EcoRenovator - View Single Post - Reviving a free, dead 12V cordless Black & Decker mower

MetroMPG · 07-19-11, 01:30 PM

Battery murderer!

So, a few mysteries solved:

First, the motor pulls about 9-10 amps once up to speed - that's just spinning the blade (not cutting grass).

Second, and most suprising, the mower doesn't seem to have a low voltage cut-off!

I hooked up one of the 12 volt, 7.2 Ah batteries, and when I started the mower, it initially dragged it down to 4.8 volts, pulling ~20 amps!

Of course, as the blade speeds up over the course of 2-3 seconds and RPM stabilizes, current drops, and battery voltage rises. But the voltage only recovered to 9.5 volts @ ~10 amps, which is way too low to safely use a small lead acid battery (risk of cell reversal = battery murder).

Of course, with a larger pack powering the motor, voltage sag will be much less.

I'm trying to track down an owners manual. Maybe it'll shed some light on the subject of how owners were supposed to know when to shut it down for the health of the battery!

07-19-11, 01:30 PM	#39
MetroMPG Infrequent noob Join Date: Aug 2008 Location: 1000 Islands region, Ontario, Canada Posts: 402 Thanks: 37 Thanked 20 Times in 19 Posts	Battery murderer! So, a few mysteries solved: First, the motor pulls about 9-10 amps once up to speed - that's just spinning the blade (not cutting grass). Second, and most suprising, the mower doesn't seem to have a low voltage cut-off! I hooked up one of the 12 volt, 7.2 Ah batteries, and when I started the mower, it initially dragged it down to 4.8 volts, pulling ~20 amps! Of course, as the blade speeds up over the course of 2-3 seconds and RPM stabilizes, current drops, and battery voltage rises. But the voltage only recovered to 9.5 volts @ ~10 amps, which is way too low to safely use a small lead acid battery (risk of cell reversal = battery murder). Of course, with a larger pack powering the motor, voltage sag will be much less. I'm trying to track down an owners manual. Maybe it'll shed some light on the subject of how owners were supposed to know when to shut it down for the health of the battery! __________________ . To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.