Champion Generator not even close to rated output

[CapnCampn]

Continued from here:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29788443/gotomsg/29792553.cfm#29792553

I have a Champion Non-inverter 3500/4000W generator that isn't putting out it's rated output - I've tried running 2 1500W electric heaters on it, and it will bog down and die.

The Gen is model C46540

I did email Champion about the issue, and they had me run electrical checks on the generator side - everything seemed ok, so it appears to them (and me) that it's an engine/hp issue.

I'm at about 2500ft, and they say that the generator will be down about 300 watts at this altitude, so should sustain 3200 watts.
My testing was done with a kill-a-watt and various combos of hi/low settings on the heaters As BFL found, once you get a ways above 1500W, the kill-a-watt starts to complain. I think all the numbers in the table below were from the Kill-a-Watt.

I tested the output with a couple of electric heaters plugged into a power strip using the 5-20R receptacle (not the TT30).

This was at the end of a 40' 12Ga extension cord (it was raining a bit so I wanted to be under cover), using the Kill-a-Watt & combinations of 2 electric heaters with hi/lo settings.

Watts Volts Hz
21 119 64
750 117 61
1220 116 59
1370 116 59
1420 116 59
1930 115 58
2050 115 58
2330 113 56

At the 2300W range, the engine on the generator was working really hard, and starting to lug - you can see this in the frequency column. At one point, it was about to die, and the kill-a-watt actually reset. I turned off a heater before the engine died though.

I feel that this load shouldn't be a problem since it is only ~66% of the generator's rated output, and these are mostly resistive loads (both heaters have small fans of course).

The temp was ~60 degrees, and I am at 2700ft elevation.
I thought maybe it had something to do with using only the 5-20R, but the schematic in the manual shows that both 120V outlets are paralleled, so they should be able to provide the same power, limited by the receptacle specs. The engine/generator shouldn't care which one is being used.

From the engine side, the gas is not new, but has had stabilizer in it, and the oil only has about 2 hours on it. I think I adjusted the valves the spring before last, but I can’t remember for sure. The Spark arrester is clean.

I'm not sure what else to check at this point. Generally it does what I want it to do, but it's a little disappointing that it won't do at least 3KW.

[whjco]

BFL13 wrote:
First suspect is the use of the extension cord(s). I found they increase the "load" as seen by the "source".

This is true of inductive loads but electric heaters are primarily resistance loads. The lower voltage from the extension cord primarily results in lower BTU output from the heater but the load at the generator isn't increased.

However, for an air conditioner unit you're right on target.

Bill J., Lexington, KY

[BFL13]

I just ran a few tests. One was to see if going from a long #12 to a short #10 made any difference for running the 75 amp converter at 75 amps while the inverter/gen is at its continuous rating 1700VA

I could not detect any difference via Kill-A-Watt or sound of gen. I went back to my regular shore power set up for generator using the longer #12.

I did not try an more exaggerated difference in cord gauge like using #16 vs the #10. Somebody else can do that. 🙂

[road-runner]

ktmrfs wrote:

a 40ft 12ga extension cord has a total resistance of 0.12 ohms.

now resistance is 9.8 ohms, or 12.25A or 1470 watts.

not much of an effect.

While I agree with this, and the cord is likely a non-issue, I was just trying to make the point that if the goal is to measure the generator, it's best to make at the measurements at the generator to get any other potential variables out of the picture.

[LittleBill]

pnichols wrote:
The comments on loss of generator power at altitude got me thinking: Some (all?) built-in Onan RV generators have a convenient twist knob labeled as "altitude in feet" to adjust their air-fuel mixture if you need to use them at higher altitudes.

Is this type of easy adjustment right on the generator a rocket science feature? Why don't portable generators have a simple twist know to adjust air-fuel ratios versus altitude?

Messing with jet-changing seems an obsolete solution. I guess fuel injection gets around the need for this, so how does non-fuel-injection Onans do it?

there are adjustable float jets, they can purchased on ebay as well.

[pnichols]

The comments on loss of generator power at altitude got me thinking: Some (all?) built-in Onan RV generators have a convenient twist knob labeled as "altitude in feet" to adjust their air-fuel mixture if you need to use them at higher altitudes.

Is this type of easy adjustment right on the generator a rocket science feature? Why don't portable generators have a simple twist knob to adjust air-fuel ratios versus altitude?

Messing with jet-changing seems an obsolete solution. I guess fuel injection gets around the need for this ... so how is it done on non-fuel-injection Onans ... and why couldn't what Onan did be included on any portable generator?

[ktmrfs]

2112 wrote:
More R = Less Load

An ideal 1500W heater would have a resistance of 9.6 ohms. At an ideal 120VAC it will draw 12.5A. Let's say an extension cord adds 1 ohm. Now R = 10.6 ohms.
120V/10.6 = 11.3A
120*11.3 = 1356W

The extension cord changed a 1500W load to a 1356W load.

a 40ft 12ga extension cord has a total resistance of 0.12 ohms.

now resistance is 9.8 ohms, or 12.25A or 1470 watts.

not much of an effect.

[BFL13]

2112 wrote:

BFL13 wrote:

LittleBill wrote:
resistive loads work different, if the voltage drops, so does the load

Not sure it is the same thing now, but it is still true that when you are plugged into 15a shore power and run things in your RV, you will not pop the breaker so often if you are closer to the house and don't have such a long extension cord. Or if you change from a #14 to a #12 same length, you don't pop the breaker as much.

Isn't it the same thing when you are plugged into a generator's 15a receptacle?

