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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 11th Feb 2020, 11:35 am   #1
TonyDuell
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Default Was there something odd about Japanese primary cells?

I was always told it was a bad idea to attempt to charge primary cells, in this case probably of the zinc-carbon type.

But a number of Japanese units from the 1960s/1970s float a battery of such cells across the output of the mains PSU. In other words there is no battery/mains changeover switch. Just a transformer/rectifier with the battery directly across the output, feeding the rest of the unit.

OK, the rectifier will prevent the cells discharging via the mains transformer, but surely the cells are being 'charged' when the unit runs on the mains.

The thing that has prompted this post is a Juliette 606 tape recorder which does this. So do the Sanyo 'briefcase' music centres. I've not seen instructions to remove the battery before connecting the mains lead on any such unit. So were they just hoping for the best (that the cells wouldn't leak or even explode) or was there something special about the (presumably) Japanese cells it was designed with?
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Old 11th Feb 2020, 11:39 am   #2
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Default Re: Was there something odd about Japanese primary cells?

Was there no diode in series with the batteries?
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Old 11th Feb 2020, 12:18 pm   #3
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Default Re: Was there something odd about Japanese primary cells?

ISTR there were several designs to "charge" dry cells

I built one in my teens seemed to work quite well.

I don't think I would try it on more recent production though!

https://www.rfcafe.com/references/po...-july-1967.htm

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Old 11th Feb 2020, 12:26 pm   #4
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Default Re: Was there something odd about Japanese primary cells?

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Originally Posted by TonyDuell View Post
I was always told it was a bad idea to attempt to charge primary cells, in this case probably of the zinc-carbon type.
Something of a myth.

They can be recharged - sort of - and it was all the rage quite some years ago with units on the market to do just that.

The sort of part is that for a start, the battery must not be too discharged, the charging voltage works best if it is dirty (ie unsmoothed) and the downside is it can only be done a few times.

So I would say that if the main supply is not significantly above the voltage of a new set of batteries, it would tend to be OK.
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Old 11th Feb 2020, 12:26 pm   #5
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Default Re: Was there something odd about Japanese primary cells?

In the 1950’s when my torch batteries ran down I put them near the fire to warm up, probably drive some moisture off then use them again, didn’t last very long though.
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Old 11th Feb 2020, 1:37 pm   #6
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Default Re: Was there something odd about Japanese primary cells?

I used to heat up the batteries ('D' cells, IIRC) which were used in my Philips Portable tape recorder, by putting them in front of the fire - this got a bit more life out of them.
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Old 11th Feb 2020, 1:58 pm   #7
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Default Re: Was there something odd about Japanese primary cells?

AFAIK, Japanese dry cells were of the same basic design as UK ones. And even if they WERE of some special type, Japanese manufacturers of portable electronics must surely have been aware that exported appliances would likely be used on non-Japanese batteries.

Much more likely IMHO, that paralleling of the battery and mains derived supplies was simply accepted as possibly non optimum but fine in practice.

Any charging of the dry cells should be minimal, and the seamless changeover to battery power in case of line power failure was probably a significant advantage.

MOST appliances of that era had an instruction to remove the batteries if unused for a significant time.
And even in the absence of such instructions, most people knew that removing unused batteries was prudent.
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Old 11th Feb 2020, 2:29 pm   #8
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Default Re: Was there something odd about Japanese primary cells?

I believe that the explosion risk is with alkaline cells rather than the ordinary zinc carbon types. I wouldn't worry about them (Z-C) but I'd be very leery about leaving alkalines in place!
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Old 11th Feb 2020, 3:21 pm   #9
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Default Re: Was there something odd about Japanese primary cells?

For charging primary cells use a Dirty DC charger, which was/is a transformer and a diode no smoothing connected to the cell. I think this was in the ARRL hand book. Not sure about the Japanese ones though.
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Old 11th Feb 2020, 4:29 pm   #10
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Default Re: Was there something odd about Japanese primary cells?

Trickle charging zinc carbons was always frowned on in the UK, but elsewhere it was quite popular, particularly in the Far East and Japan. It does work to some extent and there's nothing to lose. The cells won't explode or even leak if the charge current is kept down.
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Old 11th Feb 2020, 6:08 pm   #11
TonyDuell
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Default Re: Was there something odd about Japanese primary cells?

To answer some of the points...

There is no diode in series with the battery. It is connected straight across the output of the rectifier. No current limiting resistor or anything like that either. I guess the current is limited by the (low-ish) difference in voltage between the battery and the output of the mains PSU and the internal resistanve of the battery.

In some cases the smoothing capacitor is connected after the on/off switch. Meaning that if the unit is plugged into the mains and not turned on, the battery will get unsmoothed DC across it. But of course with the unit on the battery gets a much steadier voltage.

As for removing the battery, yes, it was common (and still is) to tell you to remove 'flat' batteries. And I never leave batteries in something I am not going to use for a time. It was more the case of using a unit (say a tape recorder) on batteries as a portable, coming home and plugging it in to listen in the evening. Most people would not think they had to remove the battery to do that. And there are no instructions/warnings on the unit to do it.

