solar panels - elmers Forum at eHam.net

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solar panels	Reply
by KF6CET on December 6, 2003	Mail this to a friend!
How big a solar panel do I need to charge a 7Ah and, do I need a controller or just the panel?

RE: solar panels	Reply
by KZ1X on December 6, 2003	Mail this to a friend!
If you use one of the Volkswagen panels you can get on eBay, you won't need a controller. The 3 watt panel works great to charge my gel cells from 2 to 10 amp-hour size. Make sure to retain the blocking diode (a 1N4007) that is inside the plug that comes with the unit; you will probably re-wire the connector. I use all PowerPoles now; just don't ever plug the solar panel into anything other than a gel cell!!

RE: solar panels	Reply
by KA5S on December 6, 2003	Mail this to a friend!
Depends on the panel. Some panels are designed to be floated across a gel-cell and don't put put more than about 14 volts. A ten watt panel of this type can recharge a comptely discharged 7 AH gell cell in about two sunny Winter days. It's best to use a charge controller which senses and adapts to battery condition, as we rarely run batteries ALL the way down. Depending on how far down you take a gel-cell, this can be as simple as a regulator to keep the voltge below 13.8 volts or so. This also lets you use a less tightly specified solar array. One easy regulator is a Radio Shack 22-504 3-amp regulated power supply with the solar cell output connected across the analog regulator input. This will handle up to about a 40 watt array. Removing the transformer makes it lighter, though not smaller. Cortland

RE: solar panels	Reply
by KC8VWM on December 6, 2003	Mail this to a friend!
It's always better to have a controller connected. This way it is an "install and forget" charging system. Otherwise you may need to monitor the charging process. 73 Charles KC8VWM Here are some plans to build your own solar powered generator on my website: http://www.angelfire.com/on/cbushell/solar/solar1.html

RE: solar panels	Reply
by AA4PB on December 6, 2003	Mail this to a friend!
A charge controller is a "requirement" unless you are very careful to manually disconnect the panel when the battery is fully charged. Even a relatively small capacity solar panel can overcharge and shorten the life of an SLA battery if you leave it connected and in bright sunlight long enough. You can get a small charge controller suitable for a 7AH SLA battery for about $25 so its a good investment to protect your battery.

RE: solar panels	Reply
by W3JJH on December 6, 2003	Mail this to a friend!
I've had very good service from my Morningstar SunGuard solar charging controller. www. morningstarcorp.com In the real world, you can expect that changing sun angle, controller losses, etc., will reduce the average charging power to about 40 to 50 % of the solar array's rated output. If you want to be able to charge a 7-Ah battery fully during a 10-h winter day, you'll need an array rated at about 20 W.

RE: solar panels	Reply
by N6AJR on December 7, 2003	Mail this to a friend!
if you use a small solar pannel, (5 to 25 watts or so) like the battery maintainers or the volkswagon panels, you can leave them on all the time if you use a larger battery ( they are made to keep a 12 volt auto or marine battery from discharging in storage or transport.) I use one on my truck as I only drive it once or twice a month and the battery used to be dead, but now it stays topped up. works well. if you use the 7 amp hour battery daily it should be ok, (5 watts at 17 volts is only a couple hundred milliamps) but any larger buy or make a controler.

RE: solar panels	Reply
by AA4PB on December 7, 2003	Mail this to a friend!
A couple hundred mills will easily overcharge a 7AH SLA battery if left on! In addition, most solar panels designed for 12V batteries climb to around 16 volts no load. If you check the specs on most 12V SLA batteries they are to be "float" charged at 13.8 volts. These little solar panels are okay with a 50AH or greater battery where it takes more current to keep up with the larger battery self-discharge. It is risky to use them without a charge controller on a small 7AH battery. If you greatly overcharge a battery it is possible to overheat it causing plates to buckle and short - immediate failure. It is also possible to "slightly" overcharge a battery causing its service life to be shortened due to the loss of water in the electrolyte (SLA batteries have a vent that allows gasses to escape when generated at a rate higher than they can be recombined inside the cell such as when overcharging). You may not notice it right away because there is no catastrophic failure. It just starts loosing capacity and a full charge starts lasting shorter and shorter times.

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