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Electros in Series II

Started by Phil Allison November 17, 2019
Hi,

just came across a Chinese made powered mixer with Class D amps and SMPS. 

Branded Fender model "Passport 150 Pro". 

The 4AT 20mm AC fuse was blown and a replacement blew spectacularly at about 90VAC input. Plus a little smoke appeared....

Standard, twin voltage input for 120/240 - set to 240V.

The smoke came from a pair of exploded "TVR" 14mm dia varistors connected across each PSU electro. Same electro caps had 100kohn resistors across each as well.

It occurs to me that using varistors in series for that job is foolish.  

Anyone care to elaborate? 



....  Phil 




On 18.11.19 04:51, Phil Allison wrote:
> > Hi, > > just came across a Chinese made powered mixer with Class D amps and SMPS. > > Branded Fender model "Passport 150 Pro". > > The 4AT 20mm AC fuse was blown and a replacement blew spectacularly at about 90VAC input. Plus a little smoke appeared.... > > Standard, twin voltage input for 120/240 - set to 240V. > > The smoke came from a pair of exploded "TVR" 14mm dia varistors connected across each PSU electro. Same electro caps had 100kohn resistors across each as well. > > It occurs to me that using varistors in series for that job is foolish. > > Anyone care to elaborate? > > > > .... Phil
If one of the caps has lost its capacitance, the varistor may get the difference on itself and not like it. In the higher voltage setting, the capacitors are in series, with the resistors and varistors equalising the voltage differences. The twin voltage supply is a straight rectifier and capacitor combination on higher voltage setting and a voltage doubler in the lower voltage setting. 90V input in the higher voltage setting points to already damaged varistors: each should stand at least around 150V without any problems. -- -TV
On Sun, 17 Nov 2019 18:51:08 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

> >Hi, > >just came across a Chinese made powered mixer with Class D amps and SMPS. > >Branded Fender model "Passport 150 Pro". > >The 4AT 20mm AC fuse was blown and a replacement blew spectacularly at about 90VAC input. Plus a little smoke appeared.... > >Standard, twin voltage input for 120/240 - set to 240V. > >The smoke came from a pair of exploded "TVR" 14mm dia varistors connected across each PSU electro. Same electro caps had 100kohn resistors across each as well. > >It occurs to me that using varistors in series for that job is foolish. > >Anyone care to elaborate? > > > >.... Phil > > >
I think we almost agreed that 'lytics can be connected in series with no added parts. Varistors or zeners are especially silly, unless it was intended to blow the fuse on input over-voltage... which maybe didn't work. We sometimes put a TVS across a DC input, in case someone plugs in the wrong wall-wart. We figure the TVS is sacrificial, dies and shorts to protect stuff downstream. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Tauno Voipio drivelled 

-------------------------

> Phil Allison wrote: > > > > Hi, > > > > just came across a Chinese made powered mixer with Class D amps and SMPS. > > > > Branded Fender model "Passport 150 Pro". > > > > The 4AT 20mm AC fuse was blown and a replacement blew spectacularly > > at about 90VAC input. Plus a little smoke appeared.... > > > > Standard, twin voltage input for 120/240 - set to 240V. > > > > The smoke came from a pair of exploded "TVR" 14mm dia varistors > > connected across each PSU electro. Same electro caps had 100kohn > > resistors across each as well. > > > > It occurs to me that using varistors in series for that job is foolish. > > > > Anyone care to elaborate? > > > > > > > > If one of the caps has lost its capacitance, the > varistor may get the difference on itself and not > like it.
** Hmmmm...
> In the higher voltage setting, the capacitors > are in series, with the resistors and varistors > equalising the voltage differences. >
** Really ?
> > 90V input in the higher voltage setting points to > already damaged varistors:
** Might explain why the unit came to me with a splattered 4AT supply fuse - eh ? The unit now works fine, minus varistors. Each was covered in shrink wrap and when opened came out in many pieces. ..... Phil
jla...@highlandsniptechnology.com wrote:

---------------------------------------

> > > > > I think we almost agreed that 'lytics can be connected in series with > no added parts. Varistors or zeners are especially silly, unless it > was intended to blow the fuse on input over-voltage... which maybe > didn't work. >
** The Fender PA unit has one of these: https://il.rsdelivers.com/product/arcolectric/k22208eaal/panel-mount-slide-switch-double-pole-double-throw/0319900 It was set to 240 on arrival - but I will enquire if there is any chance it was miss-set in the past. I fitted a cover sheet over the switch for safety. FYI An odd feature is one output channel has reverse phase to the other. So in that case the jack plug used for speaker connection has signal on the sleeve. .... Phil
jlarkin@highlandsniptechnology.com wrote:

