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Smee
Newbie

Joined: 06/06/2016
Location: New Zealand
Posts: 1

Posted: 09:06pm 06 Jun 2016

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Hi guys,

I found this forum last xmas and have been playing around with my F&P generator since - and its been very interesting!

I rewired it to a standard 7X2C, made up a windmill before I realised we dont have much wind here....

So before I gave up on it I decided to make a pelton wheel, fit it to the shaft and fire 2 garden hoses at it straight from the towns water pressure (our waters not metered....yet!).

My intention was to get it to charge a 12V battery hooked up to some outside lights, maybe my shed lights, put a solenoid on the water supply to start when the battery gets low, then turn off when its charged - so im not totally wasting the towns water, which incidentally comes from a VERY large lake and will never run out.

I thought it would make a pretty cool deck ornament or conversation piece, and I would learn some interesting stuff while I played around with it.

However, its now raised a few questions I hope some forum members could help me with.

It seems to work better (more voltage and power) with more resistance and I dont understand why - i thought it would be the other way around.

With no load - open circuit or speed no load in hydro terms - it puts out 55V.
With 1 ohm load it puts out 1V, 1.03A so has 1.03W of power.
With 10 ohm load it puts out 8.82V, 0.89A and 7.85W.
With 82 ohm load it puts out 32.5V, 0.4A and 13W.
With 100 ohm load it puts out 35V, 0.35A and 12.25W

As the load increases, it spins faster creating more voltage, therefore more power which I understand. What I dont get is why it does this - surely the more load it has, the harder it should work, therefore slow down as the water pressure isnt increasing, it has the same torque? Kinda seems like it should be in reverse. Can anyone explain this phenomenon in laymans terms please?

Which leads to my second question of using it to charge a 12V battery.

I dont know how to measure the internal resistance of a battery, but from what I googled it seems to be very low in the milliohms. If this turbine is putting out 1V at 1ohm theres no way it can charge a 12V battery. I reckon i would need the battery to be somewhere around 20ohms so it puts out a voltage higher than 12V for charging. Have I got this right?

And my last question for now - I was intending to use a solar charge controller. I dont think I need a hydro one with a dummy load as Im controlling the water supply on and off - it wont be running continuously, so wont have any danger of overcharging the battery.

What size charge controller would I need based on the figures above?

I was in Jaycar the other day looking at solar panels, and realised I could have the same output for about $30. My mates asked me why I was wasting my time with this turbine for the sake of $30 and all my time. But theres no way I would have learnt as much, or had as much fun making this gadget - its been pretty cool.

Thanks for any help, I suspect the answers will help me decide to keep going or give up!

Pete Locke
Senior Member

Joined: 26/06/2013
Location: New Zealand
Posts: 181

Posted: 11:52pm 07 Jun 2016

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Well no one has piped in with regards your numbers, so being as I'm from the same patch of dirt, I'll have a chat...
1/ Your numbers are correct regarding loading (as you posted)
2/ The higher the resistance of you load, doesn't mean the higher the drain on your creation. It's the opposite.
3/ What other tinkering have you done with such things to bring you to this point to charge batteries from an F&P conversion.

Experimenting with stuff can be REALLY rewarding, and I hope at the end of the day you can not only have a wonderful visual ornament, but one that can keep the car battery topped up in winter

Cheers
Pete'.

jack fork stik
Newbie

Joined: 08/12/2012
Location: Australia
Posts: 34

Posted: 02:49am 08 Jun 2016

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ive made up an exercise bike using a 1mm wire size fp motor with a later model rotor so it doesnt sound like a jumbo jet,i found i could only use 1 set of 2 coils in series and another set of single coils otherwise too hard to pedal with 13 to 1 gearing im using with it and your pelton wheel setup might be like that with not enough torque to run 14 coils per phrase in series. dont give up just rewire half of the stator with a few different combinations like i did and have a play with it till it does what you want it to do.being in NZ youll never run out of water no mater how long your tap is on!

Edited by jack fork stik 2016-06-09

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 03:09am 09 Jun 2016

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Simple way to control loading in this case of a pedal-gen or hydro testing, is to undo the nut on the magnet rotor so it extracts the magnets from across the face of the stator
Less magnet surface area = less power input for a increased rpm.
Regardless of what use of the alternator you always need to design so the power range can overcome Stall.

Sometimes it just works

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