1. #1
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    Thumbs up Hydraulic vs. PTO driven generators

    We are in the process of spec'ing a new Rescue/Squad unit, and we are putting no smaller than 20kw generator on it. We are not sure what we should go with either Hydraulic or PTO.

    What do you have and what do u like and dislike about it? Where do you have your generator located on your apparatus?


    Thank You for your help!!

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    Quote Originally Posted by rschultzjr View Post
    We are in the process of spec'ing a new Rescue/Squad unit, and we are putting no smaller than 20kw generator on it. We are not sure what we should go with either Hydraulic or PTO.

    What do you have and what do u like and dislike about it? Where do you have your generator located on your apparatus?


    Thank You for your help!!
    rschultzjr,

    All of the Hydraulic driven generators that I know of, have their hydraulic pump driven off a PTO

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    Ok one of the Generators we are looking at is a SMART POWER Hydralic Generator ( http://www.smartpower.com/products.html ) and a straight PTO driven generator.

    We were told that they hydralic generators can be started while the apparatus is in motion and that the PTO generators cannot be.

    The PTO generator is mounted to the chassis underneath the truck were road debris and salt can damage it. How does that effect the unit, also how is maintenace on a PTO Generator.

    vs.

    The Smart Power Hydralic generator can be mounted on top of the rescue body up away from all the road debris and salt. And I would assume that maintenace is easier on this style unit.

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    In my opinion you should go with a hydraulic generator. A hydraulic generator can be mounted on top of an apparatus, can be placed to be easily accessible for maintenance & can be placed for optimal cooling. (among other advantages in my opinion)

    But keep in mind - Chief1FF is correct. All "hydraulic" generators are ultimately driven by a PTO. So that means that even if you get a hydraulic gen. set., the PTO must still be engaged - even if your apparatus is already in motion. If you want generator current "on the roll", this must happen for the hydraulic generator to operate because the PTO drives the hydraulic generator's hydraulic pump, and that is what "spins" the generator.

    You will need to write it into your specs that the hydraulic generator "hot shift" PTO must NOT be interlocked with the parking brake (so you can engage it on the roll). If you do not spec it this way - all apparatus manufacturers I am aware of will automatically interlock the hydraulic generator PTO with the parking brake, and then it will NOT engage unless the truck's parking brake is on.

    Assuming you write it into the specs like I suggested, . The fact that the apparatus is in motion is not the problem when you engage a PTO, RPM is the issue. PTO's are generally recommended to be engaged (and disengaged) BELOW 1200 RPM. When you get a "hot shift" PTO (which you will have to in this application), "hot shift" means when you hit the PTO switch(es) - it will engage regardless of engine RPM. This means that if people are not properly trained and engage a "hot shift" PTO at higher RPMS, you will damage the PTO - proper training is a MUST.

    One thing to note: Mounting a hydraulic generator "on top" of and apparatus will possibly either increase travel height of the apparatus OR it could take up compartment space - BOTH of these items are dependant upon how your apparatus body is configured, etc. TL

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    Couldn't you just leave the PTO engaged all the time and then not worry about it? You'd end up putting more hours on the generator but response times are generally insignificant compared to scene times.

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    You "could" leave a hydraulic generator PTO switch on all the time (meaning it is possible) BUT I would NOT recommend it. The reason is because if you do it this way you can cause a terrible amount of wear and tear on that PTO - especially when you shut the truck off and then re-start it with a PTO switch engaged. The last thing there in particular can cause PTO failure or damage. To my knowledge this goes with any PTO that has engagement switches in the cab or elsewhere.

    If your PTO (no matter what it is driving) has engagement switches in the cab or at the pump panel, Never leave it engaged all the time. Only engage it when you need it.

    Even if you have a PTO that can be engaged "on the roll" to drive a hydraulic generator or something else, only engage it at a proper RPM and only engage it when it is needed. Don't allow people to just drive around with it on all the time if it is not needed.

    ALSO note: Depending on the transmission type, some have a mounting location for a PTO that are on top of the tranny. This can put a small hump in the rear floor board if you use that location. Some FD's don't like that, so spec it in that you do NOT want that location used if you don't want that hump, I say this because it can interfere if you put EMS compartments (or a wet bar) in the rear of the cab.

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    Quote Originally Posted by SSIaerialmanTIM View Post
    Only engage it when you need it.
    Let me ammend that to say that some MFG's will tell you that on arrival at the scene "every" scene, enagae the aerial PTO.

    If the MFG tells you to do it, it's ok to do... but they will never tell you to leave that same PTO switch on all the time (like driving around).

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    Default Newer Hydraulically driven generators.

    Assuming the reason you want AC power on the roll is to use it for lighting or other powered equipment. We just received a new quint with a hydraulic generator. The electronic control of the hydraulic system requires the generator come up to operating speed under "No-Load" conditions. The 60 cycles is the signal used to modulate the hydraulic control system. With our type of generator, starting under load will not allow the generator speed to match to the required 60 cycles and therefore after 2 minutes of trying, the failure mode comes on. You will need to have a relay switch in the cab along with the digital read out so that you can turn the load on after the generator completes its warm-up program. Carefully check with the manufacturer before specifying PTO ratios so that a good match can be maintained with other power equipment attached to your motor. (jaws, winch, pump, etc.)

