bigr dataframe error 'do not know how to convert 'df$V3' to class “POSIXct”'

Question

I'm trying to create a calculated column with bigr. First load the data:

> df <- bigr.frame (dataPath = "/data.csv", 
                    dataSource="DEL", delimiter=",", header=F,
                    coltypes = c("integer", "character", "character"))

Then attempt to add a column:

> df$posixct = as.POSIXct(df$V3, tz="UTC", format="%Y-%m-%d %H:%M:%S")

However, I get the error message:

Error in as.POSIXct.default(df$V3, tz = "UTC", format = "%Y-%m-%d %H:%M:%S") : 
  do not know how to convert 'df$V3' to class “POSIXct”

I've taken a look at the class:

> class(df$V3)
[1] "bigr.vector"
attr(,"package")
[1] "bigr"

The values in the V3 column look like this:

2005-01-01 00:00:00
2005-01-01 00:10:00
...

I'm not sure how to proceed - any tips?

---

Update:

I've tried converting to a character:

> df$posixct = as.POSIXct(
                   as.character(df$V3), tz="UTC", format="%Y-%m-%d %H:%M:%S")

But receive the following error

Error in as.POSIXct.default(as.character(df$V3), tz = "UTC", format = "%Y-%m-%d %H:%M:%S") : 
  do not know how to convert 'as.character(df$V3)' to class “POSIXct”