DC/DC convertor for the Grass...

[joegreen42]

I know this is off the subject of lights but I don't know where else there is such a deep well of DC/DC convertor knowledge on the net..

I have a Milwaukee 28v battery pack that I am using with my 18v Black and Decker Blower..

http://ecx.images-amazon.com/images/I/31QZVH973SL._SL500_AA280_.jpg


Under the 14.5 Amp load the 28v drops to ~25v. I added a 50w ¼ Ohm power resistor in series to get the voltage down to ~21.5 v.. WOW.. This supercharged Grass blower is almost as good as a gasoline powered blower..

However, Dumping ~70w into the power resistor is so distasteful..

Is there a off the shelf DC/DC convertor that will drop 28v to ~20v (I think the blower would be more happy)..

If there is nothing off the shelf how about any ideas on a MOSFET and a 555 timer circuit to do the job more efficiently?

Any thoughts would be greatly appreciated!!

 

[mdocod]

it can be built! I just don't know how:

http://webench.national.com/ss1/ss?...1V=20&O1I=20&op_TA=30&submit.x=62&submit.y=15

 

[joegreen42]

it can be built! I just don't know how:

http://webench.national.com/ss1/ss?...1V=20&O1I=20&op_TA=30&submit.x=62&submit.y=15

Very interesting...Seems like we are getting close. I already have a IRFS250 20Amp Mosfet from an old servo amplifier..
http://pdf1.alldatasheet.com/datasheet-pdf/view/53035/FAIRCHILD/IRFS250.html

But I also am at a loss for the fine details..

j

 

[joegreen42]

I have come across a Ryobi 18v Drill Speed Control… The P75NF Mosfet bolted to the heat sink is rated for 75v and 75 Amps. If the 36v(max) LM5642 Switching Regulator posted by Mdocod is any indication of what may be controlling the Ryobi Speed Control then can I assume that I can directly connect this to my 28v Milwaukee Power Pack?

Tonight is the night to test it.. Post your predictions on the outcome..

Will it work? Or will it Smoke?