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Old 08-15-2020, 01:46 PM   #1
eq1
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Default Tankless Water Heater causing buzz in my monitors

I have new Presonus Eris E5 XT monitors. They're not even powered ON. For my computer/'studio' I have a dedicated home wiring circuit going back to the entrance panel. I've had two different 'tankless water heaters' - I just replaced one yesterday. These are 13kW units and use SCR's (I think that's 'silicon controlled rectifier') as the power controller. Basically, it has a high power transistor-like switching mechanism to control the power output at the heating elements...

These tankless units create a buzz in my monitors, like I said, even with the monitors powered OFF!

Do you know of a rather simple but effective method or device that can be installed in the panel, perhaps on the circuit that goes to my studio, or maybe the water heater circuit?, to filter-out this noise/this kind of noise? Or maybe just a power conditioner/strip at the studio receptacle this stuff is plugged-in to?


Oh and, BTW, the tankless I installed yesterday - an 'EcoSmart' - is quite a bit noisier than the old one, a Rheem RTE13.

Last edited by eq1; 08-15-2020 at 01:56 PM.
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Old 08-16-2020, 07:25 AM   #2
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I looked at the schematics for the Rheem RTE13. It has SCR's, but...

The troubleshooting guide:

http://waterheatertimer.org/pdf/Rhee...hoot-guide.pdf

tells us

Quote:
Remember, this is a “modulating” appliance. It
will only provide the voltage necessary to heat
the water (based on dial setting) that is being
demanded.
Which sounds like a dimmer. And a badly filtered one, at that.
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Old 08-16-2020, 07:36 AM   #3
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Power the speakers from an unplugged UPS battery to see if the noise is coming through the power line or through the air to your speakers. Then you can address either shielding or noise filtering.
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Old 08-16-2020, 07:46 AM   #4
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Assuming you're using 240 V, a filter like this one:

https://uk.rs-online.com/web/p/power...lters/7084339/

as close as possible to the heater, should take care of it.

I know, expensive, but at 13 kW things tend to go up. So test for possible airborne noise first.
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Old 08-16-2020, 08:02 AM   #5
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Quote:
Originally Posted by cyrano View Post
Assuming you're using 240 V, a filter like this one:

https://uk.rs-online.com/web/p/power...lters/7084339/

as close as possible to the heater, should take care of it.

I know, expensive, but at 13 kW things tend to go up. So test for possible airborne noise first.
holy crap. I'd go back to a tank before paying that much. wow
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Old 08-16-2020, 12:29 PM   #6
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Quote:
Originally Posted by cyrano View Post
I looked at the schematics for the Rheem RTE13. It has SCR's, but... The troubleshooting guide:
http://waterheatertimer.org/pdf/Rhee...hoot-guide.pdf
tells us
Which sounds like a dimmer. And a badly filtered one, at that.
Thanks! I've been looking for something like this for ages, the troubleshooting guide. I'll take a look...

I'm pretty sure the 'noise' would be from the SCRs; I think the 'dimmer' aspect is purely digital - it has a couple small microprocessors, one must check the pot temp setting for a value, and then adjusts the gate(?) voltage at the SCRs, which modulates the overall output voltage, where the massive current and triggering ON and OFF of the SCRs is what causes voltage to fluctuate in the whole house electrical system. I think, maybe, something like that...

I tried to understand this stuff when the first RTE13 failed, but it's been a while, and I never fully grasped how the SCRs worked, or how the whole unit worked overall...
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Old 08-16-2020, 12:31 PM   #7
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Quote:
Originally Posted by Coachz View Post
Power the speakers from an unplugged UPS battery to see if the noise is coming through the power line or through the air to your speakers. Then you can address either shielding or noise filtering.
Never thought it could be noise 'through the air'... Could it? I hear the noise with monitors turned OFF but plugged-in; it goes away when I unplug them...
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Old 08-16-2020, 12:47 PM   #8
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Quote:
Originally Posted by eq1 View Post
Never thought it could be noise 'through the air'... Could it? I hear the noise with monitors turned OFF but plugged-in; it goes away when I unplug them...
It goes away when you unplug them because there is no amplifier then.

