Author Topic: My lawn mower deck broke, so I might build a generator  (Read 714 times)

Offline Smurf Hunter

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My lawn mower deck broke, so I might build a generator
« on: June 22, 2017, 09:42:00 AM »
My craftsman mower served me well for 14 years, but last night while cutting the grass, the steel body split, causing the blade to jam. It wasn't horribly rusted, but two rivets popped and I guess fatigue on the metal finally was too much.  The engine is not in top shape, but I've overhauled it and it starts and runs reliably.

Many years back I found this website that sells accessories to build your own 12vdc generator using a salvaged mower engine:
https://theepicenter.com/blog/generator-lawn-mower-vertical/

It looks like it will cost around $100 for all the supplies. As I already own some alternators and deep cycle batteries, this is more of a novelty, but could be backup method for charging batteries.
It should prove educational. I'm very busy the next few weekends, but I may get this on my list.

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Re: My lawn mower deck broke, so I might build a generator
« Reply #1 on: June 22, 2017, 10:16:50 AM »
interesting idea. let us know how it goes.


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Offline NWPilgrim

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Re: My lawn mower deck broke, so I might build a generator
« Reply #2 on: June 22, 2017, 04:20:50 PM »
Yeah, that has to be the all time classic question homeowners ask themselves: how can I re-use a lawnmower engine, it just seems there must be something it is still good for?  I find that with good engine maintenance, the engine outlasts the handles, decks, rivets, etc.

But reading the linked article above, it sounds like you need a good number of special sized parts and if that totals to $100 (not including larger gas tank and inverter), you are only getting less than 1,000W power out of it.  You can buy a 900W generator for $150 that includes Ac and DC outlets built in, and has a 1 gal tank that will last 5 hours (rather than 1 hour for the lawnmower's).

Just an example:  https://www.amazon.com/PowerPro-56101-Starting-Portable-Generator/dp/B00J261PGQ/ref=sr_1_2?ie=UTF8&qid=1498169360&sr=8-2&keywords=1000+watt+generator

But as a fun learning project that could lead to something more practical, why the heck not!

I remember my grandfather's workshop had just a few power tools but they were all belt driven and the same electric motor could drive the bandsaw, table saw, grinding wheel, and sander.  I have no idea what happened to those tools as at the time they just seemed obsolete (1970s).  But looking back that would be pretty cool to have one or two mothers (gas or electric) that could power multiple devices.  And these were large, full function shop tools, not the compromise multi-tool hand sized ones you see today.

I have a compressor and a generator that both use almost the same Honda engine, which are about the same as the larger Honda lawnmower engines (7.5hp).  Get's one to thinkin'...
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Offline Smurf Hunter

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Re: My lawn mower deck broke, so I might build a generator
« Reply #3 on: June 22, 2017, 04:37:58 PM »
Yeah, that has to be the all time classic question homeowners ask themselves: how can I re-use a lawnmower engine, it just seems there must be something it is still good for?  I find that with good engine maintenance, the engine outlasts the handles, decks, rivets, etc.

But reading the linked article above, it sounds like you need a good number of special sized parts and if that totals to $100 (not including larger gas tank and inverter), you are only getting less than 1,000W power out of it.  You can buy a 900W generator for $150 that includes Ac and DC outlets built in, and has a 1 gal tank that will last 5 hours (rather than 1 hour for the lawnmower's).

Just an example:  https://www.amazon.com/PowerPro-56101-Starting-Portable-Generator/dp/B00J261PGQ/ref=sr_1_2?ie=UTF8&qid=1498169360&sr=8-2&keywords=1000+watt+generator

But as a fun learning project that could lead to something more practical, why the heck not!

I remember my grandfather's workshop had just a few power tools but they were all belt driven and the same electric motor could drive the bandsaw, table saw, grinding wheel, and sander.  I have no idea what happened to those tools as at the time they just seemed obsolete (1970s).  But looking back that would be pretty cool to have one or two mothers (gas or electric) that could power multiple devices.  And these were large, full function shop tools, not the compromise multi-tool hand sized ones you see today.

I have a compressor and a generator that both use almost the same Honda engine, which are about the same as the larger Honda lawnmower engines (7.5hp).  Get's one to thinkin'...

I have a small collection of inverters and deep cycle batteries. 

That generator you linked is a 2-stroke.  That probably means it's noisy, and definitely means I have to keep 2-cycle oil around and/or pre-mix it with gasoline in appropriate ratios.
While my Briggs and Stratton is certainly not quiet, it's a 4 stroke. It's the bigger 7HP size.  Maybe I'll make a go-kart instead?

