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5 decade old battery pack bridge

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tedstruk

Jan 7, 2012
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Well my dad dug out his channel 9 walkies yesturday, and one of them wouldn't charge up.

They are the old style battery pack that plugs into the 110v house socket and stays there for 16hrs then powers a big handheld emergency frequency two way radio.

I got the repair manual all printed so I have the shcematic to share wtih you if it gets dicey.

It has a blown 270 ohm resistor and it looks like 3 diodes from the rectifier pack are gone.

I started looking for parts in my small collection, and found a 270 on the auction site.
I can't seem to find any diodes that interest me...

The schematic (which I will share when I take a pic of it) is clear and easy to follow, but I just wanted to see if you had anything to add before I heat up the gun and start burning things....

This charges a pack of 2 - 6.5v nickel-hydrides, and has a 4 diode full wave rectifier on a small board amid 2 resistors and is designed to deliver 18mA.
ahem...does the diode type and size effect the power output ? do I need to know what kind was in it, because I haven't seen any like this before... they have a white band and an orange band, and all the resistors seem to have the same markings.
Can I use a component diode pack rectifier instead?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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My guess is that the batteries had gone short circuit after being left discharged so long.

Attempting to charge them destroyed the resistor.

I would convert the device to use normal AA batteries, then get some AA nicads and a decent charger.

The built in charger is bad news.
 

tedstruk

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1968 model v.1 personal messenger...

That recharger is 12.5 v.
AA batteries are 1.5. About 11v shy a dozen...

I hope I can find some good replacement batteries
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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OK, now I'm using something with a larger screen I can see they're 6V batteries.

I suspect they're a stack of nicad cells - does it look like 5 small cells?

Similar answer, find modern batteries which fit (maybe lithium?) and use an external charger.
 

Alec_t

Jul 7, 2015
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Batteries that old are almost certainly NiCds and non-rescuable. Replace with NiMh?
 

tedstruk

Jan 7, 2012
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they are nickel metal hydride batteries. for those younger folks... NiMh pronounced
N I M M or knim or gnim in English.
so the schematic is... drum roll please....
IMG_20170605_124502893.jpg

I need to know what diodes to buy to replace the ones that fried.
Brown Orange White
Brown Yellow White
 

tedstruk

Jan 7, 2012
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What I need is a 14v battery pack rated at 220mA hours. and a rectifier that charges at 18mA What is a 1N881 Rectifier?

guessing here.. a one pass, cathode driven 18.8mA rectifier(881 backwards)?
 

tedstruk

Jan 7, 2012
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the diodes are 1n295 they have a rating of
Vim(V)-50
[email protected] = uA=200 V=10
and the rectifier is 1n881 which I am decifering as a "one pass, 18.8ma full wave rectifier"
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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In response to your last two posts: "No"

The 1N881 is just a normal rectifier diode.

Those really bad chargers just use a resistor to see the current.
 

duke37

Jan 9, 2011
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C1 sets the current.
Why did it fail, is the capacitor faulty?
1N4007 could do.

The circuit is not isolated from the mains so is dangerous.
 

tedstruk

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NOTE FOR QUESTION: What caused then to fry???
many years ago, these were used as communications between a haul back and a donkey in a highlead logging setup. They would send a spotter up the spar tree-(spar trees are trees with all the limbs cut off that are tall and have a block and tackle on the top for running the longest wire ropes through... you have to have one to get the trees out of the forest and to the log landing after they are cut) who would watch the choker setters(the guys who harness the trees that have been felled and limbed) for the all clear wave... then they would radio the donkey engineer, who would hoist the log up to the highlead line, where the yarder, would haul the tree out of the forest to the landing yard. when the spotter saw the highlead line was stopped, he would radio the donkey engineer, who would lower the tree on to the landing.-----The guy up the spar pole, dropped one of the radios about 50'...
I am fairly sure I have used them since then. But anyway, I may have had just another CB when I used them. They are channel 9. emergency frequency....(heh heh not so good for the loggers who were told to change radios because the local "REACT" team thought they were wierdos on drugs! The fall probably caused a small short in the charger, and the short probably became an issue after some use.


Ah yessss, the antient art of component to component connections...PC boards weren't invented yet...

I really like the configuration on these radios... unscrew a bolt or two, pull the battery pack off of the bottom of the radio, and stick it in the wall to charge.... dangerous or not, these have functioned flawlessly for 50 years....

Onboard boats back then, the name Johnson meant something. And there were thousands of boaters who owe their lives to a good Johnson radio. E.F. Johnson Company is a JVC dealer today.

I want to make these radios good again, and I have the repair manual so it shouldn't be too hard... but I don't think hacking them is the thing to do.

I am testing the cap today, just cleaned the dregs of the remains off the contacts, and have but one or two questions that need answered...

#1 the manual says to use 1n295 diodes, they are hard to come by, I found a heathkit interchange chart and it says you can use 1N60 diodes as replacements... I can get the 1N60 diodes just about anywhere. to keep it as original as possible I should use the 1N295 caps.

#2 the schematic shows a 0.56uf cap on it, but the radio boards have 0.47 caps on them.
Do you think the difference in the cap size will be an issue if I use the 1N60 diodes?
 

(*steve*)

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I recommend you do not work on this circuit. We do not wish death on you.
 

duke37

Jan 9, 2011
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I would not use the 1N60 diodes, if I remember rightly they are germanium and low voltage. You could look up the data.
If there is no load, the diodes are subjected to the full mains voltage. 1N4007 diodes (1000V, 1A) are readily available and very cheap.
The current and voltage could vary considerably out in the forest. Some time ago I used a 250kW DC motor controlled by thyristors. Turning up the torque would trip all the flourescent lights on the site since the power factor capacitors by-passed the large harmonic current.

Have you worked out the current using the mains voltage and frequency in your part of the woods?
 

tedstruk

Jan 7, 2012
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for the ed...
for whence the difference betwixt the two units seems to be 9uf in capacitance at the mains, the remaining components were tested.
R2 onboard measures at 420.9ohms while the new Red Purple Brown Silver resistors measure at 270.
here is the entire good board-
D1
uf=726mv c=23pf
D2
uf=892mv c=21pf
D3
uf=726mv c=19pf
D4
uf=731mv c=18pf
R1
1037k ohms
R2
425 ohms
C1
.56uf 200v 20%
I didn't pull the good board apart.
I tested the components onboard with the ATmega328
The bad unit had a MIDWEC0.47uf 200v 20% cap of the same generation as the MIDWEC .056uf 200v 20% on the good unit.
9uf difference.
There is 1.7v in the batteries(series 6.25v C's) of the bad unit.
Efj?
 

tedstruk

Jan 7, 2012
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OK, I am batting about 20% with this...
Does anyone have any 1N295 diodes laying around, they would trade for a couple of PSU transformers?
 

duke37

Jan 9, 2011
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Why do wish to use 1N295 diodes, they are germanium, only 40V 50mA. These will fail or be damaged if there is no load on the charger.
What is wrong with !N4007 silicon diodes, 1000V 1A. Much more robust and very cheap.

Do you drive a Ford model T?

I suggested that you calculate the current based on the capacitor impedance. Have you done this?
 

tedstruk

Jan 7, 2012
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thats what caused the thing to blow in the first place. Wrong cap.
the power required to charge the battery is 18.8mAh.
The rectifier has to deliver 18.8mAh.
 

duke37

Jan 9, 2011
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Why not answer the questions you were asked?

mAh is not a measure of power, this is W.
Get the units right and do the calculations.:)
 
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