https://en.wikipedia.org/wiki/Electr...c_interference

It is most likely interference through the wires normally but even my cell phone 2 feet from my Rokit monitors generates noise every couple minutes unless I move it further away.
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Old 08-16-2020, 01:03 PM   #9
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hmm... I don't have a UPS, is there some other way I can test for airborne RFI/EMI? I was thinking maybe I could use an AM radio, battery powered, turn it ON near the monitors, turn hot water heater ON, see if I hear new noise?
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Old 08-16-2020, 01:11 PM   #10
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Originally Posted by eq1 View Post
hmm... I don't have a UPS, is there some other way I can test for airborne RFI/EMI? I was thinking maybe I could use an AM radio, battery powered, turn it ON near the monitors, turn hot water heater ON, see if I hear new noise?
possibly but most likely the switching circuit is blasing noise over the power lines.
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Old 08-16-2020, 01:27 PM   #11
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^ I just tried something else: I actually have another tankless essentially in the same room as my studio!, about 10 feet away around the corner in an open closet. But I'm the only one who uses the bathroom - so I'm never near my monitors when the unit is ON.

So, I just turned it ON and went back to my monitors - and I hear nothing, no noise...

What, if anything, can that tell us about the source of the noise?

-It suggests to me that the noise might not be caused by the overall design of these tankless units, otherwise this one near my studio would cause the noise as well...

-It still could be a flaw in the build of the two units that did/do cause noise...

-Could it be some aspect of how the 'kitchen' water heater is wired vs. how this one near my studio is wired? I don't know, just something like the location in the electrical panel of the circuit breakers, or maybe the location/routing of the cables?

Problem with that is they're both wired pretty much identically, I can't think of any differences (I installed them both, including routing the cables)... If anything, the one near my studio has much longer cabling and I'd think that one would be more prone to inducing noise...

etc etc... Any ideas much appreciated. I'm thankful for the help both of you have provided thus far...
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Old 08-16-2020, 01:36 PM   #12
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Sounds like the switching power supply in the tankless water heater is to blame.
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Old 08-16-2020, 02:17 PM   #13
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Quote:
Originally Posted by eq1 View Post
Thanks! I've been looking for something like this for ages, the troubleshooting guide. I'll take a look...

I'm pretty sure the 'noise' would be from the SCRs; I think the 'dimmer' aspect is purely digital - it has a couple small microprocessors, one must check the pot temp setting for a value, and then adjusts the gate(?) voltage at the SCRs, which modulates the overall output voltage, where the massive current and triggering ON and OFF of the SCRs is what causes voltage to fluctuate in the whole house electrical system. I think, maybe, something like that...

I tried to understand this stuff when the first RTE13 failed, but it's been a while, and I never fully grasped how the SCRs worked, or how the whole unit worked overall...
There should be pair of toroidal coils and a cap in there, at the least. I couldn't see any and the small electronics box probably wouldn't hold those; simply too small. Of course, they could be fitted behind the box.

Noise suppression is an important part of the cost @ 13 kW. The rest of the construction would be illegal here, with the SCRs mounted on the metal water input as cooling.

It's not real digital, but something like phase cutting. Produces horrible harmonics up to MHz frequencies. They probably switch the SCRs when the AC is at zero volts to avoid noise. But timing being a tiny bit off often foils up that plan.

You could also try putting a mains isolation transformer and filter on the studio part. Might be cheaper if the studio's current draw is low.

I usually carry a small 100 VA 230 VAC isolation transformer as a troubleshooter to find the point of entry, if it's mains related. I have recently installed a 15 kVA one to remedy a hum in the stereo monitors in both recording rooms. Seems to have fixed a few other oddities too. Still rare, tho...
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Old 08-16-2020, 02:19 PM   #14
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How much was the 15kva isolation transformer?
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Old 08-16-2020, 02:22 PM   #15
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Quote:
Originally Posted by Coachz View Post
Sounds like the switching power supply in the tankless water heater is to blame.
I doubt there's a switching PSU in there, Coach. It's a kind of a dimmer that "modulates" the 13 kW heating resistor. If not done properly, it's a giant transmitter over mains. You'd probably hear it on an AM radio...
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Old 08-16-2020, 02:28 PM   #16
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How much was the 15kva isolation transformer?
It was 850 €, excl. VAT, naked. Still needs a case. Total was around 2.500 € incl. work and certification.