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Re: My lawn mower deck broke, so I might build a generator
« Reply #4 on: June 22, 2017, 04:54:00 PM »
My alternative energy files have many examples and understand that the 12 volt generator is a jump start/or fast charge kind of thing that need not run more than an hour at a time and not so good for continous duty as alternators and air cooled engines just are not best for long term use.It is a bit more efficient than my toyota 4 cylinder at idle for 2  1/2 hours per gallon as I use it as my home generator to top off house batteries and run the fridges from a big inverter for about 1 hour out of every 6 hours to chill the fridges ,keep foods frozen and top the house batteries for Ham,lights,fans etc as solar is a poor charger during storm clouds and night ...so my option now is my auto.I can maintain my house 2 weeks with the auto fuel and keep a 5 gallon reserve.
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Offline machinisttx

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Re: My lawn mower deck broke, so I might build a generator
« Reply #5 on: June 22, 2017, 11:20:10 PM »
I'll donate an alternator if you haven't sourced one. I've got a pile of them sitting around and I can get more easy/cheap. 7hp can produce around 5k watts in a perfect world, and you should be able to run a 150 amp alt with that engine....if your pulley ratio is correct. I suggest a ratio of roughly 2:1 to 2.5:1.  Less than that and you'll never get full output from the alternator. More than that and the engine may stall when the alt is heavily loaded.

I know for sure I have several 10 and 12SI alternators, which the epicenter pulley will fit. None of them are "one wire", but those aren't really ideal for this application.  I also have a few 140ish amp 22SI alts that the epicenter pulley won't fit. Some of them might be "one wire", but I will have to look up part numbers to be sure. If you use a 10/12SI or the 22SI, the connector for the voltage regulator terminals is available from O'reilly's for $2.99 as part number 85841. Alternatively, you can just use standard 1/4" female spade quick disconnects. The 22SI is a medium/heavy duty alternator and will produce more power at lower RPM than the 10/12SI. IIRC, it usually produces 80-100 amps at idle speed for a normal truck application.

The direction you spin the alternator doesn't really matter as far as power production is concerned. It will produce power either way. What won't work correctly if spun the wrong direction is the cooling fan. They are almost universally directional. Cooling is going to be critical if you expect to heavily load it for more than a few minutes at a time. Even with the "few minutes" limitation, the diodes will have a shorter lifespan. The rectifier diodes and to a lesser extent, voltage regulator, must have adequate airflow or they will fail. The fan is designed to pull air in from the rear of the alternator, cooling the rectifier and V/R.

If you need any help, or something machined, feel free to ask me. I made an eight groove serpentine pulley for my project, rather than use V belts.
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Offline Smurf Hunter

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Re: My lawn mower deck broke, so I might build a generator
« Reply #6 on: June 23, 2017, 10:03:02 AM »
I'll donate an alternator if you haven't sourced one. I've got a pile of them sitting around and I can get more easy/cheap. 7hp can produce around 5k watts in a perfect world, and you should be able to run a 150 amp alt with that engine....if your pulley ratio is correct. I suggest a ratio of roughly 2:1 to 2.5:1.  Less than that and you'll never get full output from the alternator. More than that and the engine may stall when the alt is heavily loaded.

I know for sure I have several 10 and 12SI alternators, which the epicenter pulley will fit. None of them are "one wire", but those aren't really ideal for this application.  I also have a few 140ish amp 22SI alts that the epicenter pulley won't fit. Some of them might be "one wire", but I will have to look up part numbers to be sure. If you use a 10/12SI or the 22SI, the connector for the voltage regulator terminals is available from O'reilly's for $2.99 as part number 85841. Alternatively, you can just use standard 1/4" female spade quick disconnects. The 22SI is a medium/heavy duty alternator and will produce more power at lower RPM than the 10/12SI. IIRC, it usually produces 80-100 amps at idle speed for a normal truck application.

The direction you spin the alternator doesn't really matter as far as power production is concerned. It will produce power either way. What won't work correctly if spun the wrong direction is the cooling fan. They are almost universally directional. Cooling is going to be critical if you expect to heavily load it for more than a few minutes at a time. Even with the "few minutes" limitation, the diodes will have a shorter lifespan. The rectifier diodes and to a lesser extent, voltage regulator, must have adequate airflow or they will fail. The fan is designed to pull air in from the rear of the alternator, cooling the rectifier and V/R.

If you need any help, or something machined, feel free to ask me. I made an eight groove serpentine pulley for my project, rather than use V belts.

Thank you! That's fantastic.  My only hesitation with this project is if the resulting apparatus is worth $100-150.
For that money I can get a refurbished yellow top optima deep cycle battery, or another 100 watt monoscrystaline PV panel.
Lots of energy preps that might have better ROI.

