Author Topic: Bronson ++ Isolation transformers-Any good? (Read 6978 times)

djsb · « **on:** November 11, 2021, 09:05:04 pm »

I'm considering buying one of these Bronson isolation transformers

https://bronson-energy.com/product/bronson-tt-3000/

The one available on Amazon are a different model

https://www.amazon.co.uk/Bronson-3000-Isolation-Transformer-Toroidal/dp/B07JMCT1BZ?ref_=ast_sto_dp

So, I would have to ask them what the difference is between them. The user hand book is attached. What are your thoughts? Thanks.

Gregg · « **Reply #1 on:** November 11, 2021, 10:43:43 pm »

The MII models appear to have dual windings for 110 and/or 220 volt applications depending on whether they are wired series or parallel. It could be handy for the price difference. You may want to check if they have input surge protection.

rvalente · « **Reply #2 on:** November 12, 2021, 12:43:36 pm »

It seems to me very well made but, the photo states "made in china" which leads to me believe its made for them not by them.

djsb · « **Reply #3 on:** November 12, 2021, 12:57:36 pm »

Yes, it clearly states on their website that the founder of the company is an artist who needed to use his US equipment in Germany, so he set up the company (read the marketing info on the website). It's clearly subcontracted out to someone in China. This is not a problem as far as I'm concerned. I've just bought the 3KW version, and it's arriving tomorrow.

https://bronson-energy.com/product/bronson-mii-3000/

I might do a review video at some point, as there aren't many reviews available. Or maybe just report my experience of the unit here if that would be helpful to others.

David.

rvalente · « **Reply #4 on:** November 12, 2021, 01:16:04 pm »

Cool, you should do a review and some teardown pics for us

TheBay · « **Reply #5 on:** November 12, 2021, 10:02:42 pm »

I was about to buy an isolation transformer from Screwfix, they are £99 for a 3000VA version and £89 for a 1500VA version, but all of a sudden they have no stock anywhere and no option to have one delivered either.

I saw these Bronson++ models on Amazon but was curious to know what they are like, not sure why they are using a fan in them, I wonder what the actual rating is of the transformer, I see they are using toroidal transformers possibly to get the size down a bit and that might be why but I do wonder if their rating is a bit lower than they say it is, or the transformer is lossier than it should be.

All the EI type isolation transformers I've used have never required a fan and not been remotely hot with a decent load on them.

I contacted Bronson++ a few months back to order a replacement mains socket for one of their Variacs, but they told me they do not sell spare parts nor have access to them and just told me to send it back to Amazon if it is still in warranty (It wasn't) so I assumed they completely outsource this to China and either do not do any repair in house either or were just being awkward.

It would be really interesting to see the guts on this if you're willing to open it up

djsb · « **Reply #6 on:** November 14, 2021, 01:30:54 pm »

It arrived yesterday and I'm pleasantly surprised. First, it comes fitted with 2 beefy handles that are NOT on the Amazon pictures. Secondly, the Earth connections are DISCONNECTED by default and there are warning stickers next to each socket. There is also a fan fitted. It's also quite compact but weighs 15Kg. My version is a Bronson ++ M11-3000T.
I might do a quick video once I get some cable wired up to it.

David.

TheBay · « **Reply #7 on:** November 14, 2021, 01:43:19 pm »

Take it apart and get some pics first, always wise to open these things up before power-on and check it's been wired correctly and safe

Also I'd personally rather the earth present at the sockets and if I REALLY needed a non-earthed socket I'd add a separate socket to the terminals with a big sticker stating NO EARTH on the additional socket, I do hope at least the chassis is connected to earth.

djsb · « **Reply #8 on:** November 14, 2021, 01:55:40 pm »

I can confirm that the chassis (all external metal parts) ARE connected to the Earth connection on the TERMINAL BLOCKS. So, three core mains lead should be used to feed the mains INTO the transformer terminal blocks.

TheBay · « **Reply #9 on:** November 14, 2021, 02:00:37 pm »

That's good news they got that right

I'd want the socket on the isolated side to be earthed too, or a provision to enable or disable the mains earth if really needed. Either through a switch, extra non-earthed socket with warnings or link wire with 2 banana sockets.

djsb · « **Reply #10 on:** November 14, 2021, 02:22:08 pm »

I agree, the option to connect/disconnect the earth to the sockets would be nice. I'm hoping that we can work on a modification to make this happen. I will post some detailed interior photo's during next week.

David.

