Buler Solar Digital Watch (Late 1970's) query

[JustinW]

Question - Buler Solar Digital Watch - Anybody know what type of Battery (or Capacitor possibly, since it's solar) this watch takes? I'm trying to get my dads old watch going again. The photo is not of the watch, bit it's the same, less it being on of course (however, it does still work in sunlight, but not shade )

[grsnovi]

Welcome to the forum!

Have you opened the watch to see what is in it now?

Battery Cross Reference.pdf

[JustinW]

yes, nothing inside

[grsnovi]

Is there an obviously empty location for a battery?

You might try getting in touch with them directly here.

Found online: "Never use ordinary batteries for your solar-powered watch/clock. A solar-powered watch/clock uses a special rechargeable battery called the "secondary cell." If it is replaced with batteries of different kinds, your watch/clock may be seriously damaged."

Have you tried this (found online): "If your solar powered watch has stopped working please pull out the crown/winder on the side to the first or second position, as applicable, and leave it under a light source for 24 hours as the watch may have completely depleted its charge."

[watchweasol]

Hi  Is it possible for you to post a picture of the watch movement. The name on the front does not always represent the movement maker and a picture may help members to Identify the movement and therefore what type of cell it requires.  Thank you.

[JustinW]

@grsnovi yes the cell hole is empty. The other name for these cells is capacitor, I believe.

Buler Solar Digital Watch Movement as well.

[AndyHull]

@JustinW PM'ed me because I posted about an identical watch in 2020.

Here are my thoughts for the record.

"Never use ordinary batteries for your solar-powered watch/clock. A solar-powered watch/clock uses a special rechargeable battery called the "secondary cell." If it is replaced with batteries of different kinds, your watch/clock may be seriously damaged."

As I recall, I had a similar concern, however I eventually settled on a non rechargeable cell, since I couldn't actually measure any voltage across the battery terminals with the cell removed.

I will need to try measuring this again, since as @JustinW stated, his will work with only direct sunlight.  

Mine is currently running on a standard alkaline AG3 (LR41).  I couldn't find a similar sized rechargeable cell and I'm wondering if an Alkaline LR41  was exactly what the manufacturer originally specified.

It is possible to re-charge alkaline cells, so long as you do so very slowly (i.e. at a relatively low current), so it is possible that the solar panel actually does put out a small trickle charge charge current.

The alternative possibility is that the original cell had some different chemistry, perhaps even NiCad.

Given the age of the watch, it is highly unlikely though that it was any form of capacitor. This sort of capacitor technology didn't become widespread until the likes of the Seiko Kinetics came along.   

A third possibility I considered at the time,  is that the solar panel is actually a gimmick, and doesn't actually charge anything, however since @JustinW has proved otherwise, I now know this is not the case.
 
I don't think it is the case that fitting a standard cell would kill the solar panel, since at the very least there should be a diode to prevent the cell back-feeding the solar cell. It is a pretty small solar cell though, so I guess mine might have simply died at some stage. The charging circuitry probably consists of a current limiting resistor, a diode and a zener to clamp the voltage across the cell to some maximum threshold. If that  is the case then so long as the current limiting resistor is high enough and the current therefore very low, then it would be possible to charge an alkaline cell. Possible yes, but probably not actually what the manufacturer would recommend.

Whatever the truth of the matter is, I have had mine running on a cheap Poundland - Kodak  alkaline AG3 for the last two years (since I posted that article in 2020) and it is still going strong. I couldn't state for certain whether the solar cell has extended the life of the battery though. What I can say is that it hasn't killed or popped the AG3 (yet).

All of the above applies to the version I have, so if your module is different, then all of my observations may not apply.

@Justinw in a PM to me asked.
 

Quote

 

Can you recall what the original cell type was?

The solar panels do work. My watch lights up in sunlight, but not in the shade (cell hole is empty).

I had a seiko solar in the mid 80's. I've still got it and just replaced the capacitor. it works great. I believe the alternative name for solar cells is secondary cell. This is my dads old watch (late 70's), that I'd like to get going. I remember it last working and the late 80's.

I have posted in the forum and as yet, stumped! Some of the members are having a good bash though, I'm amazed!

 

My reply was....

As I recall mine arrived with nothing in it, which is why I was struggling to find a matching cell. I eventually resorted to trying whatever fitted the hole, which turned out to be a standard LR41.

Your dad's Seiko solar, what battery did it have? What was the chemistry?

Regarding primary vs secondary cells. Primary cells are single use, their chemistry is not reversible. Typical examples would be zinc carbon cells and lithium primary cells.

