I got mine from the local EV club guys who salvage parts from whatever they find. I would imagine you could find them on ebay quite easily. The one thing you must know is what mV drop the gauge is designed to use, and then you must get a matching shunt. Most are 50, 75, or 100mV drop shunts.

Here are a few auctions:

Ammeter:
Rectangle White Plastic Housing DC 0-200A Range Ammeter | eBay

Shunt:
Shunt Resistor for DC 200A 75mV Current Meter Ammeter | eBay

Ammeter and shunt with a digital display (nice because bumps throw the analog one all over the place).
200V 200A DC Digital Blue LED Amp Volt Meter Shunt NEW | eBay

Thanks I like the dual range unit.
1 meter for volts and amps, all you need, I think I'll buy 1 or 2.

Project finished.

Today I got the batteries snugged down & wedged in place, wire connections cleaned up (taped), the mower "hood" back on, and the digital voltage gauge installed.

Ran into a slight snag with the gauge: it's hard -- OK, practically impossible -- to read an LED gauge in direct outside light! Didn't consider that when I bought it.

So I couldn't mount it directly on the mower's motor cover, like I had been planning.

The workaround for the problem: I made a deep "visor" for it, from a black plastic bottle, by cutting the bottom out and cutting the neck open enough to mount (tape) the gauge inside at that end.

Looks like this now:

http://ecorenovator.org/forum/attach...1&d=1315096974

http://ecorenovator.org/forum/attach...1&d=1315096974

Oh - and the gauge is not very accurate! It reads .2 volts lower than my multimeter.

No real surprise there (cheap junk!).

It's not really a problem though, since it's pretty consistently .2v low across a range of voltages I tested.

Even so, with this gauge installed, the batteries should enjoy a longer life -- free of battricide! I won't be accidentally over-discharging them.

PS - the gauge can also be disconnected so it's not drawing power when the mower's not being used.

Good stuff, keep us posted with updates as to how the batteries are doing.

Will do! I plan to cut tomorrow, weather permitting.

Since I took on this mower project, I've also slightly reduced the amount of lawn needing to be cut, through a combination of creative landscaping and the acquisition of a back yard shed (to house said mower, among other things).

The reduced run time means the life of the mower's jury-rigged battery pack should be extended a little bit more.

Future plans for the yard are to reduce the amount of lawn even further. The best lawn is a minimal lawn, in my opinion!

The LED gauge works great.

25 minutes running time today to cut the whole lawn saw the voltage eventually at ~11.1 indicated (~11.3 actual) under load by the time I was finished.

(Though by the end, battery sag when starting up the motor was pretty bad @ ~9v, then quickly rising to ~11).

My neighbour asked me last week how much it cost in electricity to run the battery mower.

Answer: less than 5 cents for 3 uses.

~8 months/season * ~3 mows/month = ~24 mows/season, or $0.40/season

He said his gas mower uses ~1 litre of gasoline in 3 uses, or about $1.25

~8 months/season * ~3 mows/month = ~24 mows/season, or $10.00/season

EDIT: I did also remind him that batteries are "consumables" though, and if you're not getting them for free or cheap, you have to factor their replacement cost into the overall operating cost of an electric mower.

... then again, if you are getting them for free, and you get money back when you recycle them, you could possibly be in a net positive financial situation when it's all said and done! :D

Haha, a net profit off free batteries. I laughed.

I estimate I use about 5 kWh per mow on average since I don't always mow the entire yard when I mow. 5 * 24 = 120 kWh per season for mowing. I pay about $0.12 per kWh. That gives me about $14.40 a season. I'm guessing I'd be over $100 per season if I was using gas. Thats a pretty decent savings.

Post script:

Got a lead acid battery pack that just has enough capacity to do the job in warm weather?

Well it won't quite have enough juice to do it when it gets colder out.

Ask me how I know. :)

(Also, there are some leaves down, which take more power to mulch along with cutting the grass.)

So now I'm down to doing half the yard, recharging, then doing the other half later.

