240VAC diode bridge input

[Tom]

I have a 1600AH battery bank and a 5kw hydro system that outputs 240VAC split phase. I would like to hook up two classic charge controllers, one on each 120V leg of the Hydro output. The way that I thought to do this is with two 120V diode bridges (CEHCO 6M/300A/600PIV/4D), one on each 120vleg.
When the breakers are off to the charge controllers, each diode puts out about 130VDC. However, when I installed the charge controllers and turned on the breaker to either Classic, the DC voltage from the diode shot up to 312VDC! The Classics go into HyperVOC and nothing seems to have caught fire, but obviously I can't charge the batteries with voltage this high. What am I doing wrong here?

The classics are wired directly through their breakers to the diode positives, and they each have a negative connected individually to the negative bus.

Thanks!  Tom

[Halfcrazy]

1 of 2 things possible here.

1 the meter is out of whack and it reads exceptionally high on higher voltage (More common than one thinks) or there is some funky Peak to Peak referencing going on here do to the split phase?

I would expect around 180 to 190vdc on the dc side of a rectifier fed with 120vac the fact you are seeing 130vdc seems odd. What I would suggest is to completely unwire the other Classic and rectifier and make sure the single rectifier left has 120vac on it and try it again. I may also try to have a spare meter there.

Ryan

[boB]

When the breakers are off to the charge controllers, each diode puts out about 130VDC.

Hi Tom.   I believe that in this case, (130VDC) this is because the capacitors are not in circuit and
the actual DC component IS 130VDC.   When the peak voltage of 180V or so charges up the
capacitors, (controller being off at that time), you would read around 180 VDC.

What happens if you just connect ONE of those bridge rectifiers up to ONE Classic ??

You might try this as an experiment.  (quickly maybe).

I might try to come up with an LTspice simulation for this for you to play with.
I highly suggest that people that want to play with simulations with this kind of
thing download LTspice (LTspice IV) from  the www.linear.com    site.  This can teach a LOT about
how this stuff works, especially with applications like this one. I use it all the time here.

boB

[boB]

Tom, I couldn't find a data sheet for this particular diode bridge.  Could you post a link or a data sheet ??


PS...   I am imagining 156 volts peak times 2 to get 312 volts output.  That would be something a bit
higher than that to start with but some loss due to diode drops.

Is this just 240 VAC (split) when running open circuit on the hydro ?  what is the output frequency ?


Thanks,
boB

[boB]

I just simulated this in LTspice.  It took only about 5 minutes to do using 8 discrete diodes.
(the diode number doesn't matter for this simulation.)

Yes, you will indeed get twice the peak voltage per phase doing things this way.

Download that LTspice from Linear's website and play away.  It will be obvious to see what
is going on here after a bit of playing around with the circuit and getting used to LTspice.

I have attached a .asc file that can be loaded directly into LTspice which is the schematic I used.
I did not add filter capacitors, which the Classic does add to each output.  I also loaded each one
with an arbitrary 100 Ohms which loads things down to around 4 amps or so.

Also attached is a GIF of the schematic that this .asc file will present and a waveform of the
bridge rectifier outputs (non capacitor filtered)...  Notice that every other rectified peak alternates
between what you would want or expect to see (~ 170V) and double that value (~330V)

Each sine wave generator is just 60 Hz with a 170V Peak value.  In reality, your generator will
have some small finite series resistance and inductance which you can also insert into the
circuit if you want to simulate IR drops and other effects from the sources and loads.

Interesting.

boB




[attachment deleted by admin]

[Tom]

Attached is the data sheet for the diode bridge assemblies.

More information in response to questions: Yes, the Hydro puts out 240/120 split phase at 60Hz. This is the open circuit value.

Thanks for your help boB. I'll play with LTspice.

Hooking up just one classic seems to have no effect. However, if I disconnect the positive from the classic, and then turn on the diode output breaker, I only register 190VDC.

Do you have any suggestions as to how to proceed? I could try to transform the AC down to 60VAC, which would put me into the right range. This would require a hefty investment in a transformer though, Probably rated at double my hydro turbine's output.

Would capacitors help? What's this DC clipper that I hear about?

[boB]

Attached is the data sheet for the diode bridge assemblies.

More information in response to questions: Yes, the Hydro puts out 240/120 split phase at 60Hz. This is the open circuit value.

Thanks for your help boB. I'll play with LTspice.

Hooking up just one classic seems to have no effect. However, if I disconnect the positive from the classic, and then turn on the diode output breaker, I only register 190VDC.

Do you have any suggestions as to how to proceed? I could try to transform the AC down to 60VAC, which would put me into the right range. This would require a hefty investment in a transformer though, Probably rated at double my hydro turbine's output.

Would capacitors help? What's this DC clipper that I hear about?

Thanks for the data sheet on the diodes.

The reason the voltage goes up when you connect it to the classic is because the average voltage  goes up when the peaks
of the rectified AC voltage charge those capacitors up.   The turbine / generator is unloaded so you will just see the same
waveform you had without the caps but instead of the voltage going up and down and up and down and showing an average
voltage of something lower than peak, as soon as you hook up any capacitors, it is then steady as a rock at the peak
voltage which is the 312V that you see.  WAY too high.   You will probably need to use a step down transformer like
you are talking about, OR, reduce your water flow and adjust the nozzles down so the generator makes less voltage.
Less power too of course.

Hey, how about a variac ??  Then you could adjust the voltage down before it goes into the diodes maybe.
Would probably have to be a large one though.

Yes, a Clipper could help but then you would always be wasting power.  Better to just turn the water down in that case.

boB

[Tom]

Ok, so progress has been made.
I installed a second transformer. I now see 90VDC open-circuit. The Classic connects and charges, but acts strangely. I've got it set for Hydro mode. I would expect the classic to find the MPPT, then park at a fairly constant voltage and amperage level. Instead, the volts level out at about 70, but the amps fluctuate wildly from 4 to 14 about as fast as the controller seems to be able to update the screen. This fluctuating amperage is verified by the shunt on my batter meter, which in fact is reading up to 40amps.
Additionally, the classic displays "AMP LIMIT" fairly frequently with a yellow light. I did reduce output amps to 41, but it's not getting close to this according to the Classic display. It is reaching this limit according to my battery meter's shunt.
The third odd thing is that the classic periodically goes into Resting mode, even though it's set for Hydro. The Hydro output is very constant, so I don't see what is causing the Classic to behave so erratically. I am worried that the pulsed DC from my rectifiers is confusing the Classic, but I had thought that it could handle this sort of thing.

Any thoughts?

[Tom]

I did a reset, went through the wizard again, and it seems to work fine. I think that somehow the mode was not actually Hydro, even though that's what it indicated.