Solar Garden Lighs/sidewalk lights

[Franc Zabkar]

Some of mine have ldr`s and one hasnt. the one which has no ldr powers a
string of about 30 leds by upconverting 1.5 volts to 15v pulsed.
there`s a quite complex circuit which detects whethere the cells are
producing any output and switches accordingly. It`s failed twice now due
to the leads from the cells corroding away.

Why is it always the negative lead that corrodes?

Ron(UK)

I'm not sure if this applies to you, but I've solved corrosion
problems with the solar powered "eternity" lamps at the cemetery by
using gel filled telecom "butt connectors":

http://solutions.3m.com/wps/portal/...E3E02LECIE20O4M7_nid=NZW3RHPDRDbeDP16W8FB2Ngl

- Franc Zabkar

 

[Ross Herbert]

:
:Why is it always the negative lead that corrodes?
:
:Ron(UK)

I am not a chemical engineer so I don't have any practical knowledge of galvanic
corrosion protection. There is a so-called Galvanic Table from which the degree
of corrosion can be predicted and it basically says that the higher the order of
one metal (on the table) relevant to another metal in close proximity, the the
higher order metal will corrode when an electrolyte covers them both.

Copper wire connected to the negative terminal is fairly high on the galvanic
table and assuming the casing of the solar lamp is made of stainless steel, this
metal is lower on the galvanic table. Moisture, complete with impurities will
condense across the surfaces of both metals during the night and set up
electrolytic action, thus the higher order metal will corrode.

The table is the galvanic series of metals in sea water from Army Missile
Command Report RS-TR-67-11, "Practical Galvanic Series."

The Galvanic Table

Active (Anodic)

1 Magnesium
2 Mg alloy AZ-31B
3 Mg alloy HK-31A
4 Zinc (hot-dip, die cast, or plated)
5 Beryllium (hot pressed)
6 Al 7072 clad on 7075
7 Al 2014-T3
8 Al 1160-H14
9 Al 7079-T6
10 Cadmium (plated)
11 Uranium
12 Al 218 (die cast)
13 Al 5052-0
14 Al 5052-H12
15 Al 5456-0, H353
16 Al 5052-H32
17 Al 1100-0
18 Al 3003-H25
19 Al 6061-T6
20 Al A360 (die cast)
21 Al 7075-T6
22 Al 6061-0
23 Indium
24 Al 2014-0
25 Al 2024-T4
26 Al 5052-H16
27 Tin (plated)
28 Stainless steel 430 (active)
29 Lead
30 Steel 1010
31 Iron (cast)
32 Stainless steel 410 (active)
33 Copper (plated, cast, or wrought)
34 Nickel (plated)
35 Chromium (Plated)
36 Tantalum
37 AM350 (active)
38 Stainless steel 310 (active)
39 Stainless steel 301 (active)
40 Stainless steel 304 (active)
41 Stainless steel 430 (active)
42 Stainless steel 410 (active)
43 Stainless steel 17-7PH (active)
44 Tungsten
45 Niobium (columbium) 1% Zr
46 Brass, Yellow, 268
47 Uranium 8% Mo.
48 Brass, Naval, 464
49 Yellow Brass
50 Muntz Metal 280
51 Brass (plated)
52 Nickel-silver (18% Ni)
53 Stainless steel 316L (active)
54 Bronze 220
55 Copper 110
56 Red Brass
57 Stainless steel 347 (active)
58 Molybdenum, Commercial pure
59 Copper-nickel 715
60 Admiralty brass
61 Stainless steel 202 (active)
62 Bronze, Phosphor 534 (B-1)
63 Monel 400
64 Stainless steel 201 (active)
65 Carpenter 20 (active)
66 Stainless steel 321 (active)
67 Stainless steel 316 (active)
68 Stainless steel 309 (active)
69 Stainless steel 17-7PH (passive)
70 Silicone Bronze 655
71 Stainless steel 304 (passive)
72 Stainless steel 301 (passive)
73 Stainless steel 321 (passive)
74 Stainless steel 201 (passive)
75 Stainless steel 286 (passive)
76 Stainless steel 316L (passive)
77 AM355 (active)
78 Stainless steel 202 (passive)
79 Carpenter 20 (passive)
80 AM355 (passive)
81 A286 (passive)
82 Titanium 5A1, 2.5 Sn
83 Titanium 13V, 11Cr, 3Al (annealed)
84 Titanium 6Al, 4V (solution treated and aged)
85 Titanium 6Al, 4V (anneal)
86 Titanium 8Mn
87 Titanium 13V, 11Cr 3Al (solution heat treated and aged)
88 Titanium 75A
89 AM350 (passive)
90 Silver
91 Gold
92 Graphite

