convert 12v dc to 6v dc for 12amp blower

[Goatnutz]

I need to hookup a 4d batt. air pump 6v .5ohms 12amp 72watt to a boat batt 12v lead acid how do i dissipate that many watts.

 

[Goatnutz]

I guess this is either a hard question or a very easy one can someone tell me if it is hard or not.

 

[Chippie]

My guess is it is doable but deciding on the right or most appropriate technology...

Probably the cheapest way would be to use a 7806 voltage reg with external current boosting transistors mounted on a heatsink...

The most appropriate way would be to use a switched mode reg...like this....2-transistor Black Regulator

 

[Goatnutz]

Thanks i think i will try the Black Regulator

 

[marcbarker]

Here's a couple of ideas....

1. 2N3055 on a suitable sized heatsink. Collector=12V, Emitter=6V out Base=centre-tap of two 'turn signal' light bulbs connected in series across 12V input. When it's night time a bonus is you have a light to see by when the pump is running.

2. A headlight bulb in series with the motor.

 

[Goatnutz]

I tried the light bulb but it used up to much juice. For right now i am just using a separate 6v lantern batt. I was also thinking of using a nicad pak and just using the boat batt to charge it. Thanks for the help.

 

[marcbarker]

I tried the light bulb but it used up to much juice.

Can you tell us more about it "used up too much juice"?

If you mean it drained the boat battery, I guess the series light bulb trick had saved you the time and trouble of building a 6.000V high precision, fan-cooled, lightweight voltage regulator that would of drained the battery just about as fast!

 

[MikeMl]

The Black regulator is the right approach(ie SMPS) , but not the right circuit. Your 12A current requirement is way beyond Black's circuit.

Even if you have a 100% efficient SMPS, it will still draw 6A from the 12V input. If you are using a 6V battery, the amount of energy lost during charging the battery will far exceed what can be done with a 6V 12A SMPS running on 12V input.

 

[Goatnutz]

I looked into the Black regulator like Mike said not beefy enough. What i was trying to say about the bulb using to much juice is that when i hooked the 6v blower motor to a the 12v lead acid batt. with a 12v auto bulb in series the blower did not turn fast enough to do the task and about 25% as fast as when using 4 d cell batts.

 

[marcbarker]

with a 12v auto bulb in series the blower did not turn fast enough

Used a 55 W headlamp bulb ?

 

[Mr RB]

The Black regulator is the right approach(ie SMPS) , ...

Well I would argue that...

The "right approach" I think is just to PWM the pump's DC motor with (about) a 50:50 duty cycle. The huge inductance of the pump motor should do the trick, all he needs is a 555 timer, a mosfet, and a freewheeling diode across the motor terminals.

The solar magazines sell cheap kits and devices that do this, to power 12v water pumps from 12v system with energy savings because they PWM the voltage to the motor as many water pumps dont need a full 12v to operate. The same cheap kits would be ideal for this application.

 

[MikeMl]

There is also another consideration: What else is the boat battery running while the pump is running. If there are any audio devices (Stereo/CD/XM/IPOD) involved, then the PWM or SMPS current pulses can get into the audio and drive you knuts. Ask me how I know. If this is a consideration, then go with a linear regulator and waste some heat.