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solar regulator question

Discussion in 'General Electronics Discussion' started by greigy, Apr 16, 2013.

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  1. greigy

    greigy

    6
    0
    Mar 28, 2013
    hi guys me again. is there any reason why i cany use a solar regulator on my micro hydro project. it will be charging a 48v bank of batteries. i have found on ebay a couple of controllers, one is 10a and the other 20a 48v charge controller which if there was no specific reason why it needed solar only input would be fine. I was hoping to be able to rectify the ac output and put it through some filter caps. the output range from the permanant magnet alternator is 60-90v depending on load and produices around 300w max continuious. here are the links for them.

    http://www.ebay.com/itm/MPPT30-10A-...301?pt=LH_DefaultDomain_2&hash=item51ab2953a5

    http://www.ebay.com/itm/20A-Solar-P...406?pt=LH_DefaultDomain_0&hash=item4ac38c8626

    im thinking the second one would be better as it can handel 20A although ill never get that from the alternator but can also take up to 100v on its input.

    is it worth a try? and in this situation is the MPPT one going to be any better

    cheers
     
    Last edited: Apr 16, 2013
  2. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Impulse Turbine

    I did post-grad research on turbines back in the day...(before brain atrophy set in) so I may be able to help in one way or another.

    There is no reason why you should not use a solar charge regulator (of the appropriate specifications).

    The solar charge regulator is not sentient. It does not know the electricity comes from a hydro-electric impulse turbine...as opposed to an array of solar cells. A 10 amp 48 volt solar charge regulator should be more than sufficient for a 0.3kW installation as amps x volts = watts..accordingly, 10 amps x 48 volts = 480 watts, significantly more than the maximum output of the alternator motor. The problem with this solar charge regulator is that it cannot handle the high voltage being churned out by the alternator motor.

    Solar charge regulators are useful for two reasons. They prevent batteries being overcharged (which damages them when they exceed their maximum data-sheet voltage) and they prevent batteries (batteries under load from inverters powering lights for example) from being over-discharged (which damages them when they go below their voltage parameters).

    There is no or no good reason why you should not be able to use a solar charge regulator to protect a battery bank supplied with electricity by a hydroelectric impulse (or other) turbine. They are potentially useful in any non-grid tied situation (where the installation is not connected to the mains).

    However, the solar charge regulator will probably have a built in photosensor and it would be well to ensure you do not select any of the options permitting the photosensor to turn your load on and off unless you specifically want to turn lights on at certain times etc.

    Unlike solar arrays which stop producing electricity every night, hydro installations provide power continuously, subject only to seasonal variations due for example to higher water flow in winter and lower flow in summer.

    Aside from load management options on solar charge regulators (often used to turn street lights on at night and off in daylight), I see no reason why a solar charge regulator should not be perfectly good at protecting your batteries from overcharging and over-discharging.

    In terms of preventing over-discharge under load, simply disable the photosensor options (more accurately...do not engage them) unless you want those power management options, and the solar charge regulator should adequately prevent your batteries being damaged by over-discharge under load anyway.

    I suggest using sealed deep cycle gel type batteries here as they designed for continuous charging and discharging. Lead/acid car batteries will not last long in this type of application and may emit hydrogen gas which is dangerous.

    Further data would be helpful if you require a more detailed response. In particular, a 'runaway' turbine (during flooding for example) could damage the proposed solar charge regulator (if the alternator/turbine exceeds its design specifications and churns out more than 480 watts before disintegrating). I do not suggest getting the 10A 48v solar charge regulator because it cannot handle the output voltage of the alternator motor, and rectification and conversion reduces efficiency. In order to advise more fully, I need the following further information.

