Bronson ++ Isolation transformers-Any good?

[electr_peter]

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]

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]

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]

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]

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]

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]

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]

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]

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

[TheBay]

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]

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

[djsb]

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]

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]

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]

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]

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]

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.