Every now and then you can find old industrial ones for copper prices. Around 1 € per kg.
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Old 08-16-2020, 02:35 PM   #17
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Originally Posted by eq1 View Post
-It suggests to me that the noise might not be caused by the overall design of these tankless units, otherwise this one near my studio would cause the noise as well...
Maybe the noisy one is on the same electrical circuit as the studio?

Do you have a three-phase electricity feed (AKA "industrial" power) to the building? New? Old?

Quote:
-It still could be a flaw in the build of the two units that did/do cause noise...
I wasn't exactly thrilled when I saw the internals.

Quote:
-Could it be some aspect of how the 'kitchen' water heater is wired vs. how this one near my studio is wired? I don't know, just something like the location in the electrical panel of the circuit breakers, or maybe the location/routing of the cables?
As above, different circuit? Try turning off every fuse one by one and note which outlets and devices it feeds. That'll give you a rough idea.
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Old 08-16-2020, 03:16 PM   #18
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@eq, take note of what Cyrano writes! Giant transmitter it might be! Possibly not meeting your countries regulations on EMI! (Sorry not the record label! ElectroMagnetic Interference)

There are several ways to control the power applied to the tankless heater, some good for keeping down 'noise' others bad at it. The worst generally are those that operate like dimmers switching the load switchin on part way through the mains cycle and those need excellent design to reduce the sharp edges switching resulting in interference. Usually the best of those dimmer types have the SCRs (the power switching element) close to the load, employ good filtering or convert that phase variable switching back to a pure sine wave again of variable voltage.

From what has been found you have a very crappy one!

Those are similar in operation to lighting controllers in studios (can be a similar power) or the cheapie domestic light dimmer switches.

All those potentially produce lots of high frequency interference but also some at mains frequency (and/or harmonics of). All quite easy to pick up in other electronic devices but the higher the power they control the more they might also vibrate components/wires in their circuit or wires back to the supply that can be heard.

What I find confusing in your text is that you have a powered monitor but it is switched off? That being the case it is unlikely that it is electrically borne interference making the speakers reproduce it - though not actually totally impossible!

You still need to consider first (easily and cheaply) if it is a physical vibration. It could be getting transmitted through the building structure causing some resonation in the speaker cabinet. Try moving them to a different surface/location as a test.

Remember the usual problem is the higher frequencies interference, electrostatically/magnetically transmitted like in an antenna however you describe it as a buzz. Does that imply a lot of low frequency content and a bit edgy too or more just like a hum?
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Old 08-16-2020, 03:24 PM   #19
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Quote:
Originally Posted by cyrano View Post
There should be pair of toroidal coils and a cap in there, at the least. I couldn't see any and the small electronics box probably wouldn't hold those; simply too small. Of course, they could be fitted behind the box...

No "toroidal coils." Here's an image of the PCB for RTE13 - this is all there is to the unit:



Newer units have a different Thyristor (SCR or whatever). The older ones have these 2 SCRs (discontinued) with 6 wires total, the newer ones have a single unit with only 4 wires (a Littelfuse MS0690J-DL1TE). The EcoSmart11 - which is what I installed the other day to replace an RTE13, and which produces similar but more noise, looks more like the older RTE13, with 2 SCRs, 6 wires...

I'm just including some of these details in case someone else has a similar issue, where details might come in handy...


Quote:
Originally Posted by cyrano View Post
Maybe the noisy one is on the same electrical circuit as the studio?
Not on same electrical circuit. Studio has a dedicated line back to the service entrance. Both water heaters have dedicated 240V circuits...

