[time-nuts] Portable standard

[EWKehren at aol.com]

Joe
Having OCXO's, Rb's, Tbolt's and a Cs running with battery backup, over  
time I have used AGM, Ni-CAD, and now Ni-MH,, in all cases you have to have  
ventilation. Also battery and electronics have to be separated as much as  
possible since temperature is enemy #1 for any battery. Today most electronic  
charge circuits use pulse mode and the cell voltage goes as high as 1.8 
Volt. In  addition the battery has to be electronically separate from the user 
since  having the Osc. connected directly to the battery will mess up the 
charge  controller. I have a fast switch over that also cuts out the battery 
to prevent  total discharge. If you are interested contact me directly.
I recently ordered a Li-Ion 12 V 9.5 A pack, ebay # 140512699149, have not  
received it yet, but look forward testing it, to do the same with Ni-MH 
would  cost three times as much and weight  and size would be at least twice. 
Once  tested I will share the results.
I agree with the comment on using a Rb since there is no cost differential, 
 just make sure that it has active or passive heat transfer to make sure 
that the  batteries run as cool as possible.
 Bert Kehren  Miami
 
 
 
In a message dated 4/6/2011 3:14:06 A.M. Eastern Daylight Time,  
jgray at zianet.com writes:

If I  were to buy an HP 10811A OCXO to use as a portable, battery
powered  frequency standard, how would you recommend that it be powered
and  packaged? Assume that the final package would be powered 24/7 and
sitting  on a shelf most of the time. Prior to portable use, it would
be checked  against my GPSDO. Portable use would probably be at worse a
few days, but  more likely less than a day.

I'm thinking of using a couple of 12V, 7AH  SLA batteries and float
charging them. Some charge circuits use pulsing  current for SLA
batteries. Would this affect the OCXO?

Obviously too  much air flow will be a problem. Can the OCXO, batteries
and associated  circuitry be sealed in a box with no vent holes (not
strictly air tight)?  What about putting the OCXO in a small styrofoam
box by itself? Will that  cause overheating or other issues? How about
vent holes in the overall  enclosure and baffles around the OCXO to
minimize air flow?

Should I  forget the whole idea and just buy a rubidium?

Joe  Gray
W5JG

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