12v to 6 v DC to DC converter

[sparky1]

Anyone know how to make or where I can buy a 12v to 6 v DC to DC converter ?
I have a 12v Marine battery that I want to use to continuously power a 6v water pump being recharged during the day with a 12 v solar battery charger.

Thanks,
sparky1

 

[crutschow]

How much current does the water pump require?

 

[MikeMl]

Since you are using solar, you do not want to waste half the battery energy as would happen with a linear regulator. Use a switch-mode buck-converter which can have an efficiency up to ~90%.

 

[sparky1]

there is no current rating listed on the pump just operative voltage: 7 volts and the little solar panal that runs it say peak power of solar panal is 1.2 watts

 

[sparky1]

not familiar with a switch-mode buck-converter ??

 

[MikeMl]

there is no current rating listed on the pump just operative voltage: 7 volts and the little solar panal that runs it say peak power of solar panal is 1.2 watts

You need to measure the running current of the pump. If the peak power out of the solar panel is only 1.2W, you will be lucky to get close to that for a few hours per sunny day while the sun is at right angles to the panel, say 1W for 6hrs per day. Depending on where in the world you are, that could be wildly optimistic. That would be 6Wh/day.

I cannot imagine that any pump containing a DC motor would have a running current less than 100mA, likely much more. That would be 7V*0.1A = 0.7W. If all of the energy from the panel could be utilized by the pump, you could run it for( 6Wh/day)/0.7W =~10h/day. Is this what you were expecting?

To answer this in detail, you will have to measure the running current of the pump (at 7V).

 

[Lake9398]

Maybe this will work?
12V to 6V buck converter using 555 timer IC : simple electronics

 

[colin55]

12V to 6V buck converter using 555 timer IC : simple electronics

The most critical component in the circuit is the inductor - and its value has not been given.

 

[cachehiker]

Without a variable duty cycle its regulation isn't going to impress.

I could calculate values for the timing resistors and capacitor, inductor, and output capacitor for a fixed load.

In the absence of a known and fixed load though, what can you do when Ton and Toff are fixed at 50%?

I'd go after something simple based on an MC34063 with the inductor fixed on a value that's readily available and cheap.

 

[sparky1]

12v to 6 v DC to DC converter

Ok, I've measured the current draw of the pump:

With 6 volt power supplies: The pump draws from .16 to .18 amps depending on which power supply I used.
This seems consistent with the ratings given for the small Solar Panal that came with the pump of 1.2 watts / Operating voltage 7 volts = .17 amps.

 

[MikeMl]

Ok, so how many hours per day do you want to run it off the 12V battery/solar charger.

Are you planning to use a different solar panel to charge the battery (in place of the 6V one that came with the pump)? If so, what are its specs?

Are you planning to retain the 6V panel in parallel with the step-down regulator?

 

[sparky1]

Thanks !
I've checked out the (12V to 6V buck converter using 555 timer IC : simple electronics)
Will this circuit be able to handle the surge current when attached to the 12v Marine battery?

 

[sparky1]

To solar charge the 12v Marine battery, I have a larger solar panal ( 5 watt, 450 mA, 13.5v ). I have a second if needed.
I won't use the small 6v panal. Not sure how many hours per day I will run the pump. This is my first solar panal so I'm experimenting to see what it can do. I was hopping that the panal(s) would run the pump and charge the battery during the day, then the battery would continue to run the pump until the next day...

 

[MikeMl]

I would suggest two regulators:

The first to regulate charging of the battery. Use a TL431 (fig 21) as a shunt regulator boosted with a PNP transistor.

The second to convert 12V to 6V. Use a 34063

 

[sparky1]

I have limited electronics theory knowledge.. I need to see a circuit diagram with values then I can build it. Thanks

 

[colin55]

You just need a 12v car cigarette lighter DC power supply (converter). You can change the output from 5v to 6v:


https://images10.newegg.com/ProductImageCompressAll300/58-985-015-02.jpg
**broken link removed**

Or you can build your own circuit:

This circuit is a BUCK REGULATOR. It can take the place of a 78L05 3-terminal regulator, but it is more efficient. It produces a constant 5v @ up to 200mA. This can be changed to 6v by using a 6v2 zener.







​

 

[MikeMl]

Roman's circuit is good. Just change the 5.6V Zener to a 6.8V one, and it should work at 6V output. Colin's suggestion in post 16 is likely based on the 34063 chip I referenced in post 14. I have bought those adapters at garage sales for $0.50, opened them up, changed one resistor to set the voltage to something different....

Did you read the 431 data sheet? Fig 21 is simple enough. I can help you adjust it to 13.7V (correct float voltage for a lead-acid battery)

 

[sparky1]

Great! Thank you guys.
I like Colin's cigarette lighter converter idea, a simple solution. I'll look for one of these first.
Otherwise I'll use the circuit provided or modified with the 6.8V Zener (however the pump also worked well with my 5V power supply.)
For the TL431 (fig 21) circuit: Am I supposed to use the component values in fig. 15 and 16? No values are shown in fig. 21.

 

[MikeMl]

Here is the battery charge regulator. With the trim pot set 45% up from the bottom, the voltage across the battery is clamped at 13.62V, which is a good float voltage at ~25deg C. The green trace is the battery voltage; the red trace is the power dissipation (7W) in the PNP power transistor, so it must be bolted to a good size heatsink (an aluminum project box, perhaps)