Friday, August 22, 2008

The 35 cell panels performance in the sun.

This is the panel made from damaged 3600ma tabbed cells.

The sun was nice and bright for a winter morning so I gave the panel another test run at 8am.

The first issue was condensation in the panel. A bit of remedial drying and re-sealing should fix it.
The voltage when the cells were cold read 19.23 but when the cells warmed up it dropped. Something for me to research.

The pictures tell the story.
3.56 amps x 16.88 volts = 60 watts! At 8am in winter.

At 12 o'clock I tested again. The results were 3.69 amps x 16.65 volts = 61.4 watts.
Once again a voltage drop but amperage increase.
Keeping in mind that I used only 35 ( at this rate 36 would give more than 63 watts) of the damaged cells from the batch for this panel I have no problems seeing 36 of the perfect cells making a true 70 watt panel.

I'm hoping the blocking diodes etc. in the panel lead box might help keep the voltage up. 19.8 volts at 3.69 amps would give 73 watts! Nice.
I worked out the cost of the panel based on full retail prices for all bits.
Ply x 2 = $12.00
Perspex x 1 = $38.00
18mm square wood x 6 metres = $10.20
Extra Tab wire x 1 = $5.00
Solder, flux, paint etc = $5.00
Selleys All Clear x 1 = $6.00
Alligator clips and wire = $2.00
Solar cells x 35 @ $8.00ea. = $280.00.
All of the hardware items were off the shelf at Bunnings in Wagga Wagga.
Electronic components were not.

Total $358.20 for a 70 watt panel.

The cheapest 70 watter I could find online was nearly $700 and was an amorphous panel.

I own a 20 watt ( I wish ) commercial ebay type panel (on the right just in case you couldn't tell the difference between my DIY and a commercial panel :~) ) .

It produces a whopping and nearly half wasted 29 volts but at only 0.6 of an amp. On paper that gives 17 watts but my controller can only use 18 volts so, in reality, the panel only gives about 10 watts.
Much the same as this one made from scrap cells and a Styrofoam box lid. This one cost $100 less.

I'll post again when the panel lead boxes arrive and let you know if it makes a difference.
Some people say you need the blocking diode to prevent leakage from battery to panel at night but others say there is a significant voltage drop with older diodes so the losses without the diode can be less than with one!
We'll see eh.

They never arrived.

Sunday, August 17, 2008

Solar Panel from New Tabbed Cells.

Building a 70 watt panel using 3.6 amp tabbed cells.

This is a "How I did it"with 35 of the cracked and damaged cells from the batch....not a "How You should do it" with your perfect 36 cells.

I decided to re-use some materials from an earlier, less successful, panel project.

The 900mm x600mm ply sheet with a 18mm square timber frame will only fit 35 of these big cells and will have a somewhat unusual configuration.
3 rows of 10 cells with 1 row of 5 at right angles.

This will give me a 69.3 watt 19.25 volt panel which is good enough for any system.

My major issue before actually getting started on this one has been the fact that to use the method I'm used to with small cells would mean soldering 10 big cells together face down and I would then need to turn them over when they're joined.
With the other panels I've built I've done the front soldering myself and trusted it enough to lift the strings of cells by the tabs.
The factory soldering on these much bigger cells is perfectly good enough to carry current but I'm not prepared to trust it to carry the weight of all those cells.

Consequently I've had to come up with another plan.

This is it.

I am going to tab the back of the cells with a cm or two of "tail" on the opposite side to the front bus.

Scraping the bus on these fresh cells may well be a waste of time but I did it anyway.

The flux pen makes it easy not to make a mess.
I couldn't take a pic of me actually soldering so you'll just have to take my word for it.

Using a plastic ruler as a straight edge the tabs are carefully folded at right angles to the back of the cell with the ruler touching the side of the cell.

In case you're wondering this is what happened to the corner of my cell......
I got a teeny bit too close to my extractor fan when I was soldering the tabs. The fan made the most of the opportunity and went the munch!

With the cells laid out on the board I'll mark the position of the holes then drill all holes.
A small blob of Selleys all clear will go in the centre of the back of the cells and the tabs will be fed through their holes.
In most cases there will be the positive (back) tabs of one cell and the negative (front) tabs of the next cell through the same hole.

