'overclocking' a lawn mower
Not quite your usual 'EV' but I am trying to soup up my battery powered lawn mower. The long and short of it, can I run 36V or 48V through my 24V lawn mower with any reliability / safety?
I have done a bit of reading on the issues with excess heat dissipation and potential 'runaway conditions' but I still don't really understand when it is feasible to put more volts into a DC motor.
I believe the motor with no load (but a blade) spins at around 3200RPM. I'm curious to see if I can't increase that a bit. The other thing is, how would this affect the battery performance? I am using 12V 20ah SLA batteries, connected in series for the required voltage.
Hope this is not too much of a 'newbie' post... but ya know, I'm a newbie!
Just found this post... which is probably going to prove to answer this to some extent!
Your question has got me thinking. What would I like to tweak on my lawn mower? By increasing the top RPM I would start to worry about the physical mechanisms like the bearings not standing up to the extra stress. And what would this buy? A cleaner cut? Maybe. I think I'd rather up the amps to get more torque and keep the motor from bogging so much. This might lead to heat problems, though.
Is this by any chance a Black & Decker mower? Cause I have that same one :P.
I ripped out the motor, batteries, and charger, anyway.
The motor looks pretty hefty, but it's very rusty. I'd have to clean it off. Should be interesting on 36V or so though.
Chas: You can't really increase the amperage on a lawnmower. The batteries just run straight through a high-amperage switch to the motor. You can only up the voltage.
It's actually a Yardworks 19 inch... very similar electrical specs to the B&D, but I chose this one because of the metal deck.
I do wonder if it would even make it work better with increased RPM, I imagine it would if those blades were kept really sharp! I'm interested to hear about how your expiriment goes...
Hmm, generally motors can be run at higher power levels than their spec'd ratings. But you do of course run the risk of melting something or otherwise damaging the motor and you also have to consider the whole system such as the bearings DaveW mentioned. Controllers on the other hand are more difficult to run higher than their spec'd rating.
Increasing the voltage can and most likely will increase the current that will flow. Really, the advantage one would get from increasing the voltage is the effect of increased current flow in a direct drive system like this.
As always, do at your own risk because there's potential to fry something. But, that's what makes it so interesting.
The other thing is, how would this affect the battery performance? I am using 12V 20ah SLA batteries, connected in series for the required voltage.
Increasing the voltage to increase the current will reduce run time. I'd recommend trying it at 36v first, and checking how much the motor heats up.
The main risk would be blades saying "bye-bye" to the mower and whizzing through your yard.
Not much fun.
Yeah, I know. That's why I never actually tried it. The thought of a 1/2lb sharpened bullet flying across the yard was enough to discourage this.
Plus, after I replaced the old batteries with new ones and sharpened the blade, I don't really thin increasing the voltage would actually help enough to be noticeable.
Here is my take -
1. The more RPM you can generate at the blades the faster you can cut the grass. This is what they have done with the new zero turn radius mowers on the market today. They spin the blades faster so you can cut faster.
2. Adding voltage will also increase runtime NOT decrease!
24-volts @ 20 AH = 480 Watt Hours
36-volts @ 20 AH = 720 Watt Hours
More watt hours means more run time. When I modified my Merida from 24 to 36 volts the runtime or distance I could travel increased as well as the speed of the bike.
3. Heat in the motor and wires could be a problem. I know the Merida motor did run warmer @ 36-volts but what really got hot was the wires. I had to replace them with larger wires. I used 8 gage.
Grandpa Chas S.