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Old 07-19-11, 03:10 PM   #41
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Good to hear Darin. Have you tried it with the two batteries yet?

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Old 07-19-11, 03:21 PM   #42
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Ask and ye shall receive...

I trimmed off the plastic standoffs that held the slightly narrower 28 Ah OEM battery in place, and the pair of 12 Ah ones fit in perfectly, not a millimeter to spare!



That makes me wonder if the mower may have been originally designed to possibly take two 12 Ah batteries.

Haven't fired it up yet, though. Next I need to make up some wire connectors to hook everything together.
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Old 07-20-11, 11:22 AM   #43
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"Idle test" - 2 x 12 Ah ...

Once the motor RPM stabilizes, it's only pulling 4.8 amps @ 12.3 volts from the pack of 2 x 12 Ah batteries. That's good enough!

Edit: CORRECTION - I was only measuring current off one battery. So it's more like 9.6 amps for the pair.


Time for a mowing test! I just have to solder a couple of the conectors I made first.

Not today though - stinking hot out. Maybe tomorrow morning before things get too toasty...
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Old 07-20-11, 11:40 AM   #44
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Wow, thats only 60W of power. Any chance you could get readings while cutting?
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Old 07-20-11, 11:45 AM   #45
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I'm going to try
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Old 07-20-11, 12:17 PM   #46
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Any chance you could get a picture of the blades on that thing? I'm curious as to how it idles at such low power.
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Old 07-20-11, 04:55 PM   #47
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Oops!

Current draw is not as low as I reported before. I was only measuring from one of the 2 batteries, so you have to double it for accurate numbers: 9.6 amps, not 4.8. (I edited the previous post.)

Also, looks like the mower is at least 13 years old, since it was built at the local Black and Decker plant which closed in 1998 (source: Stephen Covey, 55 - Brockville Recorder and Times - Ontario, CA )
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Old 07-20-11, 06:16 PM   #48
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Mowing test: success!

14 minutes mowing time without drawing the pack voltage below 10.5 - that's enough to do 75% of the lawn (100% of the big section), of moderate length & dampness.

This was fresh off the charger, but I don't believe the pack was fully charged. At least the LED indicators hadn't changed in all the time it was plugged in (both red & green showing - I'd expect the red to go out when it's fully charged, but I don't know this for sure).

The pack voltage was 14.0 when I unplugged it and gave it a try. So it must have been pretty darned close to full.
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Old 07-20-11, 10:08 PM   #49
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Aha! Found some useful charging info from Black & Decker (haven't been able to find a manual online)...

Quote:
Our cordless lawn mowers use a two stage charging process. The first stage of charging takes about 3 hours (depending on depth of discharge) and will recharge the battery to about 75% of its full capacity. The second stage of the charging process will charge the battery to its full capacity. Approximate times to reach full charge from a fully depleted battery are listed below:

12 Volt models: 18 hours
24 Volt models: 24 hours

In order to maintain optimum battery life and run-time, please fully charge your lawn mower’s battery after each use. (Source: Charging time for a cordless lawn mower)
That fits with what I saw today.

The charger itself is "dumb" - it just puts out a constant 1.7 amps. But the circuit board in the mower itself shunts charging current into a finned heat sink, presumably once battery voltage rises above a set point ("75% of full capacity"), so as not to cook the battery during the final 25%. Not a very efficient use of charging power.

So around lunch time tomorrow, it should be fully charged. Well, sooner than that since this "replacement" pack is smaller than OEM, plus the actual capacity is lower because the batteries are roughly 2/3 worn out.
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Old 07-20-11, 11:03 PM   #50
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Interesting. Are you using a kill a watt to measure the power it takes to recharge?

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