Buck Boost, any brand better than others?

I want to buck down my 247V to around 232V(below 235 anyway) before it goes into the Phase perfect(20hp), currently searching for an affordable 16/32V 1.5kva . Are any brands better or worse than others, anything to stay away from or they really all do the same thing and will last a lifetime ?
So far Square D seem the most expensive(local dealers are a rip off) while Hammond seems to have the best warranty which makes me think they're probably decent units too?

I never saw any of them in person, internet pictures make it hard to tell which is made where and which may be better. Ideally not made in china.

SND said:

I want to buck down my 247V to around 232V(below 235 anyway) before it goes into the Phase perfect(20hp), currently searching for an affordable 16/32V 1.5kva . Are any brands better or worse than others, anything to stay away from or they really all do the same thing and will last a lifetime ?
So far Square D seem the most expensive(local dealers are a rip off) while Hammond seems to have the best warranty which makes me think they're probably decent units too?

I never saw any of them in person, internet pictures make it hard to tell which is made where and which may be better. Ideally not made in china.

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They all work. Standards exist. Some exceed them by more than others, few fail, not even the Chinese ones. Hammond is fine. They are even Canadian. NRI - a recycler - has a Canadian presence as well, has been a good source for my used ones, and I buy used over new whenever I can do, sometimes FROM Canadian stocks.

Transformers are rather low-risk items, after all. No need to make a problem out of a solution. Just get a KVA rating large enough, or a tad - not TOO much - over spec, as well as the correct voltages, connect it in a safe manner.

Then go do something harder that needs your attention.

Thanks. One thing that had me concerned a bit about quality/brands was the difference in cost between some brands online that are only say $200-350USD but some dealers here want $1200cad for the same size unit. I'll probably just order something online if the last local place I called isn't reasonable.

The one with the lower temperature rise is better.

SND said:

Thanks. One thing that had me concerned a bit about quality/brands was the difference in cost between some brands online that are only say $250-350USD but some dealers here want $1200cad for the same size unit. I'll probably just order something online if the last local place I called isn't reasonable.

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F**ks sake! 1 to 3 KVA? Maybe $100 used? Shipping costs money, that's why I said "Canadian" in your case.

Shop Ebay. By the way you know that the KVA size is NOT the total circuit requirements, just the volt-amperes that you are transforming. Example: you have load that needs 5KVA at 230 volts. Your supply is 200 volts. So you need to bump the voltage up 32 volts (16/32 secondary). So the VA you need is 32 volts x 22 = 704 va. A 750 va or 1 Kva will do the job.

Tom

TDegenhart said:

Shop Ebay. By the way you know that the KVA size is NOT the total circuit requirements, just the volt-amperes that you are transforming. Example: you have load that needs 5KVA at 230 volts. Your supply is 200 volts. So you need to bump the voltage up 32 volts (16/32 secondary). So the VA you need is 32 volts x 22 = 704 va. A 750 va or 1 Kva will do the job.

Tom

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Per the manual, "Blue Case", DPC-20 P-P draws 88 Amps @ 230 VAC, Tom. (187 VAC to 260 VAC the listed range).

He wants to push his particular incoming DOWN by 16 VAC from 247 AC to 231 VAC, nominal??

My SWAG is 16/230, ~ 7% of 88 X 230 ~ 20 KVA is approx 1.5 KVA, minimum.

Then I double that for a max, see if anywhere from 2 to 3 KVA might be cheaper on an availability metric.

750 or 1 KVA would not be on my radar.

Every player in the mix - wire included - is taking a percentage as fee.

The amperage was "steady state" not peak or load-motor starting. Transformer won't fry. It can act as a limiting choke.

Not a bad thing, but one that should be in the plan, not a byproduct. I've no klew how hard he intends to load or NOT load - the P-P.

Note I said EXAMPLE. This because a lot of people assume that the buck/boost trans must have the same KVA as the main xfmr.

Tom

TDegenhart said:

...assume that the buck/boost trans must have the same KVA as the main xfmr.

Tom

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Gawd, I HOPE not!



15 KVA R.E. all-copper-eliptical-coil Upte-de-fuggin-graff virtual Peterman-bilt of a delta-delta transformer is just shy of 400 Avoir and size of a stout Ritz Taipei mini-bar as it is!

Wasn't for a loaded Rem 1100 12-bore, I do believe the uppity sumbitch wudda run me out of the house just to git a warm place to hum of a cold winter night!

OTOH, @ $147, ex McKean, I could probably make out off the copper value. I DID say "buy used", no?

