Micro CoGen.

OK, so, my guess in the last post was actually right. This alternator is designed to produce around 12-15V, and the electronics package contains a Boost Converter which pushes which up to 50+ to charge the battery.

I was confused by the lack of large inductances necessary for this type of converter, but someone on another forum pointed out that it's using the motor coils (stator) themselves as the inductance. I didn't know you could do this.

Once you get this, everything makes sense. The five phases come into five daughterboards which each contain a FET bridge (two large FETs bonded directly to the substrate) with one of the FETs connected directly to Ground via a precision shunt / current measuring component. The idea is to short the winding directly to ground initially in the AC cycle, let the current start to build up in the inductor/coil, and then turn the FET off; the resulting flyback voltage provides the higher output. This is being done under control of the central processing module (see the photo above). And this in turn responds to CanBus commands on the four-pin control interface.

Honestly hacking CanBus commands is beyond me and I'm after a simpler solution in any event, although this is a pretty impressive and clever machine. So I'm going to try rewiring the stator coils arrangement and seeing if I can get more voltage out of it that way, and just leave the electronics out of it. Conceivably, I could build my own boost converter - they can be extremely efficient - but that's Plan-B for now.

Ah, this is a grid tie inverter? Connected to batteries? A current limiter would have to switch the dc on and off, this would make crappy dc which might burn the inverter. I'm still not sure what your goal is here.

QuoteUsually the current limiting is done on the load on the inverter, not the supply to it. Can you tell more about what your trying to do?

This class of small Chinese inverters are notorious for drawing unlimited amperage and burning up.
Their input is determined by the size of the PV array feeding it.
As an example:
The inverter can accept 20 - 38 vdc and is rated at 1000 watts.
A 35 volt 900 watt solar PV array puts out a MAX of 30 amps and 900 watts when under load and pulled down to 30 volts.
There is zero chance of killing the inverter because the panels can never produce enough to overpower it.

However if you connect the inverter to a 24 vdc, 400 amp battery bank, the inverter runs right up to full input amps and runs so hot that it cooks the Mosfets. If the battery bank output (inverter supply) was limited to 800 watts just like a PV array, the unit would last longer.
That's what I'm trying to achieve.

Usually the current limiting is done on the load on the inverter, not the supply to it. Can you tell more about what your trying to do?

Can anyone help me with a recommendation for a device that can limit DC current from a battery bank to a device?
In this case the 24 volt battery bank is connected to a 1000 watt grid tie inverter.
When connected, the inverter immediately draws the full 1000 rated watts and runs at it's maximum capacity (and heat) with no restrictions for longer life or safety.
My goal is to restrict the supply current to 800 watts (33.3 amps) by installing some device between the battery and the inverter.
For low wattage circuits a light bulb can sometimes suffice, but for 800 watts, I have no idea what would work.

If a big resistor is a possible solution, I need some help sizing it.

Any recommendations or instruction ?

Thanks

So things have moved on a bit. Some good things, some bad things, kind of at a pause right now.

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Things got off to a bad start when I decided I needed to remove the pulley from the alternator to fit a different size one. Not having a large-enough impact wrench, I gave it to a guy at the local garage/auto workshop, forgetting to tell him the main nut was a left-had thread. I heard a loud snap and a sheepish engineer appeared, holding the alternator in two pieces. No repairing that, so I had to buy another alternator (it turns out Suzuki use exactly the same device, and it's cheaper because there's less demand than for Ford).

The alternators are nicely made - SKF bearing at the rear and the main one says "made in germany" so is likely to be good quality.

I have set up a test rig, driving the alternator using an old washing-machine motor with a speed controller so I can vary the rpm.  I'm using a bench power supply to feed the field coils/rotor, so I can adjust the current, and running the output through a five-phase bridge rectifier (just two three-phase units in parallel) and watching the AC output with an oscilloscope and the DC output with a meter. It's open-circuit output - no load - but I reckoned it would be representative.

I do indeed get very clean DC out of it. However, I'm finding I need to get the RPM up *really* high. Here's a graph at 3600 rpm, showing how output voltage varies with field current :

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Current in Amps is along the bottom (x-axis) and you can see we've pretty much reached saturation by 10 amps - no useful increase beyond that.

So let's fix the current at 10A and then wind up the speed :

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Nice linear relationship, BUT we're at 5,000 rpm before hitting 24 volts, which means to get to 48 volts (or a bit beyond it, if we want to charge batteries) we would need to be at around 11,000 rpm. Hmm.

Looking at the car this unit comes from, the crank pulley looks roughly 2 x the size of the alternator pulley, so in order to charge the batteries, the engine would need to be doing over 5,000 rpm. That doesn't seem right ! How often will it be doing that ? The idea is it does this under braking, capturing waste energy, and you're not going to braking at 5,000 rpm unless you're on a race circuit.

So, where are we ? I could probably get this useful by running it really, really fast, but I don't want to do that as 11K rpm sounds excessive even if the device is rated for that. And I don't see how in it's intended application (the car) it can do anything useful.

Is it possible the big chunk of management electronics I took off this is doing something very clever like boosting lower voltages up to enough to charge a 48v battery ? Some sort of boost converter? I am next going to try wiring it back into the circuit and trying things, although I have a feeling it may need some sort of control input to tell it to go into charge mode.

Any thoughts appreciated, as usual, and I will let you know what transpires...
Richard

The exhaust will flow through the small tubes and the water will flow around them.

Alright! Is exhaust going through the shell or tubes?

Naturally I haven't taken a finished photo yet but hopefully soon You cannot view this attachment.

id love to see bob chime in on this. Ive seen lots of talk of what he has come up with but yet to actually see any picture?

Im currently working on building a SS shell in tube exhaust heat exchanger. Hopefully ill be posting pictures soon