tractorguy1951
Member
Can a 7000 watt engine driven generator be set up to run belt driven off of a lawn mower?
- Thread starter tractorguy1951
- Start date
john *.?-!.* cub owner
Well-known Member
If the generator was originally mounted directly to an engine it probably does not have any bearings in the end. If you can get around that there is still the problem of belt slippage causing frequency to be off unless you use a notched bolt. Also, most lawnmower governors are not precise enough to hold a steady rpm under varying loads.
Mule Meat
Well-known Member
Yes one can be.
1. The minimum engine needs to be no less than 13 to 15. HP for a 7000 watt generator.
2. It must be mounted so that it turns in correct rotation.
3. Most generators run at 32-3700 rpm. So the gearing must be correct for full output.
I use to have a 55 amp single wire GM alternator powered by an 8 HP B&S engine to charge deep cycle batteries at a remote cabin. Then found that it was very usefull on the farm to charge dead or low batteries on machinary, charge fence batteries etc. I know it was not a 120 volt generator but it was very simple to build and came in handy many times.
1. The minimum engine needs to be no less than 13 to 15. HP for a 7000 watt generator.
2. It must be mounted so that it turns in correct rotation.
3. Most generators run at 32-3700 rpm. So the gearing must be correct for full output.
I use to have a 55 amp single wire GM alternator powered by an 8 HP B&S engine to charge deep cycle batteries at a remote cabin. Then found that it was very usefull on the farm to charge dead or low batteries on machinary, charge fence batteries etc. I know it was not a 120 volt generator but it was very simple to build and came in handy many times.
Generators require around one hp per 300 / 500 watts. Not quite a straight curve but pretty close. My big beast of a 1985 Homelite commercial is 8000 watts with a 16hp Cast iron block rope start 600 pound monster for the whole rig. My smaller 3300 watt Homelite from same year is around 6.6hp. Little tiny 2cycle unit is a touch over 2hp at 900 run watts. Remember you are going to need a CONSTANT 3600 rpm speed for the generator head to run at 60hz AC frequency output. You are going to need every bit of 14hp to run that thing. Car generators are a whole different field and are 12 volt dc. Have seen guys running car alternators with a couple of big batterys and a honker of an inverter. But that is another story. Let us know what and if this helped or if we can give you more advice.
Texasmark1
Well-known Member
I answered such a question on the tractor forum this am. I have 2 portables. A 10 hp runs a 5000 and a 13 runs a 6500, both commercially produced. The question really becomes what is your normal load, and how big are your starting surges which are the worst where compressors like air conditioners, furnaces, freezers, and refrigerators are concerned. ACs just whack you, some furnaces have sequential starting where maybe ⅓ the total energizes at any one time, and refs and freezers are a surge but since the compressors are fractional HP no big deal.
Most gasoline driven gens in this power range can tolerate roughly a 30% surge over max rating before the engine balks......per the surge ratings posted on my units vs their constant max power rating.
Most gasoline driven gens in this power range can tolerate roughly a 30% surge over max rating before the engine balks......per the surge ratings posted on my units vs their constant max power rating.
Destroked 450
Well-known Member
- Location
- Harned, Ky
Most small generator are designed to operate at 3600 because the engines they are connected to operate best at that rpm.
Most larger generators are designed to operate at 1800 rpm to work with the larger engines they are connected to that will not rev to 3600 rpm.
My 5500 watt Briggs powered gen runs at 3600
My 75 KW gen powered by a 145 hp diesel runs at 1800
An interesting question is what rpm does a generator (20-40KW) powered by a automotive type gas engine operate at.
I've looked at belt driven gens and found both 1800 and 3600 rpm models.
Most/all gas generators for commerical/industral use 12kw/up (onan,kohler,generac etc)are 1800 rpm units,also most 5-15 kw units designed for rv/marine use are 1800 rpm units,rule of the thumb is 2hp per 1kw(1000w) of output at 3600 rpm,at 1800 rpm for same output kw eng hp must be doubled.
Generators designed to operate at 3600 rpm are 2 pole units,1800 rpm units are 4 pole.
Generators designed to operate at 3600 rpm are 2 pole units,1800 rpm units are 4 pole.
Destroked 450
Well-known Member
- Location
- Harned, Ky
2 pole - 4 pole, good info to have, thanks
I'm a little confused on the 1800 rpm output hp, are you saying 1800 rpm units require 2hp per 1kw, same as 3600 rpm models or that they require more.
My 1800 rpm 75KW gen is powered by a 145hp engine, basically the same 2hp per 1KW as my 5.5KW gen powered by a 11hp Briggs at 3600 rpm.
When I went to several onan training classes over 45 yrs ago I was told that hp was double for 1800 rpm unit compared to a same size 3600 rpm unit,It's possible I misunderstood instructor or he may have been wrong,I lost all my onan,kohler,winco & many other make service manuals/info in a flood 6yrs ago(hurricane irene)so I have nothing to reference back to at hand,perhaps someone else that services/did service generators can offer more info on this.
here is video of a 4020 ingersoll running what looks like a HF genny.https://www.youtube.com/watch?v=LmG2ZyiVGio
Tom
Tom
If you're going to run any electronic equipment off a generator I would make it a direct drive generator not belt driven. Then also an inverter type generator is best for electronic equipment. I have a couple of 4000 watt portable units and my electronic garage door opener (18 years old) would not work on my generator. I did find out I had to turn up the RPM's on the generator to make the doors work. This is how sensitive the electronic equipment is. The inverter type generators will hold a more even Hertz Cycle. A belt driven will vary way too much.
Mule Meat
Well-known Member
Why?
A belt driven generator will run at the a given RPM that it is geared for consistently same as a direct drive unit.
Lets say that a belt driven generator head turns at the same RPM as the engine. And they are both running at 3600 rpm. If you pull the trigger on a mitre saw and the generator slows to 2000 rpm while the engine is still turning at 3600.
You have an issue with the belt. Not the generator.
tractorguy1951
Member
Thanks for all of the replies. The reason I was asking is that 65 year old shoulders do not like pull ropes.Still thinking about trying this.
buickanddeere
Well-known Member
There is not a rpm range . For 60Hz power a two pole is spun at 3600rpm, a four pole at 1800 rpm and a six pole at 1200 rpm.
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