Quote:
Originally Posted by cyrano View Post
Do you have a three-phase electricity feed (AKA "industrial" power) to the building? New? Old?
No 3-phase. Not sure what you're referring to with "new" and "old." Old house with some old wiring, but most of the wiring/cables/service panel/breakers, etc. are new. I left 3 old circuits in the panel (old wiring, new breakers), and they're mostly for lighting.

I ran the cable to the studio (and everything else); everything was done carefully... Off the top of my head I can't see why the cable path to the kitchen water heater 'downstairs' versus the cable path for the one 'upstairs' (by studio) would impact the cable path to the studio negatively. Again, it seems like it would be the opposite, if anything: The cable to the upstairs water heater runs right next to the cable to the studio...
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File Type: jpg older_style_Rheem_RTE13_tankless_PCB.jpg (59.3 KB, 1704 views)
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Old 08-16-2020, 03:49 PM   #20
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What I find confusing in your text is that you have a powered monitor but it is switched off? That being the case it is unlikely that it is electrically borne interference making the speakers reproduce it - though not actually totally impossible!
Yes, powered monitors, switched OFF.

Quote:
Originally Posted by Allybye View Post
You still need to consider first (easily and cheaply) if it is a physical vibration. It could be getting transmitted through the building structure causing some resonation in the speaker cabinet. Try moving them to a different surface/location as a test.
It's definitely not physical vibration, as in vibration transmitted through the speaker cabs.

Quote:
Originally Posted by Allybye View Post
Remember the usual problem is the higher frequencies interference, electrostatically/magnetically transmitted like in an antenna however you describe it as a buzz. Does that imply a lot of low frequency content and a bit edgy too or more just like a hum?
Not low frequency, but an edgy, distinct buzz, sounds a bit like what I recall a Cicada sounds like... Not a hum - I can hear the wave oscillations; a hum would be a smoother sound, I think. I want to say the fundamental's perhaps around 2500 Hz?, maybe 2000-3000?...

It sounds like a Cicada if the sound at about 1:35 were continuous and a bit higher pitched: https://www.youtube.com/watch?v=thbgObpfoNs

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Old 08-17-2020, 03:22 AM   #21
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You've got Cicadas in your speakers!

They make a sound very similar to dimmer interference!!!

Very likely your interference is from the switching of the SCR/Triac spikes with electrostatic coupling into your electronics. As C posted earlier you should probably also here it via an am radio to prove it and it will get louder as you approach the source.

Filtering ought to be fitted to the controller I.e the source. Not sure where in the world you are but I would first be replacing it (with a good one that includes filtering) as it is not fit for purpose (not sure what your rights are?) Fit a better one that meets Electromagnetic Compatibility and EMI requirements and only then take it from there.

A bit of a mystery how the interference is reproduced by the speaker when not powered. Have you unplugged the power plug rather than just switching off (into maybe some 'standby' mode?

As a note: a SCR /silicon controlled rectifier is a bit like a switchable diode I.e. a rectifier and conduct in one direction under covntrol. AC is bidirectional in it's waveform so you need two SCRs to conduct in both half cycles. A triac is very similar but conducts as if it were two SCRs i.e in both directions.

You could try also fitting a filter in the supply to your studio equipment. May help too and not have a downside except a small cost such as (not a particular recommendation but easy!) https://cpc.farnell.com/bentley-secu...mains%20filter.
Edit: or switch off the heater!
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Old 08-17-2020, 10:00 AM   #22
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^ Thanks for the suggestions, I'll be looking into them...

Quote:
Originally Posted by Allybye View Post
...A bit of a mystery how the interference is reproduced by the speaker when not powered. Have you unplugged the power plug rather than just switching off (into maybe some 'standby' mode)?
I hear the noise with them turned OFF but plugged in, it goes away when I unplug them. I was thinking the 'standby mode' idea too, originally. But then, it doesn't make much sense to me that they'd be powered at all when the switch is OFF.
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Old 08-17-2020, 12:10 PM   #23
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Quick note: I just noticed that the buzz noise isn't actually coming from the speaker cone itself; it seems to be coming from some electronic component inside the cabinet. If I put my ear by the front port rather than by the cone, I can hear the noise much more clearly.
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Old 08-17-2020, 02:28 PM   #24
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So now you know where the Cicadas live!