TheBay · « **Reply #11 on:** November 14, 2021, 02:40:45 pm »

Quote from: djsb on November 14, 2021, 02:22:08 pm

I agree, the option to connect/disconnect the earth to the sockets would be nice. I'm hoping that we can work on a modification to make this happen. I will post some detailed interior photo's during next week.

David.

It will be really interesting to see what's inside, I found a teardown of a smaller unit on YouTube, that one has a soft-start circuit, I'm assuming yours has it too.
https://youtu.be/C4XH7WwU7f8?t=1014

I'd definitely check yours over inside before using it as after watching that video it does appear it is just a typical far east design and re-badged for Bronson++ I wouldn't say any of that is their design internally looking at the construction, wire colours and also the PCB definitely looks a far eastern design. Very similar construction to the far east "Variacs"

Hopefully it works well and is safe/can be made safe. Do you have anything there to test the insulation resistance on the transformer, such a "Megger type tester" or a PAT tester, as it's a toroidal transformer. I wonder what voltage/va rating is on the transformer. I really want to know why they thought a fan was needed.

No luck at all hunting down one of the Screwfix 3000VA's so getting sorely tempted by one of these, I really hoping yours checks out well

djsb · « **Reply #12 on:** November 14, 2021, 03:04:47 pm »

Can't PAT test it at home.It has a soft start function as well as short circuit and over temperature protection. It's a 3KW 12A version (2400 Watts continuous). The case has a Fan aperture on the rear. I will see if there is an actual fan when I open it up. More later in the week.

TheBay · « **Reply #13 on:** November 14, 2021, 03:17:08 pm »

2400w continuous is quite impressive! I look forward to seeing it.
I've got a version of it saved on Amazon ready to purchase, but for some reason the 1:1 version is more expensive than the 110/230V in.

Is this the ASIN of the one you ordered: B07JMCFNLM ?

djsb · « **Reply #14 on:** November 14, 2021, 03:30:05 pm »

The ASIN of the one I bought is: B07JMCT1BZ

Bronson++ MII 3000 Isolation Transformer Toroidal Core 3000 Watt - In: 110V / 230V - Out: 230

Also, maybe a slide switch like this could be inserted into the front or rear panel to connect/disconnect the earth to the sockets

https://uk.farnell.com/multicomp/mcsl15-121alcj-p3a-1jcn/slide-switch-spdt-12a-250v-panel/dp/2454615

TheBay · « **Reply #15 on:** November 14, 2021, 03:44:39 pm »

Quote from: djsb on November 14, 2021, 03:30:05 pm

The ASIN of the one I bought is: B07JMCT1BZ

Bronson++ MII 3000 Isolation Transformer Toroidal Core 3000 Watt - In: 110V / 230V - Out: 230

Also, maybe a slide switch like this could be inserted into the front or rear panel to connect/disconnect the earth to the sockets

https://uk.farnell.com/multicomp/mcsl15-121alcj-p3a-1jcn/slide-switch-spdt-12a-250v-panel/dp/2454615

Ah you went for the multivoltage input model, confusing why this one is cheaper than the 1:1 version.
As there is more going on inside this and must cost more to manufacture, the PCB must detect the incoming voltage and switch over the primary transformer taps as I can't see a separate 230/110v input.

djsb · « **Reply #16 on:** November 17, 2021, 02:16:24 pm »

The transformer SEEMS (I can NOT prove this) to be contract manufactured by Huizhou Yinghua Electronic Company Ltd in China.
The transformer itself is marked GDYHDZ as are the relays on the PCB. There is also a Holtek HT46R064B OTP microcontroller on the PCB. Here are some photo's.

TheBay · « **Reply #17 on:** November 17, 2021, 05:59:31 pm »

Thanks for the teardown

Looking at the products from Huizhou Yinghua Electronic Company Ltd they have a very similar build and PCB's so I wouldn't be at all surprised if they built the whole unit.

I've got to laugh how they have doubled up the current capability of that switch, they should have used a higher rated switch and insulated the terminals. I'd dread to think what would happen if that switch popped out or fell apart, even mechanical stress or vibration could cause those soldered wires to fall off. They should have switched both L/N really as well.

The lid should have an earth cable going to the chassis or the earth point with some toothed star washers, but that can be added easily.
It all could do with a check over and tweak some things to make it safer.

Not sure what to say about the lack of earth to the sockets, I feel it should be there and down to the user to disable if they absolutely must.

djsb · « **Reply #18 on:** November 19, 2021, 05:12:27 pm »

So, are you going to buy one as well? Or are the issues you mention putting you off?