    Kuh Shise

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    Kuhshise- What brand did you get? How did you spec it and how would you RECOMMEND to spec one?? Thanks.

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    Quote Originally Posted by KuhShise View Post
    Assuming the reason you want AC power on the roll is to use it for lighting or other powered equipment. We just received a new quint with a hydraulic generator. The electronic control of the hydraulic system requires the generator come up to operating speed under "No-Load" conditions. The 60 cycles is the signal used to modulate the hydraulic control system. With our type of generator, starting under load will not allow the generator speed to match to the required 60 cycles and therefore after 2 minutes of trying, the failure mode comes on. You will need to have a relay switch in the cab along with the digital read out so that you can turn the load on after the generator completes its warm-up program. Carefully check with the manufacturer before specifying PTO ratios so that a good match can be maintained with other power equipment attached to your motor. (jaws, winch, pump, etc.) Kuh Shise
    "Ku", please clarify if you can. A "hydraulically driven generator", has a PTO that drives a small hydraulic pump, that pump then drives the generator. While not as solid as a gear drive set up; it is "solid", meaning when the operator engages the generator PTO and then "starts" the hydraulic generator with another switch - that generator has NO CHOICE but to "start".

    For instance, Onan / Smart Power and those like them have no "choice" when you hit the generator button. Starting them under a "considerable electric load" will not keep them from achieving 60 Hertz.

    The way you have it written above it sounds like you are talking about Trying to start a small GAS or DIESEL generator under a considerable load - which would cause the generator to react that way. (starting under a considerable load might make a small gas or diesel possibly fail to start).)

    But a PTO driven hydraulic generator will not act the way you outline, it will "start" and go to full hertz right away - there is no warm up period. Also, with a PTO driven hydraulic generator, he will not be worrying about specifying the PTO ratio of the PTO that will drive the hydraulic generator pump - that kind of sounds more like you are talking about a PTO that is "gear driving" something else.

    To make clear on my end; It doesn't matter if a generator is hydraulic, gas, diesel, I have always taught to start them under a "no load" condition, so don't misunderstand me a think I am telling you or anyone here to start under a full load.

    BUT advantages to having a PTO driven hydraulic generator ARE the fact that they have no "warm up" & it can be "started" under "some" load (for instance a brow light and two upper body side lights - which will need switches in the cab if you want to control them on the roll) as you drive up to the scene.

    It sounds like your talking about a different animal. TL

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    Not sure if this applies here, but also make sure the engine on the rig has enough power to run all the equipment. When we was specing our new engine, the engineers that drew up the truck at the mfg. told us that we could not put a hydraulic gen. on it as the truck would not have enough power to run the pump and some other things as well as a generator. so we ended up having a small diesel mounted generator above the pump.

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    Default For: FD1976 & SSIaerialmanTIM

    This is a "Smart Power Systems" generator, and because it is on a quint where motor speeds typically vary from idle (600) rpm to pumping at 250 psi (1700 rpm), it is necessary to oversize the hydraulic pump capacity and then carefully control the delivered pressure to maintain the 60 cycles and meet the power demand required by the electrical load. As mentioned previously, the system requires that generator be stabilized before placing an electrical load on the system. There are also electronic circuits that monitor hydraulic oil temperature, and will not allow the load to be applied unless oil temperature is within limits. (above 40 deg. F) Example below 20 deg. F (cold start) the generator is bypassed and only the oil is circulated. Above 20 deg. the generator is turned but not at speed. Above 40 the electronics adjusts the speed to match 60 cycles, and then allows the load to be switched to the on position.

    Attempting to load the system before 60 cycle synchronization is achieved simply shuts down the system after the start up timer has elapsed. However once the control requirements have been met, the pump volume and controls are able to maintain total electrical load control from the idle (while the operator engages the water pump) through the aerial set point (1500) rpm and continuing up to 1800 rpm or more. The way I understand the operation, increasing the electrical load increases the torque on the generator, this would normally slow the generator speed, but fractions of a cycle per second change in speed are electronically sensed and input hydraulic pressure is increased to keep the generator turning at exactly 60 cycles.

    I can not supply information on how the spec was arrived at, but KME had to meet a performance spec concerning reliably supplying full electrical power at all engine speeds normally encountered when pumping water and or operating the aerial device. There are a number of other electronic programs that control this equipment and can be manually or electronically activated from over temperature to purge settings. We have not done enough firefighting or practice with this device for me to form an opinion about the mfgr. or the design.

    KuhShise

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    All this discussion makes it seem a lot easier to me to not worry about the Hydr. generator running while moving and simply add a few 12 volt lights for rolling onto the scene. Once stopped on scene, then kick in the pto generator.
    "This thread is being closed as it is off-topic and not related to the fire industry." - Isn't that what the Off Duty forum was for?

