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Author Topic: Immersun went BANG - fixed (i think)  (Read 1259 times)
marcus
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« on: October 21, 2020, 09:35:41 PM »

This immersun went bang - literally and tripped out the 16A MCB on the cct. Though Id post this incase anyone else has had this issue.

It blew it's Varistor and associated triac, and initially i tried replacing them - thinking it may have been hit by a large surge or something (1st/2nd attached pic).The immersun powered up Ok and was fine until it tried to divert power to the immersion - when it went BANG again. Obviously NOT caused by a big surge - there was something else wrong.

It sat on the shelf for quire a while but, eventually, I went back to it and had another look. The varistor is a relatively low voltage one (175v) which is only connected to the a.c. rails when the triac is turned on by a TVS diode on it's gate (400v? or poss 440v) and then stays connected until the next zero-crossing which turns off the triac. This voltage limiting cct is downstream of the main a.c. input filter but before the mosfet bridge that performs the PWM to the load. The TVS diode seemed fine so something must be making spikes >400v when the immersun tries to divert power to the load.

Used a diode test on the mosfets in circuit - they all seemed fine, then looked around for anything else that was connected between the mosfets and the input filter. This led me to the two big black cuboidal caps in the middle of the PCB (pic 3); these are 5uF unpolarised 350v a.c. caps - one checked out fine (5.0uF) with a cap tester in circuit; the other didn't give a sensible reading (that doesn't prove anything - testing in circuit can be problematic), but a close inspection did reveal a slight bulge in the side facing it's sister (tried to show in the pic of the blown components|). Once removed it read as 0.35uF Ahaa!  Grin

My supposition is that without these caps smoothing the voltage on the A.C. input to the PWM bridge, the PWM pulses in conjunction with the input filter inductor was creating the voltage spikes, which coming on every 1/2 cycle of the A.C. supply was overheating the low voltage Varistor and... BANG.

So, with a new varistor, triac AND capacitor fitted, I connected it up, turned it on, put my fingers in my ears, and...  success! (final pic - 3 element storage heater as a load)  extrahappy


The reason I say 'I think' I've fixed it is because it does work and doesn't go BANG, but after working fine on my off grid system for a couple of days it goes into a strange oscillation sometimes when diverting - it turns the load fully on for a moment then fully off, then repeats once a second until the sun goes in and it stops diverting, then when it starts diverting again it's fine -until something sets it off again. But if you leave it off until the internal memory resets (clock/date reset) it'll work fine again for another couple of days.

My guess is it's to do with my off grid system - an 8kw (more like 2kw) powerjack inverter with an ageing battery being backfed by two sunnyboy inverters (one solar, one hydro) - with the immersun, it's just too many electronic 'cooks' playing with the 230v a.c. 'broth', and the immersun gets upset - it seems to be triggered when something with a low powerfactor (like my aincient washing machine) is running.


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« Last Edit: October 21, 2020, 09:39:11 PM by marcus » Logged
brackwell
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« Reply #1 on: October 21, 2020, 09:58:00 PM »

Mine went BANG also but i do not have your expertese. Sent you email.

Ken
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jonesy
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« Reply #2 on: October 23, 2020, 09:18:09 PM »

Do you have a roughish circuit you could post? I'm currently running a home brew diverter with phase control (long story,  but if you have a French smart meter, they register with burst control)  and I'm in the process of designing a PWM front end. There are a lot of circuits on the net and many are just nonsense.  If you could give me a pointer with a known good circuit  Cheesy
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Tinbum
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« Reply #3 on: October 23, 2020, 10:58:38 PM »

Do you have a roughish circuit you could post? I'm currently running a home brew diverter with phase control (long story,  but if you have a French smart meter, they register with burst control)  and I'm in the process of designing a PWM front end. There are a lot of circuits on the net and many are just nonsense.  If you could give me a pointer with a known good circuit  Cheesy

I have a meter here that I can't get to work with any type of diverter.
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Fionn
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« Reply #4 on: October 24, 2020, 01:27:02 AM »

Very interesting and will be of help to many as I'm sure the failure mode will be a common one.
Swapping out those components would be a good starting point for anyone I'm sure.

I'm also interested in your PowerJack experiences, I posted here about using mine for AC coupling a good while back.
I did the ferrite mod on it last year and it did have the expected big impact on idle consumption, had it down at 20W.
Unfortunately it went bang some time back (while running at a pretty low load) and I haven't yet gotten around to swapping out the mosfets and gate resistors.
Once I get it running again I'm planning to give it a bit of a test by bypassing some of the current around the CT. It shut down on over current long before it would have had a chance to heat up the transformers significantly.
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oliver90owner
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« Reply #5 on: October 24, 2020, 06:59:25 AM »

Is this the old type immersun (before the company went bust?), or a more recent offering from (basically) the same company? 

Particularly, if the latter, why do people still buy from this resurrected company when alternative units work faultlessly for years on end - at least one diverter having a ten year guarantee.  Is there so much advantage, if any, over the Solic offering?  It seems to me that the Solic is better, cheaper and more reliable, or am I wrong?
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brackwell
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« Reply #6 on: October 24, 2020, 08:14:50 AM »

Yes i agree ,mine was a Mk 1
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marcus
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« Reply #7 on: October 24, 2020, 07:23:37 PM »

Jonesy: sorry, i didn't draw up a circuit of the PWM section - I was just looking for failed components - so once I'd checked the fets and found them to be good i didn't look further; If I get to look at another one I may learn more, but beyond the fact that there are 4 mosfets in some sort of bridge setup I can't tell you anything.

o9o: it say V3.08.2 on the back - would that be a MK3?

Fionn: I've had the PJ for quite a few years now, It came with some ferrite rings, and whilst the idle draw isn't as good as your 20W (more like 30W), I haven't gotten around to modding it. mine has never shut down on overcurrent and I've done lots of welding, started 4hp (3kw) induction motors with it (welding and large motors tent to make the sunny boys trip on grid disturbance tho') and even when i tried to fire up the old chest freezer, not realising a rat had chewed through the flex and shorted it to live-neutral, it was the MCB that tripped, not the PJ. the lcd display has gone blank so I can't tell you what kwh it's clocked up. it's currently got 2 sunny boys connected: one with ~350w hydro and the other with just over 1000w PV - the PJ does get warm on a sunny summer day and it's fans are running hard to keep the transformers cool. might be worth looking up some of Oztules work on the PJ's: I recall his doing somethings with the current feedback but it's been too long since i looked.
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jonesy
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« Reply #8 on: October 28, 2020, 01:19:24 PM »

Jonesy: sorry, i didn't draw up a circuit of the PWM section
No worries - thank you.

might be worth looking up some of Oztules work on the PJ's: I recall his doing somethings with the current feedback but it's been too long since i looked.
Oztules did the odd mod and finally concluded IIRC that some just work and some just dont, so it's marginal design somewhere.
Last I read, another member (not clockman) is using a homebrew software on a nano to give the FET drive and avoid shoot through with homebrew hardware similar to Oztules.
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