> On Sun, 17 Nov 2019 18:51:08 -0800 (PST), Phil Allison > <pallison49@gmail.com> wrote: > >> >>Hi, >> >>just came across a Chinese made powered mixer with Class D amps and >>SMPS. >> >>Branded Fender model "Passport 150 Pro". >> >>The 4AT 20mm AC fuse was blown and a replacement blew spectacularly at >>about 90VAC input. Plus a little smoke appeared.... >> >>Standard, twin voltage input for 120/240 - set to 240V. >> >>The smoke came from a pair of exploded "TVR" 14mm dia varistors >>connected across each PSU electro. Same electro caps had 100kohn >>resistors across each as well. >> >>It occurs to me that using varistors in series for that job is foolish. >> >>Anyone care to elaborate? >> >> >> >>.... Phil >> >> >> > > I think we almost agreed that 'lytics can be connected in series with > no added parts.
Your claim of optimizing for the lowest leakage current can cause overvoltage in either of the capacitors. Capacitor tolerance of -50% to +100% means it would be difficult or impossible to get matched capacitors and virtually impossible to get matched leakage currents. Without bleed current supplied by the equalizing resistors, you risk leaving dangerous voltages on the capacitors. There is no way to determine the discharge time. You need equalizing resistors to prevent this. If you depend on the load to discharge the caps, you can cause reverse voltage across the caps. This creates a second dielectric film on the cathode (negative terminal.) This is in series with the main one, which reduces the total capacitance. You need dump diodes across the caps to prevent this.
> We sometimes put a TVS across a DC input, in case someone plugs in the > wrong wall-wart. We figure the TVS is sacrificial, dies and shorts to > protect stuff downstream.
Why destroy the unit and risk damaging the source or causing a fire? Here's a simple overvoltage protector. Adjust the sense divider for the desired trigger voltage. Version 4 SHEET 1 1940 1700 WIRE 144 -240 -80 -240 WIRE 384 -240 144 -240 WIRE 640 -240 384 -240 WIRE 832 -240 640 -240 WIRE 944 -240 832 -240 WIRE 832 -224 832 -240 WIRE 144 -160 144 -240 WIRE 384 -160 384 -240 WIRE 944 -160 944 -240 WIRE 640 -144 640 -240 WIRE 832 -144 832 -160 WIRE 832 -144 736 -144 WIRE 880 -144 832 -144 WIRE 896 -144 880 -144 WIRE 832 -80 832 -144 WIRE -80 -48 -80 -240 WIRE -32 -48 -80 -48 WIRE 16 -48 -32 -48 WIRE 144 -48 144 -80 WIRE 240 -48 144 -48 WIRE 384 -48 384 -80 WIRE 448 -48 384 -48 WIRE 480 -48 448 -48 WIRE 624 -48 560 -48 WIRE 688 -48 688 -80 WIRE 688 -48 624 -48 WIRE -80 -32 -80 -48 WIRE 16 -32 16 -48 WIRE 144 -32 144 -48 WIRE 944 -32 944 -64 WIRE 1024 -32 944 -32 WIRE 1040 -32 1024 -32 WIRE 240 0 240 -48 WIRE 304 0 240 0 WIRE 320 0 304 0 WIRE 944 0 944 -32 WIRE 832 16 832 0 WIRE -80 64 -80 48 WIRE 144 64 144 48 WIRE 384 80 384 48 WIRE 384 96 384 80 WIRE 944 96 944 80 WIRE 16 112 16 48 WIRE 48 112 16 112 WIRE 336 112 48 112 WIRE 16 144 16 112 WIRE 336 160 320 160 WIRE 320 176 320 160 WIRE 384 192 384 176 WIRE 16 240 16 224 FLAG -80 64 0 FLAG 384 192 0 FLAG -32 -48 Vin FLAG 16 240 0 FLAG 624 -48 Q1B FLAG 832 16 0 FLAG 944 96 0 FLAG 880 -144 M1G FLAG 1024 -32 Vout FLAG 320 176 0 FLAG 48 112 R1R3 FLAG 448 -48 R2R4 FLAG 144 64 0 FLAG 304 0 Q2B FLAG 384 80 Q2E SYMBOL voltage -80 -48 R0 WINDOW 39 0 0 Left 2 WINDOW 3 -8 -211 Left 2 SYMATTR Value PULSE(0 100 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 368 -176 R0 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res 0 -48 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 0 128 R0 SYMATTR InstName R3 SYMATTR Value 549 SYMBOL pnp 736 -80 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 45 161 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 576 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL pmos 896 -64 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 816 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 928 -16 R0 SYMATTR InstName R6 SYMATTR Value 48 SYMBOL sw 384 192 M180 WINDOW 0 12 104 Left 2 WINDOW 3 17 11 Left 2 SYMATTR InstName S1 SYMATTR Value TL431 SYMBOL npn 320 -48 R0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 128 -176 R0 SYMATTR InstName R7 SYMATTR Value 10K SYMBOL res 128 -48 R0 SYMATTR InstName R8 SYMATTR Value 10k SYMBOL zener 848 -160 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value BZX84C12L TEXT 128 -288 Left 2 !.tran 0 1m 0 1u TEXT 128 -320 Left 2 ;'48V Overvoltage Protection TEXT 200 248 Left 2 !.model TL431 SW(Ron=1 Roff=1Meg Vt=2.5 Vh=0) TEXT 456 136 Left 2 ;Replace the switch with a TL431
Steve Wilson Rabid Psycho Moron wrote:

