How good does your generator regulate voltage?

belfert · September 29, 2019, 06:49:08 PM

I'm trying to figure out if my 8KW Powertech generator is regulating voltage properly or not. With no or minimal load it shows 125 volts. With a single large load like battery charger or an A/C unit it will drop to about 120 volts. A second large load will drop it to 115 to 116 volts. Two A/C units and battery charger drop it to around 110 volts.

This seems low to me, but I don't know if it is normal or not. I ordered a new $350 voltage regulator when voltage was getting down close to 100 volts, but I found the neutral and grounds were loose at the generator. My voltage is better after fixing the loose wires, but not great. I decided not to open the regulator box yet so I could send it back for a refund if I don't need it. Once the box is opened I own it.

bobofthenorth · September 29, 2019, 07:27:36 PM

Measure a wall socket in your house - its probably 110 right now so I wouldn't consider that "low". Below 100 I'd get worried but as far as I'm concerned anything over 100 isn't going to hurt anything.

dtcerrato · September 29, 2019, 08:09:27 PM

Ditto on what BOTN said... Send the regulator back. Don't waste your $$$. IMO

luvrbus · September 29, 2019, 08:28:09 PM

That is probably a little Cat (Perkins) engine on the Powertech take it to Cat and have them give it more fuel and check the governor control then it will hold steady voltage ? when is the last time you changed fuel filters .A voltage regulator maintains a constant level of voltage if the voltage is not there the regulator cannot control the voltage,ship the regulator back that is not your problem

belfert · September 30, 2019, 04:13:10 AM

At 107 volts the main breaker on my generator was popping due to increased current draw from low voltage. My home power is at 119.8 volts. The standard is 120/240. A study was done in the 1970s that showed average voltage across the USA at 117 volts. 100 volts is way low. I see Cummins Onan diesel RV generators claiming their voltage doesn't vary more than .5%. I'm varying more in the 10% to 15% range.

Clifford, thank you for the thoughts on the Cat/Perkins engine. I would have never thought about it being an engine issue. I have not had the fuel filter changed in many years. I'll start with the fuel filter and then take it to the local CAT dealer if necessary.

Geoff · September 30, 2019, 06:38:31 AM

My 8kW Isuzu generator acts the same way, so so I have it at a little over 1800 rpms so as more components are turned on the voltage stays higher longer. I run two 15k roof airs, but if I also use the microwave the gen bogs down. However, if the load is too great my Trace SW2500 kicks in and boosts the voltage back to 120.

So it's not the make of your engine that is at fault, it is just marginally powered. A 10-12 HP generator would take the added load better.

Geoff · September 30, 2019, 06:43:33 AM

My 8kW Isuzu generator acts the same way, so so I have it at a little over 1800 rpms so as more components are turned on the voltage stays higher longer. I run two 15k roof airs, but if I also use the microwave the gen bogs down. However, if the load is too great my Trace SW2500 kicks in and boosts the voltage back to 120.

So it's not the make of your engine that is at fault, it is just marginally powered. A 10-12 HP generator would take the added load better.

belfert · September 30, 2019, 07:47:06 AM

But, it shouldn't be falling from 125 volts to 120 volts just by running one thing. Nor should it fall down to 115 to 117 volts by running two things. Two A/C units can only pull a max of 4,800 watts out of 8,000 watts. More realistically, two A/C units should be around 3,600 watts. I understand that an 8 KW unit can't really run three A/C units, but I can't even two A/C units running without starting to see issues.

Yes, a larger unit would be better for my needs, but I don't have $10,000 right now for a new unit. I am going to try a new fuel filter first thing.

Geoff · September 30, 2019, 08:02:15 AM

I can run three 15k rooftop airs that pull 9 amps each. So I'm guessing I can pull 30 amps without the inverter kicking in. I did have low power with my generator a few years ago and it turned out to be the injectors had clogged tips.

Also, your governor should increase the fuel output under load. Can you hear it get louder as the load increases?

belfert · September 30, 2019, 09:14:59 AM

Yes, I hear the generator load change briefly when a large load like an A/C unit starts up. I'll have to take it to the local Cat dealer if a new fuel filter doesn't help. I don't think I have changed the fuel filter in at least 1,000 hours. I change the oil yearly and really should change the fuel filter yearly like the bus.