Perhaps gives more credence to the interference coming down the mains cable! Hard to understand it rattling the blighters from an line out level, even if on standby!
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Old 08-23-2020, 12:43 AM   #25
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Could be the transformer buzzing. Check if the plate amplifiers is screwed down properly.
You might be able to tune this resonance to be less irritating when it buzzes by tightening the plate amplifier's bolts or screws slightly. Do this only so they nip, not too hard or you may crack the wood cabinet (though this is repairable it is a PITA).

This is not a cure for any ground loop issue, just potentially minimising symptoms, if it's causing mechanical resonances.
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Old 08-23-2020, 12:21 PM   #26
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Thanks for the suggestion... I don't think it's caused by any random looseness, as both monitors have the exact same noise - seems like something being loose would impact each monitor a bit differently. Then again, I guess they could both be loose in the same way?

In general I've been pretty annoyed with this replacement tankless - it itself buzzes pretty loudly, and it makes my dining room light, which is on a dimmer, flicker for a few cycles in a really extreme way. I used to get a little of that with the previous Rheem RTE13, but it was a bit more consistent and not so extreme. This EcoSmart Eco11, some seconds after it actuates, kicks-in something big time for a few seconds that makes my dining room light go to near full OFF in brightness and back to its moderately dimmed level. This only happens when the dining light switch is dimmed to a degree though, I think...

I get the same behavior with another EcoSmart unit in my laundry room (in garage): I have an outside porch light at the garage door that dims to half power unless triggered by a motion sensor which, if so, turns to full power. If I actuate the tankless when that light is in its dimmed state, the dimming will stop, the light I think goes to full power, and flickers...

Point is, I think these units just suck, that the noise I get in my monitors due to the kitchen tankless isn't a fluke or a 'bad' component; it's just a bad design. And I guess this is sort of a tangent anyway, because the monitor noise/buzz happens all the time the tankless is being used, not just during this extreme flicker period...


I have yet to wrangle out an AM radio and test whether the noise is airborne or not. Beyond that, I wouldn't spend more than like ...$100 for any power conditioning, which doesn't leave many options looking at what others have suggested above.

I'm thinking about getting some replacement SCRs for an older tankless unit I have and maybe trying that, see if it would fix the older unit and then I'd install that instead of the Eco11... I've got two defunct RTE13s now, one has a pair of older, discontinued SCRs and the other has some newer single unit 'SCR' or Thyristor or whatever, just a little different. I think I can buy the older SCRs, the newer one I've only seen available in lots of like 160 and the lead time is months... And I'm just kind of guessing that the problem with these units is the SCRs, I don't know it for a fact, though I've tinkered with the one that conked-out first and established that it was at least nothing obvious, like a bad 'reed switch' or thermistor, etc... As I recall I also tried some resistance test or something on those SCRs, but I think the results were inconclusive, or the test wasn't all that definitive in the first place. It was quite a long time ago, some years, I can't remember the details...
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Old 08-23-2020, 01:08 PM   #27
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Filters are common and affordable up to around 20 amps. Unfortunately, at 13 kW, the heater is far above that. You end up with industrial filters and those are pricey. Ther's no middle ground, AFAIK.
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Old 08-23-2020, 01:36 PM   #28
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^ If the noise turns out to be transmitted through the cable to the studio, how about Allybye's earlier suggestion - do you think that might help?:

Quote:
Originally Posted by Allybye View Post
You could try also fitting a filter in the supply to your studio equipment. May help too and not have a downside except a small cost such as (not a particular recommendation but easy!) https://cpc.farnell.com/bentley-secu...mains%20filter.
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Old 08-23-2020, 02:00 PM   #29
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That's probably the kind of filter I was talking about...

But it's only 3.5 Amps...
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Old 08-23-2020, 02:06 PM   #30
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Yeah, I saw that - 3.5A - but then I thought, really, my 'studio' is only my computer, monitors, and audio interface. Computer and screen is never more than about 100 watts alone. I don't imagine the monitors and audio interface could add more than 100W max. I was thinking 300W probably covers my power needs - 300W/120V = 2.5 amps (that linked device says it can handle up to 10 amp spikes)...

