Electric Lawnmower Parts - Page 1
Forum section: electronics / beginners

author: electromateria
author_rank: Regular Contributor
timestamp: July 12, 2021, 04:22:19 am
content: Got a free electric lawnmower from a guy who was kindly giving it away on kijiji. He said: "the battery is dead and it can't be purchased anymore.. it's discontinued..."that sounds ridiculous, but I don't even know wtf's going on, I don't know anything cuz I'm a noobI tell him I want to build a modded scooter for my nephew. We had small chat and I left. It's confusing to me cuz he just gave away a lawnmower that's 95% new. The blade looks near mint condition without even a dent.Battery condition might be fixable, he says the battery wont charge but I think they're almost new and he just stored it on a discharge for 6 months. It has a decent little carrying case that shows battery level.It's a super lightweight lawnmower and the motor is surprisingly small. I don't know much about DC motors and can't find any specs or info on this specific one.If anyone could help with specs it I'd really appreciate that! Also any tips on what kind of a motor controller will work on it (if any) would help me out tons. There's a switch wired in that moves between "fast" and "silent" mode.

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 12, 2021, 05:22:52 am
content: Battery looks like a pair of 12v sealed lead acid batteries in series, if they won't take a charge they're probably toast. Lead-acid (big deep cycle storage batteries aside) is finicky like that, you use it or lose it and there's really no bringing one back short of shredding it and melting down the lead and plastic into a new one (which is what the battery factory does).

author: james_s
author_rank: Super Contributor
timestamp: July 12, 2021, 05:39:08 am
content: That's just a simple permanent magnet brushed motor powered by a couple of gel cells. Personally I'd remove that battery and replace it with a LiFePO4 or LiPo pack and mow some grass. If you want to build a scooter you're probably better off buying a motor paired with a controller specifically intended for the task.

author: electromateria
author_rank: Regular Contributor
timestamp: July 12, 2021, 06:12:15 am
content: Quote from: BrokenYugo on July 12, 2021, 05:22:52 amAny suggestions on a source for batteries? Ideally I'd like to wire them up myself so I learn how to do it properly. Let me know quantity I should get and the best type, etc. I only need maybe 20-30 mins of ride time on a scooter before charging.Quote from: james_s on July 12, 2021, 05:39:08 amI assume it's quite high torque but decent RPMs? What kind of speeds could it push a scooter? Does it need a custom gearbox?Promised my nephew we'd build a custom scooter togetherMowing grass with a 5lbs plastic lawnmower isn't all its cracked up to beI'll take a self-propelled toro gas mower personally. Those pictures you're seeing of the motor, battery, switch are the $350 CAD in cost to buy that thing new lol. The rest is light steel tubing, and a plastic shell.

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 12, 2021, 07:31:51 am
content: If it was directly driving the 14 inch blade I'd guess ~1HP, 2 tops, at around 5000 RPM, will probably smoke fast if stalled. Batteries in there will be 12V 5AH SLA, not sure beyond that, I guess the "high rate" type.

author: wraper
author_rank: Unknown
timestamp: July 12, 2021, 07:35:50 am
content: Quote from: electromateria on July 12, 2021, 06:12:15 amThey likely have original manufacturer markings. Take one out and post a photo of it's label so people can suggest a suitable replacement.EDIT: they are "1250" batteries (12V 5AH ). You can use this or something similarhttps://www.mouser.com/ProductDetail/CSB/HR1221WF2?qs=1yTzuHgnrjpeoBcqN6FjLg%3D%3D

author: Zero999
author_rank: Super Contributor
timestamp: July 12, 2021, 08:47:01 am
content: Quote from: electromateria on July 12, 2021, 06:12:15 amIf you take the batteries out of the case, you'll find they're standard sealed lead acid batteries, which are widely available.My advice is, replace the batteries, with new ones of the same chemistry, as close to the original capacity and physical dimensions, to make the mower as good as new and sell it, if you don't have a use for it. Replacing them with a different chemistry such as lithium ion would make it lighter and have more capacity, but would require a different charger and undervoltage protection, so it cuts off, rather than completely drainging the batteries.I wouldn't recommend trying to repurpose the motor for an electric scooter. It's more likely low torque, high RPM. You'll need suitable gearing to make it work, which isn't easy to do. Most electric scooters use hub motors, with the gearing built-in. This isn't beginner friendly project.

author: Gyro
author_rank: Super Contributor
timestamp: July 12, 2021, 08:59:41 am
content: Quote from: Zero999 on July 12, 2021, 08:47:01 amThis ties in (rather unfortunately) with the OP's other thread...https://www.eevblog.com/forum/beginners/bought-this-used-ebike-kit-for-$100/He already has a hub motor, but is already sadly lacking in useable batteries.Trying to use the lawnmower motor without a lot of gearing down (it is designed to spin a light weight blade at high speed), will probably result in it burning out before it can accelerate the scooter.

