Running a Cordless Electric Lawn Mower on an eBike Battery?
As many of you know, some time ago I experimentally bought a cordless electric mower. However the largest capacity battery it would accept held only 200 watt hours of energy. This was enough to get through just under half my lawn, including the strips of grass between the sidewalk and the street.
I wound up returning it because I felt for what I paid ($350) it ought to have been able to do the job on a single charge. There exist high end lithium cordless mowers like the Ego 56v that would do the entire lawn on one charge but they're also twice as expensive, between $600 and $700 depending where you buy and when.
This is when it occurred to me that the solution to my problems was under my nose the entire time. The problem? Electric mowers are sold by power tool companies, which make their money by gouging consumers on the proprietary battery packs that lock us into using their corresponding family of power tools.
The solution? Modify your tools (mower in this case) to use a type of battery pack that has already been driven down in price as cheap as it will go by the eBike market. The wattages that ebikes need are very similar to the wattages an electric lawn mower needs, and the voltages tend to be multiples of 12.
This is because ebikes were originally powered by lead acid batteries. To maintain compatibility after the market switched over to lithium, lithium battery packs for eBikes are generally made in voltages that are a multiple of 12: 24v, 36v, 48v, 72v, etc.
This makes cordless mowers and eBike batteries a perfect match. You can pick up a 36 volt cordless mower designed around lead acid batteries used on Craigslist for perhaps $100. Since lead acid batteries are huge and bulky, the mower will have an amply large battery bay you can fit quite a sizable eBike battery into.
Alternatively, depending what type of eBike battery you already own (or can afford) you could mount it externally by drilling a pair of holes into the mower exterior and attaching the battery mounting bracket with screws, as shown below:
This would make the battery easily removable for charging, and easily swapped between your eBike and your cordless mower. Total cost of the mower, battery, extra mounting bracket and correct adapters/plugs? About $500. That's $100-$200 less than a prebuilt, top of the line lithium cordless mower with one third the battery capacity.
I plan to do this myself when money permits. But for anybody rubbing their chin and thinking about putting this plan into action, just remember that the voltage of the battery must match the voltage the mower expects, and the battery should be able to supply the amps the mower expects as well. Really, the higher amps the battery pack can put out, the better (the mower will use only what it needs).
I wish this post was documenting the build process rather than just describing the intent. When I have money to spend on anything besides rent, utilities and food again you can look forward to a step by step build process documentation here on my blog.
Stay Cozy!
May I suggest if you are going to roll your own. Run with high density high discharge packs designed for the RC FLight industry. IF you ran 2 of these guys in Series you would have 48v with 10 amps capacity for $140
The down side is that with the 10 C rate it would only be able to discharge 100 Amps consistent with out damaging the cells. But the good news is that the thing was designed for a 1C lead acid battery :)
https://hobbyking.com/en_us/multistar-high-capacity-6s-10000mah-multi-rotor-lipo-pack.html
Very valuable tip, but the mowers I'm looking to convert are 36 volt.
I use 3 Cell packs for my 12v applications. Fully charged they are 12.6v (4.2v/Cell) discharged they are about 10.8 I tend to not discharge them below 3.4v/Cell. You could run 3 in series fo 36 Volt the only down side is that you would need to either remove all 3 packs to charge them or use a bunch of balance Chargers and just keep them all hooked up all the time on the balance port.
Most things set for DC have a operating range of voltage. IE automotive accessories are about 10-15v
I really like tinkering with Electricity. I currently replaced my gasoline chainsaw and trimmer for the 40V ryobi series. I was pleasantly surprised when the trimmer head used all my old 32cc gas accessories brush blade and pole saw. Best part is that I charge my batteries off my little off grid solar setup. 200w of panels to a 100 AH 12v battery bank with a 300w 110 inverter.
On the page you linked me it says each one is 22.2 volts though.
Likewise. It's like a silent, powerful butler or genie which can be put to any use. As Captain Nemo said:
The 6 cell packs have a 22.2v nominal charge. 2 would work for a 48v.
Each Cell is 3.6v Nominal with 4.2v fully charged. Think like regular ole alkaline batteries where an AA is 1.5v :)
I have no affiliation with Hobby King they are just a cheap place to get battery packs motors speed controllers and other tinkering gear.
https://hobbyking.com/en_us/batteries/lipo-batteries-all-brands.html
@alexbeyman,
Haha now you are moving it into cordless! Yeah that great and excellent article! I wonder you might try this, coz you are a type of battery man :D
Cheers~
Electricity is the greatest innovation of humankind. The ability to store large amounts of it and take it with you, then direct it to whatever purpose you wish turns a regular person into a wizard.
@alexbeyman,
Definitely I also thinking about having a battery current when power drops happens! Atleast power up few fans at home!
Cheers~
Yes this will indeed work as I have modified my electric lawn mower. I have used the lithium batteries used for RC flight at hobbyking and just link them in parallel or series to get proper Voltage or Amps you need. The lithium polymer battery packs are light but only last about 2 years and the power will start to degrade. I have had more success with the 18650 cell packs that are used in ebike batteries and corless tools. Lunacycle is a great place to get these packs or you can find similar on Aliexpress for cheaper but not guaranteed the same quality. The key thing is to use a connect that can handle the wattage draw from your motor. I recommend the XT-60 or XT-90 connectors Good luck with your conversion.
Cheers!
ian
Fascinating choice of topics on your blog. You've got yourself a new follower.
Ditto that.
It'll save you a good $250 bucks. Go for, we await the time you're ready to build
Thanks for your post.. it s very informative. I’m looking at the ‘Husqvarna BLi300 36v Battery 9.4Ah’ – which seems very nice for an ebike set up. It has a cheap wired charger too (along with a cradle-type option) – this would make it useful to buy two and use the socket from one as an ‘onboard’ connecter of the battery through to the motor.
The battery actually connects to the motor controller, which then connects to the motor. But otherwise that sounds good. The best deals on good quality lithium eBike batteries are found at lunacycle.com and em3ev.com if you ask me.
Great ..Thanks for the answer.
There's always a solution lying in your own house for you.
You'd have been a pretty good engineer
Except I hate math, haha.
You are awesome Alex.
Every time you come up with something that blows me.
I think your can do almost anything work electrical appliances.
A cordless mower... You're a strange species of humans. It would definitely not cross the mind of many to opt for cordless mower. I think this will also help you cut cost on electricity bills. I think next you might buy solar mower..lol
This is a great idea. You are right about the limiting factor on a lot of these cordless tools being the proprietary battery packs.
One of the things I like about battery powered mowers is theoretically they should be less hassle and require less maintenance then a conventional mower. It is just the battery limitations holding them back.
I like how much you really want to get this thing working for you. That's good because in the end electricity is better.