Electric mower - AC to DC

Thread Starter

nathanking

Joined Apr 23, 2018
14
Hi everyone.

I'm hoping to get some assistance.
I'm in the process of setting up my electric mower to be a RC solar powered mower.

The mower is AC power in Australia, which is 240v. The mower is Ozito Model LMW 101 rated at 1100 watts continuous. I asked the mower company and they wrote back with "power factor is approx. 0.9 so that would mean the surge draw on startup would be approx. 2100W"
Mower works fine on AC mains. I've not modified it in any way (yet).
So, I've attached a car battery, fully charged to a 1500 watt continuous (3000 watt surge) DC to AC inverter. I originally got a Modified Sine Wave inverter. This one didn't work, it seemed to start the motor spin, then stop, a second or so later, repeat. I thought that either the watts were full of crap (it works with less power hungry power tools) or that the modified sine wave was not working with the mower.
I now have a pure sine wave inverter (as I'm told), this one:
https://www.ebay.com.au/itm/1500W-3000-watt-max-Power-Inverter-12-240V-M-Sine-Wave-Laptop-Charger-Car-fT/113893899739?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
and again the same issue.

It's got a pretty big capacitor in it, shown in photo. 20190928_155152.jpg 20190928_155129.jpg
CBB60 16 uf

I don't understand, am i doing something wrong? I don't understand why it's not powering this mower easily.

Any ideas or corrections on my logic/actions would be appreciated.

Thanks.
 

oz93666

Joined Sep 7, 2010
672
It's in no way realistic to expect to solar power this , you would need over 12 square meters of panels , 2kw of panel to expect to see 1.5Kw of power on a sunny day at noon ....

You could power it with lithium cells , unfortunately the motor is not brushed , if it was you could power it with dc ... many lithium's in series ...

If you incorporate an inverter into this machine , you can bet within a season the damp will get in and ruin it. The inverter in your link is "M sine wave " (Modified) , the price indicates it could not be pure sine wave even though in the listing it does say "pure sine wave" it definitely will not be ... large fan ventilation holes allow for ants and other critters to get inside and destroy it ( I speak from experience)...If you email seller and say this item is not as listed and is not "pure sine wave" they may give you a refund without asking for product to be returned .... they rely on an ignorant public and only get a few% complaints.
 
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Thread Starter

nathanking

Joined Apr 23, 2018
14
Hi @oz93666

Thanks for being, well, direct...

I'm not going to power this directly via solar power. It will sit in the sun and slowly charge a battery over the week or more in between mows.

If I can't get this motor to work with this setup I'll switch to a dc motor and simplify it all.

I did miss the M in the listing, not sure it was there when I bought it. I'll double check with the seller. Well spotted.

I've planned a good enclosure for the inverter and other electronic components I'll use to make it RC and solar.
 

Alec_t

Joined Sep 17, 2013
10,424
Many products coming from China these days have 'optimistic' ratings. It sounds as though your inverter is one of them and is being overloaded by the mower and going into shut-down mode to protect itself.
 

Thread Starter

nathanking

Joined Apr 23, 2018
14
Hi @Alec_t , thanks for your response.

Absolutely they do, I'd thought of that as well. It might well be the cause. I don't know how to check if it is, I'm a newby.
It isn't lighting up the fault red led. Not that is a reliable indicator.
 

jpanhalt

Joined Jan 18, 2008
8,060
Assuming your testing was with the blade attached, have you tried it with a smaller blade or no blade? That might help address whether the inverter is simply too small. A synchronous motor will not need a load.
 

dendad

Joined Feb 20, 2016
3,067
The starting current for your AC induction motor will be pretty high, probably shutting down the inverter.
A new battery mower may be a better way to go, and maybe cheaper than trying to mod your existing one.
Modifying your old AC mower with a DC motor may be an option but I doubt you could do it economically.
It is an interesting project and I hope you post updates.
I use mains electric mowers, and have for years. I'll never but a petrol on again as a couple of extension cords lets me reach all our block. The electric mowers are very easy to start ;)
 

Thread Starter

nathanking

Joined Apr 23, 2018
14
Thank you to everyone for responding.
You've helped me learn a great deal.

In the end, I've decided to make the entire thing from scratch. It's proving too difficult to mess with existing realities and far too power hungry.

So, I'm going to make the structure out of aluminium, mount 2 dc motors with whipper snipper blades, mount another 2 dc motors to control the wheels, hook it up with an arduino, solar panel controller, solar panel and SLA batteries.

If anyone is interested in the project, let me know and I'll happily share.

Thanks again.
 

jpanhalt

Joined Jan 18, 2008
8,060
Are "whipper snapper" blades what are also know as "string" cutters? If so, you will need an automatic feed or very easy way to change them. They are generally for trimming and may not last long.
 

Thread Starter

nathanking

Joined Apr 23, 2018
14
Are "whipper snapper" blades what are also know as "string" cutters? If so, you will need an automatic feed or very easy way to change them. They are generally for trimming and may not last long.
Howdy, thanks for your reply.

Absolutely, which is why I'm not going with the plastic string. There's a new system on the market in Australia. They're plastic blades, 10cm long. The ones I'll try first are nylon. Which, admittedly, isn't a very hard plastic. But, after proof of concept, I'll probably end up making my own blades.
 

jpanhalt

Joined Jan 18, 2008
8,060
Our large rotary mowers also have articulated blades like this:
upload_2019-10-2_5-21-5.png

Going to a smaller cutting circle will reduce your power needs and slow the cutting rate (hectares/min). I don't think articulation has much effect per se on power needs cutting grass.
 

Thread Starter

nathanking

Joined Apr 23, 2018
14
Hi #jpanholt, that setup looks great.
However, assuming it's made of metal, it'll be power hungry due to the weight.
So, to summarise, I'm unsure of the point/s that you're making...
I think the way of the future is surely lighter. The older generation of mowers were about reliability and durability. Far beyond the needs of the common man mowing his basic lawn in the backyard. Plastics have come a long way, as have electronics and batteries.

To me, now, it's about lighter and faster. Cut through grass, yet have some durability to deal with the human error factor. Simple cheap blade replacement, polycarbonate, etc.
 

jpanhalt

Joined Jan 18, 2008
8,060
The point I am making is that mass comes into play during acceleration. Its flywheel effect also helps as grass density varies. Once up to speed, the effect of mass is much less. Wind resistance and cutting forces are probably the major power needs.

Of course, the steel blades are probably thicker than the plastic ones and will probably require more power to overcome wind resistance. My point is to caution about being too optimistic on reducing the power needed while maintaining the same cutting rate.

Cutting rate may not be as important to you as it is to me. It takes me about 7 to 8 hours with a 60" mower to do most of my yard. :)
 

Thread Starter

nathanking

Joined Apr 23, 2018
14
WOW, your cutting rate is huge.
My yard is nowhere near that time, capacity, area.

Fair points about acceleration and mass
 
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