Generator PTO generator feedback

[IXLR8]

I could be wrong if they cycle and only one is on at a time. Guess I assumed two elements x 4500 watts each =9000watts. 4500 on each 110 leg. I never heard about them cycling back and forth.

Typically there is an element in the top of the tank and one in the bottom. From a cold tank, the top one heats up to setpoint temp, then the bottom one comes on and heats up to setpoint temp. When the bottom gets cold from incoming water, the bottom heater will come on. If enough hot water is used so that the upper setpoint is no longer met.. it will shut off the bottom heater and turn on the upper heater. This is to minimize the chance you will get cold water out of the tank.

 

[tsteahr]

Gear on gear efficiency is very high for spur/ straight cut gears, and the math professor would show you why.

This is a great place to give a intuitive example if one uses a bit if imagination. We all agree gear on gear efficiency is high. Low loss between the gears themselves. The only other remotely significant losses are viscus drag of the gear spinning in the oil bath and bearing drag.

Imagine if you removed the entire gearbox assembly from the PTO generator and mounted it on a bench. Go over to Wally World and buy the smallest, cheapest, lowest power variable speed drill they have. Connect the drill to the gearbox input shaft. With nothing connected to the gearbox output shaft this crappy drill would have no problem spinning the input shaft to 540 and beyond. You have just proven than the total losses from the bearing drag, the viscus drag of the gears spinning in the oil bath, all the rest of these little drags are all less then the power output of this tiny drill.

I leave it to the reader (if anyone is still reading this absurd discussion) that the viscus drag is only related to the speed of the gears and not related to power transfer (force transferred across the tooth face).

I also leave it to the reader to agree that bearing drag is minimal (remember the drill had no problem turning the bearings) and changes to bearing drag associated with changes to shaft loads are also small.

I propose if a gearbox is "much hotter" when transmitting load that sliding is occurring between the gear teeth. Sliding could result from many issues. Worn teeth, improper shaft alignment, improper spacing between gears could be a few.

If a gearbox is being operated within its design, is absorbing 10% of input power (and therefore getting unreasonably hot) something is defective with that particular gearbox.

 

[gerard]

Typically there is an element in the top of the tank and one in the bottom. From a cold tank, the top one heats up to setpoint temp, then the bottom one comes on and heats up to setpoint temp. When the bottom gets cold from incoming water, the bottom heater will come on. If enough hot water is used so that the upper setpoint is no longer met.. it will shut off the bottom heater and turn on the upper heater. This is to minimize the chance you will get cold water out of the tank.

So at no time will both be on together? ie long shower etc? (That woudl change the draw quite a bit)

 

[dex3361]

So at no time will both be on together? ie long shower etc? (That woudl change the draw quite a bit)

That is correct at least on my Hot water tank. I am afraid to say that all of them do because every time I go out on a limb someone comes along and cuts it off. I f you look at the name plate it should tell you the max amps.

 

[BobRip]

So at no time will both be on together? ie long shower etc? (That woudl change the draw quite a bit)

One of the reasons they do this is to limit the maximum power so the utilities don't have to generate it. This evens out their load. Basically the system give you a "quick recovery". The top heater only has to heat 1/2 of the tank before you get hot water. If you just had the bottom heater then the entire tank would have to be heated before you could get hot water. It's actually a pretty good system.

 

[tsteahr]

What do you think is the cause of such a difference? Hst does not drive the pto hydraulically. Could it be that the full picture is not being presented and that they cannot be accurately compared w/o knowing more about the tests??

Wrong. An omission of "fact" is not a statement of fact. I applaud Marks for not being wrong, but reduce it to one hand for not being complete.


No. They summarize each other for the most part. Critical evaluation is too often left to the user, who is sometimes not equipped.
I disagree that we agree. The premise for agreement is out of context.

Im tempted to have you find it yourself, but Im pretty sure you wouldnt look. ... See here: Other references to 90-95% for gear equipped systems are easy to find. Higher than that deserve a critical look.

http://web.mit.edu/2.75/resources/FUNdaMENTALs%20Book%20pdf/FUNdaMENTALs%20Topic%206.PDF

larry

Be careful what you find with Google. You realize this reference you have provided is a high school children's primer for robot design contests? It is directed at the small, course gears used in student robot contests. The 95% number is accurate for such gears.

This is a quote from pg 28 2nd column, 2nd paragraph, the section on gear trains:

"The most important fundemental points to remember about gears for robot design contests is that their relative velocity is constant. Each set of meshing teeth can be on the order of 95% efficient, and the teeth must be strong enough to transmit the torque required."


The gears used in industrial and commercial applications are of higher quality than used in student robots. Again, this leads us back to the 98% outlined in appropriate references.

Marks is the most widely respected and accepted engineering reference handbook available today. Marks is the general engineering reference handbook. All engineers know this.

 

[dcyrilc]

You guys crack me up --- debating over 3%.

 

[Redneck in training]

What if it were a positive displacement pump? Are there any centrifugal type pumps that go up in amps when the flow goes down(caution this is a loaded question)?

I took the bait. Actually required power is Head times mass flow. So pumps with flat performance curve will lose flow faster than they are gaining head and power will decrease as the flow goes down. Required power for pumps with steep curve will rise and then drop off only at very low flows.

 

[Redneck in training]

One of the reasons they do this is to limit the maximum power so the utilities don't have to generate it. This evens out their load. Basically the system give you a "quick recovery". The top heater only has to heat 1/2 of the tank before you get hot water. If you just had the bottom heater then the entire tank would have to be heated before you could get hot water. It's actually a pretty good system.

I think the reason for the split heaters is safety due to only half of the current while providing relatively quick hot water. 9kW would require substantial cable that many houses don't have installed. It is the house fire the lawyers would sue the manufacturers for.

 

[Diamondpilot]

I hope some of you went out and got a genny. Lots of folks without power today with the major storm the east central part of the country is getting.

Remember the genny is no good without fuel. I keep 100 gallons on hand which will get me through a week and a half.

Chris