Parallel portable generators

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jeremiahfpoa

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I would like to use two portable generators to feed the same buss - I don't think it's possible, but wanted to be sure. If it's not, I'm trying to understand why not.

Thanks
 
If you set them up with synchronizers, load share modules, voltage regulators, etc ... like a regular paralleled generator project, then all is good. Generally with portables, that is difficult.
 
Here's a question that may help the OP (or not), but I'm asking the rest of you and not him. What if he fed each genset to a seperate leg of a subpanel? I'm guessing this would fall outside of the UL rating? Obviously there is the potential problem of installing a double-pole breaker which would have two out-of-phase legs.
 
techntrek said:
Here's a question that may help the OP (or not), but I'm asking the rest of you and not him. What if he fed each genset to a seperate leg of a subpanel? I'm guessing this would fall outside of the UL rating? Obviously there is the potential problem of installing a double-pole breaker which would have two out-of-phase legs.
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How would you handle the neutral?

You would still be out of sync. if you had any line to line loads.
 
techntrek said:
Here's a question that may help the OP (or not), but I'm asking the rest of you and not him. What if he fed each genset to a seperate leg of a subpanel? I'm guessing this would.fall outside of the UL rating? Obviously there is the potential problem of installing a double-pole breaker which would have two out-of-phase legs.
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This would only work if all loads were 120 volt, with no 240 volt loads.
240 volt loads could not be supplied because the two generators would have to be exactly 180 degrees out of phase, even if this was achieved it would not be possible to maintain the two generators 180 degrees apart.

Also, if the two generators happened to be in phase, as would certainly happen at times, then the neutral current would be twice the line current, with the potential for overloading the neutral bus.
This might be acceptable in the case of small generators feeding a large panel. For example if two generators each with a 120 volt, 30 amp output were used to feed a 60 amp or larger panel, it would be OK.

I read of someone doing just this after hurricane Katrina.
They used two different size generators one to feed each side of a 120/240 volt panel.
The larger generator supplied fridge, freezer and window A/C units.
The smaller unit supplied computers and TVs.
The total output was far less than the panel rating, therefore no risk of overloading the neutral.

In general though I would advise against useing two generators to supply a panel, too much risk of mistakes, better by far to use a single generator of sufficient size.

Portable generators cant be parraleled unless designed for such use, which is very rare.
Honda make a portable generator that can be paraleled with another similar unit, useing a special lead supplied for the purpose, but this is not the norm.
 
jeremiahfpoa said:
I would like to use two portable generators to feed the same buss - I don't think it's possible, but wanted to be sure. If it's not, I'm trying to understand why not.

Thanks
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Well you can if you want to .
I would not do this but if you like to try it ?

This is how they did it in 1889!

Heres how both need to be the same voltage and wattage you need a switch to connect both generators to each other at the same time when in sync.

Start one generator up and connect a light or lamp between same phase leg of gen no. 1 to gen no. 2 if there out of phase then the bulb will be bright adjust speed of gen no. 2 until the lamp gos out . Do this on single phase or three phase gensets .

Your now in phase you can use a volt meter to do the same no voltage your in phase . Any voltage on meter your kinda out of phase now if your lamp is going on/ off its close to sync when each leg is in synchronized throw your switch on the strongest generator will pull in the weakest generator in to synchronization .
If your not in sync dont throw that switch you will damage the gensets and the loads do to overvoltage and bucking voltage meaning shafts start to break in the weaker generator .

So yes you can but its not a pretty picture if your not in synchronization !!
 
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jeremiahfpoa said:
I would like to use two portable generators to feed the same buss - I don't think it's possible, but wanted to be sure. If it's not, I'm trying to understand why not.

Thanks
Click to expand...
Well you can if you want to .
I would not do this but if you like to try it ?

This is how they did it in 1889!

Heres how both need to be the same voltage and wattage you need a switch to connect both generators to each other at the same time when in sync.

