Powering 80V lawnmower with non-stock battery

[Firedog]

I use Makita 18V (5s) batteries to power any brand tool, ebikes and anything else needing DC power. I've replaced a heavy old gas motor on a high end front throw reel lawnmower with early Currie brushed motor (free) and it's a perfect close cut machine for bermuda. I have tons of experience building and repairing ebikes and etandems, their motors and controllers.

I have a need for a sturdy rotary mower to control weeds at a rental with a large lot. Harbor Freight has a decent looking 80V (20s) Atlas brand machine; cheap. I'd planned to power it with 4x18V Makita's in series (20s) since I have many. A simple 2 wire 81V connection, 4 Makita's in series starts the mower fine, but cuts off after a few second burst. The troubleshoot page says the motor will cut off if overheated so I assume both battery and motor are protected.

Makita 18V tools connect to only 2 pins on the battery (+18V, ground). The Atlas battery is dual voltage (40/80V) and has 7 pins slots. The 2 outside are 80V/ground and connect to the controller, the next 2 toward center are 40V/ground and not connected, the next 2 slots have no pins. The center pin is connected to the controller and I assume monitors battery temp via a thermistor.

I don't have a Atlas 80/40v battery so I can't open to verify the center pin's function. Makita's battery thermistors are ~24k ohms at 70F. Another brand I have is ~11K ohms at 70F. I substituted a 50K ohm variable resistor and tested about 25 different resistance settings. The results were always the same; start then off.

Any suggestions to make this mower work with a non proprietary battery? Or other test to try? I could buy an Atlas battery to return after looking inside, but that doesn't seem exactly fair. I could probably also run the motor using a ebike controller but an expensive Makita mower is probably a better choice.

BTW, the Atlas Brushless 80V brushless motor is wired just like most ebike motors. 3 phase wires and 5 wires to the 3 hall sensors. The controller is fairly standard with 3 throttle input wires and 2 other wires I assume to the start switch. It has bays for two 80V 4ah batteries which are automatically switched via 2 relays. Both batteries are never used together and the manual notes there is a brief delay during the switch.

 

[fechter]

Seems like it's looking for a signal and isn't getting it. Could be something as simple as a battery thermistor or it could be a serial data string which would be harder to hack. An ebike or RC controller would be pretty straightforward and not too expensive.
You could try spoofing the thermistor with a 10k resistor from the T terminal to negative.

 

[AussieRider]

If the mower is advertised as 80v nominal, the battery would not be 20s, which are usually refered to as 72v nominal but read 80v fully charged. The controller may be hitting LVC. Fechter's solution of using an ebike controller (72v) would be the easiest especially if you have one lying around from a repair job.

AissieRider

 

[eee291]

If the mower is advertised as 80v nominal, the battery would not be 20s, which are usually refered to as 72v nominal but read 80v fully charged. The controller may be hitting LVC. Fechter's solution of using an ebike controller (72v) would be the easiest especially if you have one lying around from a repair job.

AissieRider

Power tool voltages do not follow the voltage nominal standard. They are always marked with the close to fully charged voltage like 20v for 5s and 40v for 10s.

 

[Firedog]

Power tool voltages do not follow the voltage nominal standard. They are always marked with the close to fully charged voltage like 20v for 5s and 40v for 10s. eee291

Makita sold the first Li-ion tools in 2005 and followed battery tradition of labeling batteries with working voltage. So 3.7 x 5s = 18V. The others that followed did the same until Dewalt decided to label 5s as 20V. Great for marketing since who wouldn't rather have 20V over 18V for the same cost. Now all newbies (including Makita's 40V with 21700 cells) label battery voltage as 4V/cell. The FTC should have had standards but now it's too late.

Seems like it's looking for a signal and isn't getting it. fechter

I tried 10K resistor and dozens of other values using a 0 to 50K pot; no luck. I think battery is sending a simple ID data string to the controller used to prevent use non OEM batteries.

I will test a 36/48V 17A controller with learning on the motor with 3x18vMakitas (54V) to see if the rpm and torque are sufficient. The OEM controller has the feature of increasing power if the mower slows due to thick grass. I'll report back.

