 0 on a typical cloudy, but how dense are the clouds? What is the location? It is very hard to generalise, but with 100% cloud cover, but not dense rain clouds, about 1.5 A from a 50W panel around solar noon might give you some idea.

Quote:
Originally Posted by lindabarzini View Post
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?
25w x10hours is around 20 Ahrs in consumption. The location and time of year are important, so once again it is hard to generalise, but a 50w panel will only produce 20AHr on a good day in a good location in the peak months. Normally 75-100w or so of solar will be needed to replace 20AHrs, especially when factors like battery inefficiency are taken into account, but I stress this very dependent on location and the time of year.
__________________
Our custom built cutter rigged sloop is for sale:
48' Aluminium Bluewater Cruiser For Sale

Mermaids & Anchors
noelex 77 is offline   Reply With Quote
Old 12-07-2016, 23:34   #11
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,004
Re: How to measure solar panel current

This is the DC clamp-on that I have been using for about 8 years

Sears.com

It has two DC scales--40 and 400 amps. I use the 40 amp scale for solar stuff, and the 400 amp scale for alternators and starters. Accuracy is advertised at 2.5% for less than 20 amps, which is more than you will get from an analog meter.

After hitting the zero button, you clamp around one wire of a circuit to measure the current. You could measure the solar panel/ regulator output by clamping around either the positive or negative wire going into or out of the regulator without disconnecting any wires.

To test a solar panel disconnect both wires from the regulator. First measure the open circuit voltage (Voc) across the wires. Then touch the two wires together and measure the short-circuit amps (Isc) by clamping around one of the wires. Both the Voc and Isc should be published for every panel type. This test eliminates any issues with regulator, or battery state of charge and is the first thing you should do when troubleshooting solar systems.
__________________
donradcliffe is offline   Reply With Quote
Old 12-07-2016, 23:42   #12
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: el campo
Boat: 39' Westerly Sealord
Posts: 3,457
Re: How to measure solar panel current

Quote:
Originally Posted by PaulinOz View Post
As I said I may be totally wrong and looks like I was.
I apologize.

Do any of the battery monitoring systems use this style of current measurement in stead of a shunt ?
Is it a better way to go ?
Don't apologise, I never do

To the best of my understanding those little panel ammeters have built in shunts, which is how they work.

That said I have never bust one open to have a look....
El Pinguino is online now   Reply With Quote
Old 13-07-2016, 00:06   #13
Registered User
 
ErikFinn's Avatar

Join Date: Feb 2011
Location: Malaysia, Thailand
Boat: Beneteau Oceanis 430
Posts: 764
Re: How to measure solar panel current

Quote:
Originally Posted by El Pinguino View Post
Just buy one of these AC 0 10A Analog Amp Meter Current Panel Meter Ammeter Gauge 85L1 | eBay and wire it in permanently between controller and batts. Then you will always know what is going on.
Must be AC, Not DC ammeter?

Edit: I posted too hastily, subject now clear, pls disregard.
__________________
ErikFinn is offline   Reply With Quote
Old 13-07-2016, 00:34   #14
Registered User
 
El Pinguino's Avatar

Join Date: Aug 2013
Location: el campo
Boat: 39' Westerly Sealord
Posts: 3,457
Re: How to measure solar panel current

Quote:
Originally Posted by ErikFinn View Post
Must be AC, Not DC ammeter?

Edit: I posted too hastily, subject now clear, pls disregard.
So did I
El Pinguino is online now   Reply With Quote
Old 13-07-2016, 07:28   #15
Registered User
 
captjcook's Avatar

Join Date: Jul 2008
Location: Fort Lauderdale Florida
Boat: Northstar 1500, 35', Siren
Posts: 314
Re: How to measure solar panel current

I opened up an cheap automotive battery charger to diagnose...since it was toast, I salvaged the clamp on ammeter...turned out to be good for a glance at my solar output.

Sent from my LGMS323 using Cruisers Sailing Forum mobile app
__________________

__________________
captjcook is offline   Reply With Quote
Reply

Tags
current, solar

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
36 Volt Solar Panel , 250 watts - Can I Connect to 12V Solar Regulator ? surfmachine Electrical: Batteries, Generators & Solar 53 19-04-2012 17:32
New Solar Panel Technology: Solar/Desalination sww914 Electrical: Batteries, Generators & Solar 2 14-04-2011 09:36
How to Measure Stray Current in the Water erict Electrical: Batteries, Generators & Solar 11 03-12-2010 11:07


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 18:59.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.