Maker Pro
Maker Pro

Electric mowers and thick extension cords...?

Doug3004

Sep 5, 2014
119
Joined
Sep 5, 2014
Messages
119
Anybody familiar with these things, electronics-wise?

My gas push mower died and I am pondering replacing it with a corded electric mower. One matter I frequently see in reviews is how the manufacturers will advise to use a 12-gauge extension cord long longer than 100 feet total. People who try using thinner cords (16 ga) or longer cord runs often see the mowers burn up or just stop working permanently.

Some people mention that if the factory repair cost is excessive, that there are instructions online for replacing the motor rectifier. So whatever burns up seems to usually be a input circuit on the motor.

Another question is if it would help to decrease the mower's power usage somewhat--perhaps with a 10-amp motor, limiting it to only 8 amps somehow? The motors seem to be sized and marketed based on the power consumption rating, but the ones with higher power consumption are also the ones that have the most issues with tripping GFCI outlets/requiring 12-gauge cords/burning up...... I would accept a lower power output than the manufacturer's specs if it would boost the overall reliability somewhat. Without knowing what kind of rectifier circuit is used I am only guessing however.
 

Bluejets

Oct 5, 2014
6,901
Joined
Oct 5, 2014
Messages
6,901
The larger size recommended should be adhered to as problems with voltage drop will occur if using anything smaller or longer.
You cannot put a smaller motor on a device designed for a larger unit as the result will be the same, i.e. burn out.
It takes a certain amount of power (h.p) to drive the load from the grass and smaller motor will not cut it (so to speak)
Also be aware the electric units are usually referred to as "lawn" mowers rather than grass cutters as the previous petrol version would have been. (big difference)
 

Doug3004

Sep 5, 2014
119
Joined
Sep 5, 2014
Messages
119
The larger size recommended should be adhered to as problems with voltage drop will occur if using anything smaller or longer. ...
Yea but assuming that the [motor circuit] is a rectifier for a DC motor, then how would a lower-than-normal voltage cause it to self-destruct?

There is a few youtube videos showing how to repair these things, and of the few I looked at, all that is inside is a bridge rectifier and a (DC) motor.

One thing I see immediately is that most brands have a bridge rectifier that is about 1" square and ~1/2" thick, and it is screwed down to a flat aluminum plate that is supposed to act like a heat sink.... and that's a pretty sad heat sink if that is the reason for all these failures.

One video:
Another video:

The lousy rectifier heat sink plates in both these (different-brand) mowers is almost exactly the same....
 

kellys_eye

Jun 25, 2010
6,514
Joined
Jun 25, 2010
Messages
6,514
The motor draws a certain power - or tries to - and reducing the voltage (due to volt drop along an over-long cable) causes the current to rise which MAY exceed the rating of the rectifier. Whether the motor or the rectifier blows is uncertain - but one does!

If you can't/won't drag the correct sized cable around the garden then consider getting a portable generator to put local to the mower using the OEM cord (with no extension).

It is always possible the the rectifier is a 'cheap Chinese knock-off' (there are known issues with device quality) but you can purchase a higher rated rectifier from a reputable supplier to mitigate that particular issue.

Personally I'd fit a current trip (at the mains plug) AND a thermal trip (maybe two, one to the motor, one to the rectifier) to save the motor. Ok, there's an inconvenience added when it/they trips, but it may cause you to alter the way you mow and help prevent tripping or simply save you having to replace/repair the device at intervals.
 

Doug3004

Sep 5, 2014
119
Joined
Sep 5, 2014
Messages
119
Welp, into the abyss. It is ordered.
,,,
I'vre found a couple reports that the motors only draw about half their rated current, normally. So 5-6 amps normally. And I also ordered the thicker extension cords, but I am still curious about all this. (warranty voided! :D )

Considering the voltage (~120 v) and current involved, what could be fitted to the mower to prevent over-current from low voltage? That is to say--ideally I'd want the mower to keep running, rather than just shut off...
 

Doug3004

Sep 5, 2014
119
Joined
Sep 5, 2014
Messages
119
The motor draws a certain power - or tries to - and ....
And since you are in the UK, I will also ask--how well do these Flymo "hover mowers" work? While mower shopping I found these things, but all the ones I found in Google are all UK stores and prices...

 

kellys_eye

Jun 25, 2010
6,514
Joined
Jun 25, 2010
Messages
6,514
If the mower takes 5-6A nominally then a 10A cut-out would protect it but 5-6A at 120V is only 600-700W i.e under 1hp equivalent, quite weedy for a mower. I'd expect 1200W minimum if you're looking at a replacement for a petrol (gas) driven mower. This is likely to be your problem rather than the extension cord - you are 'overloading' the motor as it's not rated to suit your cutting habit.

Hover mowers are ok if you don't mind leaving the cuttings on the garden (or raking them up) and they are easy to move around - they hover....d'uh! :D. There are versions that have collection bags/baskets but as I've used both types I prefer the standard grass-collecting type of electric push-mower myself.

Don't talk to 'me' about UK pricing either - we're the rip-off capital of the world :mad:
 
Top