OT - Make a Portable hard start Capacitor ?????

[Tycer]

I have a Honda EU2000i generator that I use in remote areas and when the power goes out.

My skill saw, miter saw, and the fridge are stressing the limits of the generator and the motors on startup.

Is it possible to make a portable hard start capacitor box to reduce the strain on my stuff?

What do I need and what's the wiring diagram look like?

Thanks in advance!

[.45]

The refrigerator already has hard start components, its already doing the best it can.
We have that same generator. When you are running your saw, is the unit on the constant high output setting or are you running on the auto feature? If on the auto, turn that off and give it a try.

[Old Time Hunter]

Guys, it is called a "soft start", not a hard start. They operate on a UPS system using the capacitors as a "buffer" or filter. Any drive system will generally have some sort of IGBT or equivalent that acts as a UPS for the motor (or generator).

[adirondakjack]

Inverter type generators have very little in the way of "surge" capacity. They give ya about all there is all the time (unlike a true generator that can handle a short duration heavy load if temps don't go too high and hurt it). The extra current for motor starting simply isn't there. He's looking to be able to charge a capacitor that would give the saw the initial "shot" it needs to get started. Seems like what ya would need is a big battery and a cap or caps to produce the initial shot, then switch out instantaneously to the "run" circuitry. I'm thinking something like a camera's flash circuit, only much bigger.

[Tycer]

The refrigerator already has hard start components, its already doing the best it can.

From what I've read on RV forums, the caps provided with factory A/C units are pretty small and the aftermarket hard start kits have much higher Farad ratings. I'm assuming that Maytag is just as cheap. I've also read that an electric motor really spikes its draw from zero RPMs.

My skill saw and miter saw are full 15A motors. The Honda is not on Ecothrottle. The overload light on the Honda flickers when I turn the saws on and I can tell there's a bit of a flicker when the fridge starts. The saws spool up faster on power company AC.

[Blaine]

I'm not an expert, but it just sounds like you need more watts..... At this one water company, many moons ago, three phase was not available, so we would wire caps together to get the pumps started.....I have no idea how this was done, but it was....

[Rusty]

I have a device that I bought at one of the big box home stores (CRS) that is intended to cut energy bills by starting your fridge in a more economical manner. It sounds like what this thing may be doing is what you want. Try looking in the major appliance section.

[Old Time Hunter]

Here, maybe this will help:

Many electronic devices will consume a large initial current when first turned on (i.e. Inrush current) that can cause voltage fluctuations and affect the performance of other circuits connected to a common power supply. The source for this problem is often large capacitors with very low Input impedance. To counteract this issue, components can be added in series to throttle back the current initially as the device comes online.

Soft starters are also used to start some types of lamps. A cold tungsten filament has a much lower resistance by a factor of 8-10 than a hot filament, and allows a large inrush of current. This inrush coupled with uneven filament wear causes local temperature overshoot in hotspots during startup, further evaporating the thinner filament sections. While soft start has little effect on GLS lamp life, it can make a sizeable difference to a halogen lamp's life.

High initial current can cause damage to other components such as semiconductors if they are not rated for the initial high current of loads such as filament lamps, motors or capacitors.

Soft starts are sometimes used on larger equipment as well, such as electric motors in various applications. The current drawn by an electric motor during a start can be 2 to 10 times the normal operating current, and this can exceed the supply's ratings if not controlled.

Finally soft start is widely used on hand held tools to prevent the tool being jerked out of position when switched on. Jumping of electric drills was a widespread issue in the 1970s when soft start was usually not fitted.

[marlinman93]

There is no magic cure all that will accomplish what you're looking to do. Soft starts do ramp up slowly by either varying frequency, or voltage, but the result is they draw a little less current, but for a much longer period. We've tried to install soft starts on heavy generator loads, and the end result is they create a big problem for a longer time, and wont cure a generator that's just too small.
Hard starts using capacitors will take so many capacitors to work without discharging too quickly, and they also wont work with the amount of space most people have. A capacitor bank discharges too quickly, and the motor wont get to speed before it discharges.
If you've got all those things trying to run on one generator, or any items that have huge inrush currents, you just need to bite the bullet and get a bigger generator. Most motors draw anywhere from 300-600% inrush currents over the nameplate rating, so if you aren't sized for these inrush currents, you'll never get good performance, and eventually you'll ruin your generator, and your equipment.

[Tycer]

There is no magic cure all that will accomplish what you're looking to do. Soft starts do ramp up slowly by either varying frequency, or voltage, but the result is they draw a little less current, but for a much longer period. We've tried to install soft starts on heavy generator loads, and the end result is they create a big problem for a longer time, and wont cure a generator that's just too small.
Hard starts using capacitors will take so many capacitors to work without discharging too quickly, and they also wont work with the amount of space most people have. A capacitor bank discharges too quickly, and the motor wont get to speed before it discharges.
If you've got all those things trying to run on one generator, or any items that have huge inrush currents, you just need to bite the bullet and get a bigger generator. Most motors draw anywhere from 300-600% inrush currents over the nameplate rating, so if you aren't sized for these inrush currents, you'll never get good performance, and eventually you'll ruin your generator, and your equipment.

I'm only running one appliance at a time. It's just that they are at the limit of my genset on startup. I'm trying to extend the life of my generator.

So what I hear you saying is that the idea of a portable hard start is not worth pursuing.

