[time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system
brooke at pacific.net
Sat Nov 1 17:31:19 EDT 2014
AFAICR on the old 6-channel Motorola GPS boards there was an option for a backup battery. Without the backup battery if
there was any power interruption the memory would erase and you needed to do a cold start. Having the almanac and
ephemeris, even if from a year ago has the effect of greatly reducing start-up time. In this case the purpose of the
super cap is to prevent memory loss because of a power glitch not for long term power failure.
Bob Camp wrote:
> Well Q = CV. If delta V = 1 and C = 0.022 then Q = 0.022. That’s 22 ma for 1 second or 22 ua for 1,000 seconds. At 5 ua you would get to about an hour. If the delta V is 2X that, the times would all double. If the current is 10X lower than the spec (it might be …) then you could get out to around a day.
>> On Nov 1, 2014, at 12:38 AM, Bob Stewart <bob at evoria.net> wrote:
>> Hi Bob et al,
>> I don't understand the direction this question about the supercap has taken. It's connected to pin 1 of the GPS receiver. It looks to be a UT+, so that's the battery backup power. According to my UT+ manual the current draw on this pin is between 5uA (at 2.5V) and 100uA (at 5V)? How many hours will a .022F supercap keep at least 2.5V at that sort of discharge rate? Unless the cap has gone bad, it seems more likely that Bob's comment about it doing a fast survey and then doing a slower one in the background probably has merit. In fact, my unit goes through its survey mode pretty quickly on power up. So do those current/voltage figures imply several hours on the cap?
>> From: Bob Camp <kb8tq at n1k.org>
>> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>> Sent: Friday, October 31, 2014 9:22 PM
>> Subject: Re: [time-nuts] Lucent KS-24361, HP/Symmetricom Z3809A, Z3810A, Z3811A, Z3812A GPSDO system
>> I sort of doubt that a GPS aux supply is quite that low current. I have seen some RTC’s that won’t last a month on a coin cell. My recollection is that the Oncore backup is closer to that category than the “many years on a cap” group.
>>> On Oct 31, 2014, at 9:26 PM, Brooke Clarke <brooke at pacific.net> wrote:
>>> Hi Bob:
>>> When HP came out with the 300 series Rocky Mountain Basic computers they were fitted with a super cap to power the RTC.
>>> I will keep time for some months.
>>> Mail_Attachment --
>>> Have Fun,
>>> Brooke Clarke
>>> Bob Camp wrote:
>>>> The ultra cap is a pretty small one (physical small). You might be able to find a larger (more farads) one that would fit in the same space. It’s not going to help for a hours and hours sort of outage. It might get you from dying in 15 minutes to dying in a half hour.
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