Your last generator Maintenance Run

[Roric]

Maintenance run puzzle

I used to load test my portable genset by plugging in a 1500w heater
into each of the 120 volt outlets. No problems with this.
I thought I coud make it easier.
I Have a ceiling hung space heater in the garage so I connected a DPDT
(doule pole double throw) switch and a generator cord connection box to it.
Started genset and plugged in twist lock cord and started heater. All was well.
After 10 minute run under load I shut off heater to let the generator cool and started to put stuff away.
When I was coiling up the cord I noticed it was very hot to the touch. Not burning
hot but hot enough to not keep still in my hands. The twist lock ends were not hot.
Just the cable. Nothing was melting.
Here are the numbers:
Champion 6250/5000 Digital Hybrid generator
240v/5000w ceiling heater
40 foot 30A Bourge cable rated for 7500 watts. 4-#10 wires. Brand new.
The generator output and the heater load are the same.

Can anyone tell me if if a digital hybrid (sine wave) generator connected to a
resistive load would cause the cable to heat? An induced current component?

The cable is rated to handle 50% more power than it was using.
(I don't know of a way to load test a cable)

Any ideas on why the cable was heating?

Thanks,
R

 

[LouNY]

Was the excess cord coiled in a nice neat coil?

 

[3930dave]

Roric - was that 40' cable coiled up, under load, by chance ? Even partially coiled, @ higher power levels, you may get some self-induced heating. (What Lou said ).

If the cable was not looped under power, then it's something else; if it was looped, that's an easy enough experiment to re-run.

I'd tend to suspect the Champion last, unless it's been through a lightning strike, or a major fight with a welder etc...... a scope (properly coupled) would be one way to check it.

Before that ^ test, I'd check the (rolled out straight) cable with the same load again, while carefully (it's 240 ) measuring the voltage @ each end under-load. If you are at all uncomfortable with meters/probes/high voltage, don't attempt this test, for your own safety - 240 is NOT where you want to start gaining experience with these type of measurements.

Assuming that ^ caveat is OK with you, and you arrive @ two different voltages from the ends of the cable under load, then a bit of work with ohms law vs. a 5000 watt load will give you an idea of what the resistance/foot of the cable looks like. Post voltages here if you need help with the ciphering....

If that heater has not been blowing your regular household breakers, chances are it's within spec, but a clamp-on current meter would be handy to measure the exact load the heater is drawing.....

Rgds, D.

 

[twowoode]

I went to a 10,000 watt duel fuel generator. Electric start runs off a 100 pound propane tank. I have never put gas in the tank but nice knowing if I had to I could. It stays connected to a battery tender. We just installed a automatic whole house generator that test runs every Tuesday morning for a few minutes. The portable will now move to the barn and mobile use around the property.

 

[Roric]

Roric - was that 40' cable coiled up, under load, by chance ? Even partially coiled, @ higher power levels, you may get some self-induced heating. (What Lou said ).

If the cable was not looped under power, then it's something else; if it was looped, that's an easy enough experiment to re-run.

I'd tend to suspect the Champion last, unless it's been through a lightning strike, or a major fight with a welder etc...... a scope (properly coupled) would be one way to check it.

Before that ^ test, I'd check the (rolled out straight) cable with the same load again, while carefully (it's 240 ) measuring the voltage @ each end under-load. If you are at all uncomfortable with meters/probes/high voltage, don't attempt this test, for your own safety - 240 is NOT where you want to start gaining experience with these type of measurements.

Assuming that ^ caveat is OK with you, and you arrive @ two different voltages from the ends of the cable under load, then a bit of work with ohms law vs. a 5000 watt load will give you an idea of what the resistance/foot of the cable looks like. Post voltages here if you need help with the ciphering....

If that heater has not been blowing your regular household breakers, chances are it's within spec, but a clamp-on current meter would be handy to measure the exact load the heater is drawing.....

Rgds, D.