"Reversibility" however is not necessarily an all or nothing problem. Some cells are completely irreversible, for example they may emit a gas, when discharging and powering their load, which is vented to the air and lost, or the chemical reaction may require heat or high voltage to reverse it, which makes recharging impractical or impossible.

Secondary cells are things like lithium polymer, lead acid, ni-cad, nimh and so forth. These have reversible chemistry, in other words you *can* re-charge them.

Alkaline cells are a slightly grey area. They are typically sold as primary cells, as they are not generally re-charged, but the chemistry is to some degree reversible. In the 80s I had a charger (from Maplin electronics, but Tandy- Radioshack sold something similar for a while) that would re-charge standard alkaline cells.

It did so, so far as I recall by charging them very slowly. If you put alkaline cells in a standard ni-cad charger, they would vent, and possibly pop dramatically and messily.

The problem with the Maplin primary cell charger was that you could only perform this trick maybe a few dozen times with any one cell before the cell died, as the effect weakened with each charge/discharge cycle. Presumably there were some chemical losses at each recharge cycle.

This perhaps wouldn't matter with a small alkaline cell in an LCD watch, as it discharges very slowly anyway, so the top up charging may be sufficient to extend the life of the cell by a significant amount, presumably years rather than months, and the degradation of deep discharge would not really occur.

It might be interesting to do a patent search to see if there are any patents associated with solar watches around that time,  that might apply here.

Note that there are Lithium primary cells and lithium secondary cells. Some CMOS/Bios memory backup in older computers relied on re-chargeable lithium secondary cells, and I have actually blown one up, a primary lithium button cell which was miss-sold as a secondary version of the same cell, many years ago. The pop was quite loud, and caused a few raised eyebrows and some strong language in the workshop.

Trawl the internet for re-chargeable lithium button cells, you may find one with the same dimensions as an LR41/AG3

The dimensions for alkaline LR41 and AG3 batteries are diameter of 7.9mm (0.311 inches) and a height of 3.6mm (0.142 inches). With a nominal voltage of 1.5v - there may be a slight variation in these dimensions between manufacturers, but anything within 0.1mm should fit I would guess.

The voltage should be in the 1.5V ballpark, so a 3.7V lithium polymer or lithium ion chemistry would not be a good idea.

 
If you do find a secondary cell that matches, I would be interested to know, as such a cell would seem a likely candidate for this application.

Note also that the LR41 comes in different chemistries. There are silver oxide versions (hence the "Ag" in AG3), and I believe there used to be a mercury version, now discontinued, due to the use of toxic mercury.

I wouldn't risk recharging the latter, and I think the silver oxide chemistry may be irreversible, which is why I used an alkaline. So far it hasn't vented, blown up  or died, but you obviously use one at your own risk.

There is a useful battery dimension chart on wikipedia - > https://en.wikipedia.org/wiki/List_of_battery_sizes

It lists these as equivalent size - > AG3/SG3/G3-A ,LR41, 192/384[157]/392,6135-99-949-0402 (NSN)(S),QR41

Some I have never heard of, so it might be worth a google trawl to see if any are secondary cells.

Edited July 17, 2022 by AndyHull

[Neverenoughwatches]

22 minutes ago, AndyHull said:

@JustinW PM'ed me because I posted about an identical watch in 2020.

Here are my thoughts for the record.

"Never use ordinary batteries for your solar-powered watch/clock. A solar-powered watch/clock uses a special rechargeable battery called the "secondary cell." If it is replaced with batteries of different kinds, your watch/clock may be seriously damaged."

As I recall, I had a similar concern, however I eventually settled on a non rechargeable cell, since I couldn't actually measure any voltage across the battery terminals with the cell removed.

I will need to try measuring this again, since as @JustinW stated, his will work with only direct sunlight.  

Mine is currently running on a standard alkaline AG3 (LR41).  I couldn't find a similar sized rechargeable cell and I'm wondering if an Alkaline LR41  was exactly what the manufacturer originally specified.

It is possible to re-charge alkaline cells, so long as you do so very slowly (i.e. at a relatively low current), so it is possible that the solar panel actually does put out a small trickle charge charge current.

The alternative possibility is that the original cell had some different chemistry, perhaps even NiCad.

Given the age of the watch, it is highly unlikely though that it was any form of capacitor. This sort of capacitor technology didn't become widespread until the likes of the Seiko Kinetics came along.   

