BCDx36HP: RTC Battery?

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kruser

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Anyone know where this so called RTC battery is located inside the 436 and 536?
And what it is as far as capacity and voltage or is it really just a super capacitor?

I've only had mine open once and did not see the battery on the main board unless it is inside a RTC chip.
Or it is extremely small and also a super low charging current.
My guess is that it's located on the logic board near the display in both models as I never needed to look at that board.

I'd be tempted to install something with a higher capacity for those times I may leave mine unpowered for several weeks.

It seems kind of odd that you can have a wristwatch with a tiny button cell that will run the watch with an LCD display or even a mechanical movement for up to a year yet these new x36HP's only hold the charge for about a week before needing the 50 hour charge cycle again. That's why I mentioned a super cap with a very low charge current.
Heck, the small rechargeable cells used in bluetooth headsets are very tiny but would run the RTC for longer than a week unless there is something else pulling current from the x36 battery or super cap.

If anyone has actually opened up a 4 or 536HP and identified the RTC battery, please post info!

edit: after searching a bit better, I think I've found that there is no RTC battery in these radios. The RTC is maintained by a super cap it seems.
 
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kruser

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If it helps the one in the Home Patrol (336) is a little over 1/4-3/8 in size and yes they both have batteries.

Read this thread.
http://forums.radioreference.com/uniden-owner-tech-support/282558-bcdx36hp-losing-clock-setting.html

David Kb7uns
I found it in the 536. It's about 3/16th in diameter on the front board. And it's not a super cap like someone suspected in another thread.
I was looking for something a tad larger when I'd opened up my first defective 536.
It kept going into an endless reboot or power cycle loop at powerup that would not stop.
I opened that one just to check that the ribbon cables had all been inserted fully before sending it back.
 
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Boatanchor

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Just because it is labelled 'BT1' on the PCB does not guarantee it is a battery..
It looks like a ~0.5Farad, SMD, Super Cap to me.

Just like this one:
 

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SquierStrat

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It seems kind of odd that you can have a wristwatch with a tiny button cell that will run the watch with an LCD display or even a mechanical movement for up to a year yet these new x36HP's only hold the charge for about a week before needing the 50 hour charge cycle again.
that is pretty pathetic, isnt it? How a 20 year old scanner can go months and months on end without power and still not lose its memory, but this new scanner cant even keep track of the time..
 

kruser

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Just because it is labelled 'BT1' on the PCB does not guarantee it is a battery..
It looks like a ~0.5Farad, SMD, Super Cap to me.

Just like this one:
I'm not doubting you at all.
Its possible Uniden has used both. Mine is definitely a small lithium cell.
Very similar to the Panasonic ML-621S/ZTN but it has solder tabs.
The Panasonic model is a 3V rechargeable Lithium button cell.
Sorry, no pictures but I did buy some at Digi-Key with their part number of P007-ND or P048-ND for a vertically mounted version with solder tabs.

I'm very familiar with super caps and that is not what is in mine.
Mine look exactly like the Panasonic cells mentioned above but are slightly smaller in diameter so less capacity most likely.

I'd not had mine powered on for a week or two and the voltage measured 2.65 at the battery.
After a couple hours of leaving the power on, the charge voltage appeared to stabilize at 3.290 VDC at the battery.

A rechargeable lithium cell or a super cap would work for this application so I'm guessing they have used both going from you seeing a super cap at BT1's location and myself seeing a lithium button cell.

I wonder if one has more capacity or a lower self discharge over the other and that is why some users are seeing so many "Set Clock" prompts at power on.
I've never had to set the clock in my 536 since the initial set and I do leave it off for up to 2 weeks at times.
 

Boatanchor

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A closer inspection proves that you could well be right kruser.

And it was BT40 not BT1 - My mistake.

If they are in fact tiny 5mAh lithium manganese cells, it will be interesting to see how long they last in this environment.

The specs I've read on Li-Mn2O4 button cells indicate up to 1500 charge/discharge cycles. However, to obtain this kind of longevity, the depth of discharge must be limited to only 10%.

If the RTC battery is fully discharged over a period of 5 days as Uniden indicate (Acknowledging your comment about being able to leave the radio off for 2 weeks), a 10% discharge level would be reached after only 12hrs of the radio being powered down. From what you've said though, I think the more likely scenario is that a (new) fully charged RTC battery actually lasts up to 2 weeks on a full charge.

Given the above characteristics, if you switched your scanner on (or recharged the RTC battery) every one to two days, which limited the battery depth of discharge level to 10%, you should be able to expect about 4 years of life from the RTC battery.

However, if the battery were allowed to discharge to 20% or more on a regular basis (battery not being charged for two or more days), the projected lifespan reduces to only 500 charge/discharge cycles or less - That's only 1 1/2 years!.

If the battery is permitted to discharge to even lower depths of discharge, or the RTC battery is left in a discharged condition for extended periods of time, the lifespan of the battery would plummet.

