Backup Generator Overload protection

[wanderer]

I purchased a Allmand Light tower with 6KW diesel generator built in. It's a pretty cool unit, and I'm really happy with it. Problem is that the power output function only had a 15A breaker on it, so I had to upgrade the wiring and breaker to a 25A. For a variety of reasons, I installed a small two circuit panel on the unit and installed a 2 pole breaker that feeds both the lights and power outlet.

What I am wondering is the sensitivity of a household breaker for generator protection. I have noticed that I can overload the breaker slightly for a short period of time with no trip. Maybe this isn't a big deal, but my impression is that these light tower units were "value engineered."

Is there a difference in the sensitivity of a household type breaker that would make it undesirable for protecting the generator?

 

[mm08822]

My first concern is that the 6000w rating may have been peak and not continuous. Be wary of marketing hype. Hopefully you have this info.

The trip curves for breaker families can vary. Those with delayed trip curves (in the magnetic region) are for special applications such as high motor inrush. In comparison to a standard trip curve found on the common run of the mill cb protecting most residential branch ckts.

What did you remove (mfr/part #) and what did you install?

 

[wyliesdiesels]

rated 6KW but only has a 15a breaker?

Do you have a link to a manual?

 

[wanderer]

The manual is confusing. It ways is a 240v DC output (IT'S NOT). Remember that it's a light tower. AC power output wasn't a priority. Interestingly, if you pulled 15 amps from the outlet at the same time the lights were on there was nothing to prevent you from overloading the generator at all, the lights have no breakers on them and the outlet was "added on" to the L1 and L2 feeds of the light switches. You could pull 15 amps from AC power at the same time your drawing 1250 watts from each light (4).

http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=jehmtDX-nfBhU7y

 

[wanderer]

My first concern is that the 6000w rating may have been peak and not continuous. Be wary of marketing hype. Hopefully you have this info.

The trip curves for breaker families can vary. Those with delayed trip curves (in the magnetic region) are for special applications such as high motor inrush. In comparison to a standard trip curve found on the common run of the mill cb protecting most residential branch ckts.

What did you remove (mfr/part #) and what did you install?

No, it's 6kw continuous. Load from the lights would be 5kw. PF of 1. 1800 RPM diesel generator with kubota engine. Pretty slick little units, and cheap. I gave $700 for mine with 2000 hours. 70 hour run time under load with the on board tank.

 

[mm08822]

I’ve seen various protection schemes on generators – some protecting gen from total output overload and yours which is not the best from the factory.
There are 4 breaker/switches for the lights. So 4@ 1250w = 5000w
Plus
15a 120vac recept = 1800w (or less)
If all lights on and recept loaded full tilt, total load ~ 6800w . Not so bad.

But…..
there is also a 240 vac recept, breaker size =?. This too, can also be fully loaded with the other full loads. This is where the issue is with the original wiring allowing gen overload.

If you rewired this so terms 6/7 provide 240vac (thru a 2 pole 25a “main”cb) and term 5 provides a center-tapped neutral (6-5 =120vac & 7-5 = 120vac) overall gen output is properly limited. (term 5 = term "G".)
Then using the branch cb’s downstream of the “main”, you can properly protect each branch circuit according to wiring size/recept size.

Still need mfr/part # info.

 

[wanderer]

I posted the link to the panel. The original wire for the generator was (4) 1250 watt lights plus (1) 15A 240v twistlock plus (1) 20A 120v outlet. the outlets had breakers but not the lights. All were in parallel. that's why I rewired it. I guess it's not an issue since most people don't use these for power.

Now the generator output is directly wired to the incoming lugs of the two pole circuit breaker I mentioned, and the output is wired to the 30A twistlock and lights, which are downstream of my 25A breaker.

My only concern is that the breaker won't be sensitive enough to overloading the generator since it wasn't intended for this purpose. I already did it, but have noticed that it will allow light overloads of a few amps without tripping.

 

[mm08822]

I know you posted the manual and I’ve already looked at the w/d on page 62 – it was missing details.
You have now just replied with the full details for what the maximum imposed load on the generator could be. “(4) 1250 watt lights plus (1) 15A 240v twistlock plus (1) 20A 120v outlet.”

The original overload potential was worse than I first understood. Based on that - it is a moot point needing mfr/part #’s of any original cb’s. There is no usable data to be had from the original wiring scenario to be able to compare overload protection against the new wiring/components.

Call the mfr.

What is the mfr/part # of the 25a 2pole cb you installed? That trip curve should be available.

 

[wanderer]

Yes, I was shocked when I figured out what they did. It's mind boggling. how overloaded it could be, with no circuit breaker either!

This is the breaker I installed, directly to the generator leads:

https://www.schneider-electric.us/e...category-id=50300&parent-subcategory-id=50310

https://www.homedepot.com/p/Square-...r-Main-Lug-Load-Center-HOM24L70RBCP/100194428

I put it in the above enclosure.

I don't see a load curve. I guess the biggest question is that it occurs to me that a circuit breaker is intended for circuit overloads, and I am asking it to protect a motor (generator). I originally assumed they would be similar, but now I am wanting to make sure that they are the same.

 

[mm08822]

this is for a qo, but HOM's have the same internals.
http://download.schneider-electric....+curves&p_File_Name=730-5.pdf&p_Doc_Ref=730-5

Call mfr and ask what the surge rating/duration of gen is.

 

[Lamakocklee]

Hmm.. I was wondering..

If the this was built like I am thinking, it would run out of motor before running out of copper. In other words, overloading the generator for any appreciable amount of time would stall the engine before damaging the generator. The only way to find out would to to get the continuous rating of the generator. And then find out how much horsepower you are driving it with at the 1800 rpm.

If the outlets are all protected by breaker, the the only risk is damaging your loads if the voltage/frequency was to drop out to much.

What do you guys think?

 

[wanderer]

Thanks, that does answer my question! I’m thinking I’ll leave it alone.

 

[wanderer]

Hmm.. I was wondering..

If the this was built like I am thinking, it would run out of motor before running out of copper. In other words, overloading the generator for any appreciable amount of time would stall the engine before damaging the generator. The only way to find out would to to get the continuous rating of the generator. And then find out how much horsepower you are driving it with at the 1800 rpm.

If the outlets are all protected by breaker, the the only risk is damaging your loads if the voltage/frequency was to drop out to much.

What do you guys think?

https://www.allmand.com/content/dam.../Marathon_Generator_Troubleshooting_Guide.pdf

This is the gen head. Engine is a Kubota d905. I think there is some head room. 13.4hp I think. Voltage was pretty stable during overload. 115v and 58hz at 30 amps.

 

[Lamakocklee]

Here is some fun reading.

I am not a generator expert but I do find this stuff quite fun.

https://www.smokstak.com/forum/showthread.php?t=55097

This helps make everything clear as mud.

I myself have a little 8 kva rated generator head mated to a small cat (perkins) powerpack diesel engine. Best time to test it is in the winter so that the generated electricity doesn't go to waste