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  1. #1
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    Default Generator question

    We currently use Harrison hydraulic generators on our apparatus. While working on specifications for a new squad, am looking at generators - both Harrison and Onan.

    My question is, most generators are single-phase. Is there, or would there be an advantage in going to a 3-phase generator versus a single phase generator? Looking in the 25-30kW range.



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    Quote Originally Posted by Tower9Truckie View Post
    We currently use Harrison hydraulic generators on our apparatus. While working on specifications for a new squad, am looking at generators - both Harrison and Onan.

    My question is, most generators are single-phase. Is there, or would there be an advantage in going to a 3-phase generator versus a single phase generator? Looking in the 25-30kW range.

    Why would you need a generator that big?? What are you going to run off the generator? A 30kW genset would run most firehouses.

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    Quote Originally Posted by johnsb View Post
    Why would you need a generator that big?? What are you going to run off the generator? A 30kW genset would run most firehouses.
    Three electric hydraulic extrication tool pumps, 9kW light tower, etc........

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    On our new Rescue truck, we had similar requirements for tools, light tower, lots of truck mounted 120v outlets, 240V flood lights on each side of the truck, portable tripod lights and two 240V 200' reels.

    Our new rescue has an Onan, 1 phase, 35KW PTO driven generator. If necessary, we can power a firehouse or other building.

    Our previous rescue had an Onan, 15KW PTO driven generator. There were issues if all the lighting was on, the generator could not handle the starting loads of the electric hydraulic pumps. We addressed this with an SOP to turn on the pumps before turning on the lights.

    Lesson is that it's better to have too much power then not enough.

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    Quote Originally Posted by Tower9Truckie View Post
    Three electric hydraulic extrication tool pumps, 9kW light tower, etc........
    Why 3 electric power units? Our heavy Rescues only have 1 or 2, the rest are gas in case we need to move it closer to where we need it if the reels won't reach, or if there's multiple cars needing to be cut on. And have you looked at LED lighting to see what your power requirements vs cost would be? I don't really know of any 3-phase equipment that gets used in our line of work, unless there was a building you needed to supply.

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    I guess I wonder why you would need 3 electric hydraulic rescue tool pumps...Do your neighbors that you are trying to outshine only have 2?
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    Good points so far. Also, electric motors that are single phase cannot be run on three phase and vice versa.

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    I already know equipment runs on single phase. We are not trying to "outdo" another department with electric motors - we will have 3 electric motors running 6 pre-connected hydraulic rescue tools (to handle multiple vehicle extrications as had happened several times). What some are thinking is that we can use multiple phases, like 1 phase feeding the pumps for the tools, another phase for scene lighting, etc...
    Harrison looks like they only have single phase generators. However, Onan does produce a 3-phase generator.

    Not here to debate the number of electric power units for hydraulic tools, or scene lighting....just trying to see if anyone out there has used a 3-phase generator and how they set it up for their unit.

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    Instead of splitting a 3 phase, I'd opt for 2 generators. If that 1 35k shuts down...you have nothing. 2 units would allow splitting items and serve as a backup as well.

    Ya, I know....they never "break".
    "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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    Take a look at Harrison's IHT system for powering your hydraulic rescue tools vs. electrical power plants.

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    A couple of things you have to look at.

    1- Space, the generators options, the Harrison is almost 10 cubic feet of space (before clearance requirements). The Onan can be mounted on the frame rails, with no compartment loss.

    2 - Power, I agree if you plan on loading up the generator with A LOT of electronics, go bigger initially. In the fire service we do things in a hurry, with no warm up. Many times we roll up and need everything lit up and tools running right away. If your tools and generator are running at 100% efficiency you may never have an issue, but that doesn't happen. A generator may not always run at 100% efficiency, whether it be due to a lack of maintenance, age, or anything. The initial cost difference is minimal. That being said, go single phase, unless like someone pointed out you plan on removing the truck from service to run the firehouse.

