Electric ride on lawn mower conversion

Post by **Mowerman** » Thu, 28 Jan 2010, 18:38

Hello everyone this is my first post and I am a complete beginner with electric conversions but have a basic understanding so please bear with me.
I would like to convert my twin blade 42 inch cut yardman to electric.
I need 2 hours running time and the motor can run at a constant speed for the blades as drive speed adjustment is via pulleys.
The current petrol motor is a 17hp v twin which is more than I need.

What would you suggest for this conversion as far as motor. battery pack, controllers etc?

I would like to do this conversion as economically as possible.

I look foward to any suggestions and thank you in advance.

Post by **Richo** » Thu, 28 Jan 2010, 19:32

The 30-40kWh battery pack will be the killer...

Post by **Richo** » Thu, 28 Jan 2010, 19:33

Ooops where's my manners

Welcome to AEVA mowerman

The battery cost will pretty much decide if you want to do the project.
Assuming you could fit that much on a ride on mower

Post by **Tritium_James** » Thu, 28 Jan 2010, 19:37

Yes, not really feasible, unless you're going to run it with a long extension lead.

17hp = about 13kW. Say controller/inverter efficiency = 90%, so 13kW / 0.9 = 14.5kW. You want to run it for two hours, so you need 14.5kW * 2 in battery capacity = 29kWh. For a lithium pack, you only want to run them to 80% discharge or so, so you need 29kWh / 0.8 = 36kWh. This pack will weigh about 300kg and cost around $20000. Probably a bit much for a mower!

Post by **Richo** » Thu, 28 Jan 2010, 19:38

Motorwise maybe an Etek (RT)

Post by **Mowerman** » Thu, 28 Jan 2010, 19:52

Oh Dear!
$20000 for Battery pack! 300kg! and here I was dreaming maybe 4 truck batteries might do the job!
Oh well, thanks for the replies guys, better get back to my ECO DREAMS

Post by **Richo** » Thu, 28 Jan 2010, 20:11

Smaller changable power packs would help with the weight
But you'd have to stop every 30min or so to swap packs.

Would be interesting for the running cost comparison between petrol tho.

But as pointed out very expensive for a mower.

Post by **woody** » Thu, 28 Jan 2010, 22:39

Woah, hang on - 17hp is peak.

An old rough calc was l/100km * 20 = Wh/km.

10 litres / 100 km = 200 Wh / km = 20kWh / 100km

10 litres = 20 kWh
1 litre = 2 kWh.

So - you need approx 2 kWh for each litre of fuel you use.

So how much fuel do you use?

Post by **Mowerman** » Thu, 28 Jan 2010, 23:41

The actual motor is a kohler SV710 peak 20hp(14.9kw) @ 3600rpm v twin
but a lot of ride on mowers are only 15hp(11.2kw)@ 3600rpm single cylinder with max peak torque of 36 N-n @ 2200rpm which is fine for existing lawns.
I bought the 20hp because I had some rough bush that I had to mow into a lawn
My 20hp uses about 1.5 to 2 litres of fuel per hour but the 15hp maybe 1.3 to 1.5 litres per hour.

Does this help any?

Post by **Tritium_James** » Fri, 29 Jan 2010, 00:11

Yes, that helps heaps. I thought that sort of thing usually ran flat out the whole time...

Woody's numbers are in the ballpark, so if you say 2 litres per hour, 4 litres for a session. 4 litres is *about* equal to 8kWh required capacity. You probably still want to take into account not flattening them completely every time, so 8kWh/0.8 = 10kWh. So almost a quarter of the worst-case estimate I had above, ie $5000 and about 75kg.

You really need to consider if you need it to run for 2 hours in a stretch.

You're still a long way from truck batteries though. Very rough numbers you might be looking at 100Ah at 24V for a big truck battery, which is 2.4kWh. But lead-acid batteries can't be deep cycled if you want them to last, so you're probably going to get half of this amount, ie 1.2kWh per big truck battery. So for your 10kWh required, you'll need 8 to 9 batteries. That's going to be several hundred kg.

Post by **Richo** » Fri, 29 Jan 2010, 00:44

woody wrote: Woah, hang on - 17hp is peak.

Good to see some1 is on the ball

Post by **EClubman** » Fri, 29 Jan 2010, 00:57

Another thing to consider is to not use the gearbox and pulleys from the ICE setup.

Much more efficient to have two small motors direct driving the blades and another larger motor (with speed control) driving the wheels.

Sounds like you have a decent sized property.
Keep the petrol mower, get a used mower (with stuffed engine) to convert to electric. Let it be an experiment that, if it doesn't work out the way you expected, won't stop the lawn from getting mown.

Work out how big the motors need to be, how much battery you need, how you are going to attach it all on the experimental jobbie.

Once you have built and run and broken and fixed and ended up mowing your lawn on electric power, then you can decide if you want to electrify the "good" mower.

Post by **Gow864** » Fri, 29 Jan 2010, 02:09

17hp is the ICE power?!?! If he uses a etek motor, that's only 5-7kw cont, 15 peak. he's already said "17hp is more than i need".