Start one generator up and connect a light or lamp between same phase leg of gen no. 1 to gen no. 2 if there out of phase then the bulb will be bright adjust speed of gen no. 2 until the lamp gos out .

Your now in phase you can use a volt meter to do the same no voltage your in phase . Any voltage on meter your kinda out of phase now if your lamp is going on/ off its close to sync when each leg is synchronized throw your switch on the strongest generator will pull in the weakest generator in to synchronization .
If your not in sync dont throw that switch you will damage the gensets and the loads do to overvoltage and bucking voltage meaning shafts start to break in the weaker generator .
 
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Another concern is that when you put two generators in parallel, you essentially double the amount of fault current that can be supplied to the panel to which they are connected. Have you verified that that panel can handle the higher fault current.
 
Interesting that (no one says) its not against code or UL rating to supply one panel with two sources. I expected an immediate "no"! :)
 
charlie b said:
Another concern is that when you put two generators in parallel, you essentially double the amount of fault current that can be supplied to the panel to which they are connected. Have you verified that that panel can handle the higher fault current.
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This could be a large issue...

techntrek said:
Interesting that (no one says) its not against code or UL rating to supply one panel with two sources. I expected an immediate "no"! :)
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I was thinking the same as I was reading this thread.


I understand trying to save money, etc... but I have a hard time wrapping my thoughts around some of the ways people try to save money.
 
techntrek said:
Interesting that (no one says) its not against code or UL rating to supply one panel with two sources. I expected an immediate "no"! :)
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I had presumed (bad thing to do) that the OP meant that there would be a synchronizing panel ahead of the one panel to get two sources. If you meant that you use one "main breaker" on a panel to connect one generator, and use a second "main breaker" on the same panel to connect the other generator, then the panel in question will have to have been designed for that configuration.
 
For small consumer grade generators, don't even try this. You will probably blow up one or both of the generators. The only exception I know of is the Honda brand of inverter generators. Indicated by EU in beginning of the model number. They sell a specific cable that allowes the generators to sync to each other automagically.

Larger, much more capable portable generators can be run paralleled, but you have to get models that are capable of this, and additional equipment and operators from your generator rental company. Lots of hassle and easier to just upgrade to a generator capable of powering the load by itself.
 
dalesql said:
automagically
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I'm gonna use that one! It'll be great for management and nosy operators that won't understand your answers any way.

brian john said:
What do you think the utility does nationwide. Multiple generators supplying the loads. Paralleling generators is a a VERY common practice.
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But theirs aren't portable ;) :grin:


No one's mentioned a sync. with mechanical linkage (belt/chain)?


Now that my wackiness is on hiatus... Do the inverter gen. sets have built in fault monitoring, and are hence current limiting? ( I would assume anything of even median quality would. )

Regards,
Doug S.
 
charlie b said:
Another concern is that when you put two generators in parallel, you essentially double the amount of fault current that can be supplied to the panel to which they are connected. Have you verified that that panel can handle the higher fault current.
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Considering the tone of the posts, what do you think this guy is paralleling? - a pair of 100kw 208V 3ph into a house panel? I would doubt it, but even if he was, that's about 250A Fla each, probably .20 - .25 Xd'' - say 2500A tops for the both. I really don't think there is a problem here.

cf
 
Doug S. said:
But theirs aren't portable ---
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Just in your mind. i'm currently working with a pair of 800kw, on trailers, self contained, even a fuel tank. You really need to get out of this Coleman/Briggs mindset.;):grin:
Doug S. said:
--- No one's mentioned a sync. with mechanical linkage (belt/chain)? ---
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Never seen one, and I wouldn't think one ever would. For this application, one could assume the gen sets are not electronic feedback allowing positive rotor lock - rather it is likely they are in droop. They will load share fine, just not perfect. That means the power angle is not the same, so the rotors will not be in the same postion.

cf
 
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