Hi There: What a neat site and your projects are after my own heart!

Anyway, I have this mower (or a similar one) and I absolutely love it. Mine was 'dead' because the orange safety 'key' was missing. It's been running 4 years on the same as-found battery. I power it entirely off 5W or 10W solar panels that amazingly are 'plug and play' once you get the right connector. I've detailed it on this wikisorta page:

solarpowermower.wikia.com

sorry for having to cheat the 'no url's thing for new posters. Boohoo!
and for making me wait 30 secs to repost!

Hi Wogga - welcome to the site.

I'm planning to solar charge the mower next year too.

And thanks for reminding me: I need to look after the battery this winter so it doesn't self-discharge and die.

End of season update, 1 year later:

Another year of happy electric mowing. (Well, I'm not exactly happy to be mowing, but you get the idea.)

The mower had less work to do this year than last, since I installed a driveway and did some landscaping that exposed a good amount of granite bedrock in the front yard. Which means: yay, less grass to cut! Also, we had a severe drought which caused the grass to go dormant for much of the summer.

The old battery pack is holding up: it's still enough to do my small-ish property on one charge if I hustle (~15-20 mins), or over 2 charges (over 2 days) if I take my sweet time (usually how I did it).

3rd season for the free, previously dead, 12v lawnmower has begun!

I've only used it 3 times so far this year, but I think one of the pair of batteries might be acting up. I've been seeing some wonky voltage readings when charging & running. Have to investigate further...

Looking for an update. How have things been going with the mower? Did you get the voltage issue sorted out?

It's been working just fine!

Fortunately, the wonky voltage issue turned out to be an instrumentation issue: intermittent flaky connection to the permanently attached voltmeter/display.

The mower has seen regular weekly service this year, unlike last summer when we had a serious drought that gave me a month or two break from mowing!

And I haven't done any more landscaping this year, but the plan for next year is to replace more lawn to give me & the mower even more time off. The less lawn, the better!

back in action... season #4
 

Just thought I'd post that the freebie mower has gone back into service ... beginning of its 4th season.

The batteries are getting tired for sure. I've only used it 3 times, and haven't been able to do both the front & back yards on a single charge. Though it's possible they may "wake up" a bit with a few cycles after sitting all winter with just an occasional top-up charge.

Doesn't bother me too much, really - I let it charge up and come back to it later.

I haven't shrunk the lawn area any further which would accommodate the declining battery capacity, though that's an ongoing goal (for other reasons). I'll probably do more of that later this summer.

Funny story:

A neighbour emailed me recently saying he was searching for battery replacement options for his Black & Decker mower and found this thread.

He ended up going with a new, OEM style replacement instead of messing around like I did.

How much did that set him back?

"$70.19 - $94.49" Canadian prices

Black & Decker M3300 replacement 12V Battery Batterybuyer.com

season 5!
 

Hard to believe this is the start of year #5.

I plugged the mower in several times over the winter to keep the batteries happy (or as happy as they can be at this advanced age) and sharpened the blade a couple of weeks ago.

And the freebie e-mower rides again! ... I mean "is pushed again!"

The batteries are now well past being able to do both the front & back yards on a single charge. Grass cutting is now a 2 day event with an overnight re-charge. Assuming they hold up for the rest of this summer, next year will need new batteries, a smaller lawn, faster pushing, a hybrid approach (a bit of manual reel mower usage mixed in), or some combination of the above.

Not too bad getting a few years out of it!

year #6!
 

The salvage mower runs again!

Hard to believe it's on its 6th season.

But it's definitely not happy this year. So far I've only mowed 3 times, and I'm sagging the voltage well below safe levels to get the job done in 2 cuttings (front... overnight recharge .... rear).

I've always used the guideline of not dragging a 12v battery below 10.5v under load to avoid battricide. But I'm seeing ~9.x volts this year if I want to get the job done. I expect that'll kill the batteries before too long. We'll see!

However, since I got the mower, a new source of cheap, used 12v batteries has shown up in town in the form of an electric bicycle & scooter shop. I may go see what he has available. He even offers a 30 day exchange if the used one he sells doesn't work.

