diff --git a/aodntools/timeseries_products/aggregated_timeseries.py b/aodntools/timeseries_products/aggregated_timeseries.py
index 87c38ed..c95de7c 100644
--- a/aodntools/timeseries_products/aggregated_timeseries.py
+++ b/aodntools/timeseries_products/aggregated_timeseries.py
@@ -288,8 +288,8 @@ def main_aggregator(files_to_agg, var_to_agg, site_code, input_dir='', output_di
             LATITUDE[index] = nc.LATITUDE.values
             LONGITUDE[index] = nc.LONGITUDE.values
             NOMINAL_DEPTH[index] = get_nominal_depth(nc)
-            source_file[index] = stringtochar(np.array(file, dtype='S256'))
-            instrument_id[index] = stringtochar(np.array(get_instrument_id(nc), dtype='S256'))
+            source_file[index] = stringtochar(np.array(file, dtype='S256'), encoding='ascii')
+            instrument_id[index] = stringtochar(np.array(get_instrument_id(nc), dtype='S256'), encoding='ascii')
 
         start = end
 
diff --git a/aodntools/timeseries_products/velocity_aggregated_timeseries.py b/aodntools/timeseries_products/velocity_aggregated_timeseries.py
index b5649ad..452fd23 100644
--- a/aodntools/timeseries_products/velocity_aggregated_timeseries.py
+++ b/aodntools/timeseries_products/velocity_aggregated_timeseries.py
@@ -168,8 +168,8 @@ def velocity_aggregated(files_to_agg, site_code, input_dir='', output_dir='./',
             LATITUDE[index] = nc.LATITUDE.values
             LONGITUDE[index] = nc.LONGITUDE.values
             NOMINAL_DEPTH[index] = utils.get_nominal_depth(nc)
-            source_file[index] = stringtochar(np.array(file, dtype='S256'))
-            instrument_id[index] = stringtochar(np.array(utils.get_instrument_id(nc), dtype='S256'))
+            source_file[index] = stringtochar(np.array(file, dtype='S256'), encoding='ascii')
+            instrument_id[index] = stringtochar(np.array(utils.get_instrument_id(nc), dtype='S256'), encoding='ascii')
             ## add time offset to the middle of the measuring window, if it exists
             if 'seconds_to_middle_of_measurement' in nc.TIME.attrs:
                 SECONDS_TO_MIDDLE[index] = nc.TIME.seconds_to_middle_of_measurement
diff --git a/aodntools/timeseries_products/velocity_hourly_timeseries.py b/aodntools/timeseries_products/velocity_hourly_timeseries.py
index 9a7e491..f9da4f9 100644
--- a/aodntools/timeseries_products/velocity_hourly_timeseries.py
+++ b/aodntools/timeseries_products/velocity_hourly_timeseries.py
@@ -230,8 +230,8 @@ def velocity_hourly_aggregated(files_to_agg, site_code, input_dir='', output_dir
             LATITUDE[index] = nc.LATITUDE.values
             LONGITUDE[index] = nc.LONGITUDE.values
             NOMINAL_DEPTH[index] = np.array(utils.get_nominal_depth(nc))
-            source_file[index] = stringtochar(np.array(file, dtype='S256'))
-            instrument_id[index] = stringtochar(np.array(utils.get_instrument_id(nc), dtype='S256'))
+            source_file[index] = stringtochar(np.array(file, dtype='S256'), encoding='ascii')
+            instrument_id[index] = stringtochar(np.array(utils.get_instrument_id(nc), dtype='S256'), encoding='ascii')
             ## add time offset to the middle of the measuring window, if it exists
             if 'seconds_to_middle_of_measurement' in nc.TIME.attrs:
                 SECONDS_TO_MIDDLE[index] = nc.TIME.seconds_to_middle_of_measurement