Linear current booster

Wondering where I might find a schematic for a home brew linear current booster to control PV module power to a very small 12V 2.5A bilge pump? My
googling didn't turn up anything. Chuck
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cjensen wrote:

OK, So what is a "linear current booster"? It may be an expression that we call something different in the UK. Mind you, I didn't quite understand what you meant by a "PV module power", either.
Now 12V 2.5A bilge pumps, no problem. I could imagine that you have a low current analogue control signal that you want to "boost" into something in the range 0 <-> 2.5A in order to drive the bilge pump. Not, I would imagine, for actually pumping out bilges as on/off is normally quite enough. I assume that you won't want to reverse it, lol?
So, if you would like to explain what your inputs are and what outputs you want, then I may be able to help.
Although, for boats, every watt is normally precious, so I would be using switched mode controllers rather than linear. So you are perhaps using this bilge pump for something else.
--

Sue

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PV ... portable voltage module? battery?
PV ... positive voltage? pump velocity? pump valve?
to a very small 12V 2.5A bilge pump? My

please explain what you want to accomplish.
if you want to make it pump faster or slower look for "variable power supply" or "DC voltage regulator"

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Palindr☻me wrote:

Linear current booster or "LCB" is used in solar energy photovoltaic applications involving direct-drive systems, that is, a PV module wired directly to a dc motor, usualloy a pump. PV modules basically produce full voltage at reduced current during low light conditions such as early morning, clouds, or shading. LCBs will convert power to lower voltage at higher current to help the pump get started or avoid stalling out, although at a lower voltage, lower speed. At full sunlight in low ambient temps a PV module can produce much higher than their nominal voltage. The LCB limits the voltage to protect the pump.
Here is an example of a typical LCB:     http://www.solarconverters.com/ppt3.htm Typical PV module IC curve:     http://www.kyocerasolar.com/learn/modules.htm
I like to roll my own components if it's not too advanced. Chuck
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On Mon, 07 Feb 2005 18:38:34 -0700, Chuck Jensen

That all you been rolling?
Regards
Daveb
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Chuck Jensen wrote:

Thanks for that! As I understand it, it is basically two standard applications rolled into one. One is to produce a fixed power, low voltage, high current output to start the pump. The other is to produce a fixed 12 volt, up to 2.5 A constant voltage supply to run it. Both will need protection circuitry to deal with overloads.
I couldn't get your second link to work but found this one useful:
http://www.kyocerasolar.com/support/spec_kswaterpump.html
I have a bit of a credibility gap that anyone would choose a linear solution for this over switched mode. So I am only going to suggest non-linear solutions.
Now you could do this by using the two standard application building blocks and having a simple change-over control circuit that switches between the two as the voltage output of the constant current starting circuit reaches a preset limit. However, there is a neater way:
I would suggest looking at modifying a buck-boost switch mode power supply design. Modify in the sense of adding a simple additional control circuit and a second output winding, with its associated energy recovery diode and filter. It would also need some additional, simple, control circuits to protect things, for example, if the pump stalled or did not come up to speed quickly enough.
Can I suggest that you try google on buck boost switch mode supplies and, in particular, go to the web sites of some of the chip manufacturers that produce ICs aimed at buck-boost reguators? They have many application notes that I am sure will be useful.
You can email me (leave off the invalid bit) if you want more specific help - but a 12V 2.5A buck boost design suitable for working with your range of input voltages is a good place to start. For the high current, low voltage, starting current, putting an extra winding on the transformer would have advantages. That design should be very efficient. The output from the two controllers could simply be paralleled, with blocking diodes. A very simple control circuit monitoring the output voltage could be used to disable the controller not needed at the time.
--
Sue





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Palindr☻me wrote:

Hi, thanks for the info. Bill Kaszeta also gave some good background on LCBs. You've got the idea. I might add there is one more application that precedes the two you mentioned. Maximum power point tracking (MPPT). So the LCB: 1)Finds and utilizes the MPPT on the solar module I-V curve as solar irradiance and cell temperature vary; 2)Boosts current and lowers voltage (or the other way around if that setting is available); and 3)regulates voltage output to a set point.
Why the device is called "linear" I don't know, but from what I have found out, they are a fast switching pulse width modulation device with IC controller. Much more to it than my PV Design and Installation classes disclose.
Thanks for those suggestions and I will research buck boost dc-dc transformers, manufacturers websites, and the TL494 that Bill mentioned.
Chuck
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Background information:
A linear current booster (LCM) is a special purpose switch mode 'buck' converter that is used in photovoltaic (PV), solar electric, systems to provide a better match between the PV array and a motor load (or lower voltage battery).
The voltage output of a PV is relatively fixed as the level of sunshine varies. Motors on the other hand are basically constant current devices with the voltage varying with power and speed. The LCM acts as an automatically adjusting dc/dc converter to convert high voltage/low current pv array outputs (low sun conditions) to lower voltage/higher current to better operate a dc motor.
The original circuits were built using a TL494 integrated circuit as a controller with a feedback loop to limit the output current. A Google search on 'TL494 integrated circuit' produces several application notes on this device and its more modern replacements. Understanding a buck converter is a good starting place.
This same basic circuit with more modern control of the pulse width is used with solar charge controllers and inverters that offer maximun power tracking. Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA snipped-for-privacy@pvri-removethis.biz
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