Could my Bobcat drive a hydraulic generator?

bebey
bebey Solar Expert Posts: 27 ✭✭
in Off Grid Solar & Battery Systems #1
My current system does not often need a generator to top it off unless we get a few days of clouds, which in Central TX is not a common occurence. I have a bobcat that has auxiliary hydraulics that can drive numerous attachments. How practical would it be, and any idea how it could be done, to have some type of hydraulic pump drive a generator to charge the bank? Would it be better to do it through 110v on the inverter like a standard generator, or if I was custom building something, how about a direct connection to the 48v battery bank?

Appreciate all of the insight!
Bret
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Could my Bobcat drive a hydraulic generator?

    It would cost less and be far more efficient to buy a small inverter-generator for those times when the sun doesn't shine. Trust me.
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  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    #3
    Re: Could my Bobcat drive a hydraulic generator?

    I'm with cariboocoot, but depending on what type of bobcat you have, it might not be that difficult if you're mechanically/welding inclined.

    http://www.northerntool.com/shop/tools/product_200321051_200321051 - spins at 3600RPM necessary for a direct drive gen head...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Could my Bobcat drive a hydraulic generator?

    Hydraulics tend to be horribly inefficient at power transmission... But this can be somewhat reduced if your Bobcat has a diesel engine and good overall fuel economy.

    As to 110/220 VAC or 48 VDC--For random use I would go with what makes the best overall use of your money.

    If you can use portable AC power--I would go with that. AC powered battery chargers are not that expensive and will provide a good/universal backup for Grid/alternative generator power.

    48 VDC would be pretty specialized and only be useful for recharging your battery bank and not for much else (i.e., the genset non-battery charging value is near zero--so only buy if you can get for very low costs).

    Overall--I agree with Marc that a portable genset is going to be less expensive, more portable, probably more fuel efficient, quieter (really a big thing if you have anyone within ear shot. If you are really a belt and suspenders type person, I would suggest a Honda eu family (or Yamaha or other inverter/genset) as your main genset for charging (there are propane conversions for the Honda, and some Yamaha's are tri-fuel from the factory--gas, propane, natural gas (I think). And you can get a second (larger) genset for running the home/shop/larger power tools if needed with one of the "Cheap" 5kW or so gensets (they will drink fuel if operated at less than ~1/2 load).

    The actual choice of the "smaller" genset--I am a big believer in "balanced" system design. A genset (plus AC charger) that is "just right" for your battery bank size (5% to 13% of battery bank rated AH, and for a genset/AC charger, a maximum of 25% of rated output).

    So, if you have a 400 AH @ 48 volt battery bank (using 10% nominal rate of charge):
    • 5-13% battery bank, 10% nominal => 400 AH (20 hour rate) * 10% = 40 amp charger @ 48 volts
    • Solar array => 40 amps * 58 volts charging * 1/0.77 panel+charger derating = 3,013 Watt array "nominal"
    • Genset with "average" AC charger (poor power factor) => 40 amps * 58 volts * 1/0.80 charger eff * 1/0.67 PF = 4,328 VA min Genset rating for "40 amp charger" with poor power factor
    • Genset with "average" AC charger (good power factor) => 40 amps * 58 volts * 1/0.80 charger eff * 1/0.95 PF = 3,053 VA min Genset rating for "40 amp charger" with good power factor

    So, while you pay for "watt*hours" for generator fuel/grid power... Poor Power Factor AC power supplies will "load" the genset so that other loads cannot be used (VA rating vs Watt rating).

    Stevek's thread on the optimum AC battery charger for a Honda eu2000i has lots of discussions about who/what/when/where/why about the subject.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bebey
    bebey Solar Expert Posts: 27 ✭✭
    #5
    Re: Could my Bobcat drive a hydraulic generator?

    A small generator is not out of the question, but I have a couple reasons for considering this as an option and appreciate the pump info. My bobcat is an older 7753 and operates at 12GPM so that pump looks to be exactly what I would need (I would need to experiment with engine RPM to be sure the right pump RPM was working. I'm not sure how slower or faster RPM would affect the generator head.) Are generator heads available or would I need to salvage one off of an old generator somewhere?

    P.S. Yes it is diesel and sips the fuel lightly.

    Thanks again!
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  • bebey
    bebey Solar Expert Posts: 27 ✭✭
    #6
    Re: Could my Bobcat drive a hydraulic generator?

    great advice BB. Thanks!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Could my Bobcat drive a hydraulic generator?