With so many garden and other high demand battery garden tools now available it makes sense to be able to use ebike batteries we already own on those tools. After all, ya can't ride and mow at the same time. (although I suspect amberwolf probably could)

 

[eee291]

My brother has a push mower where he also needed more capacity.
I tied a 36V30Ah battery into the original one with 2 wires, the large battery has its own BMS, has been working for 3 years now.
Maybe you'll have to do something similar.

 

[AussieRider]

"Power tool voltages do not follow the voltage nominal standard. They are always marked with the close to fully charged voltage like 20v for 5s and 40v for 10s."

Ah, I did not know that, thanks for sharing the knowledge mate.
That's what we're all here for innit.

AussieRider
(I don't know how to do quotes properly)

 

[Firedog]

So... no success substituting 4 18V Makita directly. I still think the center pin of the battery is probably providing a specified resistance I haven't found. Anyone who owns an Atlas 80/40v battery, please measure the resistance between the center pin and ground and report along with a rough temperature of the battery.

I did go ahead and power the mower with 3, 9ah 18V Makitas (54 to 60V) using a 36/48V 17amp max cheap learning controller with a
5K pot instead of a spring throttle. It's great.... I cut a clean path 20" through 12" wet oat grass as fast as I could walk, no stalling.
If anyone is interested, I'll post the build details and pictures. BTW don't assume any thing is conventional. For example, the red wire in the Hall sensor ribbon cable isn't the 5V wire.

FYI the mower was $150 with coupon.
If I had to buy batteries, each cost $230 for 80V4ah; 2 recommended. Rapid charger $85. Totaling almost $600 with tax.
A simple modification allows the use of batteries we already own for less than $40.

 

[fechter]

Nice!
Not sure how the handle looks on that one but you might be able to use a thumb throttle for a bike.

 

[amberwolf]

or cable operated throttle uisng whatever cable it has for the safety bail lever, if any.

assuming that full speed isn't needed all the time...if it is then using a pot to set the speed and the ebrake switch to turn it on and off would probably work best.

 

[Firedog]

I finished the conversion of the new Atlas 80V push mower to operate on 3 18V Makita mount batteries. I mowed over a half acre of weeds with 40% of my 9ah battery capacity remaining. I'm very happy with the results.

Since I could not get the stock controller to recognize a non-Atlas battery, I substituted a cheap ebike controller that I that works well to 60V. I kept all the safety features so the motor won't run unless the handle bail is held down and won't run if the handle is folded. I'm sure the blade rpm with a 15s battery is less than the stock 20s but it cuts clean and the battery life is much more than I expected.

Before and after pic.

 

[eee291]

That mower looks exactly the same as the one I did for my brother, just different brand name. If found that a greenworks battery fits from AliExpress.
€ 48,41 Dixsg Li-ion Rechargeable Battery 40V 6000mAh for GreenWorks 29462 29472 29282 G-MAX GMAX Lawn Mower Power Tools Battery
https://a.aliexpress.com/_mOkub5g

 

[Firedog]

a greenworks battery fits from AliExpress.
€ 48,41 Dixsg Li-ion Rechargeable Battery 40V 6000mAh ee291

Did you test and measure 40V 6Ah? 20 18650 (10S x 2P) cells just fit that batteries dimensions. Quality 3.0-3.4AH 10A max cells do exist but are very expensive. "Not genuine" tool batteries never deliver the capacity (AH) promised. I tried and tested dozens and 60% of promised is the best I've found. "Genuine" tool batteries are always honest 'cause the manufacture can be sued. Ebike batteries are usually honest since many ebike displays report AH used. With tool batteries, very few have a way to test and are happy stick the battery back on the charger after drilling a few holes. Tons of $ is made by builders, sellers, Amazon, Aliexpress and Ebay and none of those will ever want changes made.

There is so much $ in the fraud, if you write the seller with your test results, they will offer a big discount which will become a full refund if you say no.

