ST-5 output to multiple voltages

[bschwartz]

OK, here goes if you can follow this picture....

The ST has 4 poles.
Each pole makes 60v AC
If connected as follows, and I tap points A,C for 120v, and C,E for 120V, and A,E for 240, and install the bridge rectifiers as shown, I'll also have rippled 60v DC.
I can then filter this DC into a charge controller-grid tie inverter setup.

I wouldn't need switches, breakers, etc.
I'd have every combination at all times!!!!

Does anyone see flaws in my thinking?

[Tom Reed]

Yes.  you don't need to jumper the connections to b,c & D. If you do so you're back to ensuring that all the coils are in correct polarity. Sending an individual coil to an individual rectifier eliminates that need.

[bschwartz]

If I don't jumper B,C and D, how do I get normal 120/240?

[Tom Reed]

Short answer: from the inverter, Long answer: I was thinking to wire my st5 with a 4 pole marine transfer switch to allow a simple change of operation. That was until I saw the price of the switch. How important is it to be able to do both at the same time.

[Crofter]

I got a mess of squiggly lines on paper here and muddling myself so not much luck at trying to explain it even if I do have a bit of a grip on it.   I think I see a conflictthough. All 4 coils must be in series with the phase correct to give 240 V scenario; i think that is a given, but for the 60V scenario you want to take all of each coils current but cannot have the voltages additive or opposing. Since all 4 coils produce simultaneously they need to be in same polarity and parallel connected.

When I try to draw to suit 120 or 240, it seems to have the bridges trying to conduct ~ current in different directions at the same time. If I draw it to satisfy DC configuration it screws up the other.



Lead thou me on, the night is dark and I am far from home.

[bschwartz]

On a normal setup ST, if you have 240, you simply center tap for two legs of 120.
this would simply center tap each set of 120 for two legs of 60 (total of 4)

How is this any different?

I'm not arguing, I just can't wrap my head around why this won't work.

[d34]

Looks like it will work fine. I basically wanted to do the same thing til I realized I have a nice transformer that was given to me.

[Crofter]

If you take the two 120 legs of the center tapped 240 you cannot combine them into a single load as that creates a dead short. I get screwed up when I try to visualize FW rectification and combining.

[mbryner]

Brett,

I don't want to pour water on your parade but I think you've diagrammed a big spark and fried rectifiers.   It would take me a few minutes to wrap my mind around it, but first of all take your negative output:   Isn't the negative rectifier output of A-B going to be 60 V different than the neg output of B-C?   But I'm not an electrician or electrical engineer....

Marcus

[Crofter]

The DC bus that ties the bridge rectifier units output together also would connect internal AC bridge components to a common reference voltage, yet the series connections of the windings would attempt to have them at different voltages.

I think you could have four separate floating DC outputs and still maintain the stated 120 / 240 connectability, but to put full output into a common DC bus the series connections of the windings would have to go and be separately connected to each bridge.

[mbryner]

The DC bus that ties the bridge rectifier units output together also would connect internal AC bridge components to a common reference voltage, yet the series connections of the windings would attempt to have them at different voltages.

Yes.

You have diagrammed your outputs in parallel, not in series.   The parallel circuit ties your reference voltage together, but the windings of the generator are tied in series (at B, C, and D).   That's what I was trying to say last night after midnight.

Marcus

[bschwartz]

My brain simply refuses to see it, but I will bow down and accept that I can get 60v DC from each separated pole, or 120/240, but not both.

Oh well, it was worth a try.

Thanks for keeping me from doing something 'smokey'

[Crofter]

Ye Gads! I would like to see someone come up with a more definitive description of what the exact problem is. Dont give up on my say so as I admit to being weak on the internals of solid state devices.

I am sure though, that you can combine all the rectified ~60V outputs of the bridge rectifiers into one of 60 x 1.44 VDC output. You also might be able to get away with putting the coils all properly phased and parrallel connected through the rectifiers for similar output, but that risks one or more of the diodes running away with a larger portion and overloading if they are not perfectly matched. I just dont think you can have the coils interconnected for either/or 120/240 at the same time.

I like what you did with bringing the ends of all coils out so they could be connected such to get rid of the single leg load groan. It is something my gen. could benefit from too, but that is very elective surgery.

[mbryner]

OK, lets break it into pieces.  Bear with me.

Take out the red & black leads from the diagram for a minute.   You're left with a 4 poles wired in series, with a bridge rectifier across each pole, correct?  

Across A-B there's 60 VAC.  Same for B-C, C-D, D-E.
Across A-C there's 120 VAC.  Same for B-D and C-E.
Across A-D there's 180 VAC.  Same for B-E.
Across A-E there's 240 VAC.

Everything just like in the ST manual so far.

Now, take a multitester and read the output voltage of each of your rectifiers (with the black and red leads removed).
Across each rectifier from "pos" to "neg" there should be approx 60 x 1.44 volts DC.

Now measure from "neg" output from bridge 1 to "neg" output on bridge 4.   There's going to be a 180 volt difference.  Same thing from "pos" on bridge 1 to "pos" on bridge 4.   Each rectifier will have a different "ground" or "negative" voltage reference because the gen poles are connected in series.  It doesn't matter that it is called negative, rectifier 1 has a different "ground" voltage with respect to each of the others.  Get what I'm saying?  Now if you put connections (red and black wires in your diagram) across all the "pos" and all the "neg", there's a short.

You've got the generator poles in series but the rectifiers in parallel.   If you want to keep the poles in series, you can't parallel the outputs.

On the other hand, if you separate out the poles (i.e. don't connect them at B, C, or D), and hook up each separately to the rectifiers, then you can connect the rectifiers in series.  
Output of "pos" on rectifier 1 to "neg" on rectifier 2, and so on.   Then you can select 60-120-180-240 volts.
Of course there is the caveat that rectified DC = 1.44xAC.   You'll have to slow down your engine or put the appropriate resistor in the ST excitation circuit to decrease the output V AC.   Also, if you're drawing off the 240 V DC circuit, if one of the rectifiers burns up the whole 240 V leg is dead.

Hope I got that right....

Marcus

[mbryner]

Yes, Jens is saying exactly the same thing but got his thoughts on "paper" before I did.

Suffice it to say, your concept will work if the generator windings are situated in parallel instead of the current series arrangement.

Exactly, see my post above.

Of course this would also mean no 120/240 at the same time.

For AC, that is correct, but not for DC.   You could series connect the rectifiers and get different combo's.   Analogy: think stacked batteries with leads coming out between them.  What would you do with 180 V DC, though? 

Note that I simplified things so please don't tell me that the voltages are all wrong by a factor of 1.44.

If you use a large choke on the output, it will smooth out the pulses to near RMS, IIRC.   Forgot to mention that in the above post.

Marcus