Identifying diodes?

Other Hardware General Electronics
1

I have a solar charger (BatteryMinder brand) that we adopted to use for an arduino project.
Despite their claims, the thing was not weather resistant & the board lasted a short time. Well; some of the components lasted a short time. Rust was not our friend.

10 resistors & 2 diodes were rusted thru at one end. The resistors are easy to identify (except 1 is about 2x as thick as the rest); but two diodes look like standard 14n148 type diodes (one is a bit bigger). They will not provide me any support or schematics; so I am on my own to fix it.

There were a couple other diodes on the board that looked healthy and similar sizes; so I unsoldered them to test them with a transistor/component tester. One tested out as a good diode with uf=789 and IR=4na; the other tested with uf=704, IR=10uA -- note that I was able to test the 1st one repeatidly and got similar results; the 2nd one now fails as a diode and is sub 1.5 ohm in one direction and .6ohm the other... (so now I actually have 3 diodes I need to identify).

Is there a way to know / guess what diode would work w/o schematic? are their markings that I just can't see w/o proper magnification? IOW: is there a way I can replace these diodes ?

My camera has dead batteries, but I'll go buy some if pictures will help...
Thanks

2

Hi,
Do the diodes have any markings?? Use a magnifier. Are they physically smaller or larger?

The two diodes you have are silicon (forward voltage about .7 V).

3

Thanks Terry...
I pulled out an old jeweler's loupe and gently cleaned them.. Under a bright light there was markings (I had initially thought they were just specs of paint)

so, with the band on the left (sounds like a song) the diodes had:
Larger sized diode #1: 16 & 1 (colour is a more uniform red)
Larger sized diode #2: 5 & C3 (colour is a red on about 1/3 and a burnt-orange on the rest)
Smaller diodes appear to be similarly marked with a capital/italics "F", 41, & 48 marked on it.

4

It's really tough to identify a diode without a circuit diagram. If it's working, you can get the basic voltage drop, which gives you one bit of information. Then I would look at the size or whatever I know about the current in that part of the circuit to purchase a diode with a bigger current rating. Usually the other characteristics of a diode are not significant to the operation of the circuit.

90% of the time the voltage drop is also unimportant. Just buy a diode which is fatter than the original, to get a bigger current rating.

If it's inside a switchmode power supply, then the other characteristics probably are important and it's time to throw the device away and buy a new one.

5

"resistant" as in weather resistant or water resistant means approximately nothing, you need
something that is 'for outdoor use' (aka fully weatherproof). All weather-resistant means it will
survive light rain occasionally if dried out afterwards.

6

"Conformal coating" on the PCB will help keep moisture out. The official stuff smells exactly like clear ladies' nail varnish, so now I buy all my conformal coating supplies in the makeup aisle. Clear is best, but you can use colours if you feel like you never need to see those components again.

I just slather it all over the components and every bit of exposed metal. It doesn't seem to give any trouble when soldering a repair through the old coating.

7

MarkT:
"resistant" as in weather resistant or water resistant means approximately nothing, you need
something that is 'for outdoor use' (aka fully weatherproof). All weather-resistant means it will
survive light rain occasionally if dried out afterwards.

the manual states "if using outside, be sure to mount it vertically so the label is facing you with the wires hanging straight down" (or words to that affect).

This is how it was mounted, actually, it was under a small roof too. The inside was ugly -- very clear that it should never have been out in the elements.

MorganS:
It's really tough to identify a diode without a circuit diagram. If it's working, you can get the basic voltage drop, which gives you one bit of information. Then I would look at the size or whatever I know about the current in that part of the circuit to purchase a diode with a bigger current rating. Usually the other characteristics of a diode are not significant to the operation of the circuit.

Yea -- I tried to get the schematic or some information, but they don't want to repair, they want to sell. and looking at it; I'm not sure how they justify $110 for it...

MorganS:
90% of the time the voltage drop is also unimportant. Just buy a diode which is fatter than the original, to get a bigger current rating.