Yet another free e-mower
 

Good news: since the weather warmed up and the growth has slowed down, it looks like the old batteries may just deliver another season of service!

---

The Mower Fleet Expands Yet Again!

Also, a neighbour gave me his old 24v mower, which just quit working.

"It's probably just the battery," I said.

"I checked the voltage, and it seemed OK," he said, "and my wife wanted the lawn cut an hour ago, so I just went and bought a new mower".

25 minutes of tinkering confirmed its battery is toast. I haven't decided if I'll fix it or just give it away to someone else, along with the diagnosis.

Update on my similar mower
 

Just to let anyone who cares know, I got just about 10 years from my similar B&D rechargeable 12v mower. In the end, the tenth year was a bit of a joke. My 6000 sq ft lot often needed two separate mows to get it all done.

In any case, 10 years for lead acid batteries isn't bad at all. I credit it to the constant trickle charge the battery got, the small size of the lot and a desulfator I bought on ebay and used over the years when the battery seemed tired.

I paid about $90 locally for a replacement battery. It was interesting to see yours said 28AH; mine was original, I think, and said 24 AH. It was replaced with same sized 26AH "Duracell".

In case I didn't say it before, the connector to charge the unit is the only tricky thing -- if you don't have an OEM B&D charger. Any old charger above 13V will work. I used, as mentioned earlier, 10W solar panels designed for a "12v" system, meaning they put out about 20 V open circuit. That's how I got the 10 years. I only used the OEM charger when I needed another mow within a few days ... and after the solar panel wiring got eaten away a year ago.

Carl

Year #7
 

Hi Carl - Thanks for the update on yours. I'm also surprised at how long the batteries are lasting.

I just started year #7 on my used batteries of unknown condition/age. Maybe the charger is particularly suited to not killing them?

Though the capacity is at minimum. I'm doing the small yard over the course of 2 days: front lawn, recharge, rear lawn, recharge. I will be pleasantly surprised if it will do even that for another year.

---

And update on the free 24v mower I mentioned a few posts back: I gave that one away. Too many projects!

Darin

I'm partial to using a few batteries as possible, so mine is a 12v. I think continuous trickle charge mixed with never bringing the battery below 50% capacity, preferably not down below 70% helps a lead acid battery. My solar 'array' of 2 5 watt panels stopped working last year, due to wire damage, so I hope to get a 15 watt replacement up and running again soon to get the free charge and trickle again. It helps to lubricate the motor bearings, keep the wheels set very high and sharpen the blade frequently in addition to the obvious things like not mowing wet or waiting until the grass is very very high to mow.

Funny thing is: I do everything that you mention that shouldn't be done.

I know I'm hard on these batteries. I watch voltage as I mow, and I try to keep from drawing them below 10.5v under load (on battery expert advice to prevent potentially reversing a weak cell), but I sometimes even exceed that.

About the only "nice" thing I do is make sure the batteries never sit discharged for any period of time after mowing, which prevents sulfation if memory serves. They go on the charger as soon as I'm done cutting the grass.

She's dead, Jim
 

I went to use the mower this week and when I checked the voltage before starting (my usual habit), it read only 9.x.

Hmm!

I always recharge the mower right after using it, so my first thought was that I must have forgotten last time. So I plugged it in and left it over night.

Next day: voltage reading topped out at just 12.1. I confirmed the charger output voltage was OK.

So, the batteries are toast. (Well, just one of them is. But in parallel, it was dragging down the good one with it.)

A local e-bike store has used 12Ah batteries for $20 apiece that will work, but considering I have a spare corded electric mower, that's the route I'm going to take from here on.

All good things must come to an end! R.I.P., Black & Decker M3300!

Yes, well if one is hard on a battery (use it below 50% often) it will die. If you've not been constantly trickle charging it (solar panel?) then that was hard on it also. You were doing something right if you got 7 years out of it - congratulations...