TheBay · « **Reply #19 on:** November 20, 2021, 01:40:13 am »

Quote from: djsb on November 19, 2021, 05:12:27 pm

So, are you going to buy one as well? Or are the issues you mention putting you off?

I rang Screwfix today as I've been trying to buy their 3000VA (1500VA Continuous) Isolation transformer and it is never in stock for Click and Collect or Delivery, they informed me that it's on back order and delayed from their supplier. I may hang on a little bit and see if they come back in to stock.

But if they don't I'm sorely tempted by the Bronson++ unit, check its all wired correctly and safe then do a couple of modifications.

djsb · « **Reply #20 on:** November 20, 2021, 04:05:47 am »

Thanks. What specific mods would you recommend?

TheBay · « **Reply #21 on:** November 21, 2021, 01:28:11 pm »

Quote from: djsb on November 20, 2021, 04:05:47 am

Thanks. What specific mods would you recommend?

I'd want to do an insulation test on the transformer first.
Then a few things I would do is change, rewire and insulate that main switch, check over the quality/spec of all the wiring to see if it's suitable. Fit ferrules to all the wires that go in to any screw terminal connectors (if not already fitted) I would personally want all the sockets earthed and another earth cable going from the chassis to the lid. And if I wanted an un-earthed socket I would run a separate one from the terminal block output to an external socket with a big warning on it. I'd also want to check over the quality of the built in sockets too.

The model I'm looking at is a bit different as it is a 1:1 transformer not one with a switchable input transformer for 110-230V as I would never be in a situation where I require a 110V input. So it will have a less complicated circuit board and possibly none at all if it doesn't have a soft start function. But I would check the circuit board over and make sure it is safe and has correct clearances and creepage distances etc.

djsb · « **Reply #22 on:** November 24, 2021, 07:38:36 am »

DO NOT BUY THIS UNIT. The unit I have bought is FAULTY AND DANGEROUS.
1/ The unit turns on immediately that the power is plugged in. THE ON/OFF SWITCH HAS NO EFFECT.
2/ There is mains potential between the Chassis and the LIVE OR NEUTRAL, depending on how the mains outlet socket is plugged in.
This unit is NOT suitable for its purpose, and I'm returning it to Amazon ASAP. Problem is, I have to buy a printer, so I can print out the return label for Hermes to pick up the box from home. Or I can get the label printed out at my local library.

PS There was a thin piece of wire bridging the terminals on the ON/OFF switch. I removed this piece of wire and now the ON/OFF switch works. There appears to be very little quality control on these units.

TheBay · « **Reply #23 on:** November 24, 2021, 10:37:35 am »

Quote from: djsb on November 24, 2021, 07:38:36 am

DO NOT BUY THIS UNIT. The unit I have bought is FAULTY AND DANGEROUS.
1/ The unit turns on immediately that the power is plugged in. THE ON/OFF SWITCH HAS NO EFFECT.
2/ There is mains potential between the Chassis and the LIVE OR NEUTRAL, depending on how the mains outlet socket is plugged in.
This unit is NOT suitable for its purpose, and I'm returning it to Amazon ASAP. Problem is, I have to buy a printer, so I can print out the return label for Hermes to pick up the box from home. Or I can get the label printed out at my local library.

PS There was a thin piece of wire bridging the terminals on the ON/OFF switch. I removed this piece of wire and now the ON/OFF switch works. There appears to be very little quality control on these units.

Sorry to hear that, I really would report this to your local trading standards and they will investigate it. It shouldn't be on sale and would pass no approval in this country.

djsb · « **Reply #24 on:** November 30, 2021, 10:39:13 am »

I've tried to return the item to Amazon on 4 occasions over the last week and Hermes who is the courier who collects on behalf of Amazon has cancelled the collection. I complained to Amazon UK, and they have refunded my money AND cancelled the requirement to return the item (I have a confirmation email confirming this as well). SO, now I have an isolation transformer for FREE that I have to make safe. They suggest I keep it or donate it to charity. I won't be donating anything UNSAFE to anyone.
1/ Make sure that the toroidal transformer itself actually has ISOLATED WINDINGS and is NOT an autotransformer.
2/ Do a thorough documentation of the wiring before I go any further.
3/ Change the ON/OFF switch wiring. Any tips on this (a better switch. terminals etc.)

Can anyone recommend anything else I can do to first make it safe and then to possibly improve it? Thanks.

