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

MetroMPG · 07-13-11, 08:37 PM

Capacity testing, part 1...

So far it looks like all the smaller 7.2 Ah batteries are probably duds.

I tested the "best" one first (the one with the starting/resting voltage of 13.1), using a 40 watt, 120 volt incandescant light on an inverter. It pulls 3.7A from the battery at the start (when batt voltage is high), but it goes as high as 4.15A as voltage falls close to 11.0. The inverter shuts off automatically when the battery gets below 11.0v. So let's call it a 4 amp load.

Note that different inverters vary on their shut off points. And some capacity tests go as low as 10.5 volts to evaluate a 12v battery - eg. How to Measure Capacity – Battery University

The "best" 7.2 Ah batt could only deliver 4 amps for 7 minutes before the inverter automatically shut off when the battery slid down to 11.0 volts.

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The 12 Amp hour batteries look more promising. I've been pulling 4 amps from one of the pair for 45 minutes now, and voltage is at 12.06 and falling reasonably slowly.

EDIT: pulled 4 amps for 53 minutes before the inverter shut things down @ 11.0v. Obviously voltage falls much faster at the end of the discharge - but you probably already knew that!

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It'll be interesting to see how the mower treats the batteries: what amperage the motor pulls under normal conditions, and at what voltage it shuts things down to protect the batteries (assuming it has an automatic shut off).

07-13-11, 08:37 PM	#32
MetroMPG Infrequent noob Join Date: Aug 2008 Location: 1000 Islands region, Ontario, Canada Posts: 402 Thanks: 37 Thanked 20 Times in 19 Posts	Capacity testing, part 1... So far it looks like all the smaller 7.2 Ah batteries are probably duds. I tested the "best" one first (the one with the starting/resting voltage of 13.1), using a 40 watt, 120 volt incandescant light on an inverter. It pulls 3.7A from the battery at the start (when batt voltage is high), but it goes as high as 4.15A as voltage falls close to 11.0. The inverter shuts off automatically when the battery gets below 11.0v. So let's call it a 4 amp load. Note that different inverters vary on their shut off points. And some capacity tests go as low as 10.5 volts to evaluate a 12v battery - eg. How to Measure Capacity – Battery University The "best" 7.2 Ah batt could only deliver 4 amps for 7 minutes before the inverter automatically shut off when the battery slid down to 11.0 volts. --- The 12 Amp hour batteries look more promising. I've been pulling 4 amps from one of the pair for 45 minutes now, and voltage is at 12.06 and falling reasonably slowly. EDIT: pulled 4 amps for 53 minutes before the inverter shut things down @ 11.0v. Obviously voltage falls much faster at the end of the discharge - but you probably already knew that! --- It'll be interesting to see how the mower treats the batteries: what amperage the motor pulls under normal conditions, and at what voltage it shuts things down to protect the batteries (assuming it has an automatic shut off). __________________ . 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.