You guys are very perceptive. I had the remainder of the cable in a couple of large loops.
This was a case of self-induced heating and I should have thought of that.

Thanks for pointing it out to me.
regards,
R

 

[3930dave]

You guys are very perceptive. I had the remainder of the cable in a couple of large loops.
This was a case of self-induced heating and I should have thought of that.

Thanks for pointing it out to me.
regards,
R

NP..... like my recent post about an experienced wrench (not me, but I've had my own stories that are similar ) overlooking a plugged air-filter, we all benefit from this TBN sounding board, kicking around these puzzles.....

Rgds, D.

 

[3930dave]

I went to a 10,000 watt duel fuel generator. Electric start runs off a 100 pound propane tank. I have never put gas in the tank but nice knowing if I had to I could. It stays connected to a battery tender. We just installed a automatic whole house generator that test runs every Tuesday morning for a few minutes. The portable will now move to the barn and mobile use around the property.

Nice setup two !

Is the whole-house on propane too ? I do like the cleanliness of propane and natgas, and the inherent stablity vs. time - provides less ammunition to 'ol Murphy .

Rgds, D.

 

[Patrick Herd]

Any ideas on why the cable was heating?

Does your cable have aluminium conductors perchance? I'm seeing more and more "stuff" made with alloy that should not be.

Also re: extension cables coiled up, it's just resistive heat build up (cable touching cable has less surface area to shed heat) and nothing to do with induction

 

[daugen]

it's just resistive heat build up (cable touching cable has less surface area to shed heat) and nothing to do with induction
\
ok professor, can you explain that in more detail?
good to know, hot cables never a good idea, hot connectors even worse

I ask this partially due to what may be a misunderstanding on my part.
I thought if you coiled a higher amperage cable, the circular coil created an electrical effect of its own.
as in the "oscillating magnetic field" described below

perhaps you could explain induction as it might apply here? : in an induction stove (also "induction hob" or "induction cooktop"), a cooking vessel with a ferromagnetic base is placed on a heat-proof glass-ceramic surface above a coil of copper wire with an alternating electric current passing through it. The resulting oscillating magnetic field wirelessly induces an electrical current in the vessel. This large eddy current flowing through the resistance of the vessel results in resistive heating.

curious minds ask
clearly I am no EE

 

[Fallon]

it's just resistive heat build up (cable touching cable has less surface area to shed heat) and nothing to do with induction
\
ok professor, can you explain that in more detail?
good to know, hot cables never a good idea, hot connectors even worse

I ask this partially due to what may be a misunderstanding on my part.
I thought if you coiled a higher amperage cable, the circular coil created an electrical effect of its own.
as in the "oscillating magnetic field" described below

perhaps you could explain induction as it might apply here? : in an induction stove (also "induction hob" or "induction cooktop"), a cooking vessel with a ferromagnetic base is placed on a heat-proof glass-ceramic surface above a coil of copper wire with an alternating electric current passing through it. The resulting oscillating magnetic field wirelessly induces an electrical current in the vessel. This large eddy current flowing through the resistance of the vessel results in resistive heating.

curious minds ask
clearly I am no EE

On a really hot night when the A/C is out, do you want to crawl underneath the covers, cuddle up to your significant other, or sprawl out ontop of the covers away from everything? I my love my wife, but cuddling when it's 100 degrees is not in the cards.

Similar principle for cables. You want as much air to get to every bit of cable as possible to keep them cool. Electrical codes specify the maximum fill capacity for conduit so that there is a bit of air that can cool things.

It's generally not a problem in most circumstances. But you don't want to fight it if you are maxing out cables amp rating. The hotter a cable thing gets, the higher the resistance, which (assuming the same current draw) creates more heat. You can get a nasty negative feedback loop. Not likely to happen with properly rated cable, but it is possible if you have other issues.

Looping wire creates an inductor. Inductors can mess with the timing of the AC waveform & increase the power factor of a circuit.