Connecting 2 isolation transformers to double the current capacity

[FPALB]

I have 2 of these DALE TECHNOLOGY medical grade transformers, but they are only 3.5 amps each. Can I make a male to male 120V cable and jumper their secondary outlets to double the current capacity?

Only 1 of the outlets shown has a green dot on it, but Ive confirmed they are in parallel as a normal outlet would be.

 

[Speedskater]

If you have an old AC output wall-wort on hand.
You can test the transformers with a low voltage AC input.

 

[FPALB]

If you have an old AC output wall-wort on hand.
You can test the transformers with a low voltage AC input.

Good idea - I can do it with a Variac

 

[emrr]

At best you would have to assume one has barely lower wire resistance and will always draw some % more of the total load. In fact the wire resistance of your jumper and of the connectors may dictate the unit most directly plugged with respect to load with draw the most.

 

[JohnRoberts]

A 120VAC male to male cable is a shock hazard and possible house fire waiting to happen... An old neighbor of mine (now RIP) had an extension cord wired up with two male ends to provide power to his shed when the existing underground power line failed. This was wrong for several reasons, but I was unable to stop him from doing it.

-To parallel two iso-transformers the first consideration is to make sure the windings being combined are in the same polarity. Connecting them opposite polarity will end badly.

-confirm that they are making the same voltage output. If one is higher or lower than the other they will try to drive into each other.

-for modest current needs you can force sharing using degeneration resistors not unlike the emitter resistors inside power amps to force device sharing. A 0.1 Ohm resistor would drop 0.35 V @ 3.5A

Have fun and be careful, even with iso-transformers mains voltage can still kill you.

JR

 

[Rob Flinn]

Just a thought, but could you not just power different bits of gear from each of the 2 different transformers ? Is it essential that everything is being powered from the pair of transformers in parallel on the same circuit ?

 

[FPALB]

Just a thought, but could you not just power different bits of gear from each of the 2 different transformers ? Is it essential that everything is being powered from the pair of transformers in parallel on the same circuit ?

When I put my bench together I really went through and wired all the power to be tidy and out of sight and I try and do the same with any gear that gets added - it was a major oversight that I would eventually run the load too big and have to buy a larger Isolated transformer (first happened when repairing a RCA BC5B Broadcast Console). With the higher amperage Iso transformer being so pricey and since I have 2 duplicate 3.5 Amp transformers I thought I would give it a shot. Jumper is rated at 15 Amps so It shouldn't even begin to get hot before the fuse on the Iso pops.

Atleast these are my thoughts and I would love to hear Yalls.

I went ahead and jumped the units and put the whole thing on a variac and it started up just fine. Plugged in a space heater (Southern California is cold this time of year...something like 68 degrees brrrr.) and it runs great while popping the fuse when only 1 iso is used. It still pops both Isos when the space heater is really going which puts it around 9 amp draw.

thank you all for your inputs. I will keep an eye on this solution for the next couple of weeks.