What you are referring to is an inductive load such as your AC compressor and blower motor. They are trying to turn at a certain RPM. You can think of them as a constant power load due to when the voltage drops the current goes up to compensate for the lower voltage in order to maintain its speed. The motor requires a certain amount of power to maintain its torque. The high current demand of the AC causes a voltage drop across the extension cord. This is commonly referred to as IR. This voltage drop means there is less voltage at the AC. The longer the cord or the thinner the wires, the higher the IR.

A resistive load is a fixed load. When the voltage drops the current drops proportionally. One caveat to an electric heater is the coil resistance will change with temperature. It will draw slightly more current when you first turn it on. As it heats up the coil resistance goes up slightly, causing it to draw slightly less current.

Interesting, thanks. I did see that with my Kill-A-Watt running the RV fridge by itself (120v heater) Started out at 359 watts then that fell off quickly to 353 watts before I stopped.

I have seen that where amps go up while volts go down using the inverter/gen and also with the inverter on battery. I thought this was the inverter trying to maintain the watts, but now I am unclear on that from the above description--perhaps it is really the "demand" and not the inverter that makes it do that?

Also what kind of load is the converter/charger for whether the extension cord matters or not?

[2112]

BFL13 wrote:

LittleBill wrote:
resistive loads work different, if the voltage drops, so does the load

Not sure it is the same thing now, but it is still true that when you are plugged into 15a shore power and run things in your RV, you will not pop the breaker so often if you are closer to the house and don't have such a long extension cord. Or if you change from a #14 to a #12 same length, you don't pop the breaker as much.

Isn't it the same thing when you are plugged into a generator's 15a receptacle?

What you are referring to is an inductive load such as your AC compressor and blower motor. They are trying to turn at a certain RPM. You can think of them as a constant power load due to when the voltage drops the current goes up to compensate for the lower voltage in order to maintain its speed. The motor requires a certain amount of power to maintain its torque. The high current demand of the AC causes a voltage drop across the extension cord. This is commonly referred to as IR. This voltage drop means there is less voltage at the AC. The longer the cord or the thinner the wires, the higher the IR.

A resistive load is a fixed load. When the voltage drops the current drops proportionally. One caveat to an electric heater is the coil resistance will change with temperature. It will draw slightly more current when you first turn it on. As it heats up the coil resistance goes up slightly, causing it to draw slightly less current.

[Spridle]

You might want to consider a new carburetor. They cost under 20 dollars:
Click here for carburetor

Another thing to mention is your extension cord probably has 15 amp rated ends and you are trying to draw 25 amps. It will eventually overheat the cord ends, plug strip and 5-20r receptacle. Maybe you should try two separate extension cords, if the load is going to be continuous.

[BFL13]

LittleBill wrote:
resistive loads work different, if the voltage drops, so does the load

Not sure it is the same thing now, but it is still true that when you are plugged into 15a shore power and run things in your RV, you will not pop the breaker so often if you are closer to the house and don't have such a long extension cord. Or if you change from a #14 to a #12 same length, you don't pop the breaker as much.

Isn't it the same thing when you are plugged into a generator's 15a receptacle?

[DrewE]

LittleBill wrote:
resistive loads work different, if the voltage drops, so does the load

Most loads work that way; exceptions under some circumstances are actively regulated supplies (where the regulator adjusts for the voltage) and some electric motors in some applications. As the batteries in a flashlight wear down (the voltage drops), the light gets dimmer, not brighter. At low voltages, motors run more slowly, not more quickly. At lower voltages, microwaves take longer to cook, not less time.

Heaters and other resistive loads are especially easy to analyze because the relationship between the voltage applied to them and the current they consume is linear, as defined in Ohm's law.

[LittleBill]

resistive loads work different, if the voltage drops, so does the load

[BFL13]

2112 wrote:
More R = Less Load

An ideal 1500W heater would have a resistance of 9.6 ohms. At an ideal 120VAC it will draw 12.5A. Let's say an extension cord adds 1 ohm. Now R = 10.6 ohms.
120V/10.6 = 11.3A
120*11.3 = 1356W

The extension cord changed a 1500W load to a 1356W load.

That all works out, but I am still puzzled.

I think the loaded voltage would go down by adding the extension cord, and that if loaded voltage goes down that means you have more load. I must not be looking at it right.

[2112]

More R = Less Load

An ideal 1500W heater would have a resistance of 9.6 ohms. At an ideal 120VAC it will draw 12.5A. Let's say an extension cord adds 1 ohm. Now R = 10.6 ohms.
120V/10.6 = 11.3A
120*11.3 = 1356W

The extension cord changed a 1500W load to a 1356W load.

[BFL13]

DrewE wrote:

BFL13 wrote:

LScamper wrote:
Long cord lowers load not increase it.
High altitude equal less air but same amount of fuel equal rich mixture.

Years ago I didn't understand when you told me current limiting was a way of keeping current constant. I thought you needed a way to keep the current up too. Later I got that.

So now I an stuck on how a longer cord (more R?) is less load.

Your heater or whatever on its own has a resistance R. Your longer cord adds a bit, for the resistance seen by the generator of R + a bit. Since the generator output voltage is supposed to be constant, by ohm's law the current (and hence power) is lower.

More generally, for a constant voltage source, the applied resistance is inversely related to the load. The minimum load is an open circuit, with no power being consumed; the maximum theoretical load is a short circuit with infinite power being consumed...but of course in real life you can't supply or dissipate infinite power, so something somewhere gives out, possibly with spectacular results.

But "loaded voltage" is not constant.

So why would a cord that does add R not add more R if it were longer?

Assuming that more R = more "load".