    If you run a 46 HP diesel to supply 5 HP worth of electrical power you won't think it sips so lightly. :roll:

    Most small generators have the armature supported by the crank bearing of the engine (for compactness) so they don't lend themselves to being adapted. The hunt for an "any engine" generator with right size input shaft for direct drive from that hydraulic motor could be tedious.

    You would need both a Volt meter and a frequency counter on the output of the gen to make sure its power was in spec, and you'd have to check this every time as variation of the RPM due to differences in the hydraulic pressure/flow will alter it. On those lines the gen itself will lack inertia enough to make up for sudden load changes. This could be quite a problem to keep the output right. The hydraulic motor will actually act as a brake too, instead of 'free spinning' under no load the way an engine does.

    On the whole not a very practical exercise in power generation.
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  • bebey
    bebey Solar Expert Posts: 27 ✭✭
    #8
    Re: Could my Bobcat drive a hydraulic generator?

    Alright, I'm convinced it is not such a great idea. :) Thanks all!
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  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    #9
    Re: Could my Bobcat drive a hydraulic generator?

    Coot, what about PTO driven generators? Same idea no?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Could my Bobcat drive a hydraulic generator?
    TheBackRoads wrote: »
    Coot, what about PTO driven generators? Same idea no?

    They tend to be of the very large variety, with inertial mass, and built-in electrical regulation. Not the most accurate, but certainly on par with standard engine driven gens. Biggest problem is people not matching the tractor to the generator. Yes, that 160 HP Oliver will run the 10 kW generator. But you only need to use the 35 HP John Deere! :p
    Seen quite a few back when I was doing motors in agricultural. Amazing the number of motors that fail to start when the power goes down (no I'm not kidding - they'd call).

    Trying to govern the speed on the hydraulic-drive idea would be pretty close to impossible.
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  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    #11
    Re: Could my Bobcat drive a hydraulic generator?

    Couldn't you use the hydraulic pump to run a PTO type gen that would then have the regulation vs just pump coupled to a gen head? Obviously not a cheap option, but sometimes nice to have options.. Not trying to argue or anything here, just trying to feel the audience. It is nice to use equipment for more than just 1 purpose sometimes.. but maybe that's just me.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Could my Bobcat drive a hydraulic generator?
    TheBackRoads wrote: »
    Couldn't you use the hydraulic pump to run a PTO type gen that would then have the regulation vs just pump coupled to a gen head? Obviously not a cheap option, but sometimes nice to have options.. Not trying to argue or anything here, just trying to feel the audience. It is nice to use equipment for more than just 1 purpose sometimes.. but maybe that's just me.

    Yes you could if the hydraulic motor developed enough HP for the gen. The trouble is still with maintaining RPM against fluctuating loads. With direct-drive PTO the tractor engine and thus output shaft are fairly well governed for speed. Once you introduce the hydraulic coupling you lose that certainty. Like the efficiency difference between standard shift and automatic. Or more like the old Fluid Power trannies of the 1950's.

    The basic flaw is using so much HP when you simply don't need to. If the call was for some very large kW generator then Bobcat power would be much more viable. A matter of scale, so to speak.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #13
    Re: Could my Bobcat drive a hydraulic generator?
    Cariboocoot wrote: »
    Yes you could if the hydraulic motor developed enough HP for the gen. The trouble is still with maintaining RPM against fluctuating loads. With direct-drive PTO the tractor engine and thus output shaft are fairly well governed for speed. Once you introduce the hydraulic coupling you lose that certainty. Like the efficiency difference between standard shift and automatic. Or more like the old Fluid Power trannies of the 1950's.

    The basic flaw is using so much HP when you simply don't need to. If the call was for some very large kW generator then Bobcat power would be much more viable. A matter of scale, so to speak.

    An important consideration here is whether the hydraulic pump and the hydraulic motor form a hydrostatic transmission (no slip except from piston leakage, variable speed ratio based on swash plate angle, etc.) or a hydrodynamic transmission (as in torque convertor, turbine motor, etc.) In general I see only hydrostatic setups in PTOs, since this allows high pressure low flow rate design, just as high voltage low current has advantages in battery banks, only more so.)
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Could my Bobcat drive a hydraulic generator?
    inetdog wrote: »
    An important consideration here is whether the hydraulic pump and the hydraulic motor form a hydrostatic transmission (no slip except from piston leakage, variable speed ratio based on swash plate angle, etc.) or a hydrodynamic transmission (as in torque convertor, turbine motor, etc.) In general I see only hydrostatic setups in PTOs, since this allows high pressure low flow rate design, just as high voltage low current has advantages in battery banks, only more so.)

