Shopsmith Forums

Unless you have a lot of power outages, I would suggest you consider skipping the whole house generator and install a transfer switch. I recently installed a Reliance Controls transfer switch and hooked two Honda EU2200i generators in parallel which produce 3600 W continuous, 4400 W peak power. Worked great this summer when we lost power for a couple of days due to hurricane Nicholas. Granted, there are much cheaper generators out there but the Honda's are very reliable and super quiet. The beauty of a transfer switch they are relatively cheap, pretty easy to install, and you can use whatever generator you want.

Independent generators in parallel??????

BTW WTH is "peak power"?

JPG wrote: ↑Thu Oct 14, 2021 10:27 pm Independent generators in parallel??????

BTW WTH is "peak power"?

Best I can tell the peak power rating is marketing spin. Generators have inherent limitations in providing the sort of start-up current typical for an induction motor, for one common example. My generator is 6250 MAXIMUM WATTS, as written in giant bold font on the label. Or, in much smaller print, 5000 Continuous Watts. So, will it run my 230V 10A compressor on its 240V 20A outlet? No, it will not. Because it cannot reliably start it. Because as you know induction motors draw a ton of current at startup for a few cycles. The more current they get, the less time they need it. The generator does not do well in this scenario because 1) it takes some time to start producing its max power, and 2) its max current seems to be much lower than what would normally correlate with a household 240V 20A outlet.

From https://www.magnum-dimensions.com/knowl ... generators (They want you to buy an inverter rather than a generator, but this is consistent with my experience):

"PEAK OUTPUT POWER
Peak output power or inrush current, is the ability of a power source to provide more than its rated power to start a load. Motor loads are especially demanding. They can require five to ten times their running power when starting. Generators have poor peak power capability due to their inherent operating characteristics. Peak power is usually no more than 110%-125% of their continuous power rating. They must be greatly oversized to successfully start some motor loads. On the other hand, because static inverters can take advantage of the large instantaneous power from a storage battery, they have very high peak capability, often three to four times their UL continuous power rating. There is normally no need to purchase an oversized inverter to run any given motor load. Magnum-Dimensions rates all inverters in horsepower to allow a comparison with engine generators."

- David

BS

HP as a comparison???

That sounded like marketing spin from a battery provider. Peak wattage from a generator is the momentary surge of power it can handle when electrical devices start up. That's mostly of concern for AC induction motors but any electrical device can startup with a brief inrush of current. Any power source can be overwhelmed if enough devices start up at the same time. An inverter is not a power source, when used with a battery to provide AC the battery will be just as much of a limiting factor as a generator, I've been using one for years and had to reset when if it was powering too much when the refrigerator compressor kicked in.

I can only make the assumption that a generator is limited by the momentum in the engine and some small amount of energy stored in capacitors in it's own inverter electronics to handle surges, but it should never be used so close to it's maximum steady or peak capacity anyway.

edma194 wrote: ↑Fri Oct 15, 2021 10:34 am That sounded like marketing spin from a battery provider. INVERTER provider. But certainly needs a charging source and storage system, which should be included in any comparison.Peak wattage from a generator is the momentary surge of power it can handle when electrical devices start up. That's mostly of concern for AC induction motors but any electrical device can startup with a brief inrush of current. Any power source can be overwhelmed if enough devices start up at the same time. An inverter is not a power source, when used with a battery to provide AC the battery will be just as much of a limiting factor as a generator, I've been using one for years and had to reset when if it was powering too much when the refrigerator compressor kicked in.Sure, at some level of power. But their assessment of what a generator won't do is consistent with my experience. I haven't done the math, but I'm well under 50% of rated continuous power.

I can only make the assumption that a generator is limited by the momentum in the engine and some small amount of energy stored in capacitors in it's own inverter electronics to handle surges, but it should never be used so close to it's maximum steady or peak capacity anyway.

I'm prepared to be wrong about this, but most of the generators I'm familiar with don't have inverters. They are literally motor-generators. Those that have electric start have a separate DC circuit for startup; scaled, but otherwise similar to a car. Their ability to handle a surge is limited to their momentum of the motor, as you say, and how fast the motor controls respond to the increased power demand.

- David

'Inverter' is not a very specific term so when some generator info mentions an inverter I don't know exactly what they mean. I think it is unlikely to specifically mean a device to convert DC to AC as you were referring to.

Ed,

I have a 5500 watt (7000 peak) 230 volt output gas generator I have had for at least 15 years now. It was used several days last winter for our power outage. It can be temperamental and since it is not used frequently that can add to problems. I had left some gas in it, my bad, and so getting it started while freezing outside was no fun. I had to empty the fuel tank, change the plug, run some fuel system cleaner through it and finally add fresh (non-ethanol) gas. After that it ran great. So much for the problems.

With the 5500 watts I am able to run refrigerator/freezers, our natural gas furnace which needs electricity for the fan and electronics, lights and other small appliances. It does not power the electric water heater and we do not use the range while on the generator. It is wired in via a 230 volt power cord to the house transfer switch panel. Of course it is necessary to have power disconnects from the power infeed to the house so as not to back feed to the power grid.

One thing to keep in mind is that if you're running a bunch of 120v stuff, you want to as best possible balance the load between the two legs of the 240v circuit. In other words you don't want all the load on one half of the generator and no load on the other

JPG wrote: ↑Fri Oct 15, 2021 10:19 am BS

HP as a comparison???

You are referring to this: "Magnum-Dimensions rates all inverters in horsepower to allow a comparison with engine generators?" I don't think HP as a comparison works, as I don't think the generator companies are providing that data. But I've no reason to doubt their claim that a 3600 W inverter will start and power a 2HP induction motor (depending, I'm sure, on the installation) and I have strong reason to agree with their claim that a 3600 W Generator will not.

As Ed points out, an inverter is not really a power source. So the inverter by itself is not much of a comparison to a generator anyway.

I was using the inverter data only because it supports my understanding of what Peak Power means, and my motor example because it explains what, to me, is a serious limitation in portable-sized generators. I was unaware of this nuance, and fully expected my 5000/6250 W generator to easily power my 120V welder (it struggles some, but gets the job done) and power my compressor. So my lesson learned is that the peak power rating tells me more about what the generator won't do than what it will do. Peak power is kinda useless unless I'm armed with peak power requirements.

- David