--------------------------------------
> > Your claim of optimizing for the lowest leakage current can cause > overvoltage in either of the capacitors.
** It does not, testing by experiment proves it beyond doubt. Steve is very clearly mentally defective and needing treatment. But he may well already be beyond all help. ...... Phil
On Mon, 18 Nov 2019 13:34:32 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

>Steve Wilson Rabid Psycho Moron wrote: > >-------------------------------------- >> >> Your claim of optimizing for the lowest leakage current can cause >> overvoltage in either of the capacitors. > > >** It does not, testing by experiment proves it beyond doubt. > > Steve is very clearly mentally defective and needing treatment. > > But he may well already be beyond all help. >
He is determined to not get it, and he's succeeding. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Steve Wilson <no@spam.com> wrote:

> jlarkin@highlandsniptechnology.com wrote: > >> On Sun, 17 Nov 2019 18:51:08 -0800 (PST), Phil Allison >> <pallison49@gmail.com> wrote: >> >>> >>>Hi, >>> >>>just came across a Chinese made powered mixer with Class D amps and >>>SMPS. >>> >>>Branded Fender model "Passport 150 Pro". >>> >>>The 4AT 20mm AC fuse was blown and a replacement blew spectacularly at >>>about 90VAC input. Plus a little smoke appeared.... >>> >>>Standard, twin voltage input for 120/240 - set to 240V. >>> >>>The smoke came from a pair of exploded "TVR" 14mm dia varistors >>>connected across each PSU electro. Same electro caps had 100kohn >>>resistors across each as well. >>> >>>It occurs to me that using varistors in series for that job is foolish. >>> >>>Anyone care to elaborate? >>> >>> >>> >>>.... Phil >>> >>> >>> >> >> I think we almost agreed that 'lytics can be connected in series with >> no added parts. > > Your claim of optimizing for the lowest leakage current can cause > overvoltage in either of the capacitors. > > Capacitor tolerance of -50% to +100% means it would be difficult or > impossible to get matched capacitors and virtually impossible to get > matched leakage currents. > > Without bleed current supplied by the equalizing resistors, you risk > leaving dangerous voltages on the capacitors. There is no way to > determine the discharge time. > > You need equalizing resistors to prevent this. > > If you depend on the load to discharge the caps, you can cause reverse > voltage across the caps. This creates a second dielectric film on the > cathode (negative terminal.) This is in series with the main one, which > reduces the total capacitance. You need dump diodes across the caps to > prevent this. > >> We sometimes put a TVS across a DC input, in case someone plugs in the >> wrong wall-wart. We figure the TVS is sacrificial, dies and shorts to >> protect stuff downstream.
Why destroy the unit and risk damaging the source or causing a fire? Here's a simple overvoltage protector in case the original is too expensive or complicated. It uses a zener instead of a TL431, so you are limited to the zener voltages that are available. Version 4 SHEET 1 1940 1700 WIRE 384 -240 176 -240 WIRE 496 -240 384 -240 WIRE 640 -240 496 -240 WIRE 832 -240 640 -240 WIRE 944 -240 832 -240 WIRE 832 -224 832 -240 WIRE 384 -192 384 -240 WIRE 944 -160 944 -240 WIRE 640 -144 640 -240 WIRE 832 -144 832 -160 WIRE 832 -144 736 -144 WIRE 880 -144 832 -144 WIRE 896 -144 880 -144 WIRE 176 -112 176 -240 WIRE 832 -80 832 -144 WIRE 384 -48 384 -112 WIRE 448 -48 384 -48 WIRE 480 -48 448 -48 WIRE 624 -48 560 -48 WIRE 688 -48 688 -80 WIRE 688 -48 624 -48 WIRE 944 -32 944 -64 WIRE 1024 -32 944 -32 WIRE 1040 -32 1024 -32 WIRE 384 0 384 -48 WIRE 944 0 944 -32 WIRE 832 16 832 0 WIRE 176 80 176 -32 WIRE 384 80 384 64 WIRE 944 96 944 80 FLAG 176 80 0 FLAG 624 -48 Q1B FLAG 832 16 0 FLAG 944 96 0 FLAG 880 -144 M1G FLAG 1024 -32 Vout FLAG 448 -48 R2R4 FLAG 384 80 0 FLAG 496 -240 Vin SYMBOL voltage 176 -128 R0 WINDOW 39 0 0 Left 2 WINDOW 3 -38 247 Left 2 SYMATTR Value PULSE(0 50 0 1m 0 0 1m 1) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 368 -208 R0 SYMATTR InstName R2 SYMATTR Value 4.7k SYMBOL pnp 736 -80 M270 WINDOW 0 -6 42 VLeft 2 WINDOW 3 45 161 VLeft 2 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 576 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 4.7k SYMBOL pmos 896 -64 M180 SYMATTR InstName M1 SYMATTR Value Si7489DP SYMBOL res 816 -96 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL res 928 -16 R0 SYMATTR InstName R6 SYMATTR Value 28 SYMBOL zener 848 -160 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value BZX84C12L SYMBOL zener 400 64 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value PTZ30B TEXT 360 -296 Left 2 !.tran 0 1m 0 1u TEXT 360 -328 Left 2 ;'Simple 28V Overvoltage Protection
jlarkin@highlandsniptechnology.com wrote:

> On Mon, 18 Nov 2019 13:34:32 -0800 (PST), Phil Allison > <pallison49@gmail.com> wrote:
>>Steve Wilson Rabid Psycho Moron wrote:
>>--------------------------------------
>>> Your claim of optimizing for the lowest leakage current can cause >>> overvoltage in either of the capacitors.
>>** It does not, testing by experiment proves it beyond doubt.
>> Steve is very clearly mentally defective and needing treatment.
>> But he may well already be beyond all help.
> He is determined to not get it, and he's succeeding.
If you can keep the electrolytics matched to with 25%, you can keep the maximum capacitor voltage under the 450V rating. The 100k equalizing resistors will discharge the capacitors in under 4 seconds. The power drain is 3.2W. If you can get low leakage caps, you can increase the equalizing resistors to 1Meg, and the power drain will drop to 0.32W. The dump diodes prevent reverse voltage across the caps. Version 4 SHEET 1 1532 0 WIRE 752 -256 688 -256 WIRE 768 -256 752 -256 WIRE 864 -256 832 -256 WIRE 928 -256 864 -256 WIRE 1088 -256 928 -256 WIRE 1248 -256 1088 -256 WIRE 1472 -256 1248 -256 WIRE 688 -240 688 -256 WIRE 928 -240 928 -256 WIRE 1088 -240 1088 -256 WIRE 1248 -240 1248 -256 WIRE 1472 -176 1472 -256 WIRE 688 -144 688 -160 WIRE 928 -144 928 -176 WIRE 1008 -144 928 -144 WIRE 1088 -144 1088 -176 WIRE 1088 -144 1008 -144 WIRE 1248 -144 1248 -160 WIRE 1248 -144 1088 -144 WIRE 1248 -128 1248 -144 WIRE 928 -112 928 -144 WIRE 1088 -112 1088 -144 WIRE 1472 -48 1472 -96 WIRE 928 -32 928 -48 WIRE 1088 -32 1088 -48 WIRE 1248 -32 1248 -48 FLAG 688 -144 0 FLAG 928 -32 0 FLAG 1248 -32 0 FLAG 864 -256 D1C1 FLAG 1008 -144 C1C2 FLAG 752 -256 Vin FLAG 1088 -32 0 FLAG 1472 -48 0 SYMBOL voltage 688 -256 R0 WINDOW 123 0 0 Left 2 WINDOW 3 -61 161 Invisible 2 WINDOW 39 0 0 Left 2 SYMATTR Value PULSE(0 800 1 1 10m 50 100 1) SYMATTR InstName V1 SYMBOL cap 912 -240 R0 SYMATTR InstName C1 SYMATTR Value 1250uf SYMBOL cap 912 -112 R0 SYMATTR InstName C2 SYMATTR Value 1000uf SYMBOL res 1232 -144 R0 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL res 1232 -256 R0 SYMATTR InstName R1 SYMATTR Value 100k SYMBOL res 1456 -192 R0 SYMATTR InstName Rd SYMATTR Value 1k SYMBOL diode 768 -240 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMBOL diode 1104 -176 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMBOL diode 1104 -48 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D3 TEXT 720 -352 Left 2 !.tran 0 100 0 1m TEXT 720 -384 Left 2 ;'800V Series Capacitor Discharge TEXT 1016 -352 Left 2 !.ic V(c1c2) = 0