I was actually just musing about making an 'off-grid' system with a pure sign wave inverter of around 300-500W. If I need to spend money I'd probably be more prone to going that direction than an expensive power conditioner...

But, I'm thinking ahead here, I still need to dig out that AM radio, and stuff...
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Old 08-24-2020, 01:24 PM   #31
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^^^ I agree with Allybye!

That filter or similar should cope with your studio equipment, at worst two of them for a split feed.

If you are competent with electricity (?) post the version of the SCR you think is unavailable. Probably plenty of modern equivalents....unless it's one of those huge ones used in electric locomotives!!

Your house of horrors lighting dimmers could also be a supply issue. Have you ever monitored the supply voltage on/off load? Dimmer circuits (and similarly pulse edge controlled systems do not like getting spikes on their inputs!

Battery idea with PSW inverter should work well and would be a reasonable cost but might still be over your budget. I have run a system off my car battery and not even with a PSW inverter, just a cheap stepping one and was surprised that it worked so well!...but then I had good linear power supplies on everything!

Last edited by Allybye; 08-24-2020 at 01:30 PM.
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Old 08-24-2020, 02:19 PM   #32
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If you are competent with electricity (?) post the version of the SCR you think is unavailable. Probably plenty of modern equivalents...
I actually found what should be the right replacement and ordered it. It was for a different brand tankless ("Titan") but the design looks exactly the same, like Rheem simply slapped a "Rheem" badge on the Titan version. Incidentally, I will probably be going with Titan in the future, as they seem to have all the parts available, plus the way they describe their upgraded models makes it sound like they actually know what they're doing, like they know what the issues are with the older ones and address those in the newer ones...

In any event, for reference, here's the part number for the SCR for the newer Rheem RTE13: MS0690J-DL1TE. 'Newer' should not be confused with their latest model, I think it's called the RTE13X or RTEX13, or maybe there's an S... The oldest model uses 2 SCRs, the second model uses a single. That's what this part number is for.

The older model part numbers are something like this: Sxx65x & Sxx70x Series.

Both older and newer are Littelfuse...


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Originally Posted by Allybye View Post
Your house of horrors lighting dimmers could also be a supply issue. Have you ever monitored the supply voltage on/off load? Dimmer circuits (and similarly pulse edge controlled systems do not like getting spikes on their inputs!)
The supply to the water heater? If so, no. I have looked at voltage on the household 120V circuit/s, which were right around 120V. I guess that probably doesn't help us though... hmm, I think I'll go plug-in my 'watt-o-meter' and turn my upstairs tankless ON, see what voltage on a random 120V circuit does*...

Meanwhile, my guess is that the 'dimming' issues - with the garage light and the dining light - are related to voltage drop and fluctuation when the water heater is going, especially when it first kicks-in, when the water is cold and the power is the highest...

* hmm, it read 122.9V without tankless ON, and then dropped to about 120V minimum with tankless ON. It didn't seem to fluctuate that much or fast, not it any regular pattern at least, like a flickering pattern. But this is my upstairs unit that doesn't cause any noise in my monitors... Maybe I'll try the same thing later with the downstairs unit...

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Battery idea with PSW inverter should work well and would be a reasonable cost but might still be over your budget. I have run a system off my car battery and not even with a PSW inverter, just a cheap stepping one and was surprised that it worked so well!...but then I had good linear power supplies on everything!
Yeah, not sure, I could bear investing more in a small solar/off-grid system than just a single power conditioning unit. My main problem is that I live in a pretty overcast area in the Pacific Northwest, so I can't see getting much power out of the 'sun' in the fall and winter months...
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Old 08-25-2020, 06:04 AM   #33
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Wasn't really suggesting solar or other off grid system but charging the battery off your supply. Disconnected from supply whilst in use if needs be to remove any down-the-supply interference and being able to keep the battery and interference source more distanced?
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Old 08-25-2020, 07:14 AM   #34
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Had a look at the data sheet for that SCR.
That power of heater (13kW) on a USA supply voltage really pushes it to it's limits. 90A is it's short term max (will do transient peaks to a lot higher but ignore that!) and it average is only 40Amps. So at times when heating on full it may well be exceeded (104A). Design criteria suggests running at only 75% max for longevity.