A third possibility I considered at the time,  is that the solar panel is actually a gimmick, and doesn't actually charge anything, however since @JustinW has proved otherwise, I now know this is not the case.
 
I don't think it is the case that fitting a standard cell would kill the solar panel, since at the very least there should be a diode to prevent the cell back-feeding the solar cell. It is a pretty small cell though, so I guess mine might have simply died at some stage. The charging circuitry probably consists of a current limiting resistor, a diode and a zener to clamp the voltage across the cell to some maximum threshold. If that  is the case then so long as the current limiting resistor is high enough and the current therefore very low, then it would be possible to charge an alkaline cell. Possible yes, but probably not actually what the manufacturer would recommend.

Whatever the truth of the matter is, I have had mine running on a cheap Poundland - Kodak  alkaline AG3 for the last two years (since I posted that article in 2020) and it is still going strong. I couldn't state for certain whether the solar cell has extended the life of the battery though. What I can say is that it hasn't killed or popped the AG3 (yet).

All of the above applies to the version I have, so if your module is different, then all of my observations may not apply.

@Justinw in a PM to me asked.
 

My reply was....

As I recall mine arrived with nothing in it, which is why I was struggling to find a matching cell. I eventually resorted to trying whatever fitted the hole, which turned out to be a standard LR41.

Your dad's Seiko solar, what battery did it have? What was the chemistry?

Regarding primary vs secondary cells. Primary cells are single use, their chemistry is not reversible. Typical examples would be zinc carbon cells and lithium primary cells.

"Reversibility" however is not necessarily an all or nothing problem. Some cells are completely irreversible, for example they may emit a gas, when discharging and powering their load, which is vented to the air and lost, or the chemical reaction may require heat or high voltage to reverse it, which makes recharging impractical or impossible.

Secondary cells are things like lithium polymer, lead acid, ni-cad, nimh and so forth. These have reversible chemistry, in other words you *can* re-charge them.

Alkaline cells are a slightly grey area. They are typically sold as primary cells, as they are not generally re-charged, but the chemistry is to some degree reversible. In the 80s I had a charger (from Maplin electronics, but Tandy- Radioshack sold something similar for a while) that would re-charge standard alkaline cells.

It did so, so far as I recall by charging them very slowly. If you put alkaline cells in a standard ni-cad charger, they would vent, and possibly pop dramatically and messily.

The problem with the Maplin primary cell charger was that you could only perform this trick maybe a few dozen times with any one cell before the cell died, as the effect weakened with each charge/discharge cycle. Presumably there were some chemical losses at each recharge cycle.

This perhaps wouldn't matter with a small alkaline cell in an LCD watch, as it discharges very slowly anyway, so the top up charging may be sufficient to extend the life of the cell by a significant amount, presumably years rather than months, and the degradation of deep discharge would not really occur.

It might be interesting to do a patent search to see if there are any patents associated with solar watches around that time,  that might apply here.

Note that there are Lithium primary cells and lithium secondary cells. Some CMOS/Bios memory backup in older computers relied on re-chargeable lithium secondary cells, and I have actually blown one up, a primary lithium button cell which was miss-sold as a secondary version of the same cell, many years ago. The pop was quite loud, and caused a few raised eyebrows and some strong language in the workshop.

Trawl the internet for re-chargeable lithium button cells, you may find one with the same dimensions as an LR41/AG3

The dimensions for alkaline LR41 and AG3 batteries are diameter of 7.9mm (0.311 inches) and a height of 3.6mm (0.142 inches). With a nominal voltage of 1.5v - there may be a slight variation in these dimensions between manufacturers, but anything within 0.1mm should fit I would guess.

The voltage should be in this ballpark, so a 3.7V lithium polymer or lithium ion chemistry would not be a good idea.

 
If you do find a secondary cell that matches, I would be interested to know, as such a cell would seem a likely candidate for this application.

Note also that the LR41 comes in different chemistries. There are silver oxide versions (hence the "Ag" in AG3), and I believe there used to be a mercury version, now discontinued, due to the use of toxic mercury.

I wouldn't risk recharging the latter, and I think the silver oxide chemistry may be irreversible, which is why I used an alkaline. So far it hasn't vented, blown up  or died, but you obviously use one at your own risk.

There is a useful battery dimension chart on wikipedia - > https://en.wikipedia.org/wiki/List_of_battery_sizes

It lists these as equivalent size - > AG3/SG3/G3-A ,LR41, 192/384[157]/392,6135-99-949-0402 (NSN)(S),QR41

Some I have never heard of, so it might be worth a google trawl to see if any are secondary cells.

