Generator running two AC units, outlet appliances get hot

[Jackie_Treehorn]

I have an Onan 5500 with about 240 hours on it right now which is supposed to run two rooftop AC units, but I can only get it to run the primary unit and not the bedroom. Both units work fine when I'm hooked up to a 30 amp circuit.

I also notice that when I have the generator on, anything I plug into an outlet (like a cell phone charger) gets pretty warm to actually hot, and that happens in a short period of time.

Any guidance on what I should be doing to correct the above is appreciated.

[wildmanbaker]

As others have said, you should be OK at 118 volts. If you have a microwave with a digital clock, start the generator, set the clock, and check how close it is to your watch, or clock for 10 minutes. If it is running fast or slow, load the generator with an AC and check again. If it is within a minute or two, your hertz are close enough to not cause problems.

[jhilley]

I don't think you have any thing to worry about with your generator. Just change the oil and fuel filter and you should be good to go. As long as it maintains 118 volts under load it is fine. Depending on your volt meter, the accuracy might be between .2% and 5%. Even a high quality .2% accuracy meter is 2.4 volts AC.

[BigRabbitMan]

You do definately need to have someone who is knowledgeable and has the right test equipment (good multimeter) and knows how to use it. That may be you, but probably not.

The risk to you is that if the controller is malfuctioning it could cause voltage problems that will damage the various electrical items in the coach. If that happens, it will be much more expensive than having the generator looked at/repaired by a knowledgeable person.

As a "do it myself" person, the most important thing is to know when I do NOT know how to do something. Know what you know, and know what you do not know.

[tropical36]

Jackie Treehorn wrote:

tropical36 wrote:

wildmanbaker wrote:
You should be all right at 118v. You should not get into trouble until about 110v or less. The voltage went up when you loaded the gen, and the governor called for more power from the engine, more rpms.

I'd say it has more to do with the regulator which may be automatic and yes the engine speed might appear to increase when actually trying to maintain it, but the RPM must stay within limits to produce the 60HZ required frequency, as per the formula....Generator Frequency (f) = Number of revolutions per minute of the engine (N) * Number of magnetic poles (P) / 120

So if I'm reading between the lines, you both would be looking to take this in to a dealer who services Onans(of which I found one close by if that's the route I need to take)?

That will have be your decision, but it doesn't sound like you have any serious problems as yet and cummings/onan is an expensive place to visit for any reason. I mean if I was looking for reasons with my Generac, I'd probably have to junk it, so I ignore a lot, keep adding oil, restarting when necessary and keep on trucking.

[Jackie_Treehorn]

tropical36 wrote:

wildmanbaker wrote:
You should be all right at 118v. You should not get into trouble until about 110v or less. The voltage went up when you loaded the gen, and the governor called for more power from the engine, more rpms.

I'd say it has more to do with the regulator which may be automatic and yes the engine speed might appear to increase when actually trying to maintain it, but the RPM must stay within limits to produce the 60HZ required frequency, as per the formula....Generator Frequency (f) = Number of revolutions per minute of the engine (N) * Number of magnetic poles (P) / 120

So if I'm reading between the lines, you both would be looking to take this in to a dealer who services Onans(of which I found one close by if that's the route I need to take)?

[tropical36]

wildmanbaker wrote:
You should be all right at 118v. You should not get into trouble until about 110v or less. The voltage went up when you loaded the gen, and the governor called for more power from the engine, more rpms.

I'd say it has more to do with the regulator which may be automatic and yes the engine speed might appear to increase when actually trying to maintain it, but the RPM must stay within limits to produce the 60HZ required frequency, as per the formula....Generator Frequency (f) = Number of revolutions per minute of the engine (N) * Number of magnetic poles (P) / 120

[wildmanbaker]

You should be all right at 118v. You should not get into trouble until about 110v or less. The voltage went up when you loaded the gen, and the governor called for more power from the engine, more rpms.

[Jackie_Treehorn]

tropical36 wrote:

I'm heading to the Onan website to see if there is an adjustment I can make to bring that voltage down towards 110. It will also be a good time to find out how many hours I should be running it between servicing it-

I like about 125vac at no load so I can hope to maintain a reasonable level when at full load. I think 120v is optimum and hopefully it never drops below 115v, but that's just wishful thinking in a lot of cases.
With some if not all generac gensets, there's a LED on the voltage regulator board, along with the adjustment screw and I drilled a hole in the cover so that I can see it, as it doesn't always have an output and requires restarting. Just saying, in case you feel the need to see this light as well.

