Posted: 7/4/2013 10:03:43 AM EDT
| I have a older Generac 5500xl that is about 17 years old. I see most 5500 watt gennys are 9 to 11hp with most being 11hp. Mine is a 13hp and with doing a little searching it was rare for the Generacs to be 13hp. Generac also did a short run with a few 5500's with a 15hp. Why would they upsized the engines when a 11hp would have worked? Is this to make it better surge rating? Any advantages to having a larger engine on a smaller generator head? |
| The rule of thumb is 2 HP for every 1000 watts as to the question of why they use a 15HP motor is anyone guess. As far as the surge rating that depends more on how the generator is built than the engine size. A generator that is 5500 watts with a 6000 watt surge rating would only need a 12 HP engine. |
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I have a older Generac 5500xl that is about 17 years old. I see most 5500 watt gennys are 9 to 11hp with most being 11hp. Mine is a 13hp and with doing a little searching it was rare for the Generacs to be 13hp. Generac also did a short run with a few 5500's with a 15hp. Why would they upsized the engines when a 11hp would have worked? Is this to make it better surge rating? Any advantages to having a larger engine on a smaller generator head? If it's that old that's probably before they changed the standards for rating horsepower on these small engines. What is the displacement and is it an L head engine? It may be that that engine would be rated a couple of horsepower less today. |
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I have a older Generac 5500xl that is about 17 years old. I see most 5500 watt gennys are 9 to 11hp with most being 11hp. Mine is a 13hp and with doing a little searching it was rare for the Generacs to be 13hp. Generac also did a short run with a few 5500's with a 15hp. Why would they upsized the engines when a 11hp would have worked? Is this to make it better surge rating? Any advantages to having a larger engine on a smaller generator head? If it's that old that's probably before they changed the standards for rating horsepower on these small engines. What is the displacement and is it an L head engine? It may be that that engine would be rated a couple of horsepower less today. Its a 360cc engine...not sure what a L head is? |
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I have a older Generac 5500xl that is about 17 years old. I see most 5500 watt gennys are 9 to 11hp with most being 11hp. Mine is a 13hp and with doing a little searching it was rare for the Generacs to be 13hp. Generac also did a short run with a few 5500's with a 15hp. Why would they upsized the engines when a 11hp would have worked? Is this to make it better surge rating? Any advantages to having a larger engine on a smaller generator head? If it's that old that's probably before they changed the standards for rating horsepower on these small engines. What is the displacement and is it an L head engine? It may be that that engine would be rated a couple of horsepower less today. Its a 360cc engine...not sure what a L head is? L head is a side valve engine (i.e. not and Overhead Valve Engine OHV), which makes less HP per cc. Looking at the current Generac GP5500 generator, it is 389cc and it is an OHV engine, so likely your generator doesn't make as much horsepower. Present day generators usually don't even spec horsepower, they spec displacement. Manufactures got into trouble years ago by over spec'ing their HP. What they were doing is spec'ing the HP at the maximum the engine was capable of making, which was typically at an RPM well above where they were normally operated at. Lawn mowers were particularly bad about claiming a horsepower that was at an RPM that the governor would not even allow the engine to reach. There was a lawsuit and engines that were 6.5HP in the previous year were suddenly 5HP without any mechanical changes. Manufactures eventually got away from spec'ing horsepower and settled on spec'ing displacement. This can make it difficult to compare older engines to their modern day equivalents. |
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1HP = 746 watts
If you had a 100% efficient generator, that's how HP would translate to usable electric power. In practice, cheap ones may give you 50% efficiency, good ones 70% or a little more. Then there is the question of whether it is good clean (low distortion sine wave) power or junk (square wave or stepped approximation) Bottom line, ya get what ya pay for. Go buy a Honda EU3000is and be done with it. |
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You no longer see HP rating on small engines anymore because they all got sued in a class action lawsuit over how they rated their engines.
