48V charging via ST generator and solar charge controller (no ST mod)

[Geno]

Well, I only spent one night in Lk. Placid and Mondays are pretty quiet but it was still better than most places.

It appears my gen head problem was caused by a field cable from the rec to the brushes that was rubbing on something. It was worn just to the point where the wires were exposed. I didn't find it until reassembly. There was a fine coating of black greasy stuff all over the internals. I need to vent the engine breather asap, the old sock aint good enough. The doghouse is gone. It was quite time consuming to get it all clean, dried, moved, and mostly rewired. It's a heavy SOB. The only testing I'm doing tonight is some fuel consumption (it was all set up when the gen head quit) and some taste testing on a rack of ribs and some beer that's been buried in a snow bank for a while.

Thanks, Geno

[BruceM]

Geno- glad it was something readily fixable!

[mike90045]

some taste testing on a rack of ribs and some beer that's been buried in a snow bank for a while.

I suggest heating the ribs before testing.

[Geno]

I suggest heating the ribs before testing.

They were heated just fine thank you. Based on your avatar you'd know, those ribs must be scorched ashes by now.

Thanks, Geno

[Geno]

I got to do a charge efficiency test today. The results are in the attachment.

Thanks, Geno

[BruceM]

Hi Geno, Wery impressive.  Looks especially impressive for the lower wattage absorption phase, which is more KWH. Your transformers seem to be slightly overtaxed a bit at higher currents- I can't explain the greater efficiency at lower power levels otherwise.  I'll have to study the hardcopy of your data a bit more.  A toroidal choke might buy you some improvement at higher currents, as it would reduce the peak current demand on the transformer.  But I'm not sure it's worth the bother.




 

[Geno]

I'll do some more tests as time permits. As you know, repeatable results are what counts.

Thanks, Geno

[BruceM]

Geno, I tried to find it in the back pages (!) of this thread but can't locate your transformer specs. I'm just trying to get a better understanding of why your efficiency is reduced somewhat at higher loads. I would have expected it to be the other way around. 

What specs do you have for your transformer?

Thanks for your data, time and for helping us all learn from your very successful ST to Flexmax charger project!

Best Wishes,
Bruce

[Geno]

Geno, I tried to find it in the back pages (!) of this thread but can't locate your transformer specs. I'm just trying to get a better understanding of why your efficiency is reduced somewhat at higher loads. I would have expected it to be the other way around.

Best Wishes,
Bruce

I agree but I'd like to get a few more runs in before I draw any conclusions.

I don't think I ever posted the xformer specs.

Input on H1/H4 Output on X1/X4 with X2/X3 shorted. Mistake
X1/X3 and X2/X4 shorted and their the outputs.

Thanks, Geno

[BruceM]

Hi Geno, What is the VA rating, or current rating of this transformer?

Driving H1, H2 with your 120V nom. output will give you about 64% of the rated VA output.

The transformer does see the full VA load, so this is one place where PF does factor in.

So I'm wondering if at around 18 amps output if the transformer is overtaxed; if it is rated less than 2200VA, then that is likely the problem.  If not, then watching via oscilloscope a shunt resistor(0.01 ohm)  in the post rectifier(DC) line to the Flexmax might tell us something about what the real time Flexmax current draw looks like. 

[Geno]

Oops, didn't notice that was missing.
5 KVA

Thanks, Geno

[BruceM]

Thanks Geno. With that much headroom, we don't have to worry about the transformer. 

Given the lumpy DC, perhaps the Flexmax is a just bit off on it's calculations. 

[yellowhead]

Yellowhead sent me a note questioning my comment on power factor correcting circuitry.  I did some research on PFC chips and applications this morning and I think he is right-  a PFC front end on a switcher should be helpful for low frequency operation (bulk storage cap is less affected), and is not inherently problematic as I thought.

I had assumed most implementations of PFC would be AC zero cross and time based, but I was wrong. Of the three most common schemes, none would seem to care about AC frequency.

Thanks, Yellowhead, for your message and for forcing me to get a better understanding of PFC circuitry.

I have this in service as of this morning. I eventually went for a 48V system so I bought 2 of the PFC corrected power supplies and wired the outputs in series to get 96V into the charge controller. This seems to work just fine and I can throttle my set back to about 1400rpm which subdues the Changfa roar a bit Below this the power supplies drop the AC input. I still need to figure if this is because the AC frequency is below spec. (47Hz) or because the voltage from the head has dropped too much. It gets down to 160-170 at 1400 rpm which is also below spec.

I'm going to add AVR to the head to see if I can hold the output voltage up at lower rpm. If this works I'll try dropping towards 1200 rpm and see if everything still hangs together. I can't see going any lower as I'll be running out of hp and I'm worried about the thumping on the coupler and the reduced cooling in the head. Still I only need ~3kw in bulk charge so I might be lucky ...

FWIW the reason I want to do this is that my set is (for better or worse) direct drive and at 1800 rpm it simply makes too much power for battery charging without a substantial diversion load.

Either way it looks like the use of 2 of these power supplies connected in series is a viable alternative to a passive approach using transformers/rectifiers/chokes etc.

Simon.

[d34]

I'll do some more tests as time permits. As you know, repeatable results are what counts.

Thanks, Geno

Is the setup you have capable of using more of the available watts that the genset can produce?  Or do you have it limited in the flexmax due to the size of the battery bank? 

[d34]

I'm sure your transformer stays nice and cool, Geno.  You sure have more capacity there as well as with the Flexmax, right?   Did you limit the charge rate via the Flexmax setting for max battery charge current?

I think the FM is set at 20A which gives me 1200-1300 watts into the batteries. I have 8, T105s and if I figured it out correctly I don't want to put much more than 150 watts into each one.

Thanks, Geno

:-[I found the answer.  I didnt read back far enuf...