ANY maker is pricing NEW goods at current copper market, and I just do not DO "Aluminium" for 'lectricity.

My 20hp PP is on a 100Amp breaker, current set up with compressor(7.5hp screw, full load) and VMC running doesn't draw much more than 40amp on the 1ph side, but new machine(turning center) that will soon be on it will take all she's got to spin it up/down, but likely be in the 50-60amp range most times. Compressor is getting put on the 10HP PP I think. Until I get more power in there and maybe a 30hp PP...

Would a 2KVA have less of a choke factor/resistance than 1.5kva? and should I maybe just buck it by 12Volts instead of 16 to keep it near the 235V max(for that machine), not that 3-4V's will make much difference anyhow I guess... the VMC with fanuc control seemed to run fine so far on 247V, but a few times I wondered...

SND said:

My 20hp PP is on a 100Amp breaker, current set up with compressor(7.5hp screw, full load) and VMC running doesn't draw much more than 40amp on the 1ph side, but new machine(turning center) that will soon be on it will take all she's got to spin it up/down, but likely be in the 50-60amp range most times. Compressor is getting put on the 10HP PP I think. Until I get more power in there and maybe a 30hp PP...

Would a 2KVA have less of a choke factor/resistance than 1.5kva?

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Yep. Relatively weaker magnetic field per more Iron, plus larger wire, Ohmic losses. Both enter play. Just don't over-do it.

and should I maybe just buck it by 12Volts instead of 16 to keep it near the 235V max(for that machine), not that 3-4V's will make much difference anyhow I guess... the VMC with fanuc control seemed to run fine so far on 247V, but a few times I wondered...

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12 V might be more common and lower-cost.

If I was going to do it - and I may, as my Genset is 208-Wye - I'd use a full-isolation transformer as they don't pass crap as badly as an autotransformer.

But I only have 10 HP P-P and 12 KVA of genset, so lesser spend and space than you are dealing with.

BTW - the trans would be on the OUTPUT side of my PP. I want to re-derive a Neutral, Earthed.

Monarchist said:

Yep. Relatively weaker magnetic field per more Iron, plus larger wire, Ohmic losses. Both enter play. Just don't over-do it.


12 V might be more common and lower-cost.

If I was going to do it - and I may, as my Genset is 208-Wye - I'd use a full-isolation transformer as they don't pass crap as badly as an autotransformer.

But I only have 10 HP P-P and 12 KVA of genset, so lesser spend and space than you are dealing with.

BTW - the trans would be on the OUTPUT side of my PP. I want to re-derive a Neutral, Earthed.

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Not necessarily. This is where the reputation of the builder comes into play. As mentioned above, the cheaper xfmrs probably have higher running temperature. The grade of magnet steel, the flux density, size of the wire, these all have a bearing on the end product and will vary from one manufacturer to another. As the size of the transformer goes up, the losses will increase. The more iron the more iron losses. The larger the core area, the more copper is needed to maintain the same flux density.

Going from 1.5 to k KVA probably will not be noticeable with the same manufacturer.

Tom

Lots of options when designing a transformer. Balance the losses against expense, weight, etc. Most all the existing US/Canada/EU manufacturers can be trusted to do it acceptably. I'd say "all" but I do not know all of them.

Not necessarily so with "Happy Boy Shenzen Transformer and Wok Co Ltd", although even they might be OK if they actually existed.

Forget about kVA. Yes, it is a way to look at the requirements, but the best way is to directly look at current and voltage. Same thing, but no conversion needed.

If the existing transformer, or service, or branch circuit breaker, etc, can supply 65A, you obviously need at least that capability from the buck boost secondary. Then you figure out what voltage you need your "no less than 65A" at, and whatever gives you that will be fine.

There is a small adjustment, since the same power at the new voltage will take a bit more current if you are bucking down the volts.

Selecting and Connecting A Buck/Boost Transformer For 1Φ Phase Converter Feeder

SND,

Some things to consider when selecting a buck transformer to run a machine with a spindle drive.

I would not recommend selecting a unit that puts you at the top limit of the voltage range for the machine in question. Many Asian machines are built for 220 or 200V input, the 235V is the upper limit for reliable operation. Check the machine spec for the desired voltage, not the upper limit.

Utility voltages are not always stable and tend to shoot up when the HV line is lightly loaded, that is nights, weekends, and winter when the grid loads are lessened. Take some readings over time to find out what your swing typically is, before selection.

Sizing the unit, can be a little tedious at times because most tables and calculators provide a part number for the brand in question. Then you need to look up the part number in their catalog to find the actual KVA size and voltage range needed.