Back in the day, generator, and pressure washer manufacturers for that matter, didn't like to get into what is called the "service factor" of the motor. So older generators had higher HP engines on them. As competition became more and more fierce to supply a piece of equipment at lower and lower costs, the manufacturers started going deeper and deeper into the service factor of the engine in an attempt to continue to keep prices low. For a pressure washers the formula is pretty straight forward. You take GPM X PSI and divide that by 1460 to get he HP required to drive the pump for an electric motor. An electric motor would typically have a 1.15% service factor meaning you could run it at 115% of is rating before you started causing it harm. To get the HP required to drive the same pump with gasoline you take the electric HP requirement and multiply by 2. Now if you factor in the service factor of the electric motor, you can use a smaller gasoline engine. Here is an example of what would be typical. A 5GPM 3000PSI unit would take a 10HP electric motor to drive that pump. If you factor in the service factor, you can lower that HP required to 9. Then you multiple that by 2 you get a 18HP engine to drive the pump. Even though the physics say 20HP. It is not uncommon at all to see 5@3000 units with 16 HP engines on them nowadays. The same thing is happening to generators. |
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1HP = 746 watts If you had a 100% efficient generator, that's how HP would translate to usable electric power. In practice, cheap ones may give you 50% efficiency, good ones 70% or a little more. Then there is the question of whether it is good clean (low distortion sine wave) power or junk (square wave or stepped approximation) Bottom line, ya get what ya pay for. Go buy a Honda EU3000is and be done with it. I did! But I instead got the Yamaha 2400ishc for the smaller demands. The Generac is for running the central AC when its hot. |
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You no longer see HP rating on small engines anymore because they all got sued in a class action lawsuit over how they rated their engines. Back in the day, generator, and pressure washer manufacturers for that matter, didn't like to get into what is called the "service factor" of the motor. So older generators had higher HP engines on them. As competition became more and more fierce to supply a piece of equipment at lower and lower costs, the manufacturers started going deeper and deeper into the service factor of the engine in an attempt to continue to keep prices low. For a pressure washers the formula is pretty straight forward. You take GPM X PSI and divide that by 1460 to get he HP required to drive the pump for an electric motor. An electric motor would typically have a 1.15% service factor meaning you could run it at 115% of is rating before you started causing it harm. To get the HP required to drive the same pump with gasoline you take the electric HP requirement and multiply by 2. Now if you factor in the service factor of the electric motor, you can use a smaller gasoline engine. Here is an example of what would be typical. A 5GPM 3000PSI unit would take a 10HP electric motor to drive that pump. If you factor in the service factor, you can lower that HP required to 9. Then you multiple that by 2 you get a 18HP engine to drive the pump. Even though the physics say 20HP. It is not uncommon at all to see 5@3000 units with 16 HP engines on them nowadays. The same thing is happening to generators. Great info! Thanks! |
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I have a older Generac 5500xl that is about 17 years old. I see most 5500 watt gennys are 9 to 11hp with most being 11hp. Mine is a 13hp and with doing a little searching it was rare for the Generacs to be 13hp. Generac also did a short run with a few 5500's with a 15hp. Why would they upsized the engines when a 11hp would have worked? Is this to make it better surge rating? Any advantages to having a larger engine on a smaller generator head? If it's that old that's probably before they changed the standards for rating horsepower on these small engines. What is the displacement and is it an L head engine? It may be that that engine would be rated a couple of horsepower less today. Its a 360cc engine...not sure what a L head is? L head is a side valve engine (i.e. not and Overhead Valve Engine OHV), which makes less HP per cc. Looking at the current Generac GP5500 generator, it is 389cc and it is an OHV engine, so likely your generator doesn't make as much horsepower. Present day generators usually don't even spec horsepower, they spec displacement. Manufactures got into trouble years ago by over spec'ing their HP. What they were doing is spec'ing the HP at the maximum the engine was capable of making, which was typically at an RPM well above where they were normally operated at. Lawn mowers were particularly bad about claiming a horsepower that was at an RPM that the governor would not even allow the engine to reach. There was a lawsuit and engines that were 6.5HP in the previous year were suddenly 5HP without any mechanical changes. Manufactures eventually got away from spec'ing horsepower and settled on spec'ing displacement. This can make it difficult to compare older engines to their modern day equivalents. It is a OHV engine. I suspected they either over rated them or at different times they ran out of the smaller engines. Heck I didn't know maybe it was for not taxing the engine to death when running the max wattage. All this info explains a lot. Thanks |
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Yes, higher altitudes reduces hp, hence the need for a larger engine at higher elevation.
I have a older Generac 5500xl that is about 17 years old. I see most 5500 watt gennys are 9 to 11hp with most being 11hp. Mine is a 13hp and with doing a little searching it was rare for the Generacs to be 13hp. Generac also did a short run with a few 5500's with a 15hp. Why would they upsized the engines when a 11hp would have worked? Is this to make it better surge rating? Any advantages to having a larger engine on a smaller generator head? |