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PARALLEL

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kwame

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Hi folks
i want to learn about how to wire two gasoline generators with identical voltage and current rating in parallel , to increase the combined current output.
Thanks
kwame
 
Wiring in parallel is easy. Making them run in sync is tricky.
Be very careful. You'll need minimum a filament lightbulb and nerves of steel.
 
How big is your generators?

If they are like toys for show in classroom, then there should be no problem.

For bigger generators (like really big ones) you need instruments to ensure that the phases goes in same direction, that the voltage is equal, and that the phases is in sync.
 
The gen sets Are 4Hp apiece from the same producer,single phase

.I want to harness the current from both simultaneously
 
I suggest you check Northern lights or Onan literature to see how they get them in sync and the same rpm.
 
How do you start the generators?

Will the voltage rise as the motor gains rpm? Or is there a switch that connect the generator to load when stable rpm is reached?

If the first is true, and if you can manage to start both of them in the same moment, you could try to connect them together before you start them up. Still, you are in risk of damage the generators unless they are both fused properly.
 
i'm not convinced that starting them together would be successful. are you suggesting that they will sync themselves as they come up to speed?

Kwame - there's a trick sometimes used where you adjust the throttle & use a lightbulb connected between Live A and Live B to check that there's no voltage between the two phases....when the bulb goes out, you throw the switch connecting the two together.
IF you end up taking this approach (having researched in more detail than I'm providing) then I recommend using two lightbulbs, so that if one blows you won't don't make a big mistake & get a firework display
 
Hi folks
i want to learn about how to wire two gasoline generators with identical voltage and current rating in parallel , to increase the combined current output.
Thanks
kwame

Well kwame I think that this is one of those things that looks good on paper and makes sense on paper but is not a very good idea to try in real life.

As mentioned the biggest problem is sync. I have a 4 KW generator gasoline powered out in my shed. When I first got it I did some experimenting with it and it did pretty much what it was supposed to do. It provided 120 / 240 VAC and for here in the US 60 Hz.

The frequency of an AC machine is expressed by the formula:

F = (P * N) / 120

where F = Frequency, in hertz
P = the number of poles of the generator rotor
N = the speed of the generator rotor (in RPM)

When synchronous generators (alternators) are connected in parallel with each other on an AC grid, they are all operating at a speed that is directly proportional to the frequency of the AC grid. No generator can go faster or slower than the speed which is proportional to the frequency.

There are great magnetic forces at work in the synchronous generator to keep the rotating magnetic field of the generator in locked synchronicity with the magnetic fields induced in the stator winding by the current flowing in the stator windings. These forces keep every generator's rotor locked in synchronous speed with the frequency of the grid with which they are connected.

As per the above formula, a 2-pole generator producing an output frequency of 60 Hz has an engine speed of 3,600 rpm. To change the output frequency to 50 Hz for the same generator configuration, the engine speed needs to be reduced to 3,000 rpm.

So we know the frequency is a function of rotational speed. My generator is happily running along but I did notice the output frequency was about 60 Hz. I say about because it would vary between 58 and 62 Hz which is no problem really. If my heating furnace blower would come on the gasoline engine would load down and return to normal speed. Again, no problem but when you try to parallel two, even two identical units the gasoline engines will not respond the same to changing loads. A speed control governor controlling a gasoline motor with changing loads is not an exacting science. Doing what you want to do is not as easy as it initially looks on paper, believe me.

Try a little experiment. You mention I believe 4 horsepower single phase generators. My rough guess is 2KW units. Run a single unit and place a few assorted loads on it. Note the sound of the engine as it loads and returns to speed. Now do the same with the other unit. I will bet they each respond slightly different to the changing loads. This is why I have doubts as to ever getting these two independent units in sync with the same voltages out.

Just My Take...
Ron
 
What are you running off of them? If it's something like a heater you could just rectify the outputs. Brushed motors will also work fine on DC.

Mike.
 
Unless they're inverter generators specifically disigned to be synced, you absolutely cannot connect them in parallel.
 
Oh wait, I have it all figured out. Just go to the store and buy one of these, I am sure you can get a 240 VAC 50 Hz model. Only $650 USD. That is option #1.

Then we have option #2 which is just a tad more complicated. First we take the outputs of your two generators and convert the 240 VAC 50 Hz to 12 VAC 50 Hz. Now to be safe I like to overrate everything. I estimate you have 2 KW generators based on the 4 HP. So I figure a pair of 5 KVA transformers like these units. They only cost about $900 USD each and you may want a truck to move them around. Then off each transformer build a nice full wave bridge using stud mount diodes and add a few large capacitors as generator power is sort of dirty. Now just parallel the two 12 VDC lines and hope the generator regulation is happy with that and they don't try to compete. So now we have 12 VDC and a pile of amps. Finally just buy a nice 6 KW (remember I like to overrate) inverter. **broken link removed** which only cost about $600 USD. All said and done I figure a little under $3,000 USD including shipping (darn transformers are heavy) and you are done. Granted not as inexpensive as just buying a new larger generator but when all connected if it doesn't smoke it will be really, really cool and impressive.

Option #3 is run with what you have and divide the loads off each generator independently. The good news is during low demand you only need to run a single generator the bad news is you will need a small mountain of extension cords. As NorthGuy mentions, unless what you have are designed to be synched you cannot connect them in parallel. Generators designed to be synched are expensive and usually much larger than what you have. I would choose option #3. There is no practical or easy let alone inexpensive way to do this. Like I mentioned earlier looks good on paper but just won't work.

Now on a serious note, the 4 KW generator I mentioned earlier easily supported our home during a power outage. My wife's mother was totally invalid and as medical machines came into the house I had concerns about power outages. I could run every lamp in this house, all the medical equipment, home computers and the medical equipment and the furnace on about 3 KW. A big pain was it, unlike the new units, only had a 1.5 US Gallon gasoline tank. I needed to fuel it every two hours. It was also 8 HP pull start and all transfers were done manually. However, on a few occasions it was literally a life saver. Today we have a whole house fully automatic system with automatic transfer. Power grid drops out and in 8 seconds we are totally back to normal. It runs on natural gas so no fuel tank or gasoline storage needed. With 18 KW I can help my neighbors during long outages which is nice. Anyway, that little old 4 KW unit sure worked out great when it was needed.

What exactly is your goal? What do you plan to run? How often and how long?

Ron
 
Serious note: Remember to tell your electric company when generators are installed. You may not be allowed to install if your generator is able to feed into the power grid.

There have being at leat one known fatal accident here in Norway the latest years because somebody has hoocked up a generator to their power intake in the house, and one of the crew from the local electric company has died because there was still voltage at the primary side of the transformer (22kV).
 
Serious note: Remember to tell your electric company when generators are installed. You may not be allowed to install if your generator is able to feed into the power grid.

There have being at leat one known fatal accident here in Norway the latest years because somebody has hoocked up a generator to their power intake in the house, and one of the crew from the local electric company has died because there was still voltage at the primary side of the transformer (22kV).

Real good point. Every year we see people in the US running all sorts of dangerous back feed systems. Article 702 of the US NEC (National Electric Code) clearly defines the required compliance of optional standby systems. Here is an example of a guy doing it the correct way, note how the lockout works. I was totally blown away by the number of Utube videos I have seen out there with people doing it all wrong and totally unsafe.

Ron
 
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