Presumably, if I'm correct, those owners that use their scanners (daily) are likely to get much longer life out of their RTC battery, than those who only user their scanner occasionally.

Regardless, it would appear that someone out there is going to make a few bucks replacing x36HP RTC batteries in the not too distant future :)

Funny - Why does the Toyota Prius come to mind all of a sudden?
 

kruser

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The specs I've read on Li-Mn2O4 button cells indicate up to 1500 charge/discharge cycles. However, to obtain this kind of longevity, the depth of discharge must be limited to only 10%.

If the RTC battery is fully discharged over a period of 5 days as Uniden indicate (Acknowledging your comment about being able to leave the radio off for 2 weeks), a 10% discharge level would be reached after only 12hrs of the radio being powered down. From what you've said though, I think the more likely scenario is that a (new) fully charged RTC battery actually lasts up to 2 weeks on a full charge.
All good scenarios!

Do you think the Li-Mn204 5mAh sized cell is what is actually found in the radios or did you just take a guess from a similar sized example?
The cell in the radio is closer to 5/32nds to 3/16th inch diameter compared to the 1/4" diameter of the Panasonic LiMn I mentioned earlier. Thickness is similar though judging by eye alone.
I could not see it well enough to read any markings on it without removing the front panel on a 536. And the solder tab is often spot welded over any markings in many cases. My cell location is marked BT401.

I think it was you that saw a current draw spec on the VBAT line to the RISC chip between 0.6 and 1.0 mA. I read the datasheet and I'd swear it said 0.6 to 1.0 uA (micro) amps so that may help a lot if my eyes were seeing correctly!

If your calculations are correct, will Uniden will replace that battery in the 536 models now that they have a 3 year warranty for those that fell in the serial number range for the headphone jack noise issue. I'd bet they have a battery exclusion in the warranties.

I think the specs for the RTC VBAT input listed a decent low voltage before the RTC may need to be reset. I forget exactly but I think it was near 1.6 VDC or so. So anything equal or above should maintain the clock settings.
I can't recall looking at the discharge curve of a Li or Li-Mn cell but do they fall rapidly when they hit a certain voltage (like NiMH does) or do they fall gracefully towards zero like a Carbon Zinc or Alkaline cell does?

I think they would have been better off using something like a CR2032 in a socket similar to a computer motherboard.

Remember the fiasco with some of the Icom R71 era radios where the operating code was stored in a battery maintained memory board?
I think those used a CR2016 size Li cell but soldered in place. When they went dead, your radio no longer worked.
There are still some of those radios running today with the original factory cell that is now over 30+ years old! Way longer than the average 5 year life of the Li cells from that era.
What was found is that the owners that use them daily are the ones with cells that are still maintaining the OS memory. The very diode that was installed to prevent the cells from charging has a very small leakage current that is believed to be responsible for those 30+ year old cells to still work and hold the memory.
It was the owners that shelved the radios for years that found them to no longer work when they drug them back out.
Luckily, a few companies built drop in memory boards for the affected Icom models. Some even had jumpers that you set so it used the memory contents for your specific model so one board fit all models.
Mine still had the original Li cell in it when I swapped it out. It was still showing near 3.0 volts and was about 20 years old when I did the swap. I did a live swap with the memory board externally powered while I replaced the Li cell. I later replaced the board as the 3rd party boards extended the tuning range some. Of course one could build a programmer and reload the original memory board code (including extended tuning ranges) but just $40 dollars for a non volatile memory board sounded to be much easier! I still have my original memory board and the 2032 Li cell I soldered in place of the original 2016 is still showing over 3.0 volts event though it has not been inside a radio in 7 or more years now.

Anyway, Uniden could have used a 2032 in a socket that is only drawn from when the radio is off. I'd imagine a 2032 would run the RTC circuit for a long time compared to the tiny Li-Mn cell used now.
Of course a 2032 should never be charged but it never seemed to hurt any of the thousands of Icom's still running strong out there with 30+ year old 2016 Li cells!
Of course the reverse leakage current through the charge protection diode in the Icom's had to be very very small. So small that it never caused the 2016 Li cells to heat up and explode but enough that it allowed them to maintain voltage near 3VDC.

When you had mentioned in another thread that you thought the x36HPs used a super cap, I thought that was good news as they should have a much longer life when you factor in total or partial discharge/recharge cycles that some users may see in a year.

My weather stations use super caps that do discharge pretty darn low each night if I have cloudy days and the solar panel cannot provide the needed current. I've not had a super cap fail me yet. They also have a CR3 Li cell that provides operating voltage for extended periods.
Some of the super caps Davis used have failed they found. They believe it was caused by improper forming of the super caps leads when bending them at a right angle to insert into the circuit board. Another words, they bent the leads by hand instead of holding them with something so the leads did not move inside the caps body when being formed.

I guess in this case, time shall tell!
 
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