Google data download with getSymbols - is there a limit/quota ?

I am trying to use getSymbols(...,src='google') from the quantmod
package for downloading google finance data for about 1600 symbols, once
a week. Some of that will be used in several quantstrat strategies.

I am seeing that after having gotten about 500 symbols, trying to
download more will produce http errors.  If I re-try those symbols the
next day, then the quota seems to have been reset and I can download
around 500 symbols again.

Question: Is anyone else experiencing this ?  Would anyone know what is
the minimum time I have to wait before I can download the next batch of
500 symbols (I hope it's somewhere around several minutes or
several hours, but not more than that) ?  

many thanks

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Soren Wilkening

http://censix.com