120-240V Transformer

keyturbocars · November 2012

I wanted to get some of your opinions on a 120-240V transformer that I have. It's an old Jefferson Electric transformer in a steel case and the transformer itself is encapsulated (potted - or whatever the right word is) inside the steel case. It's a heavy chunk weighing around 60 lbs. The label specifies it as 3kVa transformer.

Can a transformer take a momentary surge above the rated kVa or is that the absolute maximum?

I've got a 2HP well pump (240V) that Franklin Electric told me requires 2,500w to run, but it requires as much as 7,500w surge to start up. I realize that there is a big difference between continuous and intermittent ratings, and I know this transformer that I have is rated for 3kVa continuous, but I'm not sure if transformers can accommodate brief surges. Just thinking about if I could ever use this transformer with a 120V inverter to run my well pump. At this point, it's just a matter of curiosity. At the moment, I don't have any need to be able to do so.

Cariboocoot · November 2012

Re: 120-240V Transformer

I may be looking at this sideways but ...
Your sig shows an Exeltech XP1100, which will never start that pump, and an APC Matrix 5000 split phase which already has 240 VAC ability.
What inverter are you planning on trying to run this from?
If the inverter won't handle the load the transformer's rating becomes irrelevant. Otherwise one rated for 3kVA continuous will take a momentary surge to about 6kVA maybe 7.5 - it's all about heat dissipation.

BB. · November 2012

Re: 120-240V Transformer

Transformers can also be wound/rated for maximum surge current (once you saturate the iron--You cannot get any more current though the transformer).

-Bill

peakbagger · November 2012

Re: 120-240V Transformer

Depdends on the transformer, when I deal with the big utility size transformers some have a triple rating, air cooled no fan, air cooled with fan, air cooled with fan and air cooled oil cooler.

keyturbocars · November 2012

Re: 120-240V Transformer

Thanks for the input. I don't plan to actually have to do this, but I am just thinking about a worse case scenario and what I might do. I guess the way I think about things is that I plan for the worst and hope for the best. Anyway, my primary plan would be to run the well pump with my Onan 6DJE generator (no problem for it), or my Xantrex XW6048 inverter. In those cases, I don't need a transformer. But in a worst case scenario, if my XW6048 was dead and my Onan 6DJE was not operational, then I have an AIMS (don't laugh me off the forum) 5kW inverter. It has a surge rating of 10kW. I know that AIMS is not a "real" inverter to many people, and I sure would not want it to be my primary inverter, but I have an old unit sitting around here. I also have that old transformer sitting around. So I was just putting some pieces together in my mind and wondering if I could make it work. By the way, in the past I have tested the AIMS up to near full rated capacity with some heaters and it worked. Pulling so many AMPS through 4/0 on the battery side with 12V is a bit nuts, but it did work. If my memory serves me right, I was seeing over 400 amps with my clamp on. Again, I know this is nuts. Cables did get warm after prolonged running like this, but not too hot. In any case, I'm just saying that the inverter surprised me at what it could do. I have read of other people using this same AIMS 5kW inverter (it's older version than the current model) for many years on work trucks and such without any problems. I thought that perhaps if it was dedicated to just run the well pump, the 2.5kW load would be reasonable. The 7.5kW surge should not be a problem for it as long as I have a big enough battery bank so the voltage doesn't dip too low during pump startup. Based on my testing in the past, I'm pretty confident the inverter itself could take it, but I just don't know about the transformer.

Like I said, don't laugh me off the forum. I'm not recommending the AIMS to anyone. I'm not even planning to use it. I know that it's a modified sine and it's not best for motors. I'm just thinking that if my XW6048 was not working and my generator was not an option, then I'd consider something more "risky". Having no water at all is not a very good option. Thanks for the feedback.

mike95490 · December 2012

Re: 120-240V Transformer

If the AIMS inverter is pure sine version, it may work, but then the transformer becomes the roadblock. At some point, the iron core will saturate (as someone pointed out before) and you can push no more power through it. And if your inverter is mod-square wave, the transformer or pump motor won't like the waveform, will run 20% more power, and heat up a lot.
It may be better to invest in an above-ground storage tank for water, instead of a pump system.

keyturbocars · December 2012

Re: 120-240V Transformer

I agree that the AIMS inverter is not the best way. I was mainly just curious about how transformers work and how they would handle surges.

ChrisOlson · December 2012

Re: 120-240V Transformer

keyturbocars wrote: »

Can a transformer take a momentary surge above the rated kVa or is that the absolute maximum?