Would be worth a try if I had them, but it's sounding like it's not worth the effort, or more correctly, that it won't work if we just take shots in the dark:

MorganS:
If it's inside a switchmode power supply, then the other characteristics probably are important and it's time to throw the device away and buy a new one.

It's supposed to do maintenance charging with desulfating... I didn't verify that it did do pulse charging; but it did keep the battery charged all year long...

Attached are some pictures, for whatever it's worth...

DesulfSolarChargerBottom.png

DesulfSolarChargerDiodes.png

DesulfSolarChargerResistors.png

DesulfSolarChargerTop.png

8

Probably 1N4004's will be fine - slow silicon
diodes good for an amp

regards

Allan.

9

The diode marked 41 48 is probably a 1N4148
The diode marked 5 C3 is probably a 5.3volt zener diode
Your'e photos are quite useful in that they indicate a degree of complexity to the circuit so be prepared for the eventuality of having to purchase a replacement. You will note there are three adjustment pots and without suitable calibration instructions you may well find that replacing the diodes (even with the correct types) may not give the degree of calibration required.

10

Thanks all! (cool idea about nail polish).

IF I had a good working unit; would that help narrow down specifics?

Hmm. I hadn't thought about those trimmers, sort of hoped they'd just magically still be working.

I will try with 5.3v zeners, since that's what I have, and ignore the 'fatness' differences.
Since I have the parts, It doesn't is only my time -- if it fails, there's the option of getting another unit. Just does't seem like it's 100 worth of complexity.

starting to seem like it's not (easily) repairable... I hate tossing things and buying replacements. (I might just be cheap.)

Thank you for your thoughts.

11

You are putting the storage battery too close to the charger. The vapors from the battery are getting into the controller housing and the sulfuric acid is destroying the copper in the component leads. Water, particularly rain water will not cause the damage you have described. If by "rust" you are referring to iron oxide, the only iron/steel will be on the leads of the 4000 series diodes. The resistors will all be copper and coated with tin.

Please move the controller away from the battery top surface.

Paul

12

Paul_KD7HB:
You are putting the storage battery too close to the charger. The vapors from the battery are getting into the

They are not close. the solar panel is on the roof, the controller is right under the overhang, the battery is on the ground, around the corner in open air.

13

daveyjones:
They are not close. the solar panel is on the roof, the controller is right under the overhang, the battery is on the ground, around the corner in open air.

Seems you have done everything correctly. Do you live near salt water?

Paul

14

Close enough that madrone trees grow but not close enough to see, hear, or smell it...

15

daveyjones:
Larger sized diode #1: 16 & 1 (colour is a more uniform red)

That may be a zener dode although the voltage i suspect.
Solar panels are often optimised for charging lead acid batteries at 14.6 volts.

16

daveyjones:
Close enough that madrone trees grow but not close enough to see, hear, or smell it...

whe you have it all working, again, do what MorganS suggested and cover all, except any connectors, with clear nail polish.

Paul

17

Boardburner2:
That may be a zener dode although the voltage i suspect.
Solar panels are often optimised for charging lead acid batteries at 14.6 volts.

Thanks. It is for a lead acid batteries... Too bad diodes are not marked as well as other parts.
I'll give the working board back and not mess with it; just buck up and buy a new one... Seems a small charge controller & desulfating pulser will run about $50 for cheap units from china, so the $115 for a new one might not be that bad ...

Will cover the exposed metals with the nail polish & seal up the seams...
thanks

18

Hi,
Before you return it, take some closeup pictures of the repaired PCB, if you can't focus part numbers then add them by hand to the picture later.

Including resistor values, burnt resistors are unreadable, and diode part numbers id possible.

This could be the best you will ever see it, so document it, including the PCB trace side, in case tracks get blown out.

Tom... :slight_smile:

19

I didn't see anything that some acetone and a brush wouldn't fix.