I guess (now I know the circuit) I'll just remove the battery if I am using it on the mains.
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Old 11th Feb 2020, 7:12 pm   #12
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Default Re: Was there something odd about Japanese primary cells?

You could just fit a Schottky diode to protect the battery. It's probably what the manufacturer would have done if the tech had been available and cheap enough.
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Old 11th Feb 2020, 8:58 pm   #13
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Default Re: Was there something odd about Japanese primary cells?

In times-past I recall various bits of gear where the batteries [either zinc-carbon primary-cells or lead-acid secondary batteries] in mains/battery gear used the batteries as a sort-of 'big electrolytic capaitor' to provide additional power-line smoothing when run from an AC supply.
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Old 11th Feb 2020, 10:22 pm   #14
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Default Re: Was there something odd about Japanese primary cells?

I have a feeling my 1970s 'petrol-pump' air-band radio (made from cardboard with alligator-skin style vinyl covering it) was wired like that.

When I was an electrician in the late '70s we would very occasionally recharge D-cell zinc-carbon torch batteries with dirty d.c. Got us out of a hole if the stores were closed and we needed to see in the dark.
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Old 12th Feb 2020, 12:12 am   #15
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Default Re: Was there something odd about Japanese primary cells?

Regarding the smoothing capacitor being connected after the switch, this would be most desirable.
If the smoothing cap was permanently across the battery, then the leakage current through the capacitor would discharge the battery in a few weeks.

A leakage current of 3ma is a reasonable guestimate for an older type electrolytic capacitor. That would fully discharge new 3AH C cells in 1000 hours, or about 6 weeks. After half that time operation would be significantly impaired.
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Old 12th Feb 2020, 1:02 pm   #16
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Default Re: Was there something odd about Japanese primary cells?

In the 1960's I had a Philips EL3585 battery tape recorder. A set of the old blue U2 batteries used to last about 20 hours. When Dad built a simple 9V mains unit for his tranny from a design in I think Radio Constructor ( 8V bell transformer, 1 diode, 1 zener diode, and a 1000 microfarad electrolytic) I tried using it with my recorder. I found it produced significant hum, so I tried leavng the internal batteries connected rather than switched out when using the mains unit. This reduced the hum to an acceptable level, and I found that the battery voltage was higher after disconnecting the mains unit. AFAIR I managed to get about 60 hours from a set in this way. I never ever had any of the blue Ever Ready U2 cells leak in 8 years or so. Unfortunately the blue U2 cells were discontinued and their sealed replacements, as well as being 25% more expensive, were prone to leak with this treatment.

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Old 12th Feb 2020, 7:29 pm   #17
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Default Re: Was there something odd about Japanese primary cells?

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I never ever had any of the blue Ever Ready U2 cells leak in 8 years or so. Unfortunately the blue U2 cells were discontinued and their sealed replacements, as well as being 25% more expensive, were prone to leak with this treatment.
The blue cardboard-cased Ever Ready U2 calls were almost certainly Zinc-Carbon (the traditional Leclanchee technology) which can tolerate a bit of 'recharging' without releasing their magic goo.

Ever Ready in the late-60s/early-70s went up a developmental dead-end with 'High Power' Zinc Chloride cells (which were easy to make on essentially the same production-equipment as the old Zinc-Carbon cells, so saving money over completely rebuilding the plants to use the rather-different Alkaline/Manganese technology like everyone else).

I wonder if your 'leak prone' U2-replacements were zinc-chloride? From memory these were sold as "Silver Seal" by Ever Ready.
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Old 12th Feb 2020, 11:36 pm   #18
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Default Re: Was there something odd about Japanese primary cells?

AFAIR the U2 replacements that were available simultaneously were SP2 in white cases. There was also available at the same time the HP2 high power cells in orange cases. They were unsatisfactory as when fresh, they were too powerful for the EL3585's speed regulator, making it run fast. The EL3585's regulator consisted of a centrifugal switch that repetitively shorted (or not) a resistor in series with the motor, and must have relied on the internal impedance of the Zinc Carbon cells for correct operation. I never thought at the time of replacing one of the cells by a dummy, as the recorder would still work ok when the battery voltage had dropped to about 6.5V.

By the time the silver seal cells came out I had switched to a cassette recorder.
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Old 13th Feb 2020, 1:34 pm   #19
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Default Re: Was there something odd about Japanese primary cells?

Fidelity Radio manufactured a transistor radio in the 60's that 'recharged' PP9 batteries a number of times. It's a long time ago but I don't think it was pure DC that was employed.
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Old 13th Feb 2020, 4:48 pm   #20
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Default Re: Was there something odd about Japanese primary cells?

I remember 2 models from Fiidelity around 1980/1 called the Battery Saver and the BS2 that recharged the dry cell and it caused a bit of excitement at the time with mentions in the press. My parents bought a BS2 and seemed happy with it.
Unfortunately the circuit eludes me as it does not appear to have appeared in Trader or or R&TV at the time.
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