The rated kVa is not maximum - it will handle surge up to core saturation and overload up to the maximum safe temp for the insulation on the winding wire. The rated kVA is usually a continuous rating at a certain ambient temp and the overload capacity will have a duty cycle based on temperature.
--
Chris

BB. · December 2012

Re: 120-240V Transformer

Look for a temperature/class code on the transformer plate--It may say something like:

Transformer and Insulation Systems Ratings
Insulation Rating     Transformer Rating     Max. Ambient Temperature     Hot Spot Allowance
Class 105     55°C Rise     40°C     10°C
Class 150     80°C Rise     40°C     30°C
Class 180     115°C Rise     40°C     30°C
Class 220     150°C Rise     40°C     30°C

It may be a letter code too (Not sure--Not my area of knowledge).

Obviously, from our point of view, you don't want a "hot transformer"--That is a waste of energy.

-Bill

ChrisOlson · December 2012

Re: 120-240V Transformer

Actually, that AIMS inverter will not put out enough power to even warm that transformer up. I had one of those "5000 watt" AIMS 24V inverters once. It is lucky if it is a 3,000 watt inverter in the real world. Taiwanese "watts" are different than real watts.
--
Chris

keyturbocars · December 2012

Re: 120-240V Transformer

Bill, It has an insulation code of 180, so it looks like it can tolerate some heat. Just wonder if the iron core would be able to deal with such a big surge. Right now, it would not be convenient to test this out, because I don't have very many free batteries. I'd have to take apart my 48V battery bank to get enough batteries to really test this out, and that's too much lead to move and too much work!

Chris, Haha... yes, Taiwanese watts might not be the same as US watts. That really seems to be true with Chinese watts vs US watts. Must be that some of the watts get lost on the long journey to the US!

Actually, I did set up my 12V Aims 5kW inverter (it is the older version of the AIMS inverter) with several Group 31 12V batteries. It might have been 5 or 7 batteries in parallel. Can't remember right now. In any case, I did push the inverter real close to the 5kW limit, and it was able to sustain it for a short time. But, the battery voltage was dropping and the output AC voltage did droop as well when the battery voltage dropped after running for a little while. So, it did sustain peak load for a while, but I agree that I wouldn't consider 5kW to be a wise continuous rating on this.

ChrisOlson · December 2012

Re: 120-240V Transformer

If you take that inverter apart you'll see that they got a single 10 gauge wire on the AC output and it is daisy chained with the plugs. 5000 watts is 42 amps. 10 gauge wire might take that for a little while. But not long.

The 24V one I had would run 124 volts no load and the voltage would crash to 110 at 3,000 watts. I burned it out trying to run the well pump with it (thru a Trace 240 transformer) while the fridge and freezer were running at the same time. AIMS replaced it under warranty. I sold the new one - never even took it out of the box.

The day it burned out my wife stood with her hands on her hips, told me to get out, and go buy a decent inverter because she'd had it. And don't come back until I find one. I spent $6,500 that day.
--
Chris

Cariboocoot · December 2012

Re: 120-240V Transformer

Can't say I'm surprised at Chris's experience with AIMS.

Tum-te de-dum *Don't mind me; just gloating a bit.*

"Awful Inverters Made Stupidly"
De-te tum dum

keyturbocars · December 2012

Re: 120-240V Transformer

Chris, I agree. That's why I bought the XW6048. I decided that if I was going to have to depend on something when grid power was down, then it better be dependable. Earlier, I did experiment with some redneck ideas. I never pushed the Aims inverter much other than a little testing. I suppose that the people that have had good experiences with this AIMS inverter probably don't push it too hard when using it on their service vehicle. When running off a single battery, or maybe dual batteries on a diesel rig, there is no way they are going to be able to push the power limits very far without drawing down their battery. Plus, I don't know how they could wire the inverter in. I used 4/0 and only 3 feet of it, and the cables were getting warm when pulling over 400 amps. By the way, how big (HP) is your well pump?

Cariboocoot, Nice acronym!

Ken Marsh · December 2012

Re: 120-240V Transformer

For you technical types, it is not core saturation that limits transformer current.
Cores are saturated by over voltage not over current.
Transformers can handle huge over currents for a short time.
About the only thing limiting current is the copper loss.

Case in point; Why does code require breakers with 20,000 amp interrupting capacity for a 100 or 200 amp service?
The reason is that you can get this much current in the case of a direct short.
That is a 200 or 100 times over current situation for the transformer.