Oonrahnjay · October 01, 2019, 08:10:04 AM

Quote from: belfert on September 30, 2019, 07:47:06 AMBut, it shouldn't be falling from 125 volts to 120 volts just by running one thing. Nor should it fall down to 115 to 117 volts by running two things. Two A/C units can only pull a max of 4,800 watts out of 8,000 watts. ...

Brian, I think that what you have here is a generator that's marginal on its output (as others have said, probably because of an engine in the generator that's being starved for fuel). But I sometimes have to plug my bus into a 15Amp 120V outlet that's some distance from the breaker box. At the breaker box, a "Kill-a-Watt" meter (not great, but OK) will show me 122V. At the socket, it will be 119V and in my bus (using a 10Ga heavy duty 25 ft. outdoor cord) it will be 119V with no 120V loads in the bus. However, if I run my 12 watt microwave, the voltage on another socket in the bus may drop to 114 - 115V. As soon as the microwave dings, it's right back up to 119V again. Obviously, there isn't enough power available in this condition to do much more than run the fridge and keep batteries charged - any loads under use in the bus have to be very carefully managed; but it's all that available and it works in a pinch.
So, your performance isn't far out of range of what I've seen when forced to use a weak system. And with this in mind, I'm wondering if maybe your generator is putting out OK but part of the problem is voltage drop in the system between the generator and the sockets on your bus. Maybe your main cables from the generator got spec'd a little too small, maybe there's a connection or two loose, maybe corrosion in connectors or breaker box. Is there a transfer switch in your system that might be causing excess resistance?
In my opinion, your voltage supply isn't really up in the good range but it's not terrible. If the voltage at the generator is OK and low at the sockets, I'd look at the system between the two. If the voltage at the generator sags along with the voltage at the sockets, then it might be a poorly running engine on the generator.
Good luck on running this down, but I don't think it will work out to be a terrible problem. After all, the power companies started putting out 120V in the 1800s, but appliances were rated at 110V because that was what was expected at the users' sockets. Only in the past few decades has technology advanced enough that we're actually seeing 120V in homes or offices so that appliances are rated at 120V.

belfert · October 01, 2019, 11:35:17 AM

If the voltage stayed consistent at 120 volts I would have no concern. I should be able to run two A/C units without the voltage falling by 10 volts. Two A/C units should not be overloading the generator.

richard5933 · October 01, 2019, 11:46:57 AM

What was the ambient air temp while this was happening?

My 45-year-old Kohler 12.5KW usually can handle both of my a/c units along with the water heater and battery chargers with a drop of 7-8 volts with everything running. I noticed this weekend while in Blytheville that as the daytime temps climbed closer to 100 my voltage dropped a few volts more. Not sure if it was the extra continuous load on the a/c units or if it was the heat itself affecting the generator's regulator. Engine temp stayed constant, but the compartment temps had to be climbing as the ambient air temps climbed.

luvrbus · October 01, 2019, 11:58:18 AM

Quote from: richard5933 on October 01, 2019, 11:46:57 AM
What was the ambient air temp while this was happening?

My 45-year-old Kohler 12.5KW usually can handle both of my a/c units along with the water heater and battery chargers with a drop of 7-8 volts with everything running. I noticed this weekend while in Blytheville that as the daytime temps climbed closer to 100 my voltage dropped a few volts more. Not sure if it was the extra continuous load on the a/c units or if it was the heat itself affecting the generator's regulator. Engine temp stayed constant, but the compartment temps had to be climbing as the ambient air temps climbed.

Tempature affects the amp draw for the AC units and the generators will lose watts at altitude and higher temperatures,my ESP generator will not drop a 1/2 volt with all 5 roof tops going in 115 degree heat above 115 it will drop 1 volt or 1.5 volts

Lee Bradley · October 01, 2019, 01:13:27 PM

What Bruce said. As long as the rpm recovers the voltage should be OK. I would start checking voltages from the generator to the load at each connection and find where the voltage drops are occuring. If your multi meter reads cycles/sec that will tell you if the generator is actually recovering to correct rpm under load.