    Impulse turbine specification (Pelton, Francis, reverse archimedes screw etc),
    Turbine radius in metres
    Pitch circle diameter in metres (the smaller diameter circle marking the point in the centre of the cups where water actually strikes the turbine buckets)
    Cup materials and number and design of cups (steel, aluminium, plastic etc, and dimensions/design.
    Flow rate of water in cubic metres per second
    Seasonal variations in water flow (m3/s/min and m3/s/max)
    Height (Head) in metres the water or other working fluid falls before striking cups of the turbine
    The number of turbines contained in the apparatus (one, two, etc)
    Alternator motor maximum output in kW (you mentioned 0.3kW?) and inertial torque in N.m (how much rotational force is required to turn the alternator motor from a standstill?
    Precise datasheet information on alternator motor
    Precise datasheet information on proposed solar charge regulators
    Estimated maximum speed of the outer circumference of the turbine under max load in radians per second or RPM/60
    Estimated efficiency of alternator motor (80%...85%?)
    Density of working fluid in kg/m3, which is to say, is your working fluid fresh water with no material impurities (1000kg/m3), saltwater (1020kg/m3), etc).
    Water velocity in m/s as it exits the nozzle before striking the turbine cups or pressure in Pa or N/m2 at that point (to apply Bernoulli's equation)
    The type, aperture diameter and number of nozzles applied to the turbine runner and nozzle distance from turbine.
    Penstock specifications (water must be able to flow out at least as fast as it flows into the penstock) and consider also eddy currents, runner speed versus working fluid velocity, as runner speed cannot exceed 50% of working fluid velocity or it actually reduces the efficiency of the turbine for complex mathematical reasons, and turbulence.

    Alternatively, go with the 20A 48v solar charge regulator. It is unlikely that even a runaway turbine rated at 0.3kW is going to exceed 0.96kW though even then, voltage spikes outside the specifications of the solar charge regulator are still possible. This is why it makes sense to do the maths (in terms of flow rates, head etc) before buying an alternator motor.

    Always begin with your flow rate in m3/s and your head in metres. Gravity is not going to change anytime soon. Then pick your turbine after considering force in terms of F = m*a, and go on to apply Bernoulli's equation and finally a Pmech (watts) power output equation. Check your calculations for reasonableness using the conventional equation for power output from hydroelectric installations. If it all scans, pick an alternator motor appropriate for the force in Newtons your impulse turbine is going to be supplied with by the falling water. The force may be inferred from the nozzle pressure as pressure is force/area. But force in Newtons on the cups of the turbine is always the starting point. Then comes turbine diameter selection and then, always last, selection of the alternator motor.

    Torque (N.m) and angular velocity (radians/s) are inversely related. The bigger your turbine diameter, the more torque, but the less angular velocity and vice versa. So turbine selection is always difficult, and then and only then, can you begin to select an alternator motor.

    Once certain of the alternator motor you need, then get an inverter appropriate for that alternator motor in grid tie situations or a charge regulator for off-grid battery bank situations. But from first principles, tell us your flow rate and head and we can work from there as a starting point.
     
    Last edited: Apr 18, 2013
  3. greigy

    greigy

    6
    0
    Mar 28, 2013
    cheers for some great news

    thanks heaps for the info that confirms my suspicions about the controller.

    the system is sort of a diy build it yourself project unit but has proved itself so far.

    i already have the pelton wheel and the alternator.

    the pelton wheel which is from www.powerspout.com though i got it from ebay is approximatelt 300mm in diameter and has about 15 cups i think, made from plastic. the water would hit at approx 275mm diameter, a rough guess sorry

    the alternator is made from an old fisher and paykel smart drive washing machine with a very simple permanant magnet motor. the motor has 42 fixed poles which can be easily cut and wired in numerous ways to change the voltage and current output when used as an alternator, simply by changing how many poles are wired in series/parallel. the output is still 3ph ac.

    the site has a fall of 20m (gps) from a creek up the hill which has good flows all year round. the pipe is 600m long and 85mm diamater. static pressure at the bottom is 30-35 psi. and about 4.5 - 5 litres a second based on filling a 20l bucket

    we had a play with different jets last weekend and managed to get a peak no load output of 90v. when we loaded it up to about 2a using light bulbs the voltage dropped to around 75-77v. the 20A controller has a stated max input voltage of 100v

    also do i connect the inverter to the batteries or the charge controller. im guessing the batteries as it is a 2000w sine wave. the load is only going to be a fridge/freezer and lighting at night. the extra capacity is just to supply start up currents and occasional other appliances

    i have included pics of the generator in question _Fisher_&_Paykel_re-wiring_2.JPG

    _Fisher_&_Paykel_re-wiring.jpg
     
    Last edited: Apr 18, 2013
  4. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    I did some rough calculations based on your head and flow figures. These are my preliminary (back of a cigarette packet) estimates for maximum power output in watts based on head of 20m and a flow rate of 5 litres per second (= 0.005 cubic metres per second).