Fantastic piece of info Andy. I too had a charger 30 odd years ago for alkaline pencil batteries and upwards. Its possible i still have it in my loft somewhere. If i remember rightly they have a limited number of charges somewhere around 20 times as opposed to ni cad at around 800, ni mercury hydride of around 1200 and lithium up to 3000.

17 hours ago, JustinW said:

@grsnovi yes the cell hole is empty. The other name for these cells is capacitor, I believe.

Buler Solar Digital Watch Movement as well.

Tbh i dont get the solar although i do have a seiko diver with it. For the extra battery change period of maybe two possibly 3 times longer running agaist the extra technology and availability of the batteries.  I think i would rather spend a few minutes changing a decent battery every 3-5 years.

[AndyHull]

I posted a fresh picture of my Buler Solar LCD watch in the WOTD thread today.

As I said, its still going strong and nothing has blown up (so far), so I think my choice of an alkaline LR41 cell was safe (if, arguably, not actually recommended).

 

Some of you may find this interesting.

https://www.batterypowertips.com/difference-between-primary-secondary-battery-chemistries-faq/

.. and the original WOTD post in 2020 is here.

When correctly used, the designation of LR cells are for Alkaline, AG cells are silver, however it is rare for sellers to use the correct designation and LR41 is used interchangeably with AG3 and so forth.
 

The cell I uses is strictly speaking an LR41 and not an AG3, but it actually has both stamped on it.

Edited July 17, 2022 by AndyHull

[JustinW]

The Seiko Solar used a CG920 capacitor (modern equivalent MT920). However, I managed to find a real seiko CG920.

Seiko Solar 150 Sports (mid to late 80's). working great. 

Capacity: 5mAh

Voltage: 1,5 Volt

System: Lithium-ion battery (Li-Ion)

The question know is - what is the original battery type for my Buler Solar digital LCD watch? I am stumped!

[AndyHull]

These (MT920) are typically larger (so called coin cell sized). I wonder if Panasonic do a smaller button cell version of this technology.

https://industry.panasonic.eu/energy-and-building/batteries/secondary-batteries/coin-type-rechargeable-lithium-batteries/aaf4005/mt920-mt920

 

Full list here

https://industry.panasonic.eu/productfinder?category=Secondary+Batteries&group=Batteries&lineup=Coin-type+Rechargeable+Lithium+Batteries&mode=FILTER_MODE&search=&series=Coin+type+rechargeable+lithium+batteries+(ML+series)%2CCoin+type+rechargeable+lithium+batteries+(MT+series)%2CCoin+type+rechargeable+lithium+batteries+(VL+series)&sort=attribute_283%2Casc

 

You might get away with  an MT621 I guess, if you can find one.

https://industry.panasonic.eu/energy-building/batteries/secondary-batteries-rechargeable-batteries/lithium-coin-type-rechargeable-batteries/titanium-rechargeable-lithium-coin-batteries-mt-series/mt621-mt621

 

Not cheap though, and they seem to all have solder tabs on.

https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=+MT621&_sacat=0&_sop=15

Edited July 17, 2022 by AndyHull

[jdm]

37 minutes ago, AndyHull said:

You might get away with  an MT621 I guess, if you can find one.

Also SII (Seiko) makes these https://www.sii.co.jp/en/me/datasheets/ms-rechargeable/ts621e/

Electronics distributors (Farnell, Digikey, etc) have them.

[AndyHull]

One other thing about the MT621 - it is smaller than the LR41, so it may, or my not make good contact. The spring battery contact may make up for the difference in height though. Also all of the MT621 cells I found online have a spot welded tab of one form or another that you would need to carefully remove before fitting the cell to the Buler.

Let me know if you decide to go down this line as I am curious to see if it works, and if it charges correctly.  

[JustinW]

When I replaced my seiko solar watch, I removed one of those tags and then put the correct tag on it and that turned out fine (but that was the correct cell anyway, just the wrong tag). If I make progress with the Bular Solar I'll let you know.

[Marko]

Hi, like most solar watches from this era the capacitor cells are no longer available but these watches are designed to run quite happily on normal button batteries,AG3 in this case. I have two of these myself which have run perfectly well for years on normal batteries. If the alarm is not working it is very likely the little spring which sits in a small circular recess on the module is missing. Replace it with one from a spring bar etc and cut it to no more than 2mm. Also,make sure it is narrow enough to contact the metal at the bottom of the recess. If it is too long it will short on the metal part of the module and knock out the light when you put the caseback on. The alarm won't work either.