That particular brand is not easily available (as you have found) but an equivalent is the IXYS MMO 90-12io6 in an identical physical package. Much more readily available such as from Farnel in the UK (It is Newark in the states but they have no stock at present) so you may need to search for it.

I must admit I would prefer to have a higher current carrying capacity but those are even more rare (or just for bulk ordering) or redesign for back to back Thyristors but that is something else!
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Old 08-25-2020, 12:41 PM   #35
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Wasn't really suggesting solar or other off grid system but charging the battery off your supply. Disconnected from supply whilst in use if needs be to remove any down-the-supply interference and being able to keep the battery and interference source more distanced?
That's right, I wouldn't necessarily need to go the full 'off-grid/solar' route. I guess I've been thinking about something like that for a long time, though, such as moving 'my studio' to the garage and building a solar system for that...


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Had a look at the data sheet for that SCR.
That power of heater (13kW) on a USA supply voltage really pushes it to its limits...
Yeah, I've gotten that impression over the years of using these. The oldest one I have still works fine (probably about 8 years now), but it's only used for a single bathroom for one person (me) and I'm mindful of minimizing flow to keep it from maxing-out all the time. The downstairs one is used for the kitchen and a bathroom, a bathroom used by two people and a kitchen used by 3 people. It gets super-heavy use. It generally keeps up, produces enough hot water and hot enough -- but obviously it's getting pushed too hard too often and apparently ends up failing...

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90A is it's short term max (will do transient peaks to a lot higher but ignore that!) and it average is only 40Amps. So at times when heating on full it may well be exceeded (104A). Design criteria suggests running at only 75% max for longevity.
I'm not sure where you get 104A from. If the max power of the tankless is 13000 watts and the supply voltage is 240V, isn't the max current only 54 amps? That's what the spec sheet for the tankless says. I use a 60 amp breaker, it never trips, though I don't think it would if current spikes above 60 amps were short lived...

I guess I don't fully grasp what exactly dictates the max current rate the SCRs see. There's 2 ~5500W nichrome heating elements... Not sure what the resistance is. Seems like those and the supply voltage would dictate the max current. I don't know, too complicated for me...

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I must admit I would prefer to have a higher current carrying capacity but those are even more rare (or just for bulk ordering) or redesign for back to back Thyristors but that is something else!
The latest 'Titan' model that's a step up from what I got I think does what you're describing: "...incorporates the new "QUAD-4" technology featuring an improved electronic proportional control system, with "dual stages" of control in response to broad variations in the amount of water flow."

In essence, I think it's a step back to the original design that used two SCRs, but it instead uses two of the newer, better single SCR (the one you looked up). If you look up the parts for that unit, it shows 2 of those SCRs instead of just one. Here's a link to that model:

https://usatankless.com/collections/...products/n-160
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Old 08-25-2020, 01:11 PM   #36
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Ah! Apologies! You are quite correct!
From your location and the measured voltage I presumed you were on a 120v supply!

For practical purposes every kW consumption takes 4amps at 240v. It does vary and depends upon the heating element resistance that will vary with temp and supply voltage. Your 13kW system will take over 53amps typically. (Switching that on mid cycle gives big big spikes!!)

So for the average current of those devices will be ok provided good heatsync keeps it's temperature down and is run normally to no more than 75 of max reading according to spec.

The newer Titan model should have less 'strain' on the SCRs but also provides better (proportional control) and maybe softer starting and better filtering design too!
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Old 08-25-2020, 01:19 PM   #37
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Quote:
Originally Posted by Allybye View Post
Had a look at the data sheet for that SCR.
That power of heater (13kW) on a USA supply voltage really pushes it to it's limits. 90A is it's short term max (will do transient peaks to a lot higher but ignore that!) and it average is only 40Amps. So at times when heating on full it may well be exceeded (104A). Design criteria suggests running at only 75% max for longevity.