I would try a desulfator after a good slow charge to bring it up to 13 or 14. The desulfating takes a week or more to work sometimes. Also be sure to check that your mower connections are clean and tight, that your mower motor is oiled, blade is sharp (file works on removed blade just after you oiled the bearing by a few drops of the correct oil on the central shaft) and that your battery acid level is not low (if the battery cells can be accessed - not possible on AGM and some SLA units) If that doesn't work, you don't need a new mower...you just need a new single $50 battery. multiple batteries is always worse than a single one when replacing.

I just replaced my 29AH battery in my 12v Black and Decker mower. I got 10 years out of it. It was constantly trickle charged. It was used on a 6,000 sq ft property (grass area less of course - house is about 2000 sq ft 2 floor) for 10 years 1x a week. 10 years is rather good; the battery guy congratulated me. The battery was $90 in store vs $50 online.

I did get my solar panels working again (45 w this time, because I had a Harbor Freight kit lying around). The mower charges in a day or two and i can plug 12v devices into a port I made on the mower, so now there's 12v lighting in the garage!

New battery seems to be okay - I might try an online battery next time. The almost twice more money local battery doesn't seem anything super powerful - A Duracell 29AH from BatteriesPlus - $90 with coupon.

9 lives
 

Just a post-script, WELL after the fact...

I put the mower & charger at the curb on our little city's "treasure hunt" garbage day with a sign on it saying "works, but needs new battery".

It was gone within an hour.

So for all we know, someone has resurrected it, and it's living its 3rd or 4th life! Meow.

Necro bump. But, having your experience, would you recommend a battery powered mower over a gas powered mower?

I don't have direct experience but I've used a corded Black and Decker electric mower that I got for about $20 with a bad top bearing that caused the rotor to grind into the permanent magnet and tore apart the magnet a bit and jammed it into the rotor. I fished out all of the broken chunks of magnet and replaced the top bearing with a random grease type ball bearing on the top. I didn't expect it to work and the bearing was very draggy but it worked. I used it for two years consistently until I got a gas mower from my mom's house.

I love that it can grind through grass twice as high as my "6.5 horsepower" 21" lawn mower and I can actually get the mowing done on tall grass 10 minutes faster than the gas mower because I can walk as fast as I want because it won't stall out or even really slow down like a gas engine does.

With the experience I've had of using the corded model, I've always wanted a cordless one but I just couldn't justify replacing a working gas mower with one in the $200-650 range. It's getting mighty enticing though because the newest cordless mowers have 21" mower decks instead of the 18" mower decks, they have self-propelled and mulching functions and advertise being able to cut a 1/3 acre of grass. So basically now the cordless mowers are now a non-compromise option with all of the standard features you'd expect in a mower. I suppose I've always wondered how much juice my 1/4 acre lot uses. I know some market themselves as coming with a battery and having a caddy so you can swap in a second battery but don't come with that second battery, which makes me wonder if I need a second battery or not and I don't see the guidance on either runtime or average cut sq footage on a charge. If I get 75% done with the yard and need to plug in for an hour to do the rest, it wouldn't be worth it if it means I'm shelling out for a bigger battery, but I don't know what to expect.

I wouldn't touch a lead-acid one though unless I had a NiMh or lithium retrofit project planned for it, I'm sure I'll do what I normally do and wait to find a used lithium one on Craigslist from someone with a bigger yard than mine and ask about the battery performance.

Like so many things, it depends.


I've owned many types of mowers: manual, gas, battery & corded electric. (All at the same time!)



I prefer the relative quiet & better reliability of the electric mowers. They're also lighter and easier to use.



Pure economics probably favours gas mowers, at least comparing to the old lead-acid-powered mowers I had. The much more durable lithium batteries you can get today may have tipped the total cost of ownership balance though. Environmental impact probably favours electrics.


My gas mower is far more powerful than my electrics, though. You can let the grass grow longer between cuts, so it's arguably more convenient that way.


Currently I use a gas mower on one larger lot and a corded electric (and sometimes the manual reel mower) on 2 smaller lots that I look after.