PS If I'm actually able to make it safe (assuming the basics are there) then I might make a video of my investigations and what steps I take.

electr_peter · « **Reply #25 on:** November 30, 2021, 03:07:07 pm »

I think you could reuse it with relatively low cost improvements and testing. My recommendations:

make proper schematic of transformer and make sure it is correct. If you change something, update schematic. Default mode should be PE carried through and L/N floating w.r.t. PE
check grounding connections, make sure they are all up to standand, remove paint where necessary
Check all cables and fuses for size, test wire and connection resistance (cables maybe not be from real copper, but from CCA!). Consider ceramic fuses
add input socket with double fuses (as in medical transformers teardown-and-modification-of-noratel-imed-e-150-isolation-transformer)
add double pole AC switch which lights up if energized
test isolation between primary/secondary/ground (POT testing or similar)
test leakage currents/stray capacitance (data sheet on medical transformer leakage test, noted in page 15 https://www.noratel.com/fileadmin/content/downloads/medico/en/IMED2014_en.pdf)
check thermal performance. Add more fans/holes in the case if necessary
investigate soft start circuit (inrush current limiting)

If above checks out, then you will have a very usable item.

djsb · « **Reply #26 on:** November 30, 2021, 03:17:27 pm »

Thanks. Please excuse my ignorance, but in your first bullet point what does PE mean? And also in your third point what is CCA?
Thanks for the link in point 4 and I'll look into what you suggest.

PS. Just bought myself a UNI-T UT210D Digital clamp meter as I'm going to need it. Require one anyway for non-intrusive current measuring.

electr_peter · « **Reply #27 on:** November 30, 2021, 03:40:30 pm »

PE - protective earth (or ground) in mains socket.
CCA - copper clad aluminum i.e. aluminum strands coated in copper. It may look like copper, but it is a bad choice as cable conductor for many reasons.
Also, run with a strong magnet over the wires. Wires should not be magnetic, but who nows what you will find at this quality level.
Double fuse idea is for potential line/neutral reversal or unusual situations, just in case.

Alti · « **Reply #28 on:** November 30, 2021, 06:17:15 pm »

Quote from: djsb on November 24, 2021, 07:38:36 am

There is mains potential between the Chassis and the LIVE OR NEUTRAL(..)
PS There was a thin piece of wire bridging the terminals on the ON/OFF switch. I removed this piece of wire and now the ON/OFF switch works. There appears to be very little quality control on these units.

Do you think the transformer itself is made to a higher standard? I wonder what you are going to find under this plastic foil wrap. Maybe you could reuse some of its components to build a decent unit but I'd be cautious about its "isolation" properties at this stage. It must either include double isolation between pri-sec (class II) or must be pri-sec separated by PE (class I). So I wonder which path they took. Most likely it is class II and does not include any PE or shielding.

threephase · « **Reply #29 on:** November 30, 2021, 08:53:19 pm »

I note that the OP is from the UK. Independent fusing of the neutral is prohibited in the UK and can lead to dangerous scenarios, especially for class 1 appliances.

You either have a single fuse in the live only or you can have a double pole trip unit that walloped both the live and neutral simultaneously.

I am almost tempted to buy one myself to do a full inspection on and see if it has similar issues, or the OP is unlucky.

djsb · « **Reply #30 on:** November 30, 2021, 10:01:34 pm »

Interesting discussion here about fusing in the live feed only.

https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=62064

Can isolation truly ever happen simultaneously in the live and neutral wires? Surely any time overlap is an opportunity for electrocution?

threephase · « **Reply #31 on:** December 01, 2021, 07:45:02 am »

Quote from: djsb on November 30, 2021, 10:01:34 pm

Interesting discussion here about fusing in the live feed only.

https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=62064

Can isolation truly ever happen simultaneously in the live and neutral wires? Surely any time overlap is an opportunity for electrocution?

Ultimately no it can't, but the opportunity for electrocution also exists for the duration that it takes the protective device in the live conductor to break. The extra time taken for a 2-pole device to clear both poles would be negligible. The same argument also applies to 3 phase supplies, technically a 3-pole breaker will not clear all 3 phases simultaneously, but the time differential between them is very low, so in practice it is not a concern, all 3-poles will be cleared within the trip time specification for the circuit.

djsb · « **Reply #32 on:** December 02, 2021, 01:18:30 pm »

I have removed the PCB in order to investigate the relay contact layout and the additional support circuitry. I have requested a datasheet for the relays (3 off GDYHDZ YH-T90-30-2A and 1 off GDYHDZ YHT72-15-2A) from GDYHDZ in china. I will gradually be building up a schematic layout as I go along. It may take me a while as I have to reverse engineer the board layout. I'm concentrating on the relays first, as they are the business end of the transformer.