These tabs will be soldered together at the back of the panel.


Okay....the above was written before a lot of the work had been done and all went to plan.
The cells were all laid out with a gap of 4 or 5 mm on the board in position and the holes marked for drilling and drilled.

I then bent all tabs at right angles to the cell using the plastic ruler against the edge of the cell to create 2 mm or so of gap between the edge of the cell and the right angle in the tab.

I put a blob of All Clear on the board for the centre of where each cell was to go and positioned the cells.
I started with the designated positive out pair of drilled holes and worked from there taking care to match neg to pos.

The last cell to go into place was the negative out cell.

The back of the board looks a lot worse than it actually is at this stage.

The back of this panel was complicated by the configuration so care was needed.
Alligator clips make perfect clamps! I bought mine from ebay seller allgateopeners at a great price and got excellent service.

I bent the tabs apart and soldered the join.

The longer joins on this panel took a bit more effort.

I used copper wire here both for the insulation and it's greater carrying capacity.

All the pairs of tabs are now soldered and trimmed and the longer joins are done with tab and copper wire.

The back cover trim is glued and screwed ready for the ply back cover.

The perspex front cover was put in place and carefully drilled for the 10 screws that will help the bead of All Clear hold it on.

My panel lead boxes haven't arrived so I can't quite finish the panel yet but I soldered a pair of wires directly and took it outside for a test run........
It was 5.15pm and it's winter evening and the panel did Great. Over spec at 19.7 volts and a credible 1.8 amps!....that's 35 Watts just on sundown in Winter!
I used the chipped and cracked cells out of the batch so I can't wait to see what the perfect ones can do!
I ran out of paint so the back ply got a coat of estapol ( in Maple no less!). It should be okay but I'll keep an eye on it.

Solar Panel from Scrap Cells.

Please read my post on building Solar Panels from new (untabbed) Cells before this post on scrap cells. A lot of the info is applicable to both.

My major problem was finding the right temp to solder at.

270 to 280 seems to work best.

For the front silver strip (centre bus) I scratched a 1cm area with my pocket knife until it was really shiny (being careful not to go right through) then applied a little resin flux to the area.

I next applied the tip of the soldering iron for a few seconds before applying the solder to the bus at the tip of the iron. Overheating at this point will prevent the solder taking as much as underheating will.

I found the solder balled at first and stuck to the tip, then I lightly rubbed the tip of the iron back and forwards along the bus till it felt a bit "sticky".

That "sticky" feel indicates the solder has taken.

You only need a line of 1/2cm or so of solder (opinions vary from 1cm to the whole bus).

I did no more to the front at this stage.

For the backs of the cells I applied resin flux to a small area in line with the front silver strip (bus) but near the opposite edge to where I put the solder on the front bus.

Temperature is more important here.

No bus to solder to means you have to make one.

Apply resin flux to the area you want to create the bus on. You only need one.

Heat the area with the iron for 3 seconds then apply a small amount of solder to the tip of the iron.

When the cell is the right temp the solder will spread easily and obviously "take" to the surface (If the cell/iron is too hot the solder will spread but not take If it's too cold the solder won't spread).

I then put the tab in place. Holding it gently with the tip of the iron I heat it and the solder on the cell.

I then apply a little more solder to the tip of the iron.

This causes the solder under the tab to melt giving a nice bond.

Once again heat is important.

The pics show a little "budgie poo" of solder on the front bus, the tab attached to the back of the cell and two cells ready to join.

Joining them works just the same as tabbing the back....put the end of the tab over the solder on the front bus, heat, apply a little solder and jobs done as long as you got a nice "take" when you soldered the front.

If you struggle using tab try with a little fine copper wire instead of the tab.....maybe your iron isn't giving you what you need for the heavier tab.

Another major helpful thing I did was to mount a little "extractor" fan (off an old P2 processor) on my workboard.

A lot of solders per panel meant a lot of fumes were going up my nose.

The fan means I can breathe and solder at the same time....a nice feeling.

I also use a magnifier lamp...I'm an old bugger and it helps.

Panels from New Cells (untabbed).

My first Solar Panel using New Cells (the seconds from a batch of cells).

You will be joining all 36 cells, in series, in 4 “strings” of 9.


· 1 900mm X 600mm sheet of plywood (enough for 2 panels).

