Sanwa 29e31s Step down transformer

[Jollywest]

Hi,
I’m looking for a suitable step-down transformer to use with a Sanwa 29e31s monitor.
From the monitor manual it seems to use max 180w;

So would this 200w one be ok?

I used this one previously and it worked but think it was only 85w;

I don’t have it anymore but there is another one like this available I can acquire if it is suitable.
Thanks.

[lilshawn]

So would this 200w one be ok?

dunno. you have supplied no link or specifications other than it's "200w step-down". unfortunately with this monitor, you can't simply dumb down the voltage with a voltage converter circuit...which is what i believe your linked picture to be. these devices typically use diodes or mosfets/transistors/triacs to chop up the voltage down to a level of a duty cycle that emulates 120v.

your voltage convertor you choose MUST be an isolating transformer type. this monitor uses a linear regulator circuit to produce it's voltages and as such MUST be isolated from mains by a 1:1 (aka "unity gain") transformer... or in your case... a 2:1 transformer since you need to carve down 240ish down to 120ish. The voltage regulator output cannot be tied in any way to the line voltage because the way the regulator works. the linear regulator, when connected to mains will draw infinite current from those mains and blow up/short out.

[Jollywest]

Yikes!… cheers for the reply.
Definitely not my forte as you can tell.
Here’s a link to the 200w step down transformer;
https://www.ebay.co.uk/itm/126300590879

I found on old photo of the transformer I used to use with my old monitor and it was definitely 85w.

[lilshawn]

the transformer you are going to need to obtain is going to be about 4 kilos of iron and copper. not going to be available shipped too far.

something like

https://store.sacelec.com/index.php?l=product_detail&p=18648

or maybe

https://www.dicksmith.com.au/da/buy/genpower-300w-step-down-transformer-240v-110-stepdown-voltage-converter-au-us-09348948011797/

possibly

https://panther.ph/product/300w-dv-step-down-transformer/

basically looking for a big transformer. if it comes in a little plastic box... not interested. it's going to be the weird chopping circuit type that the monitor will absolutely not like.

maybe try and load up ebay and search for "220v to 110v transformer" and ignore anything in a plastic box.

[Jollywest]

Thanks for the info and links, very much appreciated 

I’m hoping this one might do the job;

https://amzn.eu/d/ijd4xNi

2.5kg
Metal
500W
Commercial use
Unlike others though, it doesn’t say if it is an isolating transformer or not.

[lilshawn]

trying to peek in the vents it looks like it may have a toroidal transformer.... here is a link to a youtube video showing the inside of a similar unit by the same brand...only bigger so it could be the one.

https://youtu.be/O3EeBrJFlbE?si=G0tPs09CR_1itJSZ

NOTE: i have not watched the video in it's entirety, just linking for the info

[Jollywest]

Again, thanks for the help and for the video link… what an absolute legend that guy is 😎

The last 3 minutes of the video he says it is an auto-transformer and isn’t an isolating one unfortunately.
I’ll have another look about and see if I can find an isolating one, thanks.

[lilshawn]

I have found conflicting information as to whether or not this chassis requires an isolation transformer or not and nobody seems to have come back to say whether it has or not.

I'd initially started digging into this to see if the chassis could be just converted to run on 240v and started looking at the Sanken STRM6511. now typically the chassis using Sanken regulators of the STR series such as the STR30130 and STR2105 are all not capable of being put directly on the mains (as mentioned before)  but the STRM6511 is not specified as a "voltage regulator" per se in it's datasheet, but as a "switching regulator" which seems to me is different than the other regulators... and does actually say "switch mode"

From what i've been able to dig up, apparently this chassis may be Sanwas kind of first crack at a "switch mode" power supply... if this is the case, then an isolation transformer would not be needed. unfortunately the one version of the schematic i've come across has a schematic that is the second most terrible i've ever seen and is hardly legible, i honestly don't even know why it's been included. if it was more legible, i might be able to ascertain if it is in fact, switch mode or not.

so... the simple auto-transformer MAY work... but i cannot find any information confirming or disproving the requirement of an isolation transformer... the service manual does not say either way, as such i cannot make a recommendation either way.

I mean you can roll the dice and see if the autotransformer type supply works. worst case, you have to source another STRM6511 and probably replace the AC input diodes... 

[Jollywest]

Cheers for digging into this some more.
Agreed about the schematic, anything I’ve found online is just a fuzzy mess.
I’ve asked on a UK based arcade forum if anyone with this monitor can send me details of the transformer they are using with it, just waiting on responses.
There seems to be a few slightly differing versions of this monitor as well, I’ll see if I can work out which one I have.
One question rattling around my brain though is this; How did an 85w Isolation step-down transformer work for many years without issue with my old monitor of this type, when the monitors power output is around 160w?

[lilshawn]

typically the stated load of a device on its nameplate would assume a "100% load" scenario. all lights lit, all relays activated, load at 100% etc. for instance your computer's power supply could say it draws 600 Watts... that number would assume that every rail in the supply was at its maximum rated capacity. it very likely draws much much less that that just sitting at idle (and not even able to get to the maximum attainable if you don't' have a bunch of 4090 videocards and piles of hard drives in it to begin with.)

it's also possible they simply calculated the "load" of the monitor doing a quick and dirty ohms law calculation by taking the devices input fuse value (amps) divide it by the voltage and assuming a complete system failure mode draw that would cause the fuse to blow. so it's normal operating draw is much less than the nameplate suggests.

due to this it's possible your old monitor running at its normal operating mode consumes somewhere thereabouts of 80 or 90 watts. not totally detrimental to your 85 watt transformer (which likely has its own rating within a similar margin or over , but certainly hard on the longevity of the transformer.

[Jollywest]

That makes a lot of sense, thanks.
I’ve had some responses from the forum over here and apparently the monitor doesn’t need an isolating transformer as you suspected.
I’m also hopefully getting an original manual with schematic for this monitor, the seller is just checking that the schematic can be clearly made out.
Cheers again for all the help, been very interesting to know more about the in’s & out’s of these things.
I’ve now ordered a transformer and should have it by early next week.
Hopefully the monitor actually works as it was bought untested 🫣