six cheap car battery chargers the older the better?

Nick the rectifiers out of them then.

300 Watts of AC is something like 25 Amps into 12 Volts which implies 250 A/Hrs of capacity. Using a linear charger would involve a huge transformer, with high-current semiconductors. A switchmode circuit would be more sensible. Your best bet may be to consult manufacturers of charging equipment.

" 300 wats of ac power into DC power" , Keith, this 300W is it at nominally at 24V?. i.e. 30 V at 10A?. The diodes would cost £10 or so. Now this would actually produce 30 X 1.4 V DC -= 42V, so a regulator would also be required, or at least a 1.4 ohm resistor ( 42 - 28* = 14V /10 A = 1.4 Ohms). A more sexy way of doing it would to be build a forward convertor, this is an electronic box that turns the 42V into pulses and pushes them into the battery and when the current has risen to 10 A switches them off. The advantage is that the resistor dissipates 1.4 X 10 X 10 wats = 140W!!, the forward convertor runs at about 90% efficiency, looses 40W?
The reason for the hassle around the 10Amps , is not to protect the batteries, but to protect the generator, cos if its wiring is only rated at 10A, then taking more then this out of it for a prolonged period could burn it out.
* a fully charged lead acid battery is more like 28v then 24.
Frank

These are switchmode chargers. What do you think of them Bluemoon /Chuckey / Tony?

http://www.adverc.co.uk/products/charger/slp.asp

These sort of boxes turn the incoming ac into dc then use this dc to run a big oscillator, The resulting pulses are applied to a transformer and the rectified again back into dc, which is the output. The oscillator runs at a high frequency of say 40,000 Hz so the transformer can be made 50/40,000 times smaller i.e. 1/800 of the size of a conventional mains transformer. The voltage output is regulated by switching the oscillator on and off.
Now applying your problem to this sort of box, is that the oscillator is optimised for a minimum of 90V ac, so running it at only 30V ac, might result in the oscillator not working at all. it certainly would not be able to handle its rated power, at a guess it would be 1/3 rd and the losses would be correspondingly higher.
Telecommunication stuff runs of 50V and there may some thing in this area which will do for you. After a 2 minute search on google I found:-http://www.power.tycoelectronics.com/Family.aspx?FID=b9231c81-7275-470e-bc74-3ce82a3ca5db
This is a 24v out 18 - 36V in Dc to dc convertor.
Frank

Frank

A switchmode charger made for the UK market should suit, they accept input varying between 100 and 300Volts with a wide frequency range, and the outputs don't vary.

Sorry frank. The other thread is about my Proven wind turbine but this one is about my small hydro power unit. Sorry to confuse. I'll adapt the heading and add hydro in. But to refresh. I am about to switch on a small hydro unit which is capable (I hope) of delivering 300 watts at 240 volts (an AC alternator). I am going to feed it 2 litres per second with a head of 23 metres then send the power 240 metres along a 6mm cable to the workshop. At which point I have the choice of trying to use the 300 watts directly on some small regular load OR converting it to dc and using it to help charge my 840ah battery bank along with my other technologies. From the batteries it then goes through a Trace inverter to power the loads of the house and office.

Would you consider stepping the voltage UP at the turbine end, then down again at the load ?. This would save on power loss along the long cable.

As a side issue, how much head and size of penstock and flow do you use to get full output from the generator?

Interesting points Workaholic. I'm learning fast with all your help in fact I ordered just the model you mention last Thursday. Incidentally they have upgraded this model to 12.5 amp. I hope to have it here by next thursday so I'll report how it goes. I have been charging in the meantime with a 3amp (24v) switchmode charger until I could find the model I wanted.

To answers Bluemoon's question I have a 23 metre head fed by a collection pond and I am using a 10mm nozzle at the moment but I need to change it to a 12mm nozzle so I can get 2.5 litres per sec.

2.5 l/s is a surprising large volume of water. I'll take some pics over the next few days of my setup because I have finally achieved this from a non hydro site. However I have had plenty of land to play with to create the top ponds.

The generator, a 300watt model is actually designed for a 14 metre head and 4.5 l/s. I got it from Navitron and it is a turgo type runner.
http://www.navitron.org.uk/hydro_power.htm

By the way, if anyone wants to buy a four nozzle, 240 volt pelton turbine capable of up to ten 10 l/s complete with all nozzles alternator (240 or 24 volt) and load controller then I have one for sale. But be warned, you need a lot of water. But when I had it available I could get 1200 watts!

Many thanks to everyone that has commented on this thread.

Yes it is.

Keith,
do you just keep it running full pelt and the lights on continuously or have you some kind of variable restrictor on the water inlet ?. If you have enough water you may have a good reason to use good old fashioned tungsten filament lights !!! (heat source)

Keith, could you say a bit more about how this set-up has been running over the last year? I'm a complete noob to this but am looking at installing a hydro unit in a similar situation -- ie. where there's a large head (potentially around 25m) but little flow (at the moment guessing about 1l/s but the land is very overgrown and it's conceivable that could be improved once I've cleared upstream and dug a collecting pond or two -- and have been wondering whether an AC turbine like yours would be the one to go for or whether DC is more sensible. I'd be looking to supplement output with photovoltaics as well (this is Central Portugal) and hoping that together this will be sufficient to cater for our modest domestic needs.

Thanks Keith. So it looks like DC might be a lot more sensible. Not least because I can site the turbine very close to the battery store, which in turn is very close to the house. Thanks for the mention of the Stream Engine. Having looked at it, it may well be just what I need.

Another question: all the various sites I've looked at talk about head and flow, and only some mention pipe length, but it seems logical that not just pipe length but diameter and the angle of the pipe delivering the water to the turbine would also have some relevance bearing in mind potential friction losses, particularly with low flow situations. Do you know of any good reference material which goes into ideal pipe angles, etc? Have you or anyone else here got any experience/opinions on that?