Tring to convert Black and decker 18 volt battery Grass Hogg to plug in--Help?

[crackersx5]

OK, want to convert my Black and decker 18 Volt battery Black and Decker Grass Hogg to run off house current.  Bought a 18 Volt 20 Amp DC power supply.  First measured the voltage of the battery, 19+volts, snapped it into a test tool B&D 18V GC818 Garden Cultivator) that uses the same battery pack and it ran fine.  Adjusted the power supply to 18.5 volts, hooked to GC818 and the motor would not run.  Motor started for a ½ second then stopped.  Adjusted output to 15.5 V and motor ran fine.  Snapped battery into Grass Hogg to test-ran fine.  Hooked leads of power supply at 15.v volt to Grass Hogg leads and motor started for a ½ second then stopped. Adjusted to max and minimum output and still get same result: motor started for a ½ second then stopped.  Any suggestions? Recommendations? Help?!

[alpher]

I don't have good answer to your question, but I wonder if for the price of 18V, 20A psu you couldn't just buy a decent gas trimmer?
Sometimes is best to just cut  your losses .

[james_s]

Have you measured the actual current that the motor draws? I have a 24V cordless lawnmower that can draw up to 40A, mine had dead SLA batteries so I modified it to use a series-parallel arrangement of the LiPo packs I use in my RC airplanes.

[JohnnyMalaria]

Are you sure you want to do that?

I've seen (okay, did it myself) a corded Grass Hog cause a lot of scary damage to the cord. I would assume the corded version is grounded in someway. Not sure how you'd modify the battery version to be safe around 120V.

I agree with alpher, looking at the PSU prices you could get a reasonable Stihl.

Anyhoo, I found this: http://www.instructables.com/id/Cordless-Power-Tool-Conversion-18VDC-to-120240VAC/

[james_s]

I've been using corded string trimmers for years and it's a pain, I've been keeping my eye out for an older cordless one I can convert to use LiPos. I can't imagine why one would want to go the other way, batteries are not particularly expensive and it saves dragging a cord around.

[Brumby]

I have an aversion to batteries for medium to high power applications.  Mostly because they can run out on you and waiting for a recharge is annoying.  The other part of it is that the battery gear I have used in the past hasn't been used that often and battery degradation increases the annoyance factor of my previous point.  Anything mains powered just keeps going for as long as I want.

That doesn't mean to say I think the adaptation of a unit designed for battery to mains is a brilliant move.  It's certainly possible, but where will this power supply be placed when in use and what cabling will be used?  A unit designed for mains won't have the voltage drop issues that a low voltage solution will.

Petrol powered units stink, are noisy and when you run out of fuel, it's a trip for more.


On the question as to why the unit behaves as it does, my first thought is that the unit is expecting battery power - which is very clean.  No transients, noise or hum.  It will likely have electronics that will manage the battery power and I suspect these electronics could be susceptible to the sort of "uncleanliness" you get from mains power supplies.  If this is the case, then some additional filtering may address this - but the question is "How much?".  There are a couple of other thoughts - but this is the first that comes to mind.

[james_s]

Well in my case batteries work out really well because my yard is small enough to mow in about 10 minutes. A set of LiPo packs that I can charge in ~15 minutes is more than enough to mow the whole thing. Obviously if you need longer run time then batteries may not be the way to go.