solar panel on sealed lead acid battery

The manual is rather vague. I expect it has to do with liability if you stick it in your window while you drive.

There are a zillion issues here.

Claims to have IC to protect against overcharge. Depending on how much money they spent on protection, starting your car with it attached may break it. There are HORRIBLE voltage spikes in an automobile environment.

For your application, it probably doesn't matter, unless their IC is insufficient to handle its power dissipation with full sun and minimum battery voltage under load. A bad design might go into limit-cycle oscillation. Bad designs do exist.

Depending on where you live and the insolation numbers there, you won't get much out of this. Certainly won't run your 20W amplifier for long. You're gonna have to have half a watt of average power consumption to make this work in a very sunny location. Gets horribly worse if you have a week of overcast.

Consider weather and your power budget very carefully.

electrically a solar cell battery a series string of low quality diodes pointed the wrong way. A "load dump" could fry it. If you're not running an altenator to charge the battery you're probably safe.

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Are you saying that they don't even have a nickel or dime "blocking diode" to protect the panels?

I suspect that's it. Depending on where the wires run, starting the car can create a 100V p-p spikes. I've seen brake lights create 40V spikes.

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Or just put a diode in series with the solar collector. I think the unit listed above says it has one, no?

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Rick

But...but...did you not know that SOLAR POWER is _the_ solution for GW and will solve all of the power problems for humanity? How dare you!

On a sunny day (Fri, 12 Sep 2014 19:28:28 -0700 (PDT)) it happened Fibo wrote in :

Seems a toy.

Maybe because of back EMF from things on your battery (motors etc).

I am using a BIG solar panel to keep a sealed lead acid charged. I use a simple current and voltage regulated converter from ebay. The issue with those batteries is: READ THE BATTERY DATA SHEET, it will tell you what the charge curve should look like, usually a maximum voltage limit is mentioned [1]. You can - or cannot use current limiting, depends how much current your solar panel can supply, how fast you want to charge, etc. There are charge controllers that go for maximum possible power from the panels, but in my case you HAVE to stop at some voltage anyways.

[1] If you do not voltage limit, then the 'open' voltage of a solar panel is way up there... and will kill the battery. Lead acid batteries (sealed or not) will die anyways after some years, and / or some number of full discharge cycles.

But this thing in your link will only output 2.5 W at 12 V say 200 mA in the BRIGHTEST sunlight. So that battery will be empty anyway in a few hours with a few watt or a 20 W load. It cannot charge at night ... So if you live in the Sahara desert, and only use power at night, OK, maybe then it could keep your battery up.

If present it's probably a 50V (or lower) part, but it turns out there's a regulato chip too, that's probably even more fragile.

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You can add a 1000V 1A diode for less than a quarter:

Thanks for the replies... my 20W load will never run 20W, it's a "20W" amplifier, but that's a marketing term for the amplifier and is talking about peak power, maybe for a bass intensive track or something.

I can add a diode, would a 15V Zener help voltage limit protect the battery?

Don't get too fast and loose adding diodes. Not only did you loose 0.7/14% of the power, you reduced the number of daylight hours that there's enough voltage to do any charging at all. Take a look at the graph of amps vs volts at various insolation levels and subtract off that diode voltage.

And if the regulator electronics are built into the cell enclosure, where are you gonna put the diode? Not at the output! The devil is in the details.

I predict that once the OP does the math, calculates the standby power required, the actual amount of energy that you can get from the sun in his actual situation and the weight of that battery, he's gonna find another alternative.

Here is some useful info on float charging an SLA battery.

Looks like you would want to limit the voltage to the 12 volt battery to around 13.8 volts, somewhat lower than your 15 volt zener will set. The limit should be even less if the temperature can rise. Be aware that zener diodes have rounded knees, that is, the voltage depends on the current.

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Rick

no, you don't want to use a zener, that is, if you plan on putting it across the line in parallel?

The idea of putting a clamp in parallel at the power entrance of the device is good since the lead wire is most likely of a small gage. This will act as your current limiting for the short load dump you may get from the the car's alternator. The diode will clamp it.

Get a TVS diode instead, they clamp faster and can handle higher current peaks.

Jamie

I think the consensus is that so long as you're not using the battery in an automobile or to power an electric fence energiser leaving the solar charger connected without any modifications is unlikely to be problematic. A bunch of us are talking about other things now.

Even in an automobile at rest there is a small power draw for the radio's memory, and for the clock. and alarm, etc... so using it to run the beaglebone should not be problematic. also in an automobile you can operate the radio (and the diome light) with the engine stopped so the amplifier is probably OK too.

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and was thinking about buying this Solar Battery Maintainer to keep it charged

Nether am I, for the situation discussed below.

You can add one, if you like, but it will need to handle at least 2.5W and I would suggest a 5W device if you choose to do so. But you probably don't need one.

If I understand your needs, you will not be connecting this set-up to an automobile or other system that can generate large transients. That is, you are interested only in your battery, solar cell, and your load. Yes? If I am wrong, then ignore the rest of this post.

If you are taking some energy from the battery daily, then you can leave the solar cell connected. This is called cyclic use. If you are taking energy from the battery only periodically, such as during a power failure, then that is called standby use.

It is not good for a battery to get too much charge, so if you decide that you will not be using the battery for a week or so, then disconnect the solar cell.

Can you come up with a power budget? It would help immensely. For example, your Beaglebone uses, say, 50mA 24 hours a day and your amplifier uses, say 1A 2hours a day. So your Beagle bone uses .05*24 AH or about 1.2AH per day. The amp is 2AH per day. Total is 3.2AH per day. At 12V, that's about 38W*Hours per day.

Your solar cell, under *ideal* conditions provides 2.5W at maximum sunlight input (insolation). You can expect that input, maybe, only at noon at the equator on either summer or autumnal equinox (if not cloudy) and for less than 12 hours per day. Using the best of these numbers, you can expect about 0.64*2.5W or about 1.6W*Hours per day of recovered energy.

So, you see how important it is to do these estimates? Gather your information and apply it as above. Or, connect the solar cell to your battery and see what happens. After all, the battery only costs $17.

Any calculation mistakes above are not mine.

Cheers, John

Is he actually using this in an automotive application? I did not get that from either his OP, links, nor follow-up.

Thanks for your response, I will make a power budget. No, no not an automotive application, just the beaglebone and the little audio amplifier.

thanks!

How often and for how long do you run your stuffs? The 2.5W panel won't provide much power other than just maintaining the battery.

He said he would do a power budget. Wait for it.