    Working fluid = Fresh water of density 1000kg/m3
    Flow rate of working fluid: 0.005 cubic metres per second
    Height water falls before striking turbine = 20m
    Diameter of turbine = 0.3m
    Pitch Circle Diameter of turbine (estimated) = 0.27m

    To calculate the theoretical maximum power output in watts a highly efficient system is capable of generating, multiply the density of the working fluid (water of estimated density 1000kg/m3) by the height the fluid falls before hitting the turbine (20m), then by acceleration due to gravity (9.81 m/s/s) and by the flow rate in cubic metres per second of the water (here 0.005 m3/s) and finally by a unit-less fraction representing estimated turbine efficiency (85% = 0.85).

    Pw ([power in watts) = 1000kg/m3 x 20m x 9.81 m/s/s x 0.005m3/s (flow rate) x 0.85 (efficiency of turbine)

    Pw = 833.85 watts = 0.83385 kW

    So this is the absolute theoretical maximum output you can ever get out of your impulse turbine if 85% efficient, which is a good approximation for a turbine of 0.3m in diameter. Larger (huge) turbines can have efficiencies as high as 92%.

    Other inefficiencies in the system must also be taken into account, but this is a good general starting point for maximum theoretical output in watts based on head and flow rate.

    Note how critical the head and flow rate variables are. If the water really falls 20 metres, this is your max theoretical output. If however it trickes down the side of a hill, and then free-falls a couple of metres, I would have to change the projection. A photo of the locus (the waterfall) would be helpful.

    Some inverters have features that prevent them over-discharging batteries. If you are unsure, I would connect the inverter to the charge controller output (load) +ve and -ve pins, and connect the battery to the charge controller battery connection terminals observing the polarity markings...however I still have reservations about the set up and should appreciate more data and time to do more detailed calculations.

    My best estimate of actual power output in watts is as follows:

    35 psi = 241316 Pascals

    Applying Bernoulli's equation tells us the velocity of the working fluid as it strikes the cups of the impulse turbine.

    P = ½ r . V2

    P = Pressure (Pa)
    r = density (kg/m3)
    V = velocity (m/s)

    P = 35psi = 241316 Pa = 241316 N/m2
    rwater = 1000 kg/m3

    The mystery value is velocity (m/s)
    241316 = 500 * V2
    482.632 = V2
    V = 21.96888709 m/s
    V = 22 m/s

    However because this is an impulse turbine where turbine speed may not exceed 50% of water jet speed if maximum efficiency is to be maintained, we have to do some subtraction:

    Vrunner may not exceed 50% of Vjet
    Vjet = 22 m/s
    Vrunner = 11 m/s

    Delta Mom = mass flow rate x Delta V
    Delta Mom = mass flow rate x (Vjet - Vrunner)
    Delta Mom = 5kg/s x (22 m/s - 11 m/s)
    Delta Mom = 55 N

    This limits the Fjet force figure in Newtons to 55 Newtons, but we can now calculate the RPM figure for the turbine based on runner velocity of 11 m/s.

    First we need to calculate the circumference of the turbine.

    Diameter = 0.3m
    radius = 0.15m
    2.pi.r = 0.942477796 m circumference

    Vrunner = 11 m/s
    RPS = 11.67136249 revolutions per second x 60
    = 700.28 RPM

    Applying this figure to the Pmech equation used to calculate mechanical power output in watts based on RPM of 700 RPM and the Fjet value of 55 Newtons:

    Pmech = Fjet x Njet x pi x RPM x 0.85 x 0.27m / 60
    = 55 N x 1(jet) x pi x 700RPM x 0.85(eff) x 0.27m (turbine pitch circle diameter) / 60
    = 462.63 watts

    That is my best estimate of actual power output in watts. Hopefully one of the other engineers here will check my calculations as it is easy to fall into error when doing calculations like this after a long days work.

