cryptocompare has the utility you need.

1. Go to Coins at the top, find your coin
2. Analysis
3. Change the bar graph at the bottom to display by Hour
4. Use the interface to see the volume per second

If this is too unwieldy, cryptocompare does have an api and a useful npm package to play around with.

The cheapest way to do this yourself would be to read the API docs of each exchange and write your own code for downloading minutely price data and that will also include volume data. You can then resample later according your needs.

For example,

• https://docs.bitfinex.com/docs
• https://docs.gdax.com/