Here is the SqD online calculator, You will also need to get their catalog to look up the part number from the calculator result, to find the actual recommended unit specs. Once you know the specs you need, then you can use that info to do your price shopping with other vendors.

Buck and Boost Transformer Calculator - Schneider Electric United States

Digest 177 Sec. 14: Transformers | Schneider Electric

Next up is the connection diagram. All of them have two secondary voltages, 12/24, 16/32, 24/48. It matters which way they are connected to get the change you desire. Each unit is capable of two levels of transformation depending on the connections used.

Then just about all standard connection diagrams supplied by the manufacturers, supply unequal voltage outputs on the two legs, with respect to neutral and ground, from your split phase service. The transformation adjustment occurs only on one leg, the other leg passes straight through, with no voltage change. This imbalance can cause issues with some machinery, especially when being run through a phase converter, and then sent to a drive that normally wants a balanced Y system. You'll already have a high leg from your phase conversion manufactured output leg, when you combine that with one low leg and one high leg from your buck output, you end up with even more of an unbalanced output. Not the best setup for a drive that wants a symmetrical input legs.

There is a fix for this situation. And that is to modify the factory connection diagram, so that the adjustment occurs equally on both legs, feeding the converter. Then you only have the one hi leg (manufactured) from the converter.

Here's an example for one type of connection diagram, a standard OEM drawing, and a modified one for balance.





Running the numbers for your setup...

I selected your given input of 247V, Then I selected 225V (10%)buck output to stay well below your given maximum voltage. Then I used 60A for the capacity of your converter, and 100A for the capacity of your feeder.

Results were 1.5KVA 12/24 for the Converter capacity
and 3KVA 12/24 for the Feeder capacity
That would put the 2KVA unit right in the middle ground.

SAF Ω

I'm alone on my pole transformer, at the end of the line up my driveway. Balance of 123v to ground/neutral seems good on both legs last I checked.
There's no neutral going into my PP, I just have 2 hot and the ground as far as I remember. I definitely need to be able to buck both 123'vs going into it equally, don't want off balance. Should I get 2 smaller units and wire each as single pole 120V units? or its sure that I can hook up only 1 240V buck boost to buck both legs equally? looks like its doable with that last diagram. I guess I'll have to be careful with that.

I thought about bucking it down at the machine and letting the normal 247V feed the PP, but then figured it'd likely better to just buck its supply since I'll have 2 cnc's on it, don't want to buy 4 or 6 of these buck boost...

SND said:

I'm alone on my pole transformer, at the end of the line up my driveway. Balance of 123v to ground/neutral seems good on both legs last I checked.
There's no neutral going into my PP, I just have 2 hot and the ground as far as I remember. I definitely need to be able to buck both 123'vs going into it equally, don't want off balance. Should I get 2 smaller units and wire each as single pole 120V units? or its sure that I can hook up only 1 240V buck boost to buck both legs equally? looks like its doable with that last diagram. I guess I'll have to be careful with that.

I thought about bucking it down at the machine and letting the normal 247V feed the PP, but then figured it'd likely better to just buck its supply since I'll have 2 cnc's on it, don't want to buy 4 or 6 of these buck boost...

Click to expand...

What has Phase-Perfect advised?

SND said:

I'm alone on my pole transformer, at the end of the line up my driveway. Balance of 123v to ground/neutral seems good on both legs last I checked.
There's no neutral going into my PP, I just have 2 hot and the ground as far as I remember. I definitely need to be able to buck both 123'vs going into it equally, don't want off balance. Should I get 2 smaller units and wire each as single pole 120V units? or its sure that I can hook up only 1 240V buck boost to buck both legs equally? looks like its doable with that last diagram. I guess I'll have to be careful with that.

I thought about bucking it down at the machine and letting the normal 247V feed the PP, but then figured it'd likely better to just buck its supply since I'll have 2 cnc's on it, don't want to buy 4 or 6 of these buck boost...

Click to expand...

With no neutral, how would anything KNOW there was an off-balance? There is no reference, if there is no neutral. You should be good with one buck transformer. It's not a problem if you use two, but there should be no need for that.

Now, if it happened that the total you needed to buck was equal to the two secondaries in series, then you might think that one secondary in each side of the line was good. But, unless it is specified as OK by the manufacturer, there is no guarantee that the insulation between the two low voltage secondaries is rated for full line voltage (plus transients). While it may be, it also may not be, since the usual connections are simple series and parallel, with minimal voltage between.

It is better not to do that, and again, there should be no need.

There is no reference, if there is no neutral.

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That's correct, But there is a reference to ground, inside the drive with the MOV's. And the ground bus has the same reference as the neutral.

