Electronics > Projects, Designs, and Technical Stuff

eBay SMPS as a Lead Acid Battery Charger

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tribat:
I'm not sure how aware people are of this but SMPS modules on eBay are dirt cheap and very available these days. Chinese sellers are selling them for very low prices, and from what I hear their pretty decent quality too. At least the ones from seller called 'stoneined2009'.

Here's an example: http://cgi.ebay.com/DC-12V-12A-145W-Power-Supply-Regulated-Switching-New-/170567024030?pt=LH_DefaultDomain_0&hash=item27b6963d9e

Cool thing about them is that they seem to have a pretty decent voltage adjust range, and from what I hear the range is usually wider than the specs say, for example that model goes up to 14.6V.

The voltage range needed for lead acid batteries is about 13-15V so one of those 13.5V models with 12-15V voltage range should be perfect ( http://cgi.ebay.com/350W-13-5V-DC-Regulated-Switching-Power-Supply-K004-/180455569172?pt=LH_DefaultDomain_0&hash=item2a03fd7714 )

I was wondering what kind of modification would those things needs to work as a lead acid battery charger? Could you just set the voltage to 13.5V and hook it to a battery and forget about it? Or would there have to be some kind of current limiting or something?

I read about charging lead acid batteries and the way I understood it is that 13.5V is the magic voltage where a battery can be kept fully charged indefinitely without damaging it. It won't charge the battery very fast but will eventually get the job done. Still I wonder if the voltage adjust trimmer could be replaced with some circuitry that adjusts the voltage of the SMPS automatically.

Bored@Work:

--- Quote from: tribat on December 04, 2010, 11:41:25 am ---At least the ones from seller called 'stoneined2009'.

--- End quote ---

Pointless. The idiot claims "worldwide" shipping, but then excludes whole continents.


--- Quote ---Excludes: Africa, Asia, Central America and Caribbean, Middle East, North America, Southeast Asia, Argentina, Bolivia, Colombia, Falkland Islands (Islas Malvinas), French Guiana, Guyana, Paraguay, Suriname, Uruguay, Venezuela, American Samoa, Cook Islands, Fiji, French Polynesia, Guam, Kiribati, Marshall Islands, Micronesia, Nauru, New Caledonia, Niue, Palau, Papua New Guinea, Solomon Islands, Tonga, Tuvalu, Vanuatu, Wallis and Futuna, Western Samoa, Albania, Andorra, Austria, Belarus, Belgium, Bosnia and Herzegovina, Croatia, Republic of, Czech Republic, France, Germany, Gibraltar, Guernsey, Iceland, Italy, Jersey, Latvia, Liechtenstein, Lithuania, Luxembourg, Macedonia, Moldova, Monaco, Montenegro, Netherlands, Romania, San Marino, Serbia, Spain, Svalbard and Jan Mayen, Ukraine, Vatican City State
--- End quote ---

If a seller starts with a lie like "Shipping to: worldwide", I immediately exclude him as a supplier I trust.

Balaur:
The problem with Chinese electronics is that the quality ranges for perfectly designed & made, high-quality, not expensive devices to absolutely POS stuff.

As a general, personal observation, the power supply units tend to be on the POS side, especially those on eBay. Cheaply made, unreliable capacitors (of course), idiotic design, especially on the SMPS units, stupidly high ripple, but cheap as air, though.

You can buy one and be very happy with that or you can have a horror story like this gentleman:
http://www.ludens.cl/Electron/chinverter/chinverter.html

Cheers,
Dan

tecman:

--- Quote from: tribat on December 04, 2010, 11:41:25 am ---I read about charging lead acid batteries and the way I understood it is that 13.5V is the magic voltage where a battery can be kept fully charged indefinitely without damaging it. It won't charge the battery very fast but will eventually get the job done. Still I wonder if the voltage adjust trimmer could be replaced with some circuitry that adjusts the voltage of the SMPS automatically.

--- End quote ---

What you are looking for is called "float charge".  It will maintain, but not overcharge a battery.  It is nominally 2.15 volts per cell, but that is at somewhere around 70 degF.  The specific voltage varies with temperature.  This drops about 0.1 volts for every 10 deg increase.  You can read more at:  http://www.hss.doe.gov/nuclearsafety/ns/techstds/standard/hdbk1084/hdbk1084.pdf

paul

tribat:

--- Quote from: tecman on December 04, 2010, 02:13:54 pm ---
--- Quote from: tribat on December 04, 2010, 11:41:25 am ---I read about charging lead acid batteries and the way I understood it is that 13.5V is the magic voltage where a battery can be kept fully charged indefinitely without damaging it. It won't charge the battery very fast but will eventually get the job done. Still I wonder if the voltage adjust trimmer could be replaced with some circuitry that adjusts the voltage of the SMPS automatically.

--- End quote ---

What you are looking for is called "float charge".  It will maintain, but not overcharge a battery.  It is nominally 2.15 volts per cell, but that is at somewhere around 70 degF.  The specific voltage varies with temperature.  This drops about 0.1 volts for every 10 deg increase.  You can read more at:  http://www.hss.doe.gov/nuclearsafety/ns/techstds/standard/hdbk1084/hdbk1084.pdf

paul

--- End quote ---
But will just setting the power supply to that voltage be enough? Do you have to also a throw a current limiting circuitry there?

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