author: Zero999
author_rank: Super Contributor
timestamp: July 12, 2021, 12:54:38 pm
content: I Googled the part number, AEM40902104 and found this:https://www.aliexpress.com/i/32977222278.htmlhttps://imall.com/product/400W-12-24V-High-Power-Four-Carbon-Brush-DC-Motor-Torque-Spindle-For-Propeller-mower/Home-Improvement-Electrical-Equipments-Supplies-Motors-Parts/aliexpress.com/32977222278/144-18259803/enQuoteEven if you run it off 12V, you'll need gearing to reduce the speed. The current required will be far too high to turn the wheels at even 1800rpm. Suppose the wheels are 0.3m in diameter, giving a circumference of 0.3π = 0.942m. If the wheels turn at 1800rpm, that's 1696m per miniute, or 101.8km/h, which is impossible with a 400W motor and even if it was, it's dangerously fast, for such small wheels.If you run it off 12V, you need a reduction of at least 4:1, to give a top speed of 25km/h, which is as fast as a reasonably fit young man can sprint short distances, or cycle long distances. Perhaps a bicycle chain and gears could be used to provide the necessary reduction. A 11 tooth sprocket on the motor and 44 chainring to drive the wheel, would give a ratio of 4:1, but it might be physically too large and would require good fabrication skills to do safely. More than one stage might be required.The existing motor controller will be designed/configured for the blades, which don't require much starting torque. It will need a motor controller capable of limiting the start current to prevent wheelspin and overheating.

author: electromateria
author_rank: Regular Contributor
timestamp: July 12, 2021, 03:44:59 pm
content: Appreciate the help guys! Kind of shocking to me how that motor's so cheap.Zero999 - I forgot I have a timing chain kit like this (includes chain and sprockets along with a tensioner etc) -https://www.amazon.ca/ECCPP-Timing-Chain-Accord-Crosstour/dp/B06XKNHJDK/or I could pull parts off a bicycle like you mentioned. Thanks for explaining the gearing conversion!What's the difference between running the motor at 12v instead of 24v?For the motor controller are most of these good for my application or do I have to look out for something specific?https://www.banggood.com/search/24v-motor-controller-dc.htmlWould it be worth it to invest in lithium ion batteries instead of lead acid? If I'm gonna buy new batteries I'd probably prefer to get really powerful ones I can swap out and use across multiple projects. Is this kind of product good for undervoltage protection?https://www.aliexpress.com/item/1005001840031640.html

author: Zero999
author_rank: Super Contributor
timestamp: July 12, 2021, 07:06:21 pm
content: The speed is roughly proportional to the applied voltage, so running at a higher voltage, will make it go faster. An interesting thing to note is it works in both directions. If you were to set the voltage and gearing, so it does 25km/h, then go down a steep hill, it would still only go 25km/h, even if the hill was very steep. What would happen is the motor would start to act as a generator and charge the battery up, as the motor's open circuit voltage, would exceed that of the battery. A motor controller can do this deliberately, at lower speeds, to perform regenerative braking.If the listing is right, that the motor is rated to 400W, the maximum current will be 400/24 = 16.7A. Torque is proportional to the current and the amount of torque required, goes up with the cube of speed, if I remember rightly. This is because wind resistance increases, at higher speeds. Suppose you set your peddle bicycle so it travels 5m, for every turn of the crank. If you peddle at 60rpm, you'll go 5*60*60 = 18km/h, which is fairly easy for most people, even over a long distance. Now set the gearing so it goes 10m, for every crank. Most people will struggle to peddle at 60rpm, with that gear ratio, over a considerable distance: 36km/h is a racing pace, over a long distance. Perhaps if you're quite fit, you'll do it, but it's much more than twice as hard, as only going 18km/h.Another thing to bear in mind is the safety aspect. How good are the wheels, tyres and brakes? What's the maximum speed you trust them to perform safely, on a wet surface, or over gravel? How old is your nephew? If it's still a child, you'll probably want to restrict it to an even lower speed.

author: electromateria
author_rank: Regular Contributor
timestamp: July 12, 2021, 08:03:38 pm
content: Quote from: Zero999 on July 12, 2021, 07:06:21 pmVery interesting stuff, thanks!I'll be using small kids bike tires, breaks off that same bike, and I'll cap the speed (somehow - maybe only using 12v is a good option).

author: james_s
author_rank: Super Contributor
timestamp: July 12, 2021, 08:43:56 pm
content: Quote from: Zero999 on July 12, 2021, 08:47:01 amI have an electric mower that came with dead SLA batteries. I removed them and added a plug so I can connect a pair of LiPo packs I use for my RC airplanes. I didn't include any kind of low power shutoff, I just monitored the voltage for a few cycles and determined that a set of fully charged packs will mow my whole (small) lawn and be pretty close to a perfect storage charge when I finish. Low voltage alarms that plug into the balance port are cheap and readily available.

author: james_s
author_rank: Super Contributor
timestamp: July 12, 2021, 08:46:31 pm
content: Quote from: electromateria on July 12, 2021, 06:12:15 amYou could fix it up and sell it for a profit to someone who can use it. For those of us with small lawns a cordless electric mower is a godsend. I gave away my gas powered mower when I got my electric, I was spending more time messing with the stupid carburetor than I spend mowing. Unless I some day live somewhere with a big enough lawn to have a riding mower I'll never go back to gas powered. I replaced my string trimmer and blower with cordless electric too and I'd never go back.

