HP for a 3510 @ 1200 RPM?

KYMike · Mar 17, 2006

I need help figuring out what my PTO generator can power in my house (DHW, range, heat pump, etc.). I have a 3510 (30 PTO hp @ 2600 RPM) and a Winco 25kw generator. I figure a capacity of about 15kw at full RPM in the 540 PTO setting, but how do I figure what the hp is when using the 1000 PTO setting?

When I don't need to use any high-demand appliances, I can set the PTO to the high setting and the gen purrs right along at 120 volts with the engine around 1100-1200 RPM. I would like to figure just what kind of load I can put on it at the high PTO setting. I can run the amp/watts calculations, but how do I know what my PTO hp is at half the rated RPM?

hbaird · Mar 17, 2006

To know the Horse Power at any RPM, you must know the Torque at the desired RPM. HP = (Torque X RPM) / 5252.
Harold

KYMike · Mar 17, 2006

Thanks for that info, Harold. I've always wondered what the relationship was between torque & hp. Now all I need is to find out what torque the 3510 has. When I Googled it I found out the torque of a Branson 3510 Centrifugal Cleaner, but nothing on the tractor. Anyone know?

Fredex · Mar 17, 2006

Don't know what the hp might be at lower rpm. Sometimes the hp vs. rpm curves are a bit difficult to find. I would offer a couple of other comments that may be helpful.

1. You may be able to get close to 20 KW at full power. Usually figure 1.4 hp per KW; 1.5 per to be conservative. But I wouldn't want to load it that heavily if I had motors or compressors to start.

2. When running in 540 PTO mode always run at engine speed specified to give 540 on the PTO. The Alternator (generator) will be geared to provide the requisite 60 cycle AC at that PTO rpm.

3. When running in 1000 PTO mode run engine at the speed to give 540 rpm at the PTO because the generator is geared for that (unless the generator was designed and built for 1000 PTO input). Example: If engine speed for 540 in the 540 mode is 2600, then engine speed to get 540 in 1000 mode would be 1404. Of course if your tach or manual tells you the engine rpm for 1000 PTO speed then you can just reduce to 54% of that engine rpm.

The reason you always want to run the generator at its design speed is to get 60 cycle AC current. If you drop below, to say a pto speed that allows the generator to only produce 50 cycle current, there can be some ill effects to electronics such as over heating; also electric motors will run slower. Dropping from 60 cps to 50 cps will cause motor speed to drop to 83% of rated speed; again there can be overheating. The cps (cycles per second) thing is a function of generator rpm & thus PTO rpm. A bit more than can be described in detail here - just keep the pto rolling as close to 540 as possible in either mode.

Fred

redfoxco · Mar 21, 2006

KYmike,

I queried Cummins about the HP and TQ at 1404 RPM (crankshaft) on the A1700 IDI motor. This will be the rated output of the motor at the flywheel when the 1000 RPM PTO option is used but running the PTO @ 540 RPM (i.e. running on the 1000 RPM PTO gear with the PTO actually spinning 540 RPM)

Cummins Response:
"The HP at 1400 rpm is 20 and the torque at that speed is 77 ft-lbs."

Hope this helps some.

KYMike · Mar 21, 2006

Wow, that's exactly the info I was looking for. Thanks, Redfoxco!

BTW, to Fredex, I have a query into Winco to confirm this, but I think they have some circuitry to correct the current to 60 hz independently of the PTO rpm.

Fredex · Mar 21, 2006

Mike: My training in this stuff was in the USN far too many years ago. Later worked as a technician in Ma Bell's microwave network where each tower had a diesel emergency power supply. You probably figured I was a bit dated because I used the term "cps" instead of "hz" That change of terminology happened after I was already doing other telephony things. Back then the only way to change the output hz of an alternator was via rpm and number of field poles in the alternator. Much has changed/improved since then. I know the alternator mfgr's have done a lot to clean up the waveform of the smaller, self-excited machines. There is so much electronic magic out there now (it's amazing), they may have done some work on frequency (hz) correction. I haven't heard of it, but I haven't kept up with the technology either. Post back what Winco tells you. I would even like to see the diagram of the circuitry, but they probably won't give you that detail. Sure would be quieter and more fuel efficient to let the tractor loaf a little, particularly for those who have more tractor than alternator.

Fred

Reg · Mar 25, 2006

</font><font color="blue" class="small">( Wow, that's exactly the info I was looking for. Thanks, Redfoxco!

BTW, to Fredex, I have a query into Winco to confirm this, but I think they have some circuitry to correct the current to 60 hz independently of the PTO rpm. )</font>

The frequency can be independant of input shaft speed IF the generator design is inverter based. In these designs raw AC at any old frequency is rectified to DC, an oscillator runs at the desired frequency (50 or 60 Hz) and that usually drives an output transformer. Some generate DC in the first stage.
So, the question to ask Winco is; "Is it an inverter based design ?"

BTW, this is VERY popular in current welding machine designs and can be found in camping generators around 2 or 3 KVA.

Fredex · Mar 25, 2006

For sure, Reg. There is a similar technology used for variable speed drives. For example: 220 V, 60 Hz, ac input - variable frequency, 3 phase 208 output to a motor. I've seen that on variable speed pumps in wineries. They will slow down to nearly nothing or all the way up to motor design speed. Just twist the knob on the controller. Wunderbar!

A bit off topic. Locomotive designers have begun using AC traction technology. Wonder if it is similar?

Adding the AC-DC-AC inverter to a pto alternator of 20 kva would probably run the price up considerably. Also I would want to know quite a bit about the inverter design before I plugged into my house. Many of the more basic designs generate more of a square wave than a sine wave. My house has things that don't like square waves very much. A good one will be cleaned up. Winco's response should be interesting if they have it.

Fred

KYMike · Mar 27, 2006

Well, here's the answer from Winco, although it wasn't what I hoped for:

"PTO generator frequency is solely dependent on the speed of the tractor. Generally speaking if you have the voltage in the correct range on the volt meter you frequency is going to be in a usable range. The only way to adjust the frequency is to adjust the tractor speed.

JR Rethwill
Service Manager
WINCO Inc."

I've never burned up any motors or anything using my genny yet, so I guess I'll continue to monitor the voltage and assume the frequency will be within range. Thanks for everyone's help and input.