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    Thanks “KU” for clarifying. Good info. I suppose I have been more involved with Harrison and Onan generators but I will be honest – I never described it down to the level you documented.

    I will say one thing for those out there who may be worried about all the technical workings of the hydraulic generator and some of the sensors / temperatures / requirements “KU” mentioned. I have been training on quints for a long time with mostly Onan & Harrison gen sets and in all types of weather I encountered during training – I never had one fail to “start” no matter what the outside temp was. And this ranged from well below zero Fahrenheit to well over 100 degrees Fahrenheit. Additionally I never once had one not achieve 60 hertz almost immediately and I never had one kick the load off when it was applied or shut down. Perhaps the smart power has a few more sensors on it, not sure. But I do know I have run them in extremely severe climates and they are all very, very dependable.

    I do know that both the Onan and the Harrison come with their own proper displacement hydraulic pump automatically when you order a particular size of generator. I bet Smart Power does too. So for those of you thinking you will have to “build” an entire system and understand all the hydraulic theory and pick your own pump, etc.., don’t worry about it. Go to the particular wesite of the generator you want and copy the specs of the one you want into your specs. The MFG will order it as a package and install it. No offense intended to “KU” – EXCELLENT info on his part. I just thought I would offer my practical experience with these systems. TL

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    One down side is that when you engage the PTO generator and have the pump engaged at the same time it kicks up the pressure on the hose tremendously and is impossible to bring back down because the generator needs a much higher rpm to run than the pump. The pressure on the hose goes around 200+. You might want to ask your dealer about problems like that.

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    Quote Originally Posted by Bones42 View Post
    All this discussion makes it seem a lot easier to me to not worry about the Hydr. generator running while moving and simply add a few 12 volt lights for rolling onto the scene. Once stopped on scene, then kick in the pto generator.
    I've also seen a dedicated inverter to power an eyebrow mounted floodlight. Might be something to consider to get some extra lights when rolling and then engage the generator when stopped.

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    Our new Pierce has a Harrison 10kw hydraulic generator with a hot shift pto. The pto and generator can be engaged while going down the road from cab switches or switched when needed from the pump panel. The brow lights and side floods are relay operated and can be switched from the cab or the pump panel. The rear flood and FRC pole raise lights are switched from the circuit breaker panel. We engage the generator and the floods when approaching the scene. The generator can be started at full load also. Everything works like a champ.

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    The timing of this thread is perfect. i just got done reviewing the HGAC, COSTAR-13 and LA purchasing price sheets and was wondering how different the PTO vs. hydraulic generator were as the prices are extremely different. So maybe on our new Rescue Pumper we can put plenty of 12 volt scene lighting around the truck for rolling in and initial scene lighting and a PTO generator to power the hydraulic tool pump, light tower and cord reels. Sound like a workable set up? Anyone?

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    Default Hydraulic vs PTO Generators

    Depending on the application if it's primarily a Rescue Truck I'd suggest going with the ONAN PTO generator. Yes it is mounted underside between the frame rails but is a sealed unit and I've sold a number of them to FD's in Canada with lots of snow and ice conditions. (Edmonton, Calgary etc) and they are simple and easy to use and less expensive than the hydraulic generator. They also don't take up compartment space in the upper body. They range from a 10-40 Kw and if you want larger then you can go with a LIMA brand tbat is commonly used for onboard air compressor apparatus.

    If the apparatus has a Pump on it or you want to operate the generator while moving (don't really know why as you could have 12V front "Brow" or side scene lights and then when stopped engaged the PTO generator) Then go with the Hydraulic version and I'd recommend either a Onan or Harrison brand as they are the two most popular IMHO. Ensure that the builder provides sufficient cooling (air circulation) for the installation to avoid any overeheating problems when stationary during pumping operations as the ambient temperature from the Pump/Exhaust can cause problems with them.

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    Default Pto Gen

    My 2007 Pierce Rescue Pumper has a 30 KW Harrison with a soft start that delays the engagement 10 seconds and will allow the lights on all 4 side to come on at once. WE havent tried it with the light tower but we also put 12 volt scene lighta on 3 sides of the apparatus for redundancy.
    Lights night into daytime

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    So what's the basic objection to a standalone genset (other than consumes compartment space)?

    Underhood belt driven hydraulic pumps are available for trucks, possible alternative to PTO driven pump? I'd guess less expensive, PTOs are not cheap.
    Last edited by neiowa; 08-14-2007 at 10:50 PM.

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    I think the one major one is what you mentioned Iowa. Another one I have always heard and somewhat agreed with is the fact a stand alone gen. requires separate maintenance of all its systems (fuel, battery cable, oil changes, filters, etc). Starting problems may crop up after a few years. A stand alone is also physically larger for the current produced compared to the others it seems.

    But an advantage to a some small stand alones is that they might be somewhat portable and as you said most stand alones have to cost less on the average. TL

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