beginner solar question

[birdhouse]

hello-
i'm getting ready to install some 245w solar laminates i bought from sunelec a while back. 

my question has to do with the four tabs (flat wire) that exit the back of the panel.  i don't know what is what.  if the panels were here at my home, i'd just stick them in the sun and use a VOM to figure it out, but they are up at my ranch, so connections ect. will be made up there. 

if i remember correctly, the two tabs in the middle are for a blocking diode, though there has been much discussion here about removing the diodes, as they can cause trouble when they blow.  does this mean i can just leave the two middle wires isolated...  ie: not connected to anything?

if this is the case, can i use just the outer two wires and run them to the charge controller? 

sorry for the idiot question.  i'm much more akin to putting up panels with the j-box and mc-4 connectors already in place. 

panel specs:
Vmp  30.5
Voc   37.5
Isc    8.73
Imppt 8.04

thanks for any help!

adam

[philb]

I did several experiments with my laminates. I think your panels are similar to the ones I bought.

The best arrangement for me was using a j box with mc connecters already attached. I soldered the two outside tabs into the j box and removed the diodes.

The entire box was filled with Dap non-acetic acid silicon according to Ghurd's advise. Be aware that you won't be able to get to the connections if you make a mistake. Dap is very difficult to remove after it has set up.

[ghurd]

It is Not a "blocking diode".

"Bypass diodes" are what goes on the panel's tabs, and I don't like them in low voltage systems.  They serve no purpose in a 12V or 24V system.

I should refine that to say they serve no purpose in a 12V or 24V nominal string of cells.  They can serve a purpose if the string of cells is 60V or 100V going into a MPPT controller.

You do not want a blocking diode either.
The blocking diode, or something that does the same thing better, will be in the charge controller.

Clean the flux off the tab/wire when finished soldering.  Anything you can do to help make sure you never have to see those connections again is a good idea.
Like Phil said, it is not fun digging any kind of goop out of a box to get to delicate connections.
G-

[birdhouse]

thanks for the advice!

there are three of these panels that i'm going to be putting in series into a tristar mppt-45.  does this mean that bypass diodes would be a good idea? 

i've already got the j-boxes installed with dap silicone 3.0.  i didn't go the mc-4 route because standard electrical flex was cheaper, and you have to run the stuff for the final connection anyways, so i figured i'd just stick with that. 

and yes, after the soldering, and potting with silicone, i hope to never have to work on those connections again!

thanks
adam

[rossw]

You do not want a blocking diode either.
The blocking diode, or something that does the same thing better, will be in the charge controller.

One of the few times I disagree with you, G!
If you have more than one string in parallel, and especially if those strings are moderate to high voltage, you MOST CERTAINLY want blocking diodes in series with each string.

The absence of said diodes destroyed 6, 100W panels here a few years ago.

[birdhouse]

ross-
there's only one string of three panels, for a total Voc of ~112vdc. 

[rossw]

ross-
there's only one string of three panels, for a total Voc of ~112vdc.

Yes, understand that.
My comment was for reference to others who may read this thread and take the comment out-of-context.

I also note that in your case, 3 panels in a string is fine... but what do you do if you decide later to add more?
Depending on your CC, you may not just add another in series - which would indicate 3 more in parallel - and then you'd be in exactly the position to want to retrofit them. (Like Ghurd says - for a single string, there's no point. It's only when you have more than one string in parallel that it becomes an issue)

[ghurd]

Nice catch Ross.

Also: Potting the tabs does not have to fill the whole box.
A couple words or phrases above made me a bit nervous.
G-

[birdhouse]

thanks all.

no, i wasn't planning on using a full tuber per box   but thanks for clarifying!  i assume just a decent glob of silicone to encapsulate the tabbing wire and solder connection.  thus keeping it from bending and eventually breaking. 

adam

[rossw]

i assume just a decent glob of silicone to encapsulate the tabbing wire and solder connection.  thus keeping it from bending and eventually breaking. 

Just make absolutely sure you use a compatible silicon. Any of the acid-cure ones will be deadly to your panel.

[birdhouse]

like dap 3.0??

[rossw]

like dap 3.0??

DAP 3.0 is not a product I'm familiar with. Never seen it over here, but a quick google refers to it as caulk, not silicon. Also claims to be "quick dry", but so far I've not found a reference to "neutral cure".

After about 10 mins, I can't find a reliable materials specification to confirm either way - if it's neutral cure, or acid cure. I've found multiple references from 3rd parties that suggest both!

Even the dap.com site itself doesn't seem to say - even goes out of its way to avoid saying!

From http://householdproducts.nlm.nih.gov/cgi-bin/household/brands?tbl=brands&id=4008042

"WARNING! May cause eye, skin, nose, throat and respiratory tract irritation. Harmful if swallowed or absorbed through the skin.
Primary Routes Of Entry: Skin Contact, Inhalation, Eye Contact
Eye Contact: May cause eye irritation, characterized by a burning sensation, redness, tearing, and inflammation."

Suggests it's an irritant if not acidic.

"Titanium dioxide is listed as possible carcinogen by IARC." suggests it's not all sweetness and light.

[birdhouse]

since we've moved into the caulk/silicone talk...  what's up with the vinegar smell that many silicons have?  makes me sneeze every time! 

i think Ghurd recommends the DAP 3.0 as being a non acid silicon. 

adam

[rossw]

Quick search for materials specifically designed for electronics use shows a heap of products, here's just one:

http://www.acc-silicones.com/content/products/as1800.ashx

[ghurd]

The DAP 3.0 I have here is "Kwik Dry" (3 hours is a long time for regular silicone to be exposable to water), Crystal Clear, not paintable (for best results), won't shrink or crack, sub-zero application, clean-up with mineral sprits, low-VOC.

It does Not have the vinegar/acid smell.  It doesn't have much of a scent at all really.

I don't think I can tell any difference between it and 'regular silicone' after it is cured.

Car test?
16 year old car windshield frame rotted around the top, water pouring in like Niagara Falls.
(I think it was broken at one time and replaced by less than careful techs)
Cleaned the rust and loose paint.
"Regular silicone" ate the metal in a few weeks(?), and I mean ate it at an astounding rate.

Had an occasion to talk to a good auto body guy.  He said "No!  Dig that crap out and use non-acid silicone."
(No need to dig it out.  It dug itself out, which is why I asked him about it)

Repeated it with Dap 3.0, no problem for a year now?  Paint under it still look OK (wasn't great when I started), last time I looked. Even started raining before I finished application.  0 to 100F, salt, acid rain, steel mills, AL and CU processing, etc. 
This is an area where car metal and paint does not last long anyway (ask my late truck, which is probably being recycled into Kia's or Hyundai's as I type  ).
G-

I doubt any of that narrows it down to what is in it.