· 1 tube Selleys All Clear.

· 45cm Red 25mm wire.

· 15cm Black 25mm wire.

· 1 Roll of very thin resin cored solder (60/40 tin to lead or 60/38/2 tin to lead to silver).

· 1 Resin Flux pen.

· A bit of “leftover” undercoat, some topcoat and a brush.


· A good soldering Iron. Adjustable voltage. About 48watt and the best you can afford. I bought one of these and it’s a ripper!

· A pair of tweezers and a pocket knife..

Paint your board and let it dry.

After it dries attach your junction box if using one.

“How To”

*Prepare the cells for Soldering.

The backs of these cells have 4 positive contact points (called busses).

The front of the cells have 2 strips of negative contact point (also called busses).

Scratch the surface of the busses lightly with your pocket knife to remove oxidization and make the surface shiny.

*Pre heat your soldering iron to about 290deg C.

Tab only the back of the cells at this stage but do them all.

Apply flux to each bus before soldering.
Heat the clean, fluxed bus with the iron (about 290c) and apply a little solder. The solder should ball then spread a bit. Adjust your temperature until it does.

Do this to all 4 busses.

Take one of the tabs, place one end over the solder on a bus and heat with the iron. Apply a little more solder to the tip of the iron.

This will help the solder on the bus melt and adhere to bus and tab.

The tab should be also resting on the solder on the next bus. Do as above.

The “tail” of the tab will be sticking out one side of the cell.

Do the next tab in the same direction.

Repeat this step until all cells are tabbed.

Lay one of the tabbed cells (cell 1) on your workbench face up.

Prepare the front bus strips as you did the rear.

Pick up another cell (cell 2).

Place cell 2 face up on your workbench.

Place the tabs of cell 2 over the bus strips on the front of the first cell (cell 1).

Solder as with the rear..

Pick up another cell (cell 3).

Place the tabs of cell 3 over the prepared front bus strips of cell 2.


Repeat this until you have joined 9 cells (string 1).

Solder 2 tabs (or lengths of tab) to the front of cell 9 facing away from the string of cells.

Only do this with string 1.

This will become your negative out.

Carefully slide string 1 onto your (now dry) plywood.

Mark where the cells will sit the put 4 smallish “blobs” of silicone for each cell (so that the rear busses will sit on them).

This next bit will test your soldering and your nerve .

Lift the string of cells by the tabs and place it on the blobs of silicone. Lightly press each cell so that the cell is level and sitting a few mm clear of the plywood..

Repeat the above steps for the next 3 strings.

The strings need to be laid on the board “top to tail”, that is so that the negative (front) tabs of one string are adjacent to the positive (back) tabs of the next.

The positive tabs coming from the rear of string 4 are your positive out.

This diagram quite clearly shows why I’m not in graphic design……but it also shows how to lay your strings out.

Glue wires etc to board with blobs of silicone.

Allow 24 hours to dry.

Go outside and make lots of electricity.

My panels connect to a cheap controller, 85ah battery and 500watt inverter. They run fans and lights (for free!) and reduce my carbon footprint by a teeny bit.

I’ll add more DIY panels as soon as I can.

Most important Tip:

Your panel can only be as good as your worst soldered join allows. A bad join will restrict the flow of the good stuff.

Tip: Sellys All Clear melts when heated enabling the removal of cells from your board. Just apply heat to the top bus above the bottom bus a bit of a juggling trick to get all 4 hot at once but you can….then slide the cell off by gently pulling the tabs.

Tip: Don’t believe a lot of what you read in some of the tutorials online. Experience will soon show you which ones know what they’re talking about.

Tip: Join panels in parallel to maintain voltage (< >18v, your panels will peak at almost 20v) and increase wattage. Joining panels in series may fry your battery or blow a fuse in your control box.

Tip: Make your board/ply inflexible before you attach the cells. I cracked a cell when my ply bent.

Tip: Look after your soldering iron tip…..the user manual will tell you how.

Tip….last one I promise: Stay positive when you’re practicing on the scrap cells…..they’re much harder to solder than your good ones ( especially the backs….no busses). Once you’ve mastered them the worlds your oyster.

Enjoy the feeling of making your own power…’s a good thing to be doing.

All the best.