Measuring 4 Panels output - Is this right?

KozmoK · May 2014

First my Setup:

I have four 327w Panels (2 are one model, and 2 are another similar model with almost identical params)

54.7 VMP
5.98A IMP
6.46 Isc
VOC 64.9

Testing each panel individually I get

60v
4.75a

If I test each series individually I will get one with ~120v 8.0a, and the other series ~120v 7.8a

When I combine them shouldn't I get 120v at 13-15 amps? I am only getting roughly 8 amps - where are my missing combined amps? I am using MC4 Y Connectors to combine them. I have a combiner box, and got the same results.

I am thinking maybe one of the connectors isn't engaging correctly - but its working with my probes

Any Ideas?

BB. · May 2014

Re: Measuring 4 Panels output - Is this right?

Voc ~ 64 volts is a cool panel open circuit (no current draw).

On a very hot day, the Vmp-panel-hot may be as low as 80% of the rated Vmp--Or:

54.7v * 0.80 temperature derating = 44 volts Vmp-hot

And Imp for your panels is around 6 amps (at Vmp).

So, in hot weather/full sun I would expect a single panel to run around Vmp~44 volts at ~6 amps in full sun.

4 panes in 2 series * 2 parallel--I would expect ~88 volts at ~12 amp on a good sunny day.

As array voltage increases to Voc--Current will fall, and eventually stop flowing at Voc-measured (at temperature).

-Bill

KozmoK · May 2014

Re: Measuring 4 Panels output - Is this right?

So if I am only getting around ~8 amps with 4 panels in 2 series * 2 parallel (on a very sunny day) wouldn't that indicate somethings wrong?

BB. wrote: »

Voc ~ 64 volts is a cool panel open circuit (no current draw).

On a very hot day, the Vmp-panel-hot may be as low as 80% of the rated Vmp--Or:

54.7v * 0.80 temperature derating = 44 volts Vmp-hot

And Imp for your panels is around 6 amps (at Vmp).

So, in hot weather/full sun I would expect a single panel to run around Vmp~44 volts at ~6 amps in full sun.

4 panes in 2 series * 2 parallel--I would expect ~88 volts at ~12 amp on a good sunny day.

As array voltage increases to Voc--Current will fall, and eventually stop flowing at Voc-measured (at temperature).

-Bill

Cariboocoot · May 2014

Re: Measuring 4 Panels output - Is this right?

KozmoK wrote: »

So if I am only getting around ~8 amps with 4 panels in 2 series * 2 parallel (on a very sunny day) wouldn't that indicate somethings wrong?

How are you measuring the current?
The only way you can measure for panel testing purposes is with Isc: panels fed to a dead short in full sun using either a clamp-on DC Ammeter (best for current potential >10 Amps) or a good in-line meter that can handle the current.

Trying to measure Imp is difficult as current will vary with load. Current will also vary with insolation, and you'd be surprised at how little of an angle change from 'ideal' can alter that.

KozmoK · May 2014

Re: Measuring 4 Panels output - Is this right?

Cariboocoot,

I am measuring using using the probes of my MASTECH DC Clamp meter - with no load. I have not ran the wire to the Midnite classic 150 lite yet (75ft). I am just sticking the probes in the mc4 connectors and the Combiner box, and wanted to make sure I had it hooked up properly, and I was expecting a higher amp reading.

Thanks for your inputs

Cariboocoot wrote: »

How are you measuring the current?
The only way you can measure for panel testing purposes is with Isc: panels fed to a dead short in full sun using either a clamp-on DC Ammeter (best for current potential >10 Amps) or a good in-line meter that can handle the current.

Trying to measure Imp is difficult as current will vary with load. Current will also vary with insolation, and you'd be surprised at how little of an angle change from 'ideal' can alter that.

Cariboocoot · May 2014

Re: Measuring 4 Panels output - Is this right?

KozmoK wrote: »

Cariboocoot,

I am measuring using using the probes of my MASTECH DC Clamp meter - with no load. I have not ran the wire to the Midnite classic 150 lite yet (75ft). I am just sticking the probes in the mc4 connectors and the Combiner box, and wanted to make sure I had it hooked up properly, and I was expecting a higher amp reading.

Thanks for your inputs

So you are using your meter to provide a short circuit on a panel string. That is the correct way to do it and it should show near Isc if insolation is strong. You can also connect the MC4 outputs together to form a short and measure with the clamp.

Photowhit · May 2014

Re: Measuring 4 Panels output - Is this right?

Just a guess, on probes? I'd guess the max is 10amps... Perhaps? clamps up to unit max 3-400amps.

BB. · May 2014

Re: Measuring 4 Panels output - Is this right?

Get yourself an inexpensive (or expensive) DC Current Clamp DMM, like this one from Sears (low cost, good enough for our needs).

That will allow you to measure the Per String current under normal operation. The battery bank needs to be somewhat discharged and/or you need some loads on your DC power bus--So the charge controller will be drawing full power from the array (around noon+/- will give you the most current/power).

If you have a circuit breaker per string (not need for one or two string arrays), you can turn off one breaker, then the other, to estimate the amount of current each string is supplying (another nice reason for circuit breakers in solar array combiner boxes).

-Bill

Photowhit · May 2014

Re: Measuring 4 Panels output - Is this right?

Bill, I think he's got one...

"...using the probes of my MASTECH DC Clamp meter"

Typically the probes are only good for up to 10 amps, hence my comment.

KozmoK · May 2014

Re: Measuring 4 Panels output - Is this right?

Yes thanks, I have one. It looks really close to that sears model.