However, a donated alternator might tweak the economics a bit :)
My understanding of the different wiring styles, is the "switch"  that must be toggled off before starting the engine, and toggled back on for operation.


I'd of course pay your shipping costs. I've got a busy afternoon and am doing amateur radio field day all weekend, but I'll read up more on the parts you mentioned and put together a shopping list when I am able.

PM me if you want to talk specifics.

Thanks again



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Re: My lawn mower deck broke, so I might build a generator
« Reply #7 on: June 23, 2017, 10:27:09 AM »
That generator you linked is a 2-stroke.  That probably means it's noisy, and definitely means I have to keep 2-cycle oil around and/or pre-mix it with gasoline in appropriate ratios.
While my Briggs and Stratton is certainly not quiet, it's a 4 stroke. It's the bigger 7HP size.  Maybe I'll make a go-kart instead?
Yep, that will be a pretty noisy generator.  You can get a very similar one from Harbor Freight.  If you get coupons, you can have the Harbor Freight version of that generator for about $80 at times.

With generators, quiet = expensive.  Just check out the Honda inverter generators.  But if you need quiet, like in a campground, this is what you need.
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Offline machinisttx

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Re: My lawn mower deck broke, so I might build a generator
« Reply #8 on: June 23, 2017, 10:24:57 PM »
Diagram 1 is the one you want, and I was wrong, the switch goes on the lamp terminal. Yes, you'll toggle off to start and/or let the engine warm up. Toggle on to excite the alternator and charge a battery. Toggle off before killing the engine too.

Here is an almost completely disassembled 12SI. The arrow is pointing to the voltage regulator. Not the best pic, but the tabs are visible.


Another pic, a 22SI(right) next to a 10SI(middle) and a 12SI(left). The voltage regulator tabs are easier to see in this pic.


Close up.


I'm nearly 100% sure the 22SI won't fit the epicenter mounts, if you're set on using their stuff. It's physically larger and the mounting hole spacing is farther apart. On the other hand(since you are worried about how worthwhile this venture is), the 22SI would make a better welder with it's higher output.  ;D  Easy conversion, and it could be set up as a charger/welder. Would be easier with an externally regulated alt, but it's possible to convert an SI to do this.
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Offline Zef_66

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Re: My lawn mower deck broke, so I might build a generator
« Reply #9 on: June 29, 2017, 11:22:15 AM »
Yep, that will be a pretty noisy generator.  You can get a very similar one from Harbor Freight.  If you get coupons, you can have the Harbor Freight version of that generator for about $80 at times.

With generators, quiet = expensive.  Just check out the Honda inverter generators.  But if you need quiet, like in a campground, this is what you need.

I own the harbor freight version. Where I live, no one cares about quiet. It works great for what it is, a cheap generator. I've pushed it to over 1200 watts without issue. For stuff like running a circular saw, drill, lights, etc, it works great. It's not going to power my well pump. But it does run a regular sized refrigerator and large chest freezer all while sipping gas. I can run it about 5 hours on a gallon of gas.
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Offline machinisttx

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Re: My lawn mower deck broke, so I might build a generator
« Reply #10 on: August 02, 2017, 06:21:28 PM »
I have been pondering on how to easily convert the SI series alternators to function as a dual purpose charger or welder. I was debating how to do it with the original regulator,  which I believe is entirely possible, but could also pose additional problems. I am not knowledgeable enough to know for sure, or if there is even a problem to worry about. What I know for sure though is that there are three types of alternator "control" circuits.

One type is rarely used, so I will ignore it. The other two are "A" circuit and "B" circuit. This page explains the difference. https://alternatorparts.com/difference-between-a-b-circuit-regulator.html

I think that the easiest way to accomplish both functions with an Si series is to simply remove the original voltage regulator, and bring the connections to the brushes outside the alternator case. This would allow easy connection of a switch that would allow a manual control circuit for welding, or when the switch is flipped, connection to an external voltage regulator for charging. Many ford and dodge vehicles had external regulators even into the 1980s, possibly later. I looked one up for a dodge earlier and found them to be in the neighborhood of $15. That is cheaper than a good replacement for the original internal regulator, and also eliminates the need to remove and disassemble the alternator to replace it when it eventually fails. Some of the external regulators also allow adjustment of the output voltage setpoint, whereas the internal versions are only sold in a few fixed voltage options. It would also mean that your local autoparts store likely has something in stock that will work as a replacement, when they might not have a replacement regulator for a random 1970s or 80s gm product.

Perhaps this info will be useful to someone. It is a route I am likely to take with my project, though I have an additional twist I want to try with mine.  ;D
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