# Electric Lawnmower

Okay, I need some help with what I can do with the following parts.

600 watt 36 volt bicycle hub motors, one for each rear wheel.

Batteries: NiMH 12 volt 3.5 Ah from Panasonic (Drill Battery)
3 in series to make 36 volt with 14 Ah.

How long will this set up run and will it drive a 300Lb setup (including driver)?

Al

(3) 12v 3.5ah batts in series (designated as 3s1P) is still 3.5ah for the new “pack”. That is one of the reasons I use the XsXp nomenclature- it helps visualize and do the math on voltage and capacity. There are two ways to wire batts or individual cells. Series or parallel.

Let’s take your 3 drill packs each rated as mentioned- 12v 3.5ah. Wired in series (3s1P) the math would be 3x12v and 1x3.5 for 36v at 3.5ah. In parallel (1s3p) the math would be 1x12v and 3x3.5ah for 12v at 10.5ah.

Series wiring multiplies the initial voltage of the cells or packs being joined and keeps the same ah rating.

Parallel wiring keeps the same voltage, but multiplies the ah rating.

Here are the numbers for your 3 batteries in the two configurations.
12v 3.5ah:
Series (3s1p) = 36v 3.5ah
Parallel (1s3P) = 12v 10.5ah

One other consideration would be the amperage draw the initial batteries can take before meltdown. Most likely those packs are AA cells or something close. If they can take a draw 5x the capacity (termed as 5c) then each battery can take a max load of 17.5 amps. If you wire in parallel (1s3P) that results in a total max draw of 52.5amps.

I have no idea what the max draw (how many “c”) those batts can take so maybe they are only 5c or maybe they are 20c. The formula for determining amperage draw from wattage escapes me at the moment. You could always google for that. My guess however, would be that you would not get very far and the batts may not even survive. Since you are putting a pack in a riding mower I would just go with 3 golf cart or similar batts. Like something from this page…http://www.electricvehiclesusa.com/category_s/220.htm
(disclaimer: I am NOT affiliated with this site in any way. The link is solely for reference.)
Are you scratch building the mower?

Cheers

Try this for link for calculating your power requirements. http://www.vias.org/wirelessnetw/wndw_09_08_03.html

Thanks InSANe,

I know nothing about electric vehicles. I first thought of using a electric golf cart to do the conversion, but then I saw the hub motors for the bicycles. I thought if I could us a lighter battery I could get more performance from the mower. I did get confused on the series and parallel, I also did some bad math on the Ah.

I am planning to use an existing mower base to build from. I wanted to use a the hub motors because they are supposed to be more efficient and I wanted the extra room for the batteries. I do not know the draw from the hub motors, just the 600 watts and 36 volts.

I guess I need to do more research on the motors.

Thanks,
Martin

more help needed.

If I have a 600 watt motor running on a 48 volt system, then it will draw 12.5 amperes per hour. Is this correct?

If this is correct then I would need a 48 volt system with 50 Ah to run the 600 watt motor for 4 hours. Is this correct?

[QUOTE=Al-Bundy;545]more help needed.

If I have a 600 watt motor running on a 48 volt system, then it will draw 12.5 amperes per hour. Is this correct?

If this is correct then I would need a 48 volt system with 50 Ah to run the 600 watt motor for 4 hours. Is this correct?[/QUOTE]

Al

According to the formula in the link you are correct. I did some calculations with other numbers and I’m not too sure about that formula and I can’t seem to find the other site I first mentioned.

I’m not too sure that hub motors would be ideal in a mower application. First, the motors are efficient on the upper end of their rpm range and unless you are making a racing mower, I doubt you’d ever see that range. Second, you are effectively cutting your pack capacity roughly in half by running two motors. Btw…how are you planning on running the blade(s)?

You may want to look into a single 600 or even 1000 watt motor like this… http://www.electricvehiclesusa.com/product_p/ki-sd-1000w.htm .
You could then gear that puppy down to pull stumps (not really, but low baby!) since you probably wouldn’t want a top speed of more than about ten mph. The higher rpms will be your friend. You could even possibly put a 3 speed internally geared bicycle hub inline in the drive train and have faster get back home gearing. Check out the book from this site www.atomiczombie.com for lotsa bike hacking ideas and techniques. I’m waiting for mine to come in so I can get started on my E-bike design- Project: Not Your Grandma’s Grocery Getter.

I mentioned racing mower earlier. If I had a lawn that contained enough grass to take longer than 5 minutes to mow I’d build an electric version of one of these!!! http://www.letsmow.com/ I know it may sound rednecky, but it’s still high performance grunt grunt.

Cheers

I went to the store and just ended up buying an electric lawn mower, it was \$200, far cheaper than i could have made one for. It IS a plug in, but i needed something to cut my grass REALLY bad with so i just broke down and got one. its nice and quiet, takes about 2 seconds to setup:eek: , so i’m happy.

[QUOTE=FEUS;567]I went to the store and just ended up buying an electric lawn mower, it was \$200, far cheaper than i could have made one for. It IS a plug in, but i needed something to cut my grass REALLY bad with so i just broke down and got one. its nice and quiet, takes about 2 seconds to setup:eek: , so i’m happy.[/QUOTE]

I’ve seen a number of the Black and Decker electrics around the neighborhood. It’s nice to see them catching on.

I wonder if one could wire in a converter/inverter and load it up with a few batts.

[QUOTE=inSANe DIEGO;571]I’ve seen a number of the Black and Decker electrics around the neighborhood. It’s nice to see them catching on.

I wonder if one could wire in a converter/inverter and load it up with a few batts.[/QUOTE]

you could but it would be annoying adding on a good 20+lbs lol…

[QUOTE=FEUS;572]you could but it would be annoying adding on a good 20+lbs lol…[/QUOTE]

Aww c’mon… consider it a workout! lol. Seriously, I bet that little motor in there wouldn’t take much to turn. Maybe two of these http://www.electricvehiclesusa.com/product_p/ba-ty-12-7.htm would do it. Then again… why? It’s not like you have any “range” requirements that would make a cord be a limitation.

Cheers