12V xformers in parallel?

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mdshunk said:
LarryFine said:
Marc made it sound like they were "slightly" out of synch, not 50 amps' worth. That's hard to miss.
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It's been maybe 10 years since I observed it, but the one was shifted maybe 30-40 degrees compared to the other.
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So, I did read his comment correctly.

However, if the primaries were paralleled, I could only imagine in phase or 180-deg. out-of-phase.
 
LarryFine said:
So, I did read his comment correctly.
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Where did Marc mention 50 amps?

However, if the primaries were paralleled, I could only imagine in phase or 180-deg. out-of-phase.
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Yes, that would be the only possibilities that I know of so either Marc was mistaken or could it be they where not similar transformers?
 
iwire said:
Where did Marc mention 50 amps?



Yes, that would be the only possibilities that I know of so either Marc was mistaken or could it be they where not similar transformers?
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Yeah, they were definately different brands, and I'm nearly certain one was a 40va and one was a 75va. This was a case where the outdoor section and the indoor section each had a factory installed 24volt transformer. I managed to get them both on the same primary phase (208 pri), but the secondaries wouldn't sync up close enough.
 
BTW, we returned to this job site and split up one of the runs of landscape lights to two runs. Installed another 300 watt xformer but still had too much VD on one of the runs.
The run giving us problems had 60' of 12/2 ROMEX run in the basement to a jbox, spliced to 12/2 LV stranded direct burial cable to outside. We replaced the 12/2 ROMEX with 10/2 stranded LV cable and reduced VD by > 2 volts.
Lights are all nice and bright now.:)

Got another section of this property to do that is even larger. Will be looking at xformers with sense leads (I think I these exist) and will be sure to do a star topology type layout to keep all the cable lenghts the same.
 
iwire said:
Where did Marc mention 50 amps?
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By placing two 25a (300w / 12v) secondaries in series (well, parallel, but out of phase). Of course, the short-circuit current of two 24v @ 25a secondaries would be more, and certainly enough to let the magic smoke out.
 
LawnGuyLandSparky said:
Could you use a transformer that boosts the output voltage to compensate for VD?
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Not a great way to go as soon as one lamp expires the voltage to the rest will rise, when the next expires the voltage will raise again and eventual the lamps will be burning out very quickly from over voltage.
 
True, yet it seems the higher end systems include the feature.

Based on what I looked up, the cost of the LV systems at the higher end, coupled with the issues of VD, the rising cost of heavier guage copper, I think the benefits of even using LV are becoming few and far between.
 
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