That particular brand is not easily available (as you have found) but an equivalent is the IXYS MMO 90-12io6 in an identical physical package. Much more readily available such as from Farnel in the UK (It is Newark in the states but they have no stock at present) so you may need to search for it.

I must admit I would prefer to have a higher current carrying capacity but those are even more rare (or just for bulk ordering) or redesign for back to back Thyristors but that is something else!

That's hardly relevant, as it isn't a typical light dimmer. It doesn't do "dimming", just on and off at the zero crossing of the sine.

Theoretically, it switches at zero volts (ergo zero amps), stays on for a number of periods and switches off again at zero volts.

Advantages: much less interference and much, much less heat from the SCR's.

BUT...

If the timing is slightly off, the SCR's will die after having produced a lot of noise before dying.

Stuff running over a 100 amps is a bit funny, at least in a home.
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Old 08-25-2020, 01:57 PM   #38
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OK, so, back to the task at hand...

I dug out a battery powered AM radio and did some 'tests'. I turned it on and verified that, indeed, turning the hot water ON in the kitchen, near the tankless, caused a very loud, distinct buzz. Turning the hot water OFF made the buzz stop.

I left the hot water running and the AM radio turned ON as I walked upstairs to the studio, the buzz continued. And it continued as I waved the radio around in different spots, sometimes it would disappear, but most everywhere it was there, same intensity.

When I held the radio up to the monitors the buzz got louder, apparently at least in part because it was now two buzzes harmonizing...

I then went back downstairs and turned the hot water off and went back to the studio with radio in hand. I held the radio up to the monitors and other things, like my viewing monitor and PC. The monitors alone made noise, the computer made noise, the viewing monitor made noise...

So, what does this all mean? I can't rule out that the noise (from the tankless) is traveling through the house wiring, right? But I can conclude that there's RFI and that could be 'a' if not 'the' source of the buzz in my monitors?

Any simple steps to take to try to block RFI from the tankless, or perhaps shield my monitors from the RFI, the airborne?

Jeez, what about the noise the monitors make by themselves? I noticed the right one emits more RFI than the left one, at least as measured by the loudness of the AM radio buzz when I hold it up to them... And remember, these monitors are still turned OFF. Is that normal?? Why would they emit RFI/EMI when they're powered down??
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Old 08-25-2020, 03:37 PM   #39
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I held the radio up to the monitors and other things, like my viewing monitor and PC. The monitors alone made noise, the computer made noise, the viewing monitor made noise...
Just be aware with that radio, or even a guitar plugged in which does a similar thing... there is RF everywhere, meaning you don't have to have any buzz in you AC lines and you will pick up the 50/60 Hz frequency of the AC. Same for monitors and computers which are full of digital clocks and switching power supplies - all of those will make something that picks up RF go crazy even when nothing is wrong.
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Old 08-26-2020, 03:20 AM   #40
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Well you have proof of lots of noise eminating from your heater! Not much of a surprise there and significant level of it in your studio!

Also no surprise that the computer and vdu create noise too. As will be read on many a thread they can be a source of interference too.

The noise you hear is coming from sources that have a wide range of frequency content which is why you get it picked up on the am radio via it's antenna.

If your monitors are in a standby mode they might be generating high frequency radiation too but it could also be due to RF 'reflections' and the like of all the interference flying around!

That such you hear on the radio much of it will not be in the audio band but is showing you the sources of that which (at lower frequencies) can well cause noise problems.

You do not say if the 'computer/vdu' source noise is less than that of the tankless-I would hope it is no more!- and should be of a different nature/sound/frequency, not that which you get in the audio circuits as your interference!

As well as adding filters you could also try screening between the tankless source and your studio, maybe around the heater itself and also between the studio equipment and heater/supply cables on the walls at points of highest pickup by the radio. Sheets of kitchen aluminium foil spread out on the walls (or around the heater) can be useful. They can be tacked in place as a temp measure and earthed to see if that can help too.
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