My experience with the low cost Chinese inverters is that they will put out full power.
You have to get enough amps to them to do that however.
Of course this is the case with any inverter.
But when people lay out 3.5 K$ for an inverter they usually will hook it up to good batteries with low Z wire etc.
My reason for not using low cost inverters here is that our batteries and inverters are in an unheated shed.
Low cost inverters tend to quit when they get cold.

MSW inverters need be followed by a transformer if you are going to meet electrical code in US.
The reason is circuit isolation
There are lots of used transformers out there.
The electrical industry calls them distribution transformers.
They used to be low cost but now since Cu and Fe is so expensive they have gone up considerably.

ChrisOlson · December 2012

Re: 120-240V Transformer

Cariboocoot wrote: »

Can't say I'm surprised at Chris's experience with AIMS.

What was really sort of bad was that it was the second one. The first one lasted two weeks. We went to bed and everything was fine. Woke up and the power was out. Everything appeared normal on it - lights were on on it and everything. That's the one I took apart because I figured it had to be a fuse or something. That's when I saw the "heavy duty" 10 gauge output in it daisy chained from the board to the "full power terminal block" and then to the outlets. We ran the generator for 10 days until the second one came. That one lasted two months. It was March when the second one went.

My wife was not impressed with my "upgrade" from the old DR2412 to the "big 5000".

Our pump is 1.5 hp deep well submersible. The head on the pump is 260 feet.
--
Chris

ChrisOlson · December 2012

Re: 120-240V Transformer

Ken Marsh wrote: »

For you technical types, it is not core saturation that limits transformer current.
Cores are saturated by over voltage not over current.

When I installed our PSX-240 I was surprised how much power it pulls due the core being bled down when it is powered up. I put my Fluke meter that has high value capture on the AC output of the inverter and turned the breaker on to the transformer. It recorded almost 120 amps surge when that transformer powered up. Idle consumption of the transformer is less than .1 amps.

I know a "5000 watt" AIMS could not even power our PSX-240 up - it would overload.
--
Chris

keyturbocars · December 2012

Re: 120-240V Transformer

I appreciate the comments Ken and Chris (and all). I find this very interesting. In fact, being of the redneck, mad scientist persuasion, I am really curious now what would happen if I tried to run this AIMS inverter through that transformer and just see what it would do. Might do nothing and I might smoke the AIMS inverter, but that would not be a huge loss. The trick would be to get enough battery power. Without messing with my battery banks, I could come up with 4 batteries that are matched and then I could try to feed them with a 80A charger while doing a test. I've got more 12V batteries than that around the farm, but they are not matched.

Chris, sounds like you really proved the AIMS 5kW inverter to be a dud with 2 failing in a short time. I can't dispute that. I never pushed my inverter in real world duty like you did. I do wonder if you had the older style AIMS 5kW inverter, or you had the newer design. Did the back of the inverter have dual +/- battery inputs (for a total of 4), or were there 2 large terminals on back for battery hook cables? Did it look like this picture?

Attachment not found.

If so, then that's the newer version. The other version with the dual battery inputs on the back was the older version that they had in production for nearly 10 years. The dual battery input on back of the old versions is pretty dumb, and I put a big copper buss bar across them so I could join them and hook up my 4/0 cables to the inverter. I'm just trying to figure out if you had the newer or older version. Obviously, whichever version you had was no good.

ChrisOlson · December 2012

Re: 120-240V Transformer

I had the one that had four studs on the back of it and it weighed maybe 30 lbs

Attachment not found.

Attachment not found.

You'd have to try the AIMS on the transformer and see what it does. Your transformer is fairly small so it might work OK. Our old Trace T240 worked with it as long as we didn't have other stuff running at the same time. Our PSX-240 is a 6 kVa transformer with a much bigger and heavier core and is wound with either 12 AWG or 13 AWG wire - it's about like a welder transformer. I think the PSX-240 will kill it when you try to magnetize the core in the transformer.

I've heard of some folks trying to power up a welder with twin SW Plus 5548's and the inverters overload and shut down when the switch is flipped on to the welder. It all depends on how much power the unit pulls when the core is bled down in the transformer.
--
Chris

keyturbocars · December 2012

Re: 120-240V Transformer

Chris,

I was sort of hoping that you had the newer version, and that there might have been issues with the newer ones. Nope, same one that I have, only mine is the 12V version. At least I will have more realistic expectations regarding its potential lifespan.

Ed

120-240V Transformer

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