ST-5 output to multiple voltages

[d34]

I wish I had the parts here to test it like that. I think he would still get what he originally thought. The reason I say that is because i believe the way he has it setup forces 60vac input per rectifier.  I have been wrong many times before tho. Lol.

[mobile_bob]

it will force 60vac to each individual rectifier, however where you get into trouble is paralleling the output
of each of the rectifiers, there ends up a problem with feedback loops iirc

you can do it as drawn only if you use each of the rectified outputs for separate applications, with no interconnects
basically all outputs with floating grounds, or you end up with the ever increasing voltages becoming additive as referenced
to the ground.

the only way to get the job done otherwise so that you can retain AC output 120/240 is to use isolation transformers
on each of the coils, the secondaries of each transformer could then be rectified and then connected in parallel without feedback loops
referenced to ground.

thats as good as i can see it, but i may well be wrong.

got a bad ass cold and i feel like crap, on cold meds  so my thinking is even slower than usual.

with a little time and about 3 bucks in diodes from radio shack, (the 50pack of in4001's) one could make up 4 bridge rectifiers
and test the output of each coil set as drawn, that should work no problem
then connect all the bridges in parallel and see what the result is, certainly it won't hurt the engine or the genhead, but i am not
very optimistic that any of the diodes will survive?


sure would put an end to the discussion in either event?

bob g

[bschwartz]

At the very least, I see some pretty bright minds trying to think through the same problem, and still not 100% sure of the result.  It isn't completely cut and dry.  I feel better.  Thanks guys.

The experimental (sacrificial) diode experiment may be in my near future.

First on the list is to get the 4 Evergreen 210w panels mounted on the workshop roof.

Even if the generator isn't doing what I want at the time, at least I know the sun will be shining (this is southern New Mexico after all).

I can't tell you all how much I appreciate being able to bounce ideas around.
I only hope I am somehow contributing to help others as much as they help me.

-Brett

[mobile_bob]

there really is no reason to risk 16 diodes when 8 will prove the concept as viable or not
just do it across 120 vac and another across the other 120vac output and then parallel the outputs

that wouldn't take long to find out what the results might be

bob g

[d34]

The transformer I have will allow me to center tap 120v. If I get time tomorrow I will test it.

[mbryner]

The transformer I have will allow me to center tap 120v. If I get time tomorrow I will test it.

Excited to hear the results.

[Tom Reed]

Great thread. I could see the problem but not articulate it. Thanks guys!

[d34]

Ok guys I did the test and have some interesting results.  This was done using a dual primary dual secondary transformer with 120vac input from the grid (I took the parts to my office with me). All tests were done with no load.

First test:
Input 121vac
Secondary A output 60.5vac
Secondary B output 60.5vac
Rectifier ouputs connected in parallel = 56.5vdc     Frequency = 59.9Hz
Rectifier outputs in series = 113vdc    Frequency = 59.9Hz
I switched the hot/neutral on one rectifier only and had the same results
Frequency on dc side = 59.9Hz

Second test:
Input 121vac
Secondary A output 60.5vac
Secondary B output 60.5vac
Secondaries series connected 121vac
Rectfiers connected in parallel = 113vdc     Frequency = 120Hz
Rectifiers connected in series tripped the breaker (with only 1+ and 1- connected and the others not connected to anything)
I switched the hot/neutral on one rectifier only and had the same results







EDIT:  I still have the parts at my office, If anyone would like me to try any other setups let me know.

[bschwartz]

Without diagrams, I'm a little fuzzy on the results of your test, so bear with me.

Do these tests show that it will work the way I originally drew it?

[d34]

No. If u had each 60v coil separate it would.

[bschwartz]

OK, than that proves that this is a dead horse.  I have to choose between normal 120/240 AC, or 4-60v AC legs separated and rectified/filtered for the grid tie setup.

Oh well.  This proves I can't have it all 

Thanks for the time you put in to proving my theories junk 

[d34]

Thats not a problem cause I am gonna use this setup for my charging.  So I needed to test it anyway.  I do have a few questions tho.  When I first hooked up the rectifier (not this test, this was done a few weeks ago) I had 106vac input and around 103vdc out with no load.  But when I hooked it up to the mx60 the vdc went up to 148vdc.  The only thing that was different was the rectifier was mounted to the cabinet when hooked to the mx60.  Does the voltage change when the casing is mounted/grounded on a rectifier?  This also shows in this test that with no load and the rectifiers not mounted that the vdc was a little lower than the input.   

[mbryner]

d34,

The decreased voltage across the bridge rectifier is easily explaned:
Each diode has an almost 1.x V drop across it, and a bridge rect has 4 diodes.   So 2 diodes to rectify each pos or neg wave gives the drop from 60.5 to 56.6 V.

For the other question:
The transformer output is electrically isolated from the input, so couldn't it be a ground problem?  Is the neutral of the secondary grounded?   I'm not the best one to answer that question though because that was a similar problem I had when routing 80 V AC to DC.   The neg lead was then 40 V higher than ground.       Watch your Voc into the MX60 because it will only tolerate up to 140 V DC, I think.

Marcus

[mbryner]

the only way to get the job done otherwise so that you can retain AC output 120/240 is to use isolation transformers
on each of the coils, the secondaries of each transformer could then be rectified and then connected in parallel without feedback loops
referenced to ground.

So, this just hit me.  Thank you Bob.  I realize this thread was dead, but I'd like to go back and stress that you can't take the neg output of a bridge rectifier and connect it to neutral or ground of the generator without a isolation transformer!   Last night I hooked it up like that and got 200+ V DC when I thought it should be 80 V DC.   Couldn't figure out what was wrong, but like mobile_bob said, "you end up with the ever increasing voltages becoming additive as referenced to the ground."   Now it makes sense after reading and re-reading.

I'm at work again, but ideas always come at the wrong time:  In a spare moment today, I'll make a diagram and see what you all think of something.

Marcus

[mike90045]

You have to watch the actual internal connections in transformers, some share coils (autotransformer) some have 2 coils but no isolation, some have 2 coils and are truly isolated to 1KV.