author: Zero999
author_rank: Super Contributor
timestamp: July 13, 2021, 07:20:12 pm
content: Yes, it seems a bit of a waste to scrap an otherwise working lawnmower, for parts, when the batteries can easily be replaced. It would be better to repair, sell it and use the money to buy a more suitable motor for an electric scooter.I forgot to comment on the motor controller. Something which limits the current is essential. If it's just an open-loop PWM controller i.e. a 555 timer driving a MOSFET, it will blow up pretty quickly. We used a motor controller on a project at work a few years ago. I could ask a colleague for the part number, but it's probably way outside your price range. Anyway, you need a motor controller with a high enough performance level to stop the motor, when commanded to do so. Another option is to add a contactor to completely disconnect the motor, or driver, when either the brake is activated, or the accelerator completely released. Thinking again, perhaps disconnecting the motor altogether isn't such a good idea, as it won't give any additional braking. It could be disconnected from the driver and reconnected to a resistor, to provide additional braking, if the brake is activated sharply. You might also want a controller which can perform regenerative breaking, when the throttle is eased off.

author: electromateria
author_rank: Regular Contributor
timestamp: July 14, 2021, 04:04:52 am
content: Sorry I hate that lawmower and tomorrow is garbage day, there's no saving it from its fate nowI get the idea of wanting to use it for its intended purpose, but it's basically a childs toy lawnmower. The guy I got it from was cutting about 9 square feet of grass every 2 weeks. I can't in good conscience allow anyone to buy that lawmower, it has the crappiest plastic shell and runs off a $20 motor ---- it sold new for $350 CAD!!Green energy marketing wankcan you imagine the profit margin? Another concern is the average lifespan of that machine before it ends up in the dump. I generally love new technologies and green tech but this thing is a cash grab and not really environmentally friendly at all. /drunken rant

author: james_s
author_rank: Super Contributor
timestamp: July 14, 2021, 08:56:09 pm
content: What makes you think there's anything wrong with that? Plastic shell is great, it's light weight and it doesn't rust. The motor looks typical of a light duty electric mower. I wish it had been offered in my neighborhood because I would have grabbed it, it's a lot nicer than the mower I have, which is similar in design but about 20 years old. It's only ending up in the dump because you tore it apart and decided to throw it away instead of replacing the consumables, there's no inherent reason it couldn't have lasted longer. The price does seem high but whatever, the really nice cordless mowers cost even more. I'll probably buy the Makita when mine finally wears out, I have several of their other cordless tools. My lawn is small, about 150 square feet, typical of suburban neighborhoods in my area. That's what mowers like that are intended for.

author: electromateria
author_rank: Regular Contributor
timestamp: July 16, 2021, 04:37:27 am
content: new green mower sacrificed for partsthis one's sooooo much better. I'd consider it worth rebuilding but it's missing a charging cable, batteries, the case screws were rusted so I tore it off, damaging the case, etc.what u guys think of that motor? looks promising to me:globe 7045 tc3610148740vdc121112-u7aI couldn't find any info on it. 40VDC should mean it's better than the 24VDC from the other mower right?

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2021, 07:57:42 am
content: Quote from: electromateria on July 16, 2021, 04:37:27 amWhat makes you think a higher voltage means better? It has the advantage for being able to deliver the same power, with thinner cables, as I = P/V, but otherwise it makes no difference.

author: wraper
author_rank: Unknown
timestamp: July 16, 2021, 09:40:36 am
content: Quote from: electromateria on July 16, 2021, 04:37:27 amMore like another thing goes to dumpster

author: james_s
author_rank: Super Contributor
timestamp: July 16, 2021, 06:19:22 pm
content: You just keep tearing good stuff apart and turning easily repairable equipment into landfill, you seem totally clueless and are not listening to what anyone is saying. I'm done with this thread.

author: G7PSK
author_rank: Super Contributor
timestamp: July 19, 2021, 02:26:03 pm
content: Google for wheel chair golf buggy battery suppliers then go through the listings looking for 12 volt gel batteries of the same dimensions. Those batteries are just 12volt gell cells so should be easy enough to find.

author: jenniferkim
author_rank: Contributor
timestamp: July 19, 2021, 10:14:48 pm
content: From the looks of it, I don't think it could get on its feet again .... Btw why you are going through all this trouble, just for a toy

author: Zero999
author_rank: Super Contributor
timestamp: July 20, 2021, 07:29:15 am
content: Plenty of decent things go to landfill.Regarding why: my guess is the original poster is doing it for fun, but he's unlikely to sucede with this attitude.

author: jenniferkim
author_rank: Contributor
timestamp: July 22, 2021, 08:10:34 pm
content: Quote from: Zero999 on July 20, 2021, 07:29:15 amYeah, seems like he has already dropped the idea ....