Combining 2 8kw pj's into one new case for double the output...Possible?

So the more "scientific" way to determine which is which would be the direction of the wire on the winding.  In this case, both black ones come off the top of the core, and the colored (red / yellow) come off the bottom of the core.  This should get the polarity forwards.

Then go ahead and power up the inverter.  Should run normally, if a bit louder due to the 2 transformers.

Then try connecting ONE of the "new" secondary wires to one of the "old" secondary wires: start with the red from the new transformer, red on the old transformer...

...measure from the other side of the secondary wires: black (secondary) on the new transformer to whatever the leftmost secondary lead of the old transformer is (black?) with AC volts.  Should be < ~5vAC.  If you get 480vAC, then the transformer phases are reversed; disconnect the one pair you connected together earlier, and this time try connecting Black (secondary) of new transformer to whatever the rightmost secondary of the old transformer is (red?)  Measure the opposing leads again...should be < 5vAC...

...obviously, at your own risk 😉.

So, paralleled leg to neutral old, gives me 120.1 and paralleled leg to neutral new gives me 126.6.... secondary old to old neutral gives me 112.5 and secondary old to new neutral gives me 129.0.....new secondary to new neutral gives me 126.4 and new secondary to old neutral gives me 172.5

1 hour ago, Thatguydidit said:

So, paralleled leg to neutral old, gives me 120.1 and paralleled leg to neutral new gives me 126.6.... secondary old to old neutral gives me 112.5 and secondary old to new neutral gives me 129.0.....new secondary to new neutral gives me 126.4 and new secondary to old neutral gives me 172.5

Those readings are not as important as the "neutral to neutral", "L1 to L1" and "L2 to L2" readings.  You want to know before you parallel the transformer secondaries together that they are a) the right phase, and b) not very far different voltage-wise. 

Reason being that if they're the wrong phase, you'll overload the inverter / blow FETs.  If they aren't very close voltagewise, there will be a much higher no-load current, and the transformers won't share load very well.

If you have the L2 lines as the parallel leg, there should be <5vAC across Old Neutral - New Neutral, and <5vAC across Old L1 - New L1.

Old neutral to new neutral is 80.4 and old l1 to new l1 is 165.6

Think I'm outta luck, the transformers are too far out from each other

1 minute ago, Thatguydidit said:

Think I'm outta luck, the transformers are too far out from each other

Not possible if they're both 36v -> 230v split-phase transformers.  Sounds like their phase is sorta reversed and/or leads are mixed up.

Might need to experiment shorting different "old" to "new" wires (only one at a time), and see if you can find a combination that gets the difference between neutral-neutral and L2 - L2 (or L1 - L1) <10v (let's say they aren't very matched!)

1 minute ago, Sid Genetry Solar said:

Might need to experiment shorting different "old" to "new" wires (only one at a time), and see if you can find a combination that gets the difference between neutral-neutral and L2 - L2 (or L1 - L1) <10v (let's say they aren't very matched!)

So maybe swap the primaries black and yellow to fix phase? Because when I ran left most old leg(red) to left most new leg(black) the other secondaries (L2 maybe?) showed 471.8 between them

56 minutes ago, Sid Genetry Solar said:

Not possible if they're both 36v -> 230v split-phase transformers.  Sounds like their phase is sorta reversed and/or leads are mixed up.

Btw they say 16/17v to 230v

Ah, you have 24v inverters then.

If you found 471v, then the transformer phases are opposing each other...and one transformer primary polarity would need swapped.  Max voltage you should be able to find across the secondaries should be ~240vAC (give or take a few)...if you can find 480vAC, then they're definitely reversed.

No matter how I connect it I still end up with 60-80v on neutral and 120-170v on the other secondary. 

Reversing the primaries on one tranny made the whole thing a lot louder, even with 2 full wraps around the ferrite

Can the as3 be that much different than the as4? 

24 minutes ago, Thatguydidit said:

No matter how I connect it I still end up with 60-80v on neutral and 120-170v on the other secondary. 

Reversing the primaries on one tranny made the whole thing a lot louder, even with 2 full wraps around the ferrite

Can the as3 be that much different than the as4? 

Shouldn't be...if they're both 16 -> 230v spec, they SHOULD be similar.  Do you measure ~240vAC across the L1 / L2 secondary leads on each transformer (separately, not with their secondaries tied together)?  It's sounding like their voltage specs are considerably different...or something else fishy is going on.

Separately they measure 10.6v of each other 245/255

So then if you have the "old" L1 tied to the "new" L1, the transformers should match up with 10vAC across the L2's, and 5vAC across the N's.

The 10.6v difference could be adjusted by adding a turn of wire to the primary on the "low" transformer.  (Mathematically, 230v / 16v = ratio of 14.375, so 245v / 14.375 = 17.04vAC on the transformer input [assumed].  Bumping that up to an effective 17.8vAC with an extra turn * 14.375 = 256vAC.  The smaller transformers usually run ~0.8v/turn; ASL5 ~1v/turn, and ASL9 ~1.5v/turn.)

I don't think wire colors make a difference on these transformers' secondary circuits, but more the physical position of the wire (left / middle / right)

Been watching this process with high hopes.  Since it's not going smoothly so far, might want to step back and compare the two obviously unequal capacity transformers.  Does voltage of L1 to L2  of the old transformer equal L1 to L2 of the new transformer?  If not, you might be wasting your time.  Next, are both tranformers either the balanced type or the unbalanced type. Both must be one or the other.  One of each is a deal breaker for your project.  Powerjack uses both types as the mood strikes them and you could have one of each.  Balanced meaning voltage of L1 to N equals voltage of L2 to N.  Unbalanced will have voltage of L1 to N reading 7-10 volts higher than voltage of L2 to N.

These things should be determined before you spend more time swapping connections. 

Still hoping it works out!