If your running near the high side of the spec, as it is, and then you introduce more imbalance, when those transients do come along, it could go over the limit the drive is designed for.

I have used the balanced connections with both 240 and 480V systems and have never had an issue, with the winding insulation. With units sized from 25 to .250 KVA

It also works fine when using a standard 4winding transformer connected as a auto-transformer step up from 240 to 480. You don't see these type connections listed in the OEM materials, but they have been used for years with success by many. Only the last edition of the NEC, started the requirement that the OEM approve their units for this use.

SAF Ω

SAF said:

That's correct, But there is a reference to ground, inside the drive with the MOV's. And the ground bus has the same reference as the neutral.

If your running near the high side of the spec, as it is, and then you introduce more imbalance, when those transients do come along, it could go over the limit the drive is designed for.

.....

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Yes,the MOV is connected to ground. BUT the source is a balanced 240V source. So if there is a problem with boosting ONE side, then there is a problem with boosting BOTH sides. The difference in voltage is way less than any designer with a brain will use as a safety margin. MOVs breakdown voltage drops a little bit every time they take a hit, so for any sensible design, there is (has to be) more range than a buck boost provides, between the safe and the breakdown ratings of the MOV. *

Besides.... The OP wants to BUCK DOWN the voltage, which means he is NOT getting CLOSER to the breakdown, but FARTHER AWAY from breakdown, So this is as "safe" as it gets. He cannot possibly get in trouble when bucking DOWN the voltage, even if you assumed a design that was right on the edge for a boost.

As for the transformer windings... That's one of those things that may be designed-in, or may not. There is no special REQUIREMENT that the windings be insulated for full line volts BETWEEN THEM, although there is a decent chance that they ARE insulated well enough to work. The two obviously are insulated quite well from the primary. The issue is what insulation exists between the two.

This is NOT the same as the "secondary used as primary" deal that was discussed before. THAT was something that is in a way "theoretical". This is a case where practical considerations may easily cause a problem.

It depends on what the transformer manufacturer could do with the design, and whether they have internal standards that call for insulating that way. The two windings could be on one layer, wound next to one another with no special insulation, or they might be on separate layers with good insulation. You just do not know. If each one is only a half layer, then the designer can save money by winding both on one layer.

In the old days, I'd bet on the windings being good for full line volts, and I'd likely use that connection no issue with older parts. It's one of those things that an old designer "just did" when doing the design. These days, it's all about fulfilling minimum requirements, and as little as you can get away with past that. So I would be less willing to do it with new units, unless the secondaries are known to be rated for full volts between. .

*
The difference between a wye and delta voltage is much more of a problem for the MOV voltages, since that is considerably over a generally decent margin of safety. But it is a 70% voltage boost, not the 10% or 15% that a regular buck/boost gives on 230V.

JST said:

Yes,the MOV is connected to ground. BUT the source is a balanced 240V source. So if there is a problem with boosting ONE side, then there is a problem with boosting BOTH sides. The difference in voltage is way less than any designer with a brain will use as a safety margin. MOVs breakdown voltage drops a little bit every time they take a hit, so for any sensible design, there is (has to be) more range than a buck boost provides, between the safe and the breakdown ratings of the MOV.

The difference between a wye and delta voltage is much more of a problem for the MOV voltages, since that is considerably over a generally decent margin of safety. But it is a 70% voltage boost, not the 10% or 15% that a regular buck/boost gives on 230V.

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On a center tapped 240V delta (hi leg), such as the output of the OP's Phase Perfect. Why do most world market drive OEM's, not directly approve of that supply system for their drives?

It's balanced for sure, symmetrical to ground, not so much. That's a 32V change or 15%, line to ground, the value in the OP case. With the buck boost, non-symmetrical to ground it's 24V or 10%. Is that 5% difference in margin all that is required for headroom?

I agree that going down in voltage further negates the hazard, and going up substantially increases it. But keeping it as symmetrical as possible to ground just makes common sense to me.

I also recognize that these world drives normally work fine on center tapped deltas, in most cases. But when you inquire for implicit permission it's usually not granted, or that you have to remove the ground reference.

Same kinda deal with the modified transformer connection, it normally works fine without issues. Some new units do come listed for use at elevated voltages if you check the specs. Others have no such mention for this use. Many of them new pricy SqD units do come with that higher voltage use listings.

Agreed that older units are most likely to have the insulation wraps between the windings. Newer units built to a price point, may not. The winders I know only stock one class of insulated magnet wire and paper, too much inventory to stock multiple classes.

SAF Ω