 

[eee291]

I do remember my brother mentioning that it had about 1/3 less runtime than the original one.
Didn't matter in the end, because we wired the large battery in parallel.

 

[skeetab5780]

Mower looks way cooler now too! Nicely done sir

Is it me or does this motor look exactly like a hub motor? I see Lawnmower bike conversions in the future!

 

[Firedog]

The motor isn't much like a hubmotor other than being brushless with hall timing sensors and a shaft with a flat on one side. The Al cover is from my scrap bin and came from an early Heinzman brushed motor used on EV Global Lead Acid battery ebikes. It happened to be the right size to keep the motor clean and dry. BTW I get no heat from the motor, batteries or the controller running full throttle continuously.

A direct drive ebike hub motor would be a simple matter to mount to any old mower deck. Mating a blade to the hub motor's axle with it's flats would be simple. I have several working hub motors I replaced because the builder forgot to install torque arms and ripped one side of the axle round; otherside still good.

 

[eee291]

A good cutting speed is something like 200 mph at the tip of the blade, you're not going to get that with a hub motor.
Inrunners with 2-4k rpm are way more suited for mowing.

 

[Firedog]

A good cutting speed is something like 200 mph at the tip of the blade, you're not going to get that with a hub motor.
Inrunners with 2-4k rpm are way more suited for mowing.

Thanks.....I didn't consider that.

 

[Firedog]

A good cutting speed is something like 200 mph at the tip of the blade, you're not going to get that with a hub motor.
Inrunners with 2-4k rpm are way more suited for mowing.

Thanks.....I didn't consider that.

 

[skeetab5780]

Lol it obviously looked like a hub motor to me because he did actually used a Heinzman hub motor cover on the darn lawnmower... :lol:

 

[eee291]

I took some pictures of my brothers lawnmower.
For some reason it started overheating recently so he took it apart and zip tied a heatsink onto it


Not the most beautiful thing, I had no part in this :lol:

 

[Firedog]

https://endless-sphere.com/forums/viewtopic.php?f=14&t=68750

Thread started in 2015 about Echo 58V (14s) batteries for ebike use and attempts to power Echo equipment on ebike batteries.

Didn't matter in the end, because we wired the large battery in parallel. eee291

Good idea that would work. Use the smallest 2ah (cheapest) 80V Atlas battery (20s) to mount in the stock battery craddle and connect a larger 72V (20s) ebike battery in parallel directly to the Atlas cell stack. The small Atlas battery would provide the necessary signal to the controller to keep the motor running with lots of AH from the ebike battery for big mowing jobs.

 

[calab]

Interesting method.

You'd have to match the voltages pretty close before connecting the batteries, how close would the capacity (ah) have to be because that would only be a connecting in series issue. Just saying connecting 12v 8ah in series with 4v 1ah would be 16v but wouldnt the 4v drain empty way quicker kicking the bms in to its lower limit way sooner - this is series not parallel. Your connecting in parallel, so voltages must match within 0.10v, but your fooling the electronics. Electronic surgery as they say, like what they do to replace cells inside those sensitive drill battery packs. That ones that brick themselves on purpose when out of spec or too much out of balance, even taking a cell out of a pack will brick some tool batteries.

 

[bigshake]

I finished the conversion of the new Atlas 80V push mower to operate on 3 18V Makita mount batteries. I mowed over a half acre of weeds with 40% of my 9ah battery capacity remaining. I'm very happy with the results.

Since I could not get the stock controller to recognize a non-Atlas battery, I substituted a cheap ebike controller that I that works well to 60V. I kept all the safety features so the motor won't run unless the handle bail is held down and won't run if the handle is folded. I'm sure the blade rpm with a 15s battery is less than the stock 20s but it cuts clean and the battery life is much more than I expected.

Before and after pic.

I know this thread is old but I was wondering if you could tell me the controller you used or recommend a good controller for 20-22 amp max.

 

[csvendsen]

@Firedog is there any chance you be interested in selling the motor controller that came with the mower. Mine has died and could use the controller to get back up and running.

Or if can tell us what controller you did use for the build could look into using that too.