Engaging 2nd string does not increase AMPS..remain the same.

DMJ72

Hi all,

First post on NAWS's foams. Have been a reader for quite some time. Many of you have helped me in the past with your posts! However on assembling my first system, I have run into a snag....

I have 4 Wuxi My Solar Technology 200w 72 cell Mono panels arranged in two strings, each having 2 panels in series going into a Midnite 3 string combiner.
http://www.my-pv.com.cn/en/html/About2.asp?ID=31

The specs of the panels are :

Voc = 44.6V
Vmp = 35.8V
Isc = 6.15A

With the first string breaker (10A) turned on (the second = off) my tristar MPPT-60 reports array data of :
Array Voltage = 72.89V
Array Current = 4.4A

When I engage the 2nd string breaker (10A) as well,
The Array voltage goes up to 75.19V
But Amps remain at 4.4A

With the second string on alone,
I get 75.2V/4.4A

These values are at noon-day, caribbean sun (17*N LAT - panels @ 17* tilt - south facing - 90*F ambient temperature). The cables to the combiner are 10g TUV approved cable. 6a cable to the Tristar MPPT-60 from the combiner box. Battery @12volts nominal.

Interestingly, the tristar meter has a realtime bar graph of array V/A .. when I enable string #2, the bar for Amps drops by one bar (out of 3).
Anyone ever see anything like this?

Do I have a short in a solar panel? I have checked and re-checked the cables and MC4 connectors.

Thanks in advance for any help..

NorthGuy

Re: Engaging 2nd string does not increase AMPS..remain the same.

May be your batteries are already charged and do not accept the current. I would suggest you discharge them to 50%, then try again.

Cariboocoot

Re: Engaging 2nd string does not increase AMPS..remain the same.

Welcome to the forum.

The key element here is that current flows through a load; if the load doesn't change, neither does the current. So if the batteries only demand 4.4 Amps from the array that is all the array will put out, no matter how many panels are engage.

Try this; connect both strings and watch the current. Now turn on every load you've got and see if the current doesn't go up.

DMJ72

Re: Engaging 2nd string does not increase AMPS..remain the same.

NorthGuy wrote: »

May be your batteries are already charged and do not accept the current. I would suggest you discharge them to 50%, then try again.

Cariboocoot wrote: »

Welcome to the forum.

The key element here is that current flows through a load; if the load doesn't change, neither does the current. So if the batteries only demand 4.4 Amps from the array that is all the array will put out, no matter how many panels are engage.

Try this; connect both strings and watch the current. Now turn on every load you've got and see if the current doesn't go up.

It appears I have made a school-kid error in understanding Thanks Guys, I will report back when I have done what you said! Have not got around to buying the inverter yet (Samlex 24V 1500w) that I want, So I was testing out my new CC with 2 Energizer/Everready Golf cart batteries, hope to transition to proper RE batteries by 2015 the latest.

Thanks again,
DMJ.

niel

Re: Engaging 2nd string does not increase AMPS..remain the same.

you have a 3v discrepancy between the strings which is a bit odd. i would check over the lower one or better yet measure the open circuit voltage of each pv to be sure you don't have a problem with the pvs.

NorthGuy

Re: Engaging 2nd string does not increase AMPS..remain the same.

niel wrote: »

you have a 3v discrepancy between the strings which is a bit odd. i would check over the lower one or better yet measure the open circuit voltage of each pv to be sure you don't have a problem with the pvs.

Might be a typo. Very unlikely that both voltage and current with only the second string on are exact the same as they are with both strings.

DMJ72

Re: Engaging 2nd string does not increase AMPS..remain the same.

Hello guys the Amps are up!, here is an update with some data :

Both strings



String 1 Alone


String 2 Alone


I attached an inverter with a 11Cuft Fridge load. Also used a Hair-dryer (1000w) to really push it, and the Pmax seems pegged at 625-630Watt.

What do you think of that power output? considering the temperature outside (Jamaica - 90* - full searing sun).

NorthGuy

Re: Engaging 2nd string does not increase AMPS..remain the same.

