LIon batteries

[Hans]

I want to use a Black & Decker 20V Max battery to power a small grinder I have, but I can't determine the maximum current the battery will produce reliably. The grinder DC motor is rated at 4 amps at 18 volts.  Can I safely pull 4 amps from the 20v Max battery?  

I haven't opened up the battery paack yet, but I'm sure it has 5 x 18650 cells inside. Those are rated for 3.6 Ah, but the battery pack is only 1.5 Ah. Why would the battery pack be rated so much lower than the individual cells?  18650 will do almost 4 amps, so 5 in series should be enough for occasional use of my grinder.

TIA

hans 

[fm2176]

I'm not sure if the battery will be adequate to power your grinder.  Is is a B&D 20v Max grinder, or are you planning to adapt the battery to fit it?

 

Regardless, that tiny 1.5Ah will provide only a miniscule amount of runtime.  If you can get your battery to work, you might want to look into eventually procuring a 4Ah or larger battery.  

[Hans]

I'm not concerned about run time. I'm trying to eliminate all the power cord wrangling that is more time consuming than actually working with the tool. My drill has adequate run time (for me) with that little battery, and I'm really surprised that the grinder has a higher power requirement than the drill. It's gonna be a lot harder to attach a bigger battery to the grinder too.

 

hans

 

[fm2176]

20 hours ago, Hans said:

I'm not concerned about run time. I'm trying to eliminate all the power cord wrangling that is more time consuming than actually working with the tool. My drill has adequate run time (for me) with that little battery, and I'm really surprised that the grinder has a higher power requirement than the drill. It's gonna be a lot harder to attach a bigger battery to the grinder too.

 

hans

 

 

I see, sorry I can't offer a more informed answer, but Ryobi offers a grinder kitted with a 1.5Ah battery, so I can't see why your battery shouldn't work for your grinder.  I can also vouch for the fact that my DeWalt 20v Max and Ridgid Gen5X grinders work with 2Ah batteries (the smallest I own for those platforms).

 

I fully understand your frustration with power cords, and I've gone cordless for nearly everything I own minus bench top tools.  The last time I used a corded tool was when I left my M18 batteries at home when replacing a floor.  I had my M18 Fuel circular saw ready to go (or so I thought), only to have to pull the blade off and use my father-in-law's old corded B&D.  I was cutting plywood length-wise and couldn't find a good extension cord, so it was a pain constantly readjusting the wood and saw/cord.

[Hans]

I went back to the innernets and found some data sheets for 18650 cells. I misinterpreted some earlier information about discharge rates. It turns out that the batteries used in power tools typically can discharge up to 10 amps, not the 1 X capacity I had thought. That's plenty for my tool, and it should last at least 20 minutes at a 4A discharge. I'll use it on a small grinder for sharpenenig ski edges. Twenty minutes is more than enough run time, and the small size doesn't change the weight or balance of the tool too much.

Thanks for everyone's interest.

 

hans

[fm2176]

That's good.  Cordless grinders are perfect for smaller, limited-use projects.  I think both of mine are 4-1/2", and they work perfect for my needs.  Glad that you were able to get the info!