Good to hear Darin. Have you tried it with the two batteries yet?

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!

http://ecorenovator.org/forum/attach...1&d=1311103228

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.

"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...

Wow, thats only 60W of power. Any chance you could get readings while cutting?

I'm going to try

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.

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 )

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.

Aha! Found some useful charging info from Black & Decker (haven't been able to find a manual online)...

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.

Interesting. Are you using a kill a watt to measure the power it takes to recharge?

Not yet (kill-a-watt).

---

Looks like I underestimated the time to cut the entire lawn. It's probably ~25 minutes, front, back & side. There's not going to be enough juice in this pair of 12 Ah batteries to do the job - they're only delivering about 14 minutes run time before voltage is flirting with the 10.5 mark and I shut things down to avoid battricide.

Need to add another battery!

So, what is the plan? Are you goign to try the 7Ah battery in parallel with the others? I think it should work. It should give you another 5-6 minutes to the run time.

5-6 additional minutes will still only put me in the "barely able to do ALL the cutting in one charge" territory.

I'll probably try it. :)

But since it's going to be pretty hard on the pack, I may just do half, recharge and do the remainder. Sort of how you're doing the lawn at your place with the e-riding mower.

If you haven't laughed at this project yet -- or at the "Mower #2" development part-way through it -- you will laugh at this:

Mower #3 ...

Yesterday I picked up another, free, identical M3300 battery-electric mower (same as Mower #1). Someone had advertised it for sale online, and I contacted him to ask if he happened to have the owners manual.

"No," he said, "but the mower's been for sale for a while now and nobody wants it, so you can have it, if you like."

This one also apparently has a cooked battery, and also possibly a dead charger (preliminary inspection). The mower itself works though - jumper cables to the car battery, a la Frankenstein, and it fired right up.

This gives me the option of going with free, used "15 minute" battery packs in both mowers, but still being able to cut all the grass in 25-30 minutes, by switching mowers half-way through. :D

Or, I have spare parts.

Either way, I will never need another lawnmower in my life.

Unfortunately, now I need a garden shed to store them all.

So, you're just going to live with the 15 minute run time? You're not gonna try to add another battery?

Oh, I'll probably try that too.

You're sick, man. I tell you: SICK!! :p

Does seem a bit excessive, eh?

Mission accomplished

So, trying one more new (used) battery arrangement means the mower now has enough juice to do the entire lawn (~20-25 mins).

I now have one 12 amp-hour battery (which seems to have about 2/3 of its rated capacity - delivered ~4 amps for 120 minutes in my inverter test) in parallel with a 7 amp-hour battery that has ~60% of its rated capacity).

http://ecorenovator.org/forum/attach...1&d=1311946054

They seem to work well together.

At this point, all that's left to do is to tape up a few connections, secure the batteries, and put the "hood" back on. I may lead a pair of wires through the hood so I can easily hook up a multimeter to monitor voltage and keep an eye on that battery pack.

It's safe to say this free mower is back in service with free used batteries (with some time invested testing their capacities). Alternatively, about $120 would have bought a new battery that would have had it back on the road (um, lawn) with little muss or fuss. (But where's the fun in that?!)

MISSION ACCOMPLISHED!

Great to hear it all worked out, and for free!

Need charger for M3300
 

Hello Metro MPG - have the same awesome mower....lost the charger and they don't make it anymore. Any ideas on where I can find one?

You could use any 12 volt rated "wall wart" style of charger that is rated to output about the same power - 1.7 amps in this case:

http://ecorenovator.org/forum/attach...2v-charger.jpg

This charger actually puts out about 20 volts, open circuit (not plugged in to any load) says my voltmeter.

You might even be able to use a standard car battery charger if it has a 2 amp "trickle" setting on it.

You would just need to get/make a male connector to fit the female one on the mower (and test to make sure you get the polarity right when wiring it).

FYI, you probably already know this, but it's very important for the health of the mower's battery (any lead acid battery, really) that you don't let it sit partially discharged.

If you do go with an aftermarket charger (thats what I would do), I'd highly suggest a Soneil charger. I have them on my battery electric riding mower and LOVE them. The price on a 2A charger is a very reasonable $38. I also bought my chargers from the vendor I've linked to and he was extremely helpful even when I had issues.

Make sure that any battery charger you get is designed for lead acid gel batteries as they do not like to be over charged, batteries like that are more and more common for motorcycles so that would be a place to start.

