Fisher and Pykel question

[domwild]

Picked up a 60S or 80S from rubbish tip. Hand turning at about 100 RPM gives me up to 60V between one phase - two out of three wires. May make up to 300V at 400 RPM. I need that voltage as the mill is far from the house.

I would like to buy a 24V DC hot water heating element. What is the suggestion to translate up to 300V AC to 24 V DC? Am on grid so do not need batteries. Can buy three transformers for 240V AC to 0-15V and 0-30V AC taps + three 35A bridge rectifiers. Am worried about 300 V AC blowing up the 240V AC transformer. Am worried about 24V DC being exceeded for the water heating element.

Any suggestions?

 

[Flux]

Those motors have a lot of poles, at 400rpm I think the frequency is well over 60 Hz so it won't hurt the transformers, the 240v limit will be at 50 or 60 Hz.

If you choose your heater so that it is rated greater than the maximum watts your generator can produce you won't damage that either.

Why do you want to use 24v dc, if it is just for heating I would have thought it would be easier to use 3 high voltage heaters direct, without transformers and rectifiers.

Flux

[tecker]

  You need to fully test the Generator set to ease you mind . Are you attempting to run the ouput of your Gen set to a transformer and stepdown to the heating elements .

  Put the finished unit on a jig and run it up with a drill or like device.

  measure the output under load and take those finding to calculate the load devices .

 The long run to your headend will require some planning Conduit, wire sizing , and code recognition . All will come from further testing . I know the fourm has data on these units a search would do some good.

 If you just want to heat water then most single phase 240 element will load down the generator to the point that the Ac out could go to the water heater . However If wind is not constant you'll have to use a battery bank . Just  Phase the windings for low voltage and rectify .  

   

[commanda]

At 400 rpm, the frequency will be in the order of 200Hz. My unit makes 137Hz at 293 rpm.

The voltage limit on your transformers (primary side 240 volts) is actually the insulation breakdown voltage.

If it was me, just to heat water,I'd be looking at connecting to heater elements directly. Just need to match them to the generators output.

Amanda

[veewee77]

just remember that a heating element in a water heater takes a lot of watts.  You could hook that F&P directly to the 24V element and likely the 24V element will draw so much current that it would load the voltage down enough to not hurt the elements.

I dont know what the watts are that the F&P will put out but I'd figure the element to be at least 1000W.

Doug

[Ungrounded Lightning Rod]

Actually the insulation breakdown voltage will typically be much higher than the rating.

The voltage rating has more to do with how much current, and thus magnetization of the core, you get at the rated frequency.  If you increase the current too far the core will saturate, at which point (if you're connected to the grid) the current will spike up to extreme values and burn up the transformer.

There is much less slop on the saturation voltage/current, because doubling the voltage before saturation (at a given frequency) means doubling the amount of core laminations, while insulation for high voltages is very easy - and over-insulating makes for a more reliable transformer while there's no significant advantage to making the insulation thin and pushing the envelope on how close you can get it to breaking down at the rated voltage.

Note that overvoltage on the transformer due to magneto overspeed is NOT a problem.  The peak magnetization of the core is proportional to the strength of your magnets in the alternator, regardless of speed.  Speeding it up increases the frequency and the voltage in lockstep, so the magnetization maximum remains the same.

[domwild]

Thanks for the advice to everybody. The solid fuel water heaters in Australia come with two threads, one for the alum sacrificial anode and one for an optional electric water heater, so I will have to stick with transformers and rectifiers, furling and choosing a high enough load for the DC heating element (US39.00) to stop the mill racing. The info available on the net has advised me that a single 1000W 240AC heating element will only draw 2A at 24VDC, so I have to stick to DC.

[Nando]

domwild:

First of all, I need to know the wire size to tell you the voltage at the desired RPMs.

Second, the Smart Drive motor produces about 1 watt per RPM, so at 400 RPM about 400 watts are produced.

Max power is around 1000 watts (1 KW).

Third get an AC heater that may have 2 elements, quite a few have two.

If the third is not possible, then there are other possibilities.

Set up the generator to produce Star/Delta configuration voltages ( 3 wires ) and at the end (load side) using a full wave 3 phase rectifier.

The decision of Star or Delta configuration depends of the conversion set up.

Also you can modify the connections of the coils to reduce the voltage to half and twice the current, though I do not recommend such change due to the distance from power source to load

Also if you got the motor without any change you may have a Star connection which means the 60 volts across two wires gives 34.7 volts across each phase winding.

NOW EXPLAIN what are you going to use to drive the motor ?.

Hydro, if so, give the head and the volume to see what you can generate.

Using power transformers would be a solution BUT define what is the generated output voltage before you acquire the needed transformers (3 each)

Regards

Nando

[domwild]

Thanks for help. You, commanda, flux and others have helped a lot. Wire size is 0.6 mm and it is wired from the factory as a star, 42 coils and 3 x 14 coils are connected in series.

Am hoping to drive the mill with the biggest PVC prop I can cut from Australian 100 mm (4") sewer pipe as per the PVC discussion on this forum. Perhaps each blade to be one metre long for a two metre diameter prop with three or four blades. The F&P smartdrive motor cogs so higher torque would be necessary. Longer than one metre will probably result in disintegration.

Any idea of what is cheaper in Australia or generally: Three bridge rectifiers from Jaycar (.com.au) 35A each (~AUS$10 or US$5) or one single full-wave three phase rectifier?

Thanks.

[commanda]

Dominic,

The bridge rectifiers in my Jaycar catalog (ZR-1324), 400 volt 35 amp, are AUS $4.95.

The F & P's can be de-cogged. Haven't tried it myself yet though. I want to get some serious test data with the unit on the lathe, so I can compare before & after data.

Amanda