As for the probes only go to 10amps - good to know.

So I am only getting ~8 Amps total with no load with the panels hooked up (2 panels serials, 2 parallel) (I thought it should be ~13-15a - is this what is giving me the lower amp reading? Or is it because I do not have the charge controller pulling a load?

I will start trenching this week, I have been procrastinating this 75' rocky trench (I'm next to a mountain) - and then I will have the real load on it.

Photowhit wrote: »

Bill, I think he's got one...

Typically the probes are only good for up to 10 amps, hence my comment.

BB. · May 2014

Re: Measuring 4 Panels output - Is this right?

Never mind.

-Bill

Cariboocoot · May 2014

Re: Measuring 4 Panels output - Is this right?

KozmoK wrote: »

Yes thanks, I have one. It looks really close to that sears model.

As for the probes only go to 10amps - good to know.

So I am only getting ~8 Amps total with no load with the panels hooked up (2 panels serials, 2 parallel) (I thought it should be ~13-15a - is this what is giving me the lower amp reading? Or is it because I do not have the charge controller pulling a load?

I will start trenching this week, I have been procrastinating this 75' rocky trench (I'm next to a mountain) - and then I will have the real load on it.

IF you are measuring against a true dead short of the panel output you can't have any more load than that. IF the insolation of the panels is correct and the sunlight direct and strong then you should read something close to Isc rating, or about 12 Amps. You're seeing around 2/3 of this so check the light conditions as that is what is most likely to reduce current output. You probably would not see >12 Amps as it is not being done under lab test conditions.

BTW I have a meter that can probe check to 20 Amps DC and it has a notation on it not to exceed 15 seconds connection. But it's fine for checking individual panels for Isc.

Photowhit · May 2014

Re: Measuring 4 Panels output - Is this right?

I'm worried you may have damaged your meter trying to test beyond it's capacity... If it's digital, it might give any reading since it is beyond it's testing capacity. I wouldn't worry about a reading taken, that can't be trusted. Testing is only worth doing if you can trust the numbers your getting.

KozmoK · May 2014

Re: Measuring 4 Panels output - Is this right?

Ok guys I have it all connected to the CC and battery Bank

I think its working well. Its almost noon here in AZ and the watt's are climbing past the rated peak values of 1 panel, so I think its seeing them correctly.

Attachment not found.

Absorb Modes is set to 2:00 hours at 14.4 A

I have four 12v 12AVR145ET batterys in parallel. float value is 13.50

I have a whizbang jr. I dont know what to set the ending amps to, so absorb is 2 hrs........Could this hurt my batterys?

Cariboocoot · May 2014

Re: Measuring 4 Panels output - Is this right?

Watch the current during Absorb. It will drop to something around 2-3% of total battery capacity and 'plateau' there (with no loads interfering). This is where you want End Amps setting. The WhizBang Jr. should allow you to program an Amp hour capacity and stop Absorb once 100% full is reached.

It's all in the manuals. Somewhere.

KozmoK · May 2014

Re: Measuring 4 Panels output - Is this right?

Thanks Cariboocoot!

I see now my system is doing well on its first full day. System is doing great now, watts is increasing. My PCB Temps are high as its hot here in the desert.
Thanks for all your help!

Now I think I am going to reconfigure my battery bank to 48v and run a DC A/C unit in my office.

Here is the latest screenshot at 9:33 AM MST

Attachment not found.

Vic · May 2014

Re: Measuring 4 Panels output - Is this right?

Hi Koz ..,

Am a bit concerned about the String Voc of around 130 Volts. Realize that in your heat, this value will be lower than rated for your PVs. This high input voltage to the CC will make it run HOT, especially when the later part of Absorb, and especially during Float with lighter loads, etc.

You could run all of your PVs in parallel, but, of course, this would double the current, if you plan on running a single pair of cables from the PVs to the CC. AND, then with "strings" of one PV, you would not be able to successfully charge a 48 V battery.

A bunch of trade-offs, and the unusually high Vmp of these PVs do not give quite as much latitude, as would ones with somewhat lower Vmp.

As stated elsewhere, your batteries and electronics are HOT ... anything/everything that you can do to reduce the temps of the environment that this system endures will be a plus.

Just my opinions. Keep Cool. Good Luck, Vic

KozmoK · May 2014

Re: Measuring 4 Panels output - Is this right?

Hey VIC!

Thanks for your reply. Yes I plan to charge a 48V Battery Bank in the end. I will try to think of a way to keeping the system cooler. Its located inside my garage, where for 4 months out of the year it will be 100-115 in there. Bringing it inside my house is not optional

I was planning on running a DC AC unit at 48v, but If this heat is going to damage my batterys life it may not be worth it.

zoneblue · May 2014

Re: Measuring 4 Panels output - Is this right?

DO NOT test Isc using probes directly into the MC4 connectors. The resulting arc will strip the silver plating off the connector thus rendering it forever vulernable to corosion, and hence unreliable.

Use a spare mc4 attached to a spare bit of wire.

Photowhit · May 2014

Re: Measuring 4 Panels output - Is this right?

zoneblue wrote: »

DO NOT test Isc using probes directly into the MC4 connectors. The resulting arc will strip the silver plating off the connector thus rendering it forever vulernable to corosion, and hence unreliable.

Use a spare mc4 attached to a spare bit of wire.

Will I agree to use 'pig tails' if possible, I wouldn't worry too much about stripping a small amount of the tinning off the connector, repeated attaching and detaching will as well.

Measuring 4 Panels output - Is this right?

Comments

Categories