End - Noble (Less Active, Cathodic)

 

[Ross Herbert]

However, since the positive lead on the solar cell is also made of copper and
the same condensation will no doubt cover this terminal, why then doesn't the
positive lead corrode too?

 

[Ron(UK)]

I'm not sure if this applies to you, but I've solved corrosion
problems with the solar powered "eternity" lamps at the cemetery by
using gel filled telecom "butt connectors":

http://solutions.3m.com/wps/portal/...E3E02LECIE20O4M7_nid=NZW3RHPDRDbeDP16W8FB2Ngl

They may help, but it`s the actual copper of the wire which turns black
and brittle, the soldered joint is usually fine.

Ron(UK)

 

[Ron(UK)]

:
:Why is it always the negative lead that corrodes?
:
:Ron(UK)

I am not a chemical engineer so I don't have any practical knowledge of galvanic
corrosion protection. There is a so-called Galvanic Table from which the degree
of corrosion can be predicted and it basically says that the higher the order of
one metal (on the table) relevant to another metal in close proximity, the the
higher order metal will corrode when an electrolyte covers them both.

Copper wire connected to the negative terminal is fairly high on the galvanic
table and assuming the casing of the solar lamp is made of stainless steel, this
metal is lower on the galvanic table. Moisture, complete with impurities will
condense across the surfaces of both metals during the night and set up
electrolytic action, thus the higher order metal will corrode.

Interesting stuff, and there is a correlation between disimilar metals
corroding - sacrificial anodes and all that, but I`m not sure that is
what happens in the case of nicad battery packs

It`s not only in metal cased fixtures tho, most of the garden lights
here are plastic - they only cost a few pounds, not worth repairing really.

I spent a great part of my youth and early adulthood messing about with
radio controlled models, and whenever a Nicad batterpack failure
occured, it was always the negative wire which had turned black and
literally rotted away. I don't think moisture has much of a role in the
matter, as many battery packs are quite well sealed.

I wonder if the same problem occurs with types of battery technology
other than Nicad, NiMH for example?

Even in cars, I believe that it`s usually the Negative battery
connection which gives trouble, either at the battery termnal or the
chassis ground connection.


Ron(UK)

 

[Ross Herbert]

:
:Interesting stuff, and there is a correlation between disimilar metals
:corroding - sacrificial anodes and all that, but I`m not sure that is
:what happens in the case of nicad battery packs
:
:It`s not only in metal cased fixtures tho, most of the garden lights
:here are plastic - they only cost a few pounds, not worth repairing really.
:
:I spent a great part of my youth and early adulthood messing about with
:radio controlled models, and whenever a Nicad batterpack failure
ccured, it was always the negative wire which had turned black and
:literally rotted away. I don't think moisture has much of a role in the
:matter, as many battery packs are quite well sealed.
:
:I wonder if the same problem occurs with types of battery technology
ther than Nicad, NiMH for example?
:
:Even in cars, I believe that it`s usually the Negative battery
:connection which gives trouble, either at the battery termnal or the
:chassis ground connection.
:
:
:Ron(UK)

I am sure there is a scientific reason for corrosion being mainly on the
negative terminal but I can't quite rationalise it at the moment. I have seen
many reports on car battery negative terminals and wiring corroding and I have
also seen a lesser number of complaints about the positive terminal.

Without going into a scientific discussion on the subject perhaps T.R.B Watson
has a plausible simplified explanation.
http://www.westcoastcorrosion.com/Papers/Why Metals Corrode.pdf