The semiconductors so far identified are
1/ Holtek HT46R064B OTP MCU.
2/ JST7805CV regulator.
3/ BD681 power darlington.
4/ 2N5551 high voltage transistors.
5/ 1N5349B Zener diodes.
6/ A few other diodes on the board where I can't see ALL the numbers.
Capacitors.
1/ Electrolytics are all 105 degree XYG make.

The blade terminals on the wires have a locking tab that prevents the blade slipping off the terminal. They won't pull off unless a tab is depressed on the blade. Good to see blades soldered into the PCB.

I will be checking the transformer wiring on Friday to make sure all the windings are actually isolated from each other.

electr_peter · « **Reply #33 on:** December 02, 2021, 01:58:51 pm »

I am curious of those 4 relays configuration. Likely inrush limiting, but why they have 4?

TheBay · « **Reply #34 on:** December 02, 2021, 03:05:06 pm »

Quote from: electr_peter on December 02, 2021, 01:58:51 pm

I am curious of those 4 relays configuration. Likely inrush limiting, but why they have 4?

To automatically switch between 110/230v Input, the relays will switch the primary transformer taps in series or parallel.

electr_peter · « **Reply #35 on:** December 02, 2021, 05:10:21 pm »

I missed that OP bought 110/230 to 230V transformer, not 230->230V. Thus more relays on PCB.

djsb · « **Reply #36 on:** December 18, 2021, 10:39:25 am »

I'm still working on creating/reverse engineering the schematic of the main PCB. Hope to make some more progress over the next few weeks. I've got to get this right so please bear with me. Thanks.

adam4521 · « **Reply #37 on:** December 19, 2021, 10:42:48 pm »

I was also interested in the Screwfix isolation transformers because they are lower cost than the equivalent bought elsewhere and look simple and robust. But no good if there is no stock. These Bronson units via Amazon are also interesting. Another cost-effective UK option I've discovered is Tripp Lite IS300HGDV, which "tekshop247.com" are offering for £72.54 incl VAT. Only 300W though, and you have to supply your own IEC leads/adapters. On the plus side, they are switchable to operate in step-down or 1:1 mode.

rdelpellegrino · « **Reply #38 on:** October 01, 2022, 10:05:04 am »

Hi. Having read through this topic, is it fair to say that this Bronson brand can provide a functional (as in safe) isolation transformer - suitable for 'hobbyist' use?

I live in UK and have a dual RCD equipped consumer unit supplying power. Is it also advisable to isolate the ground on this isolation unit for bench use?

My apologies for resurrecting this topic after so long, but I am currently eying one of these units - Bronson++ MII 1000 with a view to purchasing it. I'm not entirely clear what the final view was on the product that was examined.

On the other hand. If anyone can suggest an alternative or even better product - reasonably available in the UK - at a similar price, I would be grateful for any advice, from those more knowledgeable in this area. Thank you in advance.

djsb · « **Reply #39 on:** October 01, 2022, 10:14:00 am »

Mine's still in pieces at the moment as my priority was and remains fixing a HP8563E spectrum analyser. I was last reverse engineering the PCB and schematic to figure out what connects where. I would NOT recommend buying one at the present moment. I was looking at an Aldetronics variable isolation transformer, but the company appears to no longer be trading.

PinheadBE · « **Reply #40 on:** August 18, 2023, 06:18:45 pm »

Quote from: djsb on December 02, 2021, 01:18:30 pm

I have removed the PCB in order to investigate the relay contact layout and the additional support circuitry.

Hi,

I am interested in your progress on reverse-engineering this transformer's control PCB.
I have two questions:

1°) There are two connectors apparently for a fan: one AC and one DC. Do you know what voltage is present on the FAN DC connector ?
2°) There is a "DISP" 4-pins connector near the µC. Any idea of the pin layout and what type of display could be tried ? (Maybe a more powerful model has a display ?)

Thanks

djsb · « **Reply #41 on:** August 18, 2023, 06:28:38 pm »

I can't really answer your questions at the moment as this has been abandoned for the time being. I might have another go at some point, but please don't hold your breath.


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Author Topic: Bronson ++ Isolation transformers-Any good? (Read 6978 times)

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