can I add more starting wattage to a small power generator by adding more starting capacitors ?
I need to run a fridge on a small power generator that don't have enough staring power to run it , would adding a huge industrial capacitor make it possible ?
@ Joe : the fridge needs extra starting power for few seconds then it runs on the rated power .
- EckoLv 76 years agoFavorite Answer
This is the surge capability of the generator compared to the surge from the fridge during starting. Some fridge motors have a surge up to 9 times its running current. This is the very early fraction of a second, and is what gives grief to a lot of inverters, because they just sense "too much current" so switch off immediately. A generator might have a more useful surge rating where it can deliver more than its rated load for a few seconds. This might be 3 times or even 5 times for larger machines (diesel gensets). As it is real power, the engine must also be able to do that too, though inertia of the engine and its flywheel is often enough. With generators fitted with an inverter the engine can be idling when the fridge comes on. There is a power delay as the engine speeds up. If this is the case, run the engine fast, even with little load. There is usually a switch.
Is altitude an issue? As it affects power of the engine, it may not be able to recover form the surge in some cases. Ditto fuel quality, exhaust restrictions, air intake restrictions. The engine slowing during a surge shows that the issue is real power. Also make sure the generator is running at proper speed/frequency, even a little fast rather than a little slow.
Capacitors act as reservoirs with DC supplies (they would be huge at this power level, and batteries are much better). For AC power they might act as a reservoir on a cyclic basis, but there is no purpose there. They can correct inductive power factor, or if too big, make capacitive power factor.
The fridge has a power factor (PF) which means it draws more current than the real power suggests, hence "apparent power". This does not require more power from the engine. Adding a capacitor of the right size could correct the power factor of a motor, and allow a lower current during running, but this gets complicated during a motor start as the power factor is changing rapidly and anyone's guess. I doubt it will make much difference. The power factor does not affect real power. It is about wire thickness.
The generator is rated for power factor too. It means it can deal with a higher continuous current than its continuous kW rating implies, and this shows up as a KVA rating, more than the kW rating, or a kW rating with a allowable PF. The relationship between power factor and power is:
KVA = kW / PF
The generator specifications might state surge, kW and PF and KVA ratings. It doesn't seem common for small ones. All the considerations mean that the rating of a generator in KVA that can start a fridge will be a lot more than the fridge rating suggests. A rating in kW is better, but still not going to reflect the surge capability. Even if the generator is specified properly, the fridge is not specified. We can only make assumptions based on experience. I have a 230V 3KVA inverter generator and it can start a large fridge. This is around what is required.
Reducing fridge power:
You could play around with taking door heaters off if it seems to be almost working. I have seen stories about adding 'hard start' circuits. This is an extra start capacitor switched in automatically with a capacitor run motor (single phase compressor) applied to get the phases of the start and run windings closer to 90 degrees during starting, for more starting torque. The theory is this reduces the overall current if done properly, as the current in the split phases is spaced appropriately for less overall current. It is not going to be a dramatic difference, but it might be enough in some cases. I have also seen a resistor soft start idea (resistor switched out after start). There are also specialised electronic soft start circuits. These might work, but the starting torque of the compressor motor is reduced too. Will the fridge still work? It is all too vague. Some of these ideas could have success, especially if it was already "almost there". Note that the exact instant the compressor is switched on relative to a mains cycle has an effect on the starting surge.
Best to get a suitable generator, maybe on the proviso it will be returned if not suitable. Run it for hours, keeping an eye on things to make sure. All the other solutions are "maybes".
Another solution, that might make sense in some situations, is a battery and inverter. Get a 3kW inverter. and 12 or 24V battery for example, and charge this battery with the generator. Not cheaper, but might have some advantage. Some generators have a 30A charger built in. This might just be enough to keep an efficient fridge running. Otherwise a mains charger is needed. Do your homework for this one. A battery only delivers about 70% of what goes into it..
- biire2uLv 76 years ago
The old style, pre- electronic wash machines used that same principle. They had a relatively small motor and used one or two huge capacitor's to get the motor going.
Those capacitor's save up the maximum amplitude on the voltage sine wave (120V) and bleed out the power when the amplitude reverses each 1/60 th of a second.
You might luck out, but I'm not sure if the AC compressor motor is an induction motor like the wash machine motors are so check out how to wire the capacitor in the circuit first and if it works with a compressor motor. It should, come to think of it, a lot of compressor's have capacitor starts s I can't see why a refrigerator compressor would be much different.
You did say the running wattage of the generator is enough to keep the fridge going..right?
- 6 years ago
No the capacitor will not make it possible. The fridge needs to run on a certain amount of power and your generator gives off a certain amount of power. This means that the generator only provides a certain amount of energy for certain amount of time where is the fridge needs more. The only way to make up that difference is to increase the amount of energy generation per unit time. Capacitors themselves don't produce any energies they just store it releases suddenly therefore it may be able to start the fridge for a little bit but it won't be able to continuously run it. Also don't try this, because if you power a compressor on short cycles, this is the fastest way to destroy a compressor. You just need a bigger generator.
- psYALv 66 years ago
A capacitor won't work because its storage capacity is far too low. A lot of batteries might work if it is a DC fridge. If it is AC then a capacitor or batteries will only explode if anything; it's not a match.
Your best bet is a large power resistor and a switch, or a high wattage rheostat. Assuming 120 volts, they would be somewhere in the ballpark of 10 to 100 ohms and 1000 watts for either one. You use it to reduce the power sent to the fridge from the generator, then after the fridge motor gets going you gradually provide more power to it. That will keep you from overloading the generator.
In the case of the rheostat you wire it in series with one of the power leads and slowly turn the dial until you finally reach zero ohms. For the resistor you do the same, with a switch in parallel to it. So once the fridge starts cranking slowly then you flip the switch for full power. You might do multiple resistors in series with eachother for more gradual steps.
"In series" means you select one of the generator output wires and cut it. Or if you want to keep it intact, do this with an extension cord that you connect to the generator. Each of the two leads on the power resistor or rheostat gets soldered to one of the cut wires. Each of the two leads on a 10 amp switch (assuming 120 volts), gets soldered to the same two spots. The switch begins off. If you use a rheostat then you don't need a switch; you adjust the dial on the rheostat instead. Start it at high resistance and gradually reduce to zero.
As always be careful around high voltage. Heat shrink tubing is a good way to cover dangerous bare wire. Electrical tape might fall off over time. Also be aware that the power resistor or rheostat will get hot until a few minutes after you bypass the power resistor or turn the rheostat to zero.
- How do you think about the answers? You can sign in to vote the answer.
- 6 years ago
Add more power voltage amps with increase high power socket switches or wires.If it's capacitor consume low power consumption then check it with stabilizers.Normal mode can find easily with help of stabilizer.