Mowerman here is one from evalbum riding mower this guy gets a hours mowing with 4 lead acid batteries.

Gow.

Post by **Tritium_James** » Fri, 29 Jan 2010, 04:03

Gow, that one you've linked is practically a toy

A 42" yardman is a 250kg monster, an etek motor isn't going to cut it (sorry bad pun).

Post by **Richo** » Fri, 29 Jan 2010, 07:05

So use the Etek RT.
8hp cont 19hp peak.

Post by **Richo** » Fri, 29 Jan 2010, 07:07

Oh I already mentioned that back HERE

Post by **Gow864** » Fri, 29 Jan 2010, 12:13

A 42inch yardman, take out the motor and you've got a lot less than 250kg of plastic and tin, it's not a greenfield.

point is, the guy asks for help, and within 3 posts he's been told he needs a $20,000, 300kg battery pack, for a ride on mower????

My greenfield (it's a rideon, and Australian one made from steel) powered with a mars electric motor and lead acid batteries (6 X 18ah) gives about 20 mins mowing and 40 mins as a go cart.

Nothing beats practical experience you guys should get some.

Post by **Tritium_James** » Fri, 29 Jan 2010, 14:21

Now while I'll admit I don't have an electric ride-on, there's a pretty big difference between 20 minutes and the two hours mowerman wanted!

If your batteries are 12V, you've got about 1.2kWh of capacity. To get it to 2 hours mowing time, you need 6x that, ie 7.75kWh in batteries. Pretty close to the 8kWh in my post above. It's not going to be a small, light or cheap set of batteries.

Post by **woody** » Fri, 29 Jan 2010, 14:32

Gow864 wrote:
Nothing beats practical experience you guys should get some.

Gold.

So harsh, yet so fair.

There's a place for calculations though - help you avoid costly experience. Physics + electrical formulae are condensed from experience

Post by **Mowerman** » Fri, 29 Jan 2010, 18:45

Thanks fellas for all the replies
The link gow sent is what I was imagining
Without the engine the yardman is only plastic and pressed sheet metal maybe 90-110kg.

So lets say etec RT at 72 volts runs around 3000rpm whats would the rpm be at 48 volts?

So using the calculations what would be the running time for either
72 volt ( 6 x 12volt truck or marine batteries)
48 volt ( 4 of the above)
running an Etec RT and a rough price for parts?

It seems 2 hours running time is not practical so what would be needed in lithium for say 45min to 1 hour running time running an etek RT or perm 132.

Also how do the perm 132 and etek RT compare power, price and availability?

Thanks again

Post by **Gow864** » Fri, 29 Jan 2010, 18:50

The point I was trying to make is that it does not take a $20,000 300kg battery pack to build an effective ride-on.

Rather than scaring people away with unrealistic solutions, shouldn't we pass on what is practicable within reasonable budgets.

TJ, my batts are stuffed, I reckon 3kwh for an hour's run time (mowed often)

Post by **Electrocycle** » Fri, 29 Jan 2010, 19:08

I would go with dual motors for a ride on mower.

If you have one driving the blades (Etek-RT etc) and another motor for the drive wheels - which will give better efficiency and driving control.

You could use wheelchair motors for the drive, and the blade motor doesn't really need a controller since it'll run at close to no load a lot of the time. It'd be worth having an ammeter though!

Post by **lithbattboss** » Fri, 29 Jan 2010, 19:10

Gow864 wrote:

Nothing beats practical experience you guys should get some.

Tritium James was just speaking from his point of view as a professional engineer (which is fine).
Often rather than punching numbers into a calculator and deciding "nah...it can't be done" there are other benefits in actually completing a project like this. Especially for the more mechanically minded people it is a great opportunity to gain wiring, crimping/soldering skills etc. even if the outcome isn't exactly what was desired. It is all a beneficial learning experience and helps with future (larger) EV conversions.

So I would say have a go mowerman and gain the satisfaction of converting your mower to electric!

I only have a push mower which is fine for my suburban backyard but the lead acid batteries have finally decided to die so now is the time to replace them with a lithium pack (which I will be doing in the next few days). The old Black and Decker Stealth electric mowers are fantastic but they were deleted several years ago now. It is time to replace the battery since I don't want to get the old smoke belcher out of the shed. I haven't used it in more than five years and I aint about to start now.
I just hate it when you can smell the fumes when someone three houses down the road is mowing their lawn!

Post by **Richo** » Sat, 30 Jan 2010, 07:00

Mowerman wrote: So lets say etec RT at 72 volts runs around 3000rpm whats would the rpm be at 48 volts?

2300RPM less loading.

Etek RT Specs

Edit: added link to spec

Post by **Richo** » Sat, 30 Jan 2010, 07:11

Mowerman wrote: Also how do the perm 132 and etek RT compare power, price and availability?

Etek Prices (USD)

Perm Price (USD)

Local supplier (POA)

Price wise I'd say the Etek is about 1/2 the cost of the Perm 132.

You can also get a similar motor to the etek locally from eVworks which they have in stock.