OT More vintage electrolytic capacitor problems

[becksmachine]

Reading another thread about replacing electrolytic caps in vintage equipment, it reminded me of my current problem.

Went to an estate sale some time ago, saw some vintage Kenwood stereo gear that had a REMOTE CONTROL!

As it is now taking longer and longer to get across the shop to turn up the volume when AC-DC or Boston comes over the airwaves, I thought, yeah, remote control would save wear and tear on the shoe leather, so I bought the lot. Having fun figuring out Dolby decoders, but it all seems to work.

As part of this system upgrade, I decided it was time to remove from mothballs some other vintage/legacy equipment from the days when I would haul an overgrown stereo system around and play DJ at parties and weddings etc.

The audio amplifier section of this homegrown system consists of two Phase Linear (do they still exist?) units, one 400 and one 700 mounted in a homebrew rack designed for ease of trundling about, them dinosaurs have some seriously heavy transformers!

As it had been possibly 15 (20?) years since they had last seen an an arrangement of electrons done by the likes of Yes, Uriah Heep, or Golden Earring (well ok, Patsy Cline and Vaughn Monroe also) I thought it would be wise to at least replace electrolytic filter caps in the power supplies. The order is sent to Newark, capacitors arrive along with some LEDs that can be adapted for once in a lifetime panel illumination replacement, and are installed and POOF, snap goes the circuit breaker.

Aww crap, I labeled everything before dis-assembly, what did I do wrong?? Polarities look correct. Cycle the 15 amp breaker few times and, miracle of miracles, it stays on after the second cycle. Try this again and it does this consistently every time. The power comes from a switched outlet that is energized when I turn the lights on. So the routine is to walk in, turn on the lights, walk over to the breaker panel, cycle the tripped breaker (now a 20 amp GE plug in version) and everything is fine.

I don't remember having this problem in the past, but it seems to be related to charging those caps on turn on.

Is there a simple way to mitigate this issue? Simpler than staggering startup with a timer and relay? 50 amp breaker? Leaving them powered 24/7?


Opinions and suggestions please, Dave

Nearly forgot, 2, 220,000mf, 100v units in the 700, 2, 100,000mf units in the 400. Somewhat more farads than original, but not double.

[The Artful Bodger]

Do you think too much inrush at turn on?

I seem to recall some method of using the cold resistance of a filament lamp in series to reduce inrush turning on from cold.

[MattiJ]

Toroidal transformers?
Known to cause huge inrush currents.

[RichR]

Nearly forgot, 2, 220,000mf, 100v units in the 700, 2, 100,000mf units in the 400. Somewhat more farads than original, but not double.

I imagine those are about the size of a 5 gallon bucket. Or maybe you slipped some extra zeros in and meant 22,000mfd and 10,000mfd respectively.

[CCWKen]

My guess is the AC flabergastor isn't tuned to the quantum fluxistor causing the ported crystal demodulator to back feed into the syncolator. In other words, the caps are too big.

[wombat2go]

I found a circuit diagram.
The original 700 had two 9800 uF 100 volt.
Can you check what values you used?

[RichR]

If you go to www.thecarversite.com/shell-manuals.htm you can download the service manuals for the 400 and 700 if
you want them.

[MattiJ]

I imagine those are about the size of a 5 gallon bucket. Or maybe you slipped some extra zeros in and meant 22,000mfd and 10,000mfd respectively.

220000 millifarads, thats probably van-sized capacitor

mmf or micro-micro-farad is my personal favourite

[J Tiers]

Ah, the good old "Flame-Linear" amplifiers....... Did major repairs on many of them 40+ years ago or so.... notorious for blowing up if you looked at them oddly... protection circuits not very good, and output devices dicey at the voltage. They also ran the capacitors at nearly max voltage, IIRC. The 400 was worse than the 700.

I have seen some seriously odd things happen with those. REALLY odd.

They used good capacitors, you might have been able to re-form them by turning up voltage a little at a time, with a light bulb in series with the power line. let sit 5 to 10 min at each voltage level.

If you increased the microfarad value of the capacitors, you may have too much inrush for modern cheap circuit breakers. OR, you may have fried a rectifier or two from the inrush. Hard to say.

Are you certain you got the polarity correct?

[CCWKen]

I imagine those are about the size of a 5 gallon bucket. Or maybe you slipped some extra zeros in and meant 22,000mfd and 10,000mfd respectively.

Nah. Just went out to the shed. I saved a few caps out of a couple of old printers while scrapping for parts. The largest two are about 6x3 and they're 210,000mf x 100VDC (125 Surge). Two others are 40,000mf 50VDC and they're 2 1/2" in diameter. They scare me every time I look at them.

If anyone needs them, they're free for shipping.

[PStechPaul]

There are thermistors which are designed to limit inrush current, but mostly for transformer inrush:
https://www.ametherm.com/inrush-curr...rrent-faq.html

PTC thermistors are better suited for capacitor charging:
https://en.tdk.eu/tdk-en/374108/tech...-surges/172842

I made a circuit that handles both charge surge limitation and discharge of the capacitors in an EV charger. It may look complex but the principles are fairly simple. There is a 20 ohm power resistor R4 in series with the AC line and a relay across the resistor. When first powered up, and while charging, there is a high voltage across the resistor, which keeps the relay turned off, and current is limited to about 16 amps. When the voltage drops to a sufficiently low value (about 2 seconds), the relay turns on, closing the contacts and allowing normal operation. The discharge is enabled when the 12V supply turns off (when AC supply is turned off), and MOSFET M1 discharges C3 through 300 ohm resistor R1.

[wombat2go]

Hi Paul,
Could it be done like this :
Move the 20 R to the DC side, and just use a changeover contact on your delayed relay to
switch in the 300 R discharge resistor when the relay is off
?

[ncjeeper]

I would haul an overgrown stereo system around and play DJ at parties and weddings etc.

Been there done that. As a matter of fact I ended up charging 50 bucks an hour because I was doing it so much. Not bad for a teenage kid back in the early 80"s.

[PStechPaul]

Here's a simpler version:



However, it uses the voltage on the capacitors to determine when to kick out the precharge resistor and apply the discharge resistor. Because the discharge resistor is in place during charging, it limits the peak voltage, and when the set voltage is reached, there is a spike because of the difference between the voltage levels with and without the precharge and discharge resistors.

It is better to monitor the current through the precharge resistor by its voltage drop, and then remove it from the circuit to enable full output voltage. And the discharge resistor should be inserted when the AC power is removed. This requires two separate sensing systems, and two relays (or a relay and MOSFET). Also, it is better to apply the precharge resistor on the AC side so that the relay will be switching AC, which is much easier and can be done with a less expensive relay.

[MattiJ]

It is better to monitor the current through the precharge resistor by its voltage drop, and then remove it from the circuit to enable full output voltage. And the discharge resistor should be inserted when the AC power is removed. This requires two separate sensing systems, and two relays (or a relay and MOSFET). Also, it is better to apply the precharge resistor on the AC side so that the relay will be switching AC, which is much easier and can be done with a less expensive relay.

I'd use line voltage rated PTC instead of the 20R precharge resistor so that the precharge resistor doesn't turn red hot when someone powers the equipment with load on. (or volume turned to 11)
This is how its done also on some welding machines.