[Mich Hunter]

I love the Honda and Yamaha EI2000's but they simply do not produce enough juice. They are made for small jobs. Some folks I have spoke to about them are surprised when they can't run their house off of one. You can buy another one ($899) and run them together, you just buy a bigger gen. People love them because they are quiet, but they do have other draw backs besides being over priced.

[Rimfire McNutjob]

As has been mentioned, you are really looking to slow of soften your motor starts rather than shorten them. With the right test equipment you could probably figure out a capacitance that matches the inductance of your motor start windings and deliver more real power and probably more current to your start windings in these motors but that's kind of the opposite of what you really need to do.

You seem to like to fiddle with these kinds of problems so I'll propose another solution to your situation.

Your generator runs your tools fine, it's just that it struggles to start them. You are experiencing a design trade-off made by Honda. Let me see if I can explain it in some detail.

When your generator is running a load that is at relative equilibrium, the energy to run the electric motor at the load is being generated by the gasoline engine at your generator plus all of the efficiency losses piled up in the conversion. When a demand change occurs on the line, the control loop in the generator has to compensate but is far too slow to do so at the speed required to perfectly match the new load. The generator will slightly gain or lose rotational speed until the control loop catches up. The speed changes because the rate of energy delivery changes and the excess or deficit is added to or removed from the rotational mass of the generator.

You want your generator to buffer more energy for delivery to the start windings in your motors. Once they are spinning, your generator handles them just fine. This is where your design trade-off occurred. Your generator sacrificed rotational mass for portability. If it had more rotational mass ... it could deliver more current without sagging while starting your motors. Think about what everyone above is saying about buying a larger generator ... your motors won't be drawing any more running power than they are with your existing generator, but a larger unit will have a larger engine and a larger alternator which combined will have a larger rotating mass than your smaller unit. Hence, it will handle the starting duties easier.

So what you need is a flywheel. Or you need to change to a bigger flywheel. Generally, on a generator that's meant to be portable, you won't find a flywheel at all. The portables often rely on the mass of the engine's crankshaft and the alternator's rotor to perform the buffering that might otherwise be augmented by a flywheel.

You have a couple of things you have to consider. Increasing the rotating mass will change the frequency response of the the feedback loop that controls the generator. At the same time, you're giving the control loop more time to compensate because you're buffering energy with a larger mass. This somewhat mitigates the control issue. The other issue is that the windings in the alternator were designed to supply a certain amount of current. Excessive currents manifest themselves as heat in the alternator windings. The insulation on the alternator windings is designed to withstand a certain temperature rise for a certain period of time. If you go too far, you can cause the insulation to breakdown and thus kill your alternator. The insulation is probably Class B or F. Sometimes you will find Class H ... which has a higher temp rating than B or F. Since you're really only talking about starting currents of a relatively short duration, you shouldn't have to worry about this unless you got really crazy on the loads and ran the unit at or above it's rating.

I'm figuring anyone willing to wire various capacitors up to the start windings in the motors on their tools or appliances is also crazy enough to crack open their generator and figure out how to add in a flywheel to the arrangement.

If you do ... let me know. It should be relatively easy to calculate the size/mass of a flywheel that would help compensate for your tool or appliance motors' startup needs ... especially if you have a motor plate that shows you the RLA and LRA of the motor. You also need to know the RPM of your generator. If it's got a two wire alternator, then it's designed to run at 3600 RPM for 60Hz. A four wire alternator runs at 1800RPM for 60Hz. You need the rotational speed in radians per second to calculate the energy stored by the flywheel.

The energy for a rotating mass is 1/2 * Inertial Moment * the square of rotational velocity in radians per second. For a uniform flywheel shaped like a disc, the Inertial Moment is 1/2 * the mass in kilograms * the square of the radius in meters. Your radians per second is 2 * PI * RPM / 60. This will give you energy in Joules ... which we like in the electrical world. Remember, 2.2 pounds in a kilogram and 25.4 millimeters to an inch. God save the Queen and the English system of weights and measures.

And remember, your looking for the energy released based on the rotational speed differential ... not the total energy. For example, you might be running at 60Hz (3600 RPM say) and are willing to tolerate a drop to 52Hz on the line frequency during a heavy load change. You can use the difference to calculate what the flywheel of a certain diameter and mass would provide to augment your starting ability.

Man ... I have really got to get a life.

[Tycer]

Thanks Rimfire. Now you've got me thinking about a PTO

buffer, grinding wheel, v-pulley, grain mill................

[marlinman93]

Many of the new computer room generators are equipped with massive flywheels to ride through small outtages. These do work well for compensating for high current draws at start up, but the size of the flywheel needed may be more than your little generator can even turn.
Flywheels immediately begin to lose momentum when the current draw hits the generator's alternator. The size of a flywheel required to get the generator to "ride through" the start circuit of your various appliances would add tremendous weight to the cranksaft, and will do major damage to the little engine. If it was somehow connected to the engine by a belt the weight might be managed and not damage bearings, but it would still take as much power to bring it up to speed as it presently takes to try and start the appliances.
The only good part about a flywheel is it would aid in keeping voltage up. As your little generator is pulled down the voltage pulls down, thus the current goes up, which compounds the already too small condition. The flywheel would aid some in keeping the centifugal momentum of the engine going, but only if it's big enough, and as I said if it's big enough it will cause other issues.
Seems it would still be a wash, and better to buy a larger generator, and keep the little Honda for small tasks that it was designed for.