DMJ72 wrote: »

Hello guys the Amps are up!, here is an update with some data :

What do you think of that power output? considering the temperature outside (Jamaica - 90* - full searing sun).

Looks good. Note how voltage is low - this is mostly because of the temperature. Thus less-than-expected production.

Yesterday, the controller increased the votage way higher. It did so to decrease current because it was nowhere to put it.

Rybren

Re: Engaging 2nd string does not increase AMPS..remain the same.

Newb here myself, but isn't 45+A charge current a tad high fwo GC Batts?

BB.

Re: Engaging 2nd string does not increase AMPS..remain the same.

It is high, but should not be damaging--Especially if the remote battery temperature sensor is installed.

The 13.58 volt battery voltage @ 45 amps would indicate that the battery bank is probably below 80% State of Charge--Where they can accept high levels of current without much heating.

Once the battery voltage goes higher, starts gassing, etc... Then more charging current is turned into heat (at near 100% SOC, probably would suggest that ~1.5 to 5% rate of charge would be a good limit--For equalization, etc.).

~225 AH * 20% = 45 amps

5-13% is recommended for solar... 20-25% is common for AC battery chargers (you want to charge fast and limit genset run times--plus the Amperage is usually a lot cheaper with a genset+ac charger vs solar panels+controllers).

-Bill

Rybren

Re: Engaging 2nd string does not increase AMPS..remain the same.

Thanks Bill.

US Batteries recommend a max of 10% for my batteries, so I've set max amps to 23. Maybe that's too conservative.

mike95490

Re: Engaging 2nd string does not increase AMPS..remain the same.

Rybren wrote: »

Thanks Bill.

US Batteries recommend a max of 10% for my batteries, so I've set max amps to 23. Maybe that's too conservative.

It is if it's morning in my house, batteries are low, and the toaster is on. I think the batteries will be OK, or you can go into the custom settings, and tweak voltages. I'd do that before limiting amps. If I WANTED to limit amps, I'd have bought just 1 PV panel

NorthGuy

Re: Engaging 2nd string does not increase AMPS..remain the same.

mike95490 wrote: »

If I WANTED to limit amps, I'd have bought just 1 PV panel

If you want to have decent production when it's cloudy, you need to buy more panels. If you then see that at full Sun your amps are more that you want (for whatever reason), you got to limit them.

DMJ72

Re: Engaging 2nd string does not increase AMPS..remain the same.

BB. wrote: »

It is high, but should not be damaging--Especially if the remote battery temperature sensor is installed.

The 13.58 volt battery voltage @ 45 amps would indicate that the battery bank is probably below 80% State of Charge--Where they can accept high levels of current without much heating.

Once the battery voltage goes higher, starts gassing, etc... Then more charging current is turned into heat (at near 100% SOC, probably would suggest that ~1.5 to 5% rate of charge would be a good limit--For equalization, etc.).

~225 AH * 20% = 45 amps

5-13% is recommended for solar... 20-25% is common for AC battery chargers (you want to charge fast and limit genset run times--plus the Amperage is usually a lot cheaper with a genset+ac charger vs solar panels+controllers).

-Bill

Hey All, today was one of the hottest days here all summer. Temps went up to 96*F with no breeze at all! :grr
I had the battery temperature sensor of the Tristar Installed onto a lug, and the Inverter was powering a fridge off the two 6V GC2 golf batteries throughout the day (they started at 40%SOC). This is my first DIY solar setup and initially I was MAD (edit swearing by niel) that I was only getting a peak of 650watts out of the 800watt array. But then I remembered it was searing hot outside, and that I don't live in a Solar Test lab!

Today was the second day of testing, time to move the setup inside and start data-logging!

So the verdict is that I should be ok with that power output right? that 650w looks about the typical 80% real-world value I see quoted here a lot.

Thanks to everyone!

BB.

Re: Engaging 2nd string does not increase AMPS..remain the same.

That is why I try to set expectations to ~77% out of a charge controller--It is much closer to what most people will get in sunny weather. A few may get 80-85% or so (or even better in winter, high altitude, measurement errors, etc.).

And if you get better than that at times--Happy Days!

-Bill