    Over the years there have been a wide variety of hydraulic system utilized on tractors, trucks, and other heavy equipment. Different pump types, flow rates, pressures, et cetera. I have seen myself where one tractor would drive a hydraulic motor whereas another wouldn't even though they both had correctly working systems. Usually tractors are designed to develop pressure to operate cylinders, not flow to operate motors. Some have adjustable valves to control the flow rate (look at a JD with its famous tortoise and hare controls). Beyond that is the issue of inevitable wear and leakage. I would assume the Bobcat has the ability to run motors since many of its accessories are driven this way! This makes it the hydrostatic transmission which in theory doesn't slip but in practice does.

    You should see the difference temperature makes on Hy-tran. Talk about tortoise and hare!
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #15
    Re: Could my Bobcat drive a hydraulic generator?
    Cariboocoot wrote: »

    You should see the difference temperature makes on Hy-tran. Talk about tortoise and hare!

    I know the feeling. My otherwise lovely Husqvarna Garden Tractor (oxymoron!) has an under-engineered hydrostatic tranny which has a tendency to score pistons and cylinders. Big difference between a cold start and after the tranny warms up. Even with 50 weight oil.


    IIRC, the JDs (at least the current ones) do not actually use valves to vary the drive ratio. Instead they change either the pump cylinders' or the motor cylinders' stroke length per revolution of the shaft.
    SMA SB 3000, old BP panels.
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  • CDN_VT
    CDN_VT Solar Expert Posts: 492 ✭✭✭
    #16
    Re: Could my Bobcat drive a hydraulic generator?
    inetdog wrote: »

    IIRC, the JDs (at least the current ones) do not actually use valves to vary the drive ratio. Instead they change either the pump cylinders' or the motor cylinders' stroke length per revolution of the shaft.

    Squash plate to change the amount of volume / or rpm for the flow control.

    I have a rear PTO on my Kubota & has a mid PTO for the snow-blower ..When a storm has killed power for days to weeks , I'll drive over to unprepared and control there power for well pumping so toilets get flushed and they can fill up lots of water cans for living plus. I drop all circuits , pick up well pump and then a coffee machine for me & it times my visit /stay, so after coffee I pick up fridge / freezer .. They have no real idea,that a good plastic garbage can that can hold water will flush a inside toilet.
    This PTO gen very expensive to run , but im out on blower & up to temp , but for me to go home , it comes with me. I can see the diesel fuel needle change after a pair of coffees.

    VT
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #17
    Re: Could my Bobcat drive a hydraulic generator?

    "Big difference between a cold start and after the tranny warms up. Even with 50 weight oil."

    Those cold starts...:grr. With my genset and tractor getting intermittent use I always mix 20% Lucas stabilizer with the engine oil. The tackiness keeps oil on cylinder walls/piston rings, so when you cold start there's still some lube in play (at least that's what the advertising says). Still a cold start, just not cold and dry between metal surfaces. It goes in all my engines including cars.

    <product promotion ends>

    Ralph
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #18
    Re: Could my Bobcat drive a hydraulic generator?
    Ralph Day wrote: »
    "Big difference between a cold start and after the tranny warms up. Even with 50 weight oil."

    Those cold starts...:grr. With my genset and tractor getting intermittent use I always mix 20% Lucas stabilizer with the engine oil. The tackiness keeps oil on cylinder walls/piston rings, so when you cold start there's still some lube in play (at least that's what the advertising says). Still a cold start, just not cold and dry between metal surfaces. It goes in all my engines including cars.

    <product promotion ends>

    Ralph

    Good to know.

    I don't think it would help with the Hy-Tran fluid density issue, though.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #19
    Re: Could my Bobcat drive a hydraulic generator?
    Cariboocoot wrote: »
    Good to know.

    I don't think it would help with the Hy-Tran fluid density issue, though.

    Right, especially since what I want is to keep the viscosity high because the #@&amp;% cylinders leak!
    SMA SB 3000, old BP panels.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #20
    Re: Could my Bobcat drive a hydraulic generator?

    My comment was only pertaining to internal combustion engine cold/dry starts, sorry.

    Ralph
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