That's interesting- no load I'm at 116 to 117 volts at each outlet but once loaded with one or both AC units the voltage goes up to 118. You're saying you wouldn't think the source of the heat for devices using the outlets is the 118 volts?

[tropical36]

I'm heading to the Onan website to see if there is an adjustment I can make to bring that voltage down towards 110. It will also be a good time to find out how many hours I should be running it between servicing it-

I like about 125vac at no load so I can hope to maintain a reasonable level when at full load. I think 120v is optimum and hopefully it never drops below 115v, but that's just wishful thinking in a lot of cases.
With some if not all generac gensets, there's a LED on the voltage regulator board, along with the adjustment screw and I drilled a hole in the cover so that I can see it, as it doesn't always have an output and requires restarting. Just saying, in case you feel the need to see this light as well.

[Jackie_Treehorn]

chuckftboy wrote:
Jersey, the a/c units are sealed systems and unless the PO had fittings installed, there isn't any way to add refrigerant. The original charge was weighed in by ounces, not charged by pressures but you might get close if you have pressure taps.

What's the sweet spot on it if I can't do it myself? We have Camping Worlds that are both about an hour from us but they seem to have a seriously high turnover of mechanical staff and with any other option, we'd take it. I presume there are other businesses who can service the AC units?

[chuckftboy]

Jersey, the a/c units are sealed systems and unless the PO had fittings installed, there isn't any way to add refrigerant. The original charge was weighed in by ounces, not charged by pressures but you might get close if you have pressure taps.

[Jackie_Treehorn]

tropical36 wrote:

While you're at it, check the 20amp breaker on the genset, as it sounds like it's off or tripped and only feeds the rear air. As for other things plugged in to various outlets, they are a separate load in themselves and yes they can draw more current if the voltage is low and produce more heat than normal.

Thanks Trop. It's a new vehicle for me and I'd never taken the cover off the Onan. Indeed the 20 amp was tripped. I can also see I'm losing some oil in there are additional concerns- with 250 hours on it I figured I might have another couple of hundred before doing much but I'll now be "spending some time" with my generator this weekend!

wa8yxm wrote:


Either way.. Voltage may be the problem Press the V button on the Kill-a-watt and report the display.

NEXT is frequency. Many of those small electronic devices are kind of particular to frequency.. Press the Hz button on the Kill-a-watt and report the findings.

Some devices if the Hz is off.. can get very hot.

Wa8- The AC voltage is in fact running between 116 to 118 (more when the AC units are lit up) while the frequency seems safe at a pretty steady 62 hz.

jerseyjim wrote:
Low voltage from the generator? I don't have an ONAN...but do have a 5500 GENERAC, and the owners manual shows a board with an adjustable screw...for voltage.

Jersey-

I'm heading to the Onan website to see if there is an adjustment I can make to bring that voltage down towards 110. It will also be a good time to find out how many hours I should be running it between servicing it-

Thanks to all for all your help- the second AC will come in handy when I'm boondocking on the edge of Death Valley in a few weeks. Do the AC units on the roof have the same LP fittings for adding propellant that I do for my truck? The rear unit seems a little weak compared to the front and I'd like to refresh it.

[Jackie_Treehorn]

wa8yxm wrote:


1: Class A built in like an ONAN or GENRAC usually 5,000 watts or more

I'm going now to check it with just a standard multimeter. It's a Class A with the Onan 5500 watt as part of thye original equipment attached in the basement. If I don't find the answer with the equipment I have I'll find the Kill-A-Watt and check it with that.

Thanks for the help.

[wa8yxm]

therink wrote:
Someone posted about low voltage increasing current causing more heat in connections, Though he is correct,, He has no understanding of ELECTRONICS.

I never said I did.

Where as I have wall paper that says I do somewhere (Sealed in an envelope in the documents safe here in the motor home).

Actually, if the O/P had been talking about a major power sucker like a heater or a vacuum cleaner.. You would be 100% correct. but for a cell phone charger which is drawing on the order of 0.10-0.25 amp. No, the current draw is just not big enough. It just won't draw enough.

Now power supplies come in several types (The cell phone charger is what I call a Power Supply)

1: Unregulated.. These will not get much warmer as voltage changes

2: Series regulated, MORE voltage WILL make them run hotter

3: SHUNT regulated (reare) Same

4: Switching... Anythign is possible with a Switching supply, But generally they shrug off most voltage changes. (Within their ratings)

5 Divider.. These are very wasteful of power and should get hotter as the voltage rises.

I have designed and built two of three of these designs. (The first 3)