    You will generate more than enough power for lighting (especially if you use large mains type LED bulbs though they are expensive at the moment).

    I am not so sure you will have enough electricity to keep a fridge freezer going continuously. Check the power consumption in watts of the fridge freezer as I think you have about 450 watts to play with in all.

    Finally, check your nozzle pipe for backed up water. Your nozzle pressure is lower than I expected and the reason for this may be that water is not escaping the penstock via the nozzle as fast as water is trying to flow into the nozzle pipe. A wider diameter pipe may solve this problem (if in fact it is a problem). I would have intuitively expected circa 400,000 Pascals or more unless the nozzle aperture is fairly humungous.
     
    Last edited: Apr 19, 2013
  5. greigy

    greigy

    6
    0
    Mar 28, 2013
    calculations are looking great thank you so much. things are starting to make sense.

    the pipe diameter is unfortunately fixed at 85mm as it was laid down a year ago and is a huge cost to replace. later on i may put a second bigger say 100-120mm pipe down. the pipe has a fall of 20m as measured on a phone gps from intake to outlet. intake is 5 x 85mm pipes about 5m long each with coarse filters running into a small tank approx 100l sitting in the stream. from the tank the penstock polythene pipe exits.

    the fridge freezer compressor is rated at 150w though i understand it will have a higher start up current and a lagging power factor. i would allow 200w for it. also it wont be running continuiously just as the thermostat determines.

    thank you for the help. i think if i get 350-400w continuiously i will have enough in the short term. ie it will get me out of the dark.
     
  6. greigy

    greigy

    6
    0
    Mar 28, 2013


    here is a video showing what i have modeled it off.
     
  7. quantumtangles

    quantumtangles

    152
    3
    Dec 19, 2012
    Pelton Turbines

    Make sure the turbine is perfectly balanced and secured, else it will wobble at high RPM and might come into contact with the nozzle or otherwise sustain damage.

    Please do not be too hasty about increasing the diameter of your water supply pipe (before doing the maths). Have a look at Bernoulli's equations for incompressible fluids. Personally, I would experiment with different nozzle aperture diameters and perhaps different turbine configurations first, to see how they affect turbine performance.

    The equations you will need to do these calculations are not as complicated as they first appear (they look horrid when you first see them). I can explain how they work and how to implement them if you would find this useful.

    Note also that high RPM is not always a good thing. If you were to point the nozzle of an electric pressure jet washer at a Pelton turbine, you would get amazing pressure at the nozzle (for example, a pressure jet that consumes 3000w might output water jet pressure of 160 bar = 16,000,000 Pascals = 16,000,000 N/m2) but the flow rate of water would be very low (perhaps 0.00015 m3/s). If you apply Bernoulli's equation as I did in the earlier post, you will see that the nozzle velocity from an electrically powered 160 bar water pressure jet is about 179 m/s.

    But despite enormous velocity and pressure at the exit nozzle, the mass flow rate is so low that force in Newtons will be disappointing (because Force = mass*acceleration, and the mass flow rate is tiny).

    You could get 3,000 to 4,000 RPM from a large (e.g. a 0.7m diameter) Pelton turbine powered by an electric pressure jet washer in this way, but if you were to attach a load, the RPM would plummet because of the low mass flow rate and it would generate very little output (considerably less than the power consumption of the electric pressure jet washer...perhaps 150w output through an alternator motor for expenditure of 3000w).

    In any event, congratulations on choosing a Pelton turbine. They have always been my favourite impulse turbines. The fluid dynamics are utterly beautiful (the way water moves around inside the cups before exiting the buckets with zero tangential velocity). You have to see it in slow motion to gain some appreciation of these amazing turbines. Nicely done. I am impressed with your choice of turbine. It should provide you with hassle free power for many years before you need to do any serious maintenance :D

    Power to the Pelton :D
     
    Last edited: Apr 21, 2013
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