You can measure ac current quite simply with a 1 foot piece of solid #10 gage copper wire in series with your load and an ac voltmeter that can read millivolts. Measure ac millivolts across this length of copper yields 1 millivolt ac = 1 amp of ac current through the wire.

Cheers.

TomW

Transformers are nearly 98 percent efficient in transferring power. Don't worry about the losses. However, in increasing your voltage you will decrease current. The reverse is also true. Increasing current will decrease voltage. It's a give and take. This is why I believe so highly in high voltage systems, which produce low loss. In any case, ferrite is good at high freqs but bad in low freqs. Most ferrite is used in apps where you want to achieve resonance (for max transfer of current) and is usually above 10 or more kHz.

To give you a rough idea of where your voltage is at present, stick a bridge rectifier with about a 100uf around 25 volts or more capacitor (after the rectifier) on the ac coming directly from your genny on each of your phases, it will cancel all the indevidual coil phases (which is why you can't read it properly now-not high freq but cancellations within coils) and give you a voltage in DC which is really close to your output voltage per phase AC. The 100uf cap will only charge to a certain limit, that being your total charging capacity. (Roughly this DC voltage is about the same as your AC voltage less rectifier loss.

Advice: Do the above DC checks to getting a clue to your true voltage. Don't change over to ferrite. Find a happy medium between charging voltage and output current from a transformer which will meet some of your specs for charging. you could also change your core and douple or thriple the coils thus voltage without changing anything else. the core is the problem, or cancellation.

The other one with a ferrite core rating is not
known to us. It transforms 1:10.

One quite high-level specialist of electricity
appliances told me that those normal transformers
cannot cope much above 100 Hz because they were
made only for 60 Hz.

Our generator is a variation of
the OP 'Volvo' generator, with 20 coils and magnets, single phase.

It means that 180 RPM makes 60 Hz,
240 RPM already 80 Hz.
So the transformer becomes
ineffective quite fast.

We might try measuring later the AC going in, one
of my friends has got such measuring device, which might be able to do the job.

We are aware that we can make quite easily a new
stator with more coil windings to get the cut-in speed lower.

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But recently it came to my mind that
actually using a transformer might be a good idea... (Even if we started to use it because of
a mistake by my friend to use too few turns in the coils.)

If you use lots of coil windings to get the voltage high with low RPM, your generator
becomes easily ineffective with higher RPM because of the resistance of the coils.

Maybe it would be
better to use thick wires with fewer turns in coils to get it effective even going fast and use
a transformer to get it charging with slow speeds?

What do you think?

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The new blades with the generator are a variation
of the 'Reinikainen' blades I've told about earlier. (The old ones were aluminum-polyurethane blades of about 4 m diameter.)

These Reinikainen blades are with four blades.
3 m diameter, made of flat 10 cm wide boards, glued and screwed together so that at the tips the boards are on the top of each other only 2,5 cm.
Five boards in each blade.

The new rotor works very well, it starts very easily and with lower wind speeds than the 4 m airfoil rotor and seems to go about as fast as the earlier aluminum-polyurethane airfoil rotor.

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When you use less turns you have less volts, but the potential for more amps.  With more turns you have more volts but less amps (for the same efficiency at the same speed).  Therefore it does not help the efficiency to change the number of turns, except in order to improve the matching of speed to load power.  And you can do this with your transformers.  So the number of turns in the stator does not really matter.

I have to say I do not understand why you use two transformers.  I would wind the stator to produce a high voltage and then use just one transformer.  Some may be 98% efficient, but not all.  And the frequency variations make them harder to design.

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I agreee that we cannot get any more power with transformers, we always loose some.
I was just thinking that we would have a bit broader range of RPM, because with fewer turns
(and thicker wires) we can spin the generator
faster, before it starts overheating.

I agree that most transformers are not at all 98% efficient. My friend has used these two different
transformers (one at the time) simply because he
happened to have them. The frequency change is
one quite big problem to cope with transformers.
Finally my friend already decided to make a new stator. It is ready now.