Diode for a 12 volt 5 watt panel

[anony]

Hello,

I have a couple of 5 watt panels used to maintain a 12 volt AGM battery.

Unable to remember the ratings, using a voltmeter output in full sunlight is around ~21.5 volts.

Each panel came with it's own diode, installed a few inches from the pos+ connection of a panel.

One of the panels pos+ wire became torn and separated the diode from it's wire making it unusable.

I can't determine the diode part number, the other diode is covered with shrink tubing. The existing diodes are fairly small in diameter. (~1 to ~2 mm)

Any recommendations for a diode to use with a 5 watt solar panel?

I have a few rectifier diodes such as 1N4001, IN4004 & 1N4007, however the diode I'm replacing is smaller in size.

[Mike90250]

A Schottky diode of about 50V, 3A should be fine.

[anony]

A Schottky diode of about 50V, 3A should be fine.

I found a Schottky 3A - 40 and 60 volt diode.

What is the reason to use a Schottky diode?

[inetdog]

I found a Schottky 3A - 40 and 60 volt diode.

What is the reason to use a Schottky diode?

The reason for using a Schottky diode is that the forward voltage drop can be as low as .2V, while a standard silicon rectifier diode would have a minimum voltage drop of .7 volts.
The effect is twofold:
1. Less heat dissipation in the diode, allowing you to use a smaller diode and maybe avoid the need for a heat sink.
2. Less power wasted in the diode, assuming that the load would even work with the higher voltage drop.

[pimpssss]

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[PNjunction]

I have a couple of 5 watt panels used to maintain a 12 volt AGM battery.

Careful! The diode you are referring to is most likely used as a very simple blocking diode for when the sun goes down and you aren't using a charge controller. If you use a controller, that in itself serves as the blocking diode.

Using a controller is highly recommended for maintaining batteries. Even a simple low-wattage panel can damage expensive batteries when they are *already* nearly fully charged. A good example from Compass Marine can be seen here:

https://www.youtube.com/watch?v=z5RtZe9AW2E

I don't know what the size of the battery it is you are trying to charge, but even if it is a low-cost UPS-style agm, like a powersonic, B&B and the like, a charge controller is better for overall life. At the low-end, something like a simple Morningstar SunGuard 4.5A unit would be worlds better than the diode in series trick.

[anony]

I found several 1N5822 3A 40V Schottky Diodes.

I do have a Sunsaver 10 I could use.

The other 5 watt solar panel has an installed diode that came with the panel.

Charging connections would be for either a Group 34 Yellow Top or a Group 31 AGM.

10 watts is probably not enough for these batteries, probably needs ~25 watt. 10 watts should supply around ~1/2 amp as a trickle charge if there is full sun.

The Yellow Top is still good but it's getting on in years, getting close to 7 years. I like to keep some sort of charge on it when not in use.

I do have a 115 watt panel, but I'm not sure how well it would install on a SUV and if it would get damaged or stolen?

[anony]

Careful! The diode you are referring to is most likely used as a very simple blocking diode for when the sun goes down and you aren't using a charge controller. If you use a controller, that in itself serves as the blocking diode.

Using a controller is highly recommended for maintaining batteries. Even a simple low-wattage panel can damage expensive batteries when they are *already* nearly fully charged. A good example from Compass Marine can be seen here:

https://www.youtube.com/watch?v=z5RtZe9AW2E

I don't know what the size of the battery it is you are trying to charge, but even if it is a low-cost UPS-style agm, like a powersonic, B&B and the like, a charge controller is better for overall life. At the low-end, something like a simple Morningstar SunGuard 4.5A unit would be worlds better than the diode in series trick.

Thanks for the link.

After connecting a Sunsaver 10 without a battery connection the solar input voltage is ~19.5 volts. However there is no output voltage without a battery connection. The charging light becomes green when connected to a 12 volt AGM battery.

Specification show no min. amp requirements. Self consumption is less than < 8 milliamps.

I think 10 watts would be good for charging small NiCads, perhaps when placed in a series. Charging small rechargeable batteries it is better to be able to charge each battery individually.

There are small wood camping stoves that produce electricity, around 5 volts to charge and produce electricity for small portable devices.