Good point.

The OEM charger for this mower is actually "dumb" - it will put out ~1.7A at ~20v until the cows come home.

However, voltage monitoring happens on the mower's circuit board: when it rises to whatever threshold it deems high enough, current is shunted to a finned resistive load/heat sink thinger to protect the battery.

So you should be good to get another cheap, dumb charger (if cheap and dumb suits you).

Ugh. The makers of the mower decided it was better to dump 30W all day and night long until you unplug the charger, rather than jack the price up a few dollars for a "smart" charger controller board. It's still better than a gas mower, but upgrading to a smart charger, or putting it on a timer, is low-hanging fruit.

Ugh is right.

In a manual I found for a similar one, they even say "it's OK to leave your mower plugged in all the time."

So, the mower's working fine. I've used it 3 or 4 times now.

The only thing it's missing is (1) I need to tidy up the battery pack connections (tape them); (2) secure the batteries better, and (3) reinstall the motor cover.

I also need (4) a way to permanently monitor battery voltage while cutting (necessary if you're using older batteries and you want to prolong their lives as much as you can).

So I just bought a 12/24v digital gauge that I'll mount on the mower ($6.28 US on eBay, with shipping). It's meant to plug into a car cigarette lighter socket, but I'll hack it & mount it on the cover, I think.

http://ecorenovator.org/forum/attach...1&d=1313176167

Measuring range: DC 8V-30V±%1.2

Oh, also Mower #2 (the 7A, AC one I picked up partway through this project) is also working fine, at the garage. I've used it 4 or 5 times, powered by the solar setup.

Ultimately I'd like to put up my spare 1A panel and use it to recharge this battery mower, so they're both grid-free & gas free.

OH! And an update on Mower #3 - the spare, identical M3300 battery mower I picked up "for parts"...

I fixed its charger - it was a short circuit (sloppy manufacturing) that blew the internal fuse.

Aside from "jump starting" the mower it to see if the switch/motor works (it does), I haven't stuck batteries in it to try mowing with it.

I have too many lawnmowers. I have backups for my backups.

Just need a goat to round out the fleet.

Did you ever get amp readings while cutting the grass?

No, I only did the "idle" test ... ~10 amps.

A lot will depend on the lawn conditions of course. Lately it's been hot & dry, so the grass cutting is very low load (slow growing, not very thick).

Found someone else trying to sell one of these:

8 year old battery "works great." Riiiiight.

Anyone who would buy that without doing some kind of capacity test on the battery is in for a rude surprise the first time they actually try to cut their lawn!

Thinking about this more, I seem to recall seeing 6-8 amps while cutting, while erroneously measuring current from only one of the 2 batteries.

So that would make it 12-16 amps in light-moderate use cutting.

Being watching this thread and have found it interesting as I have my own project on the go.
Question> do you have a source for amp meters in Ont. Canada?

For a point of reference I have 4 golf cart batteries, and a CTC 1750 watt inverter down in the laundry room that I sometimes use to run the washing machine with. I don't know how many amps the washer draws but I have done 3 loads of laundry back to back without recharging or any problems.
I mention this in response to your mower # 2 tests.

Hi Doug

I just used the 10A limited ammeter built in to my cheap digital multimeter.

Aside from that, if you want to measure higher current, you could possibly use one of the "clamp" style multimeters - I'm sure they have a higher rating than my DMM:

http://en.wikipedia.org/wiki/Current_clamp

Though they don't all measure DC current as well as AC (see the wiki article, link above).

http://viot.us/HVAC/images/3266D.jpg

Picked up multi meter at Princes Auto yesterday on sale for $18.83
Has 0 to 20amp DC, be nice to find one with 0 to 200amp on it.

You'll need a real ammeter and shunt to handle that kind of current. Thats what I have on my riding mower.

http://ecorenovator.org/forum/attach...91357537_o.jpg

My digital volt gauge arrived today. It works, but I haven't calibrated it against my digital multimeter (which is also not calibrated against anything, incidentally).

I think I'll install the gauge on the mower using a 12v socket & fuse I pulled from a junked car.

Then this "revival" project will be officially done.

I've been using the mower regularly, though haven't been monitoring battery voltage the last couple of times. It'll be nice to be able to monitor it to protect them from killer discharges.

Where did you get it from?