    3 - Hydraulics, unless you already wasted your money on 3 electric hydraulic pumps could spend that on a pto/generator driven system, Harrison has the IHT, Smartpower and Onan use XRT. You can power 3 tools with that system, saving you 2 electric pumps, you can run an extra reel or two of a small mounted electric if you NEED that many pre-connected, but I would recommend getting a cart or 2 made that can hold a gas unit and 2 tools. This will keep you very versatile when operating at incidents away from the roadway or your apparatus position, and during multiple vehicle extrication situations you can keep the tool systems separated so that you don't cross over and twist up your 6 different lines.
    Last edited by 201/65; 09-01-2012 at 10:58 AM. Reason: spelling

  12. #12
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    Quote Originally Posted by johnsb View Post
    Why would you need a generator that big?? What are you going to run off the generator? A 30kW genset would run most firehouses.
    We have a 25kW on our rescue, and a 400kW one (yes, you read that right) with a 2300 gallon fuel cell for the firehouse.

    To the OP, I know the original question was about single versus 3-phase generators, but I'd remiss if I didn't encourage you to look at the LED lighting products out there now. We've converted our engines at work to all LED floods (including the light tower) and we able to eliminate the generator altogether. Obviously you'll still need a generator for the electric pumps, but you may be able to cut down on the required size through the use of LED lighting products - ultimately providing you a cost savings as well.
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    [QUOTE= To the OP, I know the original question was about single versus 3-phase generators, but I'd remiss if I didn't encourage you to look at the LED lighting products out there now. We've converted our engines at work to all LED floods (including the light tower) and we able to eliminate the generator altogether. Obviously you'll still need a generator for the electric pumps, but you may be able to cut down on the required size through the use of LED lighting products - ultimately providing you a cost savings as well.[/QUOTE]

    Note that 12 volt LED floods take quite a bit of current to operate. In many cases, 13 amps plus per unit. So in order to use them, make sure that you have enough alternator capacity to handle the increased load. Do the math!

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    CE11, excellent point, and one that I should have included in my original post. We require the amp draw report from the manufacturer prior to signing off on the build order, specifically to ensure we don't end up with alternator issues down the road.
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    Quote Originally Posted by BoxAlarm187 View Post
    We have a 25kW on our rescue, and a 400kW one (yes, you read that right) with a 2300 gallon fuel cell for the firehouse.
    ...
    holy crap....how big is your firehouse? We have a 60kw for the building....
    "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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    Bones, it's a 16,000SF facility which includes a meeting room for 100 and 8 bunk rooms that will sleep a total of 12 personnel. The generator will run the entire building, full load, for 5 days before it would require refueling. Although it's not one of the county's designated evacuation shelters, we'd still be able to serve as a backup evac shelter, EOC, or house our member's families for a period of time.

    The generator is a monster, but the architect and county (who built the station for the volunteers) agreed that they wanted the capacity, and they were able to still fund items such as this while still coming in at 10% below the budgeted project price.
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    Wow, 400,000watts sounds like a lot of overkill for that.
    "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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    Quote Originally Posted by Bones42 View Post
    holy crap....how big is your firehouse? We have a 60kw for the building....
    I said the same thing when I saw that! We can run the whole station with our measly little 12kw generator. I can't imagine what a 400kw would be like.

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    Quote Originally Posted by Bones42 View Post
    Wow, 400,000watts sounds like a lot of overkill for that.
    I'm not an electrical engineer of any form or fashion, but I completely agree with you. However, as I said, it was a county project built on our behalf, so most of the items related specifically to the infrastructure were handled by the county facilities staff.
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    Regarding 3 phase vs. single.

    It can be difficult enough to balance loads across a single phase system, let alone a 3 phase running only single phase loads. Continuously running any generator system when out of balance will lead to maintenance issues. If you choose to go 3 phase find a local certified electrician to help you design a system that will at least be balanced most of the time.

    Regarding the three electrically driven hydraulic pumps: It seems a little redundant to power a generator which powers a motor which powers a pump which powers a tool. Since there are two pto openings on the big Allisons you might want to consider a separate pto which runs a single pump that is hard plumbed to all preconnected tools thereby eliminating the generator and motors entirely from that equation.

    Also, if you still go with the large PTO generator, don't forget to have a way to get all generator output from a single receptacle in case you have to power a police station, city hall or whatever. In a disaster it would be a shame to have